CA1257404A - System for simultaneous gamma-gamma formation density logging while drilling - Google Patents
System for simultaneous gamma-gamma formation density logging while drillingInfo
- Publication number
- CA1257404A CA1257404A CA000499259A CA499259A CA1257404A CA 1257404 A CA1257404 A CA 1257404A CA 000499259 A CA000499259 A CA 000499259A CA 499259 A CA499259 A CA 499259A CA 1257404 A CA1257404 A CA 1257404A
- Authority
- CA
- Canada
- Prior art keywords
- borehole
- formation
- gamma
- gamma radiation
- radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- 230000005855 radiation Effects 0.000 claims abstract description 118
- 230000005251 gamma ray Effects 0.000 claims abstract description 22
- 238000001514 detection method Methods 0.000 claims abstract description 16
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- TVFDJXOCXUVLDH-RNFDNDRNSA-N cesium-137 Chemical group [137Cs] TVFDJXOCXUVLDH-RNFDNDRNSA-N 0.000 claims description 2
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- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- 239000010937 tungsten Substances 0.000 description 2
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical group CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V5/00—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity
- G01V5/04—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging
- G01V5/08—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays
- G01V5/12—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays using gamma or X-ray sources
- G01V5/125—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays using gamma or X-ray sources and detecting the secondary gamma- or X-rays in different places along the bore hole
Abstract
SYSTEM FOR SIMULTANEOUS GAMMA-GAMMA
FORMATION DENSITY LOGGING WHILE DRILLING
ABSTRACT OF THE DISCLOSURE
A system for logging subterranean formations for the determination of formation density by using gamma radiation. Gamma ray source and detection means are disposed within a housing adapted for positioning within a borehole for the emission and detection of gamma rays propagating through earth formations and borehole drilling fluid. The gamma ray detection means comprises first and second gamma radiation sensors geometrically disposed within the housing the same longitudinal distance from the gamma ray source and diametrically opposed in a common plane. A
formation matrix density output signal is produced in proportion to the output signal from each of the gamma ray sensors and in conjunction with certain constants established by the geometrical configuration of the sensors relative to the gamma ray source and the bore-hole diameter. Formation density is determined without regard to the radial position of the logging probe within the borehole in a measuring while drilling mode.
FORMATION DENSITY LOGGING WHILE DRILLING
ABSTRACT OF THE DISCLOSURE
A system for logging subterranean formations for the determination of formation density by using gamma radiation. Gamma ray source and detection means are disposed within a housing adapted for positioning within a borehole for the emission and detection of gamma rays propagating through earth formations and borehole drilling fluid. The gamma ray detection means comprises first and second gamma radiation sensors geometrically disposed within the housing the same longitudinal distance from the gamma ray source and diametrically opposed in a common plane. A
formation matrix density output signal is produced in proportion to the output signal from each of the gamma ray sensors and in conjunction with certain constants established by the geometrical configuration of the sensors relative to the gamma ray source and the bore-hole diameter. Formation density is determined without regard to the radial position of the logging probe within the borehole in a measuring while drilling mode.
Description
IL25'7~
FORMATION DENSITY LOGGING WHILE DRILLING
ACKGROUND OF THE INVENTION
Field of the Invention The invention relates to logging of ubterranean formations for the determination of formation density by using gamma radiation and, more particularly, to the determination of formation density while drilling a borehole traversing the earth formation. Most par-ticularly, the invention relates to the determination of formation density without regard to the radial posi-tion of the logging probe within the borehole or colli-mation of the gamma radiation employed to obtain density measurements.
History of the Prior ~ _ In the drilling of boreholes into formations in the earth, it is hlghly desirable to obtain information related to the nature an~ ~tructure of the formation through which the borehole is passlng wh~le drilling i8 in progress. Being able to prO~ide to the drilling ~ ' ~
~5'7a~
operator information related to the characteristics of the formations while drilling is in progress enables logging of the borehole during drilling and, hence, much more efficient operation. Such mea~uring-while-drilling (MWD) logging either partially or totally eli-minates the necessity of interrupting the drilling operation to remove the drill string from the hole in order to pass wire line logging sondes lnto the bore-hole for logging the characteristics of the formations therealong. In addition, the ability to log the characteristics of the formation through which the drill bit ls passlng, such as the density of the for-mation, greatly enhance~ the safety of the drilling operation. The drilling operator may thus be notified of the entry of the borehole into formations which may be likely to produce hazardous drilling conditions, such as blow out.
Heretofore, numerous techniques have been used in the wire line logging of drilled boreholes in order to determine the na~ure of the formations through which the borehole pa~ses. One technique for formation den-sity logging ha~ included gamma ray dens~ty probes which are device~ incorporat~ng a gamma ray source and a gamma ray detector, shielded from each other to pre-~ent the counting of gamma radiation by the detectorwhich emanates directly from the source. During the operation of the probe, gamma rays (photons) are emi-tted from the source and enter the formation to be studied. In the formation they interact with the ato-mic electrons of the material of the formation by either photoelectric absorption, by Compton Scattering, or by pair production. In both photoelectric absorp-tion and pair production phenomena, the particular pho-tons involved in the interaction process are removedfrom the gamma ray beams.
In the Compton Scattering process, the involved photon loses some of its energy while changing its ori-ginal direction of travel, the loss of energy being a function of the scattering angle. Some of the photons emitted from the source into the formation material are accordingly scattered hack toward the detector.
Many scattered rays do not reach the detector, since their direction is again changed by a second Compton Scattering, or they are thereafter absorbed by the pho-toelectric ab~orption process or the pair production proce~s. The scattered photon~ which reach the detec-tor and interact with it, are counted ~y electronic counting equipment associated with the detector.
Ma jor difficulties encountered in conventional gamma ray density measurement include rigorous defini-tion of the sample size and the limited effective depth and sampling times. Other major difficulties include S the disturbing effects of undesired interferring materials located between the density probe and the formation sample, such as drilling mud and mud cake on the borehole wall, which have required that the probe be posltioned directly against the borehole wall.
Numerous prior art wire line gamma radiation logging probes have tried to compensate for the effect on formation density ~easurements produced by the den-~ity of the mudcake on the walls of the borehole by providing two detectors axially spaced along the bore-hole at different distances from the source of radiation. The near, or short spaced detector is for receiving radiation which has scattered mainly in the materials near the borehole wall, and therefore in the mudcake. The far, or lon~spaced detector is for receiving radiation which has scattered principally in the formation.
Mo~t prior art gamma logginq systems have required complex collimation ~che~es to narrowly define either the beam of radiation emanating from the source to ~2S~
direct it into a specific region of the formation or the beam of radiation received back by the detector to insure that only radiation back-scattered from a par-ticular region of the formation was detected, or both.
S In addi~ion, prior art wire line gamma ray logging son-des have been highly susceptible to variation in den~
sity measurements due to the thickness of the drilling mud as well as the mud cake on the walls of the bore-hole throu~h which the radiation must pass and, thus, the accuracy of the measurements is strongly affected by the eccentricity of the tool within the borehole.
For this reason, prior art tools include elaborate mechanisms for pressing the surface of the tool firmly against the wall of the borehole on the side of the borehole at which point measurement is being made.
Needless to say the difficulties encountered in prior art wire line gamma radiation logging would be further complicated if the density measurement tool is made part of a drill string and operated during drilling of the borehole. The only known gamma radiation formatlon density probe useful in measurement wh~le drilling apparatug i~ ~hown in B~itish Published Appllcation No. 2,136,56 A published Se~tember 19, 1984 ~y Daniel Coope, entitled Formation Den~ity Logging ~2~7~
While Drilling, and assigned to the assignee of the present inven~ion. ~his application discloses a tech-nique for gamma-gamma formation density logging while drilling which relies upon the collimation of gamma radiation and a pair of axially spaced detectors along the borehole from one another and from the source of radiation in order to examine radiation back-scattered from two different regions within the formation at dif-ferent distances from the walls of the borehole.
One prior art wire line density probe which func-tions regardless of the thickness and the chemical com-position of materials that are located between the density probe and the sample is shown in U.S. Patent No. 3,846,631. This technique comprises passing two gamma ray beams from two intermittently operated gray sources into the sample, receiving the radiation back scattered from each of the two sources by two separate detectors, and building ratios of products of the four separate counting rates in such a manner that the numerical result i5 an indication of the density of the sample. Xn such longitudinally spaced two detector probes, which must be deployed against the borehole wall, the spacing between the detectors is a critical ~s~
dimension. If the interferring formation materials are non-uniform over distances comparable to the spacing of the two detectorR, the measured density will be erro-neous.
S In gamma radiation formation density probes, which include collimation of the gamma radiation, it is yre~
supposed that the region of interaction between the radiation and the formation can be narrowly defined and restricted to a small region. Not only is precise collimation of gamma radiation beams difficult to acco~plish, but the assumption that a collimated beam only interacts with a precisely definable portion of the formatlon surrounding the borehole is erroneous.
It would be an advantage therefore to overcome the limitations and inaccuracies of the prior art through a system for measuring the denslty of subterranean for-mations while drilling a borehole traversing the for-mation without the necessity of defining a narrow region of interrelation of gamma radiation with the formation or the employment of radiation collimation , or the necessity of tool deployment against the bore-hole ~all.
The presen~ inventlon provides such a system through novel geometry of a gamma radiation source and ',: .
~25~
detectors which enables measurement of formation para-meters from back-scattered gamma radiation without regard to the eccentric position of the tool within the borehole. The measurement is also made without regard to any assumption as to the particular region of the formation from which the radiation was back~scattered.
SUMMARY OF THE INVENTION
The present invention pertains to a system and method for measuring format~on density by means of back-scattered gamma radiation in a logging-while-drilling system. One embodiment of the invention includes apparatus for logging the density of a for-mation surrounding a borehole which traverses the for-mation. The apparatus i5 adapted for use in a drill string and includes means for emitting gamma radiation into the formation and a plurality of detector means for counting gamma radiation scattered in the formation back to the apparatus. Each of the counting means is located an equal axial distance along the ~pparatus from the source and each is located sym-metrically about the longitudinal axi~ of the appara-tUB. In one preferred embodiment of the invention the apparatu~ includes first and second detector means .`j..``.:i::
. .~, ~ ~ ~ 7 located on diametrically opposite sides of the apparatus.
Another aspect of the present invention includes a method for determining the average density of the earth formation surrounding a borehole traversing the for-mation and adjacent to the measuring apparatus. The method includes the steps of emitting gamma radiation into the formation and measuring the quantity of gamma radiation back-scattered from the formation at a plura-lity of detector locations. The detector locations areequally spaced along the axiY of the borehole relative to the source from which radiation is emitted, and are located symmetrically about the longitudinal axis of the measuring apparatus.
In a further embodiment the invention includes a gamma radiation formation density logging apparatus for use in a borehole traversing an earth formation. The apparatus includes an elongate sonde having a longitu-dinal axis and a source of gamma radiation located within th~ sonde. A gamma radiation detection assembly is mounted within the sonde and includes fir~t and second gamma r~di~tion detectors each spaced the same distance in the same direc~ion from the radiation source longitudinally along the sonde. Each detector . , ~
~2 S 7404 is diametrically opposed on a common circle which lies in a plane normal to the lon~itudinal axis.
Output si~nals from the first ~nd second detectors obtained while the sonde is rotated about its longitu-dinal axis within the borehole are used to produce anoutput si~nal proportional to the matrix density of the formation surrounding the borehole in the region of the sonde. The sonde may comprise a cylindrical sub con-nected as part of a drilling string in a logging~while-drilling system.
In still another a~pect of the invent~on, a methodfor borehole gamma radiation formation density logging comprises rotating an elongate sonde within the bore-hole while emitting gamma radiation into the formation from a first location within the qonde. The emitted gamma radiation scattered from the formation i~
detected at a second and a third location within the sonde where the second and third locations are diametrically opposed on opposite sides of the sonde and equally spaced in the same longitudinal direction from the first location. An output ~ignal i~ produced in response to the gamma radiation detected ~t the second and third locations which is proportlonal to the matrix density of the formation surrounding the bore-: "
~2~
hole in the region of the sonde.
In a further aspect, the lnvention includes arotating device for use in a borehole traversing an earth formation with a drilling mud of known density filling the borehole and having a means for emitting gamma radiation into the formation surrounding the borehole. First and second gamma radiation detecting means are located on a common circle at diametrically opposed polnts with the Pirst and ~econd mean~ being spaced the same axial d~stance in the same axial direc-tion from the emitting mean~. Al~o lncluded is a ~ean3 for calculating matrix density which ls re~ponsive to the output 3ignals from the detectors; the mud density ~alue a first tool calibration factor associated with the first detector and related to the di~tance from the fir~t detector to the emitting means, the metal between the detector and the borehole wall and the ef f iciency of the first detector; a second tool calibration factor associated with the second detector and related to the distance from the second detector to the emitting means, the metal between the detector and the borehole wall and the efficiency of the ~econd detector; and a third tool calibration related to the difference bet-ween the diameter of the tool and the diameter of the 2S borehole.
-~RIEF DESCRIPTION OF THE_DRAWING
For more complete understanding of the presentinvention and Çurther objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a diagramatic side-elevational view of a borehole drilling operation illustrating a system for formation density logging while drilling constructed in accordance with the teachings of the present invention;
FIG. 2 is an illustrative, side-elevational, par-tially cross-sectional view of one embodiment of a downhole sub for gamma radiation formation density logging while drilling constructed in accordance with the teachings of the present invention;
FIG. 3 is an illustrative, cross-sectional view taken through thè line 3-3 of FIG. 2 showing the posi-tioning of the radiation detectors within the~iappa~atus of FIG. 2;
FIG. 4 i~ a block diagram of a processing system for calculating formation matrix den~ity in accordance with the teachin~s of the invention;
FIG. S is an illustrative graph showing a calibra-tion curYe for a radi~tion detector which relates count ~.
``
~'57 rate to formation den~ity, FIG. 6 is an illustratiYe graph showing a family of calibration curves which relate formation density measured by a detector in the present system and actual formation density for different standoff distances bet-ween the side of the ~ub and the walls of the borehole along the common diameter of the pair of detectors; and FIG. 7 is an illustrative graph which relate~ tool standoff distance to standoff slope and enables the determination of tool constant5 ~1 and ~2~
DETAILED DESCRIPTION OF THE PREFERR~D EMBODIMENT
Referring to FIG. 1, there is shown a drilling rig 11 disposed on top of a borehole 12. A system 10 for simultaneous gamma-gamma radiation formation den-sity logging is carried by a sonde or sub 14 romprisinga portion of a drill collar 15 and is disposed w;thin the measurement of the density of the formations surrounding the borehole while the drilling operations are in proqress.
A drill bit 22 i~ di~posed at the lower end of drill ~tring 18 and c~rves the borehole 12 out of the earth formatlons 24 while drilling mud 26 i~ pumped from the wellhead 28. Metal surface casing 29 i~ ~hown po~itioned in the borehole 12 above the drill bit 22 for maintaining the integrity of the borehole 12 near the surface. The annulus 16 between the drill string 18 and the borehole wall 20 creates a theoretically closed return mud flow path. Mud is pumped from the wellhead 28 by a pumping ~ystem 30 through mud supply line 31 coupled to the drill string 18. Drilling mud is, in this manner, forced down the central axial passageway of the drill string 18 and egresses at the drill bit 22 for carrying cuttings comprisin~ the drilled sections of earth, rock and related matter upwardly from the drill bit to the surface. A conduit 32 is supplied at the wellhead for channeling the ~ud from the borehole 18 to a mud pit 34. The drilling mud is typically handled and treated at the surface by various apparatus (not shown~ such as outgasing units and circulation tanks for maintaining a selected visco~
sity and consistency of the mud. The present gamma radiation formation density logging sy~tem permits the measurement of formation densities in the regions surroundinq the borehole durinq the pumping of drilling fluid through the drill string and borehole.
As shown in FIG. 1, the sub 14 and drill collar lS
comprise a portion of the formation density logging system 10 of the present invention and the downhole environment. The sy~tem 10 is constructed to generate a series of signals for telemetry to the wellhead or a S downhole recording system which signals are indicative of the formation matrix density of the earth formations adjacent to the borehole. The requisite telemetry and analysis sy~tems are deemed to be of conventional design and are not specifically set forth or addressed herein. The method and apparatus for measurement of formation density is, however, described in detail below and i8 a subject of the present invention.
Referring now to FIG. 2, there is shown an illustrative, diagramatic, and partially cross~
lS sectional view of a sub 14 which carries a system constructed in accordance with the teachings of the present invention. The sub 14 preferably comprises a drill collar 15 which is coupled as part of the drill string 18, and although shown to be positioned imme-diately above the drill bit 22, this is merelyillustrative and the sub 14 may be located at other positions in the drill string.
The ~ub 14 is formed from a section of drill collar 15 which includes a cylindrical inner bore 41 ~5~7~
for the transmi~sion of pre~surized drilling fluid from the surface to the drilling bit 22. The collar 15 has been modified to include a pair of gamma radiation ~ources 42 and 43 each comprising a threaded inqert to be received within threaded openings in the side walls of the collar 15. The sources of gamma radiation 42 and 43 may be any conventional sources such as cesium 137. While the system of the present invention will function adequately with a single source, the use of the two sources 42 and 43 insures that the radiation level is of a sufficient amplitude to produce large output signals from the detectors. Each of the two sources 42 and 43 are preferably located at a common axial position along the axis of the tool 10 and are illustrated as lying on a common diameter 44 which is perpendicular to the axial center line 46 of the drill collar 15.
The collar includes an enlarged central cylindrical cavity 61 coaxial with the bore 41 and extending par-tially the length of the collar lS. A pair of gammaradiation detectors 52 and 53 are positioned an axlally spaced distance from the sources 42 and 43 with~n a detector packing and tungsten sh~elding insert Sl located at the lower end of a central cavity 61. The ,,; ,.~;
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:
, : ...,.., ..: ,: ~
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two detectors 52 and S3 are both located the ~ame axial distance from the gamma radiation sources 42 and 43 and are shown to both lie in a common plane 54 which is also perpendicular to the center line 46 of the drill collar lS. Positioned between the sources 42 and 43 and the detectors 52 and 53, is a ring-shaped tungsten shielding insert 55 which is formed as part of the insert 51 and positioned in the body of the drill collar lS in order to minimize the detection of gamma radiation from the sources which reaches the detectors by ~streaming~ o the radiation axially along the drill collar and bore 41. The radiation detectors 52 and 53 may comprise any conventional gamma radiation detecting means such as an array of Geiger-Mueller tubes or may consist of sodium iodide scintillators.
Referring now to FIG. 3, there is shown a illustra-tive top cross section view taken about the lines 3-3 of FIG. 2 which shows the relative posit~oning of the gamma radiation detectors 52 and 53 within the body of the drill collar 15. The left detector 52 is illu~trated as comprising ~n array of three Geiger-~ueller tube~ 52a-52c while the r~ght detector 53 is illustrated as comprising an array of three Geiger-Mueller tube~ 53a 53c. A tung~ten shield member , .
~2~17~0 -la-5~, also formed as part of the insert 51, is shown positioned between the left detector 52 and the bore 41 while a similar shield 57 is shown positioned between the bore 41 and the right detector 53. The shield mem-bers 56 and 57 minimize the detection by the detectors 52 and 53 of radiation which does not emanate from the formation.
A significant aspect of the novel geometry of the gamma-gamma radiation formation density logqing system of the present invention is that the two detectors 52 and 53 are positioned symmetrically about the longitu-dinal axis of the collar lS at equal azimuthal angles of separation from one another, i.e., 180 degrees, on diametrically opposite sides of the collar. The two detector arrays 52 and 53 both lie on a common diameter 58 of a common circle within the plane 54 per-pendicular to the axis of the drill collar lS. Both detectors are also spaced an equal distance from the radiation sources 42 and 43. As is also shown in FIG. 3, the system of the present invention produces accurate measurement of formation density regardless of the eccentric position of the drill collar within the borehole 12 because the distances between the eccen-tered tool and the borehole wall are automatically com-pensated mathematically as well as .~
~S~74~
by the averaging effects which occur when the tool is rota~ed during the logging operation.
In order to demonstrate the significance of the unique geometry of the components of the present inven-tion and the math~natical conse~uences thereof, certainterms must be defined. The left standoff distance bet-ween the side wall of the borehole 12 and the drill collar 15 is ~A~, measured along the common diameter 58. Similarly, nB~ is the righ~ standoff distance bet-ween the side of the drill collar 15, also measuredalong the common diameter 58. The distance ~TD", along the common diameter S8, i~ the di~meter of the tool.
~BD" is the diameter of the borehole. The two detec-tors 52 and 53 are seen to be located on opposite sides of the drill collar 15, and at equal axial distances from the gamma radiation sources 42 and 43, (or from a single source if such is employed). Thus, we can incorporate the geometry of the borehole itself to solve three equations s~multaneously and determine the formation matrix density.
Using ~ to indicate the density mea~ured by the detector on the left side of the FIG. 3, we see that the ormation density is given by:
.
~t ~
~2~;7~
)p~ J(/~ or (6) ~Q (1- ~ ) + ~ p~ , where (7) = formation matrix density;
~ = poro~ity of the formation;
~ = fluid density in the formation;
P~ = mud density o~ ~ fraction of gamma ray-q interacting in the mud;
and ~= (1- ~ ) ~ ~+ ~ ~ = apparent formation density It ~hould be noted that Equations 6 and 7 above are equally valid for wire line tool configurations as for gamma formation detection in measuring while drilling applications.
If we used ~ to indicate the formation density measured by the detector on the right side of the FIG. 3, we see that the formation density is also given by.
~ ) t ~ ~ (8) where ~ is the fraction of gamma rays interacting in the mud~ We also kno~ by geometry that the tool diameter, TD, and the borehole diameter, BD, are related to the tool~ po~ition in the borehole by the followlng relationships:
,.
A + s + TD = 8D (9) where A is the perpendicular distance from the left toolface to the left borehole surface ~the left standoff), and 8 is the standoff on the right side of S the tool as shown in FIG. 3. It can be noted that the probability of a photon tgamma ray) traveling a distance A before having a collision is simply exp (-klA). The probability of having an interactlon at any distance less that A is given by (l-exp(~klA)).
Likewise, the probability of having an interaction within the distance B is given by ~l-exp(-k2B)). The values ~1 and k2 are geometric constants to be further specified below~ If we assume the above relationshlps we may write the following:
~ = 1- eklA ~10) and /3 = 1-e~k28 ( 11 ) We imply that ~ and ~ are probabilities that the gamma rays will interact in the mud, and (1- ~ ) and (1-~ ) are the prob~bilities that the photon6 will interact in the formation matrix, and not in the mud.
If we now combine Equationq 7 and 10, we find that:
e (~ , ) (12) The geometry phy~ically constrains the tool ln the borehole ~o that we can use the following relationqhip:
A = BD-TD - B = R3-B (13) S so that we can rewrite Equation 10 in terms of the standoff B as follows:
3 -B) , ~ ( 14 ) We can also rewrite Equation 8 in terms of the standoff B as follows:
e~k2B = ( ~ ~ Pm )/( P~ - ~ ) (lS) or by rai~ing to the power, k1/k2, we can write Equation 15 as follows:
e ~ k 1 B = r ( /~R - P,~ )/ ( /3~ Q /~ J ] (16) Now subs~ituting Equation 16 into Equation 14, we find that:
e (~-P~)[(~ )7 (lB) which can be ~olved for the formation matrix density, ~ follows:
., P~= P~ ~ Le (/~ ) ]
(19) Now, if kl=k2, and it will be shown later that they can be equal, we can write k=kl=k2 and Equation 19 becomes the following statement:
f ~ ~ K k3 ( ~ Y2 ~ ( 2 0 ) Based on upon these derivations, we can in prin-ciple determine the formation density based on the observed densities recorded by the left and right detectors, and on the density of the mud in use at the time of the measurements. The constant k3 is deter-mined directly from the difference between the tool diameter and the diameter of the borehole within which it is being used. The tool constants kl and k2 are determined by the distance between the detectors and the source, the thickness of the drill collar wall bet-ween the detector and the exterior surface of the collar, and the efficiency of the detectors. For matched detectors and a symmetrical drill collar k will equal k2. The tool constants ~l and k2, are determined durinq calibration of the tool in a fashion ~imilar to that in which conventional wire line tools 7~
are calibrated in a teqt pit, as set forth below.
During calibration a test pit having a plurality of formations of known litholgies is used by exposing the tool to known density conditions. FIG. 5 is prepared S to convert the logarithm of the detector count rate (in any arbitrary units) to a density indication with the tool surface directly abutting the surface of the formation.
Thereafter the tool is arranged at a preselected value of standoff distance and a series of ormations of known density are logged to obtain an indication of measured density for each actual value as shown in FIG.
6. The tool is then arranged for a series of different .
standoff distances and the process repeated to produce a family of curves, as shown in FIG. 6. ~he logarithm of each line slope of the family of curves in FIG. 6 iY
plotted against standoff distance on semilog paper to produce a straight line with a negative slope as shown ln FIG. 7. The slope of this line is the tool constant kl, or k2 associated with that detector.
As shown in FIG. 4, the count of the left detector 52 is determined at 62 while the count of the rlght detector 53 is determined at 63 per unit of time and, in conventional fashion, the formation density value iR
~2~i~7~ 4 determined at 64 and 65 for the left and right detec-tors, respectively. Thereafter, this information is entered into the proce~sor 66 along with either a measured or known mud density 67 and the measured tool calibration constantg kl and k2 from storage 68. The processor thereafter produces a calculated value of formation matrix density, and porosity can be inferred in accordance with standard practices in the industry.
The present technique involves three basic assump-tions which allow the effectiveness of the present tool geometry in technique to be utilized. First, it is assumed that the borehole is relatively cloqe to gauge and does not include a large number of wash outs or cave~. In the region of the borehole near the drilling bit, this is a reliable assumption. However, in the event that this is not the case a caliper tool can be included in the system of the present invention in order to compensate for variations in borehole diameter. Nevertheless, this limitation is not nearly as critical as in the case with wire line gamma radiation density detectors since the present tool does not predicate the validity of its operation~ on wall contact as does the vast ma~ority of wire line detec-tors. The second assumption is that the m~dcake on the ~:5~7~
walls of the borehole has not had a chance to form during the logging of the well. Since the present tool operates during the measuring while drilling operation at a point near to the drill bit this assumption is reasonable.
The third assumption is that mud density is known or readily determinable. This is ~lso a very good assumption.
It should be understood that a gamma radiation for-mation density Logglng system in accordance with the principles of the present invention may be constructed with three or more detectorq rather than two as is shown in the preferred embodiment. In each case each one of the detectorg must lie in a plane per- !
pendicular to the axis of the housing and be positioned at azimuthally symmetrical equal angles from one another, i.e., with rotational symmetry about the bore-hole axis. Of course, the equations for the deter-mination of formation matrix density are increasingly more complex for structures with ~ore than two arrays but may be solved in the same fashion as the two detector array configuration discussed above.
It should be also noted that the present logging apparatus ha~ been shown within a housing or sonde comprising a drill collar forming part of a drill . .
~' strinq. While the present system is especially useful in logging while drilling systems, the particular tool geometry could also be employed in a non-MWD sonde of the wireline type.
It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description while the method and apparatus shown and described has been characterized as being preferred it will be obvious that various changes and modifications may be made therein without departing from the spirlt and scope of the invention as defined in the following claims.
FORMATION DENSITY LOGGING WHILE DRILLING
ACKGROUND OF THE INVENTION
Field of the Invention The invention relates to logging of ubterranean formations for the determination of formation density by using gamma radiation and, more particularly, to the determination of formation density while drilling a borehole traversing the earth formation. Most par-ticularly, the invention relates to the determination of formation density without regard to the radial posi-tion of the logging probe within the borehole or colli-mation of the gamma radiation employed to obtain density measurements.
History of the Prior ~ _ In the drilling of boreholes into formations in the earth, it is hlghly desirable to obtain information related to the nature an~ ~tructure of the formation through which the borehole is passlng wh~le drilling i8 in progress. Being able to prO~ide to the drilling ~ ' ~
~5'7a~
operator information related to the characteristics of the formations while drilling is in progress enables logging of the borehole during drilling and, hence, much more efficient operation. Such mea~uring-while-drilling (MWD) logging either partially or totally eli-minates the necessity of interrupting the drilling operation to remove the drill string from the hole in order to pass wire line logging sondes lnto the bore-hole for logging the characteristics of the formations therealong. In addition, the ability to log the characteristics of the formation through which the drill bit ls passlng, such as the density of the for-mation, greatly enhance~ the safety of the drilling operation. The drilling operator may thus be notified of the entry of the borehole into formations which may be likely to produce hazardous drilling conditions, such as blow out.
Heretofore, numerous techniques have been used in the wire line logging of drilled boreholes in order to determine the na~ure of the formations through which the borehole pa~ses. One technique for formation den-sity logging ha~ included gamma ray dens~ty probes which are device~ incorporat~ng a gamma ray source and a gamma ray detector, shielded from each other to pre-~ent the counting of gamma radiation by the detectorwhich emanates directly from the source. During the operation of the probe, gamma rays (photons) are emi-tted from the source and enter the formation to be studied. In the formation they interact with the ato-mic electrons of the material of the formation by either photoelectric absorption, by Compton Scattering, or by pair production. In both photoelectric absorp-tion and pair production phenomena, the particular pho-tons involved in the interaction process are removedfrom the gamma ray beams.
In the Compton Scattering process, the involved photon loses some of its energy while changing its ori-ginal direction of travel, the loss of energy being a function of the scattering angle. Some of the photons emitted from the source into the formation material are accordingly scattered hack toward the detector.
Many scattered rays do not reach the detector, since their direction is again changed by a second Compton Scattering, or they are thereafter absorbed by the pho-toelectric ab~orption process or the pair production proce~s. The scattered photon~ which reach the detec-tor and interact with it, are counted ~y electronic counting equipment associated with the detector.
Ma jor difficulties encountered in conventional gamma ray density measurement include rigorous defini-tion of the sample size and the limited effective depth and sampling times. Other major difficulties include S the disturbing effects of undesired interferring materials located between the density probe and the formation sample, such as drilling mud and mud cake on the borehole wall, which have required that the probe be posltioned directly against the borehole wall.
Numerous prior art wire line gamma radiation logging probes have tried to compensate for the effect on formation density ~easurements produced by the den-~ity of the mudcake on the walls of the borehole by providing two detectors axially spaced along the bore-hole at different distances from the source of radiation. The near, or short spaced detector is for receiving radiation which has scattered mainly in the materials near the borehole wall, and therefore in the mudcake. The far, or lon~spaced detector is for receiving radiation which has scattered principally in the formation.
Mo~t prior art gamma logginq systems have required complex collimation ~che~es to narrowly define either the beam of radiation emanating from the source to ~2S~
direct it into a specific region of the formation or the beam of radiation received back by the detector to insure that only radiation back-scattered from a par-ticular region of the formation was detected, or both.
S In addi~ion, prior art wire line gamma ray logging son-des have been highly susceptible to variation in den~
sity measurements due to the thickness of the drilling mud as well as the mud cake on the walls of the bore-hole throu~h which the radiation must pass and, thus, the accuracy of the measurements is strongly affected by the eccentricity of the tool within the borehole.
For this reason, prior art tools include elaborate mechanisms for pressing the surface of the tool firmly against the wall of the borehole on the side of the borehole at which point measurement is being made.
Needless to say the difficulties encountered in prior art wire line gamma radiation logging would be further complicated if the density measurement tool is made part of a drill string and operated during drilling of the borehole. The only known gamma radiation formatlon density probe useful in measurement wh~le drilling apparatug i~ ~hown in B~itish Published Appllcation No. 2,136,56 A published Se~tember 19, 1984 ~y Daniel Coope, entitled Formation Den~ity Logging ~2~7~
While Drilling, and assigned to the assignee of the present inven~ion. ~his application discloses a tech-nique for gamma-gamma formation density logging while drilling which relies upon the collimation of gamma radiation and a pair of axially spaced detectors along the borehole from one another and from the source of radiation in order to examine radiation back-scattered from two different regions within the formation at dif-ferent distances from the walls of the borehole.
One prior art wire line density probe which func-tions regardless of the thickness and the chemical com-position of materials that are located between the density probe and the sample is shown in U.S. Patent No. 3,846,631. This technique comprises passing two gamma ray beams from two intermittently operated gray sources into the sample, receiving the radiation back scattered from each of the two sources by two separate detectors, and building ratios of products of the four separate counting rates in such a manner that the numerical result i5 an indication of the density of the sample. Xn such longitudinally spaced two detector probes, which must be deployed against the borehole wall, the spacing between the detectors is a critical ~s~
dimension. If the interferring formation materials are non-uniform over distances comparable to the spacing of the two detectorR, the measured density will be erro-neous.
S In gamma radiation formation density probes, which include collimation of the gamma radiation, it is yre~
supposed that the region of interaction between the radiation and the formation can be narrowly defined and restricted to a small region. Not only is precise collimation of gamma radiation beams difficult to acco~plish, but the assumption that a collimated beam only interacts with a precisely definable portion of the formatlon surrounding the borehole is erroneous.
It would be an advantage therefore to overcome the limitations and inaccuracies of the prior art through a system for measuring the denslty of subterranean for-mations while drilling a borehole traversing the for-mation without the necessity of defining a narrow region of interrelation of gamma radiation with the formation or the employment of radiation collimation , or the necessity of tool deployment against the bore-hole ~all.
The presen~ inventlon provides such a system through novel geometry of a gamma radiation source and ',: .
~25~
detectors which enables measurement of formation para-meters from back-scattered gamma radiation without regard to the eccentric position of the tool within the borehole. The measurement is also made without regard to any assumption as to the particular region of the formation from which the radiation was back~scattered.
SUMMARY OF THE INVENTION
The present invention pertains to a system and method for measuring format~on density by means of back-scattered gamma radiation in a logging-while-drilling system. One embodiment of the invention includes apparatus for logging the density of a for-mation surrounding a borehole which traverses the for-mation. The apparatus i5 adapted for use in a drill string and includes means for emitting gamma radiation into the formation and a plurality of detector means for counting gamma radiation scattered in the formation back to the apparatus. Each of the counting means is located an equal axial distance along the ~pparatus from the source and each is located sym-metrically about the longitudinal axi~ of the appara-tUB. In one preferred embodiment of the invention the apparatu~ includes first and second detector means .`j..``.:i::
. .~, ~ ~ ~ 7 located on diametrically opposite sides of the apparatus.
Another aspect of the present invention includes a method for determining the average density of the earth formation surrounding a borehole traversing the for-mation and adjacent to the measuring apparatus. The method includes the steps of emitting gamma radiation into the formation and measuring the quantity of gamma radiation back-scattered from the formation at a plura-lity of detector locations. The detector locations areequally spaced along the axiY of the borehole relative to the source from which radiation is emitted, and are located symmetrically about the longitudinal axis of the measuring apparatus.
In a further embodiment the invention includes a gamma radiation formation density logging apparatus for use in a borehole traversing an earth formation. The apparatus includes an elongate sonde having a longitu-dinal axis and a source of gamma radiation located within th~ sonde. A gamma radiation detection assembly is mounted within the sonde and includes fir~t and second gamma r~di~tion detectors each spaced the same distance in the same direc~ion from the radiation source longitudinally along the sonde. Each detector . , ~
~2 S 7404 is diametrically opposed on a common circle which lies in a plane normal to the lon~itudinal axis.
Output si~nals from the first ~nd second detectors obtained while the sonde is rotated about its longitu-dinal axis within the borehole are used to produce anoutput si~nal proportional to the matrix density of the formation surrounding the borehole in the region of the sonde. The sonde may comprise a cylindrical sub con-nected as part of a drilling string in a logging~while-drilling system.
In still another a~pect of the invent~on, a methodfor borehole gamma radiation formation density logging comprises rotating an elongate sonde within the bore-hole while emitting gamma radiation into the formation from a first location within the qonde. The emitted gamma radiation scattered from the formation i~
detected at a second and a third location within the sonde where the second and third locations are diametrically opposed on opposite sides of the sonde and equally spaced in the same longitudinal direction from the first location. An output ~ignal i~ produced in response to the gamma radiation detected ~t the second and third locations which is proportlonal to the matrix density of the formation surrounding the bore-: "
~2~
hole in the region of the sonde.
In a further aspect, the lnvention includes arotating device for use in a borehole traversing an earth formation with a drilling mud of known density filling the borehole and having a means for emitting gamma radiation into the formation surrounding the borehole. First and second gamma radiation detecting means are located on a common circle at diametrically opposed polnts with the Pirst and ~econd mean~ being spaced the same axial d~stance in the same axial direc-tion from the emitting mean~. Al~o lncluded is a ~ean3 for calculating matrix density which ls re~ponsive to the output 3ignals from the detectors; the mud density ~alue a first tool calibration factor associated with the first detector and related to the di~tance from the fir~t detector to the emitting means, the metal between the detector and the borehole wall and the ef f iciency of the first detector; a second tool calibration factor associated with the second detector and related to the distance from the second detector to the emitting means, the metal between the detector and the borehole wall and the efficiency of the ~econd detector; and a third tool calibration related to the difference bet-ween the diameter of the tool and the diameter of the 2S borehole.
-~RIEF DESCRIPTION OF THE_DRAWING
For more complete understanding of the presentinvention and Çurther objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a diagramatic side-elevational view of a borehole drilling operation illustrating a system for formation density logging while drilling constructed in accordance with the teachings of the present invention;
FIG. 2 is an illustrative, side-elevational, par-tially cross-sectional view of one embodiment of a downhole sub for gamma radiation formation density logging while drilling constructed in accordance with the teachings of the present invention;
FIG. 3 is an illustrative, cross-sectional view taken through thè line 3-3 of FIG. 2 showing the posi-tioning of the radiation detectors within the~iappa~atus of FIG. 2;
FIG. 4 i~ a block diagram of a processing system for calculating formation matrix den~ity in accordance with the teachin~s of the invention;
FIG. S is an illustrative graph showing a calibra-tion curYe for a radi~tion detector which relates count ~.
``
~'57 rate to formation den~ity, FIG. 6 is an illustratiYe graph showing a family of calibration curves which relate formation density measured by a detector in the present system and actual formation density for different standoff distances bet-ween the side of the ~ub and the walls of the borehole along the common diameter of the pair of detectors; and FIG. 7 is an illustrative graph which relate~ tool standoff distance to standoff slope and enables the determination of tool constant5 ~1 and ~2~
DETAILED DESCRIPTION OF THE PREFERR~D EMBODIMENT
Referring to FIG. 1, there is shown a drilling rig 11 disposed on top of a borehole 12. A system 10 for simultaneous gamma-gamma radiation formation den-sity logging is carried by a sonde or sub 14 romprisinga portion of a drill collar 15 and is disposed w;thin the measurement of the density of the formations surrounding the borehole while the drilling operations are in proqress.
A drill bit 22 i~ di~posed at the lower end of drill ~tring 18 and c~rves the borehole 12 out of the earth formatlons 24 while drilling mud 26 i~ pumped from the wellhead 28. Metal surface casing 29 i~ ~hown po~itioned in the borehole 12 above the drill bit 22 for maintaining the integrity of the borehole 12 near the surface. The annulus 16 between the drill string 18 and the borehole wall 20 creates a theoretically closed return mud flow path. Mud is pumped from the wellhead 28 by a pumping ~ystem 30 through mud supply line 31 coupled to the drill string 18. Drilling mud is, in this manner, forced down the central axial passageway of the drill string 18 and egresses at the drill bit 22 for carrying cuttings comprisin~ the drilled sections of earth, rock and related matter upwardly from the drill bit to the surface. A conduit 32 is supplied at the wellhead for channeling the ~ud from the borehole 18 to a mud pit 34. The drilling mud is typically handled and treated at the surface by various apparatus (not shown~ such as outgasing units and circulation tanks for maintaining a selected visco~
sity and consistency of the mud. The present gamma radiation formation density logging sy~tem permits the measurement of formation densities in the regions surroundinq the borehole durinq the pumping of drilling fluid through the drill string and borehole.
As shown in FIG. 1, the sub 14 and drill collar lS
comprise a portion of the formation density logging system 10 of the present invention and the downhole environment. The sy~tem 10 is constructed to generate a series of signals for telemetry to the wellhead or a S downhole recording system which signals are indicative of the formation matrix density of the earth formations adjacent to the borehole. The requisite telemetry and analysis sy~tems are deemed to be of conventional design and are not specifically set forth or addressed herein. The method and apparatus for measurement of formation density is, however, described in detail below and i8 a subject of the present invention.
Referring now to FIG. 2, there is shown an illustrative, diagramatic, and partially cross~
lS sectional view of a sub 14 which carries a system constructed in accordance with the teachings of the present invention. The sub 14 preferably comprises a drill collar 15 which is coupled as part of the drill string 18, and although shown to be positioned imme-diately above the drill bit 22, this is merelyillustrative and the sub 14 may be located at other positions in the drill string.
The ~ub 14 is formed from a section of drill collar 15 which includes a cylindrical inner bore 41 ~5~7~
for the transmi~sion of pre~surized drilling fluid from the surface to the drilling bit 22. The collar 15 has been modified to include a pair of gamma radiation ~ources 42 and 43 each comprising a threaded inqert to be received within threaded openings in the side walls of the collar 15. The sources of gamma radiation 42 and 43 may be any conventional sources such as cesium 137. While the system of the present invention will function adequately with a single source, the use of the two sources 42 and 43 insures that the radiation level is of a sufficient amplitude to produce large output signals from the detectors. Each of the two sources 42 and 43 are preferably located at a common axial position along the axis of the tool 10 and are illustrated as lying on a common diameter 44 which is perpendicular to the axial center line 46 of the drill collar 15.
The collar includes an enlarged central cylindrical cavity 61 coaxial with the bore 41 and extending par-tially the length of the collar lS. A pair of gammaradiation detectors 52 and 53 are positioned an axlally spaced distance from the sources 42 and 43 with~n a detector packing and tungsten sh~elding insert Sl located at the lower end of a central cavity 61. The ,,; ,.~;
j~, ~ ..
:
, : ...,.., ..: ,: ~
~LZ~
two detectors 52 and S3 are both located the ~ame axial distance from the gamma radiation sources 42 and 43 and are shown to both lie in a common plane 54 which is also perpendicular to the center line 46 of the drill collar lS. Positioned between the sources 42 and 43 and the detectors 52 and 53, is a ring-shaped tungsten shielding insert 55 which is formed as part of the insert 51 and positioned in the body of the drill collar lS in order to minimize the detection of gamma radiation from the sources which reaches the detectors by ~streaming~ o the radiation axially along the drill collar and bore 41. The radiation detectors 52 and 53 may comprise any conventional gamma radiation detecting means such as an array of Geiger-Mueller tubes or may consist of sodium iodide scintillators.
Referring now to FIG. 3, there is shown a illustra-tive top cross section view taken about the lines 3-3 of FIG. 2 which shows the relative posit~oning of the gamma radiation detectors 52 and 53 within the body of the drill collar 15. The left detector 52 is illu~trated as comprising ~n array of three Geiger-~ueller tube~ 52a-52c while the r~ght detector 53 is illustrated as comprising an array of three Geiger-Mueller tube~ 53a 53c. A tung~ten shield member , .
~2~17~0 -la-5~, also formed as part of the insert 51, is shown positioned between the left detector 52 and the bore 41 while a similar shield 57 is shown positioned between the bore 41 and the right detector 53. The shield mem-bers 56 and 57 minimize the detection by the detectors 52 and 53 of radiation which does not emanate from the formation.
A significant aspect of the novel geometry of the gamma-gamma radiation formation density logqing system of the present invention is that the two detectors 52 and 53 are positioned symmetrically about the longitu-dinal axis of the collar lS at equal azimuthal angles of separation from one another, i.e., 180 degrees, on diametrically opposite sides of the collar. The two detector arrays 52 and 53 both lie on a common diameter 58 of a common circle within the plane 54 per-pendicular to the axis of the drill collar lS. Both detectors are also spaced an equal distance from the radiation sources 42 and 43. As is also shown in FIG. 3, the system of the present invention produces accurate measurement of formation density regardless of the eccentric position of the drill collar within the borehole 12 because the distances between the eccen-tered tool and the borehole wall are automatically com-pensated mathematically as well as .~
~S~74~
by the averaging effects which occur when the tool is rota~ed during the logging operation.
In order to demonstrate the significance of the unique geometry of the components of the present inven-tion and the math~natical conse~uences thereof, certainterms must be defined. The left standoff distance bet-ween the side wall of the borehole 12 and the drill collar 15 is ~A~, measured along the common diameter 58. Similarly, nB~ is the righ~ standoff distance bet-ween the side of the drill collar 15, also measuredalong the common diameter 58. The distance ~TD", along the common diameter S8, i~ the di~meter of the tool.
~BD" is the diameter of the borehole. The two detec-tors 52 and 53 are seen to be located on opposite sides of the drill collar 15, and at equal axial distances from the gamma radiation sources 42 and 43, (or from a single source if such is employed). Thus, we can incorporate the geometry of the borehole itself to solve three equations s~multaneously and determine the formation matrix density.
Using ~ to indicate the density mea~ured by the detector on the left side of the FIG. 3, we see that the ormation density is given by:
.
~t ~
~2~;7~
)p~ J(/~ or (6) ~Q (1- ~ ) + ~ p~ , where (7) = formation matrix density;
~ = poro~ity of the formation;
~ = fluid density in the formation;
P~ = mud density o~ ~ fraction of gamma ray-q interacting in the mud;
and ~= (1- ~ ) ~ ~+ ~ ~ = apparent formation density It ~hould be noted that Equations 6 and 7 above are equally valid for wire line tool configurations as for gamma formation detection in measuring while drilling applications.
If we used ~ to indicate the formation density measured by the detector on the right side of the FIG. 3, we see that the formation density is also given by.
~ ) t ~ ~ (8) where ~ is the fraction of gamma rays interacting in the mud~ We also kno~ by geometry that the tool diameter, TD, and the borehole diameter, BD, are related to the tool~ po~ition in the borehole by the followlng relationships:
,.
A + s + TD = 8D (9) where A is the perpendicular distance from the left toolface to the left borehole surface ~the left standoff), and 8 is the standoff on the right side of S the tool as shown in FIG. 3. It can be noted that the probability of a photon tgamma ray) traveling a distance A before having a collision is simply exp (-klA). The probability of having an interactlon at any distance less that A is given by (l-exp(~klA)).
Likewise, the probability of having an interaction within the distance B is given by ~l-exp(-k2B)). The values ~1 and k2 are geometric constants to be further specified below~ If we assume the above relationshlps we may write the following:
~ = 1- eklA ~10) and /3 = 1-e~k28 ( 11 ) We imply that ~ and ~ are probabilities that the gamma rays will interact in the mud, and (1- ~ ) and (1-~ ) are the prob~bilities that the photon6 will interact in the formation matrix, and not in the mud.
If we now combine Equationq 7 and 10, we find that:
e (~ , ) (12) The geometry phy~ically constrains the tool ln the borehole ~o that we can use the following relationqhip:
A = BD-TD - B = R3-B (13) S so that we can rewrite Equation 10 in terms of the standoff B as follows:
3 -B) , ~ ( 14 ) We can also rewrite Equation 8 in terms of the standoff B as follows:
e~k2B = ( ~ ~ Pm )/( P~ - ~ ) (lS) or by rai~ing to the power, k1/k2, we can write Equation 15 as follows:
e ~ k 1 B = r ( /~R - P,~ )/ ( /3~ Q /~ J ] (16) Now subs~ituting Equation 16 into Equation 14, we find that:
e (~-P~)[(~ )7 (lB) which can be ~olved for the formation matrix density, ~ follows:
., P~= P~ ~ Le (/~ ) ]
(19) Now, if kl=k2, and it will be shown later that they can be equal, we can write k=kl=k2 and Equation 19 becomes the following statement:
f ~ ~ K k3 ( ~ Y2 ~ ( 2 0 ) Based on upon these derivations, we can in prin-ciple determine the formation density based on the observed densities recorded by the left and right detectors, and on the density of the mud in use at the time of the measurements. The constant k3 is deter-mined directly from the difference between the tool diameter and the diameter of the borehole within which it is being used. The tool constants kl and k2 are determined by the distance between the detectors and the source, the thickness of the drill collar wall bet-ween the detector and the exterior surface of the collar, and the efficiency of the detectors. For matched detectors and a symmetrical drill collar k will equal k2. The tool constants ~l and k2, are determined durinq calibration of the tool in a fashion ~imilar to that in which conventional wire line tools 7~
are calibrated in a teqt pit, as set forth below.
During calibration a test pit having a plurality of formations of known litholgies is used by exposing the tool to known density conditions. FIG. 5 is prepared S to convert the logarithm of the detector count rate (in any arbitrary units) to a density indication with the tool surface directly abutting the surface of the formation.
Thereafter the tool is arranged at a preselected value of standoff distance and a series of ormations of known density are logged to obtain an indication of measured density for each actual value as shown in FIG.
6. The tool is then arranged for a series of different .
standoff distances and the process repeated to produce a family of curves, as shown in FIG. 6. ~he logarithm of each line slope of the family of curves in FIG. 6 iY
plotted against standoff distance on semilog paper to produce a straight line with a negative slope as shown ln FIG. 7. The slope of this line is the tool constant kl, or k2 associated with that detector.
As shown in FIG. 4, the count of the left detector 52 is determined at 62 while the count of the rlght detector 53 is determined at 63 per unit of time and, in conventional fashion, the formation density value iR
~2~i~7~ 4 determined at 64 and 65 for the left and right detec-tors, respectively. Thereafter, this information is entered into the proce~sor 66 along with either a measured or known mud density 67 and the measured tool calibration constantg kl and k2 from storage 68. The processor thereafter produces a calculated value of formation matrix density, and porosity can be inferred in accordance with standard practices in the industry.
The present technique involves three basic assump-tions which allow the effectiveness of the present tool geometry in technique to be utilized. First, it is assumed that the borehole is relatively cloqe to gauge and does not include a large number of wash outs or cave~. In the region of the borehole near the drilling bit, this is a reliable assumption. However, in the event that this is not the case a caliper tool can be included in the system of the present invention in order to compensate for variations in borehole diameter. Nevertheless, this limitation is not nearly as critical as in the case with wire line gamma radiation density detectors since the present tool does not predicate the validity of its operation~ on wall contact as does the vast ma~ority of wire line detec-tors. The second assumption is that the m~dcake on the ~:5~7~
walls of the borehole has not had a chance to form during the logging of the well. Since the present tool operates during the measuring while drilling operation at a point near to the drill bit this assumption is reasonable.
The third assumption is that mud density is known or readily determinable. This is ~lso a very good assumption.
It should be understood that a gamma radiation for-mation density Logglng system in accordance with the principles of the present invention may be constructed with three or more detectorq rather than two as is shown in the preferred embodiment. In each case each one of the detectorg must lie in a plane per- !
pendicular to the axis of the housing and be positioned at azimuthally symmetrical equal angles from one another, i.e., with rotational symmetry about the bore-hole axis. Of course, the equations for the deter-mination of formation matrix density are increasingly more complex for structures with ~ore than two arrays but may be solved in the same fashion as the two detector array configuration discussed above.
It should be also noted that the present logging apparatus ha~ been shown within a housing or sonde comprising a drill collar forming part of a drill . .
~' strinq. While the present system is especially useful in logging while drilling systems, the particular tool geometry could also be employed in a non-MWD sonde of the wireline type.
It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description while the method and apparatus shown and described has been characterized as being preferred it will be obvious that various changes and modifications may be made therein without departing from the spirlt and scope of the invention as defined in the following claims.
Claims (26)
1. A gamma radiation formation density logging appara-tus for use in a borehole traversing an earth formation, comprising:
an elongate sonde having a longitudinal axis;
a source of gamma radiation located within said sonde;
a gamma radiation detection assembly within said sonde, including a plurality of gamma radiation detectors, at least two of said detectors being sensitive to gamma rays resulting from Compton scattering, said at least two detec-tors being spaced the same distance in the same longitudi-nal direction from said radiation source along said sonde and also being located symmetrically about the longitudinal axis of said sonde;
means connected to each of said at least two gamma radiation detectors for producing first output signals from each of said at least two detectors;
means to provide an indication of the density of the fluid in said borehole; and means responsive to the said first output signals from said detectors and to said indication of said borehole fluid density for producing an additional output signal proportional to the density of the formation surrounding the borehole in the region of the sonde.
an elongate sonde having a longitudinal axis;
a source of gamma radiation located within said sonde;
a gamma radiation detection assembly within said sonde, including a plurality of gamma radiation detectors, at least two of said detectors being sensitive to gamma rays resulting from Compton scattering, said at least two detec-tors being spaced the same distance in the same longitudi-nal direction from said radiation source along said sonde and also being located symmetrically about the longitudinal axis of said sonde;
means connected to each of said at least two gamma radiation detectors for producing first output signals from each of said at least two detectors;
means to provide an indication of the density of the fluid in said borehole; and means responsive to the said first output signals from said detectors and to said indication of said borehole fluid density for producing an additional output signal proportional to the density of the formation surrounding the borehole in the region of the sonde.
2. A gamma radiation formation density logging appara-tus for use in a borehole traversing an earth formation as set forth in claim 1, including in addition thereto, a drilling string having a measurement while drilling system therein, wherein said sonde comprises a cylindrical sub connected in said drilling string as part of said measuring while drilling system.
3. A gamma radiation formation density logging appara-tus for use in a borehole traversing an earth formation as set forth in claim 2, wherein said gamma radiation detec-tors comprise first and second detectors which are located on opposite sides of said sonde.
4. A gamma radiation formation density logging appara-tus for use in a borehole traversing an earth formation as set forth in claims 1, 2 or 3 wherein said additional out-put signals are produced in response to said first output signals produced by said detectors while the sonde is being rotated about its longitudinal axis within the borehole.
5. A gamma radiation formation density logging appara-tus for use in a borehole traversing an earth formation as set forth in claim 1 which also includes radiation shielding means positioned within said sonde in the region between said source of radiation and said detectors to limit the quantity of radiation received directly from said source.
6. A gamma radiation formation density logging appara-tus for use in a borehole traversing an earth formation as set forth in claim 5 which also includes; radiation shield-ing means positioned within said sonde radially inward from each detector to limit the quantity of radiation received emanating from a region of the formation on the opposite of the sonde from the detector.
7. A system for gamma radiation formation density logging for use in a borehole traversing an earth forma-tion, comprising:
a drilling string having a drilling bit at its lower end;
an elongate housing connected as part of said drilling string;
a source of gamma radiation located within said housing;
a gamma radiation detection assembly located within said housing and including a plurality of gamma radiation detectors, at least two of said detectors being sensitive to gamma rays resulting from Compton scattering, said at least two detectors being spaced the same distance in the same longitudinal direction along said housing from said source and also being positioned symmetrically about the longitudinal axis of said housing;
means connected to each of said at least two gamma radiation detectors for producing first output signals from each of said at least two detectors;
means to provide an indication of the density of the fluid in said borehole; and means responsive to the said first output signals from said detectors produced while said housing is positioned within the borehole and to said indication of said borehole fluid density for producing an additional output signal proportional to the density of the formation surrounding the borehole.
a drilling string having a drilling bit at its lower end;
an elongate housing connected as part of said drilling string;
a source of gamma radiation located within said housing;
a gamma radiation detection assembly located within said housing and including a plurality of gamma radiation detectors, at least two of said detectors being sensitive to gamma rays resulting from Compton scattering, said at least two detectors being spaced the same distance in the same longitudinal direction along said housing from said source and also being positioned symmetrically about the longitudinal axis of said housing;
means connected to each of said at least two gamma radiation detectors for producing first output signals from each of said at least two detectors;
means to provide an indication of the density of the fluid in said borehole; and means responsive to the said first output signals from said detectors produced while said housing is positioned within the borehole and to said indication of said borehole fluid density for producing an additional output signal proportional to the density of the formation surrounding the borehole.
8. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7 wherein said housing is connected into the drill string near the said drilling bit where the diameter of the borehole is relatively constant.
9. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7 which also includes radiation shielding means positioned within said housing in the region between said source of radiation and said detectors to limit the quantity of radiation received directly from said source.
10. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 9 which also includes radiation shielding means positioned within said housing radially inward from each detector to limit the quantity of radia-tion received emanating from a region of the formation on the opposite side of the sonde from the detector.
11. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7, wherein said source of gamma rad-iation comprises two radiation sources located at a common axial position and lying in a common plane which is perpendicular to the axis of said housing.
12. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7, wherein said gamma radiation detectors comprise first and second detectors which are located on opposite sides of said housing.
13. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7 or 11, wherein said radiation source is cesium 137.
14. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7 or 12, wherein said additional output signal is produced in response to said first output signals obtained from said detectors while the housing is being rotated about its longitudinal axis in the borehole.
15. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 7, wherein said radiation detectors each comprise an array of Geiger-Mueller tubes.
16. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation as set forth in claim 6, wherein said radiation detectors each comprises an array of scintillation detectors.
17. A method for gamma radiation formation density logging for use in a borehole traversing an earth forma-tion, comprising:
positioning an elongate sonde within the borehole;
emitting gamma radiation into said formation from a first location within the sonde;
detecting at a plurality of locations within said sonde the emitted gamma radiation scattered from the forma-tion, said locations being symmetrically positioned about the longitudinal axis of the sonde and equally spaced in the same longitudinal direction from the first location;
generating a signal indicative of the density of the borehole fluid; and producing an output signal in response to the Compton scattered gamma radiation detected at said plurality of locations and to said borehole fluid density, said output signal being proportional to the matrix density of the formation surrounding the borehole in the region of the sonde.
positioning an elongate sonde within the borehole;
emitting gamma radiation into said formation from a first location within the sonde;
detecting at a plurality of locations within said sonde the emitted gamma radiation scattered from the forma-tion, said locations being symmetrically positioned about the longitudinal axis of the sonde and equally spaced in the same longitudinal direction from the first location;
generating a signal indicative of the density of the borehole fluid; and producing an output signal in response to the Compton scattered gamma radiation detected at said plurality of locations and to said borehole fluid density, said output signal being proportional to the matrix density of the formation surrounding the borehole in the region of the sonde.
18. A method for gamma radiation formation density logging as set forth in claim 17 wherein said positioning step includes rotating said sonde within the borehole and wherein said plurality of locations comprise second and third locations on opposite sides of the sonde.
19. An improved system for gamma ray formation density logging for use in a borehole traversing an earth formation of the type wherein gamma ray source and detection means are disposed within a housing positionable within a bore-hole for the emission and detection of gamma rays propa-gating through said earth formation, wherein said improve-ment comprises:
said housing being longitudinally connectable as part of a rotating drilling string extending into said borehole;
said gamma ray detection means comprising a plurality of gamma ray sensors, each of said sensors being responsive to Compton scattered gamma radiation, and each being dis-posed within said housing the same longitudinal distance from said source in a common plane lying perpendicular to the longitudinal axis of said housing and at equal angles from one another;
means connected to each of said gamma radiation detec-tors for producing first output signals from each of said detectors;
means to provide an indication of the density of the fluid in said borehole; and means responsive to said first output signals from said sensors and to said indication of said borehole fluid den-sity for producing an additional output signal proportional to the density of said earth formation adjacent thereto.
said housing being longitudinally connectable as part of a rotating drilling string extending into said borehole;
said gamma ray detection means comprising a plurality of gamma ray sensors, each of said sensors being responsive to Compton scattered gamma radiation, and each being dis-posed within said housing the same longitudinal distance from said source in a common plane lying perpendicular to the longitudinal axis of said housing and at equal angles from one another;
means connected to each of said gamma radiation detec-tors for producing first output signals from each of said detectors;
means to provide an indication of the density of the fluid in said borehole; and means responsive to said first output signals from said sensors and to said indication of said borehole fluid den-sity for producing an additional output signal proportional to the density of said earth formation adjacent thereto.
20. The system as set forth in claim 19, including in addition thereto, a drill string in said system having a drilling bit at its lower end, and wherein said housing is a cylindrical sonde connectable into said drill string near the said drilling bit where the diameter of said borehole is relatively constant.
21. The system as set forth in claim 19, wherein said plurality of gamma ray sensors comprise first and second sensors disposed on opposite sides of the sonde.
22. The system as set forth in claim 19 wherein said additional output signal producing means is responsive to said first output signals from said sensors obtained while said drill string and housing are rotated.
23. The system as set forth in claim 19, wherein said source comprises two radiation sources located at a common axial position and lying in a common plane which is perpen-dicular to the axis of said housing.
24. The system as set forth in claim 19, wherein said detection means comprises arrays of scintillation detec-tors.
25. An improved system for gamma ray formation density logging for use in a borehole traversing an earth formation of the type wherein gamma ray source and detection means are disposed within a cylindrical housing positionable within a borehole for the emission and detection of gamma rays propagating through said earth formation and borehole drilling mud, wherein said improvement comprises:
said housing being longitudinally connectable as part of a rotating drilling string extending into said borehole;
said gamma ray detection means comprising first and second gamma ray sensors, each of said sensors being responsive to Compton scattered gamma radiation, and each being geometrically disposed within said housing the same longitudinal distance from said source, in a common plane lying perpendicular to the longitudinal axis of said housing and equidistant from the center thereof;
means connected to each of said gamma ray sensors for producing first output signals from each of said sensors;
and means for producing a formation density output signal while said drill string and housing are rotated, said density output signal being a function of said first out-put signals from each of said sensors, the density of said drilling mud within said borehole, the geometrical configu-ration of said sensors relative to said source and said borehole diameter relative to said housing diameter, and an established probability for the fraction of gamma rays interacting with said formation and said drilling mud.
said housing being longitudinally connectable as part of a rotating drilling string extending into said borehole;
said gamma ray detection means comprising first and second gamma ray sensors, each of said sensors being responsive to Compton scattered gamma radiation, and each being geometrically disposed within said housing the same longitudinal distance from said source, in a common plane lying perpendicular to the longitudinal axis of said housing and equidistant from the center thereof;
means connected to each of said gamma ray sensors for producing first output signals from each of said sensors;
and means for producing a formation density output signal while said drill string and housing are rotated, said density output signal being a function of said first out-put signals from each of said sensors, the density of said drilling mud within said borehole, the geometrical configu-ration of said sensors relative to said source and said borehole diameter relative to said housing diameter, and an established probability for the fraction of gamma rays interacting with said formation and said drilling mud.
26. A system for gamma radiation formation density logging for use in a borehole traversing an earth formation, wherein the borehole contains a drilling mud of known density, comprising:
a rotating tool;
means within said tool for emitting gamma radiation into the formation surrounding said borehole;
first and second gamma radiation detector means located within said tool on a common circle at diametrically opposed points on said circle, said first and second detec-tor means each being responsive to Compton scattered gamma radiation and each being spaced the same axial distance in the same axial direction from said emitting means, each of said detector means having a known efficiency, and each of said detector means being separated from the borehole wall by a known thickness of metal, and wherein the rotating tool has a known diameter compared to the diameter of the borehole;
means connected to said first and second detector meansfor producing first and second output signals, respec- tively, from said first and second detector means;
means for producing a third output signal related to the density of the drilling mud; and means for generating a fourth output signal function-ally related to the density of the formation, said fourth output signal also being functionally related to the effi-ciency of said first and second detector means, the amount of metal between said first and second detector means and the borehole wall, the difference between the diameter of the tool and the diameter of the borehole, and the axial distance of said first and second detector means from said emitting means.
a rotating tool;
means within said tool for emitting gamma radiation into the formation surrounding said borehole;
first and second gamma radiation detector means located within said tool on a common circle at diametrically opposed points on said circle, said first and second detec-tor means each being responsive to Compton scattered gamma radiation and each being spaced the same axial distance in the same axial direction from said emitting means, each of said detector means having a known efficiency, and each of said detector means being separated from the borehole wall by a known thickness of metal, and wherein the rotating tool has a known diameter compared to the diameter of the borehole;
means connected to said first and second detector meansfor producing first and second output signals, respec- tively, from said first and second detector means;
means for producing a third output signal related to the density of the drilling mud; and means for generating a fourth output signal function-ally related to the density of the formation, said fourth output signal also being functionally related to the effi-ciency of said first and second detector means, the amount of metal between said first and second detector means and the borehole wall, the difference between the diameter of the tool and the diameter of the borehole, and the axial distance of said first and second detector means from said emitting means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/734,963 US4698501A (en) | 1985-05-16 | 1985-05-16 | System for simultaneous gamma-gamma formation density logging while drilling |
| US734,963 | 1985-05-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1257404A true CA1257404A (en) | 1989-07-11 |
Family
ID=24953772
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000499259A Expired CA1257404A (en) | 1985-05-16 | 1986-01-09 | System for simultaneous gamma-gamma formation density logging while drilling |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4698501A (en) |
| CA (1) | CA1257404A (en) |
| DE (1) | DE3616399A1 (en) |
| FR (1) | FR2582108A1 (en) |
| GB (1) | GB2175085B (en) |
| NL (1) | NL8601237A (en) |
| NO (1) | NO167065C (en) |
Families Citing this family (41)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4864129A (en) * | 1986-06-11 | 1989-09-05 | Baroid Technology, Inc. | Logging apparatus and method |
| US4894534A (en) * | 1986-06-11 | 1990-01-16 | Baroid Technology, Inc. | Logging apparatus and method |
| US4814609A (en) * | 1987-03-13 | 1989-03-21 | Schlumberger Technology Corporation | Methods and apparatus for safely measuring downhole conditions and formation characteristics while drilling a borehole |
| US4845359A (en) * | 1987-11-24 | 1989-07-04 | Schlumberger Technology Corporation | Methods and apparatus for safely handling radioactive sources in measuring-while-drilling tools |
| US4879463A (en) * | 1987-12-14 | 1989-11-07 | Schlumberger Technology Corporation | Method and apparatus for subsurface formation evaluation |
| US4904865A (en) * | 1988-04-01 | 1990-02-27 | Exploration Logging, Inc. | Externally mounted radioactivity detector for MWD |
| US5017778A (en) * | 1989-09-06 | 1991-05-21 | Schlumberger Technology Corporation | Methods and apparatus for evaluating formation characteristics while drilling a borehole through earth formations |
| US5058077A (en) * | 1990-10-09 | 1991-10-15 | Baroid Technology, Inc. | Compensation technique for eccentered MWD sensors |
| US5159577A (en) * | 1990-10-09 | 1992-10-27 | Baroid Technology, Inc. | Technique for reducing whirling of a drill string |
| US5242020A (en) * | 1990-12-17 | 1993-09-07 | Baker Hughes Incorporated | Method for deploying extendable arm for formation evaluation MWD tool |
| GB2252623B (en) * | 1991-01-15 | 1994-10-19 | Teleco Oilfield Services Inc | A method for analyzing formation data from a formation evaluation measurement while drilling logging tool |
| US5250806A (en) * | 1991-03-18 | 1993-10-05 | Schlumberger Technology Corporation | Stand-off compensated formation measurements apparatus and method |
| US5184692A (en) * | 1991-03-18 | 1993-02-09 | Schlumberger Technology Corporation | Retrievable radiation source carrier |
| CA2046738A1 (en) * | 1991-04-05 | 1992-10-06 | Terry D. Osburn | Well logging radioactive detector assembly |
| US5175429A (en) * | 1991-08-30 | 1992-12-29 | Baker Hughes Incorporated | Stand-off compensation for nuclear MWD measurement |
| US5390115A (en) * | 1993-05-10 | 1995-02-14 | Schlumberger Technology Corporation | Compensated gamma-gamma density sonde using three detectors |
| US5539225A (en) * | 1994-09-16 | 1996-07-23 | Schlumberger Technology Corporation | Accelerator-based methods and apparatus for measurement-while-drilling |
| US5608215A (en) * | 1994-09-16 | 1997-03-04 | Schlumberger Technology Corporation | Method and apparatus for determining density of earth formations |
| US5804820A (en) * | 1994-09-16 | 1998-09-08 | Schlumberger Technology Corporation | Method for determining density of an earth formation |
| US5525797A (en) * | 1994-10-21 | 1996-06-11 | Gas Research Institute | Formation density tool for use in cased and open holes |
| US6648083B2 (en) | 2000-11-02 | 2003-11-18 | Schlumberger Technology Corporation | Method and apparatus for measuring mud and formation properties downhole |
| US6781115B2 (en) | 2001-03-30 | 2004-08-24 | Schlumberger Technology Corporation | Subsurface radiation phenomena detection with combined and azimuthally sensitive detectors |
| US6768106B2 (en) | 2001-09-21 | 2004-07-27 | Schlumberger Technology Corporation | Method of kick detection and cuttings bed buildup detection using a drilling tool |
| US6944548B2 (en) | 2002-12-30 | 2005-09-13 | Schlumberger Technology Corporation | Formation evaluation through azimuthal measurements |
| US7253401B2 (en) * | 2004-03-15 | 2007-08-07 | Weatherford Canada Partnership | Spectral gamma ray logging-while-drilling system |
| US8022983B2 (en) * | 2005-04-29 | 2011-09-20 | Schlumberger Technology Corporation | Borehole imaging system for conductive and resistive drilling fluids |
| US7596452B2 (en) * | 2007-06-28 | 2009-09-29 | Baker Hughes Incorporated | Compensated caliper using combined acoustic and density measurements |
| WO2009020996A2 (en) | 2007-08-08 | 2009-02-12 | Schlumberger Canada Limited | Radiation generator and power supply configuration for well logging instruments |
| US8895914B2 (en) | 2007-08-10 | 2014-11-25 | Schlumberger Technology Corporation | Ruggedized neutron shields |
| US7897915B2 (en) * | 2008-12-19 | 2011-03-01 | Schlumberger Technology Corporation | Segmented tubular body |
| US8742328B2 (en) * | 2010-12-03 | 2014-06-03 | Schlumberger Technology Corporation | Logging-while-drilling tool incorporating electronic radiation generator and method for using same |
| US8481920B2 (en) * | 2011-07-19 | 2013-07-09 | Baker Hughes Incorporated | Apparatus and method for determining formation density from nuclear density measurements made using sensors at more than one location |
| US8583377B2 (en) * | 2011-10-26 | 2013-11-12 | Halliburton Energy Services, Inc. | Methods and systems of formation density measurements in the presence of invasion of drilling fluids |
| US9052404B2 (en) * | 2011-12-30 | 2015-06-09 | Schlumberger Technology Corporation | Well-logging apparatus including azimuthally-spaced, noble gas-based detectors |
| CA2937353C (en) * | 2014-01-24 | 2020-08-04 | Nabors Drilling Technologies Usa, Inc. | Mwd system for unconventional wells |
| US9541671B2 (en) * | 2014-05-05 | 2017-01-10 | Vale S.A. | Method and system for evaluation of gamma-gamma well logging data in mineral exploration |
| US10132158B2 (en) | 2014-12-19 | 2018-11-20 | Halliburton Energy Services, Inc. | Roller cone drill bit with embedded gamma ray detector |
| US9933544B2 (en) | 2014-12-24 | 2018-04-03 | Halliburton Energy Services, Inc. | Near-bit gamma ray sensors in a rotating section of a rotary steerable system |
| CN111749686A (en) * | 2020-07-08 | 2020-10-09 | 中国石油天然气集团有限公司 | Drill bit rapid optimization method based on stratum drilling resistance parameters |
| US11940591B2 (en) * | 2020-08-07 | 2024-03-26 | Nabors Drilling Technologies Usa, Inc. | Gamma ray logging tool with detector window |
| CA3211957A1 (en) * | 2021-05-21 | 2022-11-24 | Daniel C. Minette | Apparatus and method for compensation of formation evaluation tools |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2785314A (en) * | 1951-09-28 | 1957-03-12 | Texas Co | Radioactivity earth exploration |
| US2934652A (en) * | 1956-08-13 | 1960-04-26 | Socony Mobil Oil Co Inc | Selected scattered gamma-ray density logging |
| US3281599A (en) * | 1959-08-25 | 1966-10-25 | Chevron Res | Mud-cake-thickness measuring device for gamma-gamma density logger |
| US3333466A (en) * | 1964-12-28 | 1967-08-01 | Seismograph Service Corp | Articulated density logging tool |
| US3846631A (en) * | 1972-03-13 | 1974-11-05 | Applied Invention Corp | Gamma ray differential density probe |
| US3840706A (en) * | 1973-10-29 | 1974-10-08 | Seismograph Service Corp | Remote test circuit for carrier telephones |
| FR2298680A1 (en) * | 1975-01-24 | 1976-08-20 | Schlumberger Prospection | METHOD AND DEVICE FOR MEASURING THE DENSITY OF FORMATIONS CROSSED BY A BOREHOLE |
| US4169979A (en) * | 1977-07-15 | 1979-10-02 | Texaco Inc. | Method and apparatus for measuring azimuth and speed of horizontal fluid flow by a borehole |
| US4180727A (en) * | 1977-10-20 | 1979-12-25 | Mobil Oil Corporation | Gamma-gamma density logging method |
| US4297575A (en) * | 1979-08-13 | 1981-10-27 | Halliburton Company | Simultaneous gamma ray measurement of formation bulk density and casing thickness |
| US4342911A (en) * | 1979-12-28 | 1982-08-03 | French Lewis L | Focused nuclear interface survey instrument and method of determining density changes in mining and storage wells |
| US4492865A (en) * | 1982-02-04 | 1985-01-08 | Nl Industries, Inc. | Borehole influx detector and method |
| AU561685B2 (en) * | 1983-03-11 | 1987-05-14 | N L Industries Inc. | Formation density logging while drilling |
| US4596926A (en) * | 1983-03-11 | 1986-06-24 | Nl Industries, Inc. | Formation density logging using multiple detectors and sources |
-
1985
- 1985-05-16 US US06/734,963 patent/US4698501A/en not_active Expired - Fee Related
- 1985-12-27 NO NO855300A patent/NO167065C/en unknown
-
1986
- 1986-01-09 CA CA000499259A patent/CA1257404A/en not_active Expired
- 1986-02-20 FR FR8602342A patent/FR2582108A1/en not_active Withdrawn
- 1986-04-07 GB GB8608428A patent/GB2175085B/en not_active Expired
- 1986-05-15 DE DE19863616399 patent/DE3616399A1/en not_active Withdrawn
- 1986-05-15 NL NL8601237A patent/NL8601237A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| GB2175085A (en) | 1986-11-19 |
| DE3616399A1 (en) | 1986-11-20 |
| GB2175085B (en) | 1989-08-31 |
| GB8608428D0 (en) | 1986-05-14 |
| NO167065C (en) | 1991-09-25 |
| FR2582108A1 (en) | 1986-11-21 |
| US4698501A (en) | 1987-10-06 |
| NL8601237A (en) | 1986-12-16 |
| NO167065B (en) | 1991-06-17 |
| NO855300L (en) | 1986-11-17 |
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