US3452592A - Methods and apparatus for determining effectiveness of sidewall engagement with well bore walls - Google Patents

Description

Haw

U. E. VOETTER July 1, 1969 METHODS AND APPARATUS FOR DETERMINING EFFECTIVENESS OF SIDEWALL ENGAGEMENT WITH WELL BORE WALLS 1,1966 Sheet of2 Filed Dec.

INVENTOR.

y 1969 u E. VOETTER 3,452,592

METHODS AND APPARATUS FOR DETERMINING EFFECTIVENESS 0F SIDEWALL ENGAGEMENT WITH WELL BORE WALLS Filed Dec. 1. 1966 Sheet 8 of 2 IN ENTOR. 1 z V 4 4 Q m4 Z 4/ {4% KY United States Patent 3,452,592 METHODS AND APPARATUS FOR DETERMINING EFFECTIVENESS OF SIDEWALL ENGAGEMENT WITH WELL BORE WALLS Ulrich E. Voetter, Houston, Tex., assignor to Schlumberger Technology Corporation, Houston, Tex., a corporation of Texas Filed Dec. 1, 1966, Ser. No. 598,238 Int. Cl. E21!) 47/00 US. Cl. 73-151 8 Claims ABSTRACT OF THE DISCLOSURE This application discloses apparatus and methods by which the integrityof the sealing engagement of a sealing member with a well bore wall can be established. More particularly, a fluid-sampling tool for obtaining fluids from earth formations penetrated by a well bore is described as including a sealing member that is adapted to be sealingly engaged against a well bore wall. After the sealing member is engaged with the well bore wall and before taking a fluid sample, the pressure in an opening through the sealing member is reduced so that if the sealing member is imperfectly engaged, well bore fluids will enter this opening. By measuring the pressure in this opening, it can be determined whether or not an effective seal has been made before a fluid sample is taken.

Accordingly, as will become apparent, this invention relates to methods and apparatus for isolating a wall surface in a well bore; and, more particularly, this invention pertains to new and improved sealing members having means associated therewith by which, in the practice of the methods of the invention, the integrity of their sealing engagement with a well bore wall can be esablished.

When it is desired to obtain fluid samples from earth formations that are traversed by a cased well bore, fluidsampling apparatus such as that disclosed in the Whitten Patent No. 3,104,712 is usually employed. The tool described in this patent includes two longitudinally spaced, annular sealing members that are simultaneously urged against the well casing and held there in sealing engagement to isolate two spaced portions on the inner wall thereof. Upon command from the surface, shaped charges enclosed within the tool are selectively actuated to de velop perforating jets that respectively pass through thin barriers in the center of their associated sealing member and produce perforations through the casing and cement to gain access to the earth formations. In some instances, when the perforating jets puncture these thin barriers, the formation fluids are immediately admitted to a sample chamber in the tool, In other instances, a valve must first be opened by command from the surface to admit the formation fluids to the sample chamber. Then, in either case, once it is believed that a suflicient fluid sample has been obtained, a second valve in the tool is actuated to close the sample-receiving chamber, and the tool is returned to the surface for examination of the fluid sample.

As mentioned in this Whitten patent, it is not at all uncommon for a sealing member to make an imperfect sealing engagement with a well bore wall when the tool is set. Although that particular test would most likely be faulty, when this happens in a so-called open hole or uncased well bore, there will be no particularly adverse effects on the well bore. On the other hand, where the fluid-sampling apparatus is in a cased well bore and an imperfect seal unknowingly results, the casing will be perforated needlessly and these perforations must subsequently be plugged in one way or another. The sampling apparatus can, of course, be removed and the perforations plugged by conventional squeeze-cementing proice cedures. This, however, is obviously a time-consuming and an expensive solution that is not at all welcomed by the owner of the well. Although cementing apparatus (such as shown in the Van Ness Patent No. 3,121,459) can be included with the sampling apparatus and is quite successful where the sealing members are fully sealed with the casing, such cementing apparatus is not too reliable when one or both of the sealing members are incompletely sealed. Thus, although it is preferable to avoid perforating a well casing unless a complete seal is first obtained, no practical solution has been found heretofore to prevent such needless perforations.

Acordingly, it is an object of the present invention to provide new and improved fluid-sampling apparatus including means thereon that will permit the integrity of the sealing engagement of the sealing members with a well bore wall to be checked from the surface before any perforations are made. It is a further object of the present invention to provide new and improved methods for determining whether a packing member is sealingly engaged with a well bore wall.

These and other objects of the present invention are provided by arranging on a well tool a sealing member having an opening therein that is normally closed-01f from fluid communication with an enclosed chamber at a pressure lower than the pressure of fluids in the well bore by selectively operable closure means. Where the apparatus is a formation tester, perforating means therein are actuated to place the opening through the sealing member into communication with the adjacent earth formations.

In practicing the methods of the present invention, after th sealing member is believed to be sealingly engaged, the pressure is reduced in the supposedly sealed-off or isolated opening therein. Thus, if an imperfect seal has resulted, well bore fluids will quickly fill the isolated opening. On the other hand, if the sealing member is in fact tightly sealed, the pressure in the isolated opening will remain at a reduced pressure. Thus, by measuring the resulting pressure in this isolated opening, it can be readily determined from the surface whether or not the sealing member is in fact tightly sealed against the well bore wall. Accordingly, when the methods of the present invention are employed with fluid-sampling apparatus being used in a cased well, the perforating means will not be actuated unless these pressure measurements clearly indicate that a tight seal is in fact being provided.

The novel features of the present invention are set forth with particularity in the appended claims. The operation, together with further objects and advantages thereof, may best be understood by way of illustration and example of a certain embodiment when taken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts sample-taking apparatus employing the present invention as it might appear within a cased well bore;

FIG. 2 is a simplified, schematic representation of the sample-taking apparatus illustrated in FIG. 1;

FIG. 3 is a cross-sectional view in elevation of a portion of the apparatus of FIG. 1 and illustrates a preferred embodiment of a sealing member arranged in accordance with the present invention;

FIG. 4 is an elevational view of the forward face of the sealing member depicted in FIG. 3; and

FIG. 5 is a cross-sectional view taken along the lines 5-5 in FIG. 4.

Turning now to FIG. 1, fluid-sampling apparatus 10 incorporating the principles of the present invention is shown suspended from a multi-conductor cable 11 in a borehole 12 having a casing 13 set and secured therein in the usual fashion by cement 14. The fluid-sampling apparatus 10 has been positioned adjacent a particular earth formation for collecting a sample of connate fluids therefrom. The cable 11 is spooled from a winch 16 at the earths surface, with some of its conductors being connected to a switch 17 for selective connection to a conventional power source 18 and others being connected to typical indicating-and-recording pressure-measurement apparatus 19. The fluid-sampling apparatus 10 is comprised of an elongated body 20 which, to facilitate its manufacture and assembly, may be arranged in tandemly connected sections as shown.

Sample-admitting means 21 which, for sake of convenience, may require only a single sealing member 22 are arranged in accordance with the principles of the present invention and mounted along one side of the body 20 diametrically opposite from extendible wall-engaging means. 23. Inasmuch as the particular details of most of its various components are not necessary for fully understanding the present invention, the fluid-sampling apparatus 10 is shown only schematically in FIG. 2. Since these other components are fully disclosed in the aforementioned Whitten or Van Ness patents or in other related patents referred to therein, the forthcoming descriptions of these components will be limited to only a brief explanation of their basic operation as well as their general relation to one another and to the present invention.

As illustrated in FIG. 2, the fluid-sampling apparatus 10 is basically comprised of a hydraulic system 24 which utilizes the hydrostatic pressure of the well control fluids to develop an increased hydraulic pressure for actuating the apparatus, the sample-admitting means 21, a samplecollecting system 25 for obtaining a sample of connate fluids, and, if desired, means for plugging perforations such as, for example, a cement-injecting system 26.

Briefly stated, after the apparatus 10 has been positioned adjacent the formation 15, the hydraulic system 24 is first activated from the surface. In response thereto, the wall-engaging means 23 are extended to laterally shift the apparatus 10 and sealingly engage the sealing member 22 against the inner wall of the casing 13 in readiness for obtaining a fluid sample from the formation 15. The methods of the present invention are then employed to first establish whether or .not the sealing member 22 is completely sealed. Once it is established that a good seal is made, a sample is collected in the sample-collecting system 25. The perforation-plugging means 26 are then employed before the pressure in the hydraulic system 24 is relieved to disengage the wall-engaging means 23 and sealing member 22 for retrieval of the apparatus 10.

The hydraulic system 24 may, for example, be generally of the type described in the Desbrandes Patent No. 3,011,554 and includes a master piston 27 slidably mounted in a stepped cylinder 28. An electrically actuated mud valve 29 (such as shown in FIG. 4 of the Desbrandes patent) is selectively operable to admit well control fluids through a passage 30 into the cylinder 28 above the piston 27. Thus, whenever the mud valve 29 is opened, the hydrostatic pressure of the well control fluids will drive the master piston 27 inwardly to develop a somewhat greater hydraulic pressure in that portion of the cylinder 28 below the piston. A pressure-regulating valve 31 (such as shown in FIGS. 8 and 8A of the Desbrandes patent) is responsive to the hydrostatic pressure of the well control fluids to maintain the hydraulic pressure in an outlet conduit 32 downstream of the valve at a predetermined diflerential above the hydrostatic pressure.

The hydraulic system 24 also includes a so-called dump chamber 33 for the hydraulic fluid that is connected by a branch conduit 34 to a normally-closed, piston-actuated, pressure-equalizing valve 35, and, via a normally-closed, electrically actuated valve 36 (such as shown in FIG. 7 of the Desbrandes patent), to the main hydraulic conduit 32. As illustrated in FIG. 2, the equalizing valve normally blocks fluid communication between a conduit 37 leading to the sample-admitting means 21 and a conduit 38 opening to the exterior of the apparatus 10. Thus, it will be appreciated that whenever hydraulic fluid is admitted to the branch conduit 34, the equalizing valve 35 will shift outwardly to admit well control fluids into the conduit 37.

The dump chamber 33 is normally at atmospheric pressure and is divided into larger and smaller compartments 39 and 40 separated by a flow restriction or an orifice 41. When it is desired to retrieve the apparatus 10, the valve 36 is opened to simultaneously admit hydraulic fluid from the main conduit 32 to the smaller dump chamber compartment 40 and direct the fluid to the pressure-equalizing valve 35. Although the pressure of the hydraulic fluid will immediately drop when the valve 36 is opened, the lower compartment 40 and orifice 41 are suitably sized to enable the equalizing valve 35 to be opened before the hydraulic pressure drops to its final level. Once the equalizing valve 35 opens, the hydrostatic pressure will be equalized across the sealing member 22.

The extendible wall-engaging means 23 on the opposite side of the body 20 from the sample-admitting means 21 are arranged to shift the apparatus 10 laterally and engage the sealing member 22 against the casing 13 prior to taking fluid samples. The hydraulically actuated wall engaging means 23 are comprised of an extendible backup shoe 42 which is normally held in a retracted position against the body 20 by springs 43. A piston actuator 44 is connected by a branch conduit 45 to the main hydraulic conduit 32. Thus, whenever the mud valve 29 is opened, the increased pressure in the main hydraulic conduit 32 will urge the piston actuator 44 outwardly to extend the back-up shoe 42 against the adjacent inner wall of the casing 13.

The sample-admitting means 21 includes an enclosed lateral chamber 46 within the body 20 that is open at one end, with the annular sealing member 22 being mounted outside of the body around this open end to provide a port or central opening 47 for admitting fluid samples into the chamber. The chamber 46 is connected by a conduit 48 and, via a normally-closed, electrically actuated valve 49 and another conduit 50, to the sampleoollecting system 25. Perforating means, such as a shaped charge 51, are disposed in the rear of the chamber 46, with a thin-walled closure member 52 being mounted in front of the shaped charge to fluidly seal it therein. The perforating axis of the shaped charge 51 is, of course, directed to pass through the central opening 47. The shaped charge 51 is connected to electrically responsive igniter means, such as a blasting cap 53, that is ignitable from the surface via a conductor 53a in the cable 11. Thus, so long as it has not been detonated, the shaped charge 51 will be isolated from the sample-collecting system 25 and fluid can enter the apparatus body 20 only by way of a housing port 54 within the confines of the sealing member 22.

The sample-collecting system 25 includes a samplereceiving chamber 55 which has a normally-open, hydraulically actuated closure or seal valve 56 (such as shown in FIG. 10 of the Desbrandes patent) adapted for movement into engagement with a complementary valve seat 57 in the entrance of the chamber to block flow communication with the main fluid conduit 48. The seal valve 56 is normally held open but, once it has been actuated, it will be latched in a closed position. A normallyclosed, electrically actuated vave 58 connects the seal valve 56 to the main hydraulic conduit 32. Thus, to shut otf fluid flow from the main fluid conduit 48, opening of the valve 58 will admit fluid from the hydraulic conduit 32 to shift the piston-actuated seal valve 56 downwardly into sealing engagement with the valve seat 57.

The sample-receiving chamber 55 includes upper and lower compartments 59 and 60 separated b a partition 61 having a flow restriction or orifice 62 therein. A liquid cushion 63, such as water, is disposed in the upper compartment 59 and isolated from the upper portion thereof by a floating piston 64 which is sealingly received within the upper compartment. Since the lower compartment 60 is initially empty at a reduced or atmospherlc pressure, connate fluids entering the sample-receiving chamber 55 from the conduits 48 and 50 will move the piston 64 downwardly at a rate regulated by the flow of the water cushion 63 through the orifice 62.

Pressure transducers 65 and 66 are provided to continuously monitor the pressure in the hydraulic system 24 and sample-collecting systems 25. These transducers 65 and 66 may, for example, be of the type shown in FlG. 9 of the Desbrandes patent and are connected by electrical leads 65a and 66a in the cable 11 to the pressure indicating-and-recording apparatus 19 (FIG. 1) at the surface of the earth. Thus, by observing the variations of these pressure measurements, an operator will be advised of each step in the operating cycle of the fluid-sampling apparatus v The perforating-plugging system 26 includes an enclosed chamber 67 in which a piston 68 is slidably received. A suitable liquescent plugging agent 69, such as one of the typical well-cementing materials that is capable of quickly firming or hardening, is disposed in the upper part of the chamber 67 above the floatmg piston 68. In one typical arrangement for controlling the perforation-plugging system 26, an outlet conduit 70 is connected by way of a normally-closed, electrically actuated valve 71 to the main fluid conduit 48 leading to the sample-admitting means 21. An inlet conduit 72 connects the chamber 67 below the piston 68 to the exterior of the tool 10.

To actuate the perforation-plugging system 26, the valve 71 is opened so that the well control fluids will urge the piston 68 upwardly and expel the plugging agent 69 from the chamber 67 into the conduits 48 and 54. Inasmuch as the hydrostatic pressure acting on the underside of the piston 68 is greater than the pressure in the chamber 67 whenever the sealing member 22 is tightly engaged with the adjacent wall of the casing 13, the hydrostatic pressure will displace the sealing agent 69 through the central opening 47 and completely fill the perforation resulting from the detonation of the shaped charge 51. Thus, whenever the plugging agent 69 has firmed or hardened, the perforation will be permanently plugged to prevent entry of unwanted formation fluids into the interior of the casing 13.

To operate the sample-taking apparatus 10 illustrated in FIGS. 1 and 2, the apparatus is positioned in the casing 13 adjacent the formation 15. Then, by connecting the power source 18 through the switch 17 to the cable conductor 29a, the mud valve 29 is opened to admit well control fluids into the upper portion of the master cylinder 28. This will drive the piston 27 downwardly and develop a substantially greater hydraulic pressure in the lower, reduced-diameter portion of the cylinder 28. The pres- Sure-regulating valve 31 will operate to admit hydraulic fluid into the main hydraulic conduit 32 and maintain the pressure fluid into the main hydraulic conduit 32 and maintain the pressure therein at a substantially constant difierential above the hydrostatic pressure of the well control fluids.

Since the valves 36 and 58 are still closed, the hydraulic fluid will initially enter only the branch conduit 45 leading to the wall-engaging means 23. This will operate the piston actuator 44 to extend the back-up shoe 42 against the adjacent wall of the casing 13 and shift the apparatus 10 laterally in the opposite direction. Once the apparatus 10 has been shifted laterally, the annular sealing member 22 will supposedly be sealingly engaged against the opposite inner wall of the casing 13. It will be understood, of course, that by monitoring the pressure transducer 65, an operator can determine when the sealing member 22 has presumably been engaged.

In accordance with the methods of the present invention, the integrity of the sealing engagement of the sealing member 22 against the casing 13 is now checked before proceeding further. To accomplish this, the control switch 17 is operated to connect the power source 18 with the conductor 49a and open the flow-line valve 49. Once the flow-line valve 49 opens, whatever small quantity of fluids there are in the confines of the central opening 47 and those portions of the conduits 48 and 54 above the flow-line valve will be admitted through the open seal valve 56 into the sample chamber 55. Thus, if the sealing member 22 is in fact tightly sealed against the inner wall of the casing 13, no further well control fluids can enter the flow lines 54, 48 and 50 and the sample-collecting system 25 will remain substantially at atmospheric pressure or whatever the initial pressure is in the sample chamber 55. This pronounced decrease in pressure as indicated by the pressure transducer 66 will, of course, be readily apparent and will provide a clear indication at the surface that the sealing member 22 is tightely sealed against the casing 13.

On the other hand, should the sealing member 22 not be tightly sealed against the casing 13, the momentary reduction of pressure in the central opening 47 as the flowline valve 49 opens will admit additional well control fluids and completely fill the sample-collecting system 26. It will be appreciated, therefore, that in such an event, the pressure transducer 66 will clearly indicate that the sample-collecting system 25 is at hydrostatic pressure and that this will clearly demonstrate that an inadequate seal is being provided by the sealing member 22. Should this latter condition exist, there is, of course, nothing to do but retract the back-up shoe 42 and remove the fluid-sampling apparatus 10 from the casing 13 and make any necessary repairs.

Should, however, the above-described test prove that the sealing member 22 is in fact firmly sealed against the inner wall of the casing 13, it will be safe to continue further with the remainder of the operation of the fluidsampling apparatus 10. Thus, once the integrity of the sealing engagement of the sealing member 22 has been established by the new and improved methods of the present invention, the power switch 17 is now operated to connect it to the cable conductor 53a to detonate the shaped charge 51. Upon detonation of the shaped charge 51, the thin-walled closure member 52 will be punctured and the perforating jet will perforate the casing 13, cernent 14 and the adjacent formation 15. Accordingly, should there be recoverable connate fluids that can flow into the resultant perforation, they will enter the sampleadmitting means 21 and flow into the sample-receiving chamber 55 by way of the conduits 54, 48 and 50.

Whenever pressure measurements from the transducer 66 indicate that the sample-receiving chamber 55 is most likely full, the power switch 17 is connected to the cable conductor 58a to open the valve 58. Opening of the valve 58 will admit fluid from the main hydraulic conduit 32 to the seal valve 56 and close off the sample-receiving chamber 55.

Then, to plug the perforation (not shown) through the casing 13, the switch 17 is connected to the conductor 71a to open the valve 71. As previously mentioned, whenever the valve 71 is opened, the hydrostatic pressure of the well control fluids will displace the piston 68 upwardly in the chamber 67 and expel the plugging agent 69 therein through the conduits 70 and 48 and port 54 into the perforation. Once it is believed that a suflicient quantity of the plugging agent 69 has been injected into the perforation, the power switch 17 is connected to the conductor 36a to open the valve 36 and relieve the hydraulic pressure holding the wall-engaging means 23 in position.

Opening of the valve 36 will admit hydraulic fluid to the lower compartment 40 of the dump chamber 33 as well as to the pressure-equalizing valve 35. As previously explained, however, the hydraulic pressure in the branch conduit 34 will decrease so slowly that the equalizing valve 35 will have time to first shift outwardly from its flow-blocking position between conduits 37 and 38. Then,

once the well control fluids are admitted through the conduit 37 into the central opening 47, any pressure differential across the sealing member 22 will be equalized. Finally, as the pressure drops in the main hydraulic conduit 32, the hydrostatic pressure of the well control fluids will, with the assistance of the springs 43, retract the back-up shoe 42 to free the apparatus and allow it to be retrieved.

Turning now to FIG. 3, a partial cross-sectional view in elevation is shown of a portion of the body on which is mounted a preferred embodiment of a sealing member arranged in accordance with the present invention. In FIG. 4, an elevational view is also shown of the forward face of the sealing member 100.

The sealing member 100 is comprised of a rigid, generally flat, support member 101 of steel or the like that has an elongated recess 102 along its forward face and two holes 103 and 104 formed through its back that open into the recess. A resilient sealing material 105, such as typical elastomer, is secured, as by bonding, completely around at least the recess 102 in the front of the sealing member 100. The front face of the elastomeric material 105 is carried forwardly of the support member 101 a sufficient distance to provide a yieldable margin that completely surrounds the recess 102.

In one manner of attaching the sealing member 100 to the body 20, the forward end of the shaped charge chamber 46 may be counterbored, as at 106, to receive an annular member or ring 107 that is threadedly secured therein immediately in front of the forward end of the shaped charge 51. A tubular member 108 having its inner bore closed by a transverse web 109 that serves as the aforementioned barrier 52 is sealingly mounted in the inner bore of the ring 107 and is prevented from moving forwardly therein by outwardly directed flanges 110 at the rear end of the tubular member. The forward end of the tubular member 108 projects forwardly of the ring 107 and is arranged to be secured, as by threads 111, in the hole 103 through the support member 101. The other hole 104 in the support member 101 is arranged to be disposed over the outer end of the short lateral bore 54 that leads into the body 20 and is in communication with the longitudinal housing passage 48 or main flow line. To prevent the sealing member 100 from rotating with respect to the body 20, a tubular plug 112 is disposed in the hole 104 and threadedly secured within the outer end of the lateral bore 54.

It will be appreciated, therefore, that when the sealing member 100 is urged against the inner wall of the casing 13, the forward marginal portions of the elastomeric ma-,

terial 105 around the support member 101 will usually be capable of accommodating any irregularities in the adjacent wall of the casing to provide a tight sealing engagement therewith. However, as already mentioned, should there be some unusual irregularity in the casing 13 or should the sealing member 100 itself have been damaged as the apparatus 10 is being positioned, well control fluids can readily enter the recess 102 and pass on into the sample chamber 55 once the flow-line valve 49 is opened. It will be realized, of course, that the shaped charge 51 will remain sealed within its chamber 46 by the web 52 and the ring 107.

Accordingly, it will be appreciated that the present invention has provided new and improved methods and apparatus for establishing that a sealing member is not in fact sealingly engaged with the adjacent wall of the well bore. By employing the present invention in conjunction with fluid-sampling apparatus such as described herein, needless perforations through a well casing will be prevented. It will be appreciated, of course, that the principles of the present invention can also be applied to other well tools employing sealing or packing members to determine the effectiveness of their engagement against a wall in a well bore.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for testing the integrity of the sealing engagement of a sealing member with a cased well bore containing fluids prior to producing a perforation therein comprising the steps of: engaging the sealing member against the casing in a well bore to isolate at least a portion thereof from well bore fluids; reducing the pressure in the isolated portion below the pressure of such well bore fluids to induce their flow into the isolated portion should the sealing engagement of the sealing member with the casing be imperfect; and, before perforating the casing, measuring the pressure in the isolated portion to determine whether well bore fluids have entered the isolated portion.

2. A method for testing the integrity of the sealing engagement of a sealing member with a cased well bore containing fluids prior to producing a perforation therein comprising the steps of: engaging the sealing member against the casing in a well bore to isolate at least a portion thereof from well bore fluids; measuring the pressure in the isolated portion to determine the initial pressure therein; reducing the pressure in the isolated portion below the initial pressure to induce flow of well bore fluids into the isolated portion should the sealing engagement of the sealing member with the casing be imperfect; and, before perforating the casing, remeasuring the pressure in the isolated portion to determine whether the pressure therein has remained at a reduced magnitude.

3. Apparatus adapted for use in a cased well bore penetrating earth formations and comprising: a body; a sealing member on said body and having a central opening therein; means on said body adapted for urging said sealing member into sealing engagement with a well casing to isolate a portion thereof adjacent to said central opening from well bore fluids; perforating means aligned with said central opening and adapted, upon actuation, to penetrate an isolated portion of well casing for admitting fluids from earth formations therebeyond into said central opening; means adapted to reduce pressure in said central opening below that of such well bore fluids; and means adapted for measuring pressure in said central opening before said perforating means are actuated.

4. The apparatus of claim 3 wherein said sealing member is comprised of: a rigid support member having a forward face with a recess therein defining said central opening; an elastomeric material completely secured to said support member closely encircling the perimeter of said support member and covering said forward face of said support member around said recess; a pair of ports through said support member and respectively terminating in said recess, one of said ports being aligned with said perforating means and the other of said ports being connected to said pressure-reducing means.

5. The apparatus of claim 4 wherein the forward faces of said support member and elastomeric material are curved to accommodate the internal curvature of a well casing.

6. The apparatus of claim 4 wherein the longitudinal dimensions of said sealing member and recess are greater than their transverse dimensions and said ports are longitudinally spaced from one another.

7. The apparatus of claim 6 wherein the forward faces of said support member and elastomeric material are curved to accommodate the internal curvature of a well casing.

8. The apparatus of claim 4 wherein said apparatus is adapted for obtaining samples of fluids from earth formations penetrated by the well bore and said pressurereducing means include a sample-receiving chamber in 9 10 said body normally at a pressure lower than that of such 3,220,245 11/1965 Van Winkle 73-46 X well bore fluids.

References Cited RICHARD C. QUEISSER, Primary Examiner. UNITED STATES PATENTS JERRY W. MYRACLE, Assistant Examiner.

r 2,855,777 10/1958 Garrett 73- 0 0 US. Cl. X.R.

3,107,730 10/1963 Lebourg 166-3 X 166-4

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