US2423156A - Method of recovering desirable petroleum hydrocarbon fractions at substantially wellhead pressure - Google Patents

Description

2 Sheets-Sheet 1 July 1, 1947.

HETHOD OF RECOVERING DESIRABLE PETROLEUM HYDROGARBON FRACTIONS AT SUBSTANTIALLY WELL HEAD PRESSURE Filed arch 6, 1939 July l, 1947. L, s RE|D 2,423,156

METHOD 0F RECOVERING DESIRABLE PETROLEUM HYDROCARBON FRACTIONS AT SUBSTANTIALLY WELL HEAD` PRESSURE Filed March s, 1939 2 sheets-sheet 2 ma Y Ref/agrade Pressa/v 10a/kf Patented July 1, 1947 y, p .y 2,423,155 s i METHODv or nE'covEluNcV pEsmanLE PE- TRoLEUM nronocAnEoN Fnac'rloNs -A'r sUBsTANrrALLY WELLHEAD PRESSURE I Laurence s'. addormenta city.' om. l Application March 6, 1939, Serial No. 259,986

i e l c 'I'his invention relates to a method of recovering desirableI liqueiiable hydrocarbons I from the iiow vof high pressure natural gas wells where it is both necessary and desirable to return the `residue gas to the producing iormation'to main- "f7 oisans. (cnet- 1755) Vof this general type indicate that this optimum liquefaction pressure is` definitely fixed by the tain formation pressure orto repressure a prol ducingformatiom and v has -for its `principal object-to provide for recovery of such hydrocarbons at. approximatelythe flowing pressure of s the producing well. n

Under present conditions a great volumeof high pressure` natural gas contains profitable quantities of desirable hydrocarbons or distillate, and in order to produce and recover the desired hydrocarbon fractions, the residue gas is returned to theproducing formation to prevent its waste, to conserve formation energy and to prevent condensation and subsequent loss of the' desirable heavier hydrocarbon components of the reservoir fluid which inevitably results from declining pressures in gas reservoirs of the genera1 type under consideration. SuchV condensation, caused .byl declining pressure, is commonly termed retrograde condensation, be-

cause it is contrary to normal reactions wherein a pressurel decrease is accompanied by vaporization. Processes which recover these desirable hydrocarbons have been carried on at relatively low pressures well within the normal condensation limits of these gas-liquid mixtures. To return the residue gas to the formation, it is then necessary to provide expensive compressor equipment'to raise the pressure of the gas to the required injection pressure. Extensive studies ofthe phenomena of retrograde vaporization and condensation have resulted in process improvements which permit these hydrocarbons to be recovered at substantially high pressures, thereby greatly lowering the differential pressure between the denuded gas and the pressure required to inject the denuded gas into the producing formation. Consequently smaller and less expensive compressor equipment may be used and operated with less power consumption. The fact remains, however, that` the operating pressures or these improved processes are limited by the pressure at which normal conden- "sation ceases and retrograde vaporization takes eiect, and this pressure is denoted by a maxiv mum liquid volume condensed from a unit volurne of the gaseous well iiow when condensed under constant ntemperature conditions This pressure may :be termed optimum liquefaction pressure." Extensive studies of the reservoir fluids produced vby the 'numerous known gas nelds composition of the hydrocarbon mixture comprising the reservoir fluid and that the variation in this optimum liquefaction pressure is conined, `with but few exceptions, to the range of 800 to 1200 pounds per square inch. Moreover, these studies indicate that there is no relationship between the reservoir pressure and the optimum liquefaction pressure exhibited by the reservoir fluid, so that it is not uncommon to find that the gaseous flow from a well at 3500 pounds pressureexhibits an optimum liquefaction pressure of 1000 pounds per square inch. 'Ihe compressor equipment incorporated into present day condensation type distillate recovery systems therefore remains exceedingly costly land requires great power consumption.

, lationship between the composition 0f the reservoir fluid and the optimum liquefacticn pressure cited above, and by means of admixing definite quantities of high molecular weight hydrocarbon liquid with the well stream, I alter the composition of the hydrocarbon mixture flowing into the recovery system and thereby adjust the optimum liquefaction pressure upward to that pressure which, when considered to be the pressure at the compressor suction, will permit the compressor equipment to operate at maximum efilciency and minimum compression ratio. Not only does this enable compressor equipment to deliver a maximum volume of gas per brake' horsepower developed by reducing compression ratio to a minimum, but also it increases the volumetric capacity of the compressor equipment by taking greater advantage of the supercompressibility characteristics exhibited by all gases at high pressures since this deviation from the ideal gas laws increases directly with the prescondensate recovery and absorption system embodying the-features of my invention.

Fig. 2 is a graph showing the approximate relation between molecular weight of well fluids and the optimum lique'faction. or so-called retrograde point, which relationship has been derived from extensive tests in different high pressure gas fields of the Texas-Louisiana-Gulf area.

Referring more in detail to the drawings:

I designates a sub-surface formation containing a petroleum hydrocarbon under high pressure and temperature, and 2 designates a producing well drilled into the formation and wherethrough the formation fluid is discharged in a gaseous flow containing the desirable hydrocarbon fractions. The discharge from the well is taken from the well casing 3 and/or from the Well tubing 4,through branches 5 and 6 of a -flow line 1, preferably without any substantial reduction in pressure, and passed through a cooler 8.

The cooler 8 may be of any suitable type; 'for example, a shell having a plurality of tubes for the passage of the well ow, and around which is circulated a stream of water as a cooling medium, the water being admitted through a pipe 9 and discharged through a connection I0. The discharge line I I from the cooler is connected with a pipe I2 discharging into the base of an absorbing tower I3 through a pressure regulating valve I4.

Since the critical region, i. e., the optimum accumulation pressure, in which retrograde phenomena are observed is found to exist at progressively higher pressures as the molecular weight of the mixture of the hydrocarbons in the vapor-liquid system increases, I therefore elevate the liquefaction pressure by increasing the molecular weight of the hydrocarbon mixture through the continuous addition of definite quantities of high molecular weight hydrocarbon liquid, thereby altering the chemical and physical characteristics of the original well stream. The extent to which the optimum liquefaction pressure is elevated is dependent upon the molecular weight of the original well stream and the molecular weight and quantity of the extraneous hydrocarbon liquid that is mixed with each unit volume of the Well stream. For example, a well flowing at 2800 pounds per square inch produces a fluid having molecular weight of 20.2. Referring to Fig. 2, it is seen that the optimum liquefaction pressure exhibited by this reservoir fluid is 1200 pounds per square inch and in order to reduce the compressor requirements to a minimum it is desired to process this gas at 1900 pounds per square inch in order to return the residue gas to the formation at 2850 pounds per square inch input well head pressure, representing a compression ratio of 1.5. Again `referring to Fig. 2, it is seen that it will be necessary to increase the molecular weight of the well stream to 26.5 in order to obtain maximum condensation at 1900 pounds per square inch. A readily avail-,

able liquid hydrocarbon is selected, for example a medium gas oil having a molecular weight of 220. A calculated material balance shows that it will be necessary to mix 2.7 gallons of this heavy hydrocarbon liquid with each thousand standard cubic feet of gaseous iluid produced from the well in order to raise the molecular weight of the mixture to 26.5. The high molecular weight liquid hydrocarbon may be either straight-run or cracked naphtha, kerosene, gasoil, lube oil, lube distillate, topped (or skimmed) crude oil, and/or crude petroleum oil. It is also possible to use refined or crude coal-tar products and similar high molecular weight hydrocarbon liquids.

The heavy molecular weight liquid selected may be obtained from any available extraneous source or it may be derived from the recovered condensate by means of fractionation. In the first instance a pipe line I5' carrying the high molecular weight liquid may be connected with the pipe I5 which carries the well stream to the absorber I3 with the volume of ow regulated in accordance with the calculated amount so that the admixture has the predetermined molecular weight of 26.5. The high molecular weight liquid is preferably thoroughly mixed with the well stream by mechanical means, such as an atomizer I6, prior to admission into the absorber. The majority of the liquid content of the mixture is separated from the gaseous phase in the absorber by means of retrograde condensation at the assumed pressure of 1900 pounds. other stream of the high molecular weight liquid is preferably introduced through a branch line I1 leading to the upper tray I8 of the absorber column so that it descends through the respective trays of the column in counter-current flow with respect to the ascending gas stream, thereby removing any remaining desirable liqueable componentsy from the gaseous phase introduced through the pipe I2 and moving, upwardly through that part of the absorber which contains the respective trays. The enriched liquid collects in the base of the column together with the condensate and is discharged from the absorber through a pipe I9 under control of a valve 20. Since the molecular Weight of the injected hydrocarbon is sufficiently high to raise liquefaction pressure of the admixture to approximately the desired well head pressure, the denuded gas is delivered through a, pipe 2l at the pressure of approximately 1900 pounds, so that only a small amount of compression is required to return the gas to the formation. The gas is, therefore, delivered to a relatively small compressor unit 22 having a discharge connected by a return line 23 leading to an injection well 24 wherethrough the gas is returned to the formation for ow toward the well 2, thereby maintaining the formation pressure, and vaporizing any recoverable liquid hydrocarbons which may exist in the formation so that they may be carried to the well 2.

In the latter instance, the heavy molecular weight liquid is obtained by fractionation of the recoverable condensate as hereinafter described, the desired fraction being admitted to the absorber through the pipes I 2 and II to effect desired condensation. In both instances the lcondensed and enriched liquid is discharged from the absorber through a pipe I9 into a separator 25. When dissolved gas and/or readily vaporizable components are separated from the liquid and discharged through a line 26 under control of a pressure regulator '21, the discharge from the line 26 is collected in a suitable vessel 28 and is vented through aline 29. This vented gas may be delivered to the compressor unit for fuel purposes, processed for its natural gasoline content, compressed and injected into the formation, or otherwise suitably disposed of. The separated liquids are discharged from the base of the separator through a pilot control valve 30, by way of a pipe line 3| discharging to storage tanks 32 and 33.

When the heavy molecular weight naphtha is used a portion of, the relatively stable liquid is drawn from'the storage tanks through a line 14 connected with the bottom of the storage tanks by a pump 36, circulated through a heat exchanger It. and delivered through a pipe`31 into a fractionator tower 38.4

The high molecular weight liquid is produced in the fractionator by stripping the tower bottom product to the desired initial boiling point, probably 300 to 400 degrees F., by circulating through a reboiler 30. This liquid is withdrawn continuously from the base, oi the fractionator tower 38 through a pipe 40, and circulated in heat exchange relation with' the liquid being pumped to the' fractionator. The cooled liquid is delivered from the heat exchanger through a pipe 4|.-

passed through a refrigerating cooler l2, and delivered into the weil stream through the pipe l5 and into the absorber through the branch line i1 under the pressure of a pump II, as above described.

The overhead ,cut from the iractionator -is Y passed through a pipe 44 and circulatedv through a condenser I5, the condensate being collected in an accumulator I6: A part of the liquid collecting in the accumulator is withdrawn through a pipe 6l by a pump 65, disch'arging through a pipe 66 into the top of the i'ractionator to reflux the vapors rising in the Iractionator tower. 'Ihe stock collecting in the accumulator may command the market price for light, straight run gasoline, or possibly natural gasoline, andi is circulated by a pump 41 through a preheater I8, for discharge through a pipe 49 into a stabilizer column 50. In the stabilizer the bottom product is circulated through' a reboiler 51, and is continuously drawn on through a. line 58, passed through a, heat exchanger 59, and delivered to a stabilized gasoline storage tank 60 through a. line 6I. i

Stock from the storage tanks 32 and 33 is circulated through the heater 59 by connection therewith of a pipe 62, having connection through' aline 63 with the pump 41 where the liquid is discharged to the preheater 48 and to the stabilizer. The overhead cut from the stabilizer is discharged through a pipe 61 leading from the top of the stabilizer tower, and passed through a condenser 88 from where the condensate is delivered into an accumulator 69. 'Ihe condensed liquid collecting in the accumulator is recirculated through a pipe 10, under pressure of a pump 1 I back into the top of the stabilizer column through a, pipe 12 as reflux. The iixed gas collecting in the accumulator may be discharged through a pipe 13 under control of a pressure regulator 14, into a storage tank 15, which gas may be used `for fuel or otherwise suitably disposed of.

From the foregoing it is obvious that I have provided a system wherein the desirable hydrocarbon fractions are readily separable and recoverable at the desired high pressures, so that the denuded gas may be returned to the formation i'or pressure maintenance purposes with a relatively small increase in pressure, and that the high molecular weight hydrocarbon is readily manufactured by fractionation of a part of the recovered hydrocarbons. It is, therefore, possible to produce condensate from high pressure ,subterranean formations at the highest possible pressures in order to avoid high compression ratio between the intake and discharge sides of the compressors used in returning the denuded gas to th'e formation.

What I claim and desire to secure by Letters Patent is:

1. The method of recovering desirable liqueiiable constituents from distillate well gas initially 'at a pressure at least as high as a pressure within the retrograde condensation range oi said con- 5 stituents which comprises, expanding the gas to a pressure within the retrograde condensation v range of said constituents, separating the resulting condensed constituents from the uncondensed gas, fractionating said condensed constituents into a relatively low boiling gasoline fraction and `a relatively heavy liquid fraction, and contacting the expanding gas fwith at least a portion of said relatively heavy liquid fraction and thereby raisstituents.

2. 'I'he method of recovering desirable liquefiable constituents from a distillate gas mixture having an initialI pressure at least as'high as a pressure within the retrograde condensation range of said mixture, which comprises contacting the distillate gas mixture with a heavy liquid hydrocarbon fraction for forming a mixture having a higher normal condensation pressure than the original gas mixture to condense saidliqueiiable constituents from the gas mixture, separating the resulting condensed constituents into a relatively low boiling gasoline fraction and a relatively heavy liquid fraction for forming said contacting liquid, and conveying said heavy liquid 'fraction to the place of contact.

3. The method of recovering desirable liqueable constituents from a distillate gas mixture having an initial pressure at least as high as a pressure within the retrograde condensation range of said mixture, which comprises expanding the gas mixture to a pressure within the retrograde condensation range of said constituents, contacting the expanding distillate gas mixture with a relatively heavy liquid hydrocarbon fraction for forming a mixture having a higher normal condensation pressure than the original gas mixture to condense said liqueable constituents from the gas mixture, separating the resulting condensed constituents from the residue gas, processing the resulting condensed constituents to obtain a heavy liquid hydrocarbon fraction for forming said contacting liquid, and conveying said heavy liquid fraction to the place of contact.

4. The method of recovering desirable liqueiiable constituents from a distillate gas mixture having an initial pressure at least as high as 'a pressure within the retrograde condensation range of said mixture, which comprises contacting the distillate gas mixture while at said pressure with a relatively heavy liquid hydrocarbon fraction for forming a mixture having a higher normal condensation pressure than the original gas mixture to condense said liquenable constituents from the gas mixture, separating the resulting condensed 50 constituents from the residue gas, processing the resulting condensed constituents to obtain a relatively heavy liquid hydrocarbon fraction for forming said contacting liquid, and conveying said heavy liquid fraction to the place of contact.

5. The method of recovering desirable liqueiiable constituents from a distillate gas mixture having an initial pressure at least as high as a pressure within the retrograde condensation range of said mixture, which comprises contacting the distillate gas mixture with a heavy liquid hydrocarbon fraction for forming a mixture having a higher normal condensation pressure than the original gas mixture to condense said liqueiiable constituents from the gas mixture, contacting the 76 residual gas with a relatively heavy liquid hydroing the normal condensation pressure of said con-- 7 carbon fraction .to absorb portions of the desirable hydrocarbons which remain in the vapor phase at said pressure, separating the resulting condensed constituents from the residual gas, processing the condensed constituents to obtain the relatively heavy liquid fraction for forming said contacting liquids, and conveying said heavy liquid fraction to the places of contact.

6. The method of recovering desirable liquefiable constituents from a distillate gas mixture having an initial pressure at least as high as a pressure within the retrograde condensation range of said mixture, which comprises contacting the distillate gas mixture while at said pressure with a heavy liquid hydrocarbon fraction for forming a mixture having a higher normal condensation pressure than the original gas mixture to condense sald liqueflable constituents from the gas mixture, separating the resulting condensed constituents from the residual gas, contacting the residual gas with relatively heavy liquid hydrocarbon fractions to absorb portions of the desirable liqueable constituents which remain in the vapor phase at said higher condensation pressure of said mixture, processing said liquids to obtain the heavy liquid hydrocarbon fraction for forming said contacting liquid, cooling the heavy liquid hydrocarbon fraction. and conveying said cooled heavy liquid hydrocarbon fraction to the places of contact.

7. The method of recovering desirable liqueable constituents from distillate well gas initially at a pressure at least as high as a pressure within the retrograde condensation range of said constituents which comprises, expanding the gas to a pressure within the retrograde condensation range of said constituents, separating the resulting condensed constituents from the uncondensed gas, fractionax'ng said condensed constituents into a relatively low boiling gasoline fraction and a relatively heavy liquid fraction, contacting the expanding gas with at least a portion of said relatively heavy liquid fraction and thereby raising the normal condensation pressure of said constituents, and contacting the uncondensed gas with another portion of said heavy liquid fraction to absorb portions of desirable liqueable constituents remaining in vapor phase at said higher condensation pressure.

LAURANCE S. REID.

REFERENCES CITED The following references are of record in the i'lle of this patent:

UNITED STATES PATENTS Number Name Date 1,192,529 Kendall July 25, 1916 1,336,893 Darier Apr, 13, 1920 1,437,102 Garner et al Nov- 28, 1922 1,621,821 Armstrong Mar. 22, 1927 2,080,351 Walker May 11, 1937 2,133,774 Vaughan Oct. 18, 1938 2,135,319 Bays Nov. 1, 1933 2,174,336 Walker Sept. 26, 1939 Re. 21,239 Walker et al Oct. 17, 1939 FOREIGN PATENTS Number Country Date 317,780 Great Britain Nov. 25, 1930 OTHER REFERENCES The`o11Week1y,May 3o, 1938.

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