US2856000A - Production of hydrocarbons from subsurface reservoirs - Google Patents

Description

J. M. BARRON Det. 14, 1958 2 Sheets-Sheet 1 Filed July 2o, 1954 @3% mug h Smm Q www M OO QN Y QM QW k k. m.

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Get. M, 1958 J. M. BARRON 2,856,000

l PRODUCTION OF HYDROCARBONS FROM SUBSURFACE RESERVOIRS Filed July 20, 1954 2.Sheets-Sheet 2 2,856,0ilil PRODUCTION F HYDRCARBONS FRM SUBSURFACE RESERVlRS.

Joseph M. Barron,` Port Arthur, rlex., assigner to Texaco Development Corporation, New York, N. Y., a corporation of Delaware Application July 2l), 1954, Serial No. 444,610

1 Claim. (Cl. loe-9) This invention relates to the production of hydrocarbons from vsubsurface reservoirs. More particularly, thisinvention relates to a method forl increasing the overall; production of normally liquid hydrocarbonsffrom subsurface reservoirs.

A gas` condensate reservoir is a subsurface reservoir iu which the'bulk of the hydrocarbons exists as a high pressure gas subject to condensation upon isothermal pressure decline. Accordingly, a retrograde enriched high pressure gas comprises a single phase admixture of normally gaseous hydrocarbons, such as methane and ethane, together with enriching constituents comprising normally liquid hydrocarbons. In a retrograde enriched gas the amount of the enriching normally liquid hydrocarbons contained therein is far in excess of the amount which could be held by the normally gaseous hydrocarbon constituents thereof as a gas at normal atmospheric pressure. Such a subsurface high pressure reservoir is produced by withdrawing the retrograde enriched gas to the surface, subjecting it to a reduction in pressure and permitting the constituents thereof to separate into a gaseous natural gas fraction and a .liquid hydrocarbon condensate fraction.

It is an object to provide an improved method and apparatus for producing hydrocarbons from a plurality of subsurface reservoirs.

It is another object of this invention to provide an improved method for Aproducing hydrocarbons from subsurface reservoirs wherein at least one of the reservoirs is originally at a substantially higher pressure than at least one other of said reservoirs.

It is still another object of this invention to provide an improved method for producing hydrocarbons from a -high pressure reservoir underlying a relatively low pressure reservoir.

Stilljanother object of this invention is to provide an improvedk method for producing hydrocarbons from a highV4 pressure reservoir containing normally liquid hydrocarbons in retrograde admixture with normally gaseoushydrocarbons wherein said high pressure reservoir is-'associated with an overlying relatively low pressure reservoir which contains normally liquid hydrocarbons therein as a separate liquid phase.

It4 is still another object of this invention to provide a method and apparatus for recovering normally liquid hydrocarbons from a relatively high pressure reservoir without employing extensive separating and fractionating equipment on the surface.

At least one of the objects of this invention will be accomplished in at least one embodiment of this invention.

Theseand-other objects of this invention and how they are accomplished will become yapparent with reference to the accompanying disclosure and drawing where- Fig. g 1 schematically illustratesl a vertical section gthrough geological subsurface formationswhich include atent pressure.

lTice a relatively high pressure hydrocarbon producing reservoir and a relatively low pressure hydrocarbon producing reservoir;

Fig. 2 illustrates an apparatus which might be employed in the practice of my invention for controlling the ow of a retrograde enriched fluid from a high pressure formation to a low pressure formation;

Fig. 2a is a partial cross sectional View of the apparatus of Fig. 2 taken along the line A-A; and

Fig. 3 graphically illustrates some of the advantages to be obtained in the practice of my invention.

In accordance with my invention the contents of a relatively high pressure gas condensate reservoir after having been at least partially stripped of some of its retrograde enriching hydrocarbons are discharged directly into a separate, relatively low pressure hydrocarbon reservoir. The low pressure reservoir is then produced by means of a producing well extending thereinto at a point spaced from the point of introduction or injection of the high pressure gas obtained from the high pressure reservoir. As a result of the above-indicated operations, the contents of the high pressure reservoir and the low pressure reservoir are produced from the relatively low pressure reservoir through the producing well extending thereinto. It is contemplated in the practice of my invention to direct substantially all of the remaining gasiform hydrocarbons from a relatively high pressure condensate reservoir into and through a relatively low pressure reservoir. Advantageously the relatively low pressure reservoir contains gas relatively rich in normally liquid hydrocarbons with respect to the high pressure gas injected thereinto.

In accordance with the present invention, it has been found that the relatively lean high pressure gas entering the relatively low pressure and relatively rich condensate reservoir not only increases the pressure of the low pressure reservoir, but also the lean high pressure gas becomes enriched by taking up by retrograde vaporization the normally liquid phase hydrocarbons present in the lower pressure condensate reservoir. The enrichment which takes place raises amount of normally liquid hydrocarbons contained in the resulting retrograde enriched phase to a value corresponding to the enrichment characteristic of the relatively rich condensate reservoir at the pressure newly prevailing. Therefore, the amount of Vnormally liquid hydrocarbons or condensate so produced from the two reservoirs is substantially greater than the amount which could be produced if the two reservoirs were separately produced.

For example, the high pressure relatively lean retrograde fluid passing into the relatively low pressure condensate reservoir picks up or exchanges hydrocarbons until it reaches an equilibrium composition corresponding to that of the conditions prevailing in the low pressure reservoir. Since opening up or connecting the two reservoirs results in substantially increasing the pressure of the relatively low pressure reservoir from which production is effected, the total retrograde enrichment of the produced fluid is increased. This follows from the fact that, in general, the amount of normally liquid condensate contained in the retrograde enriched gas delivered by a given reservoir increases with the reservoir As the pressure decreases the amount of normally liquid fractions recovered as condensate decreases;` stated in more practical terms, the number of barrels of stock tank liquid recovered per MMCF of producedl As a result, therefore the normally liquid phase hydrocarbons which may be lefts in the relatively rich condensate reservoir by virtueof normal pressure decline, are recovered by producing a relatively high pressure and relatively lean uid derived fromfa high pressure reservoir through the relatively rich condensate reservoir.

The benefits of this operation are particularly enhanced by virtue of the fact that a typical condensate reservoir frequently contains, in addition to the retrograde enriched phase which forms the bulk thereof. a separate liquid phase of hydrocarbons which may be referred to as interstitial liquid. While the interstitial liquid may be too small in amount to permit its separate recovery, nevertheless it is obviously available for enriching the injected high pressure lean gas. It diffuses into the high pressure gas injected from the relatively high pressure formation and is finally recovered as condensate. Accordingly, in addition to recovery of liquid which would normally be condensed and lost in the relatively rich low pressure condensate reservoir due to normal pressure decline in the course Vof production, the present invention provides for recovery of the interstitial liquid phase hydrocarbons which otherwise would form a part of the irrecoverable oil, i. e. the oil remaining in the formation after completion of normal production.

In theoretical explanation of the foregoing it is believed that the increased enrichment of the relatively high pressure lean gas which occurs in the relatively lowpressure reservoir results from an actual equilibrium eX- change of constituents thereof. In the low pressure reservoir there is a readjustment of the injected high pressure gas as above indicated, which results in an enrichment corresponding to that of the relatively rich low pressure reservoir. In any event, the equilibrium composition of the resulting retrograde enriched gas phase adjusts itself to that characteristic of the relatively rich reservoir, and this equilibrium adjustment significantly occurs at a relatively rapid rate and is completed during a production operation in accordance with this invention.

This invention is also applicable to the production of liquid oil reservoirs. Injection of a relatively high pressure lean gas into the liquid hydrocarbon reservoir drives the liquid toward the production well, dissolves in the liquid oil to swell its volume which increases the volumetric displacement eiciency. Moreover, some of the reservoir liquid diffuses into the resulting retrograde enriched gas phase of the condensate reservoir to effect increased enrichment thereof, as above indicated, so that additional amounts of condensate are produced with the recovered enriched gas.

Moreover, any enriching fractions contained in the injected high pressure sweep gas, to the extent they are absorbed in the liquid oil, swell the volume of the formation liquid oil, thereby facilitating its flow to the production wells. This follows from the fact that the enriching fractions contained in the high pressure injected gas are typically composed of relatively light liquid fractions, for example in the gasoline boiling range, which tend to lower the overall density and viscosity of the formation liquid oil. As a result the crude flows more freely to the production well.

In connection with the preferred embodiment of thc present invention, reference is made to Fig. 1 of the drawing which illustrates in vertical section the ground surface and two vertically spaced condensate reservoirs 12 and 14. The two reservoirs are separate and as is typical, the lower reservoir 14 has a substantially higher original reservoir pressure than the upper reservoir 12.

For example, the overlying relatively low pressure and relatively rich reservoir 12 in its original state contained about 500,000 MMCF condensate (i. e., retrograde enriched gas phase) at 6700 p. s. i. andoriginally delivered 68 barrels of stock tank liquid/MMCF of gas. The lower relatively high pressure condensate reservoir 14 4 originally contained 430,000 MMCF gas at 7600 p. s. i.. and produced 37.4 barrels of stock tank liquid/MMCF.

As indicated in Fig. 1, lthe high and low pressure reservoirs are produced in accordance with this invention as follows. A casing 11 extends from the surface downward into the hydrocarbon producing formations and is perforated within the low pressure formation 12 and high pressure formation 14. Positioned within casing 11 is liquid conduit 13 which extends downwardly from the surface to a point beneath the bottom of the low pressure formation 12. A third conduit or so-called flow tubing 15 is positioned within the liquid conduit 13 and extends downward from the surface to a point above the upper surface of the high pressure formation 14. A flow control means or valve, shown in greater detail in Figs. 2 and 2a of the drawing, for controlling the ow of the high pressure fluid from high pressure formation 14 to low pressure formation 12 is provided at about the lower end of tubing 15. A column of contact material 17, such as Raschig rings, Berl saddles or similar gas-liquid contact promoting material is provided in the annulus between casing 11 and ow tubing 15 intermediate the lower end of ow tubing 15 and the lower end of liquid conduit 13. As indicated the mass of contact material 17 is also located within casing 11 intermediate the bottom of the low pressure formation 12 and the top of the high pressure formation 14. A pump 18 in uid communication with liquid conduit 13 via conduit 19 is provided for pumping absorber oil, such as a stripped crude oil having desired absorbing properties into conduit 13. The flow of produced rich oil and gas which flowing upwardly within ow tubing 15 is in part controlled by a valve 20 at the upper end of tubing 15. A handle or control means 21 is connected to the upper end of tubing 15 for turning the same thereby operating the ow control means or valve positioned at the lower end of ow tubing 15 and located intermediate the formations 12 and 14.

Referring now to Fig. 2 of the drawing which shows in greater detail a valve arrangement for controlling the flow of high pressure fluid from reservoir 14 through the mass of contact material 17 and for controlling the flow of produced oil and gas upwardly within tubing 15, there is shown a support means 22 which is fixed to the inside of casing 11 by threaded engagement or by Welding or by some sort of locking arrangement so as to prevent a rotation thereof with respect to casing 11 when the ow tubing 15 is turned. As indicated in Fig. 2, a support means 22 serves not only as a support for perforated plate 23 which in turn supports the mass of contact material 17 but also serves as the valve body of the valve arrangement. Support means 22 as illustrated is in the shape of a truncated cone provided with a downwardly extending ange 22a which is closed at its lower end 25 by means of a plate or similar closing member to form a liquid trap or reservoir. Openings 27 are provided in the walls of cylindrical flange 24 for the passage of high pressure fluid therethrough. Arcuate lugs 27a are fixed to the ow tubing 15 and are adapted to cooperate with openings 27 to control the amount of tluid passing therethrough as tubing 15 is rotated. Fig. 2a shows more clearly the arrangement for controlling the ow of high pressure fluid through openings 27. As indicated in Figs. 2 and 2a, tubing 15 is provided with arcuate lugs 27a which act to close off openings 27 and thereby control fluid flow therethrough.

The assembly illustrated in Figs. 1, 2 and 2a may be installed in the following manner. A string of ten or twelve inch casing 11 is run through both the high pressure 14 and the low pressure 12 formations and perforated opposite each formation, the casing having been provided with support means 22 positioned just above the top of the high pressure formation. Upon the support means 22 is set the perforated plate or control material support member 23. As indicated hereinabove, a locking arrangement is provided between the support means or" valve body 22 and the casing, since thevalve body must remain in a fixed position whenthe ow tubing 1,5 is turned. Contact material A17 isplaced within the annulus between the casing 11 and flow tubing 15, intermediate the high` and low pressure formations, preferablyin the following manner. A sectionv .of Wire screen. 28, the length of a joint of tubing,.and having a Ydiameter slightly less than the inside diameter vof the casing 11 isset on the perforated plate 23 and filled with 1/2 inch `or 3A inch Berl saddles. As each length .of tubing, is lowered within thecasing stringl another section of screen is added and ille'd with packing. This operation is continueduntil the desiredamount of packing has been provided. Additional tubing is added until vthe valve assembly rests on the ,support means 22 just above the top of the high pressure` formation 14., The lpackinglfl and tubing 15 rest onthe supportmeans 22. The, liquid conduit, 13 for absorber -oil is run into casing 11 to a point just above the top of the packing 17which isbelow the bottom of thelow pressure formation 12. Surface connections. are then, provided as indicated in Fig. l so that'absorber oil can be introduced into the annulus between the ow tubing 15 and liquid conduit 13 to thel packing. During operation` a rich oil accumulates in the trap defined by iiange 22a and closing plate 25 below the openings'27 of the flow control arrangement and is swept to thel surface through the valve provided at the surface at the upper end of the flow tubing 15. The flowcontrol valve, i. e. position of lugs 27a with respectto openings 27, is adjusted to maintain the flow of the high pressure gas or fluid to the annular column of contact material V17 below the flooding point. In actual practice the desired flow control valve settings will bedetermined by trial and error. It is contemplated that anabsorber of the type illustratedv in Fig. 1, such as` an absorber having a diameter of twelve inches and a length of several hundred feet (200400), supplied with a proper type of absorber oil, such as normally liquid hydrocarbons or mixture thereof having an average molecularfweight in the range 150-250, preferably about 200, would effectively remove the C3 andC4 hydrocarbon components and a substantial portion of the heavier normally liquid hydrocarbons from the high pressure gas fluid emanating! from thehigh pressure formation 14 to produce a relatively lean high pressure` gas for injection into and passage through lthe relatively low pressure formation 12.

Fig. 3 represents diagrammatically the. contents of the two reservoirs as a function of pressure.` The curve AB represents the instantaneous content of liquid hydrocarbon production from reservoir 12 per MMCF of produced gas between the pressures 6700 and 5200 p. s. i. Curve CD is a similar production curve from reservoir 14.

The reservoir 12 contains 1690 MMCF and the reservoir 14 contains 1200 MMCF of hydrocarbon pore space. On the above basis the total quantity of liquid produced by direct production of reservoir 14 during the 7 600-5200 p. s. i. pressure decline is represented by the area under the curve CD. This amounts to approximately 3,940,000 barrels. Likewise the area under curve AB represents the quantity of liquid recoverable by separate and independent production of reservoir 12. The area above curve AB represents the amount of liquid condensate which remains in the interstices of the porous reservoir 12 as the result of condensation during the pressure decline from 6700 to 5200 p. s. i. as reservoir 12 is produced.

In accordance with the present invention, after the production of the reservoir 12 to a pressure of 5200 p. s. i., connection is made between the two reservoirs 12 and 14 as indicated in Fig. l. passes upwardly within the packed annulus between casing 11 and tubing 15 counter-currently in contact with absorber oil and is stripped of a substantially amount of its retrograde vaporized normally liquid hydrocarbons ,to yield a relatively lean high pressure gas for injection Fluid from formation 14 f into formation 12, the stripped normally liquid hydrof carbons together with the absorber'oil beingrecovered from flow tubing 15 at the surface via-valve 20.`

As indicated, see Fig. l, reservoir 12 in turn` is produced by means of a spaced well 30 extending lfrom a surface location into the formation 12.. Flow tubing 31 of well 30 is connected to theI well head 32 which directs the produced hydrocarbon to stock tank, separators I.and any other desired recovery means not shown.,

Further explanatory of my invention, as the reservoir 12 is produced through well 30 its pressure slowly declines to about 5200 p. s. i., at which time about 47 bare rels of stock tank liquid are produced per MMCF of produced gas, see curve AB of Fig. 3. At thistime the reservoir 14 is advantageously interconnected to reser- Voir 1T. by perforating casing 11 in both reservoirs. The resultant pressure after equalization is approximately 6200 p. s. i. in both reservoirs. At this pressureenrichment of the injected relatively lean high pressure retrograde gas phase from formation 14, indicatedby curve AB, takes place by retrograde vaporization of the liquid hydrocarbons and/or previously condensed liquidhydrocarbons in the reservoir 12. As disclosed this enrichment results in delivery from well 30 of a condensate production yielding 56 barrels of stock tank liquid per MMCF of gas. Therefore, production isresumed through well 30 at the increased yield of 56 barrels of stocktank liquid/MMCF of gas which contrasts with the previous production of 47 barrels from formation12.

As production continues fromboth formations 12 and 14 via well 30 the pressure gradually declines in both formations and the yield of stock tank` hydrocarbons again follows the pattern represented by curve AB of Fig. 3the shaded area under curve AB between 6200 and 5200 p. s. i., representingtotal production attributable to the upper reservoir 12 between these pressure limits after interconnection with reservoir 14 in the manner indicated. On the basis of the pore volume .of reservoir 12 this production amounts to 4,390,000` barrels of liquid oil. However, due to the interconnection of reservoir 14 the rate of pressure decline lis correspondingly less over the same pressure differential, and there is additional production attributable to the increased pore space of the reservoir 14. The total increase in reservoir volume represented by combining reservoir 14 with reservoir 12 amounts `to or 1.71; therefore the total recovery is equal to 4,390,000 X 1.71 or 7,550,000 barrels.

This compares very favorably with only 3,940,000 barrels which would be produced during the pressure decline of the reservoir 14 between its original pressure of 7600 p. s. i. and the pressure of 5200 p. s. i. by ordinary direct production and representing an increased production of 3,6l0,000 barrels of valuable liquid hydrocarbons.

While the striking results of the foregoing example are based, in part, upon the presence of original interstitial hydrocarbon liquid in reservoir 12, it is to be noted that in any event the original production of reservoir 12 from its initial pressure of 6700 down to 5200 p. s. i., as previously indicated necessarily resulted in retrograde condensation to an extent signified by the shaded area above curve AB of Fig. 3. The actual amount of liquid oil deposited by retrograde condensation during this pressure decline is equal to 1,920,000 barrels. Accordingly, therefore, even in the absence of interstitial liquid, the production of this very material quantity of additional liquid hydrocarbon manifestly represents a valuable advantage.

This increased production, in either case, is particularly advantageous from the standpoint that the increased production is readily predictable by a skilled reservoir engineer on the basis of ordinary engineering data regarding the reservoir. The present invention is particularly applicable to deep elds when the costs of cycling or other conventional methods of secondary recovery employing extensive surface facilitates are economically prohibitive.

As previously indicated, similar advantages follow from the injection of the contents of the relatively high pressure condensate reservoir to a relatively low pressure liquid oil reservoir. This is particularly true in the case of a reservoir containing oil which is undersaturated with gas at reservoir pressure. swelling of the oil volume and the increase of fluidity, due to contact with the enriched condensate phase, materially promote ow to the well bore.` Recovery is further facilitated by the fact that the resulting retrograde enriched condensate phase, having properties as to viscosity and density more closely approaching that of the liquid oil, acts with improved volumetric displacement eiciency. In any event, the total amount of liquid hydrocarbons produced by the methods of the present invention is materially increased.

In one modification of the present invention the relatively lean (with respect to retrograde vaporized normally liquid hydrocarbons) contents of a high pressure condensate reservoir may be injected successively into a number of relatively low pressure reservoirs. For example, the contents of a high pressure relatively lean condensate reservoir may rst pass through to a lower pressure relatively rich condensate reservoir, as in the above example, and thereafter pass through into a liquid oil reservoir. Production is then carried out from the liquid oil reservoir at a point spaced from the point of which the resulting condensate gas is injected thereinto. Therefore, the first reservoir discharges through the second condensate reservoir and from the second reservoir through the liquid oil reservoir, all of the several reservoirs being produced by a well or wells extending exclusively into the oil reservoir. In this manner each of the sands is produced under conditions of maximum liquid hydrocarbon recovery.

This application is related to the copending, co-assigned patent application, Serial No. 388,113, now Patent No. 2,736,381, led October 26, 1953, in the name of Joseph C. Allen, which discloses producing a plurality of subsurface reservoirs wherein retrogradeuid from an underlying high pressure reservoir is without any intervening treatment injected directly into an overlying relatively low pressure condensate reservoir.

In such a case the resulting Obviously many modifications and variationsmay be made by those skilled in the art without departing from the. spirit and scope of this invention.

A method of producing subsurface gas condensate reservoirs wherein a relatively rich, relatively low pressure gas condensate reservoir overlies a relatively rich, relatively high pressure gas condensate reservoir which comprises placing said gas condensate reservoirs in direct uid communication by means of a rst well bore penetrating said low pressure and high pressure condensate reservoirs, providing an absorption zone within said first well bore intermediate said condensate reservoirs and interposed in the tlow path of direct uid communication therebetween, owing the contents of said high pressure gas condensate reservoir directly into said absorption zone,introducing viasaid rst well bore alliquid hydrocarbon oil having an average molecular weight in the range -250 as an absorption medium into said absorption zone into direct contact with the aforesaid contents of said high pressure gas condensate reservoir introduced into said absorption zone to remove a sub- Ystantial amount of normally liquid hydrocarbons as well as a substantial amount of C3 and C4 hydrocarbons from the high pressure gaseous materials introduced into said absorption zone from said high pressure gas condensate reservoir, removing the resulting enriched liquid hydrocarbon oil from said absorption zone, directly via said rst Well bore introducing the resulting relatively lean high pressure gasiform eluent from said absorption zone into said relatively low pressure condensate reservoir and producing said low pressure condensate reservoir via a second well bore spaced from said rst well bore and penetrating only into said low pressure reservoir whereby both said high pressure and said low pressure condensate reservoirs are produced via said second well bore.

References Cited in the file of this patent UNITED STATES PATENTS 1,433,956 Knox Oct. 31, 1922 2,185,577 Voorhies et al. Jan. 2, 1940 2,238,701 McCollum Apr. 15, 1941 2,277,380 Yancey Mar. 24, 1942 2,357,703 Teichmann Sept. 5, 1944 2,368,428 Saurenman Jan. 30, 1945 2,423,156 Reid July 1, 1947 2,736,381 Allen Feb. 28, 1956

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