US3372747A - Reservoir pressure maintenance process - Google Patents

Description

March 12, 1968 W. M. REID 3,372,747

RESERVOIR PRESSURE MAINTENANCE PROCESS Filed May 17, 1965 VV//am M //O/ /PV 6,45 EAN/f INVENTOR.

/Mmf/V sf IP/PA' VEL United States Patent O 3,372,747 RESERVOIR PRESSURE MAINTENANCE PROCESS William M. Reid, 4747 W. Alabama, Houston, Tex. 77027 Filed May 17, 1965, Ser. No. 456,344 2 Claims. (Cl. '166-7) ABSTRACT F THE DISCLOSURE A method of controlling or maintaining reservoir pressure wherein pressurized gas recovered from the reservoir is expanded to Idrive a pump to pump water into the reservoir.

This invention relates to new and improved methods for controlling or maintaining reservoir pressure in a subsurface reservoir from which fluids containing useable quantities of hydrocarbons are removed, and particularly, to methods for retarding retrograde condensation which normally occurs in reservoirs containing iluids within a certain range of temperatures and pressures when such fluids are removed therefrom.

In lrecovering hydrocarbons from certain subsurface reservoirs, it is recognized that substantial amounts of hydrocarbons remain in the reservoir as residue due to retrograde condensation which accompanies the decline of reservoir pressure. While attempts have been made to articially sustain or support reservoir pressure by gas cycling or water ilooding, these methods, as employed heretofore, have required the use of internal combustion prime movers to operate the compressors for pressurizing the gas sufficiently for injection into the high pressure reservoir or for operating pumps to inject liquids into the produced reservoir to water flood the formation.

An object of the present invention is to provide a new and improved method and for supporting or maintaining pressure in a subterranean reservoir from which hydrocarbons are removed so as to reduce retrograde condensation in the reservoir without requiring the use of internal combustion prime movers.

Another object of the present invention is to provide a new and improved method for supporting or maintaining reservoir pressure in a producing formation wherein pressurized gas produced from the reservoir is expanded through an expansion device to pump water or other suitable substances into the reservoir to maintain the reservoirs pressure.

Still another object of the present invention is to provide a new and improved method for maintaining or supporting reservoir pressure so as to retard retrograde condensation in a producing formation by expanding gas produced from the reservoir in an expansion engine to drive a pump for injecting water into the reservoir from which the gas was initially taken.

And yet another object of the present invention is to provide a new and improved method for restoring or supporting pressure of a reservoir from which gas and liquid hydrocarbons are removed wherein a separator is provided to separate the gas from the liquids produced from the reservoir and the gas is expanded through an expansion device to operate a pump to inject water into the producing reservoir.

A further object of the present invention is to provide a new and improved method for restoring or supporting the pressure of a reservoir from which gas and/or liquid hydrocarbons are produced wherein the well eflluent is heated and the hot gas separated from the heated liquids and lthereafter expanded to operate an expansion engine to inject water into the subterranean reservoir and heat from the heated liquids is exchanged with unheated fluid produced from the reservoir.

Still a further object of the present invention is to provide a new and improved method which is adapted to be used in conjunction with the conventional pressure maintenance systems such as gas cycling or water injection to provide an auxiliary power source for extracting energy from the gas produced wherein pressurized gas withdrawn from the reservoir is expanded in an expansion device which is adapted to operate a pump apparatus to pump liquids into the reservoir.

Still another object of the present invention is to provide a new and improved method for withdrawing pressurized gas from a reservoir and partially expanding the pressurized gas through an expansion device to do mechanical work. y

The preferred embodiment of this invention will be described hereinafter, together with other features thereof, and additional objects will become evident from such description.

The invention will be more readily understood from a reading of the `following specification and by reference to the accompanying drawings forming a part thereof, wherein an example of the invention is shown, and where- 1n:

FIG. 1 illustrates a low diagram of the apparatus and process of the present invention for use with high pressure reservoirs wherein the well effluent is not heated; and

FIG. 2 illustrates a tlow diagram of an embodiment of the apparatus in process of the present invention for use with reservoirs in which the well eluen-t is heated.

The process of the present invention which is shown schematically in the How diagram of FIG. 1 is designated there generally by the letter A. Such process is used for maintaining or supporting the pressure in a reservoir R containing a fluid and gaseous mixture within a range of temperatures and pressures such that retrograde condensation of liqueliable hydrocarbons occurs when reservoir pressure decreases. Such fluid and gas are removed from the reservoir R through one or more wells P and other fluids are injected into the reservoir through one or more injection wells I.

With the method of this invention, reservoir pressure is maintained or its decline is retarded by expanding gas taken from the reservoir R through an expansion device E which is adapted to operate a pumping device B to inject water into the reservoir R via the injection well or wells I.- As will be shown by example hereinafter, the pressure extracted from the uids produced will, in many instances, be sufiicient to pump enough water into the reservoir R to maintain the fluid pressure therein, and in `some instances, to actually increase reservoir pressure.

Referring more specically to the flow diagram shown in FIG. 1 of the drawings, the gaseous mixture to be'- processed is produced or allowed to tlow out of the reservoir R through the producing well or wells P in a manner well known in the art. Such gaseous mixture is normally conducted through a pipe or conduit 10 to a separator or dehydrator 12 positioned on the earths surface at some convenient location relative to the well P. It will be appreciated that with this invention, an individual separator 12 may bc used for each producing Well P or a plurality of wells P may be connected so as to pass their Veffluent through a single separator 12, as desired.

In the separator or dehydrator 12, the 4water Aand liquid hydrocarbons are removed or separated from the gas, the liquids being transmitted through the pipeline 14 to appropriate storage or disposal (not shown) and the gas being conducted to the expansion device E through a suitable conduit or pipeline 17.

The expansion device E, which is illustrated schematically in FIG. 1 of the drawings, may be a gas turbine or other suitable type of expansion engine in which the gas is allowed to expand. The gas emerging from such expansion engine E at a reduced temperature and pressure is conducted via the pipe or other suitable conduit 19 to a separator 20 in which such other hydrocarbons as may remain in the gas are separated therefrom for delivery to storage facilities (not shown). The gas emerges from the separator 20 through the outlet 21 from which it is conducted via a pipeline to a cycling plant or other processing facility or sales, as may be desired.

As shown, the expansion device or turbine E is connected to a pump B which is connected to a suitable source of liquid such as salt water (not shown) by means of an inlet line or pipe 30. The e'iuent of the pump B is transmitted 4through the pipeline 31 which conducts the liquid from the pump B to the injection well or wells I which, as shown in the drawings, penetrates the formation or stratum in the reservoir R from which the gaseous mixture is produced. Preferably, the arrangement of the producing well or wells P and the injection wells I relative to the reservoir structure R is as illustrated in FIG. 1, namely, the injection well I is bottomed in a portion of the reservoir structure which is deeper, sometimes by as much as a thousand feet or more, than the portion of the reservoir for-mation from which the gas or other fluids are being taken by the well P. Also, in most instances, it is preferred to have a dry gas bank between the water W in the reservoir R and reservoir uid F, as this will achieve the best liquid recovery from the reservoir R.

By way of example of the operation of the process of the present invention, let it be assumed that the following conditions obtain with respect to the reservoir R shown in FIG. 1 of the drawings. Assume the reservoir depth is ten thousand feet, the reservoir pressure is 7,000 p.s.i., the molecular weight of the reservoir lluid is 20, the reservoir temperature is 300 F. and that the super cornpressability of the reservoir fluid is 1.15. With these factors, it can be calculated that the density of the reservoir fluid is 14.9 pounds per cubic foot.

In actual practice, a wellhead pressure of 4,000 p.s.i. and a temperature of 200 F. is not uncommon and with long ow lines, may be as low as 3,000 p.s.i. and 80 F. With sales delivery pressure at 1,000 p.s.i., then with the foregoing data, the work available will be 46 B.t.u. per pound of reservoir uid, and assuming 80% mechanical eiciency, the work available from each cubic foot of reservoir fluid will be 545 B.t.u.

Comparing this with the work required to pump one cubic foot of water, when the liquid has a specific gravity of 1.0, the formation face pressure drop is 1,000 p.s.i., the line loss drop is 500 p.s.i., and the mechanical efficiency of the pump is 75%, it can be calculated that 1,030 B.t.u. of work will be required to pump each cubic foot of water into the injection well I as shown in FIG. 1 of the drawings. Therefore, in this example, by expanding gas taken from the reservoir R as described herein above, sufcient liquid can be pumped to lill 53% of the reservoir voidage.

It should be noted, however, that in making these calculations, various assumptions have been indulged which are more conservative than would nor-mally be found in many cases. For instance, water volume does not take into account an increase in water temperature; both the injection well I and the producing well P are assumed to be of the same depth, which occurs only occasionally; an increase in the specic gravity of the water will decrease the work, and in many instances, salt water, having a specic gravity of 1.04 or greater, is available for water injection purposes. Thus, it can be appreciated that even with less than ideal conditions, with the method or apparatus of the present invention, reservoir pressure can be supported or maintained and retrograde condensa tion thereby retarded. However, in the event of favorable circumstances, the gas may be only partially expanded to operate a pump to pump liquid into the reservoir to make up a voidage in the reservoir and the balance of the gas pressure reduction may be used to achieve refrigeration of the well effluent, or for power recovery for other uses such as generation of electric power, mechanical refrigeration or other pumping needs. And in some situations, it may be advantageous to use expansion from one reservoir to support or increase the pressure in another reservoir.

In the above illustration, the reservoir fluid molecular weight is characteristic of gas distillate or retrograde reservoirs; however, the method and apparatus of this invention is applicable to liquid reservoirs, commonly termed crude oil reservoirs, if suicient gas can be separated from the liquids produced from a crude oil reservoir to power the expansion device E. If the separated gas is not sucient to power the expansion device E, the entire well effluent could be heated, the vapor portion separated from the liquid and the vapors used to power the expansion device E as will be shown and explained in detail hereinafter.

Referring now specifically to a flow diagram in FIG. 2 of the drawings which illustrates the method and apparatus of the present invention for heating well efuent, it will be seen that the gas mixture to be processed is taken from the producing well or wells P in a manner well known in the art. Such fluid is then conducted through a pipeline or conduit 40 to a separator 41 in which the water and some liquid hydrocarbons may be separated from the gas or, if desired, the liquid hydrocarbons may be retained with the gas and the other liquids separated from the hydrocarbon fluid. The separated water or liquid hydrocarbons and water emerge from the separator 41 through the conduit 42 and are conducted thereby to suitable storage or further processing facilities (not shown. The separated gas mixture emerges from the separator 41 and then passes through a suitable conduit or pipe 43 to a heat exchanger 45 where the gas stream takes up heat from a liquid and gas stream separated out of the same gas stream at a later stage in this process as will be explained. Upon emergence from the heat exchanger 45, the gas is then heated in a heater or furnace 47 which may be directly or indirectly red, as desired.

The heated gaseous mixture is then conducted to a separator 50 in which the hot gas is separated from the hot liquids. The hot gas passes to the expansion engine E and the heated liquid is then conducted through a conduit 51 to the heat exchanger 45 where heat is given up to the incoming stream of gas coming from the separator 41 as described hereinabove. After giving up its heat, the fluid passes through a separator 60 and thence to storage or sales facilities (not shown).

The heated gas is expanded in the expander E which is connected to drive the pump B' for pumping water or other suitable liquid from a supply source (not shown) through a pipeline or conduit 53 to the injection well or wells I.

After having been expanded in the expansion engine or apparatus E', the heated gas is preferably conducted through a conduit 55, which, as shown, connects with the conduit 51 for conducting the heated gas to the heat exchanger 45 where such heated gas also gives up heat to the incoming gas passing `through the heat exchanger 45 from the separator 4I.

As shown in dotted line in FIG. 2, an alternate course or conduit 63 may be provided, if desired, for conducting the expanded gas directly from the expander E to the separator 60 rather `than going through the heat exchanger 45. In'the separator 60, the liquids and gases are separated, the gas being conducted to sales, cycling, dehydration, or the like, via a conduit 61 and the liquids going to storage or processing via a suitable conduit 62.

In some situations, it may be desired to heat the entire well eluent prior to separating liquid constituents from the gas. In that event, the separator 41 may be eliminated from the flow pattern between the well P and the heat exchanger 45, and the reservoir fluid would be heated in heat exchanger 45 and in the furnace 47 prior to having liquids such as water and liquid hydrocarbons removed therefrom. After being heated, the Well eiiiuent would be conducted through a conduit or pipe 48 to the separator 50 where the heated gas would be separated from the liquids, the gas going to the expander E and the liquids going through the conduit 51 to the heat exchanger 45.

Assuming that the form of the invention shown in the flow diagram of FIG. 2 is used for heating the well effluent and that with other conditions being as assumed in the foregoing example, that the well effluent is heated to 500 F., the Work available from expansion of gas in the reservoir liuid is increased to 1,250 B.t.u. per cubic foot of reservoir iiuid. In the example cited, this Well permit 1.2 cubic feet of Water to be pumped into the injection Well or wells I for each cubic foot of reservoir uid removed from the reservoir via the producing Well or Wells P, thus producing an increase in the reservoir pressure. Or, if desired, the system could be operated with a liquid pressure drop of approximately 800 p.s.i. in liquids being pumped into the injection well or wells I' and yet maintain full reservoir pressure.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape, and materials, as Well as in details of the illustrated construction, may be made within the scope of the appended claims Without departing from the spirit of the invention.

What is claimed is:

1. A method of producing a gaseous mixture containing liqueable hydrocarbons from a reservoir in which such gaseous mixture is confined at temperatures and pressures within a range such that retrograde condensation of liqueiiable hydrocarbons occurs when reservoir pressure decreases which method comprises:

(a) removing the gaseous mixture containing liquefiable hydrocarbons from the reservoir;

(h) heating such mixture;

(c) separating the liquid from the gas constituents of said mixture;

(d) expanding the separated gas to mechanically pump liquid into the reservoir from which said mixture was removed;

(e.) combining the expanded gas with the heated, separated liquid; and

(f) exchanging heat from the combined expanded gas and heated liquid with the unseparated gaseous mixture to heat said gaseous mixture and cool said combined expanded gas and heated liquid mixture.

2. A method of producing a gaseous mixture containing liqueable hydrocarbons from a reservoir in which such gaseous mixture is confined at temperatures and pressures Within a range such that retrograde condensation of liqueable hydrocarbons occurs when reservoir pressure decreases comprising:

(a) removing the gaseous mixture containing liquefiable hydrocarbons from the reservoir;

(b) separating the liquid from the gas constituents in such mixture;

(c) heating `the separated gaseous portion;

(d) separating liquids from such heated gaseous portion;

(e) expanding said heated gas portion to perform mechanical work;

(f) using such mechanical work t0 pump liquid into the reservoir from which the gas mixture was removed;

(g) combining the expanded hot gas with the separated heated liquids;

(h) exchanging heat from said combined expanded gas and heated liquids with the unheated gaseous portion to heat said gaseous portion and to cool said combined liquids and expanded gas; and

(i) separating said cooled gas and liquids.

References Cited UNITED STATES PATENTS 1,658,910 2/1928 Trumble.

2,309,075 1/1943 Hill 166--7 2,617,484 11/1952 Swearingen 166-7 3,149,668 9/1964- Arendt 166-7 OTHER REFERENCES Uren, Lester C.: Petroleum Production Engineering: Oil Field Exploitation. New York, McGraw-Hill, 2nd ed., 1939, pp. 280-282 and 482.

CHARLES E. OCONNELL, Primary Examiner. IAN A. CALVERT, Assistant Examiner.

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