US3083764A - Cellar oil recovery by water displacement - Google Patents

Description

April 2, 1963 M. H. GASKELL ETA]. 3,083,764

CELLAR OIL RECOVERY BY WATER DISPLACEMENT Filed Sept. 9, 1960 3 Sheets-Sheet 1 on. wATER-: A -i FIG.I. H

INVENTORS. MERWIN H. GASKELL, DONALD C. LINDLEY, FREDERICK M. PERKINS,JR,

LI BY ATTORNEY.

April 2, 1963 M. H. GASKELL ET AL 3,083,764

CELLAR OIL RECOVERY BY WATER DISPLACEMENT 5 Sheets-Sheet 2 Filed Sept. 9, 1960 OIL WATER-'H R 1 s M m H MLVHK N NLER R E 0 V T Nmm T I M A .K w OR LE WADMM RNE EOR MDF Y B A ril 2, 1963 M. H. GASKELL ET Al. 3,

CELLAR OIL RECOVERY BY WATER DISPLACEMENT Filed Sept. 9, 1960 s Sheets-Sheet :5

OIL

WATER INVENTORS. MERWIN H. GASKELL, DONALD C. LINDLEY, FREDERICK MH-PERKIINSJR,

/ E A A, ATTORNEY.

United States Patent 3,083,764 CELLAR OIL RECOVERY BY WATER DISPLACEMENT Merwin H. Gaskell, Donald C. Lindley, and Frederick M. Perkins, Jr., Houston, Tex., assignors, by mesne assignments, to Jersey Production Research Company,

Tulsa, Okla, a corporation of Delaware Filed Sept. 9, 1960, Ser. No. 55,029 2 Claims. (Cl. 1669) This invention concerns recovery of oil located below the structurally lowest well in reservoirs in which a natural water drive is not present.

Small, steeply inclined reservoirs without natural water drives are often found associated with salt domes or other highly faulted structures. Frequently, only one well may be economically justified in these reservoirs and oil is produced by an expanding gas-cap drive or by a dissolved gas drive. Although a large fraction of the oil up-structure from the well may be recovered during primary depletion, because of gravity effects, only a small fraction of the down-dip oil can be produced. The downdip oil where no natural water drive is present is defined as cellar oil in contradistinction to attic oil, which is the oil above the structurally highest well in reservoirs where a natural water drive is present.

A primary object of the present invention is an improved method for the recovery of cellar oil.

It is possible after producing a reservoir of this type for a period of time to inject into the reservoir a limited quantity of water. This technique repressurizes the reservoir and moves the oil up-dip by the gravitational segregation of the injected water down-dip. In some instances in this type of operation, because of perhaps a reduced permeability to oil adjacent the well, the length of time required for injection of water and the length of time required for gravity segregation of water, the total length of time required to produce the reservoir may be excessive, causing subsequent loss of recoverable oil.

It has also been proposed to inject water through perforations located in the lower part of the well opposite the lower part of the penetrated portion of the reservoir and isolated from a set of perforations located in the upper part of the well opposite the uppermost part of the penetrated portion of the reservoir and while injecting water into the lower perforations, producing oil from the upper set of perforations. However, this technique is operational only if the pressure gradients caused by injection of water are sufficiently low to allow gravity acting on the oil and water to maintain the oil-water contact below the upper set of perforations. This condition can be achieved by injecting water at sufliciently low rates; but once again, the time required for depleting the reservoir may be prohibitively long.

The method of the present invention overcomes difliculties inherent in the known techniques for producing cellar oil by injecting water through a tubing string which opens into the lowermost section of the well bore, injecting oil or another suitable fluid through a second tubing string which opens into the center section of the well bore, and producing oil from a third tubing string which opens into the uppermost section of the reservoir. The production rate is set to exceed the rate of injection of fluid into the center section. The fluid injected into the center section has the eflfect of blocking ofi water entering through the lowermost section. By proper adjustment of the two injetcion rates and the production rate, the cellar oil is produced at an economical rate.

The above noted object and other objects of the invention will be apparent from a more detailed description of the invention taken in conjunction with the drawings wherein FIGS. 1, 2, and 3 are cross-sectional views of a Patented Apr. 2?, 1963 well bore penetrating an inclined subsurface reservoir and serve to illustrate the mechanics of the operation of the method at different stages.

Referring to the drawings in greater detail, in FIGS. 1, 2, and 3 is shown a reservoir :10 inclined at an angle and penetrated by a well pipe 11, which is perforated at 12 in the upper portion, at 13 in the center portion, and at 14 in the lower portion of the reservoir. Three tubing strings, 15, 16, and 17, are arranged in pipe 11.Tubing string 15 extends to and fluidly communicates withupper perforations 12;tubing string 16 extends to and fluidly communicates with thecenter perforations 13; andtubing string 17 extends to and fluidly communicates with thelower perforations 14 of pipe 11. Alower packer 18 is arranged ontubing string 17 in pipe 11, and sealingly closes off the space betweentubing string 17 and the interior wall of pipe :11 betweenlower perforations 14 andcenter perforations 13. Anupper packer 19 is arranged ontubing strings 16 and 17 in. pipe 11 and sealingly closes off the space between these tubing strings and the interior wall of pipe 11 betweenupper perforations 12 andcenter perforations 13.

As seen in FIG. 1, initially, water is injected throughtubing string 17 intoformation 10, throughperforations 14 in casing pipe 11, and simultaneously a fluid such as oil is injected throughtubing string 16 intoreservoir 10 throughcenter perforations 13. The injected oil keeps the injected water down, and the water works its way along the lower side of the reservoir underneath the cellar oil and displaces the cellar oil upwardly.

As the injection of fluids is continued, water continues to displace cellar oil upwardly, and as seen in FIG. 2, the cellar oil has begun to mingle with the injected oil above the water level.

The simultaneous production of oil throughupper perforations 12 andtubing string 15 in conjunction with continued injection of oil and water is illustrated in FIG. 3, and [as seen therein, the cellar oil has been forced upwardly by the injected water to adjacent to and above the upper perforations.

In practice, to determine the most desirable rates of water and oil injection, there will be a first step of short duration of injection of water and oil throughtubing strings 16 and 17 and production of oil throughtubing string 15. The oil production is restricted. to a very low rate to ascertain that the water is all being directed downstructure by the injection of oil in the center region of the well bore throughpipe string 16 andcenter perforations 13 in the center region of the well bore. This operational phase is stopped when fresh reservoir oil appears in the production stream flowing throughtubing string 15. The appearance of fresh reservoir oil is recognized by a change in the gas-oil ratio, since the injected oil will be dead; i.e., free of dissolved gas. In this phase, water may be injected at a high rate; the oil is injected only in sufficient amounts to block the water injected from rising up-structure. Following completion of this step, the rates of injection are controlled by the desired rate of production of net oil from the well. The rate of water injection equals the net rate of oil production, and the rate of oil injection is adjusted so that it is just suflicient to prevent water production. Oil is produced in an amount equal to the net oil amount desired plus the volume of oil injected to block ofi the water, since the well will remain at substantially equilibrium conditions. The absolute rates of injection and production will vary from well to well and are best determinable in the well itself.

All of the injected oil will be recovered in this method of operation. The method is not a repressurizing process, and it allows the oil to be recovered at the low pressure existing in the reservoir. Therefore, the method has substantial economic advantages, 'because it avoids the need for injecting large volumes of fluids at high pressures.

Having fully described the objects, nature, operation, and method of the invention, we claim:

1. A method of recovery of cellar oil from an inclined reservoir in which no natural water drive is present and which is penetrated by a Well pipe perforated along a portion of its length located in said reservoir comprising simultaneously injecting water into said reservoir through the lowermost perforations in said well pipe to displace oil from the lower to the upper portions of said reservoir and injecting oil into said reservoir through the middle perforations in said well pipe and producing fluids from said reservoir through the uppermost perforations in said well pipe; the rate of Water injection, oil injection, and oil production being selected such that water-free oil is produced.

2. A method of recovery of cellar oil from an inclined reservoir in which no natural water drive is present and which is penetrated by a well pipe perforated along a portion of its length located in the reservoir comprising initially, simultaneously injecting water into said reservoir through the lowermost perforations in said well pipe to displace oil from the lower to the upper portions of said reservoir and injecting oil into said reservoir through the middle perforations in said well pipe and producing fluids from said reservoir at a low rate through the uppermost perforations in said well pipe until fresh reservoir oil appears in the oil produced through the uppermost perforations in said well pipe and then continuing to inject water and oil into said reservoir and produce fluids from said reservoir in the same way, the rates of injection being controlled by the desired rate of production of net oil from the well, the rate of water injection being equal to the net rate of oil production, the rate of oil injection being adjusted to that just suflicient to prevent water production, and the oil produced being equal to the net oil desired plus the volume injected to block off the water.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. METHOD OF RECOVERY OF CELLAR OIL FROM AN INCLINED RESERVOIR IN WHICH NO NATURAL WATER DRIVE IS PRESENT AND WHICH IS PENETRATED BY A WALL PIPE PERFORATED ALONG A PORTION OF ITS LENGTH LOCATED IN SAID RESERVOIR COMPRISING SIMULTANEOUSLY INJECTING WATER INTO SAID RESERVOIR THROUGH THE LOWERMOST PERFORATIONS IN SAID WELL PIPE TO DISPLACE OIL FROM THE LOWER TO THE UPPER PORTIONS OF SAID RESERVOIR AND INJECTING OIL INTO SAID RESERVOIR THROUGH THE MIDDLE PERFORATIONS IN SAID WELL PIPE AND PRODUCING FLUIDS FROM SAID RESERVOIR THROUGH THE UPPERMOST PERFORATIONS IN SAID

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