US3838737A

US3838737A - Petroleum production technique

Info

Publication number: US3838737A
Application number: US00357405A
Authority: US
Inventors: J Allen; J Tate
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1973-05-04
Filing date: 1973-05-04
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01
Also published as: CA1002873A

Abstract

A method for the miscible displacement of petroleum from a subterranean reservoir is provided. The method involves injecting two miscible fluids into an injection well and producing petroleum from a production well. A first solvent, more dense than water, is injected into the reservoir near the top of the reservoir, and a second solvent, less dense than water, is injected into the reservoir near or at the bottom of the reservoir. Both solvents are followed by water. The first solvent will tend to flow downward and the second solvent will tend to rise. The solvents will blend and provide piston-like displacement through the reservoir.

Description

unltea mates l'atent Allen et al. 1 Oct. 1, 1974 15 PETROLEUM PRODUCTION TECHNIQUE 3.729.053 4/1973 Froning 166/273 [75] Inventors: Joseph C. Allen, Bellaire; Jack F.

Tate Houston Tex Primary Examiner-James A. Leppink [73] Assignee Texaco Inc New York N Y Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries [22] Filed: May 4, 1973 [57] ABSTRACT [21] Appl. No.: 357,405 A method for the miscible displacement of petroleum from a subterranean reservoir is provided. The 52 U S Cl ,2 l66/274 method involves injecting two miscible fluids into an Ezlb 43/16 injection well and producing petroleum from a prod 5 306 273 duction well. A first solvent, more dense than water, is l 1 0 earc 6/ injected into the reservoir near the top of the reservoir, and a second solvent, less dense than water, is 56 R f Ct d injected into the reservoir near or at the bottom of the l 1 e erences reservoir. Both solvents are followed by water. The

UNITED STATES PATENTS first solvent will tend to flow downward and the sec- 3,003,554 10/1961 Craig, Jr. et al. 166/274 ond solvent will tend to rise. The solvents will blend 3,047,063 7/1962 Connally, Jr. et al. 166/273 and provide piston-like displacement through the res 3,221,810 12/1965 Marx 166/269 ervoir 3,369,601 2/1968 Bond et al.. 166/274 3,565,175 2/1971 Wilson 166/269 11 Claims, 3 Drawing Figures PETROLEUM PRODUCTION TECHNIQUE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for recovering petroleum by miscible displacement.

2. Description of the Prior Art Various methods for inducing the recovery of petroleum from underground reservoirs are in existence. These methods include injecting water, .steam or some aqueous based mixture to drive the oil from the reservoir. These displacement processes are inefficient. The inefficiency of these displacement processes is partly due to the retentive forces of capillarity and interfacial tension. Miscible flooding provides a method for efficiently displacing the petroleum from a reservoir.

In miscible flooding, solvent for the petroleum is introduced into the reservoir and driven through the reservoir. Dissolution of the petroleum by the solvent permits no two phase system between the solvent and the petroleum to exist at the conditions of temperature and pressure existing in the reservoir. Therefore, the retentive forces of capillarity and interfacial tension are nonexistent. These forces decrease the displacement efficiency of a recovery process where the driving fluid or displacing agent and the petroleum exist as two phases in the reservoir.

In a miscible flood process the solvent has the capability of mixing completely with the petroleum in the reservoir. A transition zone is formed at the leading edge of the solvent between the solvent and the petroleum in which miscibility exists between the solvent and the petroleum. For economic reasons the solvent is normally injected as a slug followed by another fluid such as a gas or an aqueous fluid to drive the solvent slug and the petroleum through the reservoir.

In displacement processes in general, the ideal sought after is piston-like displacement. That is, the displacing fluids should ideally present a flat front to the petroleum in the reservoir and displace it uniformly through the reservoir. Most miscible solvent slugs are followed by an aqueous fluid to drive them through the reservoir. Moreover, most miscible solvent injection methods have heretofore involved only light hydrocarbons with densities less than water. Problems have arisen with such processes, however.

In a vertical miscible flood, for example, using a light hydrocarbon solvent slug followed by water, the water will tend to finger throughthe less dense solvent, destroying piston-like displacement and resulting in premature breakthrough of the displacing medium water. In horizontal miscible flooding the light hydrocarbon solvents will tend to override the petroleum in the reservoir and leave much of it unrecovered,

SUMMARY OF THE INVENTION The invention is a throughput method for the miscible displacement of petroleum from a subterranean reservoir involving at least one injection point high in the reservoir and at least one injection point low in the reservoir. A petroleum solvent more dense than water is injected into the injection point high in the reservoir followed by a driving fluid. A petroleum solvent less dense than water is injected into the injection point low in the reservoir followed by a driving fluid. The two solvent slugs are driven through the reservoir forcing petroleum to a production well where it is produced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a hydrocarbon reservoir penetrated by an injection well and a production well at the beginning of a flood.

FIG. 2 shows the same wells at an intermediate point of the flood.

FIG. 3 shows the same wells near the end of the flood.

DESCRIPTION OF THE PREFERRED EMBODIMENTS rations 14. Well 11 equipped with conventional equipment which prevents fluid communication between fluids in the annulus l5 and the tubing 16. Well 12 has at least one set of perforations 17. A fluid 18 more dense and preferably of lower viscosity than water is injected into the reservoir 10 through the upper perforations 13 via annulus 15 of well 11. A fluid 19 less dense and preferably of lower viscosity than water is injected into reservoir 10 through the lower perforations 14 via the tubing 16 of well 11. The fluid 18 tends to flow downward in the reservoir while the fluid 19 tends to rise in the reservoir. An aqueous fluid injected into both upper and lower perforations following the solvents displaces the solvent heavier than water 18 downward and the solvent lighter than water 19 upward as the fluids flow horizontally toward the producing well 12. Aqueous fluid displacement of the solvents is very efficient due to the favorable viscosity contrast, water viscosity being higher than either solvent viscosity.

FIG. 2 shows the relative position of the solvent slugs after solvent injection has been terminated and an aqueous fluid has been injected for a short period of time. The aqueous fluid 20 is now forming a bank behind the solvents and is drivingthe solvents in a vertical slug through the reservoir.

As the solvent slug migrates through the reservoir the two solvents become mixed with each other due to density differences. This is depicted in FIG. 3.

A particularly preferred embodiment of our invention is to design the solvent slugs so that a mixture of the solvents will have a density substantially equal to water. Thus, with no density difference between the solvent mixture and the displacing water, no segregation will occur, the slug retainsits identity and the petroleum displacement approaches a piston-like configuration. g

The above description is only typical, and many variations will be obvious to one skilled in the art after reference to the teachings contained herein. For example, injection of the two solvents in different wells may provide substantially the same advantage of injection of both solvents in the same well. The character of the reservoir and location of the wells will enable one skilled in the art to choose a configuration that will most likely provide optimum performance.

The solvents for use in our invention are of two general types, more dense than water and less dense than water. Those which are more dense than water should ideally also be substantially chemically inert to water and have solubility characteristics whichenable them to dissolve adequate amounts of petroleum. It is preferred that the more dense solvent have a viscosity less than water. Ideally, the solvent should be completely miscible with the petroleum so that the interface between the leading edge of the solvent and the petroleum is removed. Examples of specific solvents include but are not limited to carbon disulfide and chlorinated hydrocarbons such as methylene dichloride and carbon tetrachloride.

In certain applications carbon disulfide is the preferred heavier than water solvent because of its unique properties or ease of manufacture and recovery. In the case of tar sand oil, for example, the bitumen is more soluble in carbon disulfide than in other solvents and certain bitumens may only be soluble to any appreciable extend in carbon disulfide. Also, where the recovered crude is to be catalytically treated in a refinery, for example, carbon disulfide is preferred. lt is a characteristic of covalently bonded halogens such as those found in halogenated hydrocarbons that they tend to poison some refinery catalysts. Carbon disulfide does not and in addition is quite easily removed from recovered crude by physical separation processes to be reused again, leaving the crude substantially free of carbon disulflde. Carbon disulflde may also have a great economic advantage over halogenated hydrocarbons since it may be manufactured by the reaction between coke (carbon) and sulfur which are often found in excess near petroleum-producing areas.

It is also within the scope of our invention to use as the heavy solvent a blend of carbon disulfide with another component, mutually soluble in carbon disulfide such as a chlorinated hydrocarbon. These materials should also be easily removed from recovered oil by physical separation techniques such as vacuum distillation.

The solvent less dense than water to be used in our invention includes any aromatic or aliphatic hydrocarbon which will solubilize partially or completely the crude petroleum to be recovered. Examples of suitable solvents include light crude oil and partially refined fractions thereof, e.g., side cuts from fractionating columns, gas oils, kerosene, naphthas, straight-run gasoline, and liquifled petroleum gases. Pure components of any of the above are also suitable, for example, toluene, xylene, and benzene.

The size of solvent slug to be used will depend on the solvents chosen and the degree of recovery desired. The degree of recovery desired is a matter of economics and may be determined by those skilled in the art without engaging in inventive effort. As an aid in determining the size of slug needed the following procedure may be used but is not intended to limit the scope of our invention or tie it to any routine calculation procedure. The size of a slug of petroleum solvent, for example, may be calculated by a formula such as:

amount ofcrude per acre-foot of formation degree of depletion desired (decimal) Routine laboratory experimentation may be used to determine the solubility of a given crude petroleum in the solvents used and core analysis will yield information on the amount of crude per acre foot of formation. Thus, the size of solvent slug for any field may be determined.

The driving fluid for use in our invention may be gaseous or liquid. For example, gases including light hydrocarbons and carbon dioxide may be used for the process of our invention. Aqueous fluids are particularly preferred driving fluids in the process of our invention. Water, brine and thickened aqueous fluids are all suitable aqueous fluids for the process of our invention.

We claim:

1. A method for producingpetroleum from a subterranean reservoir which comprises:

injecting a slug of petroleum solvent more dense than water into the upper portion of the reservoir followed by a driving fluid,

injecting a slug of petroleum solvent less dense than water into the lower portion of the reservoir followed by a driving fluid and driving these solvents through the reservoir toward a production point where petroleum is produced.

2. A method as in claim 1 wherein the solvent more dense than water comprises carbon disulfide.

3. A method as in claim 1 wherein the solvent more dense than water comprises chlorinated hydrocarbons.

4. A method as in claim 1 wherein the solvent more dense than water comprises mixtures of carbon disultide and chlorinated hydrocarbons.

5. A method for producing petroleum from a subterranean reservoir which comprises:

injecting a slug of petroleum solvent more dense than water into the upper portion of the reservoir followed by an aqueous driving fluid, I

injecting a slug of petroleum solvent less dense than water into the lower portion of the reservoir followed by an-aqueous fluid and forcing these solvents through the reservoir with an aqueous driving fluid toward a production point where petroleum is produced.

6. A method as in claim 5 wherein the solvent more dense than water comprises carbon disulfide.

7. A method as in claim 5 wherein the solvent more dense than water comprises chlorinated hydrocarbons.

8. A method as in claim 5 wherein the solvent more dense than water comprises mixtures of carbon disulfide and chlorinated hydrocarbons.

9. A method as in claim 5 wherein the solvent slugs, if blended, would have a density about equal to the aqueous driving fluid.

10. A method for producing petroleum from a subterranean reservoir which comprises:

simultaneously injecting a slug of petroleum solvent more dense than water into the upper portion of the reservoir and a slug of petroleum solvent less dense than water into the lower portion of the reservoir, both solvent slugs followed by a driving fluid and driving these solvent slugs through the reservoir toward a production point where petroleum is produced.

11. A method as in claim 10 wherein the solvent more dense than water is selected from the group consisting of carbon disulflde and chlorinated hydrocarbons and the driving fluids are aqueous fluids.

Claims

1. A METHOD FOR PRODUCING PETROLEUM FROM A SUBTERRANEAN RESERVOIR WHICH COMPRISES: INJECTING A SLUG OF PETROLEUM SOLVENT MORE DENSE THAN WATER INTO THE UPPER PORTION OF THE RESERVOIR FOLLOWED BY A DRIVING FLUID, INJECTING A SLUG OF PETROLEUM SOLVENT LESS DENSE THAN WATER INTO THE LOWER PORTION OF THE RESERVOIR FOLLOWED BY A DRIVING FLUID AND DRIVING THESE SOLVENTS THROUGH THE RESERVOIR TOWARD A PRODUCTION POINT WHERE PETROLEUM IS PRODUCED.

4. A method as in claim 1 wherein the solvent more dense than water comprises mixtures of carbon disulfide and chlorinated hydrocarbons.

5. A method for producing petroleum from a subterranean reservoir which comprises: injecting a slug of petroleum solvent more dense than water into the upper portion of the reservoir followed by an aqueous driving fluid, injecting a slug of petroleum solvent less dense than water into the lower portion of the reservoir followed by an aqueous fluid and forcing these solvents through the reservoir with an aqueous driving fluid toward a production point where petroleum is produced.

10. A method for producing petroleum from a subterranean reservoir which comprises: simultaneously injecting a slug of petroleum solvent more dense than water into the upper portion of the reservoir and a slug of petroleum solvent less dense than water into the lower portion of the reservoir, both solvent slugs followed by a driving fluid and driving these solvent slugs through the reservoir toward a production point where petroleum is produced.

11. A method as in claim 10 wherein the solvent more dense than water is selected from the group consisting of carbon disulfide and chlorinated hydrocarbons and the driving fluids are aqueous fluids.