Process For Simultaneously Increasing Recovery And Upgrading Oil In A Reservoir

Abstract

A process for simultaneously increasing recovery and upgrading oil in a reservoir by injecting gas produced by the in situ gasification of coal to increase recovery and upgrade said oil. The gas is also useful in the production of steam and other gaseous materials for injection.

Description

FIELD OF THE INVENTION

This invention relates to primary, secondary and tertiary recovery of oil from oil-bearing reservoir formations. This invention further relates to the use of gas injection techniques in the recovery of oil from oil bearing reservoir formations. The invention further relates to the use of gas produced by the gasification of coal in the recovery of oil from oil-bearing reservoir formations.

DESCRIPTION OF THE PRIOR ART

Numerous processes and methods are known for the gasification of coal to produce light hydrocarbons, carbon monoxide, carbon dioxide, hydrogen and the like. The use of gas injection as a primary, secondary, or tertiary recovery method is also known and a typical application of such techniques is shown in U.S. Pat. No. 2,734,578 issued Feb. 14, 1966 to Walter. A technique for gasifying oil-bearing shale sands and injecting the gas so produced to improve secondary oil recovery is shown in U.S. Pat. No. 3,040,809 issued June 26, 1962 to Pelzer. Other references considered in a prior art search on the concept of the present invention are: U.S. Pat. No. 1,978,655, issued Oct. 30, 1934 to Straight; U.S. Pat. No. 2,173,556, issued Sept. 19, 1939 to Hixon; U.S. Pat. No. 3,572,436, issued Mar. 30, 1971 to Riehl; U.S. Pat. No. 3,548,938 issued Dec. 22, 1970 to Parker; U.S. Pat. No. 3,459,265 issued Aug. 5, 1969, to Buxton et al.; U.S. Pat. No. 3,208,514 issued Oct. 31, 1962, to Dew et al.; U.S. Pat. No. 3,399,721 issued Sept. 3, 1968, to Strange; U.S. Pat. No. 3,480,082 issued Nov. 25, 1969 to Gilliland; U.S. Pat. No. 3,360,044 issued Dec. 26, 1967 to Lange; U.S. Pat. No. 3,386,508 issued June 4, 1968 to Bielstein et al.; U.S. Pat. No. 2,813,583 issued Nov. 19, 1957 to Marx et al.; and U.S. Pat. No. 3,500,913 issued to Nordgren et al. The references are considered further illustrative of the state of the art.

Prior attempts at the use of gas for secondary recovery have been limited by the difficulty and expense in obtaining the gas at the site of the secondary recovery operation. By their nature, such recovery techniques require that the injected materials must be available at relatively low expense and in relatively large quantities to allow successful gas injection process operations. As a result much time and effort has been directed to methods which do not suffer the shortcomings of the methods disclosed above.

OBJECTS OF THE INVENTION

It is the object of the present invention to provide a method whereby gas injection techniques may be utilized to increase oil recovery and upgrade heavy crude oils without encountering the difficulties inherent in producing the injection gas from surface sources or transporting the gas substantial distances to the injection site.

SUMMARY OF THE INVENTION

It has now been found that the object of the present invention is realized in a process for increasing recovery and upgrading heavy crude oil in a reservoir comprising producing a gaseous mixture by in situ gasification of neighboring coal deposits; injecting the gaseous mixture into oil reserviors to increase recovery of and upgrade the oils in said reservoir and recovering said oil. The gaseous mixture is also used to generate steam and other gaseous injection materials.

DESCRIPTION OF THE DRAWING

FIG. 1 is a sketch of the Continental United States showing selected oil fields and coal fields and the areas in which said coal fields neighbor said oil fields.

FIG. 2 is a sketch of a typical embodiment of the present invention.

FIG. 3 is a sketch of an embodiment of the present invention wherein the coal deposit overlies the oil formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In primary, secondary and tertiary recovery operations for the recovery of crude oils, it has long been known that numerous process utilizing gas injection are useful for such recoveries. The primary difficulty in the use of such techniques is that it oftentimes is difficult to provide large volumes of gaseous material at the oil field to be treated. The primary difficulties are economic as well as the simple handling difficulties in transferring large volumes of gas to remote areas.

It has been observed that, as shown in FIG. 1, in many areas in the Continental United States oil fields are located adjacent to coal deposits. It has now been discovered that an effective and efficient method for the primary, secondary and tertiary recovery of oil from such formations consists of the in situ gasification of the coal in said coal deposits to generate injection gas for the oil recovery operation.

The in situ coal gasification may be achieved by numerous methods well known in the art and no particular novelty is claimed in the method by which the coal is gasified. In particular, coal may be gasified by the injection of air or oxygen enriched air. The injection gas may also contain water since the injection of water with air has been shown to increase the BTU value of the produced gas.

The oil recovery process may be selected from a variety of known methods, such as "drive" processes, steam drive processes, "huff and puff" processes, and the like. The "drive" methods typically consist of the injection of gases, liquids and the like at one well in a formation and the recovery of gas, condensed gas, liquids, oil and the like at a second well in the same formation. Steam drive processes are similar with the major differences being that steam is used as the injection gas rather than other gases and latent heat is transferred to the formation. "Huff and puff" operations are well known in the art and typically comprise the injection of steam, heated gases and the like following which the well is sealed and time is allowed for the heat to permeate the formation, following which the well is reopened and oil is produced from said well. No particular novelty is claimed in the method for secondary, tertiary or primary recovery of oil, but rather, the present invention comprises a method whereby in situ gasification of coal may be utilized to provide a readily available source of gaseous injection materials for oil recovery techniques requiring an injection gas material.

FIG. 1 is a sketch of the Continental United States showing selected oil fields and coal fields and the areas in which said coal fields neighbor said coal fields.

FIG. 2 discloses an embodiment of the present invention wherein a gas drive process is used. Air is introduced through line 20, line 24, and well 3 into coal deposit 4. The gas produced by the gasification of coal deposit 4 is produced through well 5 and line 26. The gas is then passed through line 26, to well 6 and through well 6 into oil formation 7. The gas flow in oil formation 7 is from well 6 to well 8 and oil and gas are produced through well 8 and line 28. The oil-gas mixture so recovered is passed to oil recovery where the stream is separated into its respective components, i.e., gas, water and oil.

As will be obvious to those skilled in the art, the injection gas may be ignited at the base of well 6 to generate heat in oil formation 7, thus aiding the oil recovery operation. The ignition of the gas at the base of well 6 may be conducted in such a manner that well 6 is completely coked in as is well known to those skilled in the art. Numerous other modifications and variations of the gas drive process are possible and may be readily apparent to those skilled in the art upon review of the foregoing description. It will, of course, be noted that water may be supplied through lines 22 and 24 to coal deposit 4. As noted hereinbefore, the produced gas has a higher BTU content in many instances when water is injected with the air. It will, of course, be understood that air is used to generally include any oxygen-containing gas such as air, oxygen enriched air, and the like.

The produced gas may optionally be used to generate steam which may be injected into oil formation 7. The steam is generated by combustion of the gas produced by the gasification of the coal in conventional steam boilers and the like. The generated steam is then passed to oil formation 7 and the oil recovery is conducted in a manner similar to that described above wherein the gas from the coal gasification is used. As will be obvious to those skilled in the art, many variations and modifications of the above procedures are possible, for instance, water may be introduced into oil formation 7 with the produced gas, with the steam and the like.

Steam may be added with the gas produced by the gasification of the coal so that the injection gas at the bottom of well 6 may be gas produced by gasification of coal, a combination of steam and the gas produced by gasification of coal, or either of the streams may be used in conjunction with water, and the like.

FIG. 3 discloses a preferred embodiment of the present invention wherein the coal deposit overlies the oil formation. Air, oxygen enriched air, or an oxygen-containing stream mixed with water, is produced by introducing air and the like through line 22 and water through line 24 into line 20 for injection into well 1 and well 3. The injection gas is then passed into coal deposit 4 to produce producer gas by the gasification of coal deposit 4. The flow of the oxygen containing gaseous mixture is shown by arrows 30 and the producer gas flow is shown by arrows 36. The producer gas flows down the bore of well 2 and through oil formation 7 thus resulting in the production of oil and producer gas through wells 1 and 3. The producer gas and oil flow are shown by arrows 40.

The oil-gas mixture is then produced from wells 1 and 3 through lines 26 and 28, and passed to oil and gas recovery. The combustion of the coal deposit is in a reverse direction to the flow of the injection gas. The combustion front 32 is shown by arrows 34 to move in a direction opposite the flow of the oxygen-containing gas which flows as shown by arrows 30.

In a variation of the above-described method the burn rate in the coal deposit may be reduced to a minimum and the well closed in for a period of time to allow the heat to permeate oil formation 7. After the heat has permeated oil formation 7, well 2 is opened and produced. This operation is similar to a "huff and puff" operation in the sense that the heated gaseous mixture is injected into oil formation 7, allowed to permeate the formation, and thereafter oil is produced at intermittent intervals. It should also be noted that when shale layer 17 is relatively thin, heat from the gasification of the coal deposit 4 will be transmitted to oil formation 7, thus further aiding recovery. Many variations and modifications of the foreging procedures are possible and may be obvious to those skilled in the art. Such modifications are considered within the scope of the present invention and as heretofore noted the primary novelty in the present invention lies in the gasification of neighboring coal deposits to provide an economical and readily available source of gaseious mixtures for primary, secondary, and tertiary oil recovery operations.

The particular method for the gasification of coal is of no particular importance to the process of the present invention so long as a product gas comprising from about 15 to about 60 mole percent carbon dioxide, from about 1 to about 10 mole percent methane, from about 0.0 to about 0.4 mole percent oxygen, from about 5 to about 60 mole percent hydrogen, from about 2 to about 51 mole percent carbon monoxide, from about 10 to about 80 mole percent nitrogen, and from about 0.1 to about 3.0 moles of water per mole of dry gas is produced. Such gases are useful in the process of the present invention although a preferred gas composition is from about 10 to about 36 mole percent carbon dioxide, from about 2.0 to about 7.6 mole percent methane, from about 0.3 to about 0.4 mole percent oxygen, from about 10 to about 50 mole percent hydrogen, from about 10 to about 15 mole percent carbon monoxide, from about 10 to about 70 mole percent nitrogen, and from about 0.13 to about 2.0 mole of water per mole of dry gas.

It will be further recognized by those skilled in the art that wells may be coked to the point of consolidating unconsolidated formations by simply combusting the gas mixture at the bottom of the well. Such is not considered the primary objective of the present invention and normally gas would be injected and sealed in to allow recovery of oil cyclically or gas would be injected continuously and oil recovered continuously.

As shown in FIG. 1, in numerous areas in the Continental United States, coal deposits neighbor oil fields. This situation makes it possible to utilize the process of the present invention to gasify coil in situ and utilize the gaseous mixture for gas injection recovery techniques with neighboring oil fields. Neighboring as used in the context of the present specification refers to coal fields which overlie, underlie, or are near the oil fields to be treated by the gas injection procedures. The use of such neighboring coal and oil fields allows the use of gas produced in situ to provide a large volume of low cost gaseous material at the site of the injection treatment. Such a process has not been available heretofore. The advantages of such a process over processes utilizing surface generation of gas, the piping of gas over long distances, and the like are obvious to those skilled in the art. A further advantage is that in many situations a low-grade coal deposit may be utilized to generate the gaseous mixture, thereby utilizing a resource which is not economically useful otherwise. Although it is shown that in the Continental United States, many areas are adapted to the use of the process of the instant invention, it should be understood that the scope of the invention is not so limited and that any area anywhere in the world having coal deposits neighboring oil fields is adapted to the application of the process of the present invention.

The use of the gaseous mixtures described above achieves thermal stimulation of the oil formation, since the injection gas may be hot as produced or can be readily heated and the carbon dioxide and methane are readily absorbed by the crude oils, thereby reducing the viscosity. In addition, it should be pointed out that while applicants wish to be bound by no particular theory, it is believed that the hydrogen in the gaseous mixture reacts catalytically at the sand-crude oil surfaces to reduce the viscosity of the crude oil further, thereby improving the crude oil quality and increasing recovery. There are thus three mechanisms acting to increase recovery and improve crude oil quality, i.e., thermal stimulation, absorption of light materials by the crude oil, and hydrogenation of the crude oil. A further advantage is that the hydrogenation of the crude oil tends to reduce the sulfur content of the oil, thereby further improving the product quality. The use of such a mixture and a showing of synergistic qualities in improving oil recovery is shown in U.S. Pat. No. 2,734,578 issued Feb. 14, 1956 to Walter. The fact that such a mixture has been used heretofore, merely emphasizes further the utility of applicants' process. Applicants have found a novel, reliable, and economical method for providing such desirable gaseous mixtures at low cost and in large quantities to oil fields wherein gas injection techniques result in increased oil recovery and upgrade the crude oil products. Many modifications and variations are possible within the scope of the present invention and in light of the foregoing description of preferred embodiments and the following examples, it is expected that those skilled in the art will envision many such desirable modifications and process variations in the present process.

EXAMPLES

Example 1

In an embodiment of the present invention as shown in FIG. 2, one million standard cubuc feet per day of air is injected into ignited coal bed 4 through well 3. The coal bed is gasified by the air at combustion temperatures greater than about 1,500.degree.F and the product gas is removed from the coal bed through well 5 and typically has the following composition:

Mole % Carbon Dioxide 11.0 Oxygen 0.3 Illuminants 0.3 Hydrogen 10.0 Carbon Monoxide 13.0 Methane 3.0 Nitrogen 62.4 Water/Mole Dry Gas 0.1

The heating value of such gas is typically from about 25 to about 175 BTU/standard cubic foot (SCF) with an average value being about 100 BTU/SCF. The specific gravity of such gases is approximately 0.9 based upon the specific gravity of air at standard conditions.

During the coal gasification process the composition of the gas will vary therefore, the heating value will vary somewhere between about 25 and about 175 BTU/SCF but averaging about 100 BTU/SCF at an air injection rate of 1,000,000 SCF per day about 1,000,000 SCF of coal gas per day will be produced. The coal gas is inejcted into oil formation 7 through well 6 and is mixed with air at the base of well 6. The combustion at the base of well 6 generates approximately 100,000,000 BTU/day of heat in the oil formation. This technique is continued for some time and thereafter well 6 is placed on production. Assuming that oil is produced at the ratio of one barrel of oil per million BTU, then it is seen that the average oil production in response to thermal stimulation would be about 100 barrels of oil per day upon producing well 6. It is noted that 100 percent efficiency in the transmission of heat and the like has been assumed in the present example, whereas in practice lower efficiencies will be realized, but since such variations are dependent to a large degree upon the particular formation, the particular method and the like, it is not necessary to further define those parameters well known to those skilled in the art.

Claims

1. A process for increasing recovery of crube oil in a reservoir formation comprising:

a. producing a combustible gaseous mixture by in situ gasification of neighboring coal deposits;

b. burning said combustible gaseous mixture thereby producing an injection gas;

c. injecting said injection gas into said reservoir formation; and

3. The process of claim 2 wherein said crude oil is recovered by a "drive"

4. The process of claim 1 wherein said crude oil is recovered by a "huff and puff" type process.