US3830300A

US3830300A - In situ combustion oil recovery method

Info

Publication number: US3830300A
Application number: US00307742A
Authority: US
Inventors: J Allen
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1972-11-17
Filing date: 1972-11-17
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20
Also published as: PL89539B1; SU581885A3; CA992865A; BR7308354D0

Abstract

Heavy petroleum may be recovered from an underground formation by in situ combustion followed by injection of a hydrocarbon, which may be produced petroleum which thermally decomposes into light, low viscosity liquids that readily flow toward producing wells and petroleum coke which deposits on the reservoir formation, thereby providing fuel for another in situ combustion and repeating the cycle of operation until substantially all of the immobile, heavy petroleum is converted into a low viscosity liquid and/or gas.

Description

United States Patent 1191 Allen Aug. 20, 1974 IN SITU COMBUSTION OIL RECOVERY METHOD Primary Examiner-Ernest R. Purser Attorney, Agent, or Firm-T. L. Whaley; C. G. Ries [75] Inventor: Joseph C. Allen, Bellaire, Tex.

[73] Assignee: Texaco Inc., New York, NY. [57] ABSTRACT 22] il d; N 17 1972 Heavy petroleum may be recovered from an underground formation by in situ combustion followed by [21] Appl' 307742 injection of a hydrocarbon, which may be produced petroleum which thermally decomposes into light, low 52 us. 01. 166 261 viscosity liquid5 that readily flow toward Producing 51 Int. Cl E2lb 43/16 wells and Petroleum coke which deposits on the reser- [58] Field of Search 166/260-263 voir formation, thereby Providing fuel for another in Y situ combustion and repeating the cycle of operation 5 References Cited until substantially all of the immobile, heavy petroleum is converted il'ltO a 10W ViSCOSilZy and/0r 3,072,187 1/1963 Carr 166/261 x 3,126,957 3/1964 McKinnell 166/261 X 7 Claims, 1 Drawlng Figure T0 STORAGE fi w gc l 5 S I ,5 1 1% A A 2 Vi 1 i 0 2 wusss16: ?f S\ "fiylf.Zgff,

Z .4 V 2w x hill I :j .j 7/ 52 215512? -;i 2 f.

I n l l "i h. 10-- j 3 13/ 1 Q a .1 "1" H iTy -rg qtv i I: L41), -1 i PATENTED 0020014 I J s BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to in situ combustion for the recovery of petroleum from subterranean reservoirs.

2. Description of the Prior Art In recovery of petroleum from subterranean reservoirs, it usually is possible to recover only a minor portion of the petroleum in place by the so-called primary recovery techniques, that is, those techniques which utilize only the natural forces present in the reservoir. Thus, a variety of supplemental recovery techniques have been developed in order to increase the recovery of petroleum in such reservoirs. In these supplemental techniques which are commonly referred to as secon- IN SITU COMBUSTION OIL RECOVERY METHOD I dary recovery operations, although they may be tertiary in sequence of employment, energy is supplied to the reservoir as a means of moving the fluid within the reservoir to suitable production wells through which they may be withdrawn to the surface of the earth.

Secondary recovery techniques which are showing increasing promise are those which involve in situ combustion. In an in situ combustion process, a portion of the carbonaceous material within the reservoir is burned or oxidize in situ in order to extablish a combustion front. The combustion front may be moved through the reservoir by either a direct or inverse drive. In a direct insitu combustion process the combustion is initiated adjacent to one or more injection wells and the resulting combustion front is advanced through the reservoir in the direction of one or more production wells by the introduction of a combustion supporting gas through the injection well or wells. The combustion front is preceded by a high temperature zone commonly called a retort zone, within which the reservoir petroleum is heated to affect a viscosity reduction and is subjected to distillation and cracking. The hydrocarbon fluids resulting from subjecting the petroleum to such a process are displaced to the production wells where they are withdrawn to the surface of the earth. In an inverse combustion drive, the combustion front is established adjacent to the production well or wells. As the combustion supporting gas is introduced through the injection well, the combustion front advances counter-currently to the flow of such gas in the direction of the injection well. The in situ combustion procedure, whether inverse or direct, is particularly useful in the recovery of thick heavy oils (petroleum) such as viscous petroleum crude oils and the heavy tarlike hydrocarbons present in tar sands. While these tarlike hydrocarbons may exist within the reservoir in a solid or semi-solid state, they undergo a sharp viscosity reduction upon heating and in an in situ combustion process they behave somewhat like the more conventional petroleum crude oil. In situ combustion also may be employed in the recovery of hydrocarbons from oil shale.

After in situ combustion has propagated through the formation, a large quantity of heat is stored in the formation matrix. It has previously been found that the efficiency of the overall process may be improved by water injection following in situ combustion which scavenges the heat from the hot reservoir rock, transporting it in the form of steam and hot water through the combustion zone and heating the formation ahead. My process scavenges the heat from the hot reservoir rock with hydrocarbons which may be, for example, crude petroleum oil which decomposes forming some oil solvent which vaporizes, transports heat and reduces oil viscosity ahead by both heat and dilution actron.

Heavy oils and'bitumen from tar sands yield quantities of petroleum coke when refined. This material has been used as fuel but has the disadvantage of pulverizing and requires special handling equipment and burners. The produced bitumen from mining operations of the tar sands is fed to a coke still. However, all of the coke is not used. The excess presents a problem of rendering the area unsightly. In fact, governmental regulations often require burying and improving the scenery with plants. Most every refinery produces coke which has a relatively low commercial value.

I propose a procedure for eliminating the need for coking the production of oil at the surface. The coke, in the process of my invention, is generated in the formation which provides cost reduction and improved efficiency.

SUMMARY OF THE INVENTION The invention is a process for the recovery of hydrocarbons from a subterranean reservoir penetrated by spaced injection and production wells. The method involves introducing a combustion supporting gas into the reservoir and igniting the gas and hydrocarbons in the reservoir in order to propagate a combustion front between the injection and production wells, then producing hydrocarbons through the production well or wells. After this in situ combustion operation the injec tion of combustion supporting gasis terminated and a liquid hydrocarbon which may be crude petroleum oil is introduced into the reservoir through the injection well; the crude oil then separating into gradations of light and heavy fractions upon contacting the hot reservoir. The lighter fractions proceed through reservoir to the production well while the heavier fractions including for example, coke, deposit upon the reservoir matrix to provide the fuel for a repeat of the in situ combustion operation.

The invention also embodies using a reservoir to upgrade petroleum from any source by having it follow an in situ combustion operation. As the petroleum contacts the hot reservoir it will separate into light and heavy fractions and the lighter, more desirable fractions are produced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may be carried out utilizing any suitable injection and production system. The injection and production systems may comprise one or more wells extending from the surface of the earth into the subterranean reservoir. Such injection and production wells may be located and spaced from one another in any desired pattern. For example, a line drive pattern may be utilized'in which a plurality of injection wells and a plurality of production wells are arranged in rows which are spaced horizontally from one another. Exemplary of other patterns which may be used are the socalled circular drive patterns in which the injection system comprises a central injection well and the production system comprises a plurality of production wells spaced about the injection well. Typical circular drive patterns are the inverted five spot, seven spot, and nine spot patterns. The above and other patterns are well known to those skilled in the art and for a more detailed description of such patterns references made to Uren, L.C,, Petroleum Production Engineering-Oil Field Exploitation, Second Edition, McGraw, Hill Book Company Incorporated, New York and London, 1939. While the well patterns described in Uren are with reference to water flooding operations, it will be recognized that such patterns are also applicable to the procedure described herein.

In general, response to conventional, thermal oil recovery techniques is inherently slow. This presents a rather severe problem in remote areas where a pipeline and/or site refinery are needed for transporting and upgrading the crude. As high as 100,000 barrels of oil per day are required for economic operation of a surface upgrading plant and pipeline. Since it is impossible to initiate a project at an instantaneous rate of 100,000 barrels per day, surface storage or truck transport of the interim produced oil would be necessary but often prohibitively expensive. My scheme uses the formation itself for storage of produced petroleum crude oil, simultaneously upgrading it to the point which it is easily transferable via pipelines even in cold climates. This feature would grossly reduce refining construction and operating costs. The Athabasca tar sands of Canada are an example of a likely candidate for-the method of my invention. Construction and operating costs in the field are much higher than in many other areas since transportation by pipeline is necessary and the upgraded crude could be pumped through the pipeline. Having a refinery in a more desirable location would result in a decided improvement in overall economics.

The method of my invention could be used in any oil recovery operation wherein the oil must be upgraded to a higher API gravity or lower viscosity before it may be transported by pipeline. Although my invention is not limited to such use it is evident that a most convenient and likely use of the process of the invention will be for heavy oils especially in cold climates. Crude oils of about API gravity and below are generally too viscous to transport via pipeline and would likely be candidates for upgrading by the process of my invention. It should be recognized that this value is chosen for illustration only and is not intended to define limits to my invention.

In a typical embodiment of my invention the hydrocarbon to be injected after the in situ combustion step may be the crude oil produced from the same reservoir. Using this technique the crude oil from a reservoir may be recycled until it attains a desired APl gravity and/or viscosity and may then be transported away. In another embodiment of my invention a reservoir with particularly advantageous qualities for an in situ combustion operation may be used to remove coke and heavy ends from any crude which requires such treatment. Thus, the use of surface treatment facilities to upgrade heavy crudes may be avoided.

The in situ combustion step in the process of my invention is carried out by a conventional manner using known techniques. For example, a combustion supporting gas such as oxygen as contained in air, for example, is injected into the injection well or wells and is forced through the formation to the production wells. Next, ignition of reservoir hydrocarbons and the oxygen is initiated and once combustion is attained the combustion front is propagated through the formation toward the production wells. As this in situ combustion operation proceeds, the heat from the operation lowers to the viscosity of the inplace hydrocarbons which are moved toward the production wells where they are produced. After this in situ combustion step, the formation is left with a great deal of heat energy from the combustion operation. Heretofore, after in situ combustion operations, a fluid such as water would be injected into the production wells where the heat stored in the formation would convert the water into steam which would then proceed through the reservoir producing more of the oil. However, in the method of my invention the injection of hydrocarbons, preferably produced crude petroleum, is initiated instead of water. Depending on the composition of these hydrocarbons, they will then thermally decompose into a gradation of products including gas, light low viscosity liquids that readily flow toward the producing wells and petroleum coke which deposits on the reservoir rock thereby providing fuel for another in situ combustion operation as previously described. This cycle may be repeated until substantially all of the immobile hydrocarbons, such as coke, have been converted into a gas and/or low viscosity liquids by recycling the produced crude, using it as the hydrocarbon to be injected after each in situ combustion step. Finally, after all the immobile heavy hydrocarbons are upgraded into a low viscosity liquid or gas, a displacing fluid may be used to move the rest of the mobile fluids to producing wells.

EXPERIMENTAL Pressure (p) 1,000 psia Temperature (T) 1,500F. in burned out zone.

Porosity ((1)) 35 percent Oil Saturation (S0) percent Basis of calculations 1 Barrel (B) oil Specific heat of reservoir rock 36 BTU/ft. /F.

Minimum thermal decomposition temperature of crude oil 900F.

Rock Volume:

B ftf /B Available heat in volume of reservoir occupied by one barrel of oil in the reservoir (Specific heat of reservoir) X (Volume occupied by one barrel of oil) X (Temperature of reservoir after in situ combustion minimum thermal decomposition temperature of crude oil).

Degree of crackinggfil; Available heat X 100 Heat required BTU/Lb. Lb./B

Thus the available heat is over twice the heat necessary to thermally decompose the quench oil.

In full scale operation the produced crude will be upgraded in situ. One method of operation would be to re-inject all produced crude that had not been upgraded to a chosen degree. The upgraded property critical for shipping, could be density (higher API) or viscosity (lower value). The chosen value would be dictated by surface refinery requirements or adequately low viscosity for transportation by pipeline.

Full scale operation as herein described would eliminate surface coke stilling of the produced heavy oil such as the bitumen from tar sands, and substituting for expensive and bulky surface vessel an underground coking vessel, the hot reservoir rock. Steel vessels would be eliminated. Better thermal efficiencies would be experienced due to the excellent insulating properties of the adjacent beds.

The present invention may be more fully understood by reference to the attached FIGURE which depicts a typical embodiment of my invention during operation. Petroleum bearing reservoir 10 is penetrated by an injection well 11 and a production well 12. The wells are in communication with the reservoir 10 by openings 13 in the wells. An in situ combustion front 14 is proceeding through the reservoir area between the wells. This in situ combustion front was begun by injecting an oxygen containing gas through the line 15 into the injection well 11. The hydrocarbons in the reservoir are ignited by conventional techniques and injection of oxygen containing gas is continued. Ahead of the in situ combustion front 14 is an area 16 of petroleum and gaseous combustion products. The in situ combustion raises the temperature of the reserovir and lowers the viscosity of the petroleum in area 16 moving it toward production well 12 where it is removed. This petroleum is stored at the surface for injecting later. Whenever adequate heat has been added to the reservoir matrix for thermally decomposing the produced oil, air injection is terminated and petroleum is injected via well 11 through line 17. The petroleum thus injected enters the reservoir in area 18 behind the in situ combustion front 14. Area 18 has been raised to a high temperature by the in situ combustion front 14. As the injected petroleum encounters this hot reservoir thermal cracking takes place whereby the overall average molecular weight of the petroleum is lowered. Very heavy portions of this petroleum, such as coke, deposit on the reservoir formation. The lighter portions of the petro- Degree 228% leum proceed through the formation toward the production well 12. Air injection is resumed and the heavy coke-like thermal decomposition products are ignited by conventional techniques and the process is re- 5 peated.

I claim: I

1. In the recovery of hydrocarbons from a subterranean reservoir initially containing hydrocarbons of 15 API gravity or less penetrated by spaced injection and 10 production wells, the method comprising:

a. introducing a combustion-supporting gas into the reservoir,

b. forcing said gas from the injection well to the production well,-

c. igniting the hydrocarbons in the reservoir in order to propagate a combustion front to travel from the injection well to the production well,

d. producing hydrocarbons through the production well,

e. terminating the injection of the combustionsupporting gas into the reservoir,

f. injecting the hydrocarbons produced in step (d) into the injection well so that the hydrocarbons will separate into gradations of light and heavy fractions while in contact with the heated reservoir wherein a portion of the heavy fractions deposit on the reservoir matrix, and

g. producing the light fractions of the hydrocarbon.

2. A process as in claim 1 wherein the heavy fraction 3. A method of removing coke from petroleum which comprises:

a. introducing a combustion-supporting gas into a 40 subterranean reservoir containing hydrocarbons penetrated by spaced injection and production wells,

b. forcing said gas from the injection well to the production well,

d. producing hydrocarbons through the production well,

. terminating the injection of a combustionsupporting gas into the reservoir,

f. injecting the hydrocarbons produced in step (d) into the injection well so that the hydrocarbons will separate into gradations of light and heavy fractions upon contacting the heated reservoir wherein coke is deposited on the reservoir matrix, and

g. producing the lighter fractions of the injected bydrocarbons.

4. The method of claim 3 wherein the injected petroleum has an initial API gravity of 15 or less.

5. A process as in claim 3 wherein the coke deposited on the reservoir matrix in step (f) is used as fuel for an in situ combustion process to again heat the reservoir and the light fraction from step (g) is reinjected into the heat reservoir to remove additional coke.

6. In a process wherein a throughput in situ combustion operation has raised the temperature of the formaprovement which comprises:

' a. reinjecting said petroleum into the reservoir after the in situ combustion operation so that the petro- 8 reservoir, and b. producing the light fractions. 7. The process of claim 6 wherein the crude oil has leum will separate into gradations of light and an initial API gravityof 150011655- heavy fractions while in contact with the heated

Claims

2. A process as in claim 1 wherein the heavy fraction deposited on the reservoir matrix in step (f) is used as fuel for an in situ combustion process to again heat the reservoir and the light fraction from step (g) is reinjected into the heated reservoir to further upgrade it.
3. A method of removing coke from petroleum which comprises: a. introducing a combustion-supporting gas into a subterranean reservoir containing hydrocarbons penetrated by spaced injection and production wells, b. forcing said gas from the injection well to the production well, c. igniting the hydrocarbons in the reservoir in order to propagate a combustion front to travel from the injection well to the production well, d. producing hydrocarbons through the production well, e. terminating the injection of a combustion-supporting gas into the reservoir, f. injecting the hydrocarbons produced in step (d) into the injection well so that the hydrocarbons will separate into gradations of light and heavy fractions upon contacting the heated reservoir wherein coke is deposited on the reservoir matrix, and g. producing the lighter fractions of the injected hydrocarbons.
4. The method of claim 3 wherein the injected petroleum has an initial API gravity of 15* or less.
5. A process as in claim 3 wherein the coke deposited on the reservoir matrix in step (f) is used as fuel for an in situ combustion process to again heat the reservoir and the light fraction from step (g) is reinjected into the heat reservoir to remove additional coke.
6. In a process wherein a throughput in situ combustion operation has raised the temperature of the formation above 900*F. while producing petroleum the improvement which comprises: a. reinjecting said petroleum into the reservoir after the in situ combusTion operation so that the petroleum will separate into gradations of light and heavy fractions while in contact with the heated reservoir, and b. producing the light fractions.
7. The process of claim 6 wherein the crude oil has an initial API gravity of 15* or less.