Method of producing petroleum

P. D. BARTON

ETAL

METHOD OF PRODUCING

PETROLEUM

Filed Oct. 10,

1942

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Patented Dec. 11, 1945

2,390,770

UNITED STATES PATENT OFFICE

2,390,770

METHOD OF PRODUCING PETROLEUM

Paul D. Barton, Phoenixville, and Patrick F. Dougherty, Chester, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey

Application October 10, 1942, Serial No. 461,536

Claim. (Cl. 166—21)

The present invention is directed to a method for the recovery of oil from wells in oil producing formations, and more particularly relates to the recovery of oil from wells from which production by conventional methods has decreased to a point where further recovery is no longer profitable.

It is generally recognized that only a relatively small proportion of the oil present in oil producing formations is recovered by conventional means and consequently the amount of oil still remaining in such formations, after further production is no longer profitable, is frequently in excess of the amount which was profitably recoverable. Various methods of recovering a portion or portions of the oil which remains in the formations have found practical use, among them may be mentioned various gas re-pressuring, gas or water drive, water flooding methods and the like. However, such supplementary recovery methods by no means exhaust the oil producing formations of all the oil which they contain.

The present invention is directed to a method of increasing the recovery from virgin, depleted or partially depleted oil producing formations which will hereinafter be referred to as “sands,” although it is to be understood that the invention is applicable to other types of oil producing formations. It is also applicable to the exploitation of shale or asphaltic deposits.

Broadly stated, our invention comprises injecting air, or other combustion supporting gas, which will be referred to herein only as air, into an oil producing formation through one well, hereinafter called an injection well, igniting a portion of the oil, or other hydrocarbons present in the pores of the formation at the face of the injection well, and continuing the supply of air to the formation through the injection well to support combustion of a portion of the hydrocarbons present in the formation. The hot products of combustion will spread through the formation, driving oil and gas present in the pores of the formation towards other wells in the same formation located at points adjoining or surrounding the injection well, and the oil and gas may then be recovered from such other wells, which will be called herein “production wells.”

We are aware that it has heretofore been proposed to ignite the oil in the oil bearing formation and to use the products of combustion to drive oil to other’wells.. However, such methods as have been proposed have not found any practical use, since it has been impossible to control the rate and direction of combustion. Therefore, in its more specific features, our invention relates to a method of controlling the rate and direction of combustion, both for the purpose of controlling the drive of the oil from the formation to producing wells and additionally for controlling the type of products produced.

For a better understanding of the invention, reference should be made to the accompanying drawing, in which Fig. 1 is a diagrammatic sectional view of an oil field in which our invention is being practiced, while Fig. 2 is a plan view of such a field.

In the drawing A designates an oil producing formation, B designates an injection well, while C, D, E, F, G, and H represent producing wells surrounding well B. Air from a compressor I flows through line ί I to well B and is injected therethrough into the formation A. In starting up, injection of air is continued until tests show that the atmosphere in well B is such that no explosion will occur on ignition. The oil or other hydrocarbons still remaining in the pores of the formation A at the face of the well B is then ignited by any suitable means, such as an electrical ignition device, thermite bomb or the like. The injection of air through well B is continued in order to support combustion of the hydrocarbons in the formation A. The hot products of combustion are driven through the formation A toward producing wells C to H and drive oil and gas remaining in the interstices of the formation A before them toward these wells from which the oil and gas are to be recovered.

The oil, driven through formation A, will collect at the base of the producing wells C to H. Generally, at the start of operations, liquid production will be obtained, and due to the low pressure in formation A it is necessary to pump the producing wells C to H in the customary manner in order to remove the oil therefrom. However, after operations have continued for a considerable time, sufficient pressure may be built up in the formation A to cause the producing wells to flow without pumping. Unless otherwise specified, the oil and gas produced from formation A' through producing wells C to H is removed therefrom through valved line 2, flows to manifold or collecting line 3, a compressor 4 being provided in such of lines 2 as may be necessary in order to raise the pressure therein sufficiently to cause the oil or gas flowing therethrough to enter collecting line 3 and thence to flow to oil and gas separator 5 wherein the oil is separated from the gas in well known manner. The oil is. removed from separator 5

2,390,770 through line 6 and is pumped to storage. Gas is removed from separator 6 through line 7 and flows to compressor 8, where it is recompressed to the desired pressure and flows therefrom to manifold or distributing line 9. The gas may then be sold for fuel if it has sufficient calorific value and a market exists therefor, but as a general rule it is preferable to use the gas as an aid to further production in one of the manners hereinafter disclosed, since gas is generally at a premium in fields where the use of our process is economically justified. Distributing line 9 is therefor connected to each of producing wells C to H by a valved line 10.

The heat of combustion in the zone surrounding well B will heat the oil present in the formation and tend to crack heavier hydrocarbons present and vaporize any lighter hydrocarbons thus formed or naturally present in the formation. Such heating of the oil will, of course, reduce its viscosity and cause it to be more readily driven through the formation to the producing wells C to H. The lighter hydrocarbons formed by cracking will, of course, be vaporized by the high temperatures near the well B, but as they are driven through the formation will cool and condense and will therefore be absorbed by the oil present in the formation, reducing its viscosity and thereby aiding in production. The gaseous products of combustion, particularly the carbon dioxide, are readily soluble in the oil present in the formation and also aid in reducing its viscosity. If the formation A happens to be a’limestone formation, the heat of combustion will tend to decompose it and produce further carbon dioxide, which will be absorbed by oil in the formation with consequent reduction in viscosity of the oil and increase in its recovery. The injection of air through well B is continued at a rate such that combustion will be supported in the formation A and the zone of combustion will spread radially from well B through formation A.

As injection of air is continued through injection and combustion well B, it frequently occurs that combustion will progress more rapidly toward certain of the production wells C, D, E, F, G, or H than it does towards other of these wells. This condition will occur when the oil producing formation A is not of uniform permeability, as is frequently, if not generally, the case. For example, it may frequently be the case that the formation A will be more permeable in the direction of well C than it is in the direction of well D, while the permeability of formation A is substantially uniform in the direction of wells E to H inclusive. When this condition is encountered, the air injected through injection and combustion well B will flow in greater volume toward well C and in relatively small volume toward well D and in intermediate volumes toward wells E to H inclusive. Therefore, after combustion has continued for a time, the face of combustion in formation A may assume a plan view similar to that shown by dotted line X in Fig. 2, in which it will be noted that combustion has proceeded much further toward well C than it has toward well D but is proceeding in a satisfactory manner toward wells E to H inclusive.

Such unevenness in the rate of combustion from the injection well to the various production wells can generally be detected without difficulty. Thus a greater quantity of oil is generally produced from the well or wells toward which combustion is proceeding most rapidly, 75 direction of the well C and aid in maintaining well C in the example being given; also the type of products produced from tl^c well toward which combustion is proceeding most rapidly will differ from the products produced at the wells toward which combustion is proceeding at a slower rate, lighter hydrocarbons and a large quantity of gas and possibly some products of combustion being produced at those wells towards which combustion is proceeding most rapidly. In addition, the temperature of the fluids, particularly the gas and- products of combustion obtained from the well or wells toward which combustion is proceeding most rapidly, will be higher than it is at other wells.

For the more nearly perfect recovery of oil from the formation A, it is desirable that the .· combustion progress uniformly radially from well B toward all of the producing wells, and therefore it is necessary to so control the combustion as to keep the rate of combustion substantially uniform. Thus, if channels should be encountered or develop in formation A in the direction of well C with the result that the combustion tends to proceed toward this well more rapidly than toward well D, while combustion towards wells E to H inclusive is proceeding in a satisfactory manner, steps must be taken to decrease the rate of combustion toward well C or increase it toward well D, or a combination of these steps must be taken. In order to decrease the rate of combustion toward well C, well C may be shut down by throttling, to the extent if necessary of closing, the line 2 connected thereto, until such time as combustion toward well D has caught up with the combustion toward well C. Such a remedy may be sufficient if there is only a relatively slight difference in the rate of combustion toward well C and D; but, if that remedy is inadequate, additional pressure may be built up in well C by opening valved line 10. whereby all or part of the gases produced through wells D to H inclusive from formation A are injected back into well C, thereby causing the air injected through well B to pass more readily toward well D.

Another method of decreasing the rate of combustion toward well C is to inject water through well B. The water, in following the same channels that the gas follows, will pass into the more permeable formations in greater amount than into the less permeable formations and thus, when air is again injected, will decrease the rate of combustion toward well C by obstructing the air flow in this direction proportionately greater than in other directions as well as by exerting a greater quenching action on the combustion in this direction. In order to effect a more permanent throttling of the channels in the direction of production well C, we may introduce some other material, along with the water, through well B which will permanently partially close up the channels extending in the direction Of well C. This can be accomplished by injecting drilling mud instead of water through well B. Such a remedy is satisfactory when the channels are located near ’the face of well B. However, in case the channels occur further back in formation A, it is preferable to inject with the water some substance in solution therewith but which will be precipitated therefrom by chemical action with the formation after it has penetrated back into formation A. Such action will materially throttle the channels in the

2,390,770 uniform the rate of combustion toward all of the production wells.

Instead of attempting to decrease the rate of combustion toward well C it is possible to increase the rate of combustion toward well D. This may be accomplished by treating the formation A around well D in order to render it more porous. One method of accomplishing this is by introducing acid through well D preferably with an inhibiter so that it will work back into the formation A from well D toward well B before the formation A is attacked and the pores around well D opened up. Also, acid may be introduced through well B after introducing therethrough some material to close up the pores toward well C so that the acid will tend to go into the direction of well D and open up the pores in formation A toward this well.