US2924276A - Secondary recovery operation - Google Patents

Description

1960 w. o. HElLMAN ET AL 2,924,276

SECONDARY RECOVERY OPERATION Filed Aug. 8, 1955 mzEoE k =o 32$ 28 MEEQE Inventors William O. Hellman James A. Reilly Byg. Q.

Attorney United States Patent @fitice SECONDARY RECOVERY OPERATION William 0. Hellman, Short Hills, and James A. Refill, Westfield, N.J., amignors, by mesne assignments, to Jersey Production Research Company Application August 8, 1955, Serial No. 526,942

3 Claims. (Cl. 16611) The present invention is broadly concerned with an improved method for increasing the recovery of crude petroleum oil from oil-bearing subsurface formations. The invention is more particularly concerned with a particular integrated combination of steps wherein low boiling liquid solvents are used in conjunction with a natural gas drive followed by the use of a combustion front which is caused to move through the subsurface strata from an input to an output well. In accordance with the present invention a quantity of a low boiling liquid solvent which is substantially completely miscible with crude oil is injected through an input well into an oil reservoir and maintained in a liquid bank or pool of relatively high concentration as it is impelled through the reservoir. This liquid bank of solvent which is driven by a gas drive effectively washes out the crude oil in the reservoir. The driving pressure of the driving gas is utilized to advance the bank of liquid solvent through the reservoir. Substantially complete recovery of the solvent is obtained by its vaporization into the driving gas. The final phase of this integrated process is to initiate a combustion front at the input Well and to cause this front to pass through the reservoir to the output well.

In accordance with the present invention the liquid propane or other material is caused to flow through the field to another point or area in the field propelled by a stream of natural gas. Air, oxygen, or other oxygen-containing gas is then injected at the input well and a combustion front caused to move from the input to the output well.

In the first phase of the present operation after the band of propane has moved sufficiently far through the formation, it becomes relatively rich in recovered oil. It is within the scope of the present invention to remove at least a portion or" the band of propane containing the dissolved oil at this point; to segregate the recovered oil from the propane and to return the propane to the formation in order to assist in maintaining the liquid bank of concentrated solvent.

Furthermore, the natural gas driven propane band strips and recovers the residual propane from depleted portions of the formation and thus recovers appreciable amounts of propane which otherwise would be lost in the formation. Since the natural gas flows more rapidly through the formation than the propane or oil, some propane is carried forward and through the bank. However, this propane vaporized in the natural gas is absorbed from the gas by the oil ahead of the propane band. By these actions the maintenance of a concentrated band of propane is promoted.

It is also within the scope of the present invention to bring the reservoir up to the desired working pressure 2,924,276 Patented Pole. 2*, 1960 Id input well. This combustion front passes through the reservoir, serves to heat up the reservoir and thereby secures a greater recovery of the injected propane and of the remaining oil.

The invention may be readily understood by reference to the drawing illustrating the same. Referring specifically to Fig. 1, an oil-producing formation 1-0 is shown disposed below the surface of the earth 1. Well bore holes 2, 3, 4, 5 and 6 are shown extending from the surface of the earth through substrata to near the bottom of oil-bearing formation it In accordance with one concept of the present invention, a predetermined amount of liquefied propane or an equivalent material is introduced by means of bore hole 6 into the oil-producing sand 10 and is then followed by a continuous injection of a suitable natural gas into here hole 6. The band of propane is shown disposed between well bore holes 4 and 5, flowing in the direction of bore holes 3 and 2. Oil is withdrawn from core holes 3 and 3 together with gas which is separated from the oil at the surface and recycled to injection well Since the band of propane has moved from bore hole 6 to bore hole 4, the front end of the band contains dissolved ther in substantial amounts of oil. Thus, in accordance with one concept of the present invention, a portion of this fluid may be withdrawn from the reservoir by means of bore hole 4. The oil is segregated from the propane by any suitable means such as distillation and passed to suitable storage. The segregated propane is preferably returned to the formation by means of well bore hole 5 immediately back of the bank of propane in the formation and ahead of the natural gas drive.

The natural gas introduced by means of well 6 serves both to drive the oil and propane bank forward and to remove the residual propane from the oil-depleted zone of the formation by vaporization. At this point an oxygen-containing gas such as air or oxygen is introduced into well 6 and ignited. The oxygen-containing gas is continued to be injected into 6 and the flame front thus advances through the reservoir from well 6 to well 3 thereby increasing the recovery of propane and oil.

The present invention is broadly concerned with a novel procedure for the recovery of oil from reservoirs. In accordance with the present process, a band of relatively volatile liquid miscible with oil, as for example, C and C hydrocarbons is caused to flow through the formation. This band of liquid is caused to flow by utilizing a natural gas drive. The gas drive tends to recover from the formation the solvent used to Wash out the oil. By operating as described, eiiicient recovery of the oil is secured through the use of a limited amount of propane or an equivalent solvent. Furthermore, efficient recovery of residual propane from the formation is readily secured.

A specific concept of the present invention is to employ the operation in conjunction with a plurality of spaced bore holes in a particular reservoir. A solvent such as liquefied propane is introduced by means of one bore hole in a sufficient quantity followed by the introduction of natural gas through the same bore hole. The band or bank of propane is caused to How through the formation past a second spaced bore hole in the direction of a third spaced bore hole. That portion of the propane bank which has flowed from the first to the third bore hole contains appreciable quantities of recovered oil and can be withdrawn to the surface. The oil is separated from the propane which is preferably returned to the formation by means of the second bore hole, thus interposing the recovered and concentrated propane at a point near the rear of the propane bank and ahead of the gas injection point. The rearrnost portion of the propane bank being relatively free of oil constituents has a very high solvency power and readily strips the oil formation of remaining oil constituents. Thus, the bank of propane as it flows through the formation by the operation described has a relatively high quantity of oil in the front end of the pool and is relatively free of oil at the rear end of the moving pool, thus serving to more efficiently remove oil from the formation.

The recovery method of the present invention involves the utilization of a bank of liquid propane or other light hydrocarbons or other oil-miscible material such as CO by passing these liquid substances through producing formations. The solvent can either be introduced as a gas or liquid but the conditions should be such as will result in the formation of a liquid solvent in the reservoir in the form of a bank or band. The bank is driven forward by introduction of natural gas, flue gas, inert gas, air, or combinations of these back of the bank of solvents. The producing formation is subject to a washing action by the bank of propane or other material and, as a consequence, there is little oil left in the formation that has been washed. Some oil may be left due to irregularity in flow due to the fact that producing formations are not homogeneous. The gas flowing back of the bank would have residual liquid, propane, or other material vaporized into it because of the low partial pressure of these materials in the gas. Thus, the liquid propane or other materials being recovered from the formation through this evaporation procedure pass along through the formation with the gas. In accordance with the present invention, the oil is in part recovered from the formation by being increased in volume and reduced in viscosity by dilution with the solvent; but a major contribution to completeness of recovery results from the washing of the sand with the solvent. 7

As the propane travels forward, it drives ahead of it liquid oil which can be recovered as such, with little or no propane in it up to a certain point. Back of a liquid oil layer is a layer of a mixture of propane and oil which is preferably also produced, that is, drawn from a well; the propane may then be recovered and cycled back to the formation at a proper point. The gas used to drive the bank of solvent moves faster than the solvent itself, and as a result, it tends to carry propane as vapor from the propane layer into the oil layer where the propane is absorbed. This absorption action tends to prevent excessive widening of the zone of oil-propane mixture.

With respect to specific operating conditions, as for example pressure, they of necessity depend upon various field conditions such as depth of oil-producing formation and temperature of the reservoir. Among other factors controlling operating conditions is the solvent employed. In general, the practicable, useful control measure is the pressure of the operation required in order to promote the maintenance of a relatively concentrated band of the solvent material. In general, the pressure should be such as to maintain relatively pure solvent in the liquid condition, which pressure is at least equivalent to or more generally in excess of the vapor pressure of the solvent at the reservoir temperature.

Generally speaking, reservoir temperatures are in the range of from 100 F. to 250 F., although lower reservoir temperatures and higher have at times been incurred. Usual reservoir temperatures are in the range from about 150 F. to 200 F. Under typical reservoir conditions, the vapor pressure of propane will be from about 200 to 600 pounds per square inch, and if propane is employed, pressures of this order or higher may conveniently be employed.

With respect to the rate of recycling of the gas, this quantity will in general be set at the economic optimum which reflects the pressure level, permeability of the formation, separation of the injection and producing wells, etc.

As indicated above, the present invention broadly relates to a combination of solvent extraction and combustion steps for obtaining oil from a subterranean reservoir. In accordance with one embodiment of the invention, a bank of an oil solvent such as liquefied propane is injected into a reservoir to be followed by natural gas substantially in the form of a second bank. In both of these instances it will be understood that the term bank implies an effective volume of liquefied propane or natural gas which is less than the pore volume of the reservoir. In the case of the liquefied propane or other solvent, the volume of propane should constitute between 0.1 and 0.5 and preferably 0.25 and 0.4 hydrocarbon volume of the reservoir. In the case of the natural gas, the minimum amount of this component is fixed by the fact that the combustion front following the bank of natural gas should never contact or extend to the bank of propane. In other words, the bank of natural gas should be less in volume than the pore volume of the reservoir but always sufiicient in volume to prevent actual contact between the following combustion front and the bank of propane.

Once the bank of natural gas has been injected into the reservoir behind the bank of liquefied propane, a combustion front is initiated by injecting and igniting a combustible mixture of gases immediately behind the bank of natural gas. It will be understood that a great number of combustible gas mixtures may be employed, but a mixture of natural gas and air is preferred for this purpose. The injection of the combustible gas mixture and its subsequent combustion is continued until substantially all of the oil and propane within the reservoir is recovered. With this procedure virtually complete recovery of these constituents is contemplated.

The entire mechanism of the procedure just described is not entirely understood at this time, but it appears that the propane or other solvent dissolves and displaces the oil from within a reservoir. The following bank of natural gas acts to vaporize and remove residual amounts of propane and/or oil that are left within the reservoir behind the bank of propane and/or oil which is left behind in the reservoir following the preceding steps of the process. The combustion front, however, never contacts the bank of propane itself with the result that none of the propane is consumed by the process. Thus, attractive recoveries of both oil and solvent are made possible.

Another method of employing the integrated process of the present invention is to inject natural gas at the input well until substantially all the propane is recovered from the formation and the gases from the output Well contain a low concentration of propane. At this point the reservoir between the input and output well contains residual oil, a small quantity of propane and natural gas. An oxygen-containing gas such as air or oxygen is introduced into the formation at the input well. Injection of the oxygen-containing gas is continued until the gases from the output well contain oxygen in suificient concentration to support combustion. A flame or combustion front is then initiated at the input well which will propagate itself to the output well, since the reservoir contains a blend of natural gas and combustion supporting gas. In some instances the injection of the oxygencontaining gas at the input well will tend to deplete the formation of natural gas about the input well and thus combustion will not be supported. Under these conditions the gas removed from the output well which contains sufficient oxygen to support combustion is recycled to the formation in the area about the input well by means of the input well. Combustion is then initiated. By this technique in many instances it is possible to initiate a detonation or explosive wave from the input well to the output well which will serve to fracture the formation and produce additional fissures through which additional oil may flow and be recovered. A very desirable method of operation is to block off or seal the input well prior to igniting the combustion front whereby a blowback in the input well is avoided and a greater pressure drive in the direction of the output well is secured.

Having described the invention it is claimed:

1. Improved process for the recovery of hydrocarbon from an oil bearing substrata which comprises introducing a liquid pool of a normally gaseous hydrocarbon into said substrata by means of an input well, impelling said liquid pool through said formation to an output well by means of a natural gas drive introduced by means of said input well, continuing the introduction of said natural gas into said input well until the gases removed from said output well have a relatively low concentration of said normally gaseous hydrocarbon, then introducing an oxygen-containing gas into said substrata until said gases from said output well have a concentration of oxygen sufficient to support combustion, thereafter initiating a combustion front at said input well, whereby said combustion front will progress to said output well, said gases removed from said output well which have a relatively low concentration of normally gaseous hydrocarbons and which have a concentration of oxygen sufficient to support combustion being recycled to said input well prior to initiating said combustion front.

2. Process as defined by claim 1 wherein said normally gaseous hydrocarbon comprises propane.

3. Process as defined by claim 2 wherein said input well is blocked off prior to initiating said combustion front, whereby a pressure drive is exerted in the direction 10 of said output well.

References Cited in the file of this patent UNITED STATES PATENTS 1,457,479 Wolcott June 5, 1923 15 2,642,943 Smith June 23, 1953 FOREIGN PATENTS 696,524 Great Britain Sept. 2, 1953 726,712 Great Britain Mar. 23, 1955

Claims (1)

1. IMPROVED PROCESS FOR THE RECOVERY OF HYDROCARBON FROM AN OIL BEARING SUBSTRATA WHICH COMPRISES INTRODUCING A LIQUID POOL OF A NORMALLY GASEOUS HYDROCARBON INTO SAID SUBSTRATA BY MEANS OF AN INPUT WELL, IMPELLING SAID LIQUID POOL THROUGH SAID FORMATION TO AN OUTPUT WELL BY MEANS OF A NATURAL GAS DRIVE INTRODUCED BY MEANS OF SAID INPUT WELL, CONTINUING THE INTRODUCTION OF SAILD NATURAL GAS INTO SAID INPUT WELL UNTIL THE GASES REMOVED FROM SAILD OUTPUT WELL HAVE A RELATIVELY LOW CONCENTRATION OF SAID NORMALLY GASEOUS HYDROCARBON, THEN INTRODUCING AN OXYGEN-CONTAINING GAS INTO SAID SUBSTRATA UNTIL SAID GASES FROM SAID OUTPUT WELL HAVE A CONCENTRATION OF OXYGEN SUFFICIENT TO SUPPORT COMBUSTION, THEREAFTER INITIATING A COMBUSTION FRONT AT SAID INPUT WELL, WHEREBY SAID COMBUSTION FRONT WILL PROGRESS TO SAID OUTPUT WELL, SAID GASES REMOVED FROM SAID OUTPUT WELL WHICH HAVE A RELATIVELY LOW CON-

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