US 3457996 A
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United States Patent O 3,457,996 THERMAL OIL RECOVERY PROCESS UTILIZING DECOMPOSITION F C0 Harry W. Parker, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 648,221, June 23, 1967. This application July 30, 1968, Ser. No. 748,611
Int. Cl. E21b 43/16 [1.8. Cl. 166-288 Claims ABSTRACT OF THE DISCLOSURE A heat front is moved through a section of a stratum surrounding a well to produce oil therefrom and to increase the permeability of a section of stratum adjacent the well by injecting CO into said stratum adjacent said well at a pressure sufficient to inject said CO into Said stratum, heating the wall of said Well within said stratum to at least about 700 F., preferably at least 850 F., and flowing the injected CO into the hot area to cause decomposition of CO to CO and C with development of a heat front and movement thereof away from said well. H may be injected with the CO. In one embodiment, the CO is injected either through one or more offset wells or through said well to build up a slug thereof in the adjacent stratum which can be caused to flow back to the hot well upon reduction of well pressure.
This application is a continuation-in-part of my copending application Ser. No. 648,221, filed June 23, 1967.
This invention relates to a process for producing oil from an oil stratum using a heat front developed from the heat of decomposition of carbon monoxide.
The use of a heat front produced by burning a portion of the oil in an oil stratum with injected air is a conventional technique in the production of oil from various types of oil strata. A direct drive of the heat front or combustion zone from an injection well to a production well is practiced frequently in strata containing oil which is not too viscous to build up a bank of heavy oil in advance of a heat front. In strata containing highly viscous oil, a direct drive of a heat front is impractical or impossible due to the blocking effect of the bank of oil built up in advance of the heat front. In such strata a counterflow heat front is generally utilized which comprises establishing a combustion zone around a production well and injecting air to the resulting combustion zone through one or more offset wells so as to cause the heat front to move countercurrently to the flow of injected air toward the injection source.
In some strata containing highly viscous oil, it has been found impossible to establish an inverse or counterflow combustion process because of the spontaneous ignition of the in-place oil around the injection well which prevents the arrival of the oxygen-containing gas at the combustion zone surrounding the intended production well.
This invention is directed to a process which overcomes the foregoing problem and permits the use of a counterdiow heat front in an oil-bearing stratum.
Accordingly, it is an object of the invention to provide a process for producing oil from an oil stratum by a counterflow heat front which avoids spontaneous ignition of in-p1ace oil. Another object is to provide a process which heats and produces oil from an oil stratum utilizing the exothermic heat of decomposition of carbon monoxide. A further object is to provide a process for increasing the permeability of a carbonaceous stratum adjacent a well therein. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.
3,457,996 Patented July 29, 1969 In accordance with a broad aspect of the invention, a heat front is moved through a section of stratum surrounding a well penetrating an oil stratum by injecting CO into the stratum adjacent the well at a pressure which is at least sufiicient to inject said CO into said stratum, heating the wall of the well within the stratum to at least about 700 F., and flowing the injected CO into the hot area of the stratum to cause decomposition of CO to CO and C with the development of a heat front and movement thereof away from the well. In one embodiment of the invention, the carbon monoxide is injected through one or more offset wells, such as a ring of surrounding wells, at the minimum required pressure sufficient to inject said CO until CO is produced in the well around which the heat front is to be developed. During this injection period, or subsequent thereto, the wall of the well within the stratum is heated to a temperature of at least about 700 F., and, preferably, at least 850 R, such as by utilizing an electric or gas-fired downhole heater or by burning a fuel pack in the well to be heated. Therefater, the flow of CO to the heated area around the well results in the decomposition of the CO to CO and C with the development and movement of a heat front at a temperature of about 700 F. radially outwardly from the well. This advance of the heat front into the stratum away from the well toward the one or more offset wells renders the viscous oil in the stratum more fluid so that the movement of gas through the stratum drives the oil into the well from which it is produced in conventional manner.
In accordance with another embodiment of the invention, carbon monoxide is injected into an oil stratum through a Well penetrating the stratum with any surrounding wells shut in, until a substantial slug of CO has been deposited in the surrounding stratum and a pressure substantially in excess of 700 p.s.i.g., such as at least 850 p.s.i.g., has been established. The stratum adjacent the well is then heated to a temperature of at least about 700 F. while maintaining said pressure and thereafter the pressure within the well is reduced gradually so as to cause CO to flow into the heated area and initiate decomposition of the CO to establish a heat front moving away from the well. This embodiment of the invention is useful in opening up the stratum around the well to better flow of oil by increasing the permeability of the annular section of stratum through which the heat front is moved and by heating the in-place oil.
The minimum pressure which can be employed in the practice of the invention is a pressure sufficient to inject the CO into the stratum. However, since the decomposition of CO is favored by increased pressure, it is sometimes preferred to employ CO injection pressures which are greater than said minimum pressure. Thus, it is frequently preferred that said injection pressure be at least p.s.ig, more preferably in excess of about 700 p.s.i.g.
It is feasible to use substantially pure carbon monoxide or a commercial mixture including hydrogen and carbon dioxide. The CO concentration in the injected gas should be at least 50 volume percent. It is also feasible to mix air with the carbon monoxide gas to provide a concentration of 0 up to about 5 volume percent but below that at which spontaneous ignition of the in-place oil is effected. The amount of oxygen which can be tolerated in any given stratum depends upon the character of the in-place oil, the temperature of the stratum, and the pressure thereof. Any heat developed by partial combustion due to the presence of oxygen results in an increase in the heating effect of the heat front developed by the decomposition of carbon monoxide and has the effect of reducing the cost of carbon monoxide for the operation. The most economical source of oxygen, of course, is air. However, oxygen enriched air or pure 0 may be utilized.
Another embodiment of the invention comprises injecting H in admixture with the CO to effect the reaction 2CO+2H CO +CH This reaction provides more energy on a per pound basis than CO, alone, and does not deposit carbon in the stratum; however, it requires compression of a larger volume of gas. The ratio of CO to H injected may vary from 1 to 1 to 100 to 1.
The hot fiuid drive of the invention produces more Oil than an in situ combustion drive at a comparable temperature since no oil is burned to produce the heat required.
To illustrate the invention, a reservoir or oil stratum at a depth of about 3000 feet having a thickness of about 100 feet, a saturation of about 1500 barrels per acre foot of API oil, and a pressure of about 1500 p.s.i.g., is penetrated by a five-spot well pattern. The four ring wells are on a spacing from a center producing well of about 200 feet. A carbon monoxide-rich gas in injected through each of the ring wells to produce CO through the central well. While the injection proceeds, the wall of the central well within the oil stratum is heated by means of a downhole heater to a temperature of about 1000 P. so that the injected CO decomposes to CO and C upon entering the hot wall of the well. As a result, a counterflow heat front moves away from said central production well at a temperature of about 700 F. to heat and vaporize the oil in the stratum which is driven into the production well and recoverd therefrom in conventional manner through a tubing string leading to the well head.
As a further illustration of the invention, a heavy oil reservoir having a thickness of about 70 feet, about 150 to 200 feet of overburden, a reservoir pressure of about 100 p.s.i.g., and containing about 1200 barrels of oil per acre foot is penerated by three substantially parallel rows of wells spaced about 100 feet apart. Each row of wells contains 12 wells spaced about 50 to 100 feet apart. CO, or a mixture of CO with H and CO is injected into the outer rows of wells at a pressure of about 140 p.s.i.g. and is produced from the central row of wells. By means of downhole heaters said central wells are heated to a temperature of about 1000 P. so as to initiate a counterflow combustion front which advances at a temperature of about 750 F. toward said injection wells and away from said central wells. Heated oil and vaporized oil in said reservoir are driven into said central wells and recovered therefrom in conventional manner.
While the invention has been described in terms of oil strata or reservoirs, the invention is also applicable to recovering oil from naturally permeable tar sands, or tar sands which have been previously rendered permeable.
Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.
1. A process for producing oil from an oil stratum penetrated by a well which comprises the steps of:
(a) injecting a CO-rich gas into said stratum around said well at a pressure sufiicient to inject said gas into said stratum;
(b) heating said well within said stratum to a temperature of at least about 700 F.;
(c) causing said CO-rich gas to flow into the hot well to heat said gas to its decomposition temperature thereby forming C and CO with release of heat;
(d) continuing flow of CO-rich gas toward said well so as to move a heat front into said stratum, thereby heating and driving oil from said stratum into said well; and
(e) recovering the produced oil from said well.
2. The process of claim 1 wherein said pressure is in excess of 700 p.s.i.g.
3. The process of claim 1 wherein said CO-rich gas is injected into said stratum in step (a) through at least one offset well.
4. The process of claim 1 wherein said CO-rich gas is injected through said well to build up substantial pressure of said gas in the surrounding stratum in step (a) and flow into and toward said well is effected by reducing pressure Within said Well.
5. The process of claim 4 wherein said pressure is in excess of 700 p.s.i.g.
6. The process of claim 1 wherein said pressure is at least p.s.i.g.
7. The process of claim 6 wherein said temperature is at least 850 F.
8. The process of claim 1 wherein said injection of said gas in step (a) is effected through a ring of wells surrounding said well.
9. The process of claim 1 wherein O is included in the injected gas in step (a) up to a maximum of about 5 mol percent but below that sufficient to cause spontaneous ignition of in-place oil.
10. The process of claim 1 wherein H is injected in admixture with said gas in step (a) to provide a substantial concentration of H therein.
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