CA1173352A - Producing well stimulation method-combination of thermal and solvent - Google Patents
Producing well stimulation method-combination of thermal and solventInfo
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- CA1173352A CA1173352A CA000394832A CA394832A CA1173352A CA 1173352 A CA1173352 A CA 1173352A CA 000394832 A CA000394832 A CA 000394832A CA 394832 A CA394832 A CA 394832A CA 1173352 A CA1173352 A CA 1173352A
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Abstract
PRODUCING WELL STIMULATION METHOD -COMBINATION OF THERMAL AND SOLVENT
ABSTRACT OF THE DISCLOSURE
A method for the cyclic thermal stimulation of heavy oil adjacent producing wells to increase recovery of the oil produced therefrom by using an in-situ combustion process wherein oxygen or a fluid containing a minimum of about 75% by volume pure oxygen is injected into the well as the oxidizing medium, igniting the oil in the reservoir around the producing well so as to produce a combustion zone and to generate combustion gases consisting essen-tially of carbon dioxide and water in the form of steam, continuing injection of the oxygen until the combustion zone has propagated radially a distance of about 5 to 50 feet from the producing well, and thereafter recovering oil from the well. After terminating combustion, the well may be shut in for a period of time to allow the carbon dioxide and heat generated to more effectively permeate the reservoir adjacent the well prior to being returned to production status. The carbon dioxide dissolves in the oil reducing its viscosity along with the viscosity decrease resulting from the heat generated in the reservoir by combustion so that when the well is opened for production there is an improved flow of oil.
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ABSTRACT OF THE DISCLOSURE
A method for the cyclic thermal stimulation of heavy oil adjacent producing wells to increase recovery of the oil produced therefrom by using an in-situ combustion process wherein oxygen or a fluid containing a minimum of about 75% by volume pure oxygen is injected into the well as the oxidizing medium, igniting the oil in the reservoir around the producing well so as to produce a combustion zone and to generate combustion gases consisting essen-tially of carbon dioxide and water in the form of steam, continuing injection of the oxygen until the combustion zone has propagated radially a distance of about 5 to 50 feet from the producing well, and thereafter recovering oil from the well. After terminating combustion, the well may be shut in for a period of time to allow the carbon dioxide and heat generated to more effectively permeate the reservoir adjacent the well prior to being returned to production status. The carbon dioxide dissolves in the oil reducing its viscosity along with the viscosity decrease resulting from the heat generated in the reservoir by combustion so that when the well is opened for production there is an improved flow of oil.
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Description
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PRODUCING WELL STIMULATION METHOD -_ COMBINATION OF THERMAL AND SOLVENT
BACKGROUND OF THE INVENTION
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1. Field of the Invention This invention relates to an in-situ combustion process for the cyclic thermal stimulation of heavy oil around a producing well wherein oxygen or a fluid con-taining a minimum of about 75~ by volume pure oxygen is used as the oxidant so as to react with the oil to release heat of combustion and to produce high concentrations of carbon dioxide. The increased temperature, pressure, and the dissolution of the C02 in the reservoir oil reduces its viscosity and thereby increases oil production from the well when it is returned to production.
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PRODUCING WELL STIMULATION METHOD -_ COMBINATION OF THERMAL AND SOLVENT
BACKGROUND OF THE INVENTION
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1. Field of the Invention This invention relates to an in-situ combustion process for the cyclic thermal stimulation of heavy oil around a producing well wherein oxygen or a fluid con-taining a minimum of about 75~ by volume pure oxygen is used as the oxidant so as to react with the oil to release heat of combustion and to produce high concentrations of carbon dioxide. The increased temperature, pressure, and the dissolution of the C02 in the reservoir oil reduces its viscosity and thereby increases oil production from the well when it is returned to production.
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2 Desc_ ption of the Prior Art Repetitive stimulation of oil producing wells is a production practice of long standing. The phrase "cyclic stimulation" is often used to reflect anticipated production rate increases, the duration of which is rela-tively short as compared to the total life of the well.
The cause of the production increase arises from either (l) an increase in pressure driving reservoir fluids toward the producing well, or (2) a decrease in resistance ; to flow of the fluids such as reduction in viscosity or removal of impediments to flow in the reservoir rock surrounding the well. The viscosity reduction may be achieved through use of a low viscosity fluid solvent and by increasing the temperature of the reservoir fluids and rock in the proximity of the reservoir.
In wells producing heavy (viscous) oil, cyclic thermal stimulation has become widespread in use. Two somewhat different thermal stimulation techniques have .
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been developed: (l) cyclic s~eam injection, and (~) cyclic in-situ combustion. A typical cyclic steam stimulation may include~ injection of steam into a producing interval for a period that may extend up to several weeks, depending on thickness of the reservoir, well spacing, rate of steam injection, etc.; (2~ allowing a ~'soak"
period (which in some circumstances is not necessary); and
The cause of the production increase arises from either (l) an increase in pressure driving reservoir fluids toward the producing well, or (2) a decrease in resistance ; to flow of the fluids such as reduction in viscosity or removal of impediments to flow in the reservoir rock surrounding the well. The viscosity reduction may be achieved through use of a low viscosity fluid solvent and by increasing the temperature of the reservoir fluids and rock in the proximity of the reservoir.
In wells producing heavy (viscous) oil, cyclic thermal stimulation has become widespread in use. Two somewhat different thermal stimulation techniques have .
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been developed: (l) cyclic s~eam injection, and (~) cyclic in-situ combustion. A typical cyclic steam stimulation may include~ injection of steam into a producing interval for a period that may extend up to several weeks, depending on thickness of the reservoir, well spacing, rate of steam injection, etc.; (2~ allowing a ~'soak"
period (which in some circumstances is not necessary); and
(3) returning the well to production. The heat introduced into the reservoir rock continues to be effective for some time in warming and reducing the viscosity of the oil, thus increasing the production rate. The effects of the stimulation will decline over a period of a few months whereupon the treatment may be repeated.
Instead of using fuel-fed steam generators, cyclic in-situ combustion may be used to heat the reser-voir. ~ith this technique, air is injected into the reservoir through the producing well, which, after igni-tion, burns a small portion of the crude oil "in-situ", generating heat which is conveyed outward from the well into the surrounding reservoir by the flue gas formed and by vaporized crude oil and water. Water may be injected along with, intermittently, or following air injection to form steam and hot water which will convey the released heat of combustion farther into the reservoir. Although 2S this method of stimulation may utilize fuel of less value than the steam process, wherein the steam is generated prior to injection into the reservoir, use of the latter process is generally favored. One major disadvantage of the combustion method is the requirement of compressing to injection pressure approximately four mols of nitrogen for every single mol of oxygen in air to support the combus-tion reaction. This increases cost and also dilutes the carbon dioxide concentration in the flue gas1 greatly diminishing its efficacy as a solvent gas for reducing viscosity of the heavy oil.
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The method of this invention is a major improve-ment in the combustion stimulation technique in that it uses oxygen or a fluid containing a minimum of about 75 by volume pure oxygen as the oxidant injected into the reservoir through the production well. The cycle of the process would be similar to that used with air: i.e., (l) inject the oxidant, which after ignition causes movement of a burn front through the reservoir rock surrounding the well; (2) allow a "soak~ period (which is optional); and (3) return the well to production. The latter step usually requires installation of a downhole pump to remove produced liquids from the well.
The advantages resulting from the use of oxygen or a fluid containing a minimum of about 75% by volume pure oxygen includeo l. Elimination of large amounts of "inert" gas, i.e.l nitrogen, which is costly to compress for injec-tion. Also the presence of the inert nitrogen gas as a separate phase in the pores of the reservoir rock impedes the flow of oil toward the well.
2. The concentration (and partial pressure) of the C02 formed in the combustion reaction is increased, and correspondingly its solubility in the heavy oil is increased. As a result, the viscosity of the heavy ~il containing larger amounts of solvent gas is substantially reduced, and oil production rate is increased accordingly.
3. The increased C02 content in the oil phase increases the extent to which the "solution gas drive" can contribute to the displacement of oil toward the produc-tion well.
Instead of using fuel-fed steam generators, cyclic in-situ combustion may be used to heat the reser-voir. ~ith this technique, air is injected into the reservoir through the producing well, which, after igni-tion, burns a small portion of the crude oil "in-situ", generating heat which is conveyed outward from the well into the surrounding reservoir by the flue gas formed and by vaporized crude oil and water. Water may be injected along with, intermittently, or following air injection to form steam and hot water which will convey the released heat of combustion farther into the reservoir. Although 2S this method of stimulation may utilize fuel of less value than the steam process, wherein the steam is generated prior to injection into the reservoir, use of the latter process is generally favored. One major disadvantage of the combustion method is the requirement of compressing to injection pressure approximately four mols of nitrogen for every single mol of oxygen in air to support the combus-tion reaction. This increases cost and also dilutes the carbon dioxide concentration in the flue gas1 greatly diminishing its efficacy as a solvent gas for reducing viscosity of the heavy oil.
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The method of this invention is a major improve-ment in the combustion stimulation technique in that it uses oxygen or a fluid containing a minimum of about 75 by volume pure oxygen as the oxidant injected into the reservoir through the production well. The cycle of the process would be similar to that used with air: i.e., (l) inject the oxidant, which after ignition causes movement of a burn front through the reservoir rock surrounding the well; (2) allow a "soak~ period (which is optional); and (3) return the well to production. The latter step usually requires installation of a downhole pump to remove produced liquids from the well.
The advantages resulting from the use of oxygen or a fluid containing a minimum of about 75% by volume pure oxygen includeo l. Elimination of large amounts of "inert" gas, i.e.l nitrogen, which is costly to compress for injec-tion. Also the presence of the inert nitrogen gas as a separate phase in the pores of the reservoir rock impedes the flow of oil toward the well.
2. The concentration (and partial pressure) of the C02 formed in the combustion reaction is increased, and correspondingly its solubility in the heavy oil is increased. As a result, the viscosity of the heavy ~il containing larger amounts of solvent gas is substantially reduced, and oil production rate is increased accordingly.
3. The increased C02 content in the oil phase increases the extent to which the "solution gas drive" can contribute to the displacement of oil toward the produc-tion well.
4. Ignition of the combustion reaction in-situ is facilitated by the higher oxygen concentration of the injected gas. "Auto ignition" will occur with a greater number of crude oils, thus reducing the need to use down-hole burners, electric heaters, or steam preheating to start the combustion reaction. (This does not preclude the use of any of these methods where the crude oil properties do not favor auto ignition.)
5. Water injection alonq with or intermittent :5 to the injected oxidant may be used as in "wet combustion"
;using air and water. The advantages of increased heat transport farther into the reservoir by the steam formed in-situ from heat released by the combustion reaction also apply with oxygen or enriched air combustion. The in-creased solubility of C02 in the condensed water also enhances its expulsion from the reservoir to the producing well which also enhances the displacement of the heavy oil toward the producing well.
`In U. S. Patent No. 3,174,543 to Sharp there is described a method of recovering oil by producing carbon dioxide in the reservoir region surrounding an injection . well by in-situ combustion and then introducing water into the reservoir to drive the carbon dioxide through the reservoir to displace the reservoir oil toward a produc-tion well. The present process is an in-situ combustion stimulation process that takes place in the reservoir immediately surrounding the bottom of a producing well using oxygen or a fluid containing a minimum of about 75%
by volume pure oxygen as the oxidizing medium which results in the formation o~ a combustion gas comprising a high concentration of carbon dioxide. The carbon dioxide readily dissolves in the oil and reduces its viscosity.
The heat generated in the reservoir by combustion also reduces the viscosity of the oil phase thus improving its flow thrnugh the formation when production is resumed. By the process of this invention therefore, a more effective recovery of the heavy crude oil is obtained.
Thermal oil stimulation processes using the so-called "huff-n-puff" gas injection techniques are - 35 disclosed in U. S. Patent No. 3,332,482 to Trantham, 3,369,604 to Black et al. and 3,465,822 to Klein.
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~ ~'iJ3~2 U. S. Patent to Trantham, 3,332,482, discloses a process for the secondary recovery of viscous oil using an in~situ combustion process at the bottom of a producing well in which air is used as the oxidizing medium. In this process, air is injected into the production well and the oil surrounding the bottom of the well is ignited to establish a combustion zone. Combustion is continued until the reservoir is plugged by viscous oil which results in a substantial increase in pressure. Combustion is terminated and the well is opened for production so that the compressed gases within the reservoir remote from the production well and beyond the plugged area drives the oil into the hot burned-out area between the plugged area and the production well where it is heated, perhaps upgraded somewhat, and finally recovered through the pro-duction well. Inherent in this process is the production of a gas, which is normally referred to as flue gas, which gas is composed predominantly of nitrogen and lesser amounts of carbon dioxide, carbon monoxide and other gases derived from the crude oil. The carbon dioxide in the flue gas is diluted by the nitrogen and other gases and is much less soluble in the reservoir oil than a gas con-sisting of substantially pure carbon dioxide or a gas containing a higher concentration of carbon dioxide than the flue gas produced by the use of air as the oxidizing medium. The solubility in reservoir oil of carbon dioxide formed with air combustion, at a given pressure, may be five to ten times less than that formed from oxygen combustion.
U. S. Patent No. 3,369,604 discloses a method for stimulating producing wells using a combination of steam stimulation and in-situ combustion wherein air, or a mixture of air and oxygen is used as the oxidizing gas.
U. S. Patent No, 3,465,822 to Klein, discloses a thermal oil stimulation process in which in-situ combus-tion is initiated around a well by air injection followed 33~i~
:
by injection of water and injection of inert gas, sequen-tially, and thereafter opening up the well to flow of fluids, including oil.
Also, in a Society of Petroleum Engineer of AIME
article, SPE 9228, presented on September 23-26, 1979, in Las Vegas, Nevada, entitled "A Parametric Study of the ` C2 ~UF-n-PUF Process" there is disclosed the results of Y Mathematical Model studies of the use of carbon dioxide as a solvent gas in cyclic well stimulation. The carbon 10 dioxide is not prepared in the well by in-situ combustion as in the present process and offers no advantages asso-ciated with the heat generated by oxygen combustion of the reservoir oil.
None of the prior art discloses the improved 15 method of recovering oil around a well using in-situ combustion stimulation wherein the oxidizing medium is oxygen or a fluid containing a minimum of about 75% by volume pure oxygen so as to produce increased concen-trations (and partial pressures) of carbon dioxide in the 20 combustion gases. The carbon dioxide dissolves in the reservoir oil reducing its viscosity, thereby ~acilitating its flow to the production. The viscosity of the reser-voir oil is further reduced by the heat generated in the reservair by combustion.
This invention is directed toward a method for : the cyclic thermal stimulation of heavy oil producing wells by in-situ combustion around the producing well , using oxygen or a fluid containing a minimum of ~bout 75%
by volume pure oxygen as the oxidizing medium which results in improved recovery of the oil from the reser-voir. The use of such an oxidizing medium produces a combustion gas comprising high concentrations o~ carbon dioxide and water in the form of steam. The steam aids in .
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carrying heat farther into the reservoir; the carbon dioxide is an efFective solvent in that it dissolves in the heavy oil that occurs at even greater distances in the reservoir beyond the combustion and steam heated zone thereby reducing its viscosity. During combustion, the heat generated is absorbed by the reservoir which extends radially from the production well which results in further reduction of the viscosity of the heated heavy oil as it flows subsequently toward the producing well. Combustion 10 may be continued until the combustion zone travels a radial distance in the range of about 5 to 50 feet and then production operations are resumedO In addition, when combustion has been carried out in the stated portion of the reservoir, the production well may be shut in for a 15 predetermined interval of time to enhance the solvent effect of the carbon dioxide and the thermal effect of combustion. The length of this soak period will depend upon the field characteristics of the producing well.
Water may also be mixed with the oxidant to enhance the 20 transport of heat farther into the reservoir thereby increasing the effectiveness of the thermal effects.
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DESCRIPTION OF THE PREFERRED EMBODIM~NT
In accordance with the present invention, oil is 25 recovered from a reservoir by cyclic thermal stimulation of one or more producing wells using an in-situ combustion process wherein oxygen is used as the oxidizing fluid instead of air. Although the preferred oxidizing fluid is pure oxygen, some sacrifice in the actual performance of 30 the process may be needed to make it more practical and economically feasible and therefore the oxidizing fluid may contain a minimum of about 75% by volume pure oxygen.
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The oxygen, upon reacting with the hydrocarbons in the reservoir, yields principally gaseous carbon dioxide and water as follows:
(CHn)m + (m + 4 ) 2~ m C0 ~ mn H 0 The carbon dioxide acts as a solvent since it will dis-solve in the reservoir oils and therefore appreciably lower the viscosity of the oil even in the absence o~ the thermal effects. The amount of dissolution will depend on the local reservoir pressure and temperature, but will be substantially greater than that experienced iF air is used because of the higher concentration of carbon dioxide.
The water formed will be initially in the form of steam which will aid in conveying the heat of combustion farther into the reservoir, enhancing the effect of the heat released~
By using oxygen or a fluid containing a minimum of about 75% by volume pure oxygen as the oxidizing medium, the large amount of nitrogen introduced into the well when air is used would be eliminated, along with the deleterious effect of gas phase nitrogen on the perme ability of the liquid oil phase. Water injection along with the oxidizing medium after combustion is initiated may be used to moderate the high temperature generated and ~; to obtain greater distances of penetration into the reser-voir for more effective heat distribution. lt would not necessarily add gaseous products to be subsequently produced.
For the purpose of simplicity in describing the invention, reference sometimes will be made herein to only one production well in my in-situ combination stimulation process. However, it will be recognized that in practical application of the invention, a plurality of such wells may be used and in most cases will be utilized.
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~ :~7;:~352 g In carrying out this invention, an oxidizing gas comprising oxygen or a fluid containing a minimum of about . 75~0 by volume pure oxygen is injected into a producing well and combustion is initiated in any suitable conven-tional mannex such as by locating an electrical or gas-fired heater within the well so as to initiate a combus-tion zone around the well and generate combustion gases consisting principally of carbon dioxide and water in the form of steam. Continued injection of oxygen moves the resulting combustion zone outward into the reservoir and the carbon dioxide in the combustion gases dissolves in the reservoir oil reducing its viscosity. The heat generated by combustion also lowers the viscosity of the reservoir oil surrounding the production well and the lS steam aids in conveying the heat of combustion farther into the reservoir.
; Combustion is continued through the reservoir around the production well until the combustion zone advances a radial distance of about 5 to 50 feet from the production well. Combustion is then terminated and the production well is returned to a producing operation.
An alternative method of carrying out the inven-tion is to shut in the production well after the combus-tion zone has moved a radial distance of about 5 to 50 feet from the production well to allow a soak period in - which heat generated in the reservoir will distribute itself and also allow the carbon dioxide to more effec-tively dissolve in the heavy oil at greater distances from the well thereby lowering its viscosity. For cptimum results, the length of the soak period will vary depending upon the characteristics of the producing well such as depth, rate of production, frequency of stimulation periods and size of stimulate treatment. After the soak period is terminated, the well is then returned to producing operation.
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Another embodiment of this process is to inject water continuously or periodically with the oxidizing fluid in the production well after combustion is initiated which serves to obtain greater distance of penetration of combustion heat into the reservoir for more effective heat distriDution. The water serves to recuperate the heat storsd in the burned-out reservoir, which would otherwise be wasted. This heat is then used to evaporate water.
The steam thus formed condenses downstream of the combus-tion zone, where it contributes to further heating of thereservoir. This technique is known as wet combustion. As another variation, water may be injected after oxygen injection has been terminated whereupon the water would be converted into steam upon passing through the higt- tempe-rature zone created by the combustion and subsequentlywould extend the distance into the reservoir that would be benefited by the heat of combustion.
The substantial concentration of carbon dioxide produced in the reservoir in-situ acts as a local pres-surizing agent, a solvent in the oil phase lowering theviscosity of the oil, and together with the thermal ~- effects of oombustion stimulates the reservoir and significantly increases the production rate of the oil.
The oxygen used may be obtained from any type o~
separation plant capable of providing the desired purity.
A highly expedient approach is to inject oxygen into the production well that may be supplied from cryogenic units from which the oxygen i.n liquid phase is pumped at any desired pressure level and thereafter passes through a heat exchanger to vaporize the high pressure liquid oxygen. This eliminates the need for compressor and ; attendant equipment. The cryogenic units may be portable and operated at the well site. Equally effective is use of oxygen available in the gaseous phase which may be compressed with gas compression equipment to the pressure level desired for injection into a well.
;using air and water. The advantages of increased heat transport farther into the reservoir by the steam formed in-situ from heat released by the combustion reaction also apply with oxygen or enriched air combustion. The in-creased solubility of C02 in the condensed water also enhances its expulsion from the reservoir to the producing well which also enhances the displacement of the heavy oil toward the producing well.
`In U. S. Patent No. 3,174,543 to Sharp there is described a method of recovering oil by producing carbon dioxide in the reservoir region surrounding an injection . well by in-situ combustion and then introducing water into the reservoir to drive the carbon dioxide through the reservoir to displace the reservoir oil toward a produc-tion well. The present process is an in-situ combustion stimulation process that takes place in the reservoir immediately surrounding the bottom of a producing well using oxygen or a fluid containing a minimum of about 75%
by volume pure oxygen as the oxidizing medium which results in the formation o~ a combustion gas comprising a high concentration of carbon dioxide. The carbon dioxide readily dissolves in the oil and reduces its viscosity.
The heat generated in the reservoir by combustion also reduces the viscosity of the oil phase thus improving its flow thrnugh the formation when production is resumed. By the process of this invention therefore, a more effective recovery of the heavy crude oil is obtained.
Thermal oil stimulation processes using the so-called "huff-n-puff" gas injection techniques are - 35 disclosed in U. S. Patent No. 3,332,482 to Trantham, 3,369,604 to Black et al. and 3,465,822 to Klein.
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. .~ , .
''.~ .
~ ~'iJ3~2 U. S. Patent to Trantham, 3,332,482, discloses a process for the secondary recovery of viscous oil using an in~situ combustion process at the bottom of a producing well in which air is used as the oxidizing medium. In this process, air is injected into the production well and the oil surrounding the bottom of the well is ignited to establish a combustion zone. Combustion is continued until the reservoir is plugged by viscous oil which results in a substantial increase in pressure. Combustion is terminated and the well is opened for production so that the compressed gases within the reservoir remote from the production well and beyond the plugged area drives the oil into the hot burned-out area between the plugged area and the production well where it is heated, perhaps upgraded somewhat, and finally recovered through the pro-duction well. Inherent in this process is the production of a gas, which is normally referred to as flue gas, which gas is composed predominantly of nitrogen and lesser amounts of carbon dioxide, carbon monoxide and other gases derived from the crude oil. The carbon dioxide in the flue gas is diluted by the nitrogen and other gases and is much less soluble in the reservoir oil than a gas con-sisting of substantially pure carbon dioxide or a gas containing a higher concentration of carbon dioxide than the flue gas produced by the use of air as the oxidizing medium. The solubility in reservoir oil of carbon dioxide formed with air combustion, at a given pressure, may be five to ten times less than that formed from oxygen combustion.
U. S. Patent No. 3,369,604 discloses a method for stimulating producing wells using a combination of steam stimulation and in-situ combustion wherein air, or a mixture of air and oxygen is used as the oxidizing gas.
U. S. Patent No, 3,465,822 to Klein, discloses a thermal oil stimulation process in which in-situ combus-tion is initiated around a well by air injection followed 33~i~
:
by injection of water and injection of inert gas, sequen-tially, and thereafter opening up the well to flow of fluids, including oil.
Also, in a Society of Petroleum Engineer of AIME
article, SPE 9228, presented on September 23-26, 1979, in Las Vegas, Nevada, entitled "A Parametric Study of the ` C2 ~UF-n-PUF Process" there is disclosed the results of Y Mathematical Model studies of the use of carbon dioxide as a solvent gas in cyclic well stimulation. The carbon 10 dioxide is not prepared in the well by in-situ combustion as in the present process and offers no advantages asso-ciated with the heat generated by oxygen combustion of the reservoir oil.
None of the prior art discloses the improved 15 method of recovering oil around a well using in-situ combustion stimulation wherein the oxidizing medium is oxygen or a fluid containing a minimum of about 75% by volume pure oxygen so as to produce increased concen-trations (and partial pressures) of carbon dioxide in the 20 combustion gases. The carbon dioxide dissolves in the reservoir oil reducing its viscosity, thereby ~acilitating its flow to the production. The viscosity of the reser-voir oil is further reduced by the heat generated in the reservair by combustion.
This invention is directed toward a method for : the cyclic thermal stimulation of heavy oil producing wells by in-situ combustion around the producing well , using oxygen or a fluid containing a minimum of ~bout 75%
by volume pure oxygen as the oxidizing medium which results in improved recovery of the oil from the reser-voir. The use of such an oxidizing medium produces a combustion gas comprising high concentrations o~ carbon dioxide and water in the form of steam. The steam aids in .
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carrying heat farther into the reservoir; the carbon dioxide is an efFective solvent in that it dissolves in the heavy oil that occurs at even greater distances in the reservoir beyond the combustion and steam heated zone thereby reducing its viscosity. During combustion, the heat generated is absorbed by the reservoir which extends radially from the production well which results in further reduction of the viscosity of the heated heavy oil as it flows subsequently toward the producing well. Combustion 10 may be continued until the combustion zone travels a radial distance in the range of about 5 to 50 feet and then production operations are resumedO In addition, when combustion has been carried out in the stated portion of the reservoir, the production well may be shut in for a 15 predetermined interval of time to enhance the solvent effect of the carbon dioxide and the thermal effect of combustion. The length of this soak period will depend upon the field characteristics of the producing well.
Water may also be mixed with the oxidant to enhance the 20 transport of heat farther into the reservoir thereby increasing the effectiveness of the thermal effects.
:
DESCRIPTION OF THE PREFERRED EMBODIM~NT
In accordance with the present invention, oil is 25 recovered from a reservoir by cyclic thermal stimulation of one or more producing wells using an in-situ combustion process wherein oxygen is used as the oxidizing fluid instead of air. Although the preferred oxidizing fluid is pure oxygen, some sacrifice in the actual performance of 30 the process may be needed to make it more practical and economically feasible and therefore the oxidizing fluid may contain a minimum of about 75% by volume pure oxygen.
J~
The oxygen, upon reacting with the hydrocarbons in the reservoir, yields principally gaseous carbon dioxide and water as follows:
(CHn)m + (m + 4 ) 2~ m C0 ~ mn H 0 The carbon dioxide acts as a solvent since it will dis-solve in the reservoir oils and therefore appreciably lower the viscosity of the oil even in the absence o~ the thermal effects. The amount of dissolution will depend on the local reservoir pressure and temperature, but will be substantially greater than that experienced iF air is used because of the higher concentration of carbon dioxide.
The water formed will be initially in the form of steam which will aid in conveying the heat of combustion farther into the reservoir, enhancing the effect of the heat released~
By using oxygen or a fluid containing a minimum of about 75% by volume pure oxygen as the oxidizing medium, the large amount of nitrogen introduced into the well when air is used would be eliminated, along with the deleterious effect of gas phase nitrogen on the perme ability of the liquid oil phase. Water injection along with the oxidizing medium after combustion is initiated may be used to moderate the high temperature generated and ~; to obtain greater distances of penetration into the reser-voir for more effective heat distribution. lt would not necessarily add gaseous products to be subsequently produced.
For the purpose of simplicity in describing the invention, reference sometimes will be made herein to only one production well in my in-situ combination stimulation process. However, it will be recognized that in practical application of the invention, a plurality of such wells may be used and in most cases will be utilized.
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~ :~7;:~352 g In carrying out this invention, an oxidizing gas comprising oxygen or a fluid containing a minimum of about . 75~0 by volume pure oxygen is injected into a producing well and combustion is initiated in any suitable conven-tional mannex such as by locating an electrical or gas-fired heater within the well so as to initiate a combus-tion zone around the well and generate combustion gases consisting principally of carbon dioxide and water in the form of steam. Continued injection of oxygen moves the resulting combustion zone outward into the reservoir and the carbon dioxide in the combustion gases dissolves in the reservoir oil reducing its viscosity. The heat generated by combustion also lowers the viscosity of the reservoir oil surrounding the production well and the lS steam aids in conveying the heat of combustion farther into the reservoir.
; Combustion is continued through the reservoir around the production well until the combustion zone advances a radial distance of about 5 to 50 feet from the production well. Combustion is then terminated and the production well is returned to a producing operation.
An alternative method of carrying out the inven-tion is to shut in the production well after the combus-tion zone has moved a radial distance of about 5 to 50 feet from the production well to allow a soak period in - which heat generated in the reservoir will distribute itself and also allow the carbon dioxide to more effec-tively dissolve in the heavy oil at greater distances from the well thereby lowering its viscosity. For cptimum results, the length of the soak period will vary depending upon the characteristics of the producing well such as depth, rate of production, frequency of stimulation periods and size of stimulate treatment. After the soak period is terminated, the well is then returned to producing operation.
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Another embodiment of this process is to inject water continuously or periodically with the oxidizing fluid in the production well after combustion is initiated which serves to obtain greater distance of penetration of combustion heat into the reservoir for more effective heat distriDution. The water serves to recuperate the heat storsd in the burned-out reservoir, which would otherwise be wasted. This heat is then used to evaporate water.
The steam thus formed condenses downstream of the combus-tion zone, where it contributes to further heating of thereservoir. This technique is known as wet combustion. As another variation, water may be injected after oxygen injection has been terminated whereupon the water would be converted into steam upon passing through the higt- tempe-rature zone created by the combustion and subsequentlywould extend the distance into the reservoir that would be benefited by the heat of combustion.
The substantial concentration of carbon dioxide produced in the reservoir in-situ acts as a local pres-surizing agent, a solvent in the oil phase lowering theviscosity of the oil, and together with the thermal ~- effects of oombustion stimulates the reservoir and significantly increases the production rate of the oil.
The oxygen used may be obtained from any type o~
separation plant capable of providing the desired purity.
A highly expedient approach is to inject oxygen into the production well that may be supplied from cryogenic units from which the oxygen i.n liquid phase is pumped at any desired pressure level and thereafter passes through a heat exchanger to vaporize the high pressure liquid oxygen. This eliminates the need for compressor and ; attendant equipment. The cryogenic units may be portable and operated at the well site. Equally effective is use of oxygen available in the gaseous phase which may be compressed with gas compression equipment to the pressure level desired for injection into a well.
Claims (12)
1. A method for stimulating the recovery of oil from a subterranean reservoir having a relatively heavy crude oil, into which has been drilled at least one production well which comprises the steps of:
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) recovering oil from said production well.
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) recovering oil from said production well.
2. The method of Claim 1 wherein said oxidizing fluid is oxygen.
3. The method of Claim 1 or 2 wherein water is injected with said oxidizing fluid after combustion is initiated.
4. The method of Claim 1 or 2 wherein water is periodically injected with said oxidizing fluid after combustion is initiated.
5. A method for stimulating the recovery of oil from a subterranean reservoir having a relatively heavy crude oil, into which has been drilled at least one production well which comprises the steps of:
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) injecting water through said production well into the hot burned out zone to substantially reduce the temperature in said zone, form a substantial amount of steam, and drive a resulting hot zone more remote from said well; and (f) recovering oil from said production well.
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) injecting water through said production well into the hot burned out zone to substantially reduce the temperature in said zone, form a substantial amount of steam, and drive a resulting hot zone more remote from said well; and (f) recovering oil from said production well.
6. The method of Claim 5 wherein said oxidizing fluid is oxygen.
7. A method for stimulating the recovery of oil from a subterranean reservoir having a relatively heavy crude oil, into which has been drilled at least one production well which comprises the steps of:
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) shutting in said production well for a predetermined time interval; and (f) opening said production well and recovering oil from said well.
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) shutting in said production well for a predetermined time interval; and (f) opening said production well and recovering oil from said well.
8. The method of Claim 7 wherein said oxidizing fluid is oxygen.
9. The method of Claim 7 or 8 wherein water is injected with said oxidizing fluid after combustion is initiated.
10. The method of Claim 7 or 8 wherein water is periodically injected with said oxidizing fluid after combustion is initiated.
11. A method for stimulating the recovery of oil from a subterranean reservoir having a relatively heavy crude oil, into which has been drilled at least one production well which comprises the steps of:
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) injecting water through said production well into the hot burned out zone to substantially reduce the temperature in said zone, form a substantial amount of steam, and drive a resulting hot zone more remote from said well; and (f) shutting in said production well for a predetermined time interval; and (g) opening said production well and recovering oil from said well.
(a) injecting an oxidizing fluid comprising at least 75% by volume pure oxygen through said production well into said reservoir;
(b) heating said reservoir surrounding said production well to a temperature sufficient to initiate combustion of the oil contained in the reservoir so as to form a combustion zone around said production well;
(c) continuing to inject said oxidizing fluid to propagate said combustion zone into said reservoir a radial distance of about 5 to 50 feet from said production well;
(d) terminating the flow of oxidizing fluid into said reservoir; and (e) injecting water through said production well into the hot burned out zone to substantially reduce the temperature in said zone, form a substantial amount of steam, and drive a resulting hot zone more remote from said well; and (f) shutting in said production well for a predetermined time interval; and (g) opening said production well and recovering oil from said well.
12. The method of Claim 11 wherein said oxidizing fluid is oxygen.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US23210781A | 1981-02-06 | 1981-02-06 | |
| US232,107 | 1981-02-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1173352A true CA1173352A (en) | 1984-08-28 |
Family
ID=22871904
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394832A Expired CA1173352A (en) | 1981-02-06 | 1982-01-25 | Producing well stimulation method-combination of thermal and solvent |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1173352A (en) |
-
1982
- 1982-01-25 CA CA000394832A patent/CA1173352A/en not_active Expired
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