CA1238850A - Method for recovering hydrocarbons from fractured or highly stratified low viscosity subsurface reservoirs - Google Patents
Method for recovering hydrocarbons from fractured or highly stratified low viscosity subsurface reservoirsInfo
- Publication number
- CA1238850A CA1238850A CA000485472A CA485472A CA1238850A CA 1238850 A CA1238850 A CA 1238850A CA 000485472 A CA000485472 A CA 000485472A CA 485472 A CA485472 A CA 485472A CA 1238850 A CA1238850 A CA 1238850A
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Abstract
A METHOD FOR RECOVERING HYDROCARBONS
FROM FRACTURED OR HIGHLY STRATIFIED
LOW VISCOSITY SUBSURFACE RESERVOIRS
ABSTRACT OF THE DISCLOSURE:
Hydrocarbons are recovered from a highly stratified or fractured low viscosity subsurface reservoir by means of at least one injection well and at least one production well. Initially a high viscosity blocking fluid is injected through the injection well into the reservoir to fill the fractures or thief zones within the reservoir and create a fluid mobility barrier. Thereafter, a low viscosity flooding fluid is injected for driving hydrocarbons into the reservoir toward the production well.
FROM FRACTURED OR HIGHLY STRATIFIED
LOW VISCOSITY SUBSURFACE RESERVOIRS
ABSTRACT OF THE DISCLOSURE:
Hydrocarbons are recovered from a highly stratified or fractured low viscosity subsurface reservoir by means of at least one injection well and at least one production well. Initially a high viscosity blocking fluid is injected through the injection well into the reservoir to fill the fractures or thief zones within the reservoir and create a fluid mobility barrier. Thereafter, a low viscosity flooding fluid is injected for driving hydrocarbons into the reservoir toward the production well.
Description
123~SO
A METHOD FOR RECOVERING HYDROCARBONS
FROM FRACTURED OR HIGHLY STRATIFIED
LOW VISCOSITY SUBSURFACE RESERVOIRS
The present invention relates to a method for recovering low viscosity hydrocarbons from subterranean formations and, more particularly, to a method for alternately injecting water and gas into such formations to enhance recovery.
It is well known in the oil industry that so-called secondary recovery processes are employed to produce additional volumes of gas and oil from a subterranean reservoir after production by primary means has declined to an uneconomical level. The more commonly known secondary recovery procedures involve injecting either gas or water into a partially depleted reservoir through an injection system to drive oil or the like toward a production system from which the oil is produced along with portions of the driving fluid.
When the ratio of driving fluid to oil reaches an uneconomical level, the reservoir is normally abandoned, even though a substantial amount of residual oil still remains in the reservoir.
It has been recognized that greater recovery efficiencies can be obtained by flooding with both gas and water in a single recovery operation. It is theoriæed that by injecting gas before or after a waterflood, a gas saturation can be established within the reservoir wherein slugs of "trapped gas" will occupy space within the reservoir which otherwise would contain . ~
~23~50 trapped oil. This inherently reduces the amount of trapped or residual oil present in the reservoir and, accordingly, provides greater recovery.
While the foregoing described secondary recovery methods of alternating gas and water flooding have been applied to oil reservoirs, they have only met with limited success. The theory behind these alternating gas-water injection methods is that the gas would cause relative fluid mobility barriers in the permeable streaks such that the following water could flood out more of the oil zone. The problem with this theory had to do with the injected gas channeling so badly due to its low viscosity that the benefits ~o oil recovery were limited.
In accordance with the present invention, there is provided a method for recovering low viscosity hydrocarbons from fractured or stratified subsurface formations. A high viscosity blocking fluid is injected into the fractured or stratified formation through an injection well to fill the fractures or high permeability strata (thief zones) and create a fluid mobility barrier. A low viscosity flooding fiuid is also injected into the formation through the injection well. The fluid mobility barrier created by the blocking fluid prevents channeling of the lower viscosity flooding fluid into the formation fractures or thief zones, thereby enhancing the sweep efficiency of the lower viscosity flooding fluid and increasing recovery of low viscosity hydrocarbons from the formation through a production well. The injections of blocking fluid and flooding fluid may be carried out simultaneously or in successive injection cycles or phases.
123~ ;0 The viscosity difference between the blocking fluid and the flooding fluid may be increased to furthef enhance hydrocarbon production. The viscosity of the blocking fluid may be increased by the addition of a thickening additive, such as a polymer, oil, or an emulsion. The additive may be a foam for introducing a minimal gravity effect. The additive may be a thixotropic additive for increasing viscosity with time. The additive may be added during the latter portion of the injection phase of the blocking fluid.
In a further aspect, the viscosity difference between the blocking fluid and the flooding fluid is increased to an extent such that the ratio of fracture fluid mobility or thief zone fluid mobility to matrix fluid mobility is reduced to a predetermined minimum level.
In a still further aspect, the location of high fluid mobility fractures or thief zones in the formation may be identified. The high viscosity blocking fluid is injected directly into such fractures or thief zones to create the fluid mobility barrier, while the low viscosity flooding fluid is injected directly into the formation matrix.
In a yet further aspect, the blocking fluid is water and the flooding fluid is a gas. Firstly, the gas is injected into the formation through the injection well and hydrocarbons are recovered at the production well until the production ratio of gas to hydrocarbons reaches an unacceptable level due to channeling of the gas through the formation fractures or thief zones.
Secondly, water is injected into the formation and migrates into the fractures or thief zones to create the desired fluid mobility barrier. Thirdly, gas is again injected into the formation, the sweep efficiency of the 23~ S~
gas being increased due to the fluid mobility barrier created by the water filled fractures or thief zones, thereby resulting in increased low viscosity hydrocarbon production through the production well.
In the drawings appended to this specification:
Figure 1 of the present invention illustrates a subterranean reservoir penetrated by an injection and a production well;
Figures 2 and 3 are graphical representations of production rates from a hydrocarbon reservoir using the alternating water-gas injection method of the present invention and Figures 4 and 5 illustrate hydrocarbon sweep efficiency patterns along a highly stratified or fractured subsurface reservoir.
The alternating water and gas injection method of the present invention has been shown to greatly increase sweep efficiency in a highly stratified or fractured low viscosity hydrocarbon reservoir, such as a gas condensate or volatile oil reservoir. This increase occurs because the injection of high viscosity water tends to block the reservoir fractures or thief zones, thus forcing the trailing injection gas to invade the reservoir matrix with little channeling loss.
Referring to Fig. 1, an injection well 10 and a production well 12 extend from the earth's surface 14 through a highly stratified or fractured low viscosity hydrocarbon reservoir 16. Both the injection well 10 and the production well 12 are provided with perforations 18 to establish fluid communication with the reservoir 16. Firstly, a low viscosity flooding flood, such as a gas, may be injected into well 10 for flooding the reservoir 16. Production of hydrocarbons ~23~
through the production well under the drive of the flooding gas will continue until the production ratio of flooding gas to hydroearbons reeovered reaches an unacceptable level, primarily due to channeling of the low viscosity flooding gas through naturally occurring fractures or other permeable streaks in the reservoir 16. At this point, a high viscosity bloeking fluid, sueh as water, is injeeted through injeetion well 10 into the reservoir where it migrates to and fills the reservoir fractures or thief zones. Beeause of its 10 to 20-fold higher viscosity, the water acts as an effective block to channeling of a trailing gas drive and forces the trailing gas into a superior flood pattern through the reservoir matrix.
To further overcome high stratification or fracture induced problems, the viscosity difference between the blocking gas and the flooding water may be increased by the addition of a thiekening additive to the water. Any number of thiekeners may be utilized, sueh as polymers, for example. Other possibilities are foams, oils and emulsions. Foams eould be quite signifieant, espeeially in fraetured reservoirs since foams would only be minimally affected by gravity forces. Whenever gravity causes detrimental results, a foam ean be designed to eounteraet gravity. Such additives can be injected along with the initial water injection or can be injected during the latter portion of the water injection or blocking phase. Also, the additive may be a thixotropic additive that increases the viscosity of the injeeted water with time. In addition, two or more fluid injeetion eycles may be used during the bloeking phase wherein a trailing fluid interacts with one injected earlier to form a more viscous blocking of the fractures or permeable streaks.
~3~5~
soth the water and gas injection phases can be carried out continuously and simultaneously. secause of relative permeabilities, the water would tend to migrate to and fill the more permeable reservoir fractures or thief zones, thereby blocking gas flow and forcing such gas into the less permeable reservoir matrix or strata.
In a further aspect, the location of the fractures or thief zones could be identified with the water injection being directly into the fractures and the gas injection being directly into the reservoir matrix. Conventional well packers could be used to isolate the water and gas injection.
An additional feature of the invention is to increase the viscosity difference to an extent such that the ratio of fracture or thief zones fluid mobility kt to matrix fluid mobility km is reduced to a predetermined level. Fig. 2 illustrates the effect of reducing the ratio to 10 from the base case of lO0.
Curve I shows that the high fluid mobility or fracture zone is no longer a thief zone and that good sweep is achieved by nitrogen injection only. The maximum possible production from this reservoir is about 1.9 x 105 barrels, so that almost all the wet gas is produced by nitrogen injection in about 500 days. The alternating water-gas injection method of the invention reduces the production by about 3% due to some residual gas to waterflood. The thief zone has no effect.
However, for a ratio of 500, the effect of the thief zone on production is significant. Curve IV attains a 78% increase in cumulative wet gas production as compared with nitrogen injection only of curve V. In this case, it would be necessary to thicken the water with an additive in order to achieve recoveries as high as those experienced for the kt/km of lO0.
1;23~
Fig. 3 illustrates the results of a model study for base case fluid-rock properties in which wet gas production in reservoir barrels is plotted against time in days. The reservoir fluid and fluid-rock properties approximately represent those of the Anschutz Ranch field in ~tah. For the nitrogen injection only of Curve I, nitrogen breakthrough at the production well begins in 20 to 30 days, which represents about a one pore volume slug in the thief zone. wet gas production rate drops as nitrogen production rises because nitrogen is channeling through the thief zone. As with any miscible flood where crossflow occurs, hydrocarbon recovery goes on forever, but at continually declining rates. For water injection only, there is an initial high wet gas recovery due to the advantageous mobility ratio of water to wet gas. However, eventually this hydrocarbon recovery curve drops below the one for nitrogen only because of high residual gas saturation after waterflood. The alternating water-gas injection process of the invention produces a much greater recovery (Curve III), in this case, sweep efficiency is increased about 40% in 600 days over that of the gas only injection.
Such increase in sweep efficiency occurs because the high viscosity water tends to block the thief zone so as to prevent gas channeling, thus causing the trailing gas to invade the reservoir matrix. The principal factors governin~ the process are the ratio of the thief zone to matrix permeabilities, the viscosities of injected water and gas, and the residual saturation to water.
It can be seen from the foregoing description that by utilizing the alternating water-gas injection method of the invention in a highly stratified or fractured low viscosity hydrocarbon reservoir, the viscosity difference in the blocking water and the #5Q
trailing gas flood will be working against any gas channeling through the fractures or permeable streaks.
This is in contrast with the alternating gas-water injection methods previously used in which gas channeling was so severe that any blocking effects of the gas to the trailing water flood is limited. This is ~uite graphically depicted in Figs. 4 and 5, where the water blocking and gas flooding sweep pattern of the gas condensate reservoir of Fig. 5 is greatly increased over the gas blocking and water flood sweep pattern of oil reservoir of Fig. 4.
A METHOD FOR RECOVERING HYDROCARBONS
FROM FRACTURED OR HIGHLY STRATIFIED
LOW VISCOSITY SUBSURFACE RESERVOIRS
The present invention relates to a method for recovering low viscosity hydrocarbons from subterranean formations and, more particularly, to a method for alternately injecting water and gas into such formations to enhance recovery.
It is well known in the oil industry that so-called secondary recovery processes are employed to produce additional volumes of gas and oil from a subterranean reservoir after production by primary means has declined to an uneconomical level. The more commonly known secondary recovery procedures involve injecting either gas or water into a partially depleted reservoir through an injection system to drive oil or the like toward a production system from which the oil is produced along with portions of the driving fluid.
When the ratio of driving fluid to oil reaches an uneconomical level, the reservoir is normally abandoned, even though a substantial amount of residual oil still remains in the reservoir.
It has been recognized that greater recovery efficiencies can be obtained by flooding with both gas and water in a single recovery operation. It is theoriæed that by injecting gas before or after a waterflood, a gas saturation can be established within the reservoir wherein slugs of "trapped gas" will occupy space within the reservoir which otherwise would contain . ~
~23~50 trapped oil. This inherently reduces the amount of trapped or residual oil present in the reservoir and, accordingly, provides greater recovery.
While the foregoing described secondary recovery methods of alternating gas and water flooding have been applied to oil reservoirs, they have only met with limited success. The theory behind these alternating gas-water injection methods is that the gas would cause relative fluid mobility barriers in the permeable streaks such that the following water could flood out more of the oil zone. The problem with this theory had to do with the injected gas channeling so badly due to its low viscosity that the benefits ~o oil recovery were limited.
In accordance with the present invention, there is provided a method for recovering low viscosity hydrocarbons from fractured or stratified subsurface formations. A high viscosity blocking fluid is injected into the fractured or stratified formation through an injection well to fill the fractures or high permeability strata (thief zones) and create a fluid mobility barrier. A low viscosity flooding fiuid is also injected into the formation through the injection well. The fluid mobility barrier created by the blocking fluid prevents channeling of the lower viscosity flooding fluid into the formation fractures or thief zones, thereby enhancing the sweep efficiency of the lower viscosity flooding fluid and increasing recovery of low viscosity hydrocarbons from the formation through a production well. The injections of blocking fluid and flooding fluid may be carried out simultaneously or in successive injection cycles or phases.
123~ ;0 The viscosity difference between the blocking fluid and the flooding fluid may be increased to furthef enhance hydrocarbon production. The viscosity of the blocking fluid may be increased by the addition of a thickening additive, such as a polymer, oil, or an emulsion. The additive may be a foam for introducing a minimal gravity effect. The additive may be a thixotropic additive for increasing viscosity with time. The additive may be added during the latter portion of the injection phase of the blocking fluid.
In a further aspect, the viscosity difference between the blocking fluid and the flooding fluid is increased to an extent such that the ratio of fracture fluid mobility or thief zone fluid mobility to matrix fluid mobility is reduced to a predetermined minimum level.
In a still further aspect, the location of high fluid mobility fractures or thief zones in the formation may be identified. The high viscosity blocking fluid is injected directly into such fractures or thief zones to create the fluid mobility barrier, while the low viscosity flooding fluid is injected directly into the formation matrix.
In a yet further aspect, the blocking fluid is water and the flooding fluid is a gas. Firstly, the gas is injected into the formation through the injection well and hydrocarbons are recovered at the production well until the production ratio of gas to hydrocarbons reaches an unacceptable level due to channeling of the gas through the formation fractures or thief zones.
Secondly, water is injected into the formation and migrates into the fractures or thief zones to create the desired fluid mobility barrier. Thirdly, gas is again injected into the formation, the sweep efficiency of the 23~ S~
gas being increased due to the fluid mobility barrier created by the water filled fractures or thief zones, thereby resulting in increased low viscosity hydrocarbon production through the production well.
In the drawings appended to this specification:
Figure 1 of the present invention illustrates a subterranean reservoir penetrated by an injection and a production well;
Figures 2 and 3 are graphical representations of production rates from a hydrocarbon reservoir using the alternating water-gas injection method of the present invention and Figures 4 and 5 illustrate hydrocarbon sweep efficiency patterns along a highly stratified or fractured subsurface reservoir.
The alternating water and gas injection method of the present invention has been shown to greatly increase sweep efficiency in a highly stratified or fractured low viscosity hydrocarbon reservoir, such as a gas condensate or volatile oil reservoir. This increase occurs because the injection of high viscosity water tends to block the reservoir fractures or thief zones, thus forcing the trailing injection gas to invade the reservoir matrix with little channeling loss.
Referring to Fig. 1, an injection well 10 and a production well 12 extend from the earth's surface 14 through a highly stratified or fractured low viscosity hydrocarbon reservoir 16. Both the injection well 10 and the production well 12 are provided with perforations 18 to establish fluid communication with the reservoir 16. Firstly, a low viscosity flooding flood, such as a gas, may be injected into well 10 for flooding the reservoir 16. Production of hydrocarbons ~23~
through the production well under the drive of the flooding gas will continue until the production ratio of flooding gas to hydroearbons reeovered reaches an unacceptable level, primarily due to channeling of the low viscosity flooding gas through naturally occurring fractures or other permeable streaks in the reservoir 16. At this point, a high viscosity bloeking fluid, sueh as water, is injeeted through injeetion well 10 into the reservoir where it migrates to and fills the reservoir fractures or thief zones. Beeause of its 10 to 20-fold higher viscosity, the water acts as an effective block to channeling of a trailing gas drive and forces the trailing gas into a superior flood pattern through the reservoir matrix.
To further overcome high stratification or fracture induced problems, the viscosity difference between the blocking gas and the flooding water may be increased by the addition of a thiekening additive to the water. Any number of thiekeners may be utilized, sueh as polymers, for example. Other possibilities are foams, oils and emulsions. Foams eould be quite signifieant, espeeially in fraetured reservoirs since foams would only be minimally affected by gravity forces. Whenever gravity causes detrimental results, a foam ean be designed to eounteraet gravity. Such additives can be injected along with the initial water injection or can be injected during the latter portion of the water injection or blocking phase. Also, the additive may be a thixotropic additive that increases the viscosity of the injeeted water with time. In addition, two or more fluid injeetion eycles may be used during the bloeking phase wherein a trailing fluid interacts with one injected earlier to form a more viscous blocking of the fractures or permeable streaks.
~3~5~
soth the water and gas injection phases can be carried out continuously and simultaneously. secause of relative permeabilities, the water would tend to migrate to and fill the more permeable reservoir fractures or thief zones, thereby blocking gas flow and forcing such gas into the less permeable reservoir matrix or strata.
In a further aspect, the location of the fractures or thief zones could be identified with the water injection being directly into the fractures and the gas injection being directly into the reservoir matrix. Conventional well packers could be used to isolate the water and gas injection.
An additional feature of the invention is to increase the viscosity difference to an extent such that the ratio of fracture or thief zones fluid mobility kt to matrix fluid mobility km is reduced to a predetermined level. Fig. 2 illustrates the effect of reducing the ratio to 10 from the base case of lO0.
Curve I shows that the high fluid mobility or fracture zone is no longer a thief zone and that good sweep is achieved by nitrogen injection only. The maximum possible production from this reservoir is about 1.9 x 105 barrels, so that almost all the wet gas is produced by nitrogen injection in about 500 days. The alternating water-gas injection method of the invention reduces the production by about 3% due to some residual gas to waterflood. The thief zone has no effect.
However, for a ratio of 500, the effect of the thief zone on production is significant. Curve IV attains a 78% increase in cumulative wet gas production as compared with nitrogen injection only of curve V. In this case, it would be necessary to thicken the water with an additive in order to achieve recoveries as high as those experienced for the kt/km of lO0.
1;23~
Fig. 3 illustrates the results of a model study for base case fluid-rock properties in which wet gas production in reservoir barrels is plotted against time in days. The reservoir fluid and fluid-rock properties approximately represent those of the Anschutz Ranch field in ~tah. For the nitrogen injection only of Curve I, nitrogen breakthrough at the production well begins in 20 to 30 days, which represents about a one pore volume slug in the thief zone. wet gas production rate drops as nitrogen production rises because nitrogen is channeling through the thief zone. As with any miscible flood where crossflow occurs, hydrocarbon recovery goes on forever, but at continually declining rates. For water injection only, there is an initial high wet gas recovery due to the advantageous mobility ratio of water to wet gas. However, eventually this hydrocarbon recovery curve drops below the one for nitrogen only because of high residual gas saturation after waterflood. The alternating water-gas injection process of the invention produces a much greater recovery (Curve III), in this case, sweep efficiency is increased about 40% in 600 days over that of the gas only injection.
Such increase in sweep efficiency occurs because the high viscosity water tends to block the thief zone so as to prevent gas channeling, thus causing the trailing gas to invade the reservoir matrix. The principal factors governin~ the process are the ratio of the thief zone to matrix permeabilities, the viscosities of injected water and gas, and the residual saturation to water.
It can be seen from the foregoing description that by utilizing the alternating water-gas injection method of the invention in a highly stratified or fractured low viscosity hydrocarbon reservoir, the viscosity difference in the blocking water and the #5Q
trailing gas flood will be working against any gas channeling through the fractures or permeable streaks.
This is in contrast with the alternating gas-water injection methods previously used in which gas channeling was so severe that any blocking effects of the gas to the trailing water flood is limited. This is ~uite graphically depicted in Figs. 4 and 5, where the water blocking and gas flooding sweep pattern of the gas condensate reservoir of Fig. 5 is greatly increased over the gas blocking and water flood sweep pattern of oil reservoir of Fig. 4.
Claims (23)
1. A method for recovering low viscosity hydrocarbons from a naturally fractured or stratified subsurface formation, comprising the steps of:
a) injecting a high viscosity blocking fluid into said formation to fill the naturally occurring fractures or thief zones and create a fluid mobility barrier to said flooding fluid, b) reinjecting a low viscosity flooding fluid, the sweep efficiency of said flooding fluid being increased due to the fluid mobility barrier created within the naturally occurring fractures or thief zones by said fluid mobility barrier, thereby resulting in enhanced low viscosity hydrocarbon production at said production well, and c) repeating steps (a) and (b) whenever the production rate of low viscosity hydrocarbons falls below a predetermined level.
a) injecting a high viscosity blocking fluid into said formation to fill the naturally occurring fractures or thief zones and create a fluid mobility barrier to said flooding fluid, b) reinjecting a low viscosity flooding fluid, the sweep efficiency of said flooding fluid being increased due to the fluid mobility barrier created within the naturally occurring fractures or thief zones by said fluid mobility barrier, thereby resulting in enhanced low viscosity hydrocarbon production at said production well, and c) repeating steps (a) and (b) whenever the production rate of low viscosity hydrocarbons falls below a predetermined level.
2. The method of claim 1 wherein the viscosity difference between said flooding fluid and said blocking fluid is increased by the addition of a thickening additive to said blocking fluid.
3. A method for producing low viscosity hydrocarbons from a fractured or stratified subsurface formation penetrated by at least one injection well and at least one production well comprising the continuous injection of both a low viscosity flooding fluid and a high viscosity blocking fluid into said fractured or stratified formation, whereby said blocking fluid migrates into the more highly permeable fractures or strata within the formation and creates a fluid mobility barrier to said flooding fluid, thereby enhancing the hydrocarbon sweep efficiency of said flooding fluid through the lower fluid mobility formation matrix and increasing low viscosity hydrocarbon production at said production well.
4. The method of claim 3 wherein the viscosity difference between said flooding fluid and said blocking fluid is maximized.
5. A method for producing low viscosity hydrocarbons from a fractured or stratified subsurface formation penetrated by at least one injection well and at least one production well, comprising the steps of:
a) identifying the location of high fluid mobility fractures or strata within a subsurface location, b) injecting a high viscosity blocking fluid into said high fluid mobility fractures or strata to create a fluid mobility barrier, c) injecting a low viscosity flooding fluid into the low fluid mobility formation matrix surrounding said fractures or strata, whereby said flooding fluid is prevented from migrating into such fractures by the fluid mobility barrier provided by said blocking fluid, and d) producing low viscosity hydrocarbons from said formation matrix through said production well.
a) identifying the location of high fluid mobility fractures or strata within a subsurface location, b) injecting a high viscosity blocking fluid into said high fluid mobility fractures or strata to create a fluid mobility barrier, c) injecting a low viscosity flooding fluid into the low fluid mobility formation matrix surrounding said fractures or strata, whereby said flooding fluid is prevented from migrating into such fractures by the fluid mobility barrier provided by said blocking fluid, and d) producing low viscosity hydrocarbons from said formation matrix through said production well.
6. The method of claim 5 wherein said injections of high viscosity blocking fluid and of low viscosity flooding fluid are carried out simultaneously.
7. The method of claim 5 wherein said injection of high viscosity blocking fluid precedes said injection of low viscosity flooding fluid.
8. A method for recovering low viscosity hydrocarbons from fractured or stratified subsurface formations, comprising the steps of:
a) injecting a high viscosity blocking fluid into said formation through an injection well to fill the fractures or thief zones within the formation and create a fluid mobility barrier, b) injecting a low viscosity flooding fluid into said formation through said injection well, and c) producing low viscosity hydrocarbons from said formation through a production well.
a) injecting a high viscosity blocking fluid into said formation through an injection well to fill the fractures or thief zones within the formation and create a fluid mobility barrier, b) injecting a low viscosity flooding fluid into said formation through said injection well, and c) producing low viscosity hydrocarbons from said formation through a production well.
9. The method of claim 8 wherein the step of injecting a high viscosity blocking fluid into the formation comprises the steps of:
a) injecting a first fluid into said formation, and b) injecting a second fluid into said formation having the property of thickening when mixed with said first fluid to provide said high viscosity blocking fluid.
a) injecting a first fluid into said formation, and b) injecting a second fluid into said formation having the property of thickening when mixed with said first fluid to provide said high viscosity blocking fluid.
10. The method of claim 8 further including the step of increasing the viscosity difference between said flooding fluid and said blocking fluid by the addition of a thickening additive to said blocking fluid.
11. The method of claim 10 wherein said thickening additive is added during the latter portion of the injection period of said blocking fluid.
12. The method of claim 10 wherein said thickening additive is a thixotropic additive that increases the viscosity of said blocking fluid with time.
13. A method for recovering low viscosity hydrocarbons from a fractured or stratified gas condensate or volatile oil reservoir having an injection well and a production well extending into the reservoir, comprising the steps of:
a) firstly injecting water into said reservoir through said injection well to fill the high fluid mobility fractures or thief zones of said reservoir and create a fluid mobility barrier, and b) secondly injecting a low viscous gas into said reservoir, said gas being prevented from channeling into the reservoir fractures or thief zones by the fluid mobility barrier created by said injected water, whereby the sweep efficiency of the low viscous gas through the reservoir and the resulting recovering of low viscosity hydrocarbons from the reservoir through said production well are enhanced.
a) firstly injecting water into said reservoir through said injection well to fill the high fluid mobility fractures or thief zones of said reservoir and create a fluid mobility barrier, and b) secondly injecting a low viscous gas into said reservoir, said gas being prevented from channeling into the reservoir fractures or thief zones by the fluid mobility barrier created by said injected water, whereby the sweep efficiency of the low viscous gas through the reservoir and the resulting recovering of low viscosity hydrocarbons from the reservoir through said production well are enhanced.
14. The method of claim 13 wherein said gas injection is continued until low viscosity hydrocarbon recovery at said production well drops to an undesirable level, at which time steps (a) and (b) are repeated.
15. The method of claim 13 wherein said water contains a thickening additive.
16. The method of claim 13 wherein said gas injection is continued until low viscosity hydrocarbon recovery at said production well drops to an undesirable level, at which time the viscosity difference between said injection water and said injection gas is increased and at least step (b) is repeated.
17. The method of claim 16 wherein said viscosity difference is increased by the addition of a thickening additive to said injection water.
18. The method of claim 17 wherein said thickening additive is selected from the group consisting of a polymer, an oil and an emulsion.
19. The method of claim 17 wherein said additive introduces a minimal gravity effect on said water.
20. The method of claim 19 wherein said additive is a foam.
21. The method of claim 17 wherein said viscosity difference is increased to an extent such that the ratio of fracture or thief zone fluid mobility to matrix fluid mobility is reduced to a predetermined level.
22. The method of claim 21 wherein said ratio is no greater than about 100.
23. The method of claim 22 wherein said ratio is no greater than about 10.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US62914684A | 1984-07-09 | 1984-07-09 | |
| US629,146 | 1984-07-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1238850A true CA1238850A (en) | 1988-07-05 |
Family
ID=24521783
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000485472A Expired CA1238850A (en) | 1984-07-09 | 1985-06-27 | Method for recovering hydrocarbons from fractured or highly stratified low viscosity subsurface reservoirs |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1238850A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111720116A (en) * | 2020-05-14 | 2020-09-29 | 中国石油化工股份有限公司 | Fracture-cavity type oil reservoir unit nitrogen gas flooding gas channeling judgment method and injection-production channeling prevention method |
| CN112443300A (en) * | 2019-09-05 | 2021-03-05 | 沈阳烳汇科技有限公司 | Method for high-yield fractured buried hill oil reservoir |
| CN115628032A (en) * | 2022-11-10 | 2023-01-20 | 中国石油天然气集团有限公司 | Experimental device and method for simulating fractured formation multilayer leakage under directional well gas invasion condition |
-
1985
- 1985-06-27 CA CA000485472A patent/CA1238850A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112443300A (en) * | 2019-09-05 | 2021-03-05 | 沈阳烳汇科技有限公司 | Method for high-yield fractured buried hill oil reservoir |
| CN111720116A (en) * | 2020-05-14 | 2020-09-29 | 中国石油化工股份有限公司 | Fracture-cavity type oil reservoir unit nitrogen gas flooding gas channeling judgment method and injection-production channeling prevention method |
| CN115628032A (en) * | 2022-11-10 | 2023-01-20 | 中国石油天然气集团有限公司 | Experimental device and method for simulating fractured formation multilayer leakage under directional well gas invasion condition |
| CN115628032B (en) * | 2022-11-10 | 2024-04-26 | 中国石油天然气集团有限公司 | Experimental device and method for multi-layer leakage simulation of fractured stratum under directional well gas invasion condition |
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