CN115726746A - Displacement method for greatly improving recovery ratio of low-permeability reservoir - Google Patents
Displacement method for greatly improving recovery ratio of low-permeability reservoir Download PDFInfo
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Abstract
The invention belongs to the technical field of improving the recovery efficiency of oilfield development chemical flooding, and particularly relates to a displacement method for greatly improving the recovery efficiency of a low-permeability reservoir. The displacement method comprises the following steps: first water flooding, miscible solvent solution flooding and second water flooding; the miscible solvent solution flooding comprises: injecting a miscible solvent solution into the low-permeability oil reservoir, wherein the miscible solvent solution is a solution containing small molecular compounds; the small molecular compound is selected from at least two of methanol, ethanol, propanol, methyl ether, diethyl ether and acetone. The method carries a chemical agent into an oil reservoir through a miscible solvent aqueous solution, the miscible solvent penetrates through an oil-water phase interface through diffusion to enter an oil phase, the oil phase expands and starts residual oil, the residual oil is displaced through subsequent water injection, and the crude oil recovery rate is greatly improved. Indoor core displacement experiments show that the injection amount of 0.5PV can improve the crude oil recovery rate of the low-permeability reservoir by 20-55% after water flooding, and the miscible solvent displacement technology is an effective means for greatly improving the recovery rate of the low-permeability reservoir.
Description
Technical Field
The invention belongs to the technical field of oil field development chemical flooding for improving the recovery ratio, and particularly relates to a displacement method for greatly improving the recovery ratio of a low-permeability oil reservoir.
Background
Petroleum is related to national energy safety, and has important influence on national defense construction, economic development and daily life of people. At present, most of oil fields in China are in the middle and later development stages, the water content rapidly rises even to be more than 90%, and the existing technology is difficult to meet the requirements of the oil fields. With the continuous development of the oil industry and the continuous deepening of exploitation, the phenomenon of exhaustion of oil exploitation of a plurality of high-quality oil reservoirs already occurs. Under such a background, the hard-to-use reserves such as low-permeability oil reservoirs become the key direction of the petroleum industry in China. The general permeability of the low-permeability reservoir is 10-50mD, the permeability of part of the reservoir is 1-10mD, even lower than 1mD, and the water drive development is difficult, and the low-permeability reservoir has the characteristics of small pore throat pore size, poor connectivity among pores, complex stratum structure and the like, and is not beneficial to fluid flow, and the traditional displacement method is difficult to achieve a good development effect, and the oil production cost and the oil production difficulty are very high. At present, low-permeability oil reservoirs at home and abroad mainly adopt development modes such as water injection, gas injection, active water injection and the like, and obtain better effect in field application. However, the problems of outstanding interlayer contradiction, strong heterogeneity and the like commonly exist in the low-permeability reservoir, so that the phenomena of water channeling and gas channeling are obvious, and the recovery ratio is generally not high (less than 25%). On the basis of water injection/gas injection, the surfactant can further improve the recovery rate of the ultra-low-permeability reservoir through the enhanced imbibition effect, and is proved by a field test. However, the surfactant is sensitive to temperature and mineralization and has short field validity period, so that the application of the surfactant is limited. According to statistics, the national low-permeability petroleum resources are 537 hundred million tons, and account for 49 percent of the total resources; the exploitation of low-permeability oil fields is difficult, and great difficulty is caused to the stable yield of the oil fields, so how to develop the low-permeability oil fields is a problem to be solved urgently for oil workers. An oil displacement technology capable of improving the recovery ratio of crude oil of a low-permeability reservoir is developed, and the method has great significance for the development of the petroleum industry in future.
Chinese patent application 201610763500.X describes a method for extracting oil from low permeability reservoir by endogenous microorganism, which comprises screening activator for producing biopolymer functional bacteria and activator for producing biosurfactant functional bacteria, and performing field test by injecting the activator for producing biopolymer functional bacteria, the activator for producing biosurfactant functional bacteria, and normal water injection. The Chinese patent application 201010227128.3 introduces a method for improving the oil displacement recovery rate of low-permeability oil reservoirs by preparing a surfactant, a foam stabilizer and water into a mixed aqueous solution, and mixing the aqueous solution with gas to inject the gas into the oil reservoirs. The Chinese patent application 201210241250.5 introduces a method for improving the crude oil recovery rate of a low-permeability sandstone reservoir, wherein a flexible microgel deep profile control agent is injected into a water distribution pipeline of an oil extraction well in the middle and later stages of fracturing and water injection of the ultra-low permeability sandstone reservoir through a metering pump, and after the flexible microgel deep profile control agent is injected into a water injection well of the ultra-low permeability sandstone reservoir, the effect of improving the crude oil recovery rate is obvious. The Chinese patent application 202010224596.9 introduces a compound oil displacement agent for increasing the recovery ratio of a low-permeability reservoir and a preparation method thereof, the oil displacement agent can reduce the oil-water interfacial tension and change the wettability of an oil reservoir, and the compound oil displacement agent has the advantages of small adsorption quantity on the surface of an oil reservoir rock, small adsorption loss, low use concentration, low cost, high oil displacement rate and the like.
The miscible enhanced recovery technology has been a focus of research in the oil and gas industry for decades. In 1960, gatlin and Slobod proposed a miscible displacement mechanism of isopropanol and methanol dissolved in a water-flooding slug and in a porous medium, and proposed that miscible solvents can significantly improve the recovery rate of crude oil, mainly because the miscible solvents are highly dependent on the phase state of a system in reservoir fluid and the solubility difference of the system in different phases. In 1961, taber, kamath and Reed investigated the differences between the phase behavior of alcohol-oil-brine systems and solvent displacement characteristics with different partition coefficients. The concept of recovery and reinjection of produced-fluid miscella was first proposed by Block and Donovan in 1961.
Disclosure of Invention
The invention aims to provide a miscible solvent technology for improving the recovery efficiency of low-permeability oil reservoirs, aiming at solving the problems of poor recovery efficiency improvement effect and difficult injection of low-permeability oil reservoirs in the existing chemical flooding technology.
In order to achieve the aim, the invention provides a displacement method for greatly improving the recovery ratio of a low-permeability reservoir, which comprises the following steps: first water flooding, miscible solvent solution flooding and second water flooding;
the miscible solvent solution flooding comprises: injecting a miscible solvent solution into the low-permeability oil reservoir, wherein the miscible solvent solution is a solution containing small molecular compounds;
the small molecular compound is selected from at least two of methanol, ethanol, propanol, methyl ether, diethyl ether and acetone.
Preferably, the small molecule compound is selected from at least two of methanol, propanol and acetone.
As a further preferred embodiment, the small molecule compound comprises methanol.
As a further preferred embodiment, the small molecule compound is methyl ether and:
propanol and/or acetone.
Preferably, the amount of propanol and/or acetone is 7-10mL relative to 100-120mL of dimethyl ether.
Preferably, the concentration of the small molecule compound in the solution of the small molecule compound is 5-30% v/v.
Preferably, the solvent of the solution of the small molecule compound is water and/or a saline solution.
Preferably, the salinity of the saline water solution is 3000-300000mg/L, and the concentration of the divalent calcium and magnesium ions is 0-5000mg/L.
Preferably, the miscible solvent solution is injected in an amount of 0.3 to 0.6PV.
According to the invention, the low permeability reservoir fulfils the conditions comprising:
the permeability is less than or equal to 50mD.
The invention has the beneficial effects that:
the invention brings chemical agents into an oil reservoir through the miscible solvent aqueous solution, the miscible solvent penetrates through an oil-water phase interface to enter an oil phase through diffusion, expands and starts residual oil, and the residual oil is displaced through subsequently injecting water, thereby greatly improving the crude oil recovery ratio. The miscible solvent enhanced oil recovery technology is mainly driven by a phase state, has wide applicable oil reservoir condition range, can be applied to different geological reservoirs, fluid properties and oil reservoir conditions, and therefore has the application range far larger than that of any existing enhanced oil recovery technology. Indoor core displacement experiments show that the injection amount of 0.5PV can improve the crude oil recovery rate of the low-permeability reservoir by 20-55% after water flooding, and the miscible solvent displacement technology is an effective means for greatly improving the recovery rate of the low-permeability reservoir.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The invention provides a displacement method for greatly improving the recovery ratio of a low-permeability reservoir, which comprises the following steps: first water flooding, miscible solvent solution flooding and second water flooding;
the miscible solvent solution flooding comprises: injecting a miscible solvent solution into the low-permeability oil reservoir, wherein the miscible solvent solution is a solution containing small molecular compounds;
the small molecular compound is selected from at least two of methanol, ethanol, propanol, methyl ether, diethyl ether and acetone. The proper micromolecular compound and the proportion can be selected according to the oil reservoir conditions and parameters such as temperature, mineralization degree, crude oil property and the like and the dissolution distribution coefficient of the system in the oil-water phase.
According to the invention, a certain amount of micro-polar small molecule miscible solvent which is soluble in both water phase and oil phase is added into water injected in indoor experiments or mines, the miscible solvent is dissolved in the water phase to prepare solution, and the miscible solvent is brought into the deep part of an oil reservoir through the injected water. Because the miscibility agent has greater solubility in the oil phase, when the miscibility agent contacts the oil phase in the reservoir, the miscibility agent in the aqueous solution will transfer mass across the oil-water interface into the crude oil and dissolve in the crude oil. After the miscible solvent is dissolved in the oil phase, the crude oil is expanded, the reservoir energy is increased, the crude oil viscosity is reduced, and the flowing capacity of the crude oil in the stratum is increased. The injection of the miscible agent can start residual oil in the oil reservoir and form an oil wall, and the residual oil is displaced by subsequently injecting water, so that the crude oil recovery rate is improved. Meanwhile, the miscible solvent can be recovered and recycled by subsequent water injection, so that the cost of the chemical agent is reduced, and the economic benefit is improved. The oil recovery in the miscible solvent flooding process is mainly driven by a phase state, the range of applicable oil deposit conditions is wide, and the miscible solvent flooding oil recovery method can be applied to different geological reservoirs, fluid properties and oil deposit conditions (pressure, temperature and salinity), so that the application range of the miscible solvent flooding oil recovery method is far larger than that of any existing tertiary oil recovery technology. The miscible solvent flooding technology can be implemented as a tertiary oil recovery technology on the project of developing water flooding, can also be applied to a new secondary oil recovery water flooding project from the beginning, and can improve the recovery ratio of crude oil. Especially applied to low permeability oil reservoir, compared with other enhanced recovery ratio technologies, the miscible flooding technology has obvious technical advantages and economic benefits.
Preferably, the small molecule compound is selected from at least two of methanol, propanol and acetone.
As a further preferred embodiment, the small molecule compound comprises methanol.
As a further preferred embodiment, the small molecule compound is methyl ether and: propanol and/or acetone. According to the present invention, in a specific embodiment, the small molecule compound is methanol + propanol; in another specific embodiment, the small molecule compound is methanol + acetone; in yet another specific embodiment, the small molecule compound is methanol + acetone + propanol.
Most preferably, the amount of propanol and/or acetone is 7-10mL, such as 100mL of dimethyl ether +7mL of propanol, such as 100mL of dimethyl ether +10mL of acetone, relative to 100-120mL of dimethyl ether.
Preferably, the concentration of the small molecule compound in the solution of the small molecule compound is 5-30% v/v.
Preferably, the solvent of the solution of the small molecule compound is water and/or a saline solution.
Preferably, the salinity of the saline water solution is 3000-300000mg/L, and the concentration of the divalent calcium and magnesium ions is 0-5000mg/L.
Preferably, the miscible solution is injected in an amount of 0.3-0.6PV, such as 0.5PV.
According to the invention, the low permeability reservoir fulfils the conditions comprising:
the permeability is less than or equal to 50mD.
In the embodiment of the invention:
the core used in the core displacement experiment is the beret sandstone, the length is 30cm, the inner diameter is 2.5cm, the permeability is 1-50 mD, and the pore volume is 3-20 mL. The whole displacement experiment is carried out in a digital temperature control box, the fluid injection speed is 0.02-0.1 mL/min, the back pressure of the extraction end is 2-3 MPa, and the temperature of the experiment system is 40-120 ℃. The used oil is low-permeability reservoir simulation crude oil, the viscosity of the crude oil is equivalent to that of reservoir underground crude oil, and the viscosity range is 1.0-10.0mPa & s.
The core displacement experiment procedure generally comprises: the method comprises the steps of firstly, saturating a simulated formation brine after an experimental core is vacuumized, then establishing the initial oil saturation of the core by oil-flooding water, carrying out water flooding (or direct miscible solvent aqueous solution flooding) after aging for more than 24 hours at the oil reservoir temperature, injecting 0.5PV miscible solvent aqueous solution after 2PV water flooding, then injecting 1.5-2PV subsequent water flooding (or soaking for 2-12 hours), measuring and recording the produced crude oil quantity, the water content and the pressure change condition of an injection and production end at different stages, and finally calculating the crude oil recovery rate and the produced liquid water content.
Example 1
This example illustrates a displacement method that greatly increases the recovery of a low permeability reservoir.
Firstly, preparing 100000mg/L simulated formation water by NaCl, putting 350mL of simulated formation water solution into a 500mL stainless steel intermediate container, adding 7mL propanol and 100mL methyl ether into the container from the bottom end by a metering pump, adjusting the pressure in the intermediate container to be 2.5MPa from the top end, and standing at room temperature for more than 48 hours so as to be mixed uniformly, wherein the prepared miscible solvent solution is used for later use.
The method comprises the steps of placing 30cm of Bailey sandstone in a core holder, enabling gas side permeability to be 45mD, adding ring pressure to be 10MPa, enabling the temperature of a simulated oil reservoir to be 100 ℃, vacuumizing for 4 hours, injecting 100000mg/L of simulated formation water into a core, metering to obtain the volume of the injected water to be 22.0mL and the porosity of the core to be 15%, injecting 4mPa & s of simulated crude oil into the core at the speed of 0.05mL/min after aging for 2 hours, establishing initial oil saturation, enabling outlet end back pressure to be 2.4MPa, metering to obtain the displacement water to be 9.5mL and the initial oil saturation to be 44.2% after injecting 2PV of the simulated crude oil, and aging for 48 hours at the temperature of the oil reservoir. With the injection speed of 0.1mL/min, the oil displacement of 2PV by 100000mg/L simulated formation water is used to drive out 3.3mL of crude oil, and the water drive recovery ratio is 34.7%. And when the water content of the produced liquid is more than 98 percent, replacing the miscible solvent solution for driving, keeping the injection speed unchanged, and replacing the subsequent water drive until the oil is not produced at the outlet end, wherein the injection quantity of the subsequent water drive is 1.6PV. 3.8mL of crude oil is obtained by miscible solvent flooding and subsequent water flooding measurement, the miscible solvent improves the recovery ratio by 40 percent (relative to continuous water flooding), and the total recovery ratio reaches 74.7 percent.
Example 2
This example illustrates a displacement method that greatly increases the recovery of a low permeability reservoir.
Firstly, preparing 100000mg/L simulated formation water by NaCl, putting 350mL of simulated formation water solution into a 500mL stainless steel intermediate container, adding 7mL propanol and 100mL methyl ether into the container from the bottom end by a metering pump, adjusting the pressure in the intermediate container to be 2.5MPa from the top end, and standing at room temperature for more than 48 hours so as to be mixed uniformly, wherein the prepared miscible solvent solution is used for later use.
The method comprises the steps of placing 30cm of beret sandstone in a core holder, enabling gas side permeability to be 37mD, adding ring pressure to be 10MPa, enabling the temperature of a simulated oil reservoir to be 100 ℃, vacuumizing for 4 hours, injecting 100000mg/L of simulated formation water into a core, metering to obtain that the volume of the injected water is 21.7mL and the porosity of the core is 14.7%, injecting 4 mPa-s of simulated crude oil into the core at a speed of 0.05mL/min after aging for 2 hours, establishing initial oil saturation, enabling outlet end back pressure to be 2.4MPa, metering to obtain that the driven water is 9.0mL and the initial oil saturation is 41.5% after injecting 2PV of simulated crude oil, and aging for 48 hours at the temperature of the oil reservoir. With the injection speed of 0.1mL/min, the oil displacement of 2PV by 100000mg/L simulated formation water is used to drive out 3.52mL of crude oil, and the water drive recovery ratio is 39.1%. And (3) after the water content of the produced liquid is more than 98%, replacing the miscible solvent solution for driving, keeping the injection speed unchanged, replacing the subsequent water drive until the oil is not produced at the outlet end after the well is closed for 10 hours, and keeping the injection quantity of the subsequent water drive to be 1.6PV. The miscible solvent flooding and the subsequent water flooding measurement are carried out to obtain 4.86mL of the produced crude oil, the miscible solvent after the water flooding improves the recovery ratio by 54 percent, and the total recovery ratio reaches 93.1 percent.
Example 3
This example illustrates a displacement method that greatly increases the recovery of a low permeability reservoir.
Firstly, preparing 100000mg/L simulated formation water by NaCl, placing 350mL of simulated formation water solution in a 500mL stainless steel intermediate container, adding 7mL propanol and 100mL dimethyl ether into the container from the bottom end by a metering pump, adjusting the pressure in the intermediate container to be 2.5MPa from the top end, and placing for more than 48 hours at room temperature so as to be mixed uniformly, wherein the prepared miscible solvent solution is used for later use.
The method comprises the steps of placing 30cm of beret sandstone in a core holder, enabling gas-side permeability to be 40mD, adding ring pressure to be 10MPa, enabling the temperature of a simulated oil reservoir to be 100 ℃, vacuumizing for 4 hours, injecting 100000mg/L of simulated formation water into a core, metering to obtain the volume of the injected water to be 21.6mL and the porosity of the core to be 15%, injecting 4 mPas of simulated crude oil into the core at the speed of 0.05mL/min after aging for 2 hours, establishing initial oil saturation, enabling outlet end back pressure to be 2.4MPa, metering to obtain the displacement water to be 8.4mL and the initial oil saturation to be 38.8% after injecting 2PV of simulated crude oil, and aging for 48 hours at the temperature of the oil reservoir. And at the injection speed of 0.1mL/min, using 100000mg/L simulated formation water to displace 2PV to displace 2.8mL of crude oil, wherein the water displacement recovery ratio is 33.1 percent. And when the water content of the produced liquid is more than 98 percent, replacing the miscible solvent solution for driving, keeping the injection speed unchanged, and replacing the subsequent water drive until the oil is not produced at the outlet end, wherein the injection quantity of the subsequent water drive is 1.6PV. 3.8mL of crude oil is obtained by miscible solvent flooding and subsequent water flooding measurement, the recovery ratio is improved by miscible solvent after water flooding by 45.5 percent, and the total recovery ratio reaches 78.4 percent.
Example 4
This example illustrates a displacement method that greatly increases the recovery of a low permeability reservoir.
Firstly, 50000mg/L simulated formation water is prepared by NaCl, 350mL of simulated formation water solution is placed in a 500mL stainless steel intermediate container, 10mL of acetone and 120mL of dimethyl ether are added into the container from the bottom end through a metering pump, the pressure in the intermediate container is adjusted to be 2.5MPa from the top end, the container is placed at room temperature for more than 48 hours so as to be uniformly mixed, and the prepared miscible solvent solution is used for later use.
The method comprises the steps of placing 30cm of Bailey sandstone in a core holder, enabling gas-side permeability to be 35mD, adding ring pressure to be 10MPa, enabling the temperature of a simulated oil reservoir to be 85 ℃, vacuumizing for 4 hours, injecting 50000mg/L of simulated formation water into a core, metering to obtain the volume of the injected water to be 24.8mL and the porosity of the core to be 17%, injecting simulated crude oil of 6mPa & s into the core at the speed of 0.05mL/min after aging for 2 hours, establishing initial oil saturation, enabling outlet end back pressure to be 2.4MPa, metering to obtain the flooding water to be 10.5mL and the initial oil saturation to be 42.3% after injecting 2PV simulated crude oil, and aging for 48 hours at the temperature of the oil reservoir. At the injection speed of 0.1mL/min, 50000mg/L simulated formation water is used for displacing 2PV, crude oil is displaced by 4.4mL, and the water displacement recovery ratio is 42%. And after the water content of the produced liquid is more than 98%, replacing the miscible solvent solution to drive, keeping the injection speed unchanged, and changing the subsequent water drive until the oil is not produced at the outlet end, wherein the injection quantity of the subsequent water drive is 2.0PV. 2.35mL of crude oil is obtained by miscible solvent flooding and subsequent water flooding measurement, the recovery ratio is improved by miscible solvent after water flooding by 22.4 percent, and the total recovery ratio reaches 64.7 percent.
Example 5
This example illustrates a displacement method that substantially increases the recovery of a low permeability reservoir.
Firstly, 50000mg/L simulated formation water is prepared by NaCl, 350mL of simulated formation water solution is placed in a 500mL stainless steel intermediate container, 10mL of acetone and 120mL of dimethyl ether are added into the container from the bottom end through a metering pump, the pressure in the intermediate container is adjusted to be 2.5MPa from the top end, the container is placed at room temperature for more than 48 hours so as to be uniformly mixed, and the prepared miscible solvent solution is used for later use.
The method comprises the steps of placing 30cm of Bailey sandstone in a core holder, enabling gas-side permeability to be 45mD, adding ring pressure to be 10MPa, enabling the temperature of a simulated oil reservoir to be 85 ℃, vacuumizing for 4 hours, injecting 50000mg/L of simulated formation water into a core, metering to obtain the volume of the injected water to be 24.8mL and the porosity of the core to be 17%, injecting simulated crude oil of 6mPa & s into the core at the speed of 0.05mL/min after aging for 2 hours, establishing initial oil saturation, enabling outlet end back pressure to be 2.4MPa, metering to obtain the flooding water to be 9.4mL and the initial oil saturation to be 38% after injecting 2PV simulated crude oil, and aging for 48 hours at the temperature of the oil reservoir. At the injection speed of 0.1mL/min, 3.9mL of crude oil is driven out by using 50000mg/L simulated formation water for oil displacement 2PV, and the water-drive recovery ratio is 41.5%. And when the water content of the produced liquid is more than 98 percent, replacing the miscible solvent solution for driving, keeping the injection speed unchanged, and replacing the subsequent water drive until the oil is not produced at the outlet end, wherein the injection quantity of the subsequent water drive is 2.0PV. 2.35mL of crude oil is obtained by miscible solvent flooding and subsequent water flooding measurement, the recovery ratio is improved by miscible solvent after water flooding by 25 percent, and the total recovery ratio reaches 66.5 percent.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.
Claims (10)
1. A displacement method for greatly improving the recovery ratio of a low-permeability reservoir is characterized by comprising the following steps: first water flooding, miscible solvent solution flooding and second water flooding;
the miscible solvent solution flooding comprises: injecting a miscible solvent solution into the low-permeability oil reservoir, wherein the miscible solvent solution is a solution containing small molecular compounds;
the small molecular compound is selected from at least two of methanol, ethanol, propanol, methyl ether, ethyl ether and acetone.
2. The displacement method to substantially enhance low permeability reservoir recovery of claim 1, wherein the small molecule compound is selected from at least two of methanol, propanol, and acetone.
3. The displacement method to substantially enhance low permeability reservoir recovery of claim 1 or 2, wherein the small molecule compound comprises methanol.
4. The displacement method to substantially enhance low permeability reservoir recovery of claim 2, wherein the small molecule compound is methyl ether and:
propanol and/or acetone.
5. The displacement method for substantially enhancing recovery of a low permeability reservoir of claim 4, wherein the amount of propanol and/or acetone is 7-10mL relative to 100-120mL of dimethyl ether.
6. The displacement method for substantially enhancing low permeability reservoir recovery of claim 1, wherein the concentration of small molecule compound in the solution of small molecule compound is 5-30% v/v.
7. The displacement method to substantially enhance low permeability reservoir recovery of claim 1, wherein the solvent of the solution of small molecule compound is water and/or brine solution.
8. The displacement method for substantially enhancing recovery of a low permeability reservoir of claim 7, wherein the salinity of the brine solution is 3000-300000mg/L and the concentration of divalent calcium magnesium ions is 0-5000mg/L.
9. The displacement method for substantially increasing the recovery ratio of a low permeability reservoir of claim 1, wherein the miscible solvent solution displacement has an injection volume of 0.3-0.6PV.
10. The displacement method to substantially increase the recovery of a low permeability reservoir of claim 1, wherein the low permeability reservoir satisfies conditions comprising:
the permeability is less than or equal to 50mD.
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