Method for improving recovery efficiency of foam oil reservoir

Abstract

The invention provides a method for improving the recovery efficiency of a foam oil reservoir, which comprises the following steps: dispersing stable emulsion and gas as injection media, simultaneously injecting the injection media into the foam oil reservoir through an injection well, and dissolving the gas into an underground reservoir of the foam oil reservoir as driving fluid, and reducing the formation pressure to be between the bubble point pressure and the pseudo-bubble point pressure of the oil reservoir, displacing hydrocarbons of the underground reservoir into a production well of the foam oil reservoir to recover the hydrocarbons, and recovering crude oil from the horizontal well. According to the method provided by the invention, the fluidity ratio of the injected medium to the crude oil can be adjusted, and multiple purposes of improving the oil displacement efficiency and the recovery efficiency are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum exploitation, and in particular to a method for improving the recovery rate of foam oil reservoirs. Background Art

[0002] Oil is typically recovered from underground reservoirs through a flooding process, in which a flooding fluid (such as water or gas) is injected into an injection well to drive the oil to a production well where it is recovered. The fluidity of a fluid flowing through a porous medium in an underground reservoir can be defined as the ratio of the relative permeability of the fluid to the viscosity of the fluid (relative permeability / fluid viscosity). In some displacement processes, the fluidity of the displaced in-situ oil is significantly lower than the fluidity of the displacement fluid. This poor fluidity ratio can cause the injected displacement fluid to penetrate the crude oil, resulting in a large amount of crude oil being retained and unable to be recovered. The natural depletion recovery rate of foam oil reservoirs is typically only 5-8%, so the remaining 90% or more of the reserves require innovative flooding processes to achieve efficient recovery.

[0003] Therefore, for an effective oil displacement process, the composition and viscosity of the injected fluid should keep the mobility of the displacement fluid lower than the mobility of the displaced oil. The mobility ratio of the displacement process is the ratio of the mobility of the displacement fluid to the mobility of the displaced oil (displacement fluid mobility / oil mobility). The mobility ratio is usually 1.0 or lower, which can improve the displacement efficiency.

[0004] CN102942910A discloses a surfactant for improving oil recovery, and its components and mass percentages are: Na2CO3 1-3%, sodium dodecylbenzene sulfonate 30-40%, AF4018-Y type fluorocarbon surfactant 20-30%, n-butanol 4-8%, water 30-40%. After the surfactant is injected into the formation, it can play the role of alkali-surfactant in reducing interfacial tension, so that the wettability of the formation pores is converted from oil-wet to water-wet, thereby improving its permeability, and can greatly reduce the capillary force on the residual oil, thereby activating the dead-end type, film-like type and columnar type residual oil, and greatly improving the recovery rate.

[0005] CN104327824A discloses a new fracturing fluid for improving oil recovery. It mainly solves the problem that the existing guar gum fracturing fluid has no oil displacement effect and the high residue content after breaking the gel has a great damage to the formation permeability. The components and proportions of the new fracturing fluid are as follows by mass percentage: 0.2% to 0.25% polymer, 0.1% drainage agent, 0.05% to 0.1% composite cross-linking agent, 0.1% ammonium persulfate, and the balance is water. The new fracturing fluid for improving oil recovery has no residue and is applied in reservoirs with a permeability of 10 to 420mD. It can be used for both oil displacement and as a fracturing fluid working fluid. Compared with guar gum fracturing fluid, it increases the effective period of oil well production and stabilizes the output.

[0006] CN111286315A discloses a composite oil displacement agent for increasing the recovery rate of low permeability reservoirs, comprising the following components: polyacrylamide, initiator, styrene, active polymer dispersant, ethanol and water. Its preparation method comprises the following steps: dissolving styrene in ethanol and stirring evenly to obtain solution A; dissolving the initiator in 8 to 15 times of water to obtain solution B; dissolving polyacrylamide and active polymer dispersant in the remaining amount of water to obtain solution C; placing the container containing solution C in a water bath and heating it to a stable temperature, then adding solution A and stirring evenly; then dripping solution B at a uniform speed under nitrogen protection and stirring, and continuing to stir for 2 to 3 hours after the dripping is completed.

[0007] However, the above-mentioned surfactants or composite oil displacement agents still have low oil displacement efficiency for high-viscosity and high-permeability heavy oil, and the crude oil recovery rate is low. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for improving the recovery rate of foam oil reservoirs, which adopts a specific dispersed stable emulsion to reduce the mobility ratio of oil displacement medium and crude oil, and cooperates with a specific injection strategy to improve the oil displacement efficiency, thereby greatly improving the crude oil recovery rate.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for improving the recovery rate of a foam oil reservoir, wherein the foam oil reservoir satisfies the following conditions at the same time:

[0011] ① The residual dissolved gas-oil ratio of the foam reservoir is >5m 3 / m 3 ;

[0012] ② The thickness of the oil layer of the foam reservoir is >3m, the oil saturation is >60%, the porosity is >30%, and the permeability is >1 Darcy;

[0013] ③ The foam reservoir is developed by horizontal well pattern, with horizontal section length>400m, horizontal well spacing≤600m, and displacement relationship is established between adjacent wells;

[0014] The method comprises the following steps:

[0015] The dispersed stable emulsion and the gas are injected into the foam reservoir through the injection well as injection media at the same time, the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, the formation pressure is reduced to between the bubble point pressure and the pseudo-bubble point pressure of the reservoir, the hydrocarbons in the underground reservoir are displaced to the production well of the foam reservoir to recover the hydrocarbons, and the crude oil is recovered from the horizontal well;

[0016] The dispersed stable emulsion comprises a first liquid, a second liquid, a dispersant and a dispersing aid; the first liquid comprises light oil, castor oil or any one of alkanes / aromatics / alcohols / ethers with a carbon number of 6 to 12 or a combination of at least two thereof.

[0017] The foam reservoir of the present invention is developed from the original gas-containing reservoir, that is, the residual dissolved gas in the oil layer of the original gas-containing reservoir is reduced in the middle and late stages of exploitation, and the foam reservoir is formed. The method for improving the recovery rate of the foam reservoir of the present invention is mainly aimed at satisfying the oil layer residual dissolved gas-oil ratio>5m 3 / m 3 ; Oil layer thickness>3m, oil saturation>60%, porosity>30%, permeability>1 Darcy; horizontal well network development is adopted, horizontal section length>400m, horizontal well spacing≤600m, and a foam reservoir with a displacement relationship established between adjacent wells.

[0018] The bubble point pressure described in the present invention is a phenomenon unique to foamy oil reservoirs, which refers to the pressure point below which dissolved gas in crude oil precipitates to form tiny bubbles that disperse in the crude oil to form foamy oil, but does not immediately separate from the crude oil;

[0019] The pseudo-bubble point pressure is a phenomenon unique to foam reservoirs, and refers to a pressure point below which dissolved gas in crude oil separates from the crude oil to form free gas.

[0020] The method for improving the recovery rate of foam oil reservoirs disclosed in the present invention is aimed at high-porosity and high-permeability foam oil reservoirs. The viscosity of the injection medium is increased by using a dispersed stable emulsion, and the injection capacity is ensured by relying on the earthworm holes and high-permeability reservoirs formed during the original natural energy exploitation process of the foam oil reservoir, so as to reduce the fluidity ratio between the injection medium and the crude oil, thereby improving the oil displacement efficiency and the recovery rate. The method reduces the exploitation pressure to between the bubble point pressure and the pseudo-bubble point pressure of the gas-containing oil reservoir, promotes the expansion of the gas in the injection medium and the expansion of the gas originally dissolved in the crude oil to produce foam oil, greatly improves the flowability of the crude oil and the elastic performance of exploitation, and achieves the purpose of improving the oil production level.

[0021] The first liquid in the dispersed stable emulsion used in the present invention is an oil-based oil displacement medium, which has an oil-wet interface property for the original rock surface. After the above-mentioned substance is injected, the crude oil on the rock surface can be greatly stripped, thereby improving the oil displacement efficiency. The fluidity of the dispersed stable emulsion cannot be higher than the fluidity of hydrocarbons.

[0022] The residual dissolved gas-oil ratio of the foam reservoir of the present invention is >5m 3 / m 3 , for example, it can be 5.1m 3 / m 3 、5.5m 3 / m 3 、6m 3 / m3 、8m 3 / m 3 , 9m 3 / m 3 、10m 3 / m 3 or 15m 3 / m 3 The above range is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0023] The thickness of the oil layer in the foam reservoir is greater than 3 m, for example, it may be 3.1 m, 5 m, 8 m, 10 m, 12 m, 15 m or 25 m, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0024] Oil saturation>60%, for example, it can be 61%, 65%, 70%, 75%, 80%, 85% or 88%, etc., but it is not limited to the listed values, and other values ​​not listed in the range are also applicable;

[0025] Porosity>30%, for example, 31%, 31.5%, 32%, 32.5%, 33%, 34% or 35%, etc., but not limited to the listed values, other values ​​not listed in the range are also applicable;

[0026] Permeability>1 Darcy, for example, it can be 1.1 Darcy, 1.2 Darcy, 2 Darcy, 2.5 Darcy, 3 Darcy or 5 Darcy, but it is not limited to the listed values, and other values ​​not listed in the range are also applicable;

[0027] The foam reservoir is developed by a horizontal well pattern, and the horizontal section length is >400m, for example, it can be 401m, 450m, 500m, 600m, 800m, 1200m or 1300m, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0028] The horizontal well spacing is ≤600m, for example, it can be 600m, 590m, 550m, 500m, 400m, 300m or 200m, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the volume proportion of the first liquid in the dispersed stable emulsion is 10-40%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35% or 40%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the second liquid comprises any one of water, an emulsifier aqueous solution or a caustic soda aqueous solution, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of water and an emulsifier aqueous solution, a combination of a caustic soda aqueous solution and water, or a combination of an emulsifier aqueous solution and a caustic soda aqueous solution.

[0031] The second liquid of the present invention is essentially an emulsifier, which has a certain degree of viscosity reduction effect on high-viscosity crude oil and can also reduce the flow resistance at the displacement front, thereby improving the penetration of the injected medium.

[0032] Preferably, the emulsifier aqueous solution includes an oil-in-water emulsifier with a concentration of 1 to 5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 4% or 5%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the concentration of the caustic soda aqueous solution is 1-5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 4% or 5%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the volume proportion of the second liquid in the dispersed stable emulsion is 10-40%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35% or 40%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the dispersant comprises inorganic solid particles and a thickener.

[0036] Preferably, the solid phase particles include silicon dioxide nanopowder and / or lignin nanoparticles.

[0037] The solid particles of the present invention are used to adjust the viscosity of the injection medium so that it forms a certain proportional relationship with the viscosity of crude oil, thereby reducing the fluidity ratio of the injection medium to crude oil, which can greatly improve the oil recovery efficiency, avoid the penetration of the injection medium in high-viscosity oil reservoirs, and thus improve the recovery rate.

[0038] Preferably, the particle size of the solid particles is 1 to 200 nm, for example, 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 150 nm or 200 nm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the thickener includes polyacrylamide with a molecular weight of 1 to 5 million, for example, 1 million, 1.5 million, 2 million, 2.5 million, 3 million, 4 million or 5 million, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the dispersing aid comprises ethanol.

[0041] The dispersing aid of the present invention promotes the dispersion and diffusion of the injected medium in the reservoir and increases the effective radius. The inorganic solid phase particles in the dispersed stable emulsion of the present invention are suspended in the aqueous solution by the thickener polyacrylamide, and the ethanol can be dissolved in both water and crude oil to play a special cross-linking role, which can greatly improve the dispersibility of the injected medium and avoid gas channeling.

[0042] Preferably, the volume ratio of the solid particles to ethanol is 3:1 to 30:1, for example, 3:1, 5:1, 8:1, 10:1, 15:1, 20:1, 25:1 or 30:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the concentration of the polyacrylamide in the dispersed stable emulsion is 0.5-1%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95% or 1%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the volume proportion of ethanol in the dispersed stable emulsion is 10-40%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35% or 40%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the gas comprises any one of nitrogen, methane, ethane, propane, butane, carbon dioxide, natural gas or flue gas, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of nitrogen and methane, a combination of ethane and propane, a combination of butane and carbon dioxide, a combination of natural gas and flue gas, or a combination of nitrogen and butane.

[0046] Preferably, the volume proportion of the gas in the injected medium is 10% to 70%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60% or 70%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] Preferably, the hydrocarbons include crude oil and / or natural gas.

[0048] As a preferred technical solution of the present invention, the foam reservoir satisfies the following conditions at the same time:

[0049] ① The residual dissolved gas-oil ratio of the foam reservoir is >5m 3 / m3 ;

[0050] ② The thickness of the oil layer of the foam reservoir is >3m, the oil saturation is >60%, the porosity is >30%, and the permeability is >1 Darcy;

[0051] ③ The foam reservoir is developed by horizontal well pattern, with horizontal section length>400m, horizontal well spacing≤600m, and displacement relationship is established between adjacent wells;

[0052] The method comprises the following steps:

[0053] The dispersed stable emulsion and the gas are injected into the foam reservoir through the injection well as injection media at the same time, the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, the formation pressure is reduced to between the bubble point pressure and the pseudo-bubble point pressure of the reservoir, the hydrocarbons in the underground reservoir are displaced to the production well of the foam reservoir to recover the hydrocarbons, and the crude oil is recovered from the horizontal well;

[0054] The dispersed stable emulsion comprises a first liquid, a second liquid, a dispersant and a dispersing aid; the first liquid comprises any one of light oil, castor oil or alkanes / aromatics / alcohols / ethers with a carbon number of 6 to 12 or a combination of at least two thereof;

[0055] The volume proportion of the first liquid in the dispersed stable emulsion is 10 to 40%;

[0056] The second liquid includes any one of water, an oil-in-water emulsifier with a concentration of 1 to 5%, or a caustic soda aqueous solution with a concentration of 1 to 5%, or a combination of at least two thereof;

[0057] The volume proportion of the second liquid in the dispersed stable emulsion is 10 to 40%;

[0058] The dispersant includes inorganic solid particles and a thickener; the solid particles include silicon dioxide nanopowder and / or lignin nanoparticles with a particle size of 1 to 200 nm; the thickener includes polyacrylamide with a molecular weight of 1 to 5 million;

[0059] The dispersing aid includes ethanol;

[0060] The volume ratio of the solid phase particles to ethanol is 3:1 to 30:1;

[0061] The concentration of the polyacrylamide in the dispersed stable emulsion is 0.5-1%;

[0062] The volume proportion of the ethanol in the dispersed stable emulsion is 10 to 40%;

[0063] The gas includes any one of nitrogen, methane, ethane, propane, butane, carbon dioxide, natural gas or flue gas, or a combination of at least two thereof;

[0064] The volume proportion of the gas in the injected medium is 10% to 70%;

[0065] The hydrocarbons include crude oil and / or natural gas.

[0066] Compared with the prior art, the present invention has at least the following beneficial effects:

[0067] (1) The method for improving the recovery rate of foam oil reservoirs provided by the present invention uses a specific dispersed stable emulsion to increase the viscosity of the injection medium, and relies on the earthworm holes and high permeability reservoirs formed during the original natural energy exploitation process to ensure the injection capacity, thereby reducing the fluidity ratio between the injection medium and the crude oil, thereby improving the oil displacement efficiency and recovery rate;

[0068] (2) The first liquid in the dispersed stable emulsion in the method for improving the recovery rate of foam oil reservoirs provided by the present invention is an oil-based oil displacement medium, which can greatly strip the crude oil on the rock surface to improve the oil displacement efficiency; the second liquid has a certain degree of viscosity reduction effect on high-viscosity crude oil, and can also reduce the flow resistance at the displacement front and improve the penetration of the injection medium; the dispersant and the dispersing aid play a special cross-linking role, which can greatly improve the dispersibility of the injection system and avoid gas channeling;

[0069] (3) The method for improving the recovery rate of foam oil reservoirs provided by the present invention reduces the production pressure to between the bubble point pressure and the pseudo-bubble point pressure of the gas-bearing reservoir, thereby promoting the expansion of the gas injected into the medium and the expansion of the gas originally dissolved in the crude oil to produce foam oil, greatly improving the flowability and elastic performance of the crude oil, and achieving the purpose of increasing the oil production level. DETAILED DESCRIPTION

[0070] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0071] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0072] Example 1

[0073] This embodiment provides a method for improving the recovery rate of a foam reservoir, wherein the foam reservoir satisfies the following conditions at the same time:

[0074] ① The residual dissolved gas-oil ratio of the foam reservoir is 6m 3 / m 3 ;

[0075] ② The thickness of the oil layer in the foam reservoir is 22m, the oil saturation is 70%, the porosity is 32%, and the permeability is 2 Darcy;

[0076] ③ The foam reservoir is developed using a horizontal well pattern, with a horizontal section length of 500m and a horizontal well spacing of 300m, and a displacement relationship is established between adjacent wells;

[0077] The method comprises the following steps:

[0078] The dispersed stable emulsion and nitrogen are injected into the foam reservoir through the injection well as injection media at the same time, and the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, reducing the formation pressure to a bubble point pressure of 6.5 MPa to a pseudo-bubble point pressure of 4.5 MPa, displacing hydrocarbons in the underground reservoir to the production well of the foam reservoir to recover hydrocarbons, and recovering crude oil from the horizontal well;

[0079] The dispersed stable emulsion comprises a first liquid light oil, a second liquid water, a dispersant and a dispersing aid;

[0080] The volume proportion of the first liquid in the dispersed stable emulsion is 30%;

[0081] The volume proportion of the second liquid in the dispersed stable emulsion is 30%;

[0082] The dispersant includes solid phase particles of silicon dioxide nanopowder with a particle size of 100 nm and thickener polyacrylamide with a molecular weight of 1 million;

[0083] The dispersing aid includes ethanol;

[0084] The volume ratio of the solid phase particles to ethanol is 3:1;

[0085] The concentration of the polyacrylamide in the dispersed stable emulsion is 0.5%;

[0086] The volume proportion of the ethanol in the dispersed stable emulsion is 10%;

[0087] The nitrogen accounts for 30% by volume of the injected medium;

[0088] The hydrocarbons include crude oil and natural gas.

[0089] In this embodiment, the ratio of the viscosity of crude oil to the viscosity of the injected medium is between 0.5 and 1; the final crude oil recovery rate of the horizontal well is increased by 17% on the basis of cold recovery, reaching 25%.

[0090] Example 2

[0091] This embodiment provides a method for improving the recovery rate of a foam reservoir, wherein the foam reservoir satisfies the following conditions at the same time:

[0092] ① The residual dissolved gas-oil ratio of the foam reservoir is 8m 3 / m 3 ;

[0093] ② The thickness of the oil layer in the foam reservoir is 16m, the oil saturation is 87%, the porosity is 33%, and the permeability is 3 Darcy;

[0094] ③ The foam reservoir is developed using a horizontal well pattern, with a horizontal section length of 600m and a horizontal well spacing of 300m, and a displacement relationship is established between adjacent wells;

[0095] The method comprises the following steps:

[0096] The dispersed stable emulsion and methane are injected into the foam reservoir through the injection well as injection media at the same time, and the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, reducing the formation pressure to between the bubble point pressure of 6.5 MPa and the pseudo-bubble point pressure of 4.5 MPa of the reservoir, displacing hydrocarbons in the underground reservoir to the production well of the foam reservoir to recover hydrocarbons, and recovering crude oil from the horizontal well;

[0097] The dispersed stable emulsion comprises a first liquid castor oil, a second liquid, a dispersant and a dispersing aid;

[0098] The volume proportion of the first liquid in the dispersed stable emulsion is 10%;

[0099] The second liquid is EMULGEN 420 / EMULGEN 707, with a concentration of 15% in water;

[0100] The volume proportion of the second liquid in the dispersed stable emulsion is 10%;

[0101] The dispersant includes inorganic solid particles and a thickener; the solid particles are lignin nanoparticles with a particle size of 50 nm; the thickener includes polyacrylamide with a molecular weight of 2 million;

[0102] The dispersing aid includes ethanol;

[0103] The volume ratio of the solid phase particles to ethanol is 10:1;

[0104] The concentration of the polyacrylamide in the dispersed stable emulsion is 0.7%;

[0105] The volume proportion of the ethanol in the dispersed stable emulsion is 20%;

[0106] The volume proportion of methane in the injected medium is 60%;

[0107] The hydrocarbons include crude oil and natural gas.

[0108] In this embodiment, the ratio of the viscosity of crude oil to the viscosity of the injected medium is between 0.5 and 1; the final crude oil recovery rate of the horizontal well is increased by 16% on the basis of cold recovery, reaching 24%.

[0109] Example 3

[0110] This embodiment provides a method for improving the recovery rate of a foam reservoir, wherein the foam reservoir satisfies the following conditions at the same time:

[0111] ① The residual dissolved gas-oil ratio of the foam reservoir is 10m 3 / m 3 ;

[0112] ② The foam reservoir has an oil layer thickness of 20 m, an oil saturation of 83%, a porosity of 33%, and a permeability of 5 Darcy;

[0113] ③ The foam reservoir is developed using a horizontal well pattern, with a horizontal section length of 800m and a horizontal well spacing of 300m, and a displacement relationship is established between adjacent wells;

[0114] The method comprises the following steps:

[0115] The dispersed stable emulsion and propane gas are injected into the foam reservoir through the injection well as injection media at the same time, and the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, reducing the formation pressure to between the bubble point pressure of 6.5 MPa and the pseudo-bubble point pressure of 4.5 MPa of the reservoir, displacing hydrocarbons in the underground reservoir to the production well of the foam reservoir to recover hydrocarbons, and recovering crude oil from the horizontal well;

[0116] The dispersed stable emulsion comprises a first liquid, a second liquid, a dispersant and a dispersing aid; the first liquid is composed of a homogeneous component of alkanes with a carbon number of 6 to 12;

[0117] The volume proportion of the first liquid in the dispersed stable emulsion is 30%;

[0118] The second liquid is a 1% caustic soda aqueous solution;

[0119] The volume proportion of the second liquid in the dispersed stable emulsion is 20%;

[0120] The dispersant includes inorganic solid phase particles and a thickener; the solid phase particles include silicon dioxide nanopowder with a particle size of 50nm; the thickener includes polyacrylamide with a molecular weight of 4 million;

[0121] The dispersing aid includes ethanol;

[0122] The volume ratio of the solid phase particles to ethanol is 30:1;

[0123] The concentration of the polyacrylamide in the dispersed stable emulsion is 0.8%;

[0124] The volume proportion of the ethanol in the dispersed stable emulsion is 10%;

[0125] The volume proportion of the propane in the injected medium is 40%;

[0126] The hydrocarbons include crude oil and natural gas.

[0127] In this embodiment, the ratio of the viscosity of crude oil to the viscosity of the injected medium is between 0.5 and 1; the final crude oil recovery rate of the horizontal well is increased by 15% on the basis of cold recovery, reaching 24%.

[0128] Example 4

[0129] This embodiment provides a method for improving the recovery rate of a foam reservoir, wherein the foam reservoir satisfies the following conditions at the same time:

[0130] ① The residual dissolved gas-oil ratio of the foam reservoir is 12m 3 / m 3 ;

[0131] ② The thickness of the oil layer in the foam reservoir is 12m, the oil saturation is 78%, the porosity is 33%, and the permeability is 5 Darcy;

[0132] ③ The foam reservoir is developed by a horizontal well pattern, with a horizontal section length of 1200m and a horizontal well spacing of 300m, and a displacement relationship is established between adjacent wells;

[0133] The method comprises the following steps:

[0134] The dispersed stable emulsion and natural gas are injected into the foam reservoir through the injection well as injection media at the same time, and the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, reducing the formation pressure to between the bubble point pressure of 6.5 MPa and the pseudo-bubble point pressure of 4.5 MPa of the reservoir, displacing hydrocarbons in the underground reservoir to the production well of the foam reservoir to recover hydrocarbons, and recovering crude oil from the horizontal well;

[0135] The dispersed stable emulsion comprises a first liquid, a second liquid, a dispersant and a dispersing aid; the first liquid is composed of a homogeneous component of aromatic hydrocarbons having a carbon number of 6 to 12;

[0136] The volume proportion of the first liquid in the dispersed stable emulsion is 40%;

[0137] The second liquid is a 2.5% caustic soda aqueous solution;

[0138] The volume proportion of the second liquid in the dispersed stable emulsion is 40%;

[0139] The dispersant includes inorganic solid phase particles and a thickener; the solid phase particles include silicon dioxide nanopowder with a particle size of 50nm; the thickener includes polyacrylamide with a molecular weight of 5 million;

[0140] The dispersing aid includes ethanol;

[0141] The volume ratio of the solid phase particles to ethanol is 25:1;

[0142] The concentration of the polyacrylamide in the dispersed stable emulsion is 1%;

[0143] The volume proportion of the ethanol in the dispersed stable emulsion is 10%;

[0144] The volume proportion of the natural gas in the injected medium is 10%;

[0145] The hydrocarbons include crude oil and natural gas.

[0146] In this embodiment, the ratio of the viscosity of crude oil to the viscosity of the injected medium is between 0.5 and 1; the final crude oil recovery rate of the horizontal well is increased by 19% on the basis of cold recovery, reaching 24%.

[0147] In summary, the method for improving the recovery factor of foam oil reservoirs provided by the present invention adopts a specific dispersed stable emulsion to increase the viscosity of the injection medium, reduces the fluidity ratio between the injection medium and the crude oil, and greatly improves the recovery factor of the crude oil by reducing the production pressure to between the bubble point pressure and the pseudo-bubble point pressure of the gas-bearing oil reservoir, and has a prospect for large-scale promotion and application.

[0148] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for improving the recovery rate of foam reservoirs, characterized in that: The foam reservoir satisfies the following conditions simultaneously: ① The residual dissolved gas-oil ratio of the foam reservoir is >5m 3 / m 3 ; ② The thickness of the oil layer of the foam reservoir is >3m, the oil saturation is >60%, the porosity is >30%, and the permeability is >1 Darcy; ③ The foam reservoir is developed by horizontal well pattern, with horizontal section length>400m, horizontal well spacing≤600m, and displacement relationship is established between adjacent wells; The method comprises the following steps: The dispersed stable emulsion and the gas are injected into the foam reservoir through the injection well as injection media at the same time, the gas is dissolved into the underground reservoir of the foam reservoir as a driving fluid, the formation pressure is reduced to between the bubble point pressure and the pseudo-bubble point pressure of the reservoir, the hydrocarbons in the underground reservoir are displaced to the production well of the foam reservoir to recover the hydrocarbons, and the crude oil is recovered from the horizontal well; The dispersed stable emulsion comprises a first liquid, a second liquid, a dispersant and a dispersing aid; the first liquid comprises light oil, castor oil or any one of alkanes / aromatics / alcohols / ethers with a carbon number of 6 to 12 or a combination of at least two thereof.

2. The method according to claim 1, characterized in that: The volume proportion of the first liquid in the dispersed stable emulsion is 10-40%.

3. The method according to claim 1 or 2, characterized in that: The second liquid includes any one of water, an emulsifier aqueous solution or a caustic soda aqueous solution, or a combination of at least two thereof; Preferably, the aqueous emulsifier solution includes an oil-in-water emulsifier at a concentration of 1 to 5%; Preferably, the concentration of the caustic soda aqueous solution is 1-5%.

4. The method according to any one of claims 1 to 3, characterized in that: The volume proportion of the second liquid in the dispersed stable emulsion is 10-40%.

5. The method according to any one of claims 1 to 4, characterized in that: The dispersant includes inorganic solid phase particles and a thickener; Preferably, the solid phase particles include silicon dioxide nanopowder and / or lignin nanoparticles; Preferably, the particle size of the solid phase particles is 1 to 200 nm. Preferably, the thickener comprises polyacrylamide with a molecular weight of 1 to 5 million.

6. The method according to any one of claims 1 to 5, characterized in that: The dispersing aid includes ethanol.

7. The method according to claim 5, characterized in that The volume ratio of the solid phase particles to ethanol is 3:1 to 30:1; Preferably, the concentration of the polyacrylamide in the dispersed stable emulsion is 0.5-1%; Preferably, the volume proportion of the ethanol in the dispersed stable emulsion is 10-40%.

8. The method according to any one of claims 1 to 7, characterized in that: The gas includes any one of nitrogen, methane, ethane, propane, butane, carbon dioxide, natural gas or flue gas, or a combination of at least two thereof.

9. The method according to any one of claims 1 to 8, characterized in that: The volume proportion of the gas in the injected medium is 10% to 70%.

10. The method according to any one of claims 1 to 9, characterized in that: The hydrocarbons include crude oil and / or natural gas.