Method for improving crude oil recovery ratio by microbe-CO2 combination flooding based on reservoir wettability change

Abstract

The invention relates to a method for improving the crude oil recovery rate based on microbe-CO2 combination flooding for changing the wettability of a reservoir. The method comprises the following steps: (1) carrying out a water-oil displacement experiment on a rock core; (2) alternately injecting a CO2 slug and a microbial solution slug into the rock core in the step (1), and carrying out standing culture when microorganisms appear at the extraction end; and (3) carrying out a water-oil displacement experiment on the rock core subjected to standing culture in the step (2). According to the method, microorganism flooding and CO2 flooding are combined, the synergistic effect of the microorganism flooding and the CO2 flooding is brought into full play, the reservoir wettability is improved and the interfacial tension is reduced through microorganisms while the advantage of improving the oil reservoir recovery rate through CO2 flooding is utilized, then the oil reservoir recovery rate is improved, and the oil displacement efficiency of the method is larger than or equal to 65%.

Description

Technical Field

[0001] The invention belongs to the technical field of tertiary oil recovery, and in particular relates to a method for improving crude oil recovery rate based on microorganism-CO2 composite flooding that changes reservoir wettability. Background Art

[0002] With the gradual depletion of easily exploitable oil and gas resources, my country's crude oil production has gradually decreased in recent years. Low-grade oil reservoir resources have become a strategic replacement resource with huge potential for oil, and are the main body of China's crude oil production. The main methods for improving the recovery of low-grade oil reservoirs include water flooding, polymer flooding and CO2 flooding.

[0003] Among them, CO2 flooding has many advantages in the development of low-grade oil reservoirs compared with other tertiary oil recovery technologies: (1) CO2 is easy to flow and it is easy to establish an effective displacement pressure system; (2) CO2 injection methods are flexible and can be applied to various formation conditions; (3) CO2 can be miscible with crude oil after injection, and has significant effects such as expansion, viscosity reduction, extraction, and reduction of interfacial tension, which can effectively expand the swept volume and thus improve the recovery rate. CO2 flooding can also be used to store CO2 underground for a long time, thereby reducing greenhouse gas emissions. CO2 flooding has good advantages and development prospects in improving oil recovery, and has become a hot topic of research in countries around the world. However, the effect of single CO2 flooding on improving oil recovery is limited. By improving the wettability of the reservoir, CO2 can be assisted in flooding the reservoir, which greatly affects the effect of gas flooding development.

[0004] If you want to further improve the displacement effect of CO2 flooding, you need to improve the wettability of the reservoir. However, chemical agents have been widely used at home and abroad to improve the wettability of the reservoir. CN105952425A discloses a method for improving the recovery rate of ordinary heavy oil reservoirs by chemical-assisted CO2 huffing and puffing. The method combines chemical agents with CO2 huffing and puffing, and first injects a viscosity-reducing chemical agent or a foaming agent chemical solution segment into an oil well that has undergone too many rounds of CO2 huffing and puffing, and then injects a high-pressure CO2 segment into the well, and then the injection is completed. After the injection is completed, it is statically cultured. During static culture, the viscosity-reducing chemical agent forms an oil-in-water emulsion with ordinary heavy oil, which can greatly reduce the oil-water interfacial tension and reduce the flow resistance of crude oil during production. However, the cost of using chemical agents is high and the environmental pollution is more serious.

[0005] Therefore, based on improving reservoir wettability, establishing a low-cost, green and environmentally friendly composite CO2 flooding method for improving crude oil recovery is an urgent problem that technicians in this field need to solve. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing the wettability of the reservoir. The method combines CO2 flooding and microbial flooding as two means of improving crude oil recovery, gives full play to the synergistic effect of various technologies, realizes high-efficiency and low-cost exploitation of crude oil to a certain extent, creates a good ecological environment and higher economic benefits, and provides a reference for indoor experimental research and field development.

[0007] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability, the method comprising the following steps:

[0009] (1) Conduct water flooding experiments on cores;

[0010] (2) alternately injecting CO2 plugs and microbial solution plugs into the core of step (1), and culturing the core when microorganisms appear at the production end;

[0011] (3) Conducting a water flooding experiment on the core after the static culture described in step (2).

[0012] The method of the present invention combines the functional microbial bacteria (or metabolites) that change the wettability of the reservoir with CO2 flooding, giving full play to the synergistic effect of various technologies, increasing the ability of CO2 to mix with oil, making crude oil easier to be displaced, and thus achieving the effect of improving crude oil recovery, providing a reference for indoor experimental research and field development.

[0013] As a preferred technical solution of the present invention, the displacement rate of the water-to-oil experiment in step (1) is 0.01-0.5 mL / min, for example, it can be 0.05 mL / min, 0.1 mL / min, 0.15 mL / min, 0.2 mL / min, 0.25 mL / min, 0.3 mL / min, 0.35 mL / min, 0.4 mL / min or 0.45 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0014] In the present invention, the displacement rate of the water-to-oil experiment needs to be determined according to the core permeability.

[0015] Preferably, the endpoint of the water drive experiment in step (1) is: the water content at the production end is ≥98%, for example, it can be 98.2%, 98.4%, 98.6%, 98.8%, 99%, 99.2%, 99.4% or 99.6%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] As a preferred technical solution of the present invention, the microbial solution slug in step (2) includes an aqueous solution containing functional microbial bacteria.

[0017] Preferably, the functional microorganisms include microorganisms with a fast reproduction rate and / or microorganisms that metabolize to produce biosurfactants, preferably Bacillus subtilis.

[0018] Preferably, the rapidly multiplying microorganisms are those whose concentration increases from 10 to 10 within 12-24 hours. 6 / mL multiply to 10 8 More than pcs / mL.

[0019] In the present invention, the biosurfactant produced by the metabolism of Bacillus subtilis is lipopeptide.

[0020] It is worth noting that microorganisms can improve reservoir wettability by producing biosurfactants through biological reproduction or metabolism. Compared with the use of chemical agents to act on the reservoir in the prior art, microorganisms can effectively reduce the environmental damage caused by the oil recovery process and have good development prospects. Therefore, using microorganisms to change reservoir wettability and assist CO2 flooding can further improve the recovery rate.

[0021] In the present invention, the microbial functional bacteria need to be screened to ensure good compatibility with the reservoir / fluid conditions of the target oil reservoir. The microbial functional bacteria that can change the wettability of the reservoir must meet one of the following conditions: 1. Able to reproduce in large quantities, the microorganisms attached to the reservoir rock reproduce in large quantities, so that the microorganisms grow on the rock surface and form colonies. The colonies become a natural barrier to hinder the contact between crude oil and rock, thereby changing the wettability of the reservoir, increasing the ability of CO2 to mix with oil, making crude oil easier to be displaced, and ultimately improving the recovery rate of crude oil; 2. Able to generate biosurfactants. The biosurfactants generated by the metabolism of microbial functional bacteria can also assist CO2 flooding and further improve the recovery rate of CO2 flooding.

[0022] In the present invention, the functional microorganisms can be selected from species that grow widely in the natural environment, or engineered bacteria can be constructed through bioengineering, genetic engineering, and gene engineering according to the reservoir and fluid characteristics of the oil reservoir, but natural species are preferred to avoid harm to the human body and the environment.

[0023] As a preferred technical solution of the present invention, the concentration of the microbial solution in step (2) is 10 5 -10 7 / mL, for example, 3×10 5 / mL, 5×10 5 / mL, 7×10 5 / mL, 1×106 / mL, 3×10 6 / mL, 5×10 6 / mL or 7×10 6 However, it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, the injection method of the microbial solution slug in step (2) includes the following situations:

[0025] (1) When the permeability of the core is ≥20 mD, directly inject the microbial solution; or

[0026] (2) When the permeability of the core is less than 20 mD, a biosurfactant solution generated by external metabolism of microbial functional bacteria is injected, wherein the concentration of the biosurfactant solution is 2-10 g / L.

[0027] In the present invention, the concentration of the biosurfactant solution is 2-10 g / L, for example, it can be 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L or 8 g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the volume of the CO2 plug in step (2) is 0.04-0.08HCPV, for example, it can be 0.05HCPV, 0.06HCPV, 0.07HCPV or 0.08HCPV, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the volume ratio of the CO2 plug to the microbial plug in step (2) is 1:2-2:1, for example, it can be 1:3, 1:2, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] As a preferred technical solution of the present invention, the speed of the alternating injection in step (2) is 0.01-0.5 mL / min, for example, it can be 0.05 mL / min, 0.1 mL / min, 0.15 mL / min, 0.2 mL / min, 0.25 mL / min, 0.3 mL / min, 0.35 mL / min, 0.4 mL / min or 0.45 mL / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 0.01-0.1 mL / min.

[0031] Preferably, the static culture time in step (2) is ≥ 3 days, for example, it can be 3.5 days, 4 days, 4.5 days, 5 days, 6 days, 7 days, 8 days or 10 days, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 5-10 days.

[0032] As a preferred technical solution of the present invention, the displacement rate of the water-to-oil experiment in step (3) is 0.01-0.5 mL / min, for example, it can be 0.05 mL / min, 0.1 mL / min, 0.15 mL / min, 0.2 mL / min, 0.25 mL / min, 0.3 mL / min, 0.35 mL / min, 0.4 mL / min or 0.45 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the oil recovery efficiency of the method is ≥65%, for example, it can be 65%, 66%, 67%, 68%, 69%, 70% or 72%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] As a preferred technical solution of the present invention, the method comprises the following steps:

[0035] (1) Conduct water-to-oil flooding experiments on the core at a displacement rate of 0.01-0.5 mL / min until the water content at the production end is ≥98%;

[0036] (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:2-2:1 at a rate of 0.01-0.5 mL / min, and culturing the core when microorganisms appear at the production end;

[0037] The microbial solution slug is an aqueous solution containing microbial functional bacteria; the microbial functional bacteria include microbial bacteria that multiply rapidly and / or microbial bacteria that metabolize to produce biosurfactants; the concentration of the microbial solution is 10 5 -10 7 Pieces / mL;

[0038] The volume of the CO2 slug is 0.04-0.08 HCPV;

[0039] The static culture time is ≥ 3 days;

[0040] (3) performing a water-to-oil displacement experiment on the core after the static culture in step (2) at a displacement rate of 0.01-0.5 mL / min;

[0041] The oil recovery efficiency of the method is ≥65%.

[0042] The present invention also provides a practical application method of microbial-CO2 composite flooding, which utilizes the best microbial functional bacteria for changing reservoir wettability and the best displacement method obtained in the above method, and is enlarged and applied to actual oil field and mine development according to similar principles (such as determining the injection amount (segment size, concentration of microbial solution), injection timing, injection rounds and injection segment ratio of the reservoir based on the pore volume of the experimental rock).

[0043] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The method of the present invention combines microbial flooding with CO2 flooding to give full play to the synergistic effect of the two. While utilizing the advantages of CO2 flooding to improve oil reservoir recovery, microorganisms are used to improve reservoir wettability and reduce interfacial tension, thereby improving oil reservoir recovery. The oil recovery efficiency of the method is ≥65%;

[0046] (2) The method provided by the present invention provides a theoretical basis for the study of the mechanism of improving reservoir wettability by microbial functional bacteria and CO2 composite displacement to improve oil recovery. At the same time, through similar principles, the displacement mode of the best functional bacteria for improving reservoir wettability and the best microbial-CO2 composite displacement for improving reservoir wettability obtained in the indoor evaluation experiment is enlarged and applied to real oil reservoirs, forming a mine development method, which is convenient for direct application on the oil field site;

[0047] (3) The method of the present invention can flexibly adjust the displacement mode of the reservoir wettability-improving microbial functional bacteria-CO2 composite drive according to the development effect of the same oil reservoir and the characteristics of different oil reservoirs, and has universal applicability. DETAILED DESCRIPTION

[0048] 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.

[0049] Example 1

[0050] This embodiment provides a method for improving crude oil recovery based on microbial-CO2 composite flooding that changes reservoir wettability, the method comprising the following steps:

[0051] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0052] The water permeability of the core is 28.3956 mD, and the size is 2.517 cm in diameter × 18.064 cm in length;

[0053] (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:1 at a rate of 0.15 mL / min, and performing static culture for 5 days when microorganisms appear at the production end;

[0054] The microbial solution slug is an aqueous solution containing microbial functional bacteria; the microbial functional bacteria is Bacillus subtilis; the concentration of the microbial solution is 10 6 Pieces / mL;

[0055] The volume of the CO2 slug is 0.05HCPV;

[0056] (3) A water-to-oil displacement experiment was performed on the core after static culture in step (2) at a displacement rate of 0.2 mL / min.

[0057] Example 2

[0058] This embodiment provides a method for improving crude oil recovery based on microbial-CO2 composite flooding that changes reservoir wettability, the method comprising the following steps:

[0059] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0060] The water permeability of the core is 41.3085 mD, and the dimensions are 2.449 cm in diameter × 18.114 cm in length;

[0061] (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:2 at a rate of 0.15 mL / min, and performing static culture for 7 days when microorganisms appear at the production end;

[0062] The microbial solution slug is an aqueous solution containing microbial functional bacteria; the microbial functional bacteria is Bacillus subtilis; the concentration of the microbial solution is 5×10 6 Pieces / mL;

[0063] The volume of the CO2 slug is 0.06HCPV;

[0064] (3) A water-to-oil displacement experiment was performed on the core after static culture in step (2) at a displacement rate of 0.2 mL / min.

[0065] Example 3

[0066] This embodiment provides a method for improving crude oil recovery based on microbial-CO2 composite flooding that changes reservoir wettability, the method comprising the following steps:

[0067] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0068] The water permeability of the core is 7.3489 mD, and the size is 2.441 cm in diameter × 18.319 cm in length;

[0069] (2) injecting CO2 plugs and microbial solution plugs alternately at a volume ratio of 1:1 at a rate of 0.15 mL / min into the core of step (1), and when microorganisms appear at the production end, performing static cultivation for 7 days;

[0070] The microbial solution slug is a biosurfactant solution generated by external metabolism of microbial functional bacteria; the microbial functional bacteria is Bacillus subtilis; the concentration of the biosurfactant solution is 5g / L;

[0071] The volume of the CO2 slug is 0.05HCPV;

[0072] (3) A water-to-oil displacement experiment was performed on the core after static culture in step (2) at a displacement rate of 0.2 mL / min.

[0073] Example 4

[0074] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability, except that the concentration of the microbial solution in step (2) is 10 4 Except for the concentration of 1 μg / mL, other conditions were the same as those in Example 1.

[0075] Example 5

[0076] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability, except that the concentration of the microbial solution in step (2) is 10 8 Except for the concentration of 1 μg / mL, other conditions were the same as those in Example 1.

[0077] Example 6

[0078] This embodiment provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability. Except that the volume ratio of the CO2 plug to the microbial solution plug in step (2) is 1:0.3, other conditions are the same as those in Example 1.

[0079] Example 7

[0080] This embodiment provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability. Except that the volume ratio of the CO2 plug to the microbial solution plug in step (2) is 1:3, other conditions are the same as those in Example 1.

[0081] Example 8

[0082] This embodiment provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability. Except that the microbial functional bacteria in step (2) is Pseudomonas stutzeri, other conditions are the same as those in Example 1.

[0083] Example 9

[0084] This embodiment provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability. Except for the static culture time of 2 days in step (2), other conditions are the same as those in Example 1.

[0085] Comparative Example 1

[0086] This comparative example provides a method for improving oil recovery by using CO2 flooding, the method comprising the following steps:

[0087] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0088] The water permeability of the core is 28.6679 mD, and the size is 2.449 cm in diameter × 18.689 cm in length;

[0089] (2) injecting CO2 gas into the core of step (1) at a rate of 0.15 mL / min until the gas-oil ratio is greater than 1300;

[0090] (3) A water flooding experiment was performed on the core after CO2 flooding in step (2) at a displacement rate of 0.2 mL / min.

[0091] Comparative Example 2

[0092] This comparative example provides a method for improving oil recovery by microbial flooding, the method comprising the following steps:

[0093] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0094] The water permeability of the core is 29.0356 mD, and the dimensions are 2.448 cm in diameter × 18.172 cm in length;

[0095] (2) injecting the microbial solution into the core of step (1) at a rate of 0.15 mL / min, and performing static culture for 5 days when microorganisms appear at the extraction end;

[0096] The microbial solution is an aqueous solution containing microbial functional bacteria; the microbial functional bacteria is Bacillus subtilis; the concentration of the microbial solution is 10 6 Pieces / mL;

[0097] (3) A water-to-oil displacement experiment was performed on the core after static culture in step (2) at a displacement rate of 0.2 mL / min.

[0098] Comparative Example 3

[0099] This comparative example provides a method for improving crude oil recovery based on microbial-CO2 composite flooding that changes reservoir wettability, the method comprising the following steps:

[0100] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0101] The water permeability of the core is 30 mD, and the size is 2.526 cm in diameter × 18.418 cm in length;

[0102] (2) injecting the microbial solution into the core of step (1) at a rate of 0.15 mL / min, and performing static culture for 5 days when microorganisms appear at the extraction end;

[0103] The microbial solution is an aqueous solution containing microbial functional bacteria; the microbial functional bacteria is Bacillus subtilis; the concentration of the microbial solution is 10 6 Pieces / mL;

[0104] (3) injecting CO2 gas into the core after the static culture in step (2) at a rate of 0.15 mL / min until the gas-oil ratio is greater than 1300;

[0105] (4) Carry out a water-to-oil drive experiment on the core after CO2 displacement in step (3) at a displacement rate of 0.2 mL / min.

[0106] Comparative Example 4

[0107] This comparative example provides a method for improving oil recovery by using CO2 flooding, the method comprising the following steps:

[0108] (1) A water-to-oil experiment was conducted on the core at a displacement rate of 0.2 mL / min until the water content at the production end reached 98.5%;

[0109] The water permeability of the core is 31.2895 mD, and the dimensions are 2.448 cm in diameter × 18.172 cm in length;

[0110] (2) injecting a plug of CO2 and formation water solution into the core of step (1) at a volume ratio of 1:1 at a rate of 0.15 mL / min until CO2 gas is seen at the production end;

[0111] The volume of the CO2 slug is 0.05HCPV;

[0112] (3) A water-to-oil displacement experiment was performed on the core after static culture in step (2) at a displacement rate of 0.2 mL / min.

[0113] Comparative Example 5

[0114] This comparative example provides a method for improving crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability. Except that no microorganisms appear at the production end in step (2) and static culture is performed for 5 days when the gas-oil ratio is greater than 1300, other conditions are the same as those in Example 1.

[0115] The oil recovery efficiency results of the methods described in the above embodiments and comparative examples are shown in Table 1, where recovery factor = sweep coefficient × oil recovery efficiency.

[0116] Table 1

[0117]

[0118]

[0119] From Table 1, we can draw the following conclusions:

[0120] (1) The method provided in Examples 1-3 of the present invention has an oil displacement efficiency of ≥65%, which significantly improves the recovery rate and realizes high-efficiency and low-cost exploitation of crude oil;

[0121] (2) Based on Example 1, Examples 4-5, and Comparative Example 4 (equivalent to a microbial concentration of 0), it can be seen that when the concentration of the injected microbial solution is low, the metabolites produced by the small number of microorganisms have a poor effect on the change of reservoir wettability, resulting in a low improvement in the oil recovery efficiency of crude oil; when the concentration of the injected microbial solution is high, the microorganisms form a filter cake (microorganism accumulation) at the injection end due to the excessive number of microorganisms, which makes it difficult to inject into the rock, or the microorganisms are too large to penetrate into the fine pores of the core, resulting in the microorganisms failing to fully exert their effects, resulting in a low improvement in the oil recovery efficiency of crude oil;

[0122] (3) It can be seen from Example 1 and Examples 6-7 that when the volume ratio of the CO2 slug to the microbial solution slug is too high, the microbial effect is not obvious due to less microbial injection, and the improvement effect on the wettability of the reservoir is insufficient, resulting in an insignificant improvement in the oil displacement efficiency of crude oil; when the volume ratio of the CO2 slug to the microbial solution slug is too low, the CO2 injection is less, resulting in the CO2 flooding effects on crude oil expansion, viscosity reduction, extraction, and reduction of interfacial tension cannot be fully reflected, resulting in an insignificant improvement in the oil displacement efficiency of crude oil;

[0123] (4) Based on Example 1 and Example 8, it can be seen that when the microbial functional bacteria are replaced with Pseudomonas stutzeri, the oil recovery efficiency of crude oil is not significantly improved because Pseudomonas stutzeri does not have the ability to rapidly reproduce or metabolize to produce biosurfactants;

[0124] (5) Based on Example 1 and Comparative Examples 1-2, it can be seen that although the displacement of microorganisms or CO2 alone can improve the oil recovery efficiency of CO2 to a certain extent, its effect of improving recovery is much different from that of composite displacement; Based on Example 1 and Comparative Example 3, it can be seen that the method provided by the present invention is different from the sequential microbial flooding and CO2 flooding because the core is not flooded by a plug method. Therefore, although the microorganisms improve the wettability of the reservoir, CO2 as a gas is prone to gas channeling. Once a dominant channel is formed, it is difficult to displace the crude oil in other positions in the core, resulting in an insignificant improvement in the oil recovery efficiency of crude oil;

[0125] (6) Based on Example 1 and Comparative Example 5, it can be seen that when static cultivation is carried out when no microorganisms appear at the production end, the microorganisms cannot spread throughout the entire core, so the reservoir wettability at the end of the core cannot be well improved, resulting in the oil recovery efficiency of crude oil not being significantly improved.

[0126] 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 crude oil recovery by microbial-CO2 composite flooding based on changing reservoir wettability, characterized in that: The method comprises the following steps: (1) Conduct water flooding experiments on cores; (2) alternately injecting CO2 plugs and microbial solution plugs into the core of step (1), and culturing the core when microorganisms appear at the production end; (3) Conducting a water flooding experiment on the core after the static culture described in step (2).

2. The method according to claim 1, characterized in that The displacement rate of the water-to-oil experiment in step (1) is 0.01-0.5 mL / min; Preferably, the endpoint of the water drive experiment in step (1) is: the water content at the production end is ≥ 98%.

3. The method according to claim 1 or 2, characterized in that: The microbial solution slug in step (2) includes an aqueous solution containing functional microbial bacteria; Preferably, the functional microorganisms include rapidly multiplying microorganisms and / or microorganisms that metabolize to produce biosurfactants, preferably Bacillus subtilis; Preferably, the rapidly multiplying microorganisms are those whose concentration increases from 10 to 10 within 12-24 hours. 6 / mL multiply to 10 8 More than pcs / mL.

4. The method according to any one of claims 1 to 3, characterized in that: The concentration of the microbial solution in step (2) is 10 5 -10 7 Pieces / mL.

5. The method according to any one of claims 1 to 4, characterized in that: The injection method of the microbial solution slug in step (2) includes the following situations: (1) When the permeability of the core is ≥20 mD, directly inject the microbial solution; or (2) When the permeability of the core is less than 20 mD, a biosurfactant solution generated by external metabolism of microbial functional bacteria is injected, wherein the concentration of the biosurfactant solution is 2-10 g / L.

6. The method according to any one of claims 1 to 5, characterized in that: The volume of the CO2 slug in step (2) is 0.04-0.08 HCPV; Preferably, the volume ratio of the CO2 slug to the microbial slug in step (2) is 1:2-2:

1.

7. The method according to any one of claims 1 to 6, characterized in that: The speed of the alternating injection in step (2) is 0.01-0.5 mL / min, preferably 0.01-0.1 mL / min; Preferably, the static culture time in step (2) is ≥ 3 days, preferably 5-10 days.

8. The method according to any one of claims 1 to 7, characterized in that: The displacement rate of the water-to-oil experiment in step (3) is 0.01-0.5 mL / min.

9. The method according to any one of claims 1 to 8, characterized in that: The oil recovery efficiency of the method is ≥65%.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) Conduct water-to-oil flooding experiments on the core at a displacement rate of 0.01-0.5 mL / min until the water content at the production end is ≥98%; (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:2-2:1 at a rate of 0.01-0.5 mL / min, and culturing the core when microorganisms appear at the production end; The microbial solution slug is an aqueous solution containing microbial functional bacteria; the microbial functional bacteria include rapidly multiplying microbial bacteria and / or microbial bacteria that metabolize to produce biosurfactants; the concentration of the microbial solution is 10 5 -10 7 Pieces / mL; The volume of the CO2 slug is 0.04-0.08 HCPV; The static culture time is ≥ 3 days; (3) performing a water-to-oil displacement experiment on the core after the static culture in step (2) at a displacement rate of 0.01-0.5 mL / min; The oil recovery efficiency of the method is ≥65%.

Images