Microbial CO2 combination flooding recovery efficiency improving method based on improvement of gas flooding microcosmic swept volume

Abstract

The invention provides a microbial CO2 combination flooding recovery efficiency improving method based on gas flooding microcosmic swept volume improvement. The method comprises the following steps: (1) carrying out a water-oil displacement experiment on a rock core; (2) a CO2 slug and a microbial solution slug are alternately injected into the core in the step (1), the CO2 slug is injected for the first time, and when microorganisms appear in produced liquid, standing culture treatment is carried out; (3) performing a water-oil displacement experiment on the rock core subjected to the standing culture treatment in the step (2); the microbial solution slug in the step (2) comprises first microbial functional bacteria with rapid propagation capability and / or second microbial functional bacteria with biopolymer generation capability. According to the method, microbial functional bacteria strains (or metabolites) capable of improving gas flooding microscopic waves and volumes are combined with CO2 flooding, so that the synergistic effect of various technologies is fully exerted, the effect of improving the crude oil recovery rate is further achieved, and reference is provided for indoor experimental research and field development.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum development, relates to a technical field of tertiary oil recovery, and in particular to a method for improving the recovery rate of microorganism-CO2 composite flooding based on increasing the microscopic swept volume of gas drive. Background Art

[0002] With the 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 great potential for oil, and are the main source of my country's crude oil production. However, the traditional method of improving oil recovery is not ideal for the development of low-grade oil reservoirs, and a new method is urgently needed to further improve oil recovery.

[0003] Compared with other tertiary oil recovery technologies, CO2 flooding has many advantages in the development of low-grade oil reservoirs: (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) After injection, CO2 can be miscible with crude oil, 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 store CO2 underground for a long time, thereby reducing greenhouse gas emissions.

[0004] 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, CO2 is prone to gas channeling during the displacement process, which leads to a reduction in the swept volume of the gas drive, greatly affecting the effect of gas drive development. Therefore, if you want to further improve the displacement effect of CO2 flooding, you need to start with the above problems, use reasonable methods to plug and adjust the dominant channels, reduce the impact of gas channeling on the recovery rate, and achieve certain results.

[0005] However, the chemical polymers and other methods currently used at home and abroad are mainly used for macroscopic heterogeneity profile control, and it is difficult to carry out microscopic heterogeneity profile control. The chemical agents used are expensive and cause serious environmental pollution. Microorganisms can make up for this shortcoming. They can produce biopolymers through their own large-scale reproduction or metabolism to carry out microscopic heterogeneity plugging, increase the microscopic swept volume of gas drive, and enhance the profile control effect of water-gas alternation. Compared with the use of chemical polymers and other methods to act on the reservoir, microorganisms can effectively reduce the environmental damage caused by the oil production process and have good development prospects. Therefore, in the development process, the use of microbial functional bacteria that can increase the microscopic swept volume of gas drive to act on the reservoir can alleviate the impact of CO2 gas channeling on the recovery rate. However, both domestic and foreign technologies for improving the recovery rate of single CO2 drive or microbial drive have been widely studied, and the mechanism of improving the recovery rate is relatively clear, but there is a lack of research on using microorganisms to increase the microscopic swept volume of gas drive and assist CO2 drive.

[0006] Based on the above reasons, it is necessary to establish a method for improving oil recovery by microbial-CO2 composite drive based on increasing the microscopic swept volume of gas drive, select microbial functional bacteria that can increase the microscopic swept volume of gas drive for composite action with CO2, combine the two methods of improving oil recovery, CO2 drive and microbial drive, give full play to the synergistic effect of various technologies, to a certain extent achieve high-efficiency and low-cost exploitation of crude oil, create a good ecological environment and higher economic benefits, and provide a reference for indoor experimental research and field development. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas drive. The present invention combines the microbial functional bacteria strain (or metabolites) for increasing the microscopic swept volume of gas drive with CO2 flooding to give full play to the synergistic effect of various technologies, thereby achieving the effect of improving crude oil recovery, and providing a reference for indoor experimental research and field development.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for improving oil recovery by using microorganism-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding, the method comprising the following steps:

[0010] (1) Conduct water flooding experiments on cores;

[0011] (2) alternately injecting CO2 plugs and microbial solution plugs into the core of step (1), and injecting the CO2 plugs for the first time, and performing static culture treatment when microorganisms appear in the produced fluid;

[0012] (3) performing a water flooding experiment on the core after the static culture treatment in step (2);

[0013] The microbial solution slug in step (2) includes the first microbial functional bacteria and / or the second microbial functional bacteria;

[0014] The first functional microorganism has the ability to reproduce rapidly; the second functional microorganism has the ability to generate biopolymers.

[0015] The present invention combines the microbial functional bacteria strains (or metabolites) that increase the microscopic swept volume of gas drive with CO2 drive, giving full play to the synergistic effect of various technologies, thereby achieving the effect of improving crude oil recovery, and providing a reference for indoor experimental research and field development.

[0016] It is worth noting that the mechanism of action of the first microbial functional bacteria with rapid reproduction ability described in the present invention is: most oil reservoirs are heterogeneous under natural conditions. Since CO2 is easy to flow, it is also easier to establish a dominant seepage channel in the reservoir pores, thereby causing gas channeling. This will result in only a small amount of crude oil being displaced from the low permeability area of ​​the oil reservoir, so the final recovery rate is not high. Since microorganisms have a certain shape and size, and they also need a certain space to survive, the large-scale reproduction and aggregation of microorganisms can often form directional selective blockages in large pores with higher reservoir permeability, thereby achieving the purpose of profile adjustment, thereby achieving an increase in the microscopic swept volume of gas drive and improving the recovery rate of oil reservoirs.

[0017] The first microbial functional bacteria provided by the present invention can selectively form blockages in large pores with high reservoir permeability; chemical reagents cannot achieve directional selection and may ignore large pores, resulting in failure to achieve blockage.

[0018] The mechanism of action of the second microbial functional bacteria capable of generating biopolymers described in the present invention is that certain biological products such as biopolymers can also selectively block large pores in the oil layer, and at the same time can reduce the oil-water mobility ratio, thereby expanding the swept volume and improving the recovery rate. For low-permeability and dense oil reservoirs that are difficult for microorganisms to inject or oil reservoirs that are not suitable for microorganisms to survive, biopolymers produced by microorganisms after metabolism outside the oil reservoir can also be injected to achieve the purpose of selective blocking. At the same time, compared with traditional chemical polymers, biopolymers will not pollute the reservoir and are more environmentally friendly.

[0019] As a preferred technical solution of the present invention, the permeability of the core in step (1) is ≥20mD, for example, it can be 20mD, 22mD, 24mD, 26mD, 28mD or 30mD, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] As a preferred technical solution of the present invention, the displacement rate of the water-to-oil experiment in step (1) is 0.01 to 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.

[0021] As a preferred technical solution of the present invention, the endpoint of the water drive oil experiment in step (1) is: the water content of the produced fluid is ≥98%, for example, it can be 98.2%, 98.4%, 98.6%, 98.8%, 99%, 99.2%, 99.4% or 99.6%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] As a preferred technical solution of the present invention, the reproduction rate of the first microbial functional bacteria is that the bacterial concentration increases from 10 to 10 within 12-24 hours. 6 / mL multiply to 10 8 More than pcs / mL.

[0023] Preferably, the second microbial functional bacteria include Xanthomonas campestris.

[0024] It is worth noting that the functional microorganisms described in the present invention should preferably come from the target oil reservoir where the oil recovery rate is to be further improved, so as to ensure good compatibility with the reservoir / fluid conditions of the target oil reservoir. It is also possible to select strains that grow widely in the natural environment, or to construct engineered bacteria through bioengineering, genetic engineering, and genetic engineering according to the reservoir and fluid characteristics of the oil reservoir, but it is best to give priority to natural strains to avoid harm to the human body and the environment, and at the same time, functional bacteria strains other than the target oil reservoir must be tested and screened for compatibility.

[0025] 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, 1×10 6 / mL, 3×10 6 / mL, 5×10 6 / mL or 7×10 6 Pieces / mL, but not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0026] As a preferred technical solution of the present invention, the volume of the CO2 plug in step (2) is 0.04-0.1HCPV, for example, it can be 0.05HCPV, 0.06HCPV, 0.07HCPV, 0.08HCPV, 0.09HCPV or 0.1HCPV, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the volume ratio of the CO2 plug to the microbial plug in step (2) is 1:(0.3-3), for example, it can be 1:1, 1:2, 1:3, 2:1 or 3:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the speed of the alternating injection in step (2) is 0.01-0.1 mL / min, for example, 0.02 mL / min, 0.04 mL / min, 0.06 mL / min or 0.08 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; preferably, it is 0.03-0.08 mL / min.

[0029] Preferably, the static culture treatment 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, and other values ​​not listed in the numerical range are also applicable; preferably 5 to 10 days;

[0030] Preferably, the temperature of the static culture treatment in step (2) is 20-65°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C or 65°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 25-45°C.

[0031] 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.

[0032] Preferably, the oil displacement effect of the method is ≥ 65%, for example, it can be 67%, 69%, 71%, 73% or 75%, 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 method provided by the present invention for improving oil reservoir recovery by changing the microscopic sweep volume of gas drive by microorganisms comprises the following steps:

[0034] (1) conducting a water-to-oil drive experiment on the core at a displacement rate of 0.01 to 0.5 mL / min until the water content of the produced fluid is ≥ 98%; and the permeability of the core is ≥ 20 mD;

[0035] (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:(0.3-3) at a rate of 0.01-0.1 mL / min, and when the CO2 plugs are injected for the first time, when microorganisms appear in the produced fluid, performing a static culture treatment for ≥3 days;

[0036] The microbial solution slug contains the first microbial functional bacteria and / or the second microbial functional bacteria; the first microbial functional bacteria has the ability to reproduce rapidly, and the reproduction rate is that the bacterial concentration increases from 10 to 10 within 12-24 hours. 6 / mL to 10 8 The second microbial functional bacteria is Xanthomonas campestris having the ability to produce biopolymers;

[0037] The concentration of the microbial solution is 10 5 -10 7 Pieces / mL;

[0038] The volume of the CO2 slug is 0.04-0.1 HCPV;

[0039] (3) performing a water flooding experiment on the core after the static culture treatment in step (2) at a displacement rate of 0.01-0.5 mL / min.

[0040] The present invention also provides a method for actual mine application of microbial-CO2 composite drive to improve oil recovery based on increasing the microscopic swept volume of gas drive, specifically comprising: utilizing the best functional bacteria for improving the microscopic swept volume of gas drive and the best displacement method obtained in the experimental evaluation, and scaling up the application to actual oil field mine development according to similar principles (such as determining the injection volume (segment size, microbial concentration), injection timing, injection rounds and injection segment ratio of the reservoir based on the pore volume of the experimental rock).

[0041] 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.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The present invention combines microbial flooding with CO2 flooding. While utilizing the advantages of CO2 flooding to improve oil reservoir recovery, the present invention uses microorganisms to block the advantageous channels that CO2 easily forms during the displacement process, thereby reducing the impact of gas channeling, increasing the microscopic swept volume of gas flooding, and thus improving the recovery rate of CO2 flooding in oil reservoirs.

[0044] (2) In terms of indoor experimental evaluation, the present invention provides a complete set of process methods for studying the mechanism of improving the recovery rate of microbial functional bacteria and CO2 composite displacement for improving the microscopic swept volume of gas drive, as well as the evaluation of the optimal functional bacteria for improving the microscopic swept volume of gas drive and the microbial-CO2 composite displacement mode for improving the microscopic swept volume of gas drive;

[0045] (3) The present invention can, through similar principles, enlarge and apply the optimal functional bacteria for improving the microscopic swept volume of gas drive and the optimal microorganism-CO2 composite flooding method for improving the microscopic swept volume of gas drive obtained from indoor evaluation experiments to real oil reservoirs, forming a mine development method, which is convenient for direct application on the oil field site;

[0046] (4) The present invention can flexibly adjust the displacement mode of microbial functional bacteria-CO2 composite drive to improve the microscopic wave volume of gas drive according to the development effect of the same oil reservoir and the characteristics of different oil reservoirs, and has universal applicability. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by specific implementation methods. 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.

[0048] Example 1

[0049] This embodiment provides a method for improving oil recovery by using microorganism-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding, the method comprising the following steps:

[0050] (1) conducting a water-to-oil experiment on the core at a displacement rate of 0.3 mL / min until the water content of the produced fluid is 98.6%; the permeability of the core is 28.5034 mD;

[0051] (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 0.06 mL / min, and injecting the CO2 plugs for the first time, and when microorganisms appear in the produced fluid, performing a static culture treatment for 5 days;

[0052] The microbial solution slug contains a second microbial functional bacterium; the second microbial functional bacterium is Xanthomonas campestris having the ability to produce biopolymers;

[0053] The concentration of the microbial solution is 10 6 Pieces / mL;

[0054] The volume of the CO2 slug is 0.06HCPV;

[0055] (3) A water flooding experiment was performed on the core after the static culture treatment in step (2) at a displacement rate of 0.25 mL / min.

[0056] Example 2

[0057] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding, the method comprising the following steps:

[0058] (1) conducting a water-to-oil experiment on the core at a displacement rate of 0.01 mL / min until the water content of the produced fluid is ≥ 98%; the permeability of the core is 20.4867 mD;

[0059] (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 2:1 at a rate of 0.01 mL / min, and injecting the CO2 plugs for the first time, and when microorganisms appear in the produced fluid, performing a static culture treatment for 6 days;

[0060] The microbial solution slug contains a first microbial functional bacteria; the first microbial functional bacteria has the ability to reproduce rapidly, and its reproduction rate is from 10 to 10 within 12-24 hours. 6 / mL multiply to 10 8 Particles / mL or more;

[0061] The concentration of the microbial solution is 10 5 / mL;

[0062] The volume of the CO2 slug is 0.04HCPV;

[0063] (3) A water flooding experiment was performed on the core after the static culture treatment in step (2) at a displacement rate of 0.01 mL / min.

[0064] Example 3

[0065] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding, the method comprising the following steps:

[0066] (1) conducting a water-to-oil experiment on the core at a displacement rate of 0.5 mL / min until the water content of the produced fluid is 99.8%; the permeability of the core is 39.1973 mD;

[0067] (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:3 at a rate of 0.1 mL / min, and injecting the CO2 plugs for the first time, and when microorganisms appear in the produced fluid, performing a static culture treatment for 7 days;

[0068] The microbial solution slug contains a first microbial functional bacterium and a second microbial functional bacterium; the first microbial functional bacterium has the ability to reproduce rapidly, and its reproduction speed is 10% to 20% within 12-24 hours. 6 / mL multiply to 10 8 The second microbial functional bacteria is Xanthomonas campestris having the ability to produce biopolymers;

[0069] The concentration of the microbial solution is 10 7 Pieces / mL;

[0070] The volume of the CO2 slug is 0.1HCPV;

[0071] (3) A water flooding experiment was performed on the core after the static culture treatment in step (2) at a displacement rate of 0.5 mL / min.

[0072] Example 4

[0073] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding. The method is different from that of embodiment 1 only in that:

[0074] In this example, the concentration of the microbial solution in step (2) was changed to 10 4 Pieces / mL.

[0075] Example 5

[0076] This embodiment provides a method for improving oil reservoir recovery by changing the microscopic swept volume of gas drive using microorganisms. The method is different from that of embodiment 1 only in that:

[0077] In this example, the concentration of the microbial solution in step (2) was changed to 10 8 Pieces / mL.

[0078] Example 6

[0079] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding. The method is different from that of embodiment 1 only in that:

[0080] In this embodiment, the volume ratio of the microbial solution plug and the CO2 plug in step (2) is changed to 4:1.

[0081] Example 7

[0082] This embodiment provides a method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding. The method is different from that of embodiment 1 only in that:

[0083] In this embodiment, the volume ratio of the microbial solution plug and the CO2 plug in step (2) is changed to 1:4.

[0084] Comparative Example 1

[0085] This comparative example provides a method for improving oil reservoir recovery, which differs from Example 1 only in that:

[0086] In this comparative example, step (2) is revised as follows: CO2 gas is injected into the core of step (1) at a rate of 0.06 mL / min until the gas-oil ratio is greater than 1300.

[0087] Comparative Example 2

[0088] This comparative example provides a method for improving oil reservoir recovery, which differs from Example 1 only in that:

[0089] In this comparative example, step (2) is revised as follows: a microbial solution plug with a volume of 0.06 HCPV is injected into the core of step (1) at a rate of 0.06 mL / min, and when microorganisms appear in the produced fluid, a static culture treatment is performed for 5 days.

[0090] Comparative Example 3

[0091] This comparative example provides a method for improving oil reservoir recovery by changing the microscopic swept volume of gas drive using microorganisms. The method is different from Example 1 only in that:

[0092] In this comparative example, CO2 gas is first injected into the core of step (1) at a rate of 0.06 mL / min in step (2) until gas channeling occurs, and then the microbial solution is injected into the core at a rate of 0.06 mL / min. When microorganisms appear in the produced fluid, it is statically cultured for 5 days.

[0093] Comparative Example 4

[0094] This comparative example provides a method for improving oil reservoir recovery rate by microbial-CO2 composite flooding based on reducing the minimum miscible pressure of crude oil. The method is different from Example 1 only in that:

[0095] In this comparative example, the microbial solution plug described in step (2) is modified into a common formation water solution plug.

[0096] The oil reservoir was recovered by the methods provided in the above embodiments and comparative examples, and the oil recovery efficiency results are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] From Table 1, we can draw the following conclusions:

[0101] (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 oil reservoirs;

[0102] (2) It can be seen from the analysis of Example 1 and Examples 4-5 that when the concentration of the injected microbial solution is low, the microorganisms fail to multiply in large quantities or produce sufficient biopolymers to selectively block the dominant channels in the reservoir with higher permeability, resulting in an insufficient improvement in the recovery rate of crude oil; when the concentration of the injected microbial solution is high, the initial number of microorganisms is large and it is difficult to inject them into the core to act, and the directional blocking effect of increasing the microscopic swept volume cannot be achieved, resulting in a decrease in the recovery rate of crude oil;

[0103] (3) It can be seen from the analysis of Example 1 and Examples 6-9 that when the volume ratio of the CO2 plug and the microbial solution plug is too high, CO2 still plays a dominant role. Although the oil displacement efficiency is improved compared with the ordinary CO2 displacement, the plugging effect of the microorganisms cannot be fully manifested, and the CO2 microscopic swept volume is limited, resulting in a small increase in the crude oil recovery rate; when the volume ratio of the CO2 plug and the microbial solution plug is too low, the microorganisms play a dominant role, resulting in a strong plugging effect, blocking the pores that could originally be displaced by CO2, resulting in a small increase in the crude oil recovery rate;

[0104] (4) Analysis of Example 1 and Comparative Examples 1-2 shows that the use of microorganism-CO2 composite flooding is more conducive to achieving high-efficiency exploitation of oil reservoirs. On the one hand, the composite flooding slows down the gas channeling phenomenon of CO2 flooding, and on the other hand, the directional selective plugging effect of microorganisms also delays the occurrence of gas channeling, making up for the shortcomings of CO2 flooding, increasing the microscopic swept volume of CO2 flooding, and giving full play to the synergistic effect of the two.

[0105] (5) Analysis of Example 1 and Comparative Example 3 shows that, compared with sequential CO2 flooding and microbial flooding, the method provided by the present invention does not use a plugging method to displace the core. Therefore, CO2 is not plugged until gas channeling is formed. At this time, it is too late to use microorganisms to plug the gas channeling. Although the impact of gas channeling can be reduced to a certain extent, its effect is far less obvious than that of slug flooding.

[0106] In summary, the present invention combines the microbial functional bacteria strains (or metabolites) that increase the microscopic swept volume of gas drive with CO2 drive to give full play to the synergistic effect of various technologies, thereby achieving the effect of improving crude oil recovery, providing a reference for indoor experimental research and field development.

[0107] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas drive, 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 injecting the CO2 plugs for the first time, and performing static culture treatment when microorganisms appear in the produced fluid; (3) performing a water flooding experiment on the core after the static culture treatment in step (2); The microbial solution slug in step (2) includes the first microbial functional bacteria and / or the second microbial functional bacteria; The first functional microorganism has the ability to reproduce rapidly; the second functional microorganism has the ability to generate biopolymers.

2. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to claim 1, characterized in that: The permeability of the core in step (1) is ≥20mD.

3. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to claim 1 or 2, characterized in that: The displacement rate of the water-to-oil experiment in step (1) is 0.01 to 0.5 mL / min; Preferably, the endpoint of the water flooding experiment in step (1) is: the water content of the produced fluid is ≥ 98%.

4. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to any one of claims 1 to 3, characterized in that: The growth rate of the first microbial functional bacteria is that the bacterial concentration increases from 10 to 10 within 12-24 hours. 6 / mL multiply to 10 8 Particles / mL or more; Preferably, the second microbial functional bacteria include Xanthomonas campestris.

5. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to any one of claims 1 to 4, characterized in that: The concentration of the microbial solution in step (2) is 10 5 -10 7 Pieces / mL.

6. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to any one of claims 1 to 5, characterized in that: The volume of the CO2 slug in step (2) is 0.04-0.1 HCPV; Preferably, the volume ratio of the CO2 plug to the microbial plug in step (2) is 1:(0.3-3).

7. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to any one of claims 1 to 6, characterized in that: The speed of the alternating injection in step (2) is 0.01 to 0.1 mL / min, preferably 0.03 to 0.08 mL / min; Preferably, the static culture treatment time in step (2) is ≥ 3 days, preferably 5 to 10 days; Preferably, the temperature of the static culture treatment in step (2) is 20 to 65°C, preferably 25 to 45°C.

8. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding 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 for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to any one of claims 1 to 8, characterized in that: The oil displacement effect of the method is ≥65%.

10. The method for improving oil recovery by microbial-CO2 composite flooding based on increasing the microscopic swept volume of gas flooding according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) conducting a water-to-oil drive experiment on the core at a displacement rate of 0.01 to 0.5 mL / min until the water content of the produced fluid is ≥ 98%; and the permeability of the core is ≥ 20 mD; (2) injecting CO2 plugs and microbial solution plugs alternately into the core of step (1) at a volume ratio of 1:(0.3-3) at a rate of 0.01-0.1 mL / min, and when the CO2 plugs are injected for the first time, when microorganisms appear in the produced fluid, performing a static culture treatment for ≥3 days; The microbial solution slug contains the first microbial functional bacteria and / or the second microbial functional bacteria; the first microbial functional bacteria has the ability to reproduce rapidly, and the reproduction rate is that the bacterial concentration increases from 10 to 10 within 12-24 hours. 6 / mL multiply to 10 8 The second microbial functional bacteria is Xanthomonas campestris having the ability to produce biopolymers; The concentration of the microbial solution is 10 5 -10 7 Pieces / mL; The volume of the CO2 slug is 0.04-0.1 HCPV; (3) performing a water flooding experiment on the core after the static culture treatment in step (2) at a displacement rate of 0.01-0.5 mL / min.

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