A method for improving recovery of low-permeability oil reservoirs by using microbial composite waterflooding

Abstract

The application discloses a method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding, and comprises the following steps: S1, test block screening; S2, microbial system screening and performance evaluation; S3, pressure flooding injection process optimization; and S4, field application. The application is suitable for the technical field of oil reservoir development, and the recovery ratio of low-permeability oil reservoirs can be effectively improved by using the microbial composite pressure flooding mode. The injected microbial system can reduce the viscosity of crude oil, reduce the injection pressure, increase the injection amount, and reduce the oil-water interfacial tension. The pressure flooding injection mode can not only rapidly supplement the formation energy, but also form micro cracks and expand the sweep range of the microorganisms. The injected microbial system is non-toxic and harmless, has no influence on the subsequent sewage treatment, and can avoid the problem of environmental pollution caused by the injection of chemical reagents. The application has the advantages of simple construction process, simple operation, high input-output ratio, and good field test effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil reservoir development, and specifically relates to a method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding. BACKGROUND

[0002] Low-permeability oil reservoirs are widely distributed and have a huge total oil content, accounting for more than half of the total oil reserves in China. Meanwhile, the capacity construction scale of low-permeability oilfields accounts for more than 70% of the total capacity construction scale of oilfields. Therefore, the development of low-permeability oilfields is of great significance in today's increasing demand for oil. However, due to the poor reservoir physical properties, low permeability, serious heterogeneity, high content of clay minerals, strong reservoir sensitivity, complex pore structure and serious Jamin effect of low-permeability oil reservoirs, the injection water startup pressure is high, the capillary resistance is large, the injection water volume is low, and the residual oil in small pores cannot be effectively started.

[0003] At present, the two commonly used methods for oil reservoir development are polymer flooding and chemical flooding. However, due to the small pore throat of low-permeability oil reservoirs, the high viscoelasticity of polymers can quickly increase the injection pressure, so it is risky to apply polymer to improve the recovery ratio by realizing mobility control and expanding sweep in low-permeability oil reservoirs. Chemical flooding can solve the problem of low-permeability oil reservoir development to some extent, but it cannot expand the sweep range and is prone to aggravate water channeling. Therefore, it is necessary to develop an economic and efficient technical means to improve the development effect of low-permeability oil reservoirs.

[0004] The authorized patent No. CN202011623961.X, entitled "A method for improving the recovery ratio of low-permeability oil reservoirs by using microorganisms", comprises the following steps: test area screening, composite microbial oil displacement bacteria liquid screening and performance evaluation, injection parameter optimization, injection of the first composite microbial oil displacement bacteria liquid, injection of the nutrient liquid mixture slug into the target oil layer, polymer profile control, microbial huff and puff, injection of the second composite microbial oil displacement bacteria liquid, injection of the nutrient liquid mixture slug, injection of the third microbial bacteria liquid, injection of the nutrient liquid mixture slug, and field test effect evaluation. The method greatly improves the development effect of microorganisms by combining microbial oil displacement with polymer profile control and microbial huff and puff; and finally achieves the purpose of improving the recovery ratio of oil reservoirs and deepening the understanding of the mechanism and applicable conditions of microbial oil displacement. Disadvantages: The patent does not consider the injection of polymers, and is not suitable for low-permeability oil reservoirs with a permeability of less than 10 mD. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A method for improving recovery of low-permeability oil reservoirs by using microbial composite pressure drive, comprising the following steps:

[0008] S1 test block screening;

[0009] S2 microbial system screening and performance evaluation;

[0010] S3 pressure drive injection process optimization;

[0011] S4 field application.

[0012] Preferably, in step S1, the test block screening principle is:

[0013] Reservoir temperature ≤ 95℃, permeability ≤ 10mD, formation water salinity ≤ 150000mg / L, oil-water well spacing ≥ 100m, no fracturing, test block is relatively closed, edge and bottom water is not active.

[0014] Preferably, in step S2, the microbial system is screened according to the production contradictions of the reservoir, and the performance of the screened microbial system is evaluated.

[0015] Preferably, the screened microbial system includes biosurfactant-producing bacteria and biological enzymes.

[0016] Preferably, the biosurfactant-producing bacteria include one or more of Pseudomonas, Bacillus, Serratia, and Rhodococcus.

[0017] Preferably, the biosurfactant-producing bacteria are Pseudomonas or Bacillus, and the concentration is 0.5% to 1.5%.

[0018] Preferably, the biological enzymes are one or more of acetyl xylan esterase, alkyl succinic acid synthase, and glycerol ester hydrolase.

[0019] Preferably, the biological enzymes are acetyl xylan esterase or alkyl succinic acid synthase, and the concentration is 0.01% to 0.1%.

[0020] Preferably, the performance evaluation includes viscosity reduction rate performance evaluation, interfacial tension performance evaluation, interfacial wettability performance evaluation, and static imbibition efficiency performance evaluation.

[0021] Preferably, the viscosity reduction rate performance evaluation method is:

[0022] The viscosity of crude oil after the action of different microbial systems is tested by a viscosity tester, and the viscosity reduction rate performance evaluation standard is viscosity reduction rate ≥ 90%.

[0023] Preferably, the interfacial tension performance evaluation method is:

[0024] The interface tension between different microbial systems and kerosene is tested by using spin drop method and spin interface tension instrument, and the interface tension performance evaluation standard is interface tension ≤ 0.01 mN / m.

[0025] Preferably, the interface wettability performance evaluation method is:

[0026] The hydrophobic glass slide is made, the microbial system is dropped on the glass slide, and the contact angle change is observed, and the contact angle is 50°-80° under the preferred condition

[0027] Preferably, the static imbibition efficiency performance evaluation method is:

[0028] First, the core permeability and porosity are tested, the core is numbered, the core mass is weighed, the core column is immersed in the prepared simulated oil suction bottle, a vacuum pump is used for suction for more than 12 hours, and the core column is aged at the formation temperature for more than 2 weeks, and the saturated aged core column mass is recorded;

[0029] Then, the saturated and aged core is loaded into a plug imbibition bottle, different microbial systems are added, and sealed and placed, the oil volume is recorded every day, the final oil volume is recorded for more than 7 days, and the static dialysis recovery rate is obtained, and the static dialysis recovery rate calculation formula is:

[0030] ω = V·ρ·100% / (m1-m2),

[0031] Wherein, ω is the static dialysis recovery rate, V is the final oil volume, m1 is the core mass, and m2 is the saturated and aged core column mass.

[0032] Preferably, the static dialysis recovery rate is ≥40%.

[0033] Preferably, the simulated oil is obtained by mixing aged oil and kerosene at a ratio of 1:1.

[0034] Preferably, in step S3, the displacement injection amount and injection speed are determined according to the reservoir permeability, thickness and well spacing.

[0035] Preferably, the displacement injection amount and injection speed are determined according to the following standards:

[0036] ① When the reservoir thickness is ≥5 m, the permeability is 5-10 mD, and the well spacing is ≥300 m, the displacement injection amount is (3-5) ×10 4 m 3 , and the displacement amount is 1.5-2 m 3 / min;

[0037] ② When the reservoir thickness is ≥5 m, the permeability is ≤5 mD, and the well spacing is ≤300 m, the displacement injection amount is (2-3) ×10 4 m 3 , and the displacement amount is 1-1.5 m3 / min;

[0038] ③ When the reservoir thickness is ≤5m, the permeability is 5-10mD, and the well spacing is ≥300m, the injection amount of pressure drive is (2-3)×10 4 m 3 , and the displacement is 1-1.5m 3 / min;

[0039] ④ When the reservoir thickness is ≤5m, the permeability is ≤5mD, and the well spacing is ≤300m, the injection amount of pressure drive is (1-2)×10 4 m 3 , and the displacement is 0.5-1m 3 / min.

[0040] Preferably, in the step S4, the injection is performed according to the injection process optimized in the step S3, the pressure is monitored in real time, and the injection process is adjusted according to the injection pressure and the casing pressure of the oil well.

[0041] Preferably, before the injection, the water injection well is replaced with a 600-type well head, the oil well is replaced with a 350-type or 600-type well head, and the well is shut in.

[0042] Preferably, after the injection, the production well head is replaced, and the on-site effect is tracked and analyzed.

[0043] Preferably, the injection process is adjusted according to the injection pressure and the casing pressure of the oil well, and the adjustment method is as follows:

[0044] When the injection pressure of the water well is ≥50MPa, the injection is stopped, the injection is restarted when the pressure is reduced to below 30MPa, and the injection is performed at a low displacement of 0.5m 3 / min, and then gradually restored to the set displacement;

[0045] When the casing pressure of the oil well is ≥25MPa, the injection is stopped, the injection is restarted when the pressure is reduced to below 10MPa, and the injection is performed at a low displacement of 0.5m 3 / min, and then gradually restored to the set displacement.

[0046] In summary, due to the adoption of the above technical solutions, the present application has the following beneficial effects:

[0047] The present application is suitable for low-permeability reservoirs, and the microbial composite pressure drive can effectively improve the recovery rate of low-permeability reservoirs;

[0048] The present application has strong pertinence and operability, the injected microbial system can reduce the viscosity of crude oil, reduce the injection pressure, and reduce the oil-water interfacial tension; the pressure drive injection method not only can rapidly supplement the formation energy, but also can form micro-fractures and expand the sweep range of the microorganisms;

[0049] The injected microbial system is non-toxic and harmless, does not have any influence on subsequent sewage treatment, and avoids the problem of environmental pollution caused by injection of chemical reagents.

[0050] The method has the advantages of simple construction process, simple operation, high input-output ratio and good field test effect, the water content of the oil well is reduced by more than 20%, the oil production of the well group is increased by more than 1000t, and the input-output ratio is greater than 1:15. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a flow chart of the method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding. DETAILED DESCRIPTION

[0052] The specific embodiments of the method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding will be further described below in combination with the accompanying Figure 1 The method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding is not limited to the description of the following examples.

[0053] Example 1:

[0054] This example gives a specific embodiment of the method for improving the recovery ratio of low-permeability oil reservoirs by using microbial composite pressure flooding, as shown in Figure 1 includes the following steps:

[0055] S1 test block screening;

[0056] S2 microbial system screening and performance evaluation;

[0057] S3 pressure flooding injection process optimization;

[0058] S4 field application.

[0059] Further, in step S1, the test block screening principle is:

[0060] The reservoir temperature is less than or equal to 95 DEG C, the permeability is less than or equal to 10 mD, the formation water salinity is less than or equal to 150000 mg / L, the oil-water well spacing is greater than or equal to 100 m, no fracturing is implemented, the test block is relatively closed, and the edge and bottom water is not active.

[0061] Further, in step S2, the microbial system is screened according to the production contradiction of the oil reservoir, and the performance of the screened microbial system is evaluated.

[0062] Further, the screened microbial system includes biosurfactant-producing bacteria and biological enzymes.

[0063] Further, the biosurfactant-producing bacteria include one or more of Pseudomonas, Bacillus, Serratia, and Rhodococcus.

[0064] Further, the biosurfactant-producing bacteria are Pseudomonas or Bacillus, and the concentration is 0.5% to 1.5%.

[0065] Further, the biological enzyme is one or more of acetyl xylan esterase, alkyl succinic acid synthase, and glyceride hydrolase.

[0066] Further, the biological enzyme is acetyl xylan esterase or alkyl succinic acid synthase, and the concentration is 0.01% to 0.1%.

[0067] Further, the performance evaluation includes viscosity reduction rate performance evaluation, interfacial tension performance evaluation, interfacial wettability performance evaluation, and static imbibition efficiency performance evaluation.

[0068] Further, the viscosity reduction rate performance evaluation method is as follows:

[0069] The viscosity of crude oil after the action of different microbial systems is tested by using a viscosity tester, and the viscosity reduction rate performance evaluation standard is that the viscosity reduction rate is greater than or equal to 90%.

[0070] Further, the interfacial tension performance evaluation method is as follows:

[0071] The interfacial tension between different microbial systems and kerosene is tested by using a spinning drop method and a spinning interfacial tension meter, and the interfacial tension performance evaluation standard is that the interfacial tension is less than or equal to 0.01 mN / m.

[0072] Further, the interfacial wettability performance evaluation method is as follows:

[0073] A hydrophobic glass slide is prepared, the microbial system is dropped on the glass slide, and the change in the contact angle is observed, and the contact angle is 50° to 80° under the preferred condition.

[0074] Further, the static imbibition efficiency performance evaluation method is as follows:

[0075] First, the core permeability and porosity are tested, the core is numbered, the core mass is weighed, the core column is immersed in a filter bottle containing simulated oil, a vacuum pump is used for pumping for more than 12 hours, the core column is aged at a formation temperature for more than 2 weeks, and the mass of the saturated and aged core column is recorded;

[0076] Then, the saturated and aged core is loaded into a permeation bottle with a plug, different microbial systems are added, and the bottle is sealed and placed, the oil volume is recorded every day, the recording is continued for more than 7 days, the final oil volume is recorded, and thus the static imbibition recovery rate is obtained, and the calculation formula of the static imbibition recovery rate is as follows:

[0077] ω = V·ρ·100% / (m1-m2),

[0078] Wherein, ω is the static imbibition recovery rate, V is the final oil volume, m1 is the core mass, and m2 is the mass of the saturated and aged core column.

[0079] Further, the static dialysis recovery rate is ≥40%.

[0080] Further, the simulated oil is obtained by mixing aged oil and kerosene at a ratio of 1:1.

[0081] Further, in step S3, the amount of pressure drive injection and injection speed are determined according to the reservoir permeability, thickness, and well spacing.

[0082] Further, the amount of pressure drive injection and injection speed are determined according to the following specific criteria:

[0083] ① When the reservoir thickness is ≥5m, the permeability is 5-10mD, and the well spacing is ≥300m, the amount of pressure drive injection is (3-5)×10 4 m 3 , and the displacement is 1.5-2m 3 / min;

[0084] ② When the reservoir thickness is ≥5m, the permeability is ≤5mD, and the well spacing is ≤300m, the amount of pressure drive injection is (2-3)×10 4 m 3 , and the displacement is 1-1.5m 3 / min;

[0085] ③ When the reservoir thickness is ≤5m, the permeability is 5-10mD, and the well spacing is ≥300m, the amount of pressure drive injection is (2-3)×10 4 m 3 , and the displacement is 1-1.5m 3 / min;

[0086] ④ When the reservoir thickness is ≤5m, the permeability is ≤5mD, and the well spacing is ≤300m, the amount of pressure drive injection is (1-2)×10 4 m 3 , and the displacement is 0.5-1m 3 / min.

[0087] Further, in step S4, the injection process optimized in step S3 is used for injection, the pressure is monitored in real time, and the injection process is adjusted according to the injection pressure and the casing pressure of the oil well.

[0088] Further, before injection, the water injection well is replaced with a 600-type wellhead, the oil well is replaced with a 350-type or 600-type wellhead, and the well is shut in.

[0089] Further, after injection, the production wellhead is replaced, and the on-site effect is tracked and analyzed.

[0090] Further, the injection process is adjusted according to the injection pressure and the casing pressure of the oil well, and the adjustment method is as follows:

[0091] When the water well injection pressure ≥ 50 MPa, stop injection, and when the pressure is reduced to 30 MPa or less, start injection again, and when injecting again, use low discharge 0.5 m 3 / min injection, and then gradually restore to the set discharge;

[0092] When the oil well casing pressure ≥ 25 MPa, stop injection, and when the pressure is reduced to 10 MPa or less, start injection again, and when injecting again, use low discharge 0.5 m3 / min injection, and then gradually restore to the set discharge.

[0093] Example 2

[0094] A certain block A in Shengli Oilfield, reservoir temperature 90℃, burial depth 2072m-2250m, reservoir thickness 8m, permeability 10mD, surface crude oil viscosity 150mPa.s, formation water salinity 50000mg / L, oil-water well spacing 300m-360m, no fracturing, test block is relatively closed, edge and bottom water is not active. The invention is used to implement microbial composite pressure flooding to improve the recovery of the well group in the block A, and the specific implementation steps are as follows:

[0095] (1) Test block screening

[0096] The test block screening has reservoir temperature 90℃, permeability 10mD, formation water salinity 50000mg / L, oil-water well spacing 300m-360m, no fracturing, test block is relatively closed, edge and bottom water is not active, and meets the screening standard of the invention, and the invention can be implemented.

[0097] (2) Microbial system screening and performance evaluation

[0098] The microbial system includes biosurfactant-producing bacteria and biological enzymes, which can reduce crude oil viscosity, water well pressure reduction and injection increase, and oil-water interfacial tension.

[0099] The biosurfactant-producing bacteria are Pseudomonas, with a concentration of 0.5%; the biological enzyme is acetyl xylan esterase, with a concentration of 0.02%.

[0100] The performance of the microbial system is evaluated, with crude oil viscosity reduction rate 95%, interfacial tension 0.005mN / m, contact angle 60°, and static dialysis recovery rate 45%, meeting the system performance standard.

[0101] Table 1 Performance evaluation of microbial system

[0102]

[0103] (3) Pressure flooding injection process optimization

[0104] Reservoir thickness 8m, permeability 10mD, oil-water well spacing 300m-360m, pressure flooding injection amount 3x104 m 3 , 1.5 m 3 / min.

[0105] (4) Field application

[0106] The first step of the implementation of the pressure drive is to replace the wellhead of the oil and water well, replace the 600 type wellhead of the injection well, replace the 350 type wellhead of the oil well and shut down the well. According to the above-mentioned optimized injection process, injection is carried out, the pressure is monitored in real time during the pressure drive process, and the pressure

[0107] The data are shown in the following table.

[0108] Table 2 Change of pressure of oil and water wells during the injection process of the pressure drive

[0109] Displacement, m 3 / min 1.5 1.5 1.5 Injection volume, m 3 ]]> 1 x 10 4 ]]> 2 x 10 4 ]]> 3 x 10 4 ]] Water well pressure, MPa 36 42 45 Casing pressure, MPa 15 18 19

[0110] The injection pressure of the water well and the casing pressure of the oil well are both out of range, so the injection mode is not adjusted during the injection process. After the injection is completed, the wellhead of the production well is replaced, and normal production is started. The water content of the oil well is reduced by 25%, the well group increases oil by more than 2500t, and the input-output ratio is greater than 1:18.

[0111] Example 3

[0112] A block B in Shengli Oilfield, reservoir temperature 80℃, burial depth 1800m-2100m, reservoir thickness 6.2m, permeability 4.6mD, ground crude oil viscosity 286mPa.s, formation water salinity 80000mg / L, oil and water well spacing 210m-260m, no fracturing is implemented, the test block is relatively closed, and the edge and bottom water is not active. The microbial composite pressure drive is used to improve the recovery of the well group in the block B, and the specific implementation steps are as follows:

[0113] (1) Test block screening

[0114] The test block screening has a reservoir temperature of 80℃, a permeability of 4.6mD, a formation water salinity of 80000mg / L, an oil and water well spacing of 210m-260m, no fracturing is implemented, the test block is relatively closed, and the edge and bottom water is not active, which meets the screening standard of the application and can implement the application.

[0115] (2) Microbial system screening and performance evaluation

[0116] The microbial system includes biosurfactant-producing bacteria and biological enzymes, which can reduce the viscosity of crude oil, reduce the injection pressure of water wells and reduce the oil-water interfacial tension.

[0117] The biosurfactant-producing bacteria are Bacillus, with a concentration of 0.8%; the biological enzyme is acetyl xylan esterase, with a concentration of 0.05%.

[0118] The performance of the microbial system was evaluated, and the crude oil viscosity reduction rate was 92%, the interfacial tension was 0.008 mN / m, the contact angle was 62°, and the static dialysis recovery rate was 48%, which met the system performance standards.

[0119] Table 3 Performance evaluation of the microbial system

[0120]

[0121] (3) Optimization of pressure-driven injection process

[0122] The reservoir thickness is 6.2m, permeability is 4.6mD, oil and water well spacing is 210m-260m, and pressure-driven injection rate is 2.5×10⁻⁶. 4 m 3 1.2m displacement 3 / min.

[0123] (4) Field application

[0124] To implement pressure drive, first replace the wellheads of oil and water wells, replace the water injection wellheads with 600-type wellheads, and replace the oil wellheads with 350-type wellheads before shutting them in. Inject according to the optimized injection process described above. Monitor the pressure in real time during the pressure drive process; the pressure data is shown in the table below.

[0125] Table 4. Pressure changes in oil and water wells during pressure-driven injection.

[0126]

[0127]

[0128] Water injection rate: 1.5 × 10 4 m 3 When the injection pressure reaches 50 MPa, stop the injection and wait for the pressure to recover to below 30 MPa before restarting the injection. The next injection should use a low flow rate of 0.5 m³ / min. 3 Inject at / min, then gradually restore to the set displacement.

[0129] Table 5. Pressure changes in oil and water wells during pressure-driven re-injection.

[0130] Displacement, m 3 / min]]> 0.5 1.0 1.2 Injection volume, m 3 ]]> 1.5 x 10 4 m 3 ]]> 2 x 10 4 m 3 ]]> 3 x 10 4 m 3 ]]> Water well pressure, MPa 39 42 45 Casing pressure, MPa 15 16 17

[0131] After the injection was completed, the production wellhead was replaced and normal production began. The water cut of the oil well decreased by 22%, the well group increased oil production by more than 1,600 tons, and the input-output ratio was greater than 1:16.

[0132] Example 4

[0133] In Block C of Shengli Oilfield, the reservoir temperature is 75℃, the burial depth is 1720m-1850m, the reservoir thickness is 4.2m, the permeability is 8.5mD, the surface crude oil viscosity is 175mPa·s, the formation water salinity is 62000mg / L, and the well spacing is 320m-350m. No fracturing has been implemented, the test block is relatively closed, and the edge and bottom water is inactive. This invention utilizes microbial composite hydraulic displacement to improve the recovery rate of a well group in Block C. The specific implementation steps are as follows:

[0134] (1) Screening of test blocks

[0135] The selected test block has a reservoir temperature of 75℃, a permeability of 8.5mD, a formation water salinity of 62000mg / L, an oil-water well spacing of 320m-350m, has not undergone fracturing, is relatively closed, and has inactive edge and bottom water, which meets the screening criteria of this invention and can be implemented.

[0136] (2) Screening and performance evaluation of microbial systems

[0137] Microbial systems, including biosurfactant bacteria and biological enzymes, can reduce crude oil viscosity, reduce water pressure and increase injection in water wells, and reduce oil-water interfacial tension.

[0138] The surfactant-producing bacteria were Bacillus species, at a concentration of 1%; the bioenzyme was alkylsuccinate synthase, at a concentration of 0.05%.

[0139] The performance of the microbial system was evaluated, and the crude oil viscosity reduction rate was 92%, the interfacial tension was 0.002 mN / m, the contact angle was 68°, and the static dialysis recovery rate was 43%, which met the system performance standards.

[0140] Table 6 Performance Evaluation of Microbial Systems

[0141]

[0142] (3) Optimization of pressure-driven injection process

[0143] The reservoir thickness is 4.2m, permeability is 8.5mD, oil and water well spacing is 320m-350m, and pressure-driven injection rate is 2.5×10⁻⁶. 4 m 3 1.2m displacement 3 / min.

[0144] (4) Field application

[0145] To implement pressure drive, first replace the wellheads of oil and water wells, replace the water injection wellheads with 600-type wellheads, and replace the oil wellheads with 350-type wellheads before shutting them in. Inject according to the optimized injection process described above. Monitor the pressure in real time during the pressure drive process; the pressure data is shown in the table below.

[0146] Table 7. Pressure changes in oil and water wells during pressure-driven injection.

[0147]

[0148]

[0149] The injection is stopped when the casing pressure of the oil well is greater than or equal to 25 MPa, and the injection is restarted when the pressure is reduced to below 10 MPa. The injection is restarted at a low discharge rate of 0.5 m 3 / min, and then gradually returns to the set discharge rate.

[0150] Table 8 Changes in the pressures of the oil and water wells during the pressure drive injection process

[0151] Displacement, m 3 / min 0.5 1.2 Injection volume, m 3 ]] 2 x 10 4 ]] 2.5 x 10 4 ]]> Water well pressure, MPa 36 43 Casing pressure, MPa 10 16

[0152] After the injection is completed, the production wellhead is replaced, and normal production is started. The water content of the oil well is reduced by 22%, the oil production of the well group is increased by more than 1600 t, and the payback ratio is greater than 1:16.

[0153] Example 5

[0154] A block D in a Shengli oilfield has a reservoir temperature of 85°C, a buried depth of 1900 m to 2200 m, a reservoir thickness of 3.9 m, a permeability of 4.2 mD, a ground crude oil viscosity of 86 mPa.s, a formation water salinity of 50000 mg / L, and an oil and water well spacing of 180 m to 230 m. Fracturing is not implemented, the test block is relatively closed, and the edge and bottom water is not active. The microbial composite pressure drive is used to improve the recovery of the well group in the block D, and the specific implementation steps are as follows:

[0155] (1) Test block screening

[0156] The test block has a reservoir temperature of 85°C, a permeability of 4.2 mD, a formation water salinity of 50000 mg / L, an oil and water well spacing of 180 m to 230 m, and is not implemented fracturing. The test block is relatively closed, and the edge and bottom water is not active, which meets the screening standard of the present application and can implement the present application.

[0157] (2) Microbial system screening and performance evaluation

[0158] The microbial system includes a biosurfactant-producing bacterium and a biological enzyme, which can reduce the crude oil viscosity, water well pressure reduction and injection increase, and oil-water interfacial tension.

[0159] The biosurfactant-producing bacterium is Bacillus, and the concentration is 1.2%; the biological enzyme is acetyl xylan esterase, and the concentration is 0.03%.

[0160] The performance of the microbial system is evaluated, and the crude oil viscosity reduction rate is 96%, the interfacial tension is 0.004 mN / m, the contact angle is 66°, and the static dialysis recovery rate is 43%, which meets the system performance standard.

[0161] Table 9 Performance Evaluation of Microbial Systems

[0162]

[0163] (3) Optimization of pressure-driven injection process

[0164] The reservoir thickness is 3.9m, the permeability is 4.2mD, the well spacing between oil and water is 180m-230m, and the pressure-driven injection rate is 1.5×10⁻⁶. 4 m 3 Displacement 0.8m 3 / min.

[0165] (4) Field application

[0166] To implement pressure drive, first replace the wellheads of oil and water wells, replace the water injection wellheads with 600-type wellheads, and replace the oil wellheads with 350-type wellheads before shutting them in. Inject according to the optimized injection process described above. Monitor the pressure in real time during the pressure drive process; the pressure data is shown in the table below.

[0167] Table 10 Pressure Changes in Oil and Water Wells During Pressure Flooding Injection

[0168] Displacement, m 3 / min 0.8 0.8 0.8 Injection volume, m 3 ]]> 0.5 x 10 4 ]]> 1 x 10 4 ]] 1.5 x 10 4 ]]> Water well pressure, MPa 39 42 45 Casing pressure, MPa 12 13 15

[0169] After the injection was completed, the production wellhead was replaced and normal production began. The water cut of the oil well decreased by 24%, the well group increased oil production by more than 1,800 tons, and the input-output ratio was greater than 1:19.

[0170] Working principle: such as Figure 1 As shown, this invention addresses the challenges of exploiting low-permeability oil reservoirs. First, it screens a microbial enhanced oil recovery (DEOR) system that can reduce crude oil viscosity, decrease water well pressure to enhance injection, and reduce oil-water interfacial tension. Then, it optimizes the injection volume and rate of pressure-driven water injection. This pressure-driven water injection not only rapidly replenishes formation energy in low-permeability reservoirs but also creates numerous microfractures within the formation. Microorganisms, under the excess pressure of pressure-driven water injection, enter these microfractures and, through dialysis, displace residual oil from small pores into larger pores. During subsequent waterflooding, the crude oil is extracted, thereby enhancing oil recovery. This method is characterized by its targeted approach, high operability, low investment cost, and significant oil enhancement effect.

[0171] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for improving the recovery of low permeability reservoirs by microbial composite flooding, characterized in that, It comprises the following steps: S1, test block screening, the test block screening principle is: reservoir temperature is less than or equal to 95 DEG C, permeability is less than or equal to 10 mD, formation water salinity is less than or equal to 150000 mg / L, oil-water well spacing is greater than or equal to 100 m, no fracturing is implemented, the test block is relatively closed, and the edge and bottom water is not active; S2, according to the reservoir production contradiction, a microorganism system is screened, and the microorganism system screened is subjected to performance evaluation, the microorganism system screened comprises biosurfactant-producing bacteria and biological enzymes, the biosurfactant-producing bacteria comprises one or more of pseudomonas, bacillus, serratia and rhodococcus, the biological enzymes are one or more of acetyl xylan esterase, alkyl succinic acid synthase and glyceride hydrolase, the performance evaluation comprises viscosity reduction rate performance evaluation, interfacial tension performance evaluation, interfacial wettability performance evaluation and static imbibition efficiency performance evaluation, the viscosity reduction rate performance evaluation standard is that the viscosity reduction rate is greater than or equal to 90%, the interfacial tension performance evaluation standard is that the interfacial tension is less than or equal to 0.01 mN / m, the contact angle is 50 DEG to 80 DEG, and the static imbibition recovery rate is greater than or equal to 40%; According to the reservoir permeability, thickness and well spacing, the injection amount and injection speed of the pressure drive are determined, and the specific determination standards are as follows: When the reservoir thickness is ≥5 m, the permeability is 5-10 mD, and the well spacing is ≥300 m, the injection amount of the pressure drive is (3-5) × 104m 4 m 3 , and the displacement is 1.5-2 m 3 / min. When the reservoir thickness is ≥ 5 m, the permeability is ≤ 5 mD, and the well spacing is ≤ 300 m, the injection amount of the pressure drive is (2-3) x 10 4 m 3 , and the displacement is 1-1.5 m 3 / min. When the reservoir thickness is ≤5 m, the permeability is 5-10 mD, and the well spacing is ≥300 m, the injection amount of the pressure drive is (2-3)×10 4 m 3 , and the displacement is 1-1.5 m 3 / min. When the reservoir thickness is ≤5 m, the permeability is ≤5 mD, and the well spacing is ≤300 m, the injection amount of the water flooding is (1-2) x 10 4 m 3 , and the displacement is 0.5-1 m 3 / min. S3, according to the injection process optimized in step S2, injection is carried out, the pressure is monitored in real time, and the injection process is adjusted according to the injection pressure and the casing pressure of the oil well, the injection process is adjusted as follows: When the water well injection pressure ≥ 50 MPa, stop injection, and when the pressure is reduced to 30 MPa or less, start injection again, and when injecting again, use low discharge 0.5 m 3 / min injection, and then gradually restore to the set discharge; When the casing pressure of the oil well is ≥25 MPa, stop injection, and when the pressure is reduced to below 10 MPa, start injection again, and when injecting again, use low discharge 0.5 m 3 / min, and then gradually restore to the set discharge. S4, field application.

2. The method for enhancing the recovery of low permeability reservoirs using microbial complex flooding according to claim 1, characterized in that: The biosurfactant-producing bacteria is pseudomonas or bacillus, and the concentration is 0.5% to 1.5%.

3. The method for enhancing the recovery of low permeability reservoirs using microbial complex flooding according to claim 1, characterized in that: The biological enzyme is acetyl xylan esterase or alkyl succinic acid synthase, and the concentration is 0.01% to 0.1%.

4. The method for enhancing the recovery of low permeability reservoirs using microbial complex flooding according to claim 1, characterized in that, The viscosity reduction rate performance evaluation method is as follows: The viscosity of crude oil after the action of different microorganism systems is tested by using a viscosity tester.

5. The method for enhancing the recovery of low permeability reservoirs by microbial complex flooding according to claim 1, characterized in that, The interfacial tension performance evaluation method is as follows: The interfacial tension between different microorganism systems and kerosene is tested by using a rotating interfacial tension instrument by using a rotating drop method.

6. The method for enhancing the recovery of low permeability reservoirs using microbial complex flooding according to claim 1, wherein, The interfacial wettability performance evaluation method is as follows: A hydrophobic glass slide is prepared, the microorganism system is dropped on the glass slide, and the contact angle change is observed.

7. The method for enhancing the recovery of low permeability reservoirs by microbial complex flooding according to claim 1, characterized in that, The static imbibition efficiency performance evaluation method is as follows: Firstly, the core permeability and porosity are tested, the core is numbered, the core mass is weighed, the core column is immersed in a filter bottle filled with simulated oil, a vacuum pump is used for suction for more than 12 hours, the core column is aged at a formation temperature for more than 2 weeks, and the saturated aged core column mass is recorded; Then, the saturated aged core is loaded into a permeation bottle with a plug, different microorganism systems are added, and the bottle is sealed and placed, the oil volume is recorded every day, the oil volume is recorded for more than 7 days, the final oil volume is recorded, and the static imbibition recovery rate is obtained, and the static imbibition recovery rate calculation formula is as follows: ω=V·ρ·100% / (m1-m2), Wherein, ω is the static imbibition recovery rate, V is the final oil volume, m1 is the core mass, and m2 is the saturated aged core column mass.

8. The method for enhancing the recovery of low permeability reservoirs by microbial complex flooding according to claim 7, characterized in that: The simulation oil is obtained by mixing aged oil and kerosene at a ratio of 1:

1. The simulation oil is obtained by mixing aged oil and kerosene at a ratio of 1:1.

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