Microbial huff and puff method for fractured oil reservoir of petrocarboniferous igneous rock

Abstract

The present application relates to a kind of petrocarbonaceous igneous rock fractured reservoir microbial huff and puff oil production method, comprising the following steps: (1), screening test reservoir;(2), screening surfactant-producing microorganism fermentation liquor and its concentration;(3), screening activator;(4), field test;(5), well production;(6), field test effect evaluation.The present application has the following advantages and beneficial effects: (1) wide application range;(2) improve oil well production, extend oil well production period, improve igneous rock recovery, the above-mentioned comprehensive effect leads to good field test effect, field test single well oil increase 300-500 tons;(3) with the advantages of simple construction technology, simple operation, strong operability, low investment cost, good field test effect, input-output ratio is greater than 1:5, improve recovery greater than 10%.

Description

Technical Field

[0001] This invention belongs to the field of microbial enhanced oil recovery technology and relates to a microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs. Background Technology

[0002] The Carboniferous igneous rocks in the Chepaizi area are characterized by low porosity, ultra-low permeability, low temperature, and low abundance of heavy oil reservoirs. The reservoirs in this area exhibit significant fracture development and are primarily composed of tuff, andesite, volcanic breccia, and basalt. The reservoir space types are mainly volcanic dissolution-vuggy and fracture-vuggy reservoirs, exhibiting strong heterogeneity. The surface crude oil viscosity in this area ranges from 149 to 654 mPa·s, the total salinity from 7761 mg / L to 17425 mg / L, the reservoir temperature from 33 to 41℃, and the original formation pressure potential from 10 to 12 MPa. Due to the complex lithology and varying oil properties, well productivity varies greatly, with inefficient wells accounting for 40%, and efficient development technologies are currently lacking.

[0003] To improve the ultimate recovery rate of Carboniferous igneous fractured oil reservoirs, and to address the development challenges such as low formation energy, high crude oil viscosity, and complex fracture relationships in Carboniferous test reservoirs, it is necessary to implement a combined internal and external microbial CO2 huff and puff process. Microbial emulsification and dispersion reduce crude oil viscosity, improve the oil-water mobility ratio, and enhance crude oil flowability. CO2 is used to replenish formation energy, thereby increasing well production. Summary of the Invention

[0004] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs. This method is characterized by its strong targeting, wide applicability, high operability, low cost, and significant oil enhancement effect.

[0005] Technical solution: A microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs, comprising the following steps:

[0006] (1) Screening test reservoirs;

[0007] (2) Screening the microbial fermentation broth that produces biosurfactants and its concentration;

[0008] (3) Screening activators;

[0009] (4) Field test;

[0010] (5) Well opening and production;

[0011] (6) Evaluation of the on-site test results.

[0012] Furthermore, the screening criteria for the test reservoir in step (1) are as follows:

[0013] Select oil wells in Carboniferous igneous rock reservoirs with reservoir temperatures <50℃, crude oil viscosity between 100 mPa·s and 30000 mPa·s, and permeability >2×10⁻⁶. -3 μm 2 Mineralization <50000 mg / L, liquid volume 0-10 ml 3 The water content of the produced liquid reaches 0-30%.

[0014] Furthermore, step (2) includes the following steps:

[0015] Take the produced fluid from the test reservoir screened in step (1), filter it, and prepare various bio-surfactant microbial fermentation broths with a mass concentration of 2% to 10%. Use the reservoir conditions of the test reservoir as the indoor physical simulation experimental conditions. Inject the bio-surfactant microbial fermentation broths of different concentrations into 50 to 800 mD cores for 3 to 5 days at the reservoir temperature. Saturate the crude oil of the test reservoir. Use the produced fluid of the test reservoir as the blank group. Observe the change in the pressure of crude oil passing through the core during the experiment. Based on the reduction rate of crude oil starting pressure, screen the bio-surfactant microbial fermentation broths and their concentrations.

[0016] Furthermore, the bioactive surfactant microbial fermentation broth is one of yeast fermentation broth, Pseudomonas aeruginosa fermentation broth, and Bacillus subtilis fermentation broth.

[0017] Furthermore, the nutrient solution formula for the yeast fermentation broth is 3-8% cottonseed oil, 3-12% molasses, and the remainder is water.

[0018] Furthermore, the nutrient solution of the *Pseudomonas aeruginosa* fermentation broth consists of 1-4% glycerol, 0.3-1.2% sodium nitrate, 0.1-0.2% yeast powder, 0.1-0.4% K₂HPO₄, 0.1-0.4% KH₂PO₄, 0.01-0.02% MgSO₄·7H₂O, with the remainder being water.

[0019] Furthermore, the nutrient solution of the Bacillus subtilis fermentation broth consists of 2-8% brown sugar, 0.2-3% sodium nitrate, 0.05-0.1% dipotassium hydrogen phosphate, 0.01-0.05% potassium dihydrogen phosphate, 0.01-0.02% MgSO4·7H2O, with the remainder being water.

[0020] Furthermore, step (3) includes the following steps:

[0021] Take 150-300 ml of the produced liquid from the test reservoir selected in step (1) and put it into an anaerobic bottle. Prepare a nutrient solution of the bio-surfactant microorganisms selected in step (2) with a C / N ratio of 2-40:1. Then, aseptically inoculate the fermentation broth of the bio-surfactant microorganisms selected in step (2) with a mass concentration of 2-10%. Then, place 50-800 mD cores of saturated crude oil from the test reservoir into the anaerobic bottle and incubate them in a constant temperature chamber for 15-30 days. The temperature of the constant temperature chamber is set to the reservoir temperature of the test reservoir. Then, observe the amount of crude oil stripping during the incubation process and determine the amount of crude oil stripping. Based on the amount of crude oil stripping, determine the most suitable C / N ratio, which is the formula of the activator.

[0022] Furthermore, step (4) includes the following steps:

[0023] (41) Before construction, use 20m 3 The above hot water is used to wash the well;

[0024] (42) Inject the bio-surfactant fermentation broth and its nutrient solution, and simmer the well for 30-60 days:

[0025] Two wellheads of at least 20m in length were prepared for the test reservoir. 3 The wellbore has two mixing tanks: one for preparing the injection fluid and the other for injecting it. The bio-surfactant fermentation broth is transported to the wellhead. The activator is prepared at the wellhead using injection water. The prepared activator and the bio-surfactant fermentation broth are mixed at volume ratios of 2:1 and 1:1 to form slug one and slug two, respectively, which are then rapidly injected into the wellhead of the test reservoir.

[0026] The displacement of the slug is 30m. 3 / h~60m 3 / h, preferably 40-50m 3 / h, construction pressure controlled between 5MPa and 20MPa, total injection volume 300m³. 3 ~700m 3 Preferably 400-600m 3 ;

[0027] The displacement of the slug 2 is 30m. 3 / h~60m 3 / h, preferably 45-55m 3 / h, construction pressure controlled between 5MPa and 20MPa, total injection volume 300m³. 3 ~700m 3 Preferably 400-600m 3 ;

[0028] Inject 30-50m into the wellhead of the test reservoir 3Water was used as the displacement fluid, and the injection rate was 30–60 m / s. 3 / h, shut in the well for observation;

[0029] (43) Injection of carbon dioxide:

[0030] The discharge capacity is 4t / h to 10t / h, preferably 6 to 8t / h; the construction pressure is controlled at 5MPa to 20MPa, and the total injection volume is 100t to 250t, preferably 150 to 200t;

[0031] (44) Inject 50-100m³ of clean water into the wellhead of the test reservoir. 3 As a displacement fluid, 60–80 mg is preferred. 3 After shutting down the well, observe the changes in wellhead pressure. Once the pressure stops decreasing and remains stable for 5 days, the well can be reopened for production.

[0032] Furthermore, in step (5), the bacterial concentration, surface tension, well fluid volume, oil volume, and crude oil viscosity of the produced fluid are tracked.

[0033] Furthermore, the indicators for evaluating the effectiveness of the field test in step (6) include the increase in oil production, shelf life, and input-output ratio.

[0034] This invention relates to a microbial huff and puff method for oil recovery in Carboniferous igneous reservoirs, which can effectively improve the final recovery rate of fractured Carboniferous igneous reservoirs.

[0035] Firstly, the well fluid of this invention is prepared from injected water and its main components are bioactive surfactants, microbial liquid, water-soluble carbon source, nitrogen source and phosphorus source, as well as a small amount of inorganic salts. The resulting aqueous solution has a viscosity of less than 5 mPa·s, has good injection capacity, and can be adsorbed on the rock wall after injection.

[0036] Secondly, the bio-surfactants produced have strong wetting and regulating functions, which can significantly reduce crude oil start-up pressure and improve permeation efficiency. The composite carbon dioxide process enhances formation energy and assists microbial viscosity reduction, thereby increasing single-well productivity.

[0037] Therefore, the present invention can effectively improve the problems of low formation energy, high crude oil viscosity, and complex fracture relationships in Carboniferous igneous fractured oil reservoirs, increase oil well production, extend the production period of oil wells, and improve the recovery rate of igneous oil reservoirs.

[0038] Beneficial effects: Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] (1) Wide range of applications - This invention is widely applicable to low-yield, low-liquidity heavy oil wells in Carboniferous igneous rocks;

[0040] (2) The microbial huff and puff technology for Carboniferous igneous reservoirs developed in this invention injects a bio-surfactant fermentation liquid that reduces crude oil start-up pressure. After injection, the liquid can be adsorbed onto the rock wall, exhibiting strong wetting and regulation properties, improving permeability, reducing crude oil start-up pressure, increasing well production, extending well production period, and improving the recovery rate of igneous rocks. The combined effects of these factors resulted in good field test results, with single-well oil production increasing by 300-500 tons in field tests.

[0041] (3) The present invention has the advantages of simple construction process, easy operation, strong operability, low investment cost, good field test effect, input-output ratio greater than 1:5, and improved recovery rate by more than 10%. Attached Figure Description

[0042] Figure 1 This is a flowchart of a microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs, as disclosed in this invention. Detailed Implementation

[0043] The specific embodiments of the present invention are described in detail below.

[0044] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0045] like Figure 1 As shown, this invention discloses a microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs, comprising the following steps:

[0046] (1) Screening test reservoirs;

[0047] (2) Screening the microbial fermentation broth that produces biosurfactants and its concentration;

[0048] (3) Screening activators;

[0049] (4) Field test;

[0050] (5) Well opening and production;

[0051] (6) Evaluation of the on-site test results.

[0052] In the preferred case, the specific screening criteria for the test reservoirs described in step (1) are as follows: wells with Carboniferous igneous rock reservoirs, reservoir temperature <50℃, crude oil viscosity between 100 mPa·s and 30000 mPa·s, and permeability >2×10⁻⁶. -3μm 2 Mineralization <50000mg / L. Liquid volume 0~10m 3 The water content of the produced liquid reaches 0-30%.

[0053] Furthermore, the biosurfactant-producing microbial fermentation broth mentioned in step (2) includes biosurfactant-producing microorganisms and nutrient solution. The biosurfactant-producing microorganisms include yeast, Pseudomonas aeruginosa, and Bacillus subtilis. The biosurfactants produced by their metabolism are mostly glycolipids, lipopeptides, etc., which have strong wetting and regulation functions, can reduce crude oil start-up pressure, and improve the permeation effect.

[0054] In a preferred embodiment, the activator screening method is a static culture method. The activator screening is based on the yield of core crude oil obtained by stripping saturated crude oil from biosurfactant fermentation broth. The activator formulation consists of different carbon sources, nitrogen sources, and phosphorus sources. It is characterized by being soluble in water, forming an aqueous solution with a viscosity of less than 5 mPa·s, which can be utilized by bacteria, and having a carbon source content of more than 2%, while also containing trace elements required for microbial metabolism.

[0055] In this invention, preferably, the test reservoir in step (1) is a Carboniferous igneous rock oil well. Due to the development contradictions such as low formation energy, high crude oil viscosity, and complex fracture relationships, a microbial composite CO2 huff and puff process is adopted to reduce the crude oil start-up pressure, improve the permeation effect, improve the crude oil fluidity, and at the same time replenish formation energy, thereby achieving the purpose of increasing oil well production.

[0056] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0057] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0058] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

[0059] The present invention will be further described below with reference to specific embodiments.

[0060] Example 1:

[0061] A microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs includes the following steps:

[0062] (1) Screening test reservoirs;

[0063] Overview of test well A in a certain oil production plant of Shengli Oilfield: reservoir temperature 43℃, permeability 28.9μm 2 The formation water salinity was 17000 mg / L, the crude oil viscosity was 826 mPa·s, and the volume was 0.35 m³. 3 The produced liquid has a water content of 15% and is calcium chloride aqueous type, which meets the screening criteria for the test reservoir of this invention;

[0064] (2) Screening the microbial fermentation broth that produces biosurfactants and its concentration;

[0065] The produced fluid from test well A was filtered and fermented with three biosurfactants—yeast, Pseudomonas aeruginosa, and Bacillus subtilis—at concentrations of 2%, 5%, and 10%. Using the reservoir conditions of well A as the indoor physical simulation experimental conditions, the fermentation broths of different concentrations of biosurfactants were injected into a 50mD core at 43℃ for 3 days. The crude oil from test well A was then saturated. The blank group consisted of the produced fluid from test well A. During the experiment, the change in the pressure of the crude oil passing through the core was observed, and the biosurfactant fermentation broth and its concentration that reduced the crude oil start-up pressure by the largest margin were selected.

[0066] The nutrient solution formula for yeast fermentation liquid is 7% cottonseed oil, 12% molasses, and the remainder is water.

[0067] The nutrient solution formula for Pseudomonas aeruginosa fermentation broth is 3% glycerol, 0.8% sodium nitrate, 0.1% yeast powder, 0.4% K2HPO4, 0.4% KH2PO4, 0.02% MgSO4·7H2O, with the balance being water.

[0068] The nutrient solution formula for Bacillus subtilis fermentation broth is: 7% brown sugar, 2.5% sodium nitrate, 0.1% dipotassium hydrogen phosphate, 0.03% potassium dihydrogen phosphate, 0.01% MgSO4·7H2O, and the balance is water.

[0069] Table 1. Effects of different biosurfactants and microorganisms on reducing crude oil start-up pressure

[0070]

[0071] As shown in Table 1, the highest bacterial concentration of Pseudomonas aeruginosa fermentation broth was 10%, at 8.9 × 10⁻⁶. 9 The crude oil start-up pressure reduction rate was the highest, reaching 89%, with a volume of [number] particles per mL.

[0072] (3) Develop a suitable activator formula based on the growth requirements of Pseudomonas aeruginosa.

[0073] 150 ml of the produced fluid from test well A was placed into an anaerobic flask (200 mL volume). Nutrient solutions with different C / N ratios (2:1, 10:1, 20:1, 30:1, 40:1) were prepared, and then aseptically inoculated with a 10% concentration of *Pseudomonas aeruginosa* fermentation broth. A 50 mD core sample of saturated crude oil from test well A was then placed in the anaerobic flask and incubated in a constant temperature incubator at 43℃ for 30 days. The bacterial concentration and the amount of crude oil stripped from *Pseudomonas aeruginosa* were observed during the incubation process to determine the optimal nutrient system. Table 2 shows that the *Pseudomonas aeruginosa* produced the best surfactants and stripped the highest amount of crude oil from the saturated crude oil core sample when the nutrient system with a C / N ratio of 30:1 was selected.

[0074] Table 2. Effects of Pseudomonas aeruginosa on the metabolic stripping of crude oil in nutrient solutions with different C / N ratios.

[0075]

[0076]

[0077] (4) Field test

[0078] Based on the low-production and low-fluid characteristics of the Carboniferous igneous fractured reservoir in test well A, a microbial huff-and-puff injection process was developed, mainly consisting of four-stage plug injection. The specific process is as follows:

[0079] (41) Before injecting microorganisms, use 20m 3 The above hot water is used to wash the well;

[0080] (42) Injection of bio-surfactant fermentation broth and its nutrient solution, followed by well simmering for 45 days:

[0081] Two 20m wellheads are prepared 3 The wellhead consists of two mixing tanks: one for preparing the injection solution and another for injecting it. The bio-surfactant fermentation broth is transported to the wellhead by tanker truck. The activator is prepared at the wellhead using injection water. After preparation, the activator is mixed with the bio-surfactant fermentation broth at volume ratios of 2:1 and 1:1 to form slug one and slug two, respectively, for rapid injection.

[0082] The displacement of the slug is 50m. 3 / h, construction pressure controlled at 12MPa, total injection volume 600m³ 3 ;

[0083] The displacement of the second slug is 55m. 3 / h, construction pressure controlled at 12MPa, total injection volume 400-600m³ 3 ;

[0084] Inject 30m into the wellhead of the test reservoir 3Water was used as the displacement fluid, and the injection rate was 50m. 3 / h, shut in the well for observation;

[0085] (43) Inject carbon dioxide 45 days after shutting in the well:

[0086] The discharge capacity is 6t / h, the construction pressure is controlled at 12MPa, and the total injection volume is 200t;

[0087] (44) Inject 80m into the wellhead of the test reservoir. 3 Water was used as the displacement fluid, and the injection rate was 50m. 3 / h, shut in the well and observe the changes in wellhead pressure. When the pressure no longer drops and remains stable for 5 days, the well can be opened for production. The shut-in time is 25 days to allow carbon dioxide to fully dissipate underground. During the shut-in period, observe the changes in casing pressure and oil pressure.

[0088] (5) Field test:

[0089] After well commencement of production, production dynamics were monitored, with a daily oil production of 12 tons and a bacterial concentration of 80*10 in the produced fluid. 8 The oil well fluid volume was 13m³ / mL, crude oil viscosity was 153 mPa·s. 3 .

[0090] 6) Evaluation of the effectiveness of the field test

[0091] Following the injection process determined in the above steps, a field test was conducted. The injection volume of *Pseudomonas aeruginosa* fermentation broth and activator was 600 ml at a volume ratio of 2:1 and 1:1. 3 After the field test is completed, the effectiveness of the field test will be evaluated. The evaluation indicators include the increase in oil production, shelf life, and input-output ratio.

[0092] After on-site implementation, well A produced an additional 820 tons of oil, with an effective period of 90 days and an input-output ratio of 1:4. The field test results were good.

[0093] Example 2:

[0094] A microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs includes the following steps:

[0095] (1) Screening test reservoirs;

[0096] Overview of test well B in a certain oil production plant of Shengli Oilfield: reservoir temperature 38℃, permeability 234μm 2 The formation water salinity was 32,000 mg / L, the crude oil viscosity was 1534 mPa·s, and the volume was 2.3 m³. 3 The produced liquid has a water content of 18%, is calcium chloride aqueous type, and meets the screening criteria for the test reservoir of this invention;

[0097] (2) Screening the microbial fermentation broth that produces biosurfactants and its concentration;

[0098] The produced fluid from test well B was filtered and fermented with three biosurfactants—yeast, Pseudomonas aeruginosa, and Bacillus subtilis—at concentrations of 2%, 5%, and 10%. Using the reservoir conditions of well B as the indoor physical simulation experimental conditions, the fermentation broths of different concentrations of biosurfactants were injected into a 200mD core at 38℃ for 5 days. The crude oil from test well B was then saturated. The blank group consisted of the produced fluid from test well B. During the experiment, the change in the pressure of the crude oil passing through the core was observed, and the biosurfactant fermentation broth and its concentration that reduced the crude oil start-up pressure the most were selected.

[0099] The nutrient solution formula for yeast fermentation liquid is 3% cottonseed oil, 10% molasses, and the remainder is water.

[0100] The nutrient solution formula for Pseudomonas aeruginosa fermentation broth is 1% glycerol, 0.3% sodium nitrate, 0.15% yeast powder, 0.3% K2HPO4, 0.3% KH2PO4, 0.01% MgSO4·7H2O, with the balance being water.

[0101] The nutrient solution formula for Bacillus subtilis fermentation broth is as follows: 2% brown sugar, 0.2% sodium nitrate, 0.05% dipotassium hydrogen phosphate, 0.01% potassium dihydrogen phosphate, 0.015% MgSO4·7H2O, and the balance is water.

[0102] Table 3. Effects of different biosurfactants and microorganisms on reducing crude oil start-up pressure

[0103]

[0104] As shown in Table 3, the yeast fermentation broth with a concentration of 10% had the highest bacterial concentration, at 9.2 × 10⁻⁶. 9 The crude oil start-up pressure drop rate was the highest, reaching 85%, with a volume of [number] particles per mL.

[0105] (3) Develop a suitable activator formula based on the growth requirements of yeast.

[0106] 180 ml of the produced fluid from test well B was placed into a 200 mL anaerobic flask. Nutrient solutions with different C / N ratios (2:1, 10:1, 20:1, 30:1, 40:1) were prepared, and then aseptically inoculated with a 10% concentration of yeast fermentation broth. A 200 mD core sample of saturated crude oil from test well B was then placed in the anaerobic flask and incubated in a constant temperature incubator at 38℃ for 15 days. The yeast cell concentration and the amount of crude oil stripped were observed during the incubation process to determine the optimal nutrient system. Table 4 shows that the yeast with a C / N ratio of 40:1 exhibited the best surfactant production performance and the highest amount of crude oil stripped from the saturated crude oil core sample.

[0107] Table 4. Effects of yeast on the metabolic stripping of crude oil in nutrient solutions with different C / N ratios.

[0108] C / N ratio of nutrient solution <![CDATA[Cell concentration (*10 8 cells / mL)]]> Crude oil stripping volume (g) 2:1 25 1.1 10:1 38 3.1 20:1 66 4.0 30:1 80 4.5 40：1 95 5.2

[0109] (4) Field test

[0110] Based on the low production and low fluid content characteristics of the Carboniferous igneous fractured reservoir in the experimental well B, a microbial huff-and-puff injection process was developed, mainly consisting of four-stage plug injection. The specific process is as follows:

[0111] (41) Before injecting microorganisms, use 20m 3 The above hot water is used to wash the well;

[0112] (42) Inject the bio-surfactant fermentation broth and its nutrient solution, and simmer the well for 30 days:

[0113] Two 20m wellheads are prepared 3 The wellhead consists of two mixing tanks: one for preparing the injection solution and another for injecting it. The bio-surfactant fermentation broth is transported to the wellhead by tanker truck. The activator is prepared at the wellhead using injection water. After preparation, the activator is mixed with the bio-surfactant fermentation broth at volume ratios of 2:1 and 1:1 to form slug one and slug two, respectively, for rapid injection.

[0114] The displacement of the slug is 30m. 3 / h, construction pressure controlled at 5MPa, total injection volume 300m 3 ;

[0115] The displacement of the slug 2 is 30m. 3 / h, construction pressure controlled at 5MPa, total injection volume 300m 3 ;

[0116] 40 m³ of clean water was injected into the wellhead of the test reservoir as a displacement fluid at a rate of 40 m³ / h. The well was then shut in for observation, allowing the microorganisms to fully react and metabolize the biosurfactant in the reservoir.

[0117] (43) Inject carbon dioxide 30 days after shutting in the well:

[0118] The discharge capacity is 7t / h, the construction pressure is controlled at 5MPa, and the total injection volume is 100t;

[0119] (44) Inject 50m into the wellhead of the test reservoir. 3 Water was used as the displacement fluid, and the injection rate was 45m. 3 / h, shut in the well and observe the changes in wellhead pressure. When the pressure no longer drops and remains stable for 5 days, the well can be opened for production. The shut-in time is 30 days to allow carbon dioxide to fully dissipate underground. During the shut-in period, observe the changes in casing pressure and oil pressure.

[0120] (5) Field test:

[0121] After well commencement of production, production dynamics were monitored, with a daily oil production of 10 tons and a bacterial concentration of 75*10 in the produced fluid. 8 The oil well fluid volume was 11 mL / ml, crude oil viscosity was 274 mPa·s, and well fluid volume was 11 mL / ml. 3 .

[0122] (6) Evaluation of the effect of field test

[0123] Following the injection process determined in the above steps, a field test was conducted. The injection volume of *Pseudomonas aeruginosa* fermentation broth and activator was 600 ml at a volume ratio of 2:1 and 1:1. 3 After the field test is completed, the effectiveness of the field test will be evaluated. The evaluation indicators include the increase in oil production, shelf life, and input-output ratio.

[0124] After implementation on-site, well A produced an additional 980 tons of oil, with an effective period of 90 days and an input-output ratio of 1:4. The on-site test results were good.

[0125] Example 3

[0126] A microbial huff and puff method for oil recovery in fractured Carboniferous igneous reservoirs includes the following steps:

[0127] (1) Screening test reservoirs;

[0128] Overview of test well C in a certain oil production plant of Shengli Oilfield: reservoir temperature 30℃, permeability 130μm 2 The formation water salinity is 22000 mg / L, the crude oil viscosity is 13410 mPa·s, and the volume is 0.8 m³. 3 The produced liquid has a water content of 10%, is calcium chloride aqueous type, and meets the screening criteria for the test reservoir of this invention;

[0129] (2) Screening the microbial fermentation broth that produces biosurfactants and its concentration;

[0130] The produced fluid from test well C was filtered and fermented with three biosurfactants—yeast, Pseudomonas aeruginosa, and Bacillus subtilis—at concentrations of 2%, 5%, and 10%. The reservoir conditions of well C were used as the conditions for indoor physical simulation experiments. The fermentation broths of different concentrations of biosurfactants were injected into an 800mD core at 30℃ for 4 days, and then the crude oil from test well C was saturated. The blank group was the produced fluid from test well C. During the experiment, the change in the pressure of the crude oil passing through the core was observed, and the biosurfactant fermentation broth and its concentration that reduced the crude oil start-up pressure the most were screened.

[0131] The nutrient solution formula for yeast fermentation liquid is 8% cottonseed oil, 3% molasses, and the remainder is water.

[0132] The nutrient solution formula for Pseudomonas aeruginosa fermentation broth is 4% glycerol, 1.2% sodium nitrate, 0.2% yeast powder, 0.1% K2HPO4, 0.1% KH2PO4, 0.015% MgSO4·7H2O, with the balance being water.

[0133] The nutrient solution formula for Bacillus subtilis fermentation broth is 8% brown sugar, 3% sodium nitrate, 0.07% dipotassium hydrogen phosphate, 0.07% potassium dihydrogen phosphate, 0.02% MgSO4·7H2O, and the remainder is water.

[0134] Table 5. Effects of different biosurfactants and microorganisms on reducing crude oil start-up pressure

[0135]

[0136]

[0137] As shown in Table 3, the highest bacterial concentration of Bacillus subtilis fermentation broth was 10%, at 8.8 × 10⁻⁶. 9 The crude oil start-up pressure reduction rate was the highest, reaching 88%, with a volume of [number] particles per mL.

[0138] (3) Develop a suitable activator formula based on the growth requirements of Bacillus subtilis.

[0139] 300 ml of the produced fluid from test well C was placed into an anaerobic flask (500 mL volume). Nutrient solutions with different C / N ratios (2:1, 10:1, 20:1, 30:1, 40:1) were prepared, and then aseptically inoculated with 10% Bacillus subtilis fermentation broth. An 800 mD core sample of saturated crude oil from test well C was then placed in the anaerobic flask and incubated in a constant temperature incubator at 30℃ for 25 days. The Bacillus subtilis concentration and the amount of crude oil stripped were observed during the incubation process to determine the optimal nutrient system. Table 6 shows that the yeast produced the best surfactant and stripped the highest amount of crude oil from the saturated crude oil core sample when the C / N ratio was 40:1.

[0140] Table 6. Effects of Bacillus subtilis on the metabolic stripping of crude oil in nutrient solutions with different C / N ratios.

[0141]

[0142]

[0143] (4) Field test

[0144] Based on the low production and low fluid content characteristics of the Carboniferous igneous fractured reservoir in the test well, a microbial huff-and-puff injection process was developed, mainly consisting of four-stage plug injection. The specific process is as follows:

[0145] (41) Before injecting microorganisms, use 20m 3 The above hot water is used to wash the well;

[0146] (42) Injection of bio-surfactant fermentation broth and its nutrient solution, followed by well simmering for 60 days:

[0147] Two 20m wellheads are prepared 3 The wellhead consists of two mixing tanks: one for preparing the injection solution and another for injecting it. The bio-surfactant fermentation broth is transported to the wellhead by tanker truck. The activator is prepared at the wellhead using injection water. After preparation, the activator is mixed with the bio-surfactant fermentation broth at volume ratios of 2:1 and 1:1 to form slug one and slug two, respectively, for rapid injection.

[0148] The displacement of the slug is 60m. 3 / h, construction pressure controlled at 20MPa, total injection volume 700m³ 3 In another embodiment, the slug displacement is 40m³. 3 / h, construction pressure controlled at 20MPa, total injection volume 400m³ 3 ;

[0149] The displacement of the second slug is 60m. 3 / h, construction pressure controlled at 20MPa, total injection volume 700m³3 In another embodiment, the displacement of the slug 2 is 45m³. 3 / h, construction pressure controlled at 20MPa, total injection volume 400m³ 3 ;

[0150] 50m³ of fresh water was injected into the wellhead of the test reservoir as a displacement fluid. 3 The injection speed is 60m 3 / h, shut in the well for observation;

[0151] (43) After shutting in the well for 60 days, carbon dioxide is injected again at a rate of 10t / h, with the construction pressure controlled at 20MPa and the total injection amount of 250t.

[0152] (44) Inject 100m into the wellhead of the test reservoir. 3 Water was used as the displacement fluid, and the injection rate was 50m. 3 / h, shut in the well and observe the changes in wellhead pressure. When the pressure no longer drops and remains stable for 5 days, the well can be opened for production. The shut-in time is 30 days to allow carbon dioxide to fully dissipate underground. During the shut-in period, observe the changes in casing pressure and oil pressure.

[0153] (5) Field test:

[0154] After well production began, production dynamics were monitored, with a daily oil production of 9 tons and a bacterial concentration of 65*10⁻⁶. 8 Units / mL, crude oil viscosity 1845 mPa·s, well fluid volume 10m³ / mL 3 .

[0155] (6) Evaluation of the effect of field test

[0156] Following the injection process determined in the above steps, a field test was conducted. The injection volume of *Pseudomonas aeruginosa* fermentation broth and activator was 600 ml at a volume ratio of 2:1 and 1:1. 3 After the field test is completed, the effectiveness of the field test will be evaluated. The evaluation indicators include the increase in oil production, shelf life, and input-output ratio.

[0157] After implementation on-site, well A produced an additional 880 tons of oil, with an effective period of 80 days and an input-output ratio of 1:4. The on-site test results were good.

[0158] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for microbial huff and puff recovery of oil in fractured Carboniferous igneous reservoirs, characterized in that, Includes the following steps: (1) Screening test reservoirs; (2) Screening the microbial fermentation broth that produces biosurfactants and its concentration; (3) Screening activators; (4) Field test; (5) Well opening and production; (6) Evaluation of on-site test results, including: The screening criteria for the test reservoir in step (1) are as follows: Select oil wells in Carboniferous igneous rock reservoirs with reservoir temperatures <50℃, crude oil viscosity between 100 mPa·s and 30000 mPa·s, and permeability >2×10⁻⁶. -3 μm 2 Mineralization <50000 mg / L, liquid volume 0-10 ml 3 The water content of the produced liquid reaches 0-30%; Step (2) includes the following steps: Take the produced fluid from the test reservoir screened in step (1), filter it, and prepare various bio-surfactant microbial fermentation broths with a mass concentration of 2% to 10%. Use the reservoir conditions of the test reservoir as the indoor physical simulation experimental conditions. Inject the bio-surfactant microbial fermentation broths of different concentrations into 50 to 800 mD cores for 3 to 5 days at the reservoir temperature. Saturate the crude oil of the test reservoir. Use the produced fluid of the test reservoir as the blank group. Observe the change in the pressure of the crude oil passing through the core during the experiment. Based on the reduction rate of the crude oil starting pressure, screen the bio-surfactant microbial fermentation broths and their concentrations. Step (3) includes the following steps: Take 150-300 ml of the produced liquid from the test reservoir selected in step (1) and put it into an anaerobic bottle. Prepare a nutrient solution of the bio-surfactant microorganisms selected in step (2) with a C / N ratio of 2-40:

1. Then, aseptically inoculate the fermentation broth of the bio-surfactant microorganisms selected in step (2) with a mass concentration of 2-10%. Then, place 50-800 mD cores of saturated crude oil from the test reservoir into the anaerobic bottle and incubate them in a constant temperature chamber for 15-30 days. The temperature of the constant temperature chamber is set to the reservoir temperature of the test reservoir. Then, observe the amount of crude oil stripping during the incubation process and determine the amount of crude oil stripping. Based on the amount of crude oil stripping, determine the optimal C / N ratio, which is the formula of the activator.

2. The method for microbial huff and puff recovery of oil in Carboniferous igneous fractured reservoirs as described in claim 1, characterized in that, The bioactive surfactant microbial fermentation broth is one of yeast fermentation broth, Pseudomonas aeruginosa fermentation broth, and Bacillus subtilis fermentation broth.

3. The method for microbial huff and puff recovery of oil in Carboniferous igneous fractured reservoirs as described in claim 2, characterized in that, The nutrient solution formula for the yeast fermentation broth is 3-8% cottonseed oil, 3-12% molasses, and the remainder is water.

4. The method for microbial huff and puff recovery of oil in Carboniferous igneous fractured reservoirs as described in claim 2, characterized in that, The nutrient solution of the *Pseudomonas aeruginosa* fermentation broth consists of 1-4% glycerol, 0.3-1.2% sodium nitrate, 0.1-0.2% yeast extract, 0.1-0.4% K₂HPO₄, 0.1-0.4% KH₂PO₄, 0.01-0.02% MgSO₄·7H₂O, with the remainder being water.

5. The method for microbial huff and puff recovery of oil in fractured Carboniferous igneous reservoirs as described in claim 2, characterized in that, The nutrient solution of the Bacillus subtilis fermentation broth consists of 2-8% brown sugar, 0.2-3% sodium nitrate, 0.05-0.1% dipotassium hydrogen phosphate, 0.01-0.05% potassium dihydrogen phosphate, 0.01-0.02% MgSO4·7H2O, and the remainder is water.

6. The method for microbial huff and puff recovery of oil in fractured Carboniferous igneous reservoirs as described in claim 1, characterized in that, Step (4) includes the following steps: (41) Before construction, use 20m 3 The above hot water is used to wash the well; (42) Inject the bio-surfactant fermentation broth and its nutrient solution, and simmer the well for 30-60 days: Two wellheads of at least 20m in length were prepared for the test reservoir. 3 The wellbore has two mixing tanks: one for preparing the injection fluid and the other for injecting it. The bio-surfactant fermentation broth is transported to the wellhead. The activator is prepared at the wellhead using injection water. The prepared activator and the bio-surfactant fermentation broth are mixed at volume ratios of 2:1 and 1:1 to form slug one and slug two, respectively, which are then rapidly injected into the wellhead of the test reservoir. The displacement of the slug is 30m. 3 / h~60m 3 / h, construction pressure controlled between 5MPa and 20MPa, total injection volume 300m³. 3 ~700m 3 ; The displacement of the slug 2 is 30m. 3 / h~60m 3 / h, construction pressure controlled between 5MPa and 20MPa, total injection volume 300m³. 3 ~700m 3 ; Inject 30-50m into the wellhead of the test reservoir 3 Water was used as the displacement fluid, and the injection rate was 30–60 m / s. 3 / h, shut in the well for observation; (43) Injection of carbon dioxide: The discharge capacity is 4t / h to 10t / h; the construction pressure is controlled at 5MPa to 20MPa; and the total injection volume is 100t to 250t. (44) Inject 50-100m³ of clean water into the wellhead of the test reservoir. 3 As a replacement fluid, shut in the well and observe. After shutting in the well, observe the changes in wellhead pressure. When the pressure no longer drops and remains stable for 5 days, the well can be started for production.

7. The method for microbial huff and puff recovery of oil in fractured Carboniferous igneous reservoirs as described in claim 6, characterized in that, In step (42): The displacement of the slug is 40-50m. 3 / h, construction pressure controlled between 5MPa and 20MPa, total injection volume 400 to 600m³ 3 ; The displacement of the second slug is 45-55m. 3 / h, construction pressure controlled between 5MPa and 20MPa, total injection volume 400 to 600m³ 3 .

8. The method for microbial huff and puff recovery of oil in Carboniferous igneous fractured reservoirs as described in claim 6, characterized in that, In step (43): The carbon dioxide injection rate is 6-8 t / h; the construction pressure is controlled at 5MPa-20MPa, and the total injection volume is 150-200t.

9. The method for microbial huff and puff recovery of oil in Carboniferous igneous fractured reservoirs as described in claim 6, characterized in that, In step (44): Inject 60-80m³ of clean water into the wellhead of the test reservoir. 3 As a replacement fluid, shut in the well and observe. After shutting in the well, observe the changes in wellhead pressure. When the pressure no longer drops and remains stable for 5 days, the well can be started for production.

10. The method for microbial huff and puff recovery of oil in Carboniferous igneous fractured reservoirs as described in claim 1, characterized in that, In step (5), the bacterial concentration, surface tension, well fluid volume, oil volume, and crude oil viscosity of the produced fluid are tracked.

11. The method for microbial huff and puff recovery of oil in fractured Carboniferous igneous reservoirs as described in claim 1, characterized in that, The indicators for evaluating the effectiveness of the field test in step (6) include the increase in oil production, shelf life, and input-output ratio.

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