Method for improving shale oil and gas reservoir development effect by using microorganisms

Abstract

The invention discloses a method for improving the development effect of a shale oil and gas reservoir by utilizing microorganisms. The method comprises the following steps: (1) screening the shale oil and gas reservoir; (2) screening strains and activating agents thereof; (3) determining on-site injection process parameters; (4) performing composite fracturing construction; and (5) field test and effect evaluation. The method for improving the shale oil and gas reservoir development effect by using the microorganisms has the following beneficial effects: 1, the bacterial liquid and the nutritional agent thereof are injected, are water-soluble substances, are high in safety performance, and are combined with fracturing to solve the injection problem; 2, the strain acts on reservoir rocks, directly improves the porosity and permeability, and is long in period of validity, which is embodied in high primary yield and long period of validity of an oil well in production; 3, the acid-producing microorganisms are compounded, a bedding structure is utilized, the reaction effect is improved, and the dosage is low; and 4, the microbial oil displacement agent is suitable for shale oil and gas reservoirs and biological limestone reservoirs, and can be compounded with other common microbial oil displacement functional bacteria to further improve the effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of microbial oil production, and particularly relates to a method for improving the development effect of shale oil and gas reservoirs by using microorganisms. Background Art

[0002] The resource volume of shale oil and gas in China is huge. However, shale oil and gas reservoirs have small porosity, low permeability, and low abundance, and generally have no natural production capacity. Since 2010, China has carried out large-scale development of shale oil. With the progress of drilling technology and fracturing technology, significant breakthroughs and remarkable progress have been made. However, there are still problems such as low single-well production, great development difficulty, and high investment cost.

[0003] At present, an emphasis in shale oil development is the accurate identification of sweet spots, which is the basis for realizing the large-scale and efficient development of shale oil. Geophysical and engineering sweet spots are identified using technologies such as seismic data, logging data, and nuclear magnetic resonance. Currently, domestic and foreign scholars are committed to integrating various technologies to establish a method for identifying reservoir sweet spots. However, the current method still has a low accuracy rate, and the newly drilled wells still face problems such as thin thickness and low reserves.

[0004] Another emphasis in shale oil and gas reservoir development is to rely on the improvement of fracturing scale and technology. Mainly through large-scale staged fracturing technology for horizontal wells or refracturing technology for old wells, artificial hydraulic fractures are generated to connect natural fractures and form a three-dimensional fracture network. For example, Chinese Patent Application CN112983371A provides a method for extracting oil shale using hot fluid and a coupling catalyst between fractures in the same horizontal well. The method for extracting oil shale includes: fracturing the horizontal wellbore in stages to form multiple fracturing fractures perpendicular to the horizontal wellbore, and dividing the fracturing fractures into a first group of fracturing fractures and a second group of fracturing fractures; perforating at positions on the tubing corresponding to the first part of the fractures; injecting steam into the second group of fracturing fractures through the annular space formed by the tubing and the casing; and when it is monitored that oil and gas products are produced, opening the oil production valve provided at the wellhead of the horizontal well, and the oil and gas products obtained by heating in the oil shale enter the annular space and are produced through the perforations corresponding to the first group of fracturing fractures into the tubing. However, the effects of the above technical solutions are closely related to the length of the horizontal section and the scale of the transformation, and still cannot improve the permeability of the shale matrix blocks. Affected by the physical properties of the oil and gas reservoir and the current transformation process, the production cost is high while the recovery rate is low. Moreover, due to the formation of relatively narrow fractures during fracturing, it is not conducive to the migration of proppants, and it is also difficult to achieve a high sand placement concentration. After the transformation, the fractures close quickly, and the production decline is very large, seriously restricting the effective development and development economy of shale oil and gas reservoirs.

[0005] Chinese invention patent CN 112832726B discloses a tertiary oil recovery method for single-well huff and puff inter-stage oil displacement in tight oil shale wells. In this method, an injection fluid containing a microbial oil displacement agent is injected into the oil well, followed by soaking the well. Through the action of the microorganisms themselves and their metabolites, the physical properties of the crude oil are improved, and the oil well production is increased. In this method, the huff and puff method is optimized, which solves the problems of long construction period, complex construction process, and multiple well opening and closing in the existing microbial enhanced oil recovery process. However, it still only acts on the crude oil, and in shale oil reservoirs with poor physical properties, there will be problems such as difficulty in injection and short effective period.

[0006] Chinese invention patent 107387052B discloses a method for in-situ staged fracturing of oil shale, physical fragmentation and chemical modification of shale by cyclic injection of hot gas, and ultimately improving the shale recovery rate. This method requires drilling injection wells and production wells separately, fracturing the injection wells in stages, relying on packers and injecting a mixed gas at 350 - 450 °C. Through high-temperature cracking reactions, the organic matter cracks to increase the voids and permeability of the reservoir for production enhancement. Due to the need to inject high-temperature gas, this method has high requirements for the high temperature and high pressure resistance of the process, pipe string, and packers. Moreover, the injection quality and injection volume have a great impact on the effect, high energy consumption, the underground cracking reaction process is not easy to understand and control, and the on-site high temperature and high pressure operation risk is high. High-temperature cracking causes chemical reactions underground and may also produce toxic and harmful substances, which may pollute groundwater, pipeline transportation systems, the environment, etc.

[0007] Analyzing the characteristics of shale oil / gas reservoirs, the reservoirs are mainly composed of interbedded sand and mud, with strong bedding, high organic matter content. The organic matter in the reservoir minerals is mainly kerogen and asphalt, which are insoluble in ordinary acids and require strong oxidizing acids or high-temperature heating for treatment, with high treatment difficulty and high energy consumption. In addition, the mineral content is high, its carbonate content is high and it is easily acidified; and it generally contains pyrite. Summary of the Invention

[0008] Object of the Invention: Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a method for improving the development effect of shale oil and gas reservoirs using microorganisms.

[0009] In view of the characteristics of high pyrite, carbonate, and inorganic mineral components in shale oil and gas reservoirs, the present invention specifically screens out leaching bacteria to remove pyrite in oil shale, inducing microfractures in the reservoir, and compounding acid-producing microbial strains to remove carbonates. Utilizing the special bedding distribution of shale, the reaction efficiency is improved. At the same time, dissolving carbonates and other inorganic minerals soluble in acid can generate more pores. The strain screening indexes are determined for the first time: pH value change, Fe 3+ concentration measurement, and scanning electron microscopy analysis; combined with fracturing to solve the injection problem and improve the fracturing effect, ultimately increasing the production of shale oil and gas reservoirs.

[0010] The present invention utilizes the special bedding-like distribution characteristics of shale to screen specific microbial strains to treat pyrite in oil shale. The special bedding-like distribution of shale acts on the pyrite therein, requiring fewer substances to participate in the reaction, but having a large influence range, inducing a large number of microfractures in the reservoir. The composite acid-producing microbial strains react with carbonates, which can expose more surfaces of pyrite, greatly improving the action efficiency of the bacteria leaching pyrite, and generating a large number of dissolution pores. Both microfractures and dissolution pores can greatly improve the permeability of the shale reservoir. The mixed bacteria are injected simultaneously, and by using the bedding distribution, the reaction progresses layer by layer, reducing the inhibitory reaction caused by the high concentration of the bacteria themselves and their metabolites.

[0011] The compounded microbial strains that change wettability can, on the one hand, reduce the seepage resistance of crude oil in the pores. On the other hand, in tight reservoirs, during the processes of well drilling, completion, production, and measures where external fluids are injected, water sensitivity is extremely likely to occur, resulting in a sharp decline in production capacity. Adding the microbial strains that change wettability can prevent and improve the water sensitivity phenomenon and restore the production capacity of oil wells.

[0012] However, due to the poor physical properties and low permeability of oil shale reservoirs, directly injecting the bacterial liquid system will face the problem of being unable to inject, and after injection, the contact area with the reservoir is small and the action efficiency is low. If it is synergistically combined with hydraulic fracturing and implemented in horizontal wells, the two complement each other, and the effect achieves 1 + 1 > 2. It can not only ensure the large-scale injection of microorganisms and nutrient solutions in tight lithologic reservoirs, expand the contact area between microorganisms and the reservoir, thereby enhancing the reaction rate and effect, but also the small amount of precipitation in situ generated after the reaction between bacteria and the reservoir can play a role in supporting the fracture to prevent the fracture from closing, extending the effective period of fracturing, enhancing the fracturing effect, thereby greatly increasing the production of shale oil and gas wells, slowing down the decline of oil and gas wells. The process operation is simple, safe and reliable, and the cost is low. It can also lower the economic and technical production thresholds of oil shale reservoirs, which has extremely important significance.

[0013] The present invention utilizes specific bacterial microorganisms to oxidize pyrite in oil shale, which can induce the generation of microfractures and improve the permeability of the shale reservoir.

[0014] The compounded acid-producing microorganisms of the present invention remove carbonates, and by utilizing the special bedding-like distribution of shale, the reaction efficiency is improved. At the same time, dissolving carbonates and other inorganic minerals soluble in acid can generate more pores.

[0015] The present invention synergistically combines with hydraulic fracturing, which can not only ensure the injection of microorganisms and nutrient solutions in tight lithologic reservoirs, but also enhance the fracturing effect and extend the effective period of fracturing.

[0016] The microbial injection system of the present invention is injected at normal temperature and pressure, with simple operation, safe and reliable, low cost, and can also lower the economic and technical production thresholds of oil shale reservoirs.

[0017] Technical solution: A method for improving the development effect of shale oil and gas reservoirs by using microorganisms, comprising the following steps:

[0018] (1) Screening of shale oil and gas reservoirs;

[0019] (2) Screening of bacterial strains and their activators;

[0020] (21) Screening of bacterial strains producing surfactants and their nutrient solutions;

[0021] (22) Screening of bacterial strains producing acids and acting on pyrite for ore leaching and their nutrient solutions;

[0022] (3) Determination of on-site injection process parameters;

[0023] (4) Composite fracturing construction;

[0024] (5) On-site tests and effect evaluations.

[0025] Furthermore, the screening criteria for shale oil and gas reservoirs in step (1) are as follows: the carbonate content in the shale > 20%, the pyrite content > 1%, the reservoir temperature < 120°C, the formation water salinity < 100000 mg / L, and the horizontal section length of the horizontal well > 100 meters.

[0026] Furthermore, the specific steps of step (21) are as follows:

[0027] (211) Screening of bacterial strains producing surfactants

[0028] Take the formation water of the shale oil and gas reservoir screened in step (1), measure and record the contact angle between different test pieces and the formation water, and then soak the test pieces in the bacterial solution of the bacterial strains producing surfactants to be screened for 3 days, and then measure and record the contact angle between the test pieces and the formation water. Screen out the bacterial strains producing surfactants with the largest change in contact angle before and after, where:

[0029] The bacterial strains producing surfactants are one of Bacillus licheniformis, Bacillus sp., Pseudomonas sp., Serratia sp., Acinetobacter sp. and Arcobacter sp.;

[0030] (212) Screening of nutrient solutions for bacterial strains producing surfactants

[0031] Take 100 ml of the produced water of the shale oil and gas reservoir screened in step (1) and put it into an anaerobic bottle. Sterilely inoculate 1 ml of the bacterial solution of the bacterial strains producing surfactants screened in step (211) and 9 ml of nutrient solutions with different formulations, and then place the anaerobic bottle at the reservoir temperature for 10 - 20 days. After the cultivation is completed, measure the bacterial concentration, and select the nutrient formulation with the highest bacterial concentration as the on-site activator formulation, where:

[0032] The nutrient solution of the surfactant-producing strain consists of a carbon source, a nitrogen source, and a phosphorus source. The carbon source is at least one of glucose, sucrose, glycerol, and soybean oil. The nitrogen source is at least one of ammonium nitrate and urea. The phosphorus source is at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and phospholipid.

[0033] In the nutrient solution of the surfactant-producing strain, the mass concentrations of the carbon source, nitrogen source, and phosphorus source are 1.0 - 3.0%, 0.2 - 0.6%, and 0.1 - 0.3% respectively.

[0034] Furthermore, the steps of step (22) are as follows:

[0035] (221) Preliminary screening of the acid-producing strain and the strain acting on pyrite leaching

[0036] Preliminary screening of the acid-producing strain and the strain acting on pyrite leaching according to the change of pH value. The specific steps are as follows:

[0037] The bacterial solution of the acid-producing strain and the bacterial solution of the strain acting on pyrite are mixed in equal volume. The mixed bacteria are added with a culture solution, and the initial pH value is adjusted to 2.0. They are cultured at the reservoir temperature for 30 days, and the pH value of the solution is measured every day. The combination with a longer time when the pH value < 3.5 is selected to preliminarily determine the acid-producing strain and the strain acting on pyrite leaching, where:

[0038] The acid-producing strain is one of the genera Lactobacillus, Bifidobacterium, and Streptococcus thermophilus;

[0039] The strain acting on pyrite leaching is one of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Ferrooxidans ferrooxidans, Bacillus circulans, Bacillus mucilaginosus, and Bacillus mucilaginosus;

[0040] The longest number of days when the pH value of the mixed bacterial solution ranges from 2.0 to 5.0 is selected as the culture and shut-in time;

[0041] (222) Final determination of the acid-producing strain and the strain acting on pyrite

[0042] The final injected strain is determined by the leaching rock core method. The screening basis is Fe 3+ concentration measurement and scanning electron microscopy analysis. The screening criteria are: Fe 3+ high concentration and the surface is loose and the proportion of the porous state is more than 30%;

[0043] (223) Screening of the nutrient solution of the acid-producing strain and the strain acting on pyrite leaching

[0044] Take 100 ml of the produced water from the shale oil and gas reservoir screened in step (1) and put it into an anaerobic bottle. Under sterile conditions, inoculate 1 ml of the combined bacteria strain screened in step (221) that produces acid and acts on pyrite, and 9 ml of nutrient solutions with different formulations. Then place the anaerobic bottle in an incubator at the reservoir temperature for 10 - 30 days. After the incubation, measure the bacterial concentration, and preferably select the nutrient formulation with the highest bacterial concentration as the field activator formulation, where:

[0045] The nutrient solution for the bacteria strain that produces acid and the bacteria strain that acts on pyrite consists of a carbon source, a nitrogen source, a phosphorus source, and trace elements. The carbon source is at least one of glucose, sucrose, glycerol, and soybean oil. The nitrogen source is at least one of ammonium nitrate and ammonium nitrate. The phosphorus source is at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and phospholipids. The trace elements are one or more of manganese sulfate, zinc sulfate, copper sulfate, and potassium iodide;

[0046] The mass concentrations of the carbon source, nitrogen source, phosphorus source, and trace elements in the nutrient solution for the bacteria strain that produces acid and the bacteria strain that leaches ore by acting on pyrite are 0.5 - 2.0%, 0.1 - 0.3%, 0.05 - 0.3%, and 0.001 - 0.002% respectively.

[0047] Furthermore, the field injection process parameters in step (3) include the field injection volume, injection method, and shut-in time of the bacterial liquid and its nutrient solution.

[0048] Even further, the total field injection volume of the bacterial liquid and its nutrient solution in step (3) is determined by the following formula:

[0049] Q = a * L * S * h * Ф

[0050] Where:

[0051] Q—the volume injection amount of the bacterial liquid and its nutrient solution, m 3 ;

[0052] a—the dosage coefficient, with a value of 0.2 - 0.5;

[0053] L—the horizontal section length of the test oil well, m;

[0054] h—the oil layer thickness of the test oil well. If h ≤ 20 m, take the actual thickness. If h > 20 m, take 20 m;

[0055] S—the horizontally extended design length of the fracture, m;

[0056] Ф—the porosity of the test oil well, dimensionless;

[0057] If the fracturing is staged fracturing, then split according to the KH of each stage, that is, permeability * horizontal section length, to obtain the injection amount of each stage;

[0058] The mass ratio of the bacterial liquid to the nutrient solution is 1:9.

[0059] Furthermore, in step (3), the injection method is as follows: directly inject using the fracturing string of the test oil well.

[0060] Furthermore, the confirmation standard for the shut-in time in step (3) is as follows: select the longest number of days when the pH value of the mixed bacterial liquid ranges from 2.0 to 5.0 as the shut-in time, where:

[0061] If the pressure is greater than the pressure-bearing limit of the wellhead, even if the shut-in time has not reached, the well must be opened. That is, it is necessary to open the well in a timely manner in combination with the wellhead pressure situation.

[0062] Further, the steps of step (4) mainly include:

[0063] (41) Inject a preflush fluid into the fractured well section to form microfractures in the tight oil reservoir;

[0064] (42) After the injection of the preflush fluid is completed, inject a sand-carrying fluid into the pipeline. After the sand addition is completed, inject a displacement fluid to press the sand into the fractures;

[0065] (43) According to the fracturing construction design, after the construction is completed, inject the bacterial liquid and its nutrient solution, conduct a shut-in, and open the well after the shut-in is completed, where:

[0066] The on-site injection ratio of the bacterial liquid and its nutrient solution is prepared according to a volume ratio of 1:9. The bacterial liquid is composed of 50% of the bacterial liquid producing surfactants, 25% of the bacterial liquid producing acid, and 25% of the bacterial liquid acting on pyrite. The nutrient solution is composed of 50% of the nutrient solution of the bacterial strain producing surfactants and 50% of the nutrient solutions of the bacterial strains producing acid and acting on pyrite;

[0067] Further, the evaluation indicators for on-site tests and effects in step (5) include: initial production of a single well, cumulative increased oil production, input-output ratio, and slowdown of natural decline.

[0068] Beneficial effects: A method for improving the development effect of shale oil and gas reservoirs by using microorganisms disclosed in the present invention has the following beneficial effects:

[0069] 1. The injected substances are the bacterial liquid and its nutrient agent, both of which are water-soluble substances with high safety performance. Combining with fracturing solves the injectability problem;

[0070] 2. The bacterial strains act on the reservoir rock, directly improving porosity and permeability, with a long effective period, which is reflected in high initial production of oil wells and a long effective period in production;

[0071] 3. Composite acid-producing microorganisms utilize the bedding structure to improve the reaction effect and have a low dosage;

[0072] 4. It is applicable to biolithite reservoirs in shale oil and gas reservoirs, and can also be compounded with other common functional bacteria for microbial enhanced oil recovery to further improve the effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 It is a flowchart of a method for improving the development effect of shale oil and gas reservoirs by using microorganisms disclosed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] The following details the specific embodiments of the present invention.

[0075] The "range" disclosed by the present invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of the specific range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 10 - 50 is listed for a specific parameter, ranges of 10 - 40 and 20 - 50 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents the abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are listed in this article, and "0 - 5" is only the abbreviated representation of these numerical combinations.

[0076] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0077] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0078] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0079] Unless otherwise specified, the terms "comprising" and "including" used in this application are open-ended and may also be closed-ended. For example, the terms "comprising" and "including" may mean that other components not listed may also be included or contained, or it may only include or contain the listed components.

[0080] Unless otherwise specified, the reaction is carried out under normal temperature and pressure conditions.

[0081] Unless otherwise specified, all parts or percentages are by weight or weight percentage.

[0082] In the present invention, the substances used are all known substances and can be purchased or synthesized by known methods.

[0083] In the present invention, the devices or equipment used are all conventional devices or equipment known in the art and can be purchased.

[0084] A method for improving the development effect of shale oil and gas reservoirs by using microorganisms, comprising the following steps:

[0085] (1) Screening of shale oil and gas reservoirs;

[0086] (2) Screening of strains and their activators;

[0087] (21) Screening of strains producing surfactants and their nutrient solutions;

[0088] (22) Screening of strains producing acid and acting on pyrite for ore leaching and their nutrient solutions;

[0089] (3) Determination of on-site injection process parameters;

[0090] (4) Composite fracturing construction;

[0091] (5) On-site tests and effect evaluations.

[0092] Furthermore, the screening criteria for shale oil and gas reservoirs in step (1) are: carbonate content in shale > 20%, pyrite content > 1%, reservoir temperature < 120 °C, formation water salinity < 100000 mg / L, and the horizontal section length of the horizontal well is greater than 100 meters.

[0093] Furthermore, the specific steps of step (21) are as follows:

[0094] (211) Screening of strains producing surfactants

[0095] Take the formation water of the shale oil and gas reservoir screened in step (1), test and record the contact angle between different test pieces and the formation water. Then, immerse the test pieces in the bacterial solution of the surfactant-producing strains to be screened for 3 days, and then test and record the contact angle between the test pieces and the formation water. Screen out the surfactant-producing strains with the largest change in contact angle before and after, where:

[0096] The surfactant-producing strain is one of Bacillus licheniformis, Bacillus sp., Pseudomonas sp., Serratia sp., Acinetobacter sp. and Arcobacter sp.;

[0097] (212) Screening of the nutrient solution for the surfactant-producing strains

[0098] Take 100 ml of the produced water of the shale oil and gas reservoir screened in step (1) and put it into an anaerobic bottle. Under aseptic operation, inoculate 1 ml of the bacterial solution of the surfactant-producing strain screened in step (211) and 9 ml of nutrient solutions with different formulations. Then, place the anaerobic bottle in an oil reservoir temperature for 10 - 20 days. After the cultivation is completed, test the bacterial concentration, and select the nutrient formulation with the highest bacterial concentration as the on-site activator formulation, where:

[0099] The nutrient solution for the surfactant-producing strain is composed of a carbon source, a nitrogen source and a phosphorus source. The carbon source is at least one of glucose, sucrose, glycerol and soybean oil, the nitrogen source is at least one of ammonium nitrate and urea, and the phosphorus source is at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate and phospholipid.

[0100] The mass concentrations of the carbon source, nitrogen source and phosphorus source in the nutrient solution for the surfactant-producing strain are 1.0 - 3.0%, 0.2 - 0.6% and 0.1 - 0.3% respectively.

[0101] Further, the steps of step (22) are as follows:

[0102] (221) Preliminary screening of the acid-producing strains and the strains acting on pyrite for ore leaching

[0103] The preliminary screening method for the acid-producing strains and the strains acting on pyrite: Since both react with rocks to produce cracks and dissolution pores, and both strains need to grow after being mixed, so the combination with a relatively long time when the pH value < 3.5 is screened out by mixing these two strains. The strains are preliminarily screened according to the change of pH value.

[0104] The strains acting on pyrite for ore leaching are divided into two categories:

[0105] One category is chemolithoautotrophic bacteria, mainly including Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxydans. They have ferrooxidase or reduced sulfur oxidase, and these enzymes can catalyze the rapid oxidation of ferrous and reduced sulfur in minerals. As a result, the valuable metals in the minerals are converted into ions in the solution, and the low-valent sulfur is converted into SO42- and release H + , which can remove carbonate, pyrite and other acid-soluble inorganic minerals in oil shale.

[0106] Another type is chemoheterotrophic bacteria, mainly including Bacillus circulans, Bacillus mucilaginosus, Bacillus mucilaginosus, etc., which require organic nutrients such as glucose and sucrose for growth and reproduction.

[0107] According to the change of pH value, the acid-producing strains and the strains acting on pyrite leaching are preliminarily screened. The specific steps are as follows:

[0108] The bacterial solutions of the acid-producing strains and the strains acting on pyrite are mixed in equal volume. The mixed strains are added with a culture solution, and the initial pH value is adjusted to 2.0. Cultivate at the reservoir temperature for 30 days, and measure the pH value of the solution every day. Select the combination with a longer time when the pH value < 3.5, and preliminarily determine the acid-producing strains and the strains acting on pyrite leaching, where:

[0109] The acid-producing strain is one of Lactobacillus, Bifidobacterium, and Streptococcus thermophilus;

[0110] The strain acting on pyrite leaching is one of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, Bacillus circulans, Bacillus mucilaginosus, and Bacillus mucilaginosus;

[0111] Select the longest number of days when the pH value of the mixed bacterial solution ranges from 2.0 to 5.0 as the cultivation and shut-in time;

[0112] (222) Final determination of the acid-producing strain and the strain acting on pyrite

[0113] Use the leaching core method to determine the final injected strains. The screening basis is Fe 3+ concentration measurement and scanning electron microscopy analysis. The screening criteria are: a strain formula with a high Fe 3+ concentration, a loose and porous surface, and a proportion of more than 30%.

[0114] Leaching core method: Take 100 ml of the produced water from the shale oil and gas reservoir screened in step (1) and put it into a conical flask. Take 10 g of the core sample of the shale oil and gas reservoir screened in step (1) into the conical flask, add 1 mL of the combined strains screened in step (221), add 9 mL of nutrient solution, and then place it in an incubator at the reservoir temperature for cultivation, where:

[0115] Fe 3+ Concentration measurement: Measure the Fe 3+ concentration in the solution after the cultivation is completed, and select the formula with a high Fe 3+ concentration;

[0116] Scanning electron microscopy: Observe the surface structure of rock samples, and select a strain formula in which the proportion of loose and porous states on the rock sample surface is greater than 30%.

[0117] (223) Screening of acid-producing strains and nutrient solutions for pyrite-acting strains

[0118] Take 100 ml of the produced water from the shale oil and gas reservoir screened in step (1) and put it into an anaerobic bottle. Under aseptic operation, inoculate 1 ml of the combined strains of acid production and pyrite action screened in step (221), and 9 ml of nutrient solutions with different formulas. Then place the anaerobic bottle at the reservoir temperature for 10 - 30 days. After the cultivation is completed, measure the bacterial concentration, and preferably select the nutrient formula with the highest bacterial concentration as the on-site activator formula, where:

[0119] The nutrient solutions for acid-producing strains and pyrite-acting strains are screened as a whole, without screening their respective nutrient solutions separately, where:

[0120] The nutrient solutions for acid-producing strains and pyrite-acting strains are composed of a carbon source, a nitrogen source, a phosphorus source, and trace elements. The carbon source is at least one of glucose, sucrose, glycerol, and soybean oil; the nitrogen source is at least one of ammonium nitrate and ammonium nitrate; the phosphorus source is at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and phospholipids; the trace elements are one or more of manganese sulfate, zinc sulfate, copper sulfate, and potassium iodide.

[0121] The mass concentrations of the carbon source, nitrogen source, phosphorus source, and trace elements in the nutrient solutions for acid-producing strains and pyrite-acting strains are 0.5 - 2.0%, 0.1 - 0.3%, 0.05 - 0.3%, and 0.001 - 0.002% respectively.

[0122] Furthermore, the on-site injection process parameters in step (3) include the on-site injection volume, injection method, and shut-in time of the bacterial solution and its nutrient solution.

[0123] Even further, the total on-site injection volume of the bacterial solution and its nutrient solution in step (3) is determined by the following formula:

[0124] Q = a * L * S * h * Ф

[0125] Where:

[0126] Q - The volume injection amount of the bacterial solution and its nutrient solution, m 3 ;

[0127] a - The dosage coefficient, with a value of 0.2 - 0.5;

[0128] L - The horizontal section length of the test oil well, m;

[0129] h—the thickness of the oil reservoir in the test oil well. If h ≤ 20 m, take the actual thickness; if h > 20 m, take 20 m;

[0130] S—the designed horizontal extension length of the fracture, m;

[0131] Ф—the porosity of the test oil well, dimensionless;

[0132] If the fracturing is staged fracturing, then split according to the KH (i.e., permeability * horizontal section length) of each section to obtain the injection volume of each section;

[0133] The volume ratio of the bacterial solution to the nutrient solution is 1:9.

[0134] Furthermore, in step (3), the injection method: directly inject using the fracturing string of the test oil well.

[0135] Furthermore, the confirmation standard for the shut-in time in step (3): select the longest number of days when the pH value of the mixed bacterial solution ranges from 2.0 to 5.0 as the shut-in time, where:

[0136] If the pressure is greater than the pressure-bearing limit of the wellhead, even if the shut-in time has not reached, the well must be opened. That is, it is necessary to open the well in a timely manner in combination with the wellhead pressure situation. Generally, the shut-in time is 10 - 30 d.

[0137] The cultivation and shut-in time are determined according to the change of the pH value. According to the principle of bacterial leaching and reaction, the bacteria leaching pyrite are generally acid-producing and acidophilic bacteria. In order to accelerate the speed, acid can be added initially to adjust the pH value to 2.0. When the pH value is higher than 5, the bacterial activity is limited and cannot continue to act, so the cultivation can be stopped.

[0138] In step (4), according to the well pattern and well spacing situation in the early stage of the block, referring to the fracturing situation of other wells in the block, mainly pay attention to the technological parameters such as the optimized number of stages, sand addition volume, and designed horizontal extension length of the fracture.

[0139] Further, the steps of step (4) mainly include:

[0140] (41) Inject the preflush fluid into the fracturing well section to form microfractures in the tight oil reservoir;

[0141] (42) After the injection of the preflush fluid is completed, inject the sand-carrying fluid into the pipeline. After the sand addition is completed, inject the displacement fluid to press the sand into the fracture;

[0142] (43) According to the fracturing construction design, after the construction is completed, inject the bacterial solution and its nutrient solution, conduct shut-in, and open the well after the shut-in is completed, where:

[0143] The in-situ injection of the bacterial solution and its nutrient solution is prepared according to a volume ratio of 1:9. The bacterial solution consists of 50% of the bacterial solution of the surfactant-producing strain, 25% of the bacterial solution of the acid-producing strain, and 25% of the bacterial solution acting on pyrite. The nutrient solution consists of 50% of the nutrient solution of the surfactant-producing strain, and 50% of the nutrient solutions of the acid-producing strain and the pyrite-acting strain;

[0144] The nutrients of the acid-producing strain and the pyrite-acting strain are screened together and are the same set of nutrient systems.

[0145] Furthermore, the evaluation indicators for the in-situ test and its effects in step (5) include: initial production per well, cumulative increased oil production, input-output ratio, and mitigation of natural decline.

[0146] Example 1:

[0147] Overview of test block A in an oil production plant in Shengli Oilfield: shale oil reservoir, carbonate content in the reservoir is 65%, pyrite content is 1.8%, reservoir temperature is 100 °C, and formation water salinity is 65000 mg / L. The preferred implementation well A-PF has a horizontal section length of 1200 meters, an oil layer thickness of 12 meters, and an average reservoir porosity of 6.5%.

[0148] Using the method of the present invention to increase the production of this block includes the following steps:

[0149] (1) Screening of test oil reservoirs / wells that meet the requirements

[0150] Test block A is a shale oil reservoir with carbonate content in the reservoir > 20%, pyrite content > 1%, reservoir temperature < 120 °C, and formation water salinity < 100000 mg / L. The preferred implementation well A-PF has a horizontal section length greater than 100 meters. The block and the single well meet the reservoir screening criteria of the present invention, and the present invention can be implemented.

[0151] (2) Screening of bacterial strains and their activators;

[0152] (21) Screening of surfactant-producing bacterial strains and their nutrient solutions;

[0153] The screening of surfactant-producing bacterial strains is carried out as follows:

[0154] By reacting the bacterial solution of the surfactant-producing strain with limestone and measuring the contact angle of the rock surface, the results are shown in Table 1. The results show that the surfactant-producing strain S2 has the most obvious change in the contact angle of the limestone surface. The surfactant-producing strain S2 is Bacillus licheniformis.

[0155] Table 1 Effects of bacterial solutions of different surfactant-producing strains on limestone

[0156]

[0157]

[0158] Screening of nutrient solutions for surfactant-producing strain S2

[0159] Take 100 ml of the produced water from the test reservoir and put it into an anaerobic bottle with a volume of 200 mL. Under aseptic operation, inoculate 1 ml of the bacterial solution of surfactant-producing strain S2 screened in the previous step and 9 ml of nutrient solutions with 3 different formulations in Table 2. Then place the anaerobic bottle in the reservoir temperature for 15 days of cultivation. After the cultivation is completed, test the bacterial concentration, and optimize the No. 3 nutrient formulation as the on-site nutrient solution formulation according to the bacterial concentration.

[0160] Table 2 Screening of different nutrient formulations for surfactant-producing strain S2

[0161]

[0162] (22) Screening of acid-producing and pyrite-leaching strains and their nutrient solutions;

[0163] (221) Preliminary screening of acid-producing strains and pyrite-leaching strains

[0164] First, preliminarily screen the strains according to the change of pH value. Select different bacterial solutions and culture medium formulations, adjust the initial pH value to 2.0 with sulfuric acid, place it at the reservoir temperature, and continuously culture for 30 days, testing the change of pH value every day:

[0165] pH value test: Mix the bacterial solutions of acid-producing strains and pyrite-leaching strains in equal volume. Add the culture medium to the mixed strains, culture at the reservoir temperature for 30 days, test the pH value of the solution every day, and according to the combination with a longer time of the preferred pH value < 3.5. According to the test results (as shown in Table 3), the preliminary screening results of acid-producing strains and pyrite-leaching strains are:

[0166] Acid-producing strain C1 + pyrite-leaching strain K1, acid-producing strain C1 + pyrite-leaching strain K2, acid-producing strain C1 + pyrite-leaching strain K3, where:

[0167] Acid-producing strain C1 is Lactobacillus;

[0168] Pyrite-leaching strain K1 is Acidithiobacillus ferrooxidans;

[0169] Pyrite-leaching strain K2 is Acidithiobacillus thiooxidans;

[0170] Pyrite-leaching strain K3 is Acidithiobacillus ferrioxidans;

[0171] Table 3 Change of pH value with different formulations

[0172]

[0173]

[0174] Determination of cultivation and soaking time: The cultivation time is determined according to the change of pH value. Among the three preferred formulations, the one with the longest time for the pH value to reach 5 is C1 + K1, which takes 26 days. Therefore, the later cultivation and soaking time is 26 days.

[0175] (222) Final determination of acid-producing strains and strains acting on pyrite

[0176] The core leaching method is used to determine the final acid-producing strains and strains acting on pyrite, and the screening basis is Fe 3+ concentration measurement and scanning electron microscopy analysis.

[0177] Leaching core: Take 100 ml of produced water from the test oil reservoir and put it into a 250 ml conical flask. Take 10 g of oil reservoir core sample and put it into the conical flask. Add the three formulations screened in the previous step, 10% concentration of bacterial solution and 90% nutrient solution, and then place it in an incubator at the oil reservoir temperature for 26 days.

[0178] Fe 3+ Concentration measurement: Measure the Fe 3+ concentration in the solution after the cultivation ends. Select the formulation with a high Fe 3+ concentration.

[0179] SEM scanning: Observe the surface structure of the rock sample. Select the bacterial formulation with a loose and porous surface accounting for more than 30% of the rock sample surface.

[0180] Table 4 Screening of different formulations in test block A

[0181]

[0182] By measuring the Fe 3+ concentration, the concentration of bacteria C1 + K3 is the highest, and SEM scanning shows that the proportion of the loose and porous surface reaches 50%. Therefore, the formulation of bacteria C1 + K3 is preferably injected.

[0183] Based on the above, preferably inject the bacterial solution of the strain S2 producing surfactant; the mixed formulation of the acid-producing strain C1 and the strain K3 for leaching pyrite by bacteria.

[0184] (223) Screening of nutrient solutions for acid-producing strains and strains for leaching pyrite by bacteria

[0185] Take 100 ml of the produced water from the test reservoir and put it into an anaerobic bottle with a volume of 200 mL. Under aseptic operation, inoculate 1 ml of the acid-producing strain and the strain acting on pyrite (C1 + K3) screened in the previous step, and 9 ml of nutrient solutions with different formulations. Then place the anaerobic bottle in the reservoir temperature for 26 days. After the cultivation, measure the bacterial concentration, and preferably select the nutrient formulation with the highest bacterial concentration as the field activator formulation.

[0186] The nutrient solutions of the acid-producing and pyrite-acting strains are screened as a whole, and their respective nutrient solutions are not screened separately. The screening basis is the bacterial concentration. According to the results, the No. 1 formulation is selected as the final injection formulation.

[0187] Table 5 Screening of nutrient solution formulations for acid-producing strains and pyrite-leaching strains in test block A

[0188]

[0189] (3) Determination of on-site injection process parameters

[0190] The on-site injection process parameters include the on-site injection volume of the bacterial solution and its nutrient solution, the injection method, and the shut-in time.

[0191] Among them, the on-site injection volume of the bacterial solution and its nutrient solution is determined by the following formula:

[0192] Q = a * L * S * h * Ф

[0193] Where: Q - the volume injection amount of the composite bacteria and its nutrient solution, m 3 ;

[0194] a - dosage coefficient, with a value of 0.1 - 0.3;

[0195] L - the horizontal section length of the test oil well, m;

[0196] h - the reservoir thickness of the test oil well. If h ≤ 20 m, take the actual thickness; if h > 20 m, take 20 m;

[0197] S - the designed horizontal extension length of the fracture, m;

[0198] Ф - the porosity of the test oil well, in decimals;

[0199] The reservoir thickness of well A-PF is 12 meters, the horizontal section length is 1200 meters, the porosity is 0.065, the designed fracture length of the fracturing is 200 meters, and the a coefficient is taken as 0.25. Calculate the microbial injection volume of this well:

[0200] Q = 0.25 * 1200 * 200 * 12 * 0.065 = 46800 m 3

[0201] Soaking well time: The designed soaking well time is 26 days. The cultivation time is determined according to the change of pH value. Among the three preferred formulations, the one with the longest time to reach pH 5 is C1+K1, which requires 26 days. Therefore, the later cultivation and soaking well time are both 26 days. The well is opened in a timely manner according to the wellhead pressure on site;

[0202] The ratio of the injected bacterial liquid and its nutrient solution on site is prepared as 1:9. The bacterial liquid consists of 50% of the bacterial liquid of the strain producing surfactant, 25% of the bacterial liquid of the strain producing acid, and 25% of the bacterial liquid of the strain for leaching pyrite. The nutrient solution consists of 50% of the nutrient solution of the strain producing surfactant, and 50% of the nutrient solutions of the strain producing acid and the strain for leaching pyrite. Calculate that the bacterial liquid of the strain S2 producing surfactant is 2340 t, the corresponding activator is 21060 t, the bacterial liquid of the strain C1 producing acid is 1170 t, the bacterial liquid of the strain K3 for leaching pyrite is 1170 t, and the corresponding activators of the strain producing acid and the strain for leaching pyrite are 21060 t.

[0203] (4) Composite fracturing construction

[0204] According to the well pattern and well spacing of the block in the early stage, referring to the fracturing conditions of other wells in the block, optimize the fracturing of this well.

[0205] This well is fractured in 3 stages, with a total sand addition of 2600 m³, a liquid addition of 40500 m³, and the designed horizontal extension length of the fracture is 200 m. The main on-site construction steps include:

[0206] 1. Inject preflush fluid into the fracturing interval to form microfractures in the tight oil reservoir;

[0207] 2. After the injection of preflush fluid is completed, inject sand-carrying fluid into the pipeline. After the sand addition is completed, inject displacement fluid to press the sand into the fracture;

[0208] 3. After the construction of each stage of fracturing is completed, inject the bacteria and activator system;

[0209] 4. Conduct the fracturing construction of the next stage. Inject the bacteria liquid and activator system in three stages. The injection volumes are shown in Table 6. 8500 m³ of the microbial system is injected in the first stage, 14150 m³ in the second stage, and 24150 m³ in the third stage.

[0210] Table 6 Calculation table of bacterial liquid injection volume

[0211]

[0212] (5) On-site test and effect evaluation

[0213] Comparing this well with the wells in the same block, the initial daily oil production increased by 40%, the natural decline in the first year was slowed down by 25%, the cumulative increased oil production reached 12,000 tons within 2 years, the predicted final increased oil production is 20,000 tons, the current input-output ratio has reached 1:6.8, and the predicted final input-output ratio is 1:11.4. The test effect is good.

[0214] Example 2:

[0215] General situation of test block G in a certain oil production plant of Shengli Oilfield: Shale reservoir, carbonate content in the reservoir is 71%, pyrite content is 2.6%, reservoir temperature is 106°C, and formation water salinity is 85,000 mg / L. The preferred implementation well G-PM has a horizontal section length of 610 meters, an oil layer thickness of 23 meters, and an average reservoir porosity of 6.4%.

[0216] Using the method of the present invention to increase the production of this block, the specific steps are as follows:

[0217] (1) Screening of test reservoirs / wells that meet the requirements

[0218] Test block G is a shale reservoir, with carbonate content in the reservoir > 20%, pyrite content > 1%, reservoir temperature < 120°C, and formation water salinity < 100,000 mg / L. The preferred implementation well G-PM has a horizontal section length greater than 100 meters. The block and the single well meet the reservoir screening criteria of the present invention, and the present invention can be implemented.

[0219] (2) Screening of strains and their activators;

[0220] (21) Screening of strains producing surfactants and their nutrient solutions;

[0221] The screening method of strains producing surfactants is as follows:

[0222] By reacting the bacterial solution of strains producing surfactants with limestone, the contact angle of the rock surface is measured. The results are shown in Table 7. The results show that the bacterial solution of strain Q1 producing surfactants has the most obvious change in the contact angle of the limestone surface. Among them, strain Q1 producing surfactants is Pseudomonas.

[0223] Table 7 Effects of bacterial solutions of different strains producing surfactants on limestone

[0224]

[0225] Screening of nutrient solution of strain Q1 producing surfactants:

[0226] Take 100 ml of the produced water from the test reservoir and put it into an anaerobic bottle with a volume of 200 mL. Under aseptic operation, inoculate 1 ml of the surfactant-producing strain screened in the previous step and 9 ml of the nutrient solutions with 3 different formulations in Table 8. Then place the anaerobic bottle in the reservoir temperature for 20 days. After the cultivation, measure the cell concentration, and select the No. 2 nutrient formulation as the on-site nutrient solution formulation according to the cell concentration.

[0227] Table 8 Screening of different nutrient formulations for surfactant-producing strains

[0228]

[0229] (22) Screening of acid-producing strains for leaching pyrite and their nutrient solutions;

[0230] (221) Preliminary screening of acid-producing strains and strains for leaching pyrite with their functions

[0231] First, preliminarily screen the strains according to the change of pH value. Select different strains of bacteria and formulations of culture solutions, adjust the initial pH value to 2.0 with sulfuric acid, place it at the reservoir temperature, and measure the change of pH value every day for 30 consecutive days.

[0232] pH value measurement: Add the mixed strains to the culture solution, cultivate at the reservoir temperature for 30 days, measure the pH value of the solution every day, and select the combinations with a longer time when the preferred pH value < 3.5 according to the test results. According to the test results, continue to screen the three formulations of acid-producing strain F2 + pyrite-leaching strain K1, acid-producing strain F2 + pyrite-leaching strain K2, and acid-producing strain F2 + pyrite-leaching strain K3, where:

[0233] The acid-producing strain F2 belongs to the genus Bifidobacterium;

[0234] The pyrite-leaching strain K1 is Bacillus circulans;

[0235] The pyrite-leaching strain K2 is Bacillus mucilaginosus;

[0236] The pyrite-leaching strain K3 is Bacillus mucilaginosus;

[0237] Table 9 pH value changes of different formulations

[0238] Time / day Bacteria F1 + K1 Bacteria F1 + K2 Bacteria F1 + K3 Bacteria F2 + K1 Bacteria F2 + K2 Bacteria F2 + K3 1 2.0 2.0 2.0 2.0 2.0 2.0 2 2.1 2 2 2.1 2.2 2 3 2.1 2.3 2.2 2.1 2.4 2.1 4 2.1 2.3 2.4 2.1 2.5 2.3 5 2.2 2.5 2.5 2.1 2.6 2.3 6 2.9 2.6 2.6 2.1 2.8 2.3 7 3.1 2.9 2.8 2.3 2.7 2.6 8 3.3 3.1 3 2.3 2.8 2.6 9 3.4 3.1 3 2.3 2.8 2.7 10 3.6 3.3 3.3 2.4 2.9 2.8 11 3.8 3.6 3.4 2.4 3 2.9 12 3.9 3.7 3.6 2.5 3.1 3 13 3.9 3.9 3.7 2.7 3.1 3.1 14 4.1 4.1 3.9 2.8 3.1 3.2 15 4.1 4.1 3.9 2.9 3.3 3.2 16 4.3 4.3 4 3 3.4 3.2 17 4.3 4.3 4 3 3.4 3.5 18 4.5 4.3 4.1 3.1 4.1 4 19 4.7 4.5 5.1 3.2 4.4 4.3 20 5.1 4.6 5.3 3.9 4.8 4.6 21 5.1 5.4 5.4 4.3 5.1 4.8 22 5.3 5.4 5.4 4.5 5.2 5.1 23 5.5 5.4 5.5 4.9 5.3 5.3 24 5.5 5.4 5.8 5.1 5.3 5.5 25 5.5 5.4 5.8 5.1 5.5 5.8 26 5.5 5.4 5.8 5 6 6 27 5.5 5.4 5.8 5.5 6.3 6.1 28 5.5 5.4 5.8 5.9 6.5 6.2 29 5.5 5.4 5.8 6.1 6.5 6.2 30 5.5 5.4 5.8 6.1 6.5 6.2

[0239] Cultivation and shut-in time: The cultivation time is determined according to the change of pH value. Among the three preferred formulations, the one with the longest time for the pH value to reach 5 is F2 + K1, which takes 24 days. Therefore, the later cultivation and shut-in time is 24 days.

[0240] (222) Final determination of acid-producing strains and strains for leaching pyrite

[0241] The acid-producing and pyrite-acting strains are determined by the leaching core method, and the screening basis is Fe 3+ concentration measurement and scanning electron microscopy analysis.

[0242] Leaching core: Take 100 ml of the produced water from the test reservoir and put it into a 250 ml conical flask. Take 10 g of the reservoir core sample and put it into the conical flask. Add three formulations of the bacteria screened in the previous step, 10% concentration of the bacterial solution and 90% nutrient solution, and then place it in an incubator at the reservoir temperature for 24 days.

[0243] Fe 3+ Concentration measurement: After the cultivation, measure the Fe 3+ concentration in the solution. Select the formulation with a high Fe 3+ concentration.

[0244] SEM scanning: Observe the surface structure of the rock sample. When observing the surface by SEM, it will show a loose and porous state. Preferably, select the bacterial strain formulation with a loose and porous state on the rock sample surface accounting for more than 30%.

[0245] Table 10 Screening of different formulations in test block G

[0246]

[0247] By measuring the Fe 3+ concentration, both bacteria F2+K2 and bacteria F2+K2 are relatively high. Combining with SEM scanning, the loose and porous surface of bacteria F2+K2 accounts for 60%. Therefore, preferably inject the bacteria F2+K2 formulation.

[0248] Based on the above, preferably inject a mixed formulation of the bacterial solution of strain Q1 producing surfactant, strain F2 producing acid, and strain K2 acting on pyrite leaching.

[0249] (223) Screening of nutrient solutions for acid-producing strains and pyrite-acting strains

[0250] Take 100 ml of the produced water from the test reservoir and put it into an anaerobic bottle with a volume of 200 mL. Under aseptic operation, inject 1 ml of the acid-producing and pyrite-acting strains (F2+K2) screened in the previous step, and 9 ml of nutrient solutions with different formulations. Then place the anaerobic bottle at the reservoir temperature for 24 d. After the cultivation, test the bacterial concentration, and preferably select the nutrient formulation with the highest bacterial concentration as the on-site activator formulation.

[0251] The nutrient solutions for the acid-producing strains and pyrite-acting strains are screened as a whole, and their respective nutrient solutions are not screened separately. The screening basis is the bacterial concentration, and according to the results, select formulation 2 as the final injection formulation.

[0252] Table 11 Screening of nutrient solution formula for acid-producing bacteria and pyrite leaching bacteria in Test Block G

[0253]

[0254] (3) Determination of on-site injection process parameters

[0255] On-site injection process parameters include the on-site injection volume of bacterial solution and its nutrient solution, injection method, and soaking time of the well.

[0256] Among them, the on-site injection volume of bacterial solution and its nutrient solution is determined by the following formula:

[0257] Q = a * L * S * h * Ф

[0258] Where: Q - Volume injection amount of composite bacteria and its nutrient solution, m 3 ;

[0259] a - Dosage coefficient, with a value of 0.1 - 0.3;

[0260] L - Horizontal section length of the test oil well, m;

[0261] h - Oil layer thickness of the test oil well. If h ≤ 20m, take the actual thickness; if h > 20m, take 20m;

[0262] S - Horizontally extended design length of the fracture, m;

[0263] Ф - Porosity of the test oil well, decimal;

[0264] The oil layer thickness of Well G-PM is 23 meters, the horizontal section length is 610 meters, the porosity is 0.074, the designed fracture length of the fracturing is 220 meters, and the a coefficient is taken as 0.3. Calculate the microbial injection volume of this well:

[0265] Q = 0.3 * 600 * 220 * 20 * 0.064 = 50688m 3

[0266] Soaking time: The designed soaking time is 24d (the cultivation time is determined according to the change of pH value. Among the preferred 3 formulas, the one with the longest time for the pH value to reach 5 is F2 + K1, which requires 24 days. Therefore, the later cultivation and soaking time adopt 24 days). Open the well in time according to the wellhead pressure situation on site;

[0267] The in-situ injection of the bacterial solution and its nutrient solution is prepared in a ratio of 1:9. The bacterial solution consists of 50% of the bacterial solution of the surfactant-producing strain, 25% of the bacterial solution of the acid-producing strain, and 25% of the bacterial solution of the strain for leaching pyrite. The nutrient solution consists of 50% of the nutrient solution of the surfactant-producing strain and 50% of the nutrient solution of the acid-producing strain + the strain for leaching pyrite. Calculate that the bacterial solution of the surfactant-producing strain Q1 is 2534 t, the corresponding activator is 22810 t, the bacterial solution of the acid-producing strain F2 is 1267 t, the bacterial solution of the strain K2 for leaching pyrite is 1267 t, and the corresponding activator of the acid-producing strain and the strain for leaching pyrite is 22810 t.

[0268] (4) Composite fracturing construction

[0269] According to the well pattern and well spacing of the block in the early stage, referring to the fracturing conditions of other wells in the block, optimize the fracturing of this well.

[0270] This well is fractured in 2 stages, with a total sand addition of 1800 m³, a liquid addition of 32600 m³, and the designed horizontal extension length of the fracture is 220 m. The main steps of on-site construction mainly include:

[0271] 1. Inject the preflush fluid into the fracturing interval to form microfractures in the tight oil reservoir;

[0272] 2. After the injection of the preflush fluid is completed, inject the sand-carrying fluid into the pipeline. After the sand addition is completed, inject the displacement fluid to press the sand into the fracture;

[0273] 3. After the construction of each stage of fracturing is completed, inject the bacteria and activator system;

[0274] 4. Carry out the fracturing construction of the next stage, inject the bacteria solution and activator system in two stages, and the injection volumes are shown in Table 12. The microbial system of 17780 m³ is injected in the first stage and 32910 m³ in the second stage.

[0275] Table 12 Calculation table of bacterial solution injection volume

[0276]

[0277] (5) Field test and effect evaluation

[0278] Comparing this well with the wells in the same block, the initial daily oil production increases by 36%, the natural decline in the first year is slowed down by 31%, the cumulative increased oil production is 18900 tons, and the input-output ratio is 1:9.9. The test effect is good.

[0279] Example 3:

[0280] General situation of test block M in a certain oil production plant of Shengli Oilfield: Shale oil reservoir, carbonate content in the reservoir is 49%, pyrite content is 2.3%, reservoir temperature is 115°C, and formation water salinity is 45,000 mg / L. The preferred implementation well M-XX has a horizontal section length of 430 meters, an oil layer thickness of 29 meters, and an average reservoir porosity of 8.3%.

[0281] Use the method of the present invention to increase the production of this block. The specific steps are as follows:

[0282] (1) Screen test oil reservoirs / wells that meet the requirements

[0283] Test block M is a shale oil reservoir with carbonate content in the reservoir > 20%, pyrite content > 1%, reservoir temperature < 120°C, and formation water salinity < 100,000 mg / L. The preferred implementation well M-XX has a horizontal section length greater than 100 meters. The block and single well meet the reservoir screening criteria of the present invention, and the present invention can be implemented.

[0284] (2) Screening of strains and their activators

[0285] (21) Screening of strains producing surfactants and their nutrient solutions

[0286] The screening of strains producing surfactants is as follows:

[0287] By using the bacterial liquid of strains producing surfactants to act on limestone, the contact angle of the rock surface is measured. The results are shown in Table 13. The results show that the bacterial liquid of strain Z3 producing surfactants has the most obvious change in the contact angle of the limestone surface. Among them, strain Z3 producing surfactants is Serratia.

[0288] Table 13 Effects of bacterial liquids of different strains producing surfactants on limestone

[0289]

[0290] Screening of nutrient solution for strain Z3 producing surfactants:

[0291] Take 100 ml of the produced water from the test reservoir and put it into an anaerobic bottle with a volume of 200 mL. Under aseptic operation, add 1 ml of the strain producing surfactants screened in the previous step and 9 ml of 3 different formula nutrient solutions in Table 14. Then place the anaerobic bottle in the reservoir temperature for 10 days. After the cultivation, test the bacterial concentration, and select the No. 1 nutrient formula as the on-site nutrient solution formula according to the bacterial concentration.

[0292] Table 14 Screening of different nutrient formula for strains producing surfactants

[0293]

[0294] (22) Screening of acid-producing bacteria and nutrient solutions for pyrite leaching

[0295] (221) Preliminary screening of acid-producing bacteria and pyrite-leaching bacteria

[0296] First, screen the bacteria preliminarily according to the pH value change. Select different formulas of bacterial solutions and culture media, adjust the initial pH value to 2.0 with sulfuric acid, place it at the reservoir temperature, and continuously culture for 30 days, testing the pH value change every day.

[0297] pH value test: Add the mixed bacteria to the culture medium, culture at the reservoir temperature for 30 days, test the pH value of the solution every day. According to the combination with a longer time when the preferred pH value < 3.5, based on the test results, continue to screen the four formulas of acid-producing bacteria X1 + pyrite-leaching bacteria T1, acid-producing bacteria X1 + pyrite-leaching bacteria T2, acid-producing bacteria X1 + pyrite-leaching bacteria T3, and acid-producing bacteria X2 + pyrite-leaching bacteria T3, where:

[0298] Acid-producing bacteria X1 belongs to the genus Lactobacillus;

[0299] Acid-producing bacteria X2 belongs to the genus Streptococcus thermophilus;

[0300] Pyrite-leaching bacteria T1 is Acidithiobacillus ferrooxidans;

[0301] Pyrite-leaching bacteria T2 is Acidithiobacillus thiooxidans;

[0302] Pyrite-leaching bacteria T3 is Acidithiobacillus ferrioxidans;

[0303] Table 15 pH value changes of different formulas

[0304]

[0305]

[0306] Cultivation and shut-in time: The cultivation time is determined according to the pH value change. Among the preferred 4 formulas, the one with the longest time for the pH value to reach 5 is X1 + T3, which requires 27 days. Therefore, the later cultivation and shut-in time is 27 days.

[0307] (222) Final determination of acid-producing bacteria and pyrite bacteria

[0308] Use the leaching rock core method to determine the final acid-producing and pyrite-acting bacteria, and the screening basis is Fe 3+ Concentration measurement and scanning electron microscopy analysis.

[0309] Leaching core: Take 100 ml of the produced water from the test reservoir and put it into a 250 ml conical flask. Take 10 g of the reservoir core sample and put it into the conical flask. Add the four formulated bacteria, 10% concentration of the bacterial solution and nutrient solution screened in the previous step, and then place it in an incubator at the reservoir temperature for 27 days.

[0310] Fe 3+ Concentration determination: After the cultivation, measure the Fe 3+ concentration in the solution. Select the formula with a high Fe 3+ concentration.

[0311] SEM scanning: Observe the surface structure of the rock sample. When observed by SEM, the surface will show a loose and porous state. It is preferred to select the bacterial formula in which the loose and porous state of the rock sample surface accounts for more than 30%.

[0312] Table 16 Screening of different formulas in test block M

[0313]

[0314] By measuring the Fe 3+ concentration, the second and third groups are relatively high. SEM scanning shows that the proportion of the loose and porous surface of the combined bacteria X1 + T3 in the third group reaches 40%. Therefore, it is preferred to inject the bacterial formula X1 + T3 on site.

[0315] Based on the above, it is preferred to inject the mixed formula of the surfactant-producing strain Z3, the acid-producing strain X1, and the strain T3 that acts on pyrite leaching.

[0316] (223) Screening of nutrient solutions for acid-producing strains and strains that act on pyrite leaching

[0317] Take 100 ml of the produced water from the test reservoir and put it into an anaerobic bottle with a volume of 200 mL. Under aseptic operation, inoculate 1 ml of the acid-producing and pyrite-acting bacteria () screened in the previous step, and 9 ml of nutrient solutions with different formulas. Then place the anaerobic bottle at the reservoir temperature for 27 days. After the cultivation, measure the bacterial concentration, and preferably select the nutrient formula with the highest bacterial concentration as the on-site activator formula.

[0318] The nutrient solutions of the acid-producing strain and the strain that acts on pyrite are screened as a whole, and their respective nutrient solutions are not screened separately. The screening basis is the bacterial concentration, and according to the results, formula 2 is selected as the final injection formula.

[0319] Table 17 Screening of nutrient solution formulas for acid-producing strains and strains that act on pyrite leaching in test block M

[0320]

[0321]

[0322] (3) Determination of on-site injection process parameters

[0323] On-site injection process parameters include the on-site injection volume of the bacterial liquid and its nutrient solution, injection method, and soaking time.

[0324] Among them, the on-site injection volume of the bacterial liquid and its nutrient solution is determined by the following formula:

[0325] Q = a * L * S * h * Ф

[0326] Where: Q—the volume injection amount of the composite bacteria and its nutrient solution, m 3 ;

[0327] a—dosage coefficient, with a value of 0.1 - 0.3;

[0328] L—the horizontal section length of the test oil well, m;

[0329] h—the reservoir thickness of the test oil well. If h ≤ 20m, take the actual thickness; if h > 20m, take 20m;

[0330] S—the designed horizontal extension length of the fracture, m;

[0331] Ф—the porosity of the test oil well, in decimals;

[0332] For Well M-XX, the reservoir thickness of the well is 29m, the horizontal section length is 430m, the porosity is 0.083, the designed fracture length of the fracturing is 240m, and the a coefficient is taken as 0.1. Calculate the microbial injection volume of this well:

[0333] Q = 0.1 * 430 * 240 * 20 * 0.083 = 17131m 3

[0334] The injection volume is taken as 17130m 3 .

[0335] Soaking time: The designed soaking time is 27d, and the well is opened in a timely manner according to the wellhead pressure on site;

[0336] The on-site injection ratio of the bacterial liquid and its nutrient solution is prepared according to 1:9. Among them, the bacterial liquid consists of 50% of the bacterial liquid of the strain producing surfactant, 25% of the bacterial liquid of the strain producing acid, and 25% of the bacterial liquid of the strain for pyrite leaching. The nutrient solution consists of 50% of the nutrient solution of the strain producing surfactant, and 50% of the nutrients of the strain producing acid and the strain for pyrite leaching. Calculate 856t of the bacterial liquid of the strain Z3 producing surfactant, corresponding activator 7709t, 428t of the bacterial liquid of X1 strain, 428t of T3 strain, and corresponding activator 7709t of the strain producing acid and the strain for pyrite leaching.

[0337] (4) Composite fracturing construction

[0338] According to the well pattern and well spacing of the block in the early stage, and referring to the fracturing conditions of other wells in the block, optimize the fracturing of this well.

[0339] This well is fractured in a general way. The total sand addition volume is 300 cubic meters, the liquid addition volume is 4,200 cubic meters, and the designed horizontal extension length of the fracture is 240 meters. The main on-site construction steps mainly include:

[0340] 1. Inject preflush fluid into the fracturing interval to form microfractures in the tight oil reservoir;

[0341] 2. After the injection of the preflush fluid is completed, inject sand-carrying fluid into the pipeline. After the sand addition is completed, inject displacement fluid to press the sand into the fracture;

[0342] 3. After the fracturing construction is completed, inject 17,130 m of bacteria and activator system 3 .

[0343] (5) On-site test and effect evaluation

[0344] Comparing this well with the wells in the same block, the initial daily oil production increases by 30%, the natural decline in the first year is slowed down by 18%, the cumulative increased oil production is 8,820 tons, and the input-output ratio is 1:13.7. The test effect is good.

[0345] The above has made a detailed description of the implementation manner of the present invention. However, the present invention is not limited to the above implementation manner, and various changes can be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A method for improving the development effect of shale oil and gas reservoirs by using microorganisms, characterized in that, it includes the following steps: (1) Screening of shale oil and gas reservoirs; (2) Screening of bacterial strains and their activators; (21) Screening of bacterial strains producing surfactants and their nutrient solutions; (22) Screening of bacterial strains producing acids and acting on pyrite for ore leaching and their nutrient solutions; (3) Determination of on-site injection process parameters; (4) Composite fracturing construction; (5) On-site tests and effect evaluation.

2. The method for improving the development effect of shale oil and gas reservoirs by using microorganisms according to claim 1, characterized in that, the screening criteria for shale oil and gas reservoirs in step (1) are: the carbonate content in shale > 20%, the pyrite content > 1%, the reservoir temperature < 120°C, the formation water salinity < 100000 mg / L, and the horizontal section length of the horizontal well > 100 meters.

3. The method for improving the development effect of shale oil and gas reservoirs by using microorganisms according to claim 1, characterized in that, the specific steps of step (21) are as follows: (211) Screening of bacterial strains producing surfactants Take the formation water of the shale oil and gas reservoir screened in step (1), test and record the contact angle between different test pieces and the formation water, and then soak the test pieces in the bacterial solution of the bacterial strains producing surfactants to be screened for 3 days, and then test and record the contact angle between the test pieces and the formation water, and screen out the bacterial strains producing surfactants with the largest change in contact angle before and after, where: the bacterial strains producing surfactants are one of Bacillus licheniformis, Bacillus sp., Pseudomonas sp., Serratia sp., Acinetobacter sp. and Arcobacter sp.; (212) Screening of nutrient solutions for bacterial strains producing surfactants Take 100 ml of the produced water of the shale oil and gas reservoir screened in step (1) and put it into an anaerobic bottle, aseptically inoculate 1 ml of the bacterial solution of the bacterial strains producing surfactants screened in step (211), and 9 ml of nutrient solutions with different formulations, and then place the anaerobic bottle at the reservoir temperature for culturing for 10 - 20 days. After the culturing is completed, test the bacterial concentration, and select the nutrient formulation with the highest bacterial concentration as the on-site activator formulation, where: the nutrient solution of the bacterial strains producing surfactants is composed of a carbon source, a nitrogen source and a phosphorus source. The carbon source is at least one of glucose, sucrose, glycerol and soybean oil, the nitrogen source is at least one of ammonium nitrate and urea, and the phosphorus source is at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate and phospholipid; the mass concentrations of the carbon source, nitrogen source and phosphorus source in the nutrient solution of the bacterial strains producing surfactants are 1.0 - 3.0%, 0.2 - 0.6% and 0.1 - 0.3% respectively.

4. The method for improving the development effect of shale oil and gas reservoirs by using microorganisms according to claim 1, characterized in that, the steps of step (22) are as follows: (221) Preliminary screening of bacterial strains producing acids and bacterial strains acting on pyrite for ore leaching The bacterial liquid of the acid-producing strain and the bacterial liquid of the strain acting on pyrite are mixed in equal volumes. The mixed bacteria are added with a culture medium, and the initial pH value is adjusted to 2.

0. They are cultured at the reservoir temperature for 30 days, and the pH value of the solution is measured every day. Combinations with a longer time when the pH value is <3.5 are selected to preliminarily determine the acid-producing strain and the strain acting on pyrite for leaching minerals, where: The acid-producing strain is one of the genera Lactobacillus, Bifidobacterium, and Streptococcus thermophilus; The strain acting on pyrite for leaching minerals is one of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Ferrobacillus ferrooxidans, Bacillus circulans, Bacillus mucilaginosus, and Bacillus mucilaginosus; The longest number of days when the pH value of the mixed bacterial liquid ranges from 2.0 to 5.0 is selected as the culture and shut-in time; (222) Final determination of the acid-producing strain and the strain acting on pyrite Determine the final injected strains by the leaching rock core method, and the screening basis is Fe 3+ concentration measurement and scanning electron microscopy analysis method, and the screening criteria are: Fe 3+ high concentration, loose surface, and the proportion of porous state greater than 30%; (223) Screening of the nutrient solution for the acid-producing strain and the strain acting on pyrite for leaching minerals Take 100 ml of the produced water from the shale oil and gas reservoir screened in step (1) and put it into an anaerobic bottle. Under aseptic operation, inoculate 1 ml of the combined strain of acid production and acting on pyrite screened in step (221), and 9 ml of nutrient solutions with different formulations. Then place the anaerobic bottle at the reservoir temperature for culture. After the culture is completed, measure the bacterial concentration, and select the nutrient formulation with the highest bacterial concentration as the on-site activator formulation, where: The nutrient solution for the acid-producing strain and the strain acting on pyrite is composed of a carbon source, a nitrogen source, a phosphorus source, and trace elements. The carbon source is at least one of glucose, sucrose, glycerol, and soybean oil. The nitrogen source is at least one of ammonium nitrate and ammonium nitrate. The phosphorus source is at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and phospholipids; the trace elements are one or more of manganese sulfate, zinc sulfate, copper sulfate, and potassium iodide; The mass concentrations of the carbon source, nitrogen source, phosphorus source, and trace elements in the nutrient solution for the acid-producing strain and the strain acting on pyrite for leaching minerals are 0.5 - 2.0%, 0.1 - 0.3%, 0.05 - 0.3%, and 0.001 - 0.002% respectively.

5. A method for improving the development effect of shale oil and gas reservoirs using microorganisms as claimed in claim 1, characterized in that, In step (3), the on-site injection process parameters include the on-site injection volume, injection method, and shut-in time of the bacterial liquid and its nutrient solution.

6. A method for improving the development effect of shale oil and gas reservoirs using microorganisms as claimed in claim 5, characterized in that, In step (3), the total on-site injection volume of the bacterial liquid and its nutrient solution is determined by the following formula: Q = a * L * S * h * Ф where: Q——Volume injection amount of bacterial liquid and its nutrient solution, m 3 ; a - dosage coefficient, with a value of 0.2 - 0.5; L - horizontal section length of the test oil well, m; h - reservoir thickness of the test oil well. If h ≤ 20 m, take the actual thickness. If h > 20 m, take 20 m; S - horizontally extended design length of the fracture, m; Ф - porosity of the test oil well, dimensionless; If the fracturing is segmented fracturing, it is split according to the KH of each section, that is, permeability * horizontal section length, to obtain the injection volume of each section; The mass ratio of the bacterial liquid to the nutrient solution is 1:

9.

7. A method for improving the development effect of shale oil and gas reservoirs using microorganisms as claimed in claim 5, characterized in that, Injection method in step (3): Direct injection is carried out using the fracturing string of the test oil well.

8. A method for improving the development effect of shale oil and gas reservoirs by using microorganisms as described in claim 5, characterized in that The confirmation standard for the soaking time in step (3): The longest number of days when the pH value of the mixed bacterial solution ranges from 2.0 to 5.0 is selected as the soaking time, where: If the pressure is greater than the pressure-bearing limit of the wellhead, the well must be opened even if the soaking time has not reached.

9. A method for improving the development effect of shale oil and gas reservoirs by using microorganisms as described in claim 1, characterized in that The steps of step (4) mainly include: (41) Inject a preflush fluid into the fractured well section to form microfractures in the tight oil reservoir; (42) After the injection of the preflush fluid is completed, inject a sand-carrying fluid into the pipeline. After the sand addition is completed, inject a displacement fluid to press the sand into the fractures; (43) According to the fracturing construction design, after the construction is completed, inject the bacterial solution and its nutrient solution, carry out soaking, and open the well after the soaking is completed, where: The on-site injection ratio of the bacterial solution and its nutrient solution is prepared according to a volume ratio of 1:

9. The bacterial solution is composed of 50% of the bacterial solution producing surfactants, 25% of the bacterial solution producing acid, and 25% of the bacterial solution acting on pyrite. The nutrient solution is composed of 50% of the nutrient solution of the bacterial strain producing surfactants, and 50% of the nutrient solutions of the bacterial strains producing acid and acting on pyrite.

10. A method for improving the development effect of shale oil and gas reservoirs by using microorganisms as described in claim 1, characterized in that The evaluation indexes of on-site test and effect in step (5) include: initial production of a single well, cumulative increased oil production, input-output ratio, and mitigation of natural decline.

Images