A ternary microbial fracturing fluid system, a preparation method and application thereof

Abstract

The application belongs to the technical field of oil and gas field fracturing, and particularly discloses a ternary microbial fracturing fluid system, a preparation method and application. The system first proposes a ternary synergistic composite system composed of a guar gum fracturing fluid base fluid, slick water and a source functional microbial agent screened in an oil field. The source functional microbial agent synchronously produces beneficial products such as a biological surfactant with excellent oil washing capacity during a metabolic process. The system completes reservoir hydraulic fracturing and fracture creation, and injects the source microorganism and its adaptive nutrition system into the deep reservoir during a pumping process. After gel breaking, the system realizes energy supplement of the formation, and the microorganism uses the gel breaking residual liquid as a nutrition source to start large-scale fermentation and oil displacement material production in situ in the fracture system, thereby realizing integration of fracturing, oil displacement and biological energy enhancement. The final oil displacement efficiency of the system can be increased to more than 50%, which is significantly improved compared with conventional fracturing fluid technology, and the system has the advantages of low reservoir damage, environmental friendliness, controllable cost, strong adaptability and the like.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field fracturing technology, specifically involving a ternary microbial fracturing fluid system, its preparation method, and its application. Background Technology

[0002] Hydraulic fracturing is a core technology for exploiting unconventional resources such as tight oil and gas and shale oil and gas. Conventional hydraulic fracturing technology is mainly used to create fractures and expand seepage channels, but the long-term contribution of fracturing fluid flowback to improving oil recovery is limited. Currently, fracturing fluids using guar gum and its derivatives as thickeners and slickwater drag-reducing fracturing fluids are the two main systems. Both have significant limitations: guar gum fracturing fluids easily produce insoluble residues after breaking down, damaging the reservoir and fracture conductivity; while slickwater fracturing fluids cause less damage, their sand-carrying capacity is limited, and neither has the function of improving reservoir crude oil flowability, resulting in rapid decline in production after fracturing. In summary, existing fracturing fluids mostly use chemical additives, which may damage the formation and do not have oil displacement functions.

[0003] Microbial enhanced oil recovery (MEOR) technology has attracted attention due to its environmental friendliness and sustainability. However, traditional MEOR is usually used as a standalone secondary or tertiary oil recovery measure. Although it can improve oil recovery, it is slow to take effect, highly dependent on formation permeability, and difficult to effectively promote in low-permeability reservoirs when applied alone. It also faces challenges such as difficulties in the migration of functional bacteria into the formation, competition with formation microorganisms, and high additional operating costs. In existing technologies, fracturing and microbial enhanced oil recovery are two separate processes. Currently, there is a lack of an integrated technology that organically combines fracturing and microbial enhanced oil recovery to achieve rapid capacity enhancement.

[0004] Therefore, there is an urgent need for an innovative technology that can deeply integrate fracturing operations with oil displacement and energy enhancement processes, creating favorable conditions for subsequent microbial oil displacement (such as providing fracture space, nutrient sources, and injection channels) while fracturing, and achieving efficient and low-cost bio-energy enhancement by utilizing the formation's own conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing fracturing technology and microbial enhanced oil recovery technology, such as separation, high cost, and limited efficiency. It provides a ternary microbial fracturing fluid system, preparation method, and application. This system is a green fracturing fluid system that integrates fracturing, in-situ oil recovery, and microbial enhancement. This invention aims to achieve physical fracturing, resource utilization of fracturing fluid residue, and in-situ fermentation of oil displacement agents by native microorganisms in reservoir fractures through a single fracturing operation, thereby significantly improving single-well productivity and ultimate recovery rate.

[0006] According to a first aspect of the present invention, a ternary microbial fracturing fluid system is provided, wherein the ternary microbial fracturing fluid system comprises, based on the total content of the system components (100%): guar gum fracturing fluid base fluid, accounting for 30% to 70% of the total mass of the system; slickwater, accounting for 20% to 50% of the total mass of the system; oilfield-derived functional microbial agent, accounting for 1% to 10% of the total mass of the system; and the remainder being water.

[0007] Based on the above technical solution, the composition of the guar gum fracturing fluid base is as follows: 0.25~1.0wt% plant gum, 0.001~0.01wt% bio-enzyme breaker, 1~3wt% clay stabilizer or 0.2~1.0wt% crosslinking agent, pH 6.5~8.5, and the balance is water or water and pH adjuster.

[0008] Based on the above technical solution, the plant gum is selected from at least one of guar gum, hydroxypropyl guar gum, and carboxymethyl hydroxypropyl guar gum.

[0009] Based on the above technical solution, the bio-enzyme decolloid is selected from at least one of mannanase, cellulase, α-galactosidase, glucanase, and laccase.

[0010] Based on the above technical solution, the clay stabilizer is selected from at least one of potassium chloride and polylysine.

[0011] Based on the above technical solution, the crosslinking agent is sodium tetraborate.

[0012] Based on the above technical solution, the bioregulator is sodium bicarbonate.

[0013] Based on the above technical solution, the composition of the slippery water is: drag-reducing agent 0.1%~0.6%, biological enzyme 0.01~0.1wt% or clay stabilizer 1~3wt%, pH 6.5~7.5, and the balance is water or water and pH adjuster.

[0014] Based on the above technical solution, the drag-reducing agent is a polyacrylamide-based or cellulose-based drag-reducing agent.

[0015] Based on the above technical solution, the bio-enzyme is selected from at least one of amylase, cellulase, mannanase, asparaginase, lipase, esterase, monooxygenase, laccase, biodepolymerase, and horseradish peroxidase. The clay stabilizer is selected from at least one of potassium chloride and polylysine.

[0016] Based on the above technical solution, the pH adjuster is sodium bicarbonate.

[0017] Based on the above technical solution, the composition of the oilfield-derived functional microbial agent is as follows: 0.05~6.0 wt% oilfield-derived functional microorganisms and 0.05~9.0 wt% nutrient activator, wherein the oilfield-derived functional microorganisms are original bacteria isolated, screened and domesticated from the target oilfield layer or similar reservoir environment, specifically at least one of the genera Pseudomonas, Clostridium, Bacillus, and Geobacter.

[0018] Based on the above technical solution, the nutrient activator is selected from at least one of sodium nitrate, ammonium nitrate, urea, yeast extract, ammonium chloride, sodium tetraborate, disodium hydrogen phosphate, potassium dihydrogen phosphate, magnesium sulfate, calcium chloride, manganese sulfate, ferrous sulfate, sucrose, and molasses.

[0019] According to a second aspect of the present invention, a method for preparing a ternary microbial fracturing fluid system is provided, comprising the following steps: Step (1), preparation of guar gum fracturing fluid base fluid; Step (2), preparation of the slick water; Step (3), screening and culturing: The strains were placed in a culture medium containing 0.3% hydroxypropyl guar gum, 0.1% ammonium nitrate, 0.05% K2HPO4, 0.01% MgSO4, and pH 7.0, and cultured under anaerobic conditions at 37-45℃. Single colonies were isolated by streak plating using 0.5% hydroxypropyl guar gum as a carbon source, and rescreened to obtain dominant strains. The culture was then expanded to strains with a growth index of 0.8-2.0. The bacterial cells were collected by centrifugation and resuspended in sterile physiological saline to obtain a concentration of 1×10⁻⁶. 8 ~5×10 9 CFU / mL bacterial suspension, i.e., oilfield-derived functional microbial suspension, should be stored at 4℃ for later use. Step (4), system configuration: dissolve the oilfield-derived functional microbial suspension and nutrient activator obtained in step (3) in the guar gum fracturing fluid base fluid described in step (1) or the slickwater described in step (2) to form a guar gum fracturing fluid base fluid containing the original microbial agent or a slickwater containing the original microbial agent; Based on the above technical solution, the preparation of the guar gum fracturing fluid base in step (1) is as follows: plant gum is dissolved in water to form a swelling solution, clay stabilizer, biological enzyme breaker and crosslinking agent are added, and then a NaHCO3 solution with a concentration of 0.5%~2.0% is added to adjust the pH to 6.5~8.5 to obtain the guar gum fracturing fluid base. The concentration of the swelling solution in step (1) is 0.25%~1.0%; The mass ratio of plant gum, clay stabilizer, bio-enzyme degumming agent and crosslinking agent in step (1) is 0.25~1.0:1~3:0.001~0.1:0.2~1.0.

[0020] Based on the above technical solution, the preparation of the slippery water in step (2) is as follows: dissolve the drag-reducing agent in water, add clay stabilizer and biological enzyme, and then add a NaHCO3 solution with a concentration of 0.5%~2.0% to adjust the pH to 6.5~7.5 to obtain slippery water; The mass ratio of drag-reducing agent, clay stabilizer and bio-enzyme in step (2) is 0.1~0.6:1~3:0.01~0.1.

[0021] Based on the above technical solution, the strains mentioned in step (3) are derived from the produced fluid of the target block of tight sandstone oil reservoir with a formation temperature of 40~45℃, and are selected from at least one of the genera Pseudomonas, Clostridium, Bacillus, and Geobacterium. Step (3) involves screening and culturing bacteria, which also includes the special domestication of thermotolerant microorganisms. Specifically, starting from the original strain of Pseudomonas CQ-1, the strain is activated in LB medium (each LB medium contains 10 g of tryptone, 5 g of yeast extract, and 10 g of sodium chloride) at 30-35℃ to obtain an activated seed liquid. Then, it is domesticated using a special medium containing 0.3% hydroxypropyl guanidine gum, 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate as a nutrient activator. The activated seed liquid is then transferred to fresh special medium at an inoculation rate of 2-5%. The strain is cultured starting at 35℃, increasing by 5℃ each time, starting at 40℃, and then gradually increasing to 45℃ after stabilization, gradually transitioning to 50℃, and finally reaching 55℃. At each temperature step, the strain was continuously subcultured for 3-5 generations until the lag phase of growth at that temperature was significantly shortened, the logarithmic growth phase was stable, and the biomass (OD value) approached or reached the previous temperature level (1×10⁻⁶). 6 ~1×10 8 The concentration of CFU / mL was increased to the next step, and the culture was continuously passaged for 10-15 generations at 55℃. The mixed bacterial solution was then streaked to obtain single colonies. Single colonies with fast growth and full morphology were selected and purified at 55℃ to obtain multiple candidate monoclonal strains. The strains with the best performance and the most stable 55℃ acclimatization were prepared into glycerol cryovials (-80℃) or freeze-dried bacterial powder for preservation as standard production strains.

[0022] Based on the above technical solution, the mass ratio of oilfield-derived functional microbial agent and nutrient activator in step (4) is 0.05~6.0:0.05~9.0; The nutrient activator in step (4) is selected from at least one of sodium nitrate, ammonium nitrate, urea, yeast extract, ammonium chloride, sodium tetraborate, disodium hydrogen phosphate, potassium dihydrogen phosphate, magnesium sulfate, calcium chloride, manganese sulfate, ferrous sulfate, sucrose, and molasses; In step (4), the concentration of the original microbial agent in the guar gum fracturing fluid base fluid containing the original microbial agent is 1.4%~20%; In step (4), the concentration of the original microbial agent in the slippery water containing the original microbial agent is 2.0% to 33.3%.

[0023] According to a third aspect of the present invention, an application of a ternary microbial fracturing fluid system is provided, comprising the following steps: using slickwater containing native microbial agents as a pre-fluid, then pumping sand-carrying working fluid into the reservoir for fracturing and fracture creation, and shutting in the well for cultivation after the operation to achieve oil displacement.

[0024] Based on the above technical solution, the sand-carrying working fluid is formed by mixing quartz sand proppant with guar gum fracturing fluid base fluid containing native microbial agents or slickwater containing native microbial agents. Based on the above technical solution, the mass ratio of quartz sand proppant in the sand-carrying working fluid is 80~400 kg / m³. 3 ; The quartz sand proppant has a crushing rate of 9%~18%, a particle size of 20 / 40~250 / 400 mesh, and a density of 1.30~2.75 g / cm³. 3 .

[0025] Based on the above technical solution, the specific mixing mode is as follows: slickwater and guar gum fracturing fluid are first mixed uniformly in proportion, and then mixed with quartz sand proppant to form a proppant-carrying working fluid, which is then continuously pumped in. Alternatively, the mixture is alternately mixed in the order of "slickwater slug containing native microbial agents - guar gum fracturing fluid base fluid slug containing native microbial agents", with each liquid slug having a volume of 5 to 50 cubic meters. The volume ratio of the proppant-carrying fluid to the guar gum fracturing fluid base fluid in the mixture is 10~50:50~90. During the fracturing process, the glycolipid content in the metabolites of the original microorganisms is 300~600mg / L, the total organic acid content is 10~20mmol / L, and the CO2 and CH4 content is 10~20mL / g HPG. The well shut-in cultivation period is 7 to 30 days, during which the formation temperature is 40 to 60°C; The oil displacement efficiency is over 50%.

[0026] Based on the above technical solution, the oil displacement efficiency is over 50%.

[0027] Beneficial effects (1) Trinity, disruptive integration: For the first time, the three major functions of fracturing, fracturing fluid residual resource utilization and in-situ microbial oil displacement are organically integrated into one operation, which is simple and breaks through the traditional technical barriers.

[0028] (2) Carbon source recycling and green economy: The product of guar gum fracturing fluid breaking is creatively used as the carbon source of the original microorganisms, realizing the utilization of fracturing waste liquid, reducing the cost of adding additional carbon source, and is environmentally friendly.

[0029] (3) Advantages of native bacteria, high efficiency and stability: Using native microorganisms, which are highly compatible with the geological environment, avoids the competitive inhibition and migration death problems of exogenous bacteria, resulting in a high colonization success rate and metabolic activity, and a more stable and lasting effect.

[0030] (4) Significantly improved oil displacement efficiency: Indoor experiments have confirmed that this technology system can significantly improve the final oil displacement efficiency to more than 50% on the basis of conventional water flooding, and the production increase effect is significant and lasting compared with single fracturing technology.

[0031] (5) Low reservoir damage and strong adaptability: By optimizing the gel breaking system and using native bacteria, the damage to the fracture conductivity is minimized, making it suitable for various oil and gas reservoirs that require fracturing to increase production. Detailed Implementation

[0032] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0033] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0034] Example 1: This system consists of guar gum fracturing fluid base, slickwater, a suspension of native functional microorganisms, and a nutrient activator. The guar gum fracturing fluid base accounts for 40% of the total system mass and contains 0.3% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 50% of the total system mass and contains 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The native functional microorganism agent (Pseudomonas CQ-1) accounts for 5% of the total system mass, of which the nutrient activator consists of 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate, accounting for 0.2% of the total system mass. The remainder is water.

[0035] The preparation method of the system includes the following steps: Step (1), Preparation of Guar Gum Fracturing Fluid Base: Dissolve 3g of hydroxypropyl guar gum in 1000ml of water to form a swelling solution with a concentration of 0.3%, add 10g of KCl, 0.1g of α-galactosidase and 8g of sodium tetraborate, and then add 1ml of 1% NaHCO3 solution to adjust the pH to 7 to obtain the guar gum fracturing fluid base. Step (2), preparation of slippery water: Dissolve 1g of polyacrylamide in 1000ml of water, add 10g of KCl, 0.1g of asparaginase and 0.1g of cellulase, and then add 1ml of 1% NaHCO3 solution to adjust the pH to 7 to obtain slippery water; Step (3), screening and culturing: *Pseudomonas aeruginosa* WJPAB (CGMCC NO. 24852) (*Pseudomonas* CQ-1, derived from produced fluid from a tight sandstone reservoir at a formation temperature of 40-45℃, and identified as *Pseudomonas aeruginosa* WJPAB by 16SRNA sequencing and morphological analysis) was placed in a culture medium containing 0.3% hydroxypropyl guar gum, 0.1% ammonium nitrate, 0.05% K₂HPO₄, 0.01% MgSO₄, pH 7.0, and cultured anaerobically at 37-45℃. Single colonies were isolated and rescreened using 0.5% hydroxypropyl guar gum as a carbon source to obtain dominant strains. The culture was then expanded to a growth index of 0.8-2.0. The bacterial cells were collected by centrifugation and resuspended in sterile physiological saline to obtain a concentration of 1×10⁻⁶. 8 CFU / mL bacterial suspension, i.e., oilfield-derived functional microbial suspension, should be stored at 4℃ for later use. Step (4), system configuration: Dissolve 25ml of the oilfield-derived functional microbial suspension obtained in step (3) and 75ml of nutrient activator (1g ammonium nitrate, 0.5g potassium dihydrogen phosphate, 0.3g yeast extract, and 0.2g magnesium sulfate dissolved in 75ml of water) in 400ml of the guar gum fracturing fluid base fluid described in step (1) and 500ml of the slickwater described in step (2) to form a ternary microbial fracturing fluid system.

[0036] Example 2: This system consists of guar gum fracturing fluid base, slickwater, a suspension of native functional microorganisms, and a nutrient activator. The guar gum fracturing fluid base accounts for 60% of the total system mass and contains 0.5% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 30% of the total system mass and contains 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The native functional microorganism agent (Pseudomonas CQ-1) accounts for 5% of the total system mass, of which the nutrient activator consists of 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate, accounting for 0.2% of the total system mass. The remainder is water.

[0037] The difference from Example 1 is that the amount of hydroxypropyl guar gum added in step (1) is 5g, and the system configuration in step (4) is different (the proportion of slickwater, the proportion of guar gum fracturing fluid base, and the content of hydroxypropyl guar gum in the guar gum fracturing fluid base are all different). Specifically, 25ml of the oilfield-derived functional microbial suspension obtained in step (3) and 75ml of nutrient activator (1g ammonium nitrate, 0.5g potassium dihydrogen phosphate, 0.3g yeast extract, and 0.2g magnesium sulfate dissolved in 75ml of water) are dissolved in 600ml of the guar gum fracturing fluid base in step (1) and 300ml of the slickwater in step (2) to form a ternary microbial fracturing fluid system.

[0038] Example 3: This system consists of guar gum fracturing fluid base, slickwater, a suspension of native functional microorganisms, and a nutrient activator. The guar gum fracturing fluid base accounts for 45% of the total system mass and contains 0.3% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 45% of the total system mass and contains 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The native functional microorganism agent (Pseudomonas CQ-1) accounts for 8% of the total system mass, of which the nutrient activator consists of 0.13% ammonium nitrate, 0.1% yeast extract, 0.05% potassium dihydrogen phosphate, and 0.02% magnesium sulfate, accounting for 0.3% of the total system mass. The remainder is water.

[0039] The difference from Example 1 is that the system configuration in step (4) is different (the composition of nutrient activator, the proportion of slickwater, the proportion of guar gum fracturing fluid base fluid, and the proportion of oilfield-derived functional microbial agent are all different). Specifically, 40 ml of oilfield-derived functional microbial suspension obtained in step (3) and 60 ml of nutrient activator (1.3 g ammonium nitrate, 0.5 g potassium dihydrogen phosphate, 1 g yeast extract, and 0.2 g magnesium sulfate dissolved in 60 ml of water) are dissolved in 450 ml of guar gum fracturing fluid base fluid described in step (1) and 450 ml of slickwater described in step (2) to form a ternary microbial fracturing fluid system.

[0040] Example 4: This system consists of guar gum fracturing fluid base, slickwater, a suspension of intrinsic functional microorganisms, and a nutrient activator. The guar gum fracturing fluid base accounts for 40% of the total system mass and contains 0.3% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 50% of the total system mass and contains 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The intrinsic functional microorganisms (Pseudomonas CQ-1) account for 5% of the total system mass, of which the nutrient activator consists of 0.15% yeast extract, 0.15% molasses, 0.13% ammonium nitrate, 0.05% potassium dihydrogen phosphate, and 0.02% magnesium sulfate, accounting for 0.5% of the total system mass. The remainder is water.

[0041] The difference from Example 1 is that the system configuration in step (4) is different (the composition of the nutrient activator is different). Specifically, 25 ml of the oilfield-derived functional microbial suspension obtained in step (3) and 75 ml of nutrient activator (1.3 g ammonium nitrate, 0.5 g potassium dihydrogen phosphate, 1.5 g yeast extract, 1.5 g molasses, and 0.2 g magnesium sulfate dissolved in 75 ml of water) are dissolved in 400 ml of the guar gum fracturing fluid base fluid in step (1) and 500 ml of the slickwater in step (2) to form a ternary microbial fracturing fluid system.

[0042] Example 5: This system consists of guar gum fracturing fluid base, slickwater, a suspension of intrinsic functional microorganisms, and a nutrient activator. The guar gum fracturing fluid base accounts for 50% of the total mass and contains 0.4% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 40% of the total mass and contains 0.08% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The intrinsic functional microorganism agent (Pseudomonas CQ-1), after specialized acclimation at 55°C, accounts for 5% of the total mass. The nutrient activator consists of 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate, accounting for 0.2% of the total mass. The remainder is water.

[0043] The difference from Example 1 is that the amount of hydroxypropyl guar gum added in step (1) is 4g, the amount of polyacrylamide added in step (2) is 0.8g, and the screening and culturing of bacteria in step (3) are different. Specifically, Pseudomonas aeruginosa CQ-1, derived from the produced fluid of a tight sandstone reservoir in the target block with a formation temperature of 40~45℃, and identified as Pseudomonas aeruginosa WJPAB (CGMCC NO. 24852) by 16SRNA sequencing and morphological analysis, was placed in a culture medium containing 0.3% hydroxypropyl guar gum, 0.1% ammonium nitrate, 0.05% K2HPO4, 0.02% MgSO4, and pH 7.0, and cultured under anaerobic conditions at 30~35℃. It was then transferred to fresh special culture medium for subculturing at an inoculum rate of 5%. The strain started at the optimum temperature of 35℃ and increased by 5℃ each time. It was cultured from 40℃, stabilized, and then increased to 45℃, gradually transitioning to 50℃, and finally reaching 55℃. At each temperature step, the strain was continuously subcultured for 5 generations until the biomass (OD value) of the strain after 48 hours of culture at that temperature approached or reached 1×10⁻⁶. 8 CFU / mL, increase to the next temperature step. Perform 10 consecutive subcultures at 55℃. Then, streak the mixed bacterial culture using 0.5% hydroxypropyl guar gum as a carbon source to obtain single colonies. Select robust single colonies and purify them at 55℃ to obtain the dominant strain. Then, expand the culture to a growth index of 0.8–2.0. Collect the cells by centrifugation and resuspend in sterile physiological saline to obtain a concentration of 1×10⁻⁶ CFU / mL. 8 ~5×10 9 The CFU / mL bacterial suspension, namely the specially acclimated oilfield-derived functional microbial suspension, is stored at 4℃ for later use; the system configuration in step (4) is different (the proportion of guar gum fracturing fluid base fluid and the proportion of slickwater are different), specifically, 25ml of the oilfield-derived functional microbial suspension obtained in step (3) and 75ml of nutrient activator (1g ammonium nitrate, 0.5g potassium dihydrogen phosphate, 0.3g yeast extract, and 0.2g magnesium sulfate dissolved in 75ml of water) are dissolved in 500ml of the guar gum fracturing fluid base fluid in step (1) and 400ml of the slickwater in step (2) to form a ternary microbial fracturing fluid system.

[0044] Comparative Example 1: This system consists of guar gum fracturing fluid base, slickwater, and nutrient activators. The guar gum fracturing fluid base accounts for 40% of the total mass of the system, containing 0.3% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 59.8% of the total mass of the system, containing 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The nutrient activators are 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate, accounting for 0.2% of the total mass of the system, with the remainder being water.

[0045] The difference from the system preparation method in Example 1 is that step (3) is not performed, and in step (4) only a nutrient activator is added instead of the oilfield-derived functional microbial suspension. The remaining steps are consistent with those in Example 1.

[0046] Comparative Example 2: This system consists of guar gum fracturing fluid base, slickwater, exogenous commercial microbial inoculants, and nutrient activators. The guar gum base accounts for 40% of the total system mass and contains 0.3% hydroxypropyl guar gum (HPG), 1% KCl, 0.01% α-galactosidase, and 0.8% sodium tetraborate. The slickwater accounts for 50% of the total system mass and contains 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. Commercial exogenous Bacillus subtilis lyophilized powder (exogenous commercial microbial inoculant) is added, accounting for 5% of the total system mass. The nutrient activators are 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate, accounting for 0.2% of the total system mass, with the remainder being water.

[0047] The difference from Example 1 is that step (3) is omitted, and the original functional microbial suspension in step (4) is replaced with 50g of commercial exogenous Bacillus subtilis lyophilized powder. The remaining steps are the same as in Example 1.

[0048] Comparative Example 3: This system consists of slippery water, a suspension of intrinsic functional microorganisms, and a nutrient activator. Slippery water comprises 90% of the total mass of the system and contains 0.1% polyacrylamide drag reducer (AP-P4), 1% KCl, 0.01% asparaginase, and 0.01% cellulase. The intrinsic functional microorganism agent (Pseudomonas CQ-1) comprises 5% of the total mass of the system, of which the nutrient activator consists of 0.1% ammonium nitrate, 0.05% potassium dihydrogen phosphate, 0.03% yeast extract, and 0.02% magnesium sulfate, accounting for 0.2% of the total mass of the system. The remainder is water.

[0049] The difference from Example 1 is that step (1) is omitted and the system configuration in step (4) is different. Specifically, 25 ml of the oilfield-derived functional microbial suspension obtained in step (3) and 75 ml of nutrient activator (1 g ammonium nitrate, 0.5 g potassium dihydrogen phosphate, 0.3 g yeast extract, and 0.2 g magnesium sulfate dissolved in 75 ml of water) are dissolved in 900 ml of the slickwater described in step (2). The remaining steps are consistent with those in Example 1.

[0050] Test Example 1: Viscosity and Debriding Performance Test 2-20 ml of the ternary microbial fracturing fluid systems (samples) obtained in Examples 1-5 and Comparative Examples 1-3 were placed in a 45°C constant temperature water bath and mechanically stirred at 200 rpm to simulate activation. Using a Harker rheometer (MARS 60), the activation was simulated at 45°C for 170 seconds. - ¹At shear rate, the apparent viscosity of the guar gum fracturing fluid base and the initial base of the slickwater was measured.

[0051] 60 ml of the ternary microbial fracturing fluid systems (samples) obtained in Examples 1-5 and Comparative Examples 1-3 were dispensed into anaerobic bottles and sealed, then placed in a 45°C constant temperature oven to simulate well shut-in for 7 days. Samples were taken, also at 45°C for 170 seconds. -1 The conditions for conducting a gel breaking test and measuring the viscosity change (sample after the gel breaking test) were met. The gel breaking rate was calculated. The activated gel viscosity and static gel breaking performance at 45°C well shut-in are shown in Table 1. The formula for calculating the gel breaking rate is as follows: Breakage rate (%) = [(η0-η] t ) / η0]×100%; Where η0 is the viscosity before shut-in, η t The viscosity is t days after well shut-in.

[0052] Table 1: Activated gel viscosity and static gel breaking performance at 45°C well shut-in

[0053] Analysis: All examples containing guar gum, as well as Comparative Examples 1 and 2, were able to form sand-carrying fracturing fluid (η0 > 50 mPa·s) within 24 hours. Breaking stage: Examples 1-5, containing the native bacteria CQ-1 capable of metabolizing HPG, achieved a breaking rate exceeding 95% after 7 days, indicating complete breaking. Comparative Example 1, relying solely on biological enzymes for breaking, and Comparative Example 2, whose bacteria could not utilize HPG, both showed slightly lower breaking rates, indirectly demonstrating the specific carbon source utilization function of the native bacteria.

[0054] Test Example 2: Analysis of Surface / Interfacial Tension and Residue Content The sample after the gel breaking test described in Test Example 1 was centrifuged at 3000 rpm for 10 minutes, and the supernatant was taken for testing.

[0055] The surface tension was measured at 25°C using the platinum plate method and a Kruss K100 surface tension meter. The test results are shown in Table 2.

[0056] The interfacial tension between oil and water was determined using a TX-500C spin drop interfacial tension meter. The supernatant and standard white oil (viscosity 10 mPa·s) were subjected to dynamic interfacial tension measurement at 45℃, and the equilibrium values ​​were recorded. The test results are shown in Table 2.

[0057] The residue content was determined according to industry standard SY / T 5107-2016. 100 mL of the supernatant after fracturing was taken, and the container was washed with 50 mL of water before being poured into a centrifuge tube. The residue sample was stirred with a glass rod and then centrifuged for 20 min. The supernatant was poured off, dried at 105℃, and ignited at 600℃ to constant weight. The residue mass was weighed, and the concentration (mg / L) was calculated. The results are shown in Table 2. The formula for calculating the fracturing fluid residue content is as follows: η=1000×m / V0 Where: η---fracture fluid residue content, mg / L; m---residue content, mg; V0---fracture fluid volume, mL.

[0058] Table 2: Fluid performance analysis after gel breaking (supernatant fluid after 7 days of well shut-in)

[0059] Analysis: The rupture fluids of Examples 1-5 of this invention exhibited extremely low oil-water interfacial tension (<0.35 mN / m), which is direct evidence of the production of highly efficient biosurfactants by microbial metabolism. Simultaneously, their residue content was extremely low (<210 mg / L), proving that HPG was almost completely consumed / converted by microorganisms, achieving "zero residue" or "low damage" fracturing. Comparative Examples 1-3 had high interfacial tension and lacked oil displacement capability.

[0060] Test Example 3: Detection of Metabolites Glycolipid surfactants: The sulfuric acid-phenol method was used. A standard curve was prepared using rhamnose as a standard. 1 mL of the gel-breaking supernatant (the sample after the gel-breaking test described in Test Example 1, centrifuged at 3000 rpm for 10 minutes, and the supernatant was used for testing) was taken, 5% phenol solution and concentrated sulfuric acid were added, and the absorbance was measured at a wavelength of 490 nm. The glycolipid content (calculated as rhamnose equivalent) was calculated according to the standard curve.

[0061] Organic acids: The concentration of small molecule organic acids such as acetic acid and propionic acid in the supernatant was analyzed using high performance liquid chromatography (HPLC).

[0062] Biogas: 50 ml of the ternary microbial fracturing fluid system (sample) obtained in Examples 1-3 and Comparative Examples 1-3 was placed into a sealed serum bottle with an air bag and cultured at 45°C with the well shut in. The contents of CO2 and CH4 in the air bag were analyzed by gas chromatography (GC). The metabolites are shown in Table 3.

[0063] Table 3: Quantitative analysis of metabolites (7 days after well shut-in)

[0064] Analysis: Data confirms that the CQ-1 bacterium in Examples 1-5, while utilizing HPG, synthesized a large amount of glycolipids and organic acids, and produced a small amount of biogas. Comparative Example 3, lacking an HPG carbon source, had a significantly lower yield of metabolites than the examples of this invention. This demonstrates the practical effectiveness of the core technical feature of "using guar gum as a carbon source for metabolic production."

[0065] Test Example 4: Simulated Wash Oil Test 1) Wash oil test (sand-filled pipe displacement): A. Preparation of Oil Sand Pipe: Weigh 120g of 40-60 mesh quartz sand and 10g of dehydrated crude oil (obtained from the joint station of the oilfield production plant; the composition of the dehydrated crude oil is: a complex hydrocarbon mixture mainly composed of alkanes (20%~60%), followed by cycloalkanes and aromatics (total 20%~50%), as well as gums, asphaltene (1%~30%), sulfur-containing compounds, trace amounts of water (≤0.5%), and impurities). Mix thoroughly and age for 24 hours. Fill 130g of this oil sand mixture into a stainless steel / glass sand-filled pipe (with filter membranes at both ends), compact it, and obtain the sand-filled pipe.

[0066] B. Place the sand-filled tubing in a 45°C water bath. First, use simulated formation water to displace the oil until the outlet water cut reaches 98%, record the amount of oil produced by the water drive, and calculate the water drive recovery rate. Then, inject 0.5 PV (pore volume) of the fracturing fluid system to be tested (the ternary microbial system obtained in Examples 1-5 and Comparative Examples 1-3). The mixing mode is to uniformly mix slickwater and guar gum fracturing fluid at a volume ratio of 1:1, and then add quartz sand proppant to simulate the formation of the proppant-carrying working fluid (quartz sand proppant mass ratio of 100 kg / m³). 3 The mixture is continuously pumped in, the inlet valve is closed, and the entire sand-filled pipe (containing the sand-carrying working fluid) is placed in a 45°C constant temperature incubator for 7 days. Finally, subsequent water flooding is carried out until the outlet water cut reaches 98% again, and the crude oil produced in this stage is collected and weighed.

[0067] Result calculation: Water drive recovery rate R_ wf = (Waterflooding stage oil production mass / 10g) × 100% Final oil displacement efficiency R_ final =(Total oil production mass / 10g)×100% Technical oil efficiency ΔR=R_ final -R_ wf 2) Dialysis test: A. Oil sand preparation: Mix 10g of dehydrated crude oil (obtained from the oilfield production plant joint station) with 90g of 20-40 mesh quartz sand at a mass ratio of 1:9 and age for 24h.

[0068] B. Weigh 10g of oil sand mixture (containing 1g of oil) and add it to the supernatant after gel breaking of the ternary microbial fracturing fluid system obtained in Examples 1-5 and Comparative Examples 1-3, respectively (60ml of the ternary microbial fracturing fluid system obtained in Examples 1-5 and Comparative Examples 1-3 is dispensed into anaerobic bottles and sealed, and placed in a 45℃ constant temperature oven to simulate well shut-in for 7 days. Take samples and test them at 45℃ for 170 seconds). -1 The gel breaking test was performed under the following conditions: the supernatant was collected after centrifugation at 3000 rpm for 10 minutes and placed in a stoppered conical flask, then incubated in a constant temperature water bath at 45°C for 24 hours. After removal, the liquid was discarded, and the sand sample was air-dried in a ventilated place until constant weight was achieved.

[0069] Result calculation: Wash oil rate R_ w =(W_ before -W_ after ) / 1.0×100%, where W_ before The total weight of the oil sands before reaction (11g), W_ after The result is the weight (g) of the dried sand after the reaction. The experimental results are shown in Table 4.

[0070] Table 4: Results of oil displacement experiments using sand-filled pipes

[0071] Table 5: Results of the dialysis experiment

[0072] Analysis: This is the most crucial verification. The final oil displacement efficiency of Examples 1-5 all exceeded 55%, with a technical oil enhancement efficiency exceeding 20 percentage points, achieving the technical effects of "oil displacement efficiency exceeding 50%" and "more than 10 percentage points higher than conventional waterflooding" as stated in claim 8. The high oil washing rate and ultra-low interfacial tension data corroborate each other. Comparative Example 1 only improved seepage through fracture creation, resulting in limited oil enhancement. Comparative Example 2 was even worse, proving that the ineffective bacterial strain made no contribution. Comparative Example 3 had a negligible effect due to the inability to create fractures and insufficient carbon source. This strongly demonstrates the indispensability of the synergistic effect of fracturing, oil displacement, and energy enhancement, i.e., the enormous advantages of the "three-in-one" technology.

[0073] The above series of embodiments and comparative examples, through systematic experimental design and quantitative data, fully verified the microbial enhanced oil recovery green fracturing fluid system and its application method provided by the present invention. While maintaining good fracturing performance, it has excellent self-breaking gel, ultra-low interfacial tension, high production of oil displacement metabolites and significantly improved oil recovery capabilities. It is comprehensively superior to existing conventional fracturing fluids or single bio-enhanced oil recovery technologies, and has outstanding innovation, practicality and economic benefits.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ternary microbial fracturing fluid system, characterized in that, Based on a total component content of 100%, the ternary microbial fracturing fluid system consists of: guar gum fracturing fluid base fluid, accounting for 30% to 70% of the total mass of the system; slickwater, accounting for 20% to 50% of the total mass of the system; oilfield-derived functional microbial agent, accounting for 1% to 10% of the total mass of the system; and the remainder being water.

2. The ternary microbial fracturing fluid system according to claim 1, characterized in that, The composition of the guar gum fracturing fluid base is as follows: 0.25~1.0wt% plant gum, 0.001~0.01wt% bio-enzyme breaker, 1~3wt% clay stabilizer or 0.2~1.0wt% crosslinking agent, pH 6.5~8.5, and the balance is water or water and pH adjuster. Preferably, the plant gum is selected from at least one of guar gum, hydroxypropyl guar gum, and carboxymethyl hydroxypropyl guar gum; Preferably, the bio-enzyme decolloid is selected from at least one of mannanase, cellulase, α-galactosidase, glucanase, and laccase; Preferably, the clay stabilizer is selected from at least one of potassium chloride and polylysine; Preferably, the crosslinking agent is sodium tetraborate; Preferably, the bioregulator is sodium bicarbonate.

3. The ternary microbial fracturing fluid system according to claim 1, characterized in that, The composition of the slippery water is as follows: drag reducing agent 0.1%~0.6%, biological enzyme 0.01~0.1wt% or clay stabilizer 1~3wt%, pH 6.5~7.5, and the balance is water or water and pH adjuster; Preferably, the drag-reducing agent is a polyacrylamide-based or cellulose-based drag-reducing agent; Preferably, the bioenzyme is selected from at least one of amylase, cellulase, mannanase, asparaginase, lipase, esterase, monooxygenase, laccase, biodepolymerase, and horseradish peroxidase. The clay stabilizer is selected from at least one of potassium chloride and polylysine; Preferably, the pH adjuster is sodium bicarbonate.

4. The ternary microbial fracturing fluid system according to claim 1, characterized in that, The composition of the oilfield-derived functional microbial agent is as follows: 0.05~6.0wt% oilfield-derived functional microbial suspension and 0.05~9.0wt% nutrient activator, wherein the oilfield-derived functional microorganisms are original bacteria isolated, screened and domesticated from the target oilfield layer or similar reservoir environment, specifically at least one of the genera Pseudomonas, Clostridium, Bacillus, and Geobacter. Preferably, the nutrient activator is selected from at least one of sodium nitrate, ammonium nitrate, urea, yeast extract, ammonium chloride, sodium tetraborate, disodium hydrogen phosphate, potassium dihydrogen phosphate, magnesium sulfate, calcium chloride, manganese sulfate, ferrous sulfate, sucrose, and molasses.

5. A method for preparing the ternary microbial fracturing fluid system according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step (1), preparation of guar gum fracturing fluid base fluid; Step (2), preparation of the slick water; Step (3), screening and culturing: The strains were placed in a culture medium containing 0.3% hydroxypropyl guar gum, 0.1% ammonium nitrate, 0.05% K2HPO4, 0.01% MgSO4, and pH 7.0, and cultured under anaerobic conditions at 37-45℃. Single colonies were isolated by streak plating using 0.5% hydroxypropyl guar gum as a carbon source, and rescreened to obtain dominant strains. The culture was then expanded to strains with a growth index of 0.8-2.

0. The bacterial cells were collected by centrifugation and resuspended in sterile physiological saline to obtain a concentration of 1×10⁻⁶. 8 ~5×10 9 CFU / mL bacterial suspension, i.e., oilfield-derived functional microbial suspension, should be stored at 4℃ for later use. Step (4), system configuration: dissolve the oilfield-derived functional microbial suspension and nutrient activator obtained in step (3) in the guar gum fracturing fluid base fluid described in step (1) or the slickwater described in step (2) to form a guar gum fracturing fluid base fluid containing the original microbial agent or a slickwater containing the original microbial agent.

6. The preparation method according to claim 5, characterized in that, The preparation of the guar gum fracturing fluid base in step (1) is as follows: plant gum is dissolved in water to form a swelling solution, clay stabilizer, biological enzyme breaker and crosslinking agent are added, and then a NaHCO3 solution with a concentration of 0.5%~2.0% is added to adjust the pH to 6.5~8.5 to obtain the guar gum fracturing fluid base. The concentration of the swelling solution in step (1) is 0.25%~1.0%; The mass ratio of plant gum, clay stabilizer, bio-enzyme degumming agent and crosslinking agent in step (1) is 0.25~1.0:1~3:0.001~0.1:0.2~1.

0.

7. The preparation method according to claim 5, characterized in that, The preparation of the slippery water in step (2) is as follows: dissolve the drag-reducing agent in water, add clay stabilizer and biological enzyme, and then add a NaHCO3 solution with a concentration of 0.5%~2.0% to adjust the pH to 6.5~7.5 to obtain slippery water; The mass ratio of drag-reducing agent, clay stabilizer and bio-enzyme in step (2) is 0.1~0.6:1~3:0.01~0.

1.

8. The preparation method according to claim 5, characterized in that, The strains mentioned in step (3) are derived from produced fluid from the target block of a tight sandstone reservoir with a formation temperature of 40-45℃, and are selected from at least one of the genera Pseudomonas, Clostridium, Bacillus, and Geobacterium. Step (3) of screening and culturing bacteria also includes the specialized domestication of thermotolerant microorganisms; In step (4), the mass ratio of the oilfield-derived functional microbial suspension to the nutrient activator is 0.05~6.0:0.05~9.0; The nutrient activator in step (4) is selected from at least one of sodium nitrate, ammonium nitrate, urea, yeast extract, ammonium chloride, sodium tetraborate, disodium hydrogen phosphate, potassium dihydrogen phosphate, magnesium sulfate, calcium chloride, manganese sulfate, ferrous sulfate, sucrose, and molasses; In step (4), the concentration of the original microbial agent in the guar gum fracturing fluid base fluid containing the original microbial agent is 1.4%~20%; In step (4), the concentration of the original microbial agent in the slippery water containing the original microbial agent is 2.0% to 33.3%.

9. The application of the ternary microbial fracturing fluid system according to any one of claims 1 to 4, characterized in that, The process includes the following steps: using slickwater containing native microbial agents as a pre-flush fluid, then pumping sand-carrying working fluid into the reservoir for fracturing and fracture creation, and finally shutting in the well for cultivation after the operation to achieve oil displacement. The sand-carrying working fluid is formed by mixing quartz sand proppant with guar gum fracturing fluid base fluid containing native microbial agents or slickwater containing native microbial agents. In the sand-carrying working fluid, the mass ratio of quartz sand proppant is 80~400 kg / m³. 3 ; The quartz sand proppant has a crushing rate of 9%~18%, a particle size of 20 / 40~250 / 400 mesh, and a density of 1.30~2.75 g / cm³. 3 .

10. The application according to claim 9, characterized in that, The specific mixing mode is as follows: first, slickwater and guar gum fracturing fluid are mixed in a certain proportion, and then quartz sand proppant is mixed to form a proppant-carrying working fluid, which is then continuously pumped in. Alternatively, the mixture is alternately mixed in the order of "slickwater slug containing native microbial agents - guar gum fracturing fluid base fluid slug containing native microbial agents", with each liquid slug having a volume of 5 to 50 cubic meters. In the working fluid for carrying sand, the volume ratio of slickwater to guar gum fracturing fluid base is 10~50:50~90; During the fracturing process, the glycolipid content in the metabolites of the original microorganisms is 300~600mg / L, the total organic acid content is 10~20mmol / L, and the CO2 and CH4 content is 10~20mL / g HPG. The well shut-in cultivation period is 7 to 30 days, during which the formation temperature is 40 to 60°C; The oil displacement efficiency is over 50%.

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