A bio-based oil displacement gel fracturing fluid system and its preparation method

Abstract

This invention discloses a bio-based oil displacement gel fracturing fluid system and its preparation method. The bio-based oil displacement gel fracturing fluid system comprises the following components: guar gum thickener, anti-swelling agent, flow aid, pH adjuster, crosslinking agent, bio-based oil displacement agent, synergist, breaker, and water. This invention's bio-based oil displacement gel fracturing fluid system achieves significant breakthroughs in temperature and salt resistance; the system can withstand temperatures up to 180°C and temperatures up to 20 × 10⁻⁶. 4 The fracturing fluid of this invention maintains excellent oil displacement performance under salinity conditions of mg / L. At the same time, the fracturing fluid of this invention also has many advantages such as being non-toxic, non-polluting, and biodegradable. It can significantly reduce the secondary damage to the reservoir caused by the fracturing fluid system, which is of great significance for improving the recovery rate of low-permeability tight oil reservoirs and enhancing their development effect.

Description

Technical Field

[0001] This invention relates to the field of reservoir stimulation and oil extraction technology, and in particular to a bio-based oil displacement gel fracturing fluid system and its preparation method. Background Technology

[0002] As a key component of global energy, oil extraction technologies continue to evolve with increasing resource scarcity. Traditional primary and secondary oil recovery technologies, such as relying on natural reservoir energy extraction and supplementing energy through water or gas injection, played a crucial role in early extraction. However, with the growing demand for efficient oil recovery, their technological bottlenecks have become increasingly apparent. Despite their significant contributions in early extraction, many reservoirs still have high residual oil saturation, leaving substantial unexploited oil resources. As extraction difficulties increase, costs also rise, making it difficult to maximize economic benefits.

[0003] Against this backdrop, microbial enhanced oil recovery (MEOR) technology has emerged. As one of the important methods of tertiary oil recovery, MEOR has attracted widespread attention due to its unique advantages. MEOR mainly utilizes the growth and metabolic activities of microorganisms to produce substances such as biosurfactants, biopolymers, gases, and organic acids. These substances can alter the wettability of rock surfaces, reduce oil-water interfacial tension, increase crude oil viscosity, and change the seepage characteristics of oil reservoirs, thereby achieving the goal of improving oil recovery.

[0004] However, the research and development of microbial enhanced oil recovery (MEOR) technology is still in its early stages, facing numerous technical challenges and limitations. On the one hand, the microorganisms and related biological agents used in MEOR have limited adaptability. Their activity and oil displacement effects are often difficult to guarantee under different reservoir conditions such as temperature, pressure, and pH, leading to insufficient technology stability. For example, some microorganisms cannot grow and reproduce normally in high-temperature, high-salt, or high-pressure reservoir environments, and cannot continuously produce effective oil displacement substances. On the other hand, the MEOR process is relatively complex and difficult to integrate effectively with traditional oil recovery processes, increasing operating costs and difficulty. Furthermore, MEOR also faces challenges in controlling and optimizing microbial growth metabolites. How to precisely regulate the metabolic pathways of microorganisms to produce more beneficial oil displacement substances while reducing the generation of harmful byproducts remains a pressing problem to be solved.

[0005] Meanwhile, fracturing fluid plays a crucial role in oil extraction, and its performance directly affects fracturing effectiveness and oil recovery. Traditional fracturing fluids suffer from problems such as significant reservoir damage and poor environmental friendliness. During fracturing, fracturing fluid filtrate can easily infiltrate the oil reservoir, altering its physical and chemical properties, causing reservoir blockage, and reducing oil recovery. Moreover, some fracturing fluids contain toxic and harmful chemicals that are difficult to fully recover after use, causing environmental pollution. Therefore, to overcome the shortcomings of existing technologies, there is an urgent need to develop a stable and efficient bio-based oil displacement gel fracturing fluid system to meet the needs of modern oil extraction technology development and reduce negative environmental impacts. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a bio-based enhanced oil recovery (EOR) gel fracturing fluid system and its preparation method. This fracturing fluid system cleverly combines the advantages of microbial enhanced oil recovery (MEOR) and fracturing fluid technology, enabling stable improvement in oil recovery rates, environmental friendliness, and good compatibility with reservoir conditions and existing oil production processes, thus meeting the growing demand for efficient and green oil production in the petroleum industry.

[0007] In a first aspect, the present invention provides a bio-based oil displacement gel fracturing fluid system, which is achieved through the following technical solutions.

[0008] A bio-based oil displacement gel fracturing fluid system comprises the following components in parts by weight: 0.25-0.45 parts guar gum thickener, 0.15-0.35 parts anti-swelling agent, 0.15-0.35 parts flow aid, 0.05-0.15 parts pH adjuster, 0.15-0.35 parts crosslinking agent, 0.5-3 parts bio-based oil displacement agent, 0.5-1.5 parts synergist, 0.05-0.15 parts gel breaker, and 100 parts water.

[0009] Furthermore, the preparation method of the bio-based oil displacement agent is as follows:

[0010] Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 35-40℃ and 180-200 rpm for 12-24 h. Then, 1% inoculum was transferred to LB liquid medium and cultured at 35-40℃ and 180-200 rpm until the OD600 reached 0.5-0.8. Next, 5% inoculum was transferred to shake flasks containing fermentation medium for expansion culture at 35-40℃ and 180-200 rpm for 24-48 h. The expanded culture was then added at 5% inoculum to a fermenter containing fermentation medium and fermented at 35-40℃ for 48-72 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and fine filtration. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to obtain the final bio-based oil displacement agent.

[0011] Bacillus subtilis BZ-1 was deposited at the China General Microbiological Culture Collection Center (CGMCC) on November 15, 2024, with accession number CGMCC No. 32653.

[0012] Furthermore, the fermentation medium comprises the following components by weight: 5 parts glucose, 5 parts sodium acetate, 1 part ammonium sulfate, 4.8 parts dipotassium hydrogen phosphate, 1.5 parts potassium dihydrogen phosphate, 0.5 parts trisodium citrate, 0.5 parts magnesium sulfate, 0.2 parts yeast extract, 0.01 parts calcium carbonate, 0.002 parts manganese sulfate, 0.1 parts ferrous sulfate, 0.0004 parts nickel chloride, 0.0004 parts zinc sulfate, 0.0002 parts ferric chloride, 0.0002 parts sodium molybdate, and distilled water to a final volume of 1000 parts.

[0013] Furthermore, the guar gum thickener is one or more of guar gum, hydroxypropyl guar gum, and carboxymethyl guar gum.

[0014] Furthermore, the anti-swelling agent is selected from one or more of potassium chloride, ammonium chloride, and potassium sulfate;

[0015] Furthermore, the drainage aid is selected from one or more of the following: dodecyl dimethyl betaine, fatty alcohol polyoxyethylene ether (AEO-7), and sodium dodecylbenzene sulfonate.

[0016] Furthermore, the crosslinking agent is selected from one or more of tetrabutyl titanate, zirconium oxychloride octahydrate, and triethanolamine borate complex.

[0017] Furthermore, the synergist comprises the following components in parts by weight: 5-10 parts lipopeptide, 5-10 parts rhamnolipid, and distilled water to a final volume of 1000 parts.

[0018] Furthermore, the pH adjuster is selected from one or more of sodium carbonate, sodium hydroxide, and potassium hydroxide; the desiccant is selected from one or more of ammonium persulfate and potassium persulfate.

[0019] Secondly, the present invention provides a method for preparing a bio-based oil displacement gel fracturing fluid system, which is achieved through the following technical solutions.

[0020] A method for preparing the above-mentioned bio-based oil displacement gel fracturing fluid system includes the following steps:

[0021] S1. Add the specified amounts of guar gum thickener, anti-swelling agent, drainage aid, and pH adjuster to water in sequence while stirring. After mixing, let it stand to swell and obtain the original gum solution.

[0022] S2. Add the specified amount of lipopeptide to an alkaline aqueous solution with pH 9.0-10.0 and stir to form a dispersion. Then add rhamnolipin and mechanically stir at room temperature for 1-2 hours. After mixing, the synergist is obtained.

[0023] S3. Add crosslinking agent, bio-based oil displacement agent, synergist and breaker to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0024] This application has the following beneficial effects.

[0025] (1) The bio-based oil displacement gel fracturing fluid system of the present invention has achieved a significant breakthrough in terms of temperature and salt resistance. This system can withstand high temperatures up to 180°C and high temperatures up to 20×10⁻⁶. 4 It maintains excellent oil displacement performance under salinity conditions of mg / L;

[0026] (2) The bio-based oil displacement gel fracturing fluid system of the present invention not only gives full play to the excellent and efficient performance advantages of bio-based oil displacement agents, but also has many advantages such as non-toxic, non-polluting, and degradable. It can significantly reduce the secondary damage to the reservoir caused by the fracturing fluid system, which is of great significance for improving the recovery rate of low-permeability tight oil reservoirs and enhancing their development effect. Attached Figure Description

[0027] Figure 1 This is the phylogenetic tree of Bacillus subtilis BZ-1 in this application (where A: phylogenetic tree diagram; B: phylogenetic tree diagram of srfA gene).

[0028] Figure 2 This is a rheological curve of the fracturing fluid containing the bio-based oil displacement agent prepared in Example 6 of this application;

[0029] Figure 3 This is a rheological curve of the fracturing fluid without bio-based oil displacement agent prepared in Comparative Example 1 of this application;

[0030] Figure 4 This is a construction curve diagram of the test well in this application;

[0031] Figure 5 This is a comparison chart of the highest daily oil production of the test well and the adjacent well in this application. Detailed Implementation

[0032] The invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] The Bacillus subtilis strain BZ-1 of this invention was isolated from petroleum-contaminated soil samples from Dagang Oilfield, Tianjin. The isolation and culture methods of the strain are as follows: Soil samples were weighed and suspended in distilled water, glass beads were added and stirred, ultrasonicated, and allowed to stand overnight. The supernatant was collected the next day and vacuum filtered. The filtrate was sterilized to prepare the soil leachate, which was stored at room temperature for later use. 5g of soil sample stored at 4℃ was weighed and dissolved in 100mL of sterile physiological saline, glass beads were added and stirred, and the mixture was shaken at 37℃ for 30min. The solution was then serially diluted with sterile water (dilution gradient 10). -1 10 -2 10 -3 10 -4 10 -5 Take 50 μL of bacterial suspension from each dilution gradient and spread it on LB agar plates containing 20% ​​soil leachate. Incubate for 2-3 days. Streak different single colonies onto the plates until a single colony is isolated. Inoculate different single colonies into 5 mL of fermentation medium and incubate at 37°C and 200 rpm for 2-3 days. Take 2 μL of fermentation broth to measure the oil ring. Inoculate 2 μL of fermentation broth into an oil-containing inorganic salt solid medium (the inorganic salt solid medium is prepared with the following composition: 2.0 g dipotassium hydrogen phosphate, 1.0 g potassium dihydrogen phosphate, 2.0 g ammonium nitrate, 0.2 g magnesium sulfate heptahydrate, 5.0 g sodium chloride, 0.02 g calcium chloride, 15 g agar, adjust the pH to 7.2, and bring the volume to 1000 mL with distilled water. After the plate solidifies, evenly spread 1.5% (v / v) crude oil on its surface to form a uniform oil layer). After inoculation, the culture medium was placed at 37℃ and incubated for 2 days. The size of the ring-shaped area formed on the culture medium was observed. Fresh bacterial culture with a large oil drainage ring was selected and mixed with 20% glycerol in a glycerol tube and stored in a -80℃ refrigerator.

[0034] Genomic DNA was extracted and purified from the strain. Using the genomic DNA as a template, PCR amplification was performed using primers 27F: 5'-AGAGTTTGATCMTGGCTCAG-3' (SEQ ID NO.1) and 1541R: 5'-AAGGAGGTGATCCAGCC-3' (SEQ ID NO.2). The PCR products were detected by 1% agarose gel electrophoresis, purified by gel excision, and then sequenced. Sequencing results were analyzed using BLAST software, and homology was compared with 16S rRNA genes in GenBank. Genetic distances were calculated using MEGA 5.0 software, and a phylogenetic tree was constructed using the Neighbor-Joining distance matrix. Using genomic DNA as a template, the lipopeptide gene srfA was amplified using primers srfA F: 5'-ATGTCAGAACAACAGCAACAGC-3' (SEQ ID NO.3) and srfA R: 5'-TTATAAAAGCTTCGTCCATTGC-3' (SEQ ID NO.4), and a phylogenetic tree of the srfA gene was constructed using the above methods. Figure 1 It is a phylogenetic tree of Bacillus subtilis, composed of... Figure 1 It was found that the 16S rRNA of strain BZ-1 had a 99% similarity to Bacillus subtilis. The presence of the lipopeptide gene srfA in this bacterium indicates that strain BZ-1 is a Bacillus subtilis strain containing srfA.

[0035] The following examples illustrate the preparation of a bio-based oil displacement gel fracturing fluid system using Bacillus subtilis BZ-1 obtained through screening in this application.

[0036] The rhamnolipid (CAS: 869062-42-0) and lipopeptide (CAS: 171263-26-6) used in the following examples of this application were purchased from Maclean's.

[0037] The hydroxypropyl guar gum used in the following examples of this application was purchased from Guangrao Liuhe Chemical Co., Ltd.

[0038] The decyl hydroxypropyl sulfobetaine used in the following embodiments of this application was purchased from Jinan Yuno Chemical Co., Ltd.

[0039] The fatty alcohol polyoxyethylene ether ammonium sulfate used in the following embodiments of this application was purchased from Shandong Yousuo Chemical Technology Co., Ltd.

[0040] The triethanolamine borate complex used in the following embodiments of this application was purchased from Sichuan Ainergy Technology Co., Ltd.

[0041] Example 1

[0042] A method for preparing a bio-based oil displacement gel fracturing fluid system includes the following steps:

[0043] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0044] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0045] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0046] S3: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0047] S4: Add 1g of borate triethanolamine complex, 2g of bio-based oil displacement agent, 2g of synergist and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0048] Example 2

[0049] A method for preparing a bio-based oil displacement gel fracturing fluid system includes the following steps:

[0050] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0051] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0052] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0053] S3: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0054] S4: Add 1g of borate triethanolamine complex, 4g of bio-based oil displacement agent, 2g of synergist and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0055] Example 3

[0056] A method for preparing a bio-based oil displacement gel fracturing fluid system includes the following steps:

[0057] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0058] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0059] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0060] S3: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0061] S4: Add 1g of borate triethanolamine complex, 6g of bio-based oil displacement agent, 2g of synergist and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0062] Example 4

[0063] A method for preparing a bio-based oil displacement gel fracturing fluid system includes the following steps:

[0064] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0065] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0066] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0067] S3: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0068] S4: Add 1g of borate triethanolamine complex, 8g of bio-based oil displacement agent, 2g of synergist and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0069] Example 5

[0070] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0071] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0072] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0073] S3: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0074] S4: Add 1g of borate triethanolamine complex, 10g of bio-based oil displacement agent, 2g of synergist and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0075] Example 6

[0076] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0077] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0078] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0079] S3: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0080] S4: Add 1g of borate triethanolamine complex, 12g of bio-based oil displacement agent, 2g of synergist and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0081] Comparative Example 1

[0082] A method for preparing a gel fracturing fluid system includes the following steps:

[0083] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0084] S2: Add 1g of triethanolamine borate complex and 0.2g of ammonium persulfate to the original gel solution in sequence, and stir evenly to obtain the original gel fracturing fluid system.

[0085] Comparative Example 2

[0086] A method for preparing a gel fracturing fluid system includes the following steps:

[0087] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0088] S2: Measure 100mL of water, adjust the pH to 9.5 with sodium hydroxide to obtain an alkaline aqueous solution, first slowly add 0.5g of lipopeptide under high-speed shear stirring, and continue shearing for 5 minutes; then slowly add 1.0g of rhamnolipid under mechanical stirring, and continue stirring for 1 hour until the system is homogeneous, which is the synergist.

[0089] S3: Add 1g of triethanolamine borate complex, 2g of synergist and 0.2g of ammonium persulfate to the original gel solution in sequence, and stir evenly to obtain the original gel fracturing fluid system.

[0090] Comparative Example 3

[0091] A method for preparing a bio-based oil displacement gel fracturing fluid system includes the following steps:

[0092] S1: Add 1.4g hydroxypropyl guar gum, 0.6g potassium chloride, 1g dodecyl dimethyl betaine, and 0.6g sodium carbonate to 400mL of water while stirring. After mixing, let stand to swell and obtain the original gum solution.

[0093] S2: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 37℃ and 200 rpm for 12 h. The inoculum was then transferred to 500 mL of LB liquid medium at a 1% inoculum rate and cultured at 37℃ and 200 rpm until the OD600 reached 0.5. The inoculum was then transferred to a 2 L Erlenmeyer flask containing fermentation medium at a 5% inoculum rate and cultured at 37℃ and 200 rpm for 48 h. The cultured broth from the Erlenmeyer flask was then added to a 10 L fermenter containing fermentation medium at a 5% inoculum rate and fermented at 37℃ for 60 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to finally obtain a bio-based oil displacement agent.

[0094] The fermentation medium is formulated as follows: 5g glucose, 5g sodium acetate, 1g ammonium sulfate, 4.8g dipotassium hydrogen phosphate, 1.5g potassium dihydrogen phosphate, 0.5g trisodium citrate, 0.5g magnesium sulfate, 0.2g yeast extract, 0.1g ferrous sulfate, 0.01g calcium carbonate, 0.002g manganese sulfate, 0.0004g nickel chloride, 0.0004g zinc sulfate, 0.0002g ferric chloride, 0.0002g sodium molybdate, and distilled water to a final volume of 1000mL (1 liter).

[0095] S3: Add 1g of borate triethanolamine complex, 2g of bio-based oil displacement agent and 0.2g of ammonium persulfate to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

[0096] Performance testing

[0097] During fracturing operations, fracturing fluids must possess excellent thermal and shear stability. Specifically, under given temperature and shear rate conditions, they must maintain a certain viscosity to ensure successful fracture opening and extension, and efficient proppant carrying. As the fracturing fluid flows through the conduit, perforation holes, and finally into the formation, it faces significant mechanical shear forces, while simultaneously experiencing a rise in temperature. These combined factors exacerbate the potential for thermal and chemical degradation of the fracturing fluid, leading to a decrease in its apparent viscosity within the formation. This, in turn, reduces its proppant-carrying capacity and increases the likelihood of proppant loss. Therefore, evaluating the temperature and shear resistance of fracturing fluids is crucial.

[0098] In this experiment, a Harker RS6000 high-temperature and high-pressure rheometer was first used to test the fracturing fluids in Example 6 and Comparative Example 1 at a temperature of 100°C and a shear rate of 170 s⁻¹. -1 Temperature and shear resistance tests were conducted under the specified conditions, and the results are as follows: Figure 2 , 3 As shown in the figure, the rheological curves of the two types of gel fracturing fluids reveal that the temperature and shear resistance of the gels remained largely unchanged regardless of the addition of bio-based oil displacement agents and synergists. This experimental result further confirms that the addition of bio-based oil displacement agents and synergists does not negatively impact the performance of the gel fracturing fluids, indicating good compatibility between the bio-based oil displacement agents and the gel fracturing fluids.

[0099] To thoroughly evaluate the performance of bio-based flooding fracturing fluids, static oil washing capacity tests were subsequently conducted on bio-based flooding fracturing fluids of different concentrations (Examples 1-6, Comparative Examples 1-3). The experimental procedure was as follows: Bio-based flooding fracturing fluids of different concentrations were placed in a water bath and kept at 90°C for 2 hours until complete gelation to form bio-based flooding fracturing fluid breaker. 50 mL of different concentrations of bio-based flooding fracturing fluid breaker was accurately measured and added to a 100 mL beaker containing oil sands. The beaker was left to stand at 50°C for 24 hours, then shaken to allow oil to escape from the oil sands. The amount of oil washed out by the bio-based flooding fracturing fluid breaker was accurately measured. The oil washing rate was calculated using the formula: Oil washing rate = (V2 / V1) × 100%, where V1 is the original oil content of the oil sands (mL), and V2 is the amount of oil washed out (mL). The experimental results are shown in Table 1.

[0100] Table 1 Static oil washout rate of fracturing fluid with different concentrations of bio-based flooding fluid

[0101]

[0102] The results showed that Comparative Example 1 (without bio-based flood displacement agent and synergist) had an oil washout rate of only 38.7%, representing the baseline performance of the basic fracturing fluid system; Comparative Example 2 (containing only synergist, without bio-based flood displacement agent) had an oil washout rate of 40.2%, basically the same as Comparative Example 1, indicating that the use of synergist alone (lipopeptide + rhamnolipid) did not significantly improve the oil washout efficiency; Comparative Example 3 (containing 0.5% bio-based flood displacement agent, without synergist) had an oil washout rate of 75.8%, which was better than Comparative Example 1 and Comparative Example 2, proving that the bio-based flood displacement agent itself has good oil displacement ability, but it was still significantly lower than Example 1; Example 1 had a significantly higher oil washout rate than Comparative Example 3, indicating that there is a significant synergistic effect between the bio-based flood displacement agent and the synergist (lipopeptide, rhamnolipid). In this invention, the bio-based flood displacement agent provides basic interfacial activity and oil displacement ability, lipopeptide further enhances interfacial activity and emulsification efficiency, and rhamnolipid can significantly improve the wettability of the rock surface. The three elements work synergistically to significantly reduce the interfacial tension between oil and water, alter rock wettability, and form a highly efficient oil displacement network.

[0103] Furthermore, the concentration of the bio-based oil displacement agent is positively correlated with the oil washing rate; as the concentration increases, the oil washing rate increases synchronously. When the concentration reaches 2%, the oil washing rate tends to stabilize and reach saturation. Therefore, the optimal concentration range for use in fracturing fluid systems is 0.5~2%. In addition, this oil displacement fracturing fluid has significant oil washing efficiency; even under low concentration conditions, the oil washing rate can still be maintained above 80%, demonstrating excellent performance.

[0104] This invention evaluates the temperature and salt resistance of a bio-based oil displacement fracturing fluid system. The specific test method for evaluating temperature resistance is as follows: Multiple samples of the bio-based oil displacement fracturing fluid (prepared according to Example 4) were prepared and placed in a water bath at 90°C for 2 hours until complete gelation, forming the bio-based oil displacement fracturing fluid gel-breaking solution. Several 100mL beakers were selected, and the same amount of oil-containing sand was added to each beaker to ensure a consistent initial oil content (V1) in the oil sand. The beakers were placed in constant-temperature water baths at different temperatures. 50mL of the bio-based oil displacement fracturing fluid gel-breaking solution was accurately measured into each beaker at each temperature. The beakers were allowed to stand in the corresponding constant-temperature water bath for 24 hours, and then the beakers were shaken to allow oil to escape from the oil sand. The amount of oil washed out (V2) was accurately measured.

[0105] The specific test method for evaluating salt tolerance is as follows: Multiple samples of bio-based oil displacement fracturing fluid (prepared according to Example 5) were prepared, along with a series of salt solutions with different salinities to simulate the formation water salinity environment. The bio-based oil displacement fracturing fluid (prepared according to Example 5) was mixed with salt solutions of different salinities at a ratio of 4:1 to create a fracturing fluid system containing different salinities. This system was placed in a water bath and kept at 90°C for 2 hours until complete gelation to form the bio-based oil displacement fracturing fluid gelling solution. Several 100mL beakers were selected, and the same amount of oil-bearing sand was added to each beaker to ensure the original oil content of the sand was the same. 50mL of the fracturing fluid gelling solution was added to each beaker containing the oil-bearing sand. After standing at 50°C for 24 hours, the beakers were shaken to promote oil leaching, and the amount of washed-out oil was accurately measured. The wash rate of the fracturing fluid under various temperatures and salinities was calculated using the wash rate formula (wash rate = (V2 / V1) × 100%). Experimental data were recorded, and the effects of different temperatures and salinities on the wash rate were observed. This determined the adaptability and stability of the bio-based oil displacement gel fracturing fluid system under different temperature and salinity environments, and verified whether its temperature and salt resistance met the requirements of practical applications. The experimental results are shown in Tables 2 and 3.

[0106] Table 2 Static oil washout rate of bio-based flooding fracturing fluid rupture solution at different temperatures

[0107]

[0108] Table 3 Static wash-up rate of bio-based flooding fracturing fluid rupture solution under different salinity levels

[0109]

[0110] Experimental results show that even under extreme temperature and high salinity conditions, this system can effectively reduce oil-water interfacial tension and significantly improve oil recovery. Therefore, this invention is particularly suitable for the development of high-temperature and high-salinity reservoirs, effectively solving the problem of performance degradation of traditional fracturing fluids under high-temperature and high-salinity conditions, and providing new technical support for efficient extraction under complex reservoir conditions. Simultaneously, the addition of a bio-based oil displacement agent further enhances the degradation and dispersion capabilities of heavy oil components, enabling the system to exhibit excellent oil displacement effects under different reservoir conditions, significantly improving the economic benefits and environmental friendliness of oil extraction.

[0111] In the field test of bio-based oil displacement gel fracturing fluid, the reservoir temperature of the test well was 101℃. To minimize the damage caused by reservoir stimulation measures, a low-concentration guar gum fracturing fluid system was selected for the test. Based on the reservoir characteristics and formation temperature of the well, the corresponding system formulation was determined through laboratory evaluation and optimization, and 200m of the formulation was prepared according to the proportions in Example 4. 3 This is a bio-based oil displacement gel fracturing fluid used in practical field applications. The guar gum base fluid has a viscosity of 33 mPa·s. After adding 2% bio-based oil displacement agent, the base fluid viscosity remains at 33 mPa·s, with a viscosity change rate of 0. The initial crosslinking time is 25 seconds, and the gel can be lifted after 72 seconds, demonstrating overall stable liquid properties. During the fracturing operation of the test well, 100 m³ of gel was injected in the first and second stages respectively. 3 Bio-based oil displacement gel fracturing fluid. After fracturing, the well was shut in for 15 days, followed by flowback the next day after which 2mm nozzles were installed. One day after flowback, the oil pressure stabilized at 16.5 MPa, the casing pressure at 17 MPa, the daily fluid production reached 45 m³, and the daily oil production was 1.64 tons / day, with a maximum daily oil production of 1.81 tons / day. This is in stark contrast to the highest daily production of only 0.1 tons / day during the testing of neighboring wells, demonstrating significant increases in oil and production (see...). Figure 4 , 5 ).

[0112] The above results demonstrate that the bio-based oil recovery gel fracturing fluid system of this invention can exhibit excellent oil displacement performance under reservoir conditions, effectively improve the recovery rate of remaining oil, reduce damage to the reservoir, and reduce environmental pollution. It provides an innovative solution for the development of oil extraction technology and promotes the progress and practical application of bio-oil recovery technology.

[0113] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A bio-based oil displacement gel fracturing fluid system, characterized in that: It comprises the following components in parts by weight: 0.25-0.45 parts guar gum thickener, 0.15-0.35 parts anti-swelling agent, 0.15-0.35 parts drainage aid, 0.05-0.15 parts pH adjuster, 0.15-0.35 parts crosslinking agent, 0.5-3 parts bio-based oil displacement agent, 0.5-1.5 parts synergist, 0.05-0.15 parts degumming agent, and 100 parts water; The preparation method of the bio-based oil displacement agent is as follows: Bacillus subtilis strain BZ-1 was activated with LB medium. Single colonies were picked and inoculated into LB liquid medium and cultured at 35-40℃ and 180-200 rpm for 12-24 h. The inoculum was then transferred to LB liquid medium at a 1% inoculum rate and cultured at 35-40℃ and 180-200 rpm until the OD600 reached 0.5-0.

8. The inoculum was then transferred to shake flasks containing fermentation medium at a 5% inoculum rate and cultured at 35-40℃ and 180-200 rpm for 24-48 h. The cultured broth was then added to a fermenter containing fermentation medium at a 5% inoculum rate and fermented at 35-40℃ for 48-72 h. The fermentation broth was initially filtered, and the resulting filtrate was subjected to cell wall disruption and then finely filtered. Subsequently, it was compounded with decyl hydroxypropyl sulfobetaine and fatty alcohol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:2:1 to obtain a bio-based oil displacement agent. Bacillus subtilis BZ-1 was deposited at the China General Microbiological Culture Collection Center on November 15, 2024, with accession number CGMCC No. 32653; The synergist comprises the following components in parts by weight: 5-10 parts lipopeptide, 5-10 parts rhamnolipid, and distilled water to a final volume of 1000 parts.

2. The bio-based oil displacement gel fracturing fluid system according to claim 1, characterized in that: The fermentation medium comprises the following components by weight: 5 parts glucose, 5 parts sodium acetate, 1 part ammonium sulfate, 4.8 parts dipotassium hydrogen phosphate, 1.5 parts potassium dihydrogen phosphate, 0.5 parts trisodium citrate, 0.5 parts magnesium sulfate, 0.2 parts yeast extract, 0.01 parts calcium carbonate, 0.002 parts manganese sulfate, 0.1 parts ferrous sulfate, 0.0004 parts nickel chloride, 0.0004 parts zinc sulfate, 0.0002 parts ferric chloride, 0.0002 parts sodium molybdate, and distilled water to a final volume of 1000 parts.

3. The bio-based oil displacement gel fracturing fluid system according to claim 1, characterized in that: The guar gum thickener is one or more of guar gum, hydroxypropyl guar gum, and carboxymethyl guar gum.

4. The bio-based oil displacement gel fracturing fluid system according to claim 1, characterized in that: The anti-swelling agent is selected from one or more of potassium chloride, ammonium chloride, and potassium sulfate.

5. The bio-based oil displacement gel fracturing fluid system according to claim 1, characterized in that: The discharge aid is selected from one or more of the following: dodecyl dimethyl betaine, fatty alcohol polyoxyethylene ether, and sodium dodecylbenzene sulfonate.

6. The bio-based oil displacement gel fracturing fluid system according to claim 1, characterized in that: The crosslinking agent is selected from one or more of tetrabutyl titanate, zirconium oxychloride octahydrate, and triethanolamine borate complex.

7. The bio-based oil displacement gel fracturing fluid system according to claim 1, characterized in that: The pH adjuster is selected from one or more of sodium carbonate, sodium hydroxide, and potassium hydroxide; the desiccant is selected from one or more of ammonium persulfate and potassium persulfate.

8. A method for preparing a bio-based oil displacement gel fracturing fluid system according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Add the specified amounts of guar gum thickener, anti-swelling agent, drainage aid, and pH adjuster to water in sequence while stirring. After mixing, let it stand to swell and obtain the original gum solution. S2. Add the specified amount of lipopeptide to an alkaline aqueous solution with pH 9.0-10.0 and stir to form a dispersion. Then add rhamnolipin and mechanically stir at room temperature for 1-2 hours. After mixing, the synergist is obtained. S3. Add crosslinking agent, bio-based oil displacement agent, synergist and breaker to the original rubber solution in sequence, and stir evenly to obtain the bio-based oil displacement gel fracturing fluid system.

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