CN113416531B - Composition of microbial-based viscosity-reducing fracturing fluid and its application - Google Patents

Abstract

The invention provides a microbial-based viscosity-reducing oil displacement fracturing fluid composition and application thereof. The microbial-based viscosity-reducing oil displacement fracturing fluid composition includes: thickener, microorganism, cross-linking agent, gel breaker and water. The microorganism is a strain of Bacillus subtilis, the Latin scientific name is Bacillus subtilis, and the preservation number is CGMCC No. 19809. Thickeners and cross-linking agents can form polymer structures with specific structure and strength through cross-linking, and can support formation fractures in the process of heavy oil production. The gel breaker can break the gel of the above polymer structure, so that the gel breaker can flow back, and at the same time reduce the flow resistance of the heavy oil, so as to improve the recovery rate of the heavy oil. The above-mentioned specific Bacillus subtilis strains can use heavy oil, thickener, etc. as carbon sources to reproduce and secrete viscosity-reducing biosurfactants and small molecular organics, which can greatly reduce the viscosity of heavy oil and improve heavy oil recovery.

Description

Composition of microbial-based viscosity-reducing fracturing fluid and its application

technical field

The invention relates to the field of heavy oil exploitation, in particular to a microbial-based viscosity-reducing oil displacement fracturing fluid composition and application thereof.

Background technique

Heavy oil is a multi-hydrocarbon mixture with complex composition, high content of colloid and asphaltene, high viscosity, high density, and poor fluidity. At present, the main mature technologies for heavy oil recovery are thermal recovery with steam injection, oil layer combustion, combination of hot water and chemical huff and puff, cold recovery with sand, etc., but all of them have problems such as complex process and high cost.

As an important stimulation measure to enhance oil recovery, hydraulic fracturing has been widely used in the development of heavy oil. The fracturing fluid carries proppant and is pumped into the reservoir to form high conductivity channels, which can effectively improve the oil recovery of heavy oil. Heavy oil has high viscosity and poor fluidity. While fracturing to form highly conductive channels, the fracturing fluid is required to reduce the viscosity of heavy oil, increase the fluidity of crude oil, and improve the recovery of heavy oil. The effective way for fracturing fluid to reduce the viscosity of heavy oil is to add heavy oil viscosity reducer. However, because the amount of fracturing fluid injected into the reservoir is small, the volume that can be swept is small, and with the flowback of fracturing fluid , the duration of the viscosity-reducing effect of heavy oil is short.

The microbial heavy oil viscosity reduction method refers to the use of carbon sources by microorganisms to grow, reproduce and metabolize to produce biosurfactants with excellent heavy oil viscosity reduction and oil displacement functions, so that the heavy oil can be quickly emulsified and reduced viscosity, and promote the oil to flow into the well in the sandstone matrix. Bottom flow to achieve the purpose of increasing oil well production. Microorganisms can use the carbon source contained in heavy oil to grow and reproduce and metabolize biosurfactants for a long time, so the effect of microbial viscosity reduction and displacement is longer.

The existing literature provides a new type of water-based fracturing enzyme-microbial coupling fracturing fluid system for oil and natural gas extraction, which replaces the chemical additives in the water-based fracturing fluid with biological additives with the same effect. Supplemented by the addition of exogenous microorganisms to degrade residues and residual glue, the gel breaking efficiency can be improved and formation damage can be reduced. The working principle of this pressure fluid system is: use biological enzymes to break the gel, replace the chemical additives in the water-based fracturing fluid with biological additives with the same effect, supplemented by adding exogenous microorganisms to degrade residues and residual glue, and improve Gel breaking efficiency.

Another existing document provides a method for reducing the residue of guar gum fracturing fluid, adding a biological enzyme breaker into the guar gum fracturing fluid. The gel is broken in the range of ~70°C, and the cross-linked guar gum is degraded into a gel-breaking solution containing polysaccharides, monosaccharides and residues; microbial gram-negative bacilli are added to the gel-breaking solution, and the microbial gram-negative bacilli use enzymes to The gel-breaking solution is the nutrient source, and it is fermented at 40-70°C for 24-48 hours to convert the gel-breaking solution and residues into small molecular substances, and further degrade the residues not degraded by biological enzymes. The working principle of the pressure liquid system is: use biological enzymes to break the gel, degrade the cross-linked guar gum into a gel-breaking liquid containing polysaccharides, monosaccharides and residues; Gram-negative bacilli use the enzyme breaking solution as a nutrient source, convert the breaking solution and residue into small molecular substances, and further degrade the undegraded residue by the enzyme.

However, the effective reproduction of microorganisms cannot be achieved in the above two methods, so the above two guar gum fracturing fluids cannot achieve long-term viscosity reduction and oil displacement. Therefore, in view of the existence of the above problems, there is an urgent need in the field to develop a microbial-based viscosity-reducing flooding fracturing fluid system to solve the problems of short duration and limited effect of the existing chemical viscosity-reducing agents after fracturing. .

Contents of the invention

The main purpose of the present invention is to provide a microbial-based viscosity-reducing oil displacement fracturing fluid composition and its application, so as to solve the problems in the prior art.

In order to achieve the above object, the present invention provides a microbial-based viscosity-reducing oil displacement fracturing fluid composition on the one hand, and the microbial-based viscosity-reducing oil displacement fracturing fluid composition includes: thickener, microorganism, crosslinking agent, Glue and water, wherein the microorganism is a strain of Bacillus subtilis, the Latin scientific name is Bacillus subtilis, and the preservation number is CGMCC No.19809.

Further, the microorganisms exist in the formation of microbial bacterial liquid, preferably, the content of the Bacillus subtilis strain in the microbial bacterial liquid is 1.0×10 ⁷ -1.0×10 ¹¹ CFU.

Further, in parts by weight, the microbial-based viscosity-reducing oil displacement fracturing fluid composition includes: 0.10-0.30 parts of thickener, 5-15 parts of microbial bacterial liquid, 0.10-0.20 parts of cross-linking agent and 0.01-0.03 parts of breaking agent. Glue, the balance is water.

Further, the microbial-based viscosity-reducing oil displacement fracturing fluid composition also includes a clay stabilizer and/or a drainage aid.

Further, the microbial-based viscosity-reducing oil displacement fracturing fluid composition includes 0-0.3 parts of clay stabilizer and 0-0.3 part of drainage aid in parts by weight.

Further, the above-mentioned gel breaker is a biological gel breaker.

Further, the thickening agent is selected from natural galactomannan compounds (guar gum, hydroxypropyl guar gum, carboxymethyl hydroxypropyl bis-derived guar gum, hydroxypropyl carboxymethyl guar gum), polyacrylamide One or more of the group consisting of organic matter and cellulose thickener (carboxymethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose).

Another aspect of the present application also provides an application of the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided in the present application in a heavy oil viscosity-reducing system.

Further, the added amount of the microbial-based viscosity-reducing fracturing fluid composition is 20-30 wt%.

By applying the technical scheme of the invention, the thickener and the crosslinking agent can form a polymer structure with specific structure and strength through crosslinking, and can support formation fractures during heavy oil production. The gel breaker can break the gel of the above polymer structure, so that the gel breaker can flow back, and at the same time reduce the flow resistance of the heavy oil, so as to improve the recovery rate of the heavy oil. The above-mentioned specific Bacillus subtilis strain belongs to a new strain obtained by the applicant, which can reproduce with heavy oil, thickener, etc. as carbon source and secrete viscosity-reducing biosurfactant and small molecular organic matter. Moreover, the biosurfactant can greatly reduce the viscosity of heavy oil (for example, it can reduce the viscosity of 4400mPa·s to 185mPa·s, and the viscosity reduction rate can reach 95.8%), which can solve the problem of fracturing in underground heavy oil that is difficult to flow. Problems such as low output after transformation and difficulties in ground heavy oil pipeline transportation and treatment. Since the above-mentioned microorganisms can effectively reproduce in heavy oil and continuously secrete viscosity-reducing biosurfactants, applying the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by the application to the field of heavy oil production can achieve long-term, And obvious viscosity-reducing effect, so the development of the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by the application has a very good role in promoting the field of heavy oil recovery, and has high economic value.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Fig. 1 is the electron micrograph that scanning electron microscope test is carried out to the microorganism that obtains in the embodiment;

Fig. 2 is an electron microscope image obtained by scanning electron microscope test on the core before the microbial-based viscosity-reducing flooding fracturing fluid gel-breaking fluid displacement in Example 1.

Fig. 3 is an electron microscope image obtained by scanning electron microscope test on the core after the microbial-based viscosity-reducing flooding fracturing fluid is displaced by gel-breaking fluid in Example 1.

Deposit information of the strain of the present invention

A strain of Bacillus subtilis, the Latin scientific name of which is Bacillus subtilis, is preserved in the General Microbiology Center of China Committee for the Collection of Microorganisms, and the preservation address is No. 3, No. 1, Beichen Road, Chaoyang District, Beijing, and the preservation date As of May 12, 2020, the deposit number is CGMCC No.19809.

Detailed ways

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with examples.

As described in the background art, the existing chemical viscosity reducers after fracturing have the problems of short duration of viscosity reduction and limited effect. In order to solve the above technical problems, the present application provides a microbial-based viscosity-reducing oil displacement fracturing fluid composition, the microbial-based viscosity-reducing oil displacement fracturing fluid composition includes: thickener, microorganism, cross-linking agent, gel breaker And water, wherein the above-mentioned microorganism is Bacillus subtilis with a Latin scientific name of Bacillus subtilis, and the preservation number is CGMCC No.19809.

Thickeners and cross-linking agents can form polymer structures with specific structure and strength through cross-linking, and can support formation fractures in the process of heavy oil production. The gel breaker can break the gel of the above polymer structure, so that the gel breaker can flow back, and at the same time reduce the flow resistance of the heavy oil, so as to improve the recovery rate of the heavy oil. The above-mentioned specific Bacillus subtilis strain belongs to a new strain obtained by the applicant, which can reproduce with heavy oil, thickener, etc. as carbon source and secrete viscosity-reducing biosurfactant and small molecular organic matter. Moreover, the biosurfactant can greatly reduce the viscosity of heavy oil (for example, it can reduce the viscosity of 4400mPa·s to 185mPa·s, and the viscosity reduction rate can reach 95.8%), which can solve the problem of fracturing in underground heavy oil that is difficult to flow. Problems such as low output after transformation and difficulties in ground heavy oil pipeline transportation and treatment. Since the above-mentioned microorganisms can effectively reproduce in heavy oil and continuously secrete viscosity-reducing biosurfactants, applying the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by the application to the field of heavy oil production can achieve long-term, And obvious viscosity-reducing effect, so the development of the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by the application has a very good role in promoting the field of heavy oil recovery, and has high economic value.

During the application process, the above-mentioned microorganisms (Bacillus subtilis strain) exist in the form of bacterial liquid. For example, in a preferred embodiment, the seed solution is added to the culture medium at an inoculation amount of 5 wt%, and cultured at 35° C. and 170 rpm for 36 hours to obtain a microbial bacterial solution.

The culture medium used may be a composition commonly used in the art. In a preferred embodiment, the composition of the above medium is 12g/L sucrose, 1.5g/L NH ₄ Cl, 3.0g/L K ₂ HPO ₄ ·12H ₂ O, 0.5g/L KH ₂ PO ₄ , NaCl 10g/L, FeSO ₄ ·7H ₂ O 0.015g/L, MnSO ₄ 0.005g/L, CuSO ₄ ·5H2O 0.005g/L, pH 6.5.

More preferably, the content of the microorganism (Bacillus subtilis strain) in the above microorganism liquid is 1.0×10 ⁷ -1.0×10 ¹¹ CFU.

Adding the above-mentioned specific microorganisms to the microbial-based viscosity-reducing oil displacement fracturing fluid composition can make the fracturing fluid composition have a sustained and efficient viscosity-reducing effect. In order to better improve its viscosity-reducing effect, it is necessary to optimize the dosage of each component in the fracturing composition. In a preferred embodiment, in parts by weight, the microbial-based viscosity-reducing oil displacement fracturing fluid composition includes: 0.10-0.30 parts of thickener, 5-15 parts of microbial bacterial liquid, 0.10-0.20 parts of cross-linking agent and 0.01 to 0.03 parts of the breaker, and the balance is water. The amount of the above-mentioned components includes but is not limited to the above-mentioned range, and limiting them within the above-mentioned range can make the cross-linking effect of the thickener and the cross-linking agent, and the viscosity-reducing effect of microorganisms achieve a better synergistic effect , which is conducive to further improving the effects of viscosity reduction and heavy oil production increase.

Since different production formations have different formation structures and compositions, in order to further improve the actual effect of the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by the application in the heavy oil production process, in a preferred embodiment, The microbial-based viscosity reducing flooding fracturing fluid composition also includes clay stabilizers and/or drainage aids.

The addition of clay stabilizer can inhibit formation clay swelling and clay particle migration. The addition of the drainage aid is beneficial to improve the discharge of the working residual fluid from the formation during the fracturing process. More preferably, in parts by weight, the microbial-based viscosity-reducing oil displacement fracturing fluid composition includes 0-0.3 parts of clay stabilizer, 0-0.3 part of drainage aid, and 0.01-0.03 part of bio-enzyme breaker.

In the above microorganism-based viscosity-reducing oil displacement fracturing fluid composition, thickeners, crosslinking agents, clay stabilizers, drainage aids and gel breakers can all be of the types commonly used in the field.

Optionally, thickeners include but are not limited to natural galactomannan compounds (guar gum, hydroxypropyl guar gum, carboxymethylhydroxypropyl bis-derivatized guar gum, hydroxypropyl carboxymethyl guar gum), One or more of the group consisting of polyacrylamide organic matter and cellulose thickener (carboxymethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose).

The crosslinking agent includes but not limited to one or more of polyepoxide pEPC, modified organoboron, and methylenebisacrylamide. The above-mentioned gel breakers include but are not limited to biological enzyme gel breakers (such as β-mannanase, etc.). Compared with chemical breakers, biological enzyme breakers have a better breaking effect and cause less damage to the formation.

Another aspect of the present application also provides a preferred method for preparing fracturing fluid: under stirring conditions, add a thickener (such as guar gum) to water, and stir for 30 minutes; add microbial bacterial liquid and stir evenly, selectively Add clay stabilizer, drainage aid, gel breaker and crosslinking agent, stir and mix evenly to form the required guar gum fracturing fluid.

Another aspect of the present application also provides an application of the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided in the present application in a heavy oil viscosity-reducing system.

Since the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by this application has a long-term and stable viscosity-reducing effect in the process of heavy oil recovery, its application in the field of heavy oil recovery has a very good role in promoting the development of the industry , and has high economic value.

Preferably, the added amount of the microbial-based viscosity-reducing fracturing fluid composition is 20-30 wt%.

The present application will be described in further detail below in conjunction with specific examples, and these examples should not be construed as limiting the scope of protection claimed in the present application.

The cultivation process of microbial strain in the embodiment:

The seed solution was added to the culture medium at an inoculum amount of 5 wt%, and cultured at 35° C. and 170 rpm for 36 hours to obtain a microbial bacterial solution. The composition of the above medium is sucrose 12g/L, NH ₄ Cl 1.5g/L, K ₂ HPO ₄ 12H ₂ O 3.0g/L, KH ₂ PO ₄ 0.5g/L, NaCl 10g/L, FeSO ₄ 7H ₂ O 0.015g/L, MnSO ₄ 0.005g/L, CuSO ₄ ·5H2O 0.005g/L, pH 6.5.

The morphological appearance of the above-mentioned strain was observed by scanning electron microscope, as shown in Figure 1, its shape is a bacillus, the size is (0.5-0.6) μm × (2-3) μm, no capsule, perinatal flagella, mobile, preliminary identification For the genus Bacillus. Gram staining was used to identify bacteria, as shown in Figure 2, the results showed that strain XJ-21 was a Gram-positive bacillus.

The 16S rRNA gene sequence analysis was carried out on the above strains, and the phylogenetic analysis was carried out according to the 16S rRNA gene sequencing results. The phylogenetic tree is shown in Figure 3. The analysis results showed that the strain XJ-021 had the highest homology with Bacillus subtilis NBRC101239. Therefore, combined with the morphological observation and physiological and biochemical characteristics of the bacteria, it was identified as Bacillus subtilis of the genus Bacillus.

The preparation process of the fracturing fluid system includes: adding a thickener (such as guar gum) into water under stirring conditions, and stirring for 30 minutes; Agent and cross-linking agent, stir and mix evenly to form the required guar gum fracturing fluid.

Example 1

A kind of microbial-based viscosity-reducing oil displacement fracturing fluid system provided in this embodiment is made up of microbial bacterial liquid, guar gum, and fracturing fluid auxiliary agent, and includes the following components in parts by weight: thickener (hydroxypropyl Guar gum) 0.10 parts, microbial bacterial liquid 15 parts, crosslinking agent (modified organic boron, Karamay Xinju Industry and Trade Co., Ltd., XJ-03) 0.10 parts, clay stabilizer (organic quaternary ammonium salt polymer, Karamay City Zhengcheng Co., Ltd., JN-1) 0.3 part, drainage aid (rhamnolipid) 0.3 part, biological enzyme gel breaker (β-mannanase) 0.01 part, and the balance was made up to 100 parts with water.

After the above prepared fracturing fluid is broken, the fracturing fluid breaker is obtained, and the thick oil viscosity reduction performance and oil displacement performance of the breaker are tested.

(1) Viscosity reduction performance test of gel breaking fluid

Take 30g of gel-breaking solution and add it to 70g of dehydrated heavy oil (the source of heavy oil is Ji 7 well area of Xinjiang Oilfield), shake evenly, put it in a 60°C oven, and measure the viscosity change of crude oil before and after.

After 2 days, the viscosity of the heavy oil decreased from 4400mPa·s to 620mPa·s, and the viscosity reduction rate was 85.9%. After 6 days, the viscosity of the heavy oil decreased from 4400mPa·s to 188mPa·s, and the viscosity reduction rate was 95.8%.

(2) Oil displacement performance test of gel breaking fluid

Core displacement experiments: standard natural cores were dried in an oven at 105°C, and crude oil with a viscosity of 1.5mPa·s was used to establish saturated oil, and then displacement experiments were carried out. Put the prepared simulated formation water into the intermediate container, displace the oil-saturated core until no oil comes out, read the scale of the oil-water separator, and calculate the degree of crude oil recovery; record the first oil recovery; close the front and rear valves of the core, keep the confining pressure at 2 MPa, and incubate in the holder for 2 days; flood with simulated formation water until no oil comes out, and record the second oil recovery ; The sum of the secondary oil recovery is the total oil recovery, and the final recovery degree is calculated according to the total oil recovery. The ultimate recovery rate of the core displacement experiment is 64.41%, among which the water flooding rate is 49.3%, and the gel-breaking fluid flooding rate is 15.11%.

(3) The scanning electron microscope test was carried out on the cores before and after displacement by the microbial-based viscosity-reducing fracturing fluid and the gel-breaking fluid.

Observe the change of core state before and after displacement. Fig. 2 shows the electron micrograph before displacement, and Fig. 3 is the electron micrograph after displacement. From the rectangular area in Figure 3, it can be clearly seen that rod-shaped bacteria exist in the pores of the core, and the microorganisms have grown and reproduced in the core after displacement, indicating that the microorganisms in the fracturing fluid can enter the core to grow and metabolize produce active substances.

Example 2

A microbial-based viscosity-reducing oil displacement fracturing fluid system provided in this embodiment is composed of microbial bacterial fluid, guar gum, fracturing fluid auxiliary agent and crosslinking agent, and includes the following components in parts by weight:

Thickener (hydroxypropyl guar gum) 0.20 parts, microbial bacterial liquid (XJ-21 fermentation liquid) 10 parts, crosslinking agent (modified organic boron, Karamay Xinju Industry and Trade Co., Ltd., XJ-03) 0.10 parts 0.3 parts, clay stabilizer (organic quaternary ammonium salt polymer, manufacturer Karamay Zhengcheng Co., Ltd., JN-1) 0.3 parts, drainage aid (rhamnolipid) 0.3 parts, biological enzyme gel breaker (β-mannose Glycanase) 0.01 part, and the balance is made up to 100 parts with water.

After the above prepared fracturing fluid is broken, the fracturing fluid breaker is obtained, and the thick oil viscosity reduction performance and oil displacement performance of the breaker are tested.

(1) Viscosity reduction performance test of gel breaking fluid

Test specific process with embodiment 1.

After 2 days, the viscosity of the heavy oil decreased from 4400mPa·s to 612mPa·s, and the viscosity reduction rate was 86.1%. After 6 days, the viscosity of the heavy oil decreased from 4400mPa·s to 183mPa·s, and the viscosity reduction rate was 95.8%.

(2) Oil displacement performance test of gel breaking fluid

Core displacement experiment: the specific process is the same as in Example 1.

The ultimate recovery rate of the core displacement experiment is 62.76%, among which the water flooding rate is 47.59%, and the gel-breaking fluid flooding rate is 15.17%.

Example 3

A microbial-based viscosity-reducing oil displacement fracturing fluid system provided in this embodiment is composed of microbial bacterial fluid, guar gum, fracturing fluid auxiliary agent and crosslinking agent, and includes the following components in parts by weight:

Thickener (hydroxypropyl guar gum) 0.30 parts, microbial bacterial liquid (XJ-21 fermentation liquid) 5 parts, crosslinking agent (modified organic boron, Karamay Xinju Industry and Trade Co., Ltd., XJ-03) 0.20 0.3 part, clay stabilizer (organic quaternary ammonium salt polymer, Karamay Zhengcheng Co., Ltd., JN-1) 0.3 part, drainage aid (rhamnolipid) 0.3 part, biological enzyme gel breaker (β-mannan carbohydrase) 0.01 part, and the balance is made up to 100 parts with water.

After the above prepared fracturing fluid is broken, the fracturing fluid breaker is obtained, and the thick oil viscosity reduction performance and oil displacement performance of the breaker are tested.

(1) Viscosity reduction performance test of gel breaking fluid

Test specific process with embodiment 1.

After 2 days, the viscosity of the heavy oil decreased from 4400mPa·s to 723mPa·s, and the viscosity reduction rate was 83.6%. After 6 days, the viscosity of the heavy oil decreased from 4400mPa·s to 199mPa·s, and the viscosity reduction rate was 95.5%.

(2) Oil displacement performance test of gel breaking fluid

Core displacement experiment: the specific process is the same as in Example 1.

The ultimate recovery rate of the core displacement experiment is 64.55%, among which the water flooding rate is 48.25%, and the gel-breaking fluid flooding rate is 16.3%.

Example 4

A microbial-based viscosity-reducing oil displacement fracturing fluid system provided in this embodiment is composed of microbial bacterial fluid, guar gum, fracturing fluid auxiliary agent and crosslinking agent, and includes the following components in parts by weight:

Thickener (hydroxypropyl guar gum) 0.20 parts, microbial bacterial liquid (XJ-21 fermentation liquid) 2 parts, crosslinking agent (modified organic boron, Karamay Xinju Industry and Trade Co., Ltd., XJ-03) 0.10 0.3 part, clay stabilizer (organic quaternary ammonium salt polymer, Karamay Zhengcheng Co., Ltd., JN-1) 0.3 part, drainage aid (rhamnolipid) 0.3 part, biological enzyme gel breaker (β-mannan carbohydrase) 0.01 part, and the balance is made up to 100 parts with water.

After the above prepared fracturing fluid is broken, the fracturing fluid breaker is obtained, and the thick oil viscosity reduction performance and oil displacement performance of the breaker are tested.

(1) Viscosity reduction performance test of gel breaking fluid

Test specific process with embodiment 1.

After 2 days, the viscosity of the heavy oil decreased from 4400mPa·s to 2300mPa·s, and the viscosity reduction rate was 47.73%. After 6 days, the viscosity of the heavy oil decreased from 4400mPa·s to 430mPa·s, and the viscosity reduction rate was 90.23%.

(2) Oil displacement performance test of gel breaking fluid

Core displacement experiment: the specific process is the same as in Example 1.

The ultimate recovery rate of the core displacement experiment is 58.75%, among which the water flooding rate is 48.25%, and the gel-breaking fluid flooding rate is 10.5%.

Example 5

The difference from Example 2 is that the above-mentioned clay stabilizer, drainage aid and bio-enzyme breaker are not added.

(1) Viscosity reduction performance test of gel breaking fluid

Test specific process with embodiment 1.

After 2 days, the viscosity of the heavy oil decreased from 4400mPa·s to 2750mPa·s, with a viscosity reduction rate of 37.5%. After 6 days, the viscosity of the heavy oil decreased from 4400mPa·s to 740mPa·s, with a viscosity reduction rate of 83.18%.

(2) Oil displacement performance test of gel breaking fluid

Core displacement experiment: the specific process is the same as in Example 1.

The ultimate recovery rate of the core displacement experiment is 58.15%, among which the water flooding rate is 47.92%, and the gel-breaking fluid flooding rate is 10.23%.

Comparative example 1

The difference from Example 2 is that the above-mentioned microbial bacterial liquid is not added.

(1) Viscosity reduction performance test of gel breaking fluid

Test specific process with embodiment 1.

After 2 days, the viscosity of the heavy oil decreased from 4400mPa·s to 3150mPa·s, with a viscosity reduction rate of 28.41%. After 6 days, the viscosity of the heavy oil decreased from 4400mPa·s to 2670mPa·s, with a viscosity reduction rate of 39.32%.

(2) Oil displacement performance test of gel breaking fluid

Core displacement experiment: the specific process is the same as in Example 1.

The ultimate recovery rate of the core displacement experiment is 52.04%, among which the water flooding rate is 48.13%, and the gel-breaking fluid flooding rate is 3.91%.

From the above description, it can be seen that the above-mentioned embodiments of the present invention have achieved the following technical effects: compared with the existing oil displacement composition, the application of the microbial-based viscosity-reducing oil displacement fracturing fluid composition provided by the application It has obvious viscosity-reducing effect in the field of heavy oil production, and it is also conducive to greatly improving heavy oil recovery.

It should be noted that the terms "first" and "second" in the specification and claims of the present application are used to distinguish similar objects, but not necessarily used to describe a specific order or sequence. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described herein.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. The microbial-based viscosity-reducing oil-displacing fracturing fluid composition is characterized by comprising the following components in parts by weight: 0.10-0.30 part of thickening agent, 5-15 parts of microorganism, 0.10-0.20 part of cross-linking agent, 0.01-0.03 part of gel breaker, 0-0.3 part of clay stabilizer, 0-0.3 part of cleanup additive and the balance of water, wherein the dosage of the clay stabilizer and the dosage of the cleanup additive are not 0, the microorganism is Bacillus subtilis strain, the Latin is Bacillus subtilis, and the preservation number is CGMCC No.19809; the microorganism exists in the form of microorganism liquid, and the content of bacillus subtilis strain in the microorganism liquid is 1.0 multiplied by 10 ⁷ ～1.0×10 ¹¹ A CFU; the thickening agent is selected from hydroxypropyl guar gum; the gel breaker is selected from beta-mannanase.

2. The application of the microorganism-based viscosity-reducing oil-displacing fracturing fluid composition of claim 1 in a viscous oil viscosity-reducing system.

3. The application of the microbial-based viscosity-reducing, oil-displacing and fracturing fluid composition in a thick oil viscosity-reducing system according to claim 2, wherein the addition amount of the microbial-based viscosity-reducing, oil-displacing and fracturing fluid composition is 20-30 wt%.

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