High-performance guanidine gum fracturing fluid system for gas backlog fracturing of deep coal and rock and application of high-performance guanidine gum fracturing fluid system

Abstract

The invention discloses a high-performance guanidine gum fracturing fluid system for deep coal rock gas backlog fracturing and application, and relates to the technical field of oil and gas reservoir chemistry, the high-performance guanidine gum fracturing fluid system for deep coal rock gas backlog fracturing comprises the following components: 0.05-0.35% of graft modified guanidine gum, 0-0.3% of multiple cross-linking agent, 0-0.2% of conditioning agent, 0.1-0.3% of functional additive, 0-0.1% of gel breaker, and the balance of water, the grafting modified guanidine gum is prepared by performing functional group modification and side chain grafting polymerization on guanidine gum raw powder, the number of chemical crosslinking groups and branched chains is remarkably increased, after the grafting modified guanidine gum is compounded with a matched multiple crosslinking agent, the chemical and physical synergistic crosslinking effect is remarkably enhanced, and the performance of the fracturing fluid is greatly improved; the high-performance guanidine gum fracturing fluid system for deep coal rock gas backlog fracturing, provided by the invention, has the characteristics of low component dosage, low cost, low residue content, good swelling performance, good resistance reduction performance, good sand carrying performance, controllable mixing construction and controllable online crosslinking, and can effectively meet the construction requirements of coal rock gas backlog fracturing.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas reservoir chemistry, and in particular to a high-performance guar gum fracturing fluid system for deep-layer coal rock gas volume fracturing and application thereof. Background Art

[0002] At present, the development of deep coal-rock gas volume fracturing is based on sufficient fracture formation and effective support of saturated sand filling. The fracturing fluid system suitable for its volume fracturing process is the key to development. The polymer variable viscosity fracturing fluid currently used on a large scale has the advantages of adjustable viscosity, low damage, and integrated continuous construction, but it lacks fracture formation ability and sand addition strength. With the continuous development of technology, new requirements have been put forward for the fracturing fluid system, and "high performance, less fluid and more sand" has gradually become the focus of attention. As the most mature reservoir transformation working fluid in the past two decades, the guar gel fracturing fluid system has a sufficient theoretical research and field application basis. As long as targeted research and optimization are carried out to give play to its advantages (such as low filtration loss, good temperature resistance, and good sand carrying performance) and overcome its disadvantages (such as high friction resistance of frozen gel and high residue content), it can well meet the technical difficulties of fracturing fluid proposed by coal-rock gas volume fracturing, and provide strong technical support for efficient fracture formation and high-intensity sand addition of deep coal-rock gas in China. In order to meet the needs of volume fracturing of coal-rock gas, increase the volume of reservoir transformation, improve production output, and reduce construction costs, the guar gum fracturing fluid system needs to be improved and optimized in the following aspects:

[0003] ① Reasonably modify guar gum to improve its swelling and cross-linking properties, and modify the groups to reduce the adsorption of guar gum on coal and rock, thereby reducing the usage and cost;

[0004] ② Research and develop high-efficiency cross-linking agents to reasonably control cross-linking performance at low doses and reduce construction friction; improve the cross-linking strength with guar gum to meet the high-intensity sand addition requirements of coal-rock gas volume fracturing construction;

[0005] ③ The residue content is greatly reduced, which greatly reduces its impact on matrix permeability and fracture conductivity;

[0006] ④ The dosage of each additive is optimized to improve the overall performance of the liquid and greatly reduce the cost of the liquid;

[0007] ⑤The system can be mixed and cross-linked online to improve the efficiency of fracturing construction and achieve cost reduction and efficiency improvement.

[0008] At present, relevant enterprises at home and abroad have also conducted some research on guar gum fracturing fluid and achieved certain results. For example, patent CN107513383A discloses a low-concentration guar gum fracturing fluid for gas wells. The formula is complex, which increases the complexity of implementation and the difficulty of cost control. At the same time, due to the excessive addition of reagents, the damage to the formation is increased; patent CN106905948A discloses a guar gum clean fracturing fluid, the production cost increases exponentially, which is not conducive to popularization and application in reality. The multi-core cross-linking agent contains inorganic acid salts, which will increase the formation damage after breaking the gel; patent CN112391154A discloses an alcohol-containing fracturing fluid. When the ethylene glycol concentration is high, the cross-linking time increases, the amount of cross-linking agent is too large, the cost increases, the gel strength decreases, and the sand carrying capacity decreases; patent CN 102352233A discloses a low-damage small molecule guar gum fracturing fluid, the amount of organic cross-linking agent is large, the indirect cost increases, and it also causes excessive formation damage. These guar gum fracturing fluids still have significant problems in achieving the functions of improving sand carrying performance, reducing construction friction, ensuring gel breaking performance, reducing costs, and reducing reservoir damage. Summary of the invention

[0009] In view of this, the present invention proposes a high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing, which has the characteristics of low component dosage, low cost, low residue content, good swelling performance, good resistance reduction performance, good sand carrying performance, controllable mixing construction, and controllable online cross-linking. It can effectively meet the construction needs of coal-rock gas volume fracturing and achieve the purpose of increasing the transformation volume, improving the support filling strength, reducing reservoir damage, increasing production output, and reducing costs and increasing efficiency.

[0010] The present invention discloses a high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing, which comprises the following components by mass fraction:

[0011]

[0012] The balance is water.

[0013] Furthermore, the grafted modified guar gum is prepared from the following components by mass fraction:

[0014]

[0015] The preparation method comprises the following steps:

[0016] Step S1: fully dispersing guanidine collagen powder in a dispersion medium until uniform, adding an alkalizing agent, stirring and alkalizing at a speed of 200 to 300 r / min for 60 to 90 minutes at 35 to 40° C. to obtain an alkalized solution;

[0017] Step S2: adjusting the temperature to 65-70° C. and the stirring speed to 500-600 r / min, slowly adding the functionalizing agent to the alkalized solution within 40-50 min, and adjusting the speed to 200-300 r / min after the addition to react at a constant temperature for 90-120 min;

[0018] Step S3: adjusting the temperature to 40-45° C., adding the graft polymerization modifier under nitrogen protection, stirring until completely dissolved, adding a neutralizer according to the pH value of the solution, adjusting the solution pH to 7±0.2, passing nitrogen for 45-60 minutes, and then adding a 5% mass concentration of an initiator aqueous solution to the solution after adjusting the pH within 10 minutes;

[0019] Step S4: stop nitrogen flow, adjust stirring speed to 300-400 r / min, react for 210-300 min until the temperature is constant, then stop heating and stirring, wait for the temperature to cool to below 50° C., filter, dry and pulverize to obtain.

[0020] Further, the alkalizing agent is one of sodium hydroxide or sodium methoxide;

[0021] The functionalizing agent is one of propane sultone, p-toluene sulfonate, diisopropyl phosphate, trimethyl phosphate, methyl sulfonate, diethyl sulfate, methyl sulfate, sodium 3-chloro-2-hydroxypropyl sulfonate, and propylene oxide;

[0022] The graft polymerization modifier is a combination of a hydrophilic monomer and a hydrophobic modification monomer, wherein the hydrophilic monomer is acrylic acid and maleic acid; the hydrophobic modification monomer is one of 2-(trifluoromethyl)acrylic acid, trifluoropropylene, trifluoroacetic acid vinyl ester, trifluoroethyl acrylate, and trifluoroethyl methacrylate;

[0023] The neutralizing agent is one of dilute hydrochloric acid or sodium hydroxide;

[0024] The initiator is a combination of ammonium cerium nitrate and potassium persulfate, or one of benzoyl peroxide;

[0025] The dispersion medium is one of methanol (99.5%), ethanol (99%) and isopropanol (99%).

[0026] Further, the ratio of acrylic acid, maleic acid and hydrophobic modifier is 21:3:1 by weight;

[0027] The ratio of the ammonium cerium nitrate to potassium persulfate is 1.5:1.

[0028] Further, the multiple cross-linking agent is prepared from the following components by mass fraction:

[0029]

[0030] The balance is water;

[0031] The preparation method comprises the following steps:

[0032] Step 1): The nanomaterial matrix, the titanium-containing organic matter and isopropanol are stirred and reacted at 65-73° C. and 300-400 r / min for 1-2 hours, and then the chelating agent No. 1 is added and the reaction is continued for 0.5-1 hour to obtain a primary chelating intermediate;

[0033] Step 2): keeping the temperature constant, adjusting the stirring speed to 600-650 r / min, adding chelating agent No. 2 to the primary chelating intermediate and reacting for 1 hour to obtain a secondary chelating intermediate;

[0034] Step 3): Under the same conditions, a portion of chelating agent No. 3 is added to the secondary chelating intermediate, and after dissolving and mixing, the reaction temperature is adjusted to 75±1° C. and the reaction is carried out at 0.8-1 MPa for 1-1.5 h to obtain a tertiary chelating intermediate;

[0035] Step 4): Control the temperature to 70-75°C, the pressure to 0.5-0.8 MPa, set the stirring speed to 800-900 r / min, add water and borax to the tertiary chelating intermediate in sequence, add the remaining chelating agent No. 3, adjust the stirring speed to 600-650 r / min, continue the reaction for 1.5h-2h, obtain the quaternary chelating final product, reduce the pressure, and cool;

[0036] Step 5): Add the synergistic enhancer into the cooled final product of the fourth-stage chelation, stir and mix, and discharge the product.

[0037] Furthermore, the nano matrix material is hydrophilic fumed silica;

[0038] The titanium-containing organic substance is one of tetrabutyl titanate, tetraethyl titanate, and isopropyl titanate;

[0039] The chelating agent No. 1 is one of triethanolamine, acetylacetone, ethylenediamine, ethylenediaminetetraacetic acid, and aminotriacetic acid;

[0040] The chelating agent No. 2 is one of methanol, ethanol, ethylene glycol, glycerol, or a combination of any two of equal weight parts;

[0041] The chelating agent No. 3 is one of xylitol, sorbitol, sodium gluconate, and citric acid;

[0042] The synergistic enhancer is one of N,N-methylenebisacrylamide, N,N-(1,2-dihydroxyethylene)bisacrylamide and polyethylene glycol monomethyl ether monomethacrylate.

[0043] Furthermore, the ratio of the chelating agent No. 3 added to the secondary chelating intermediate in step 3) to the remaining chelating agent No. 3 added in step 4) is 28:2-5 in terms of mass fractions.

[0044] Further, the regulator is composed of the following components by mass fraction:

[0045] Triethanolamine 40~45%

[0046] Sodium bicarbonate 55-60%

[0047] The functional additives are composed of a system synergist and a damage inhibitor in equal weight ratios, wherein the system synergist is a silicone synergist or a nonionic perfluorooctyl polyoxyethylene ether surfactant, and the damage inhibitor is a member selected from the group consisting of ethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol butyl ether, propylene glycol phenyl ether, and sodium lauryl sulfate;

[0048] The gel breaker is one of ammonium persulfate and potassium persulfate.

[0049] In addition, the present invention also discloses an on-site preparation method of the high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing, which mainly comprises the following steps:

[0050] Step 1: In a mixing vehicle, the grafted modified guar gum is sucked into water in a suction cycle using a jet technology and mixed;

[0051] Step 2: After the grafted modified guar gum is absorbed, add the regulator according to the formula ratio and continue to circulate and stir for 10 minutes before stopping. The viscosity is tested to be up to standard and the fracturing base fluid is obtained for standby use;

[0052] Step 3: Add functional additives and multiple cross-linking agents to the fracturing base fluid in the sand mixing truck according to the formula ratio, and then add the degumming agent in the formula ratio, and mix well in the sand mixing truck.

[0053] And the application method of the above-mentioned high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing: the application scenario of the high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing is the volume fracturing construction of deep coal-rock gas.

[0054] The technical effects of the present invention are:

[0055] (1) By introducing functional groups into the molecular structure of guar gum and carrying out graft copolymerization modification using hydrophilic monomers and hydrophobic monomers, a grafted modified guar gum is obtained, the molecular weight of which is increased to 800,000 to 1,000,000, the insoluble matter is reduced, and the cationic groups are reduced to reduce adsorption damage;

[0056] (2) After guar gum grafting modification, the swelling performance (meeting the requirements of online mixing), cross-linking performance, temperature and shear resistance (lower concentrations can meet the temperature resistance requirements of deep coal-rock reservoirs within 80°C, and the temperature resistance of 0.35% water can reach 140°C), and sand carrying performance (cross-linked gel can carry sand without sedimentation) are greatly improved. At the same time, the advantage of guar gum fracturing fluid in reducing filtration loss is also maintained, which can well meet the high requirements of coal-rock gas volume fracturing construction for seam creation and sand addition;

[0057] (3) By fully nano-modifying the cross-linking, and then using the staged addition and pressure reaction of different chelating agents, the step-by-step encapsulation and multi-element chelation of organic titanium are achieved, and multi-level chelated titanium / boron is prepared. In addition, a synergistic enhancer component is compounded to prepare a nano-modified multiple cross-linking agent, which greatly improves the chemical cross-linking effect of guar gum molecules and synergistically enhances the spatial network structure of guar gum molecules to provide sufficient jelly viscosity and strength;

[0058] (4) Multiple cross-linking agents can slowly release cross-linking components in the fracturing fluid to achieve the purpose of delaying cross-linking. Under the regulation of the amount of the regulator, online cross-linking can be controlled, reducing the friction resistance of the fracturing fluid in the pipeline, and the resistance reduction rate can reach 70%;

[0059] (5) After guar gum modification, the insoluble matter content is reduced by nearly 90%, and the residue content of the fracturing fluid system is significantly reduced (as low as 70 mg / L), which can significantly reduce the damage to the reservoir;

[0060] (6) The present invention optimizes guar gum, cross-linking agent, regulator, and functional additive, thereby greatly reducing the amount of each additive, and greatly reducing the material cost of the fracturing fluid while ensuring the performance of the fracturing fluid;

[0061] (7) The high-performance guar gum fracturing fluid provided by the present invention can realize online mixing and fracturing construction, greatly saving the time of fluid preparation, improving the efficiency of fracturing construction, and achieving cost reduction and efficiency improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 The SEM images of the cross-linked jelly of the fracturing fluid prepared in Example 1 of the present invention and the cross-linked jelly of conventional guar gum are shown;

[0063] Figure 2 This is the rheological property test curve of Example 1 of the present invention;

[0064] Figure 3 This is the rheological property test curve of Example 2 of the present invention;

[0065] Figure 4 This is the rheological property test curve of Example 3 of the present invention;

[0066] Figure 5 This is the rheological property test curve of Example 4 of the present invention;

[0067] Figure 6 This is a diagram showing the drag reduction test results of Example 1 of the present invention;

[0068] Figure 7 The figure is a test result diagram of the drag reduction rate of Example 5 and Example 6 of the present invention;

[0069] Figure 8 This is a demonstration of the sand-carrying performance of the cross-linked jelly in Example 3 of the present invention;

[0070] Fig. 9 It is a construction curve diagram of the on-site application of the present invention. DETAILED DESCRIPTION

[0071] The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used therein are all commercially available unless otherwise specified.

[0072] Example 1

[0073] (1) Preparation of grafted modified guar gum

[0074] The raw materials and proportions for preparing grafted modified guar gum are as follows, based on mass fraction:

[0075] Guanidine collagen powder 30% (guanidine collagen powder was purchased from Kunshan Jingkun Oilfield Chemical Technology Co., Ltd.); sodium methoxide 5%; propane sultone 6%; acrylic acid 6.72%; maleic acid 0.96%; vinyl trifluoroacetate 0.32%; (30%) sodium hydroxide 0.8%; cerium ammonium nitrate 0.045%; potassium persulfate 0.03%; (99%) ethanol 50.125%.

[0076] The preparation steps are as follows:

[0077] 1) Wash and purify the guanidine collagen powder with 99% ethanol to remove some insoluble impurities in the guanidine collagen powder, then add the guanidine collagen powder and the dispersion medium to a reactor with a condensation reflux device, turn on the stirrer to fully stir so that the guanidine collagen powder is completely dispersed in the dispersion medium without agglomeration, slowly add the alkalizer to the mixed solution and stir to dissolve completely, set the low speed stirring to 300r / min, set the reactor temperature to 40°C, and alkalize the guanidine collagen powder in the solution for 60min;

[0078] 2) The temperature was raised to 70° C., the stirring speed was set to 600 r / min, propane sultone was slowly added to the reactor through a constant pressure dripping device on the upper part of the reactor, and the addition was completed within 40 min. After completion, the stirring speed was adjusted to 300 r / min, and the reaction was continued for 120 min;

[0079] 3) Set the temperature of the reaction kettle to 45 °C, introduce nitrogen into the solution, and add acrylic acid, maleic acid, and vinyl trifluoroacetate. After fully stirring and dissolving completely, add sodium hydroxide (30%) for neutralization. After the reaction kettle is purged with nitrogen for 60 min, prepare 5% ammonium cerium nitrate and potassium persulfate solutions with clear water respectively, and slowly add them to the reaction solution (added within 10 min).

[0080] 4) Stop purging nitrogen, set the stirring speed to 400 r / min, and carry out the guar gum graft polymerization modification. The reaction time is 300 min. Monitor the temperature change during the reaction. After the temperature remains constant, it indicates that the reaction is complete. After the reaction ends, stop heating and stirring, cool to below 50 °C, transfer the reactants to a suction filter for suction filtration, and then carry out drying and pulverization to obtain the graft-modified guar gum powder with the required particle size, numbered SHJ-1.

[0081] (2) Preparation of multi-crosslinking agent

[0082] In terms of mass fraction, the raw materials and proportions for preparing the multi-crosslinking agent are as follows:

[0083] Hydrophilic fumed silica 2%; tetrabutyl titanate 18%; triethanolamine 10%; isopropanol 4%; ethylene glycol 18%; sorbitol 26%; borax 4%; N,N-(1,2-dihydroxyethylene) bisacrylamide 6%; the remaining part is water.

[0084] The preparation steps are as follows:

[0085] 1) Add hydrophilic fumed silica, tetrabutyl titanate, and isopropanol to a high-temperature and high-pressure enamel reaction kettle, start the stirrer to stir at a low speed of 400 r / min, and turn on the heating device. After reacting at a constant temperature of 65 °C for 1 h, add triethanolamine and continue to react for 1 h to obtain a primary chelate intermediate;

[0086] 2) Keep the set temperature unchanged, adjust the stirring speed to 600 r / min, and add ethylene glycol to the primary chelate. After reacting for 1 h, obtain a secondary chelate intermediate;

[0087] 3) Keep the temperature and stirring speed unchanged, slowly add sorbitol (28 parts) to the secondary chelate. After dissolving and mixing evenly, set the reaction temperature to 75 ± 1 °C, pressurize the reaction kettle to 0.8 MPa to increase the chelation reaction rate, and the reaction time is 1.5 h to obtain a tertiary chelate intermediate;

[0088] 4) Keep the temperature at 75 °C and the pressure at 0.8 MPa, set the stirring speed to 900 r / min, add water to the tertiary chelate intermediate, then add borax. After the borax is completely dissolved, slowly add the remaining sorbitol (5 parts), adjust the stirring speed to 600 r / min, and continue to react for 1.5 h to obtain a quaternary chelate end product, depressurize and cool;

[0089] 5) Adding N,N-(1,2-dihydroxyethylene)bisacrylamide (10% ethanol solution) to the final product of the fourth-stage chelation, stirring and mixing evenly, and discharging the material to obtain a nano-modified boron / titanium composite cross-linking agent, code-named SH-JL2.

[0090] (3) Laboratory preparation of fracturing fluid system

[0091] According to the formula ratio, the fracturing fluid is prepared in the laboratory with a vertical stirrer. When the vertical stirrer is stirred to form a vortex, the grafted modified guar gum and functional additives are added to the water. After stirring for 2 minutes, the regulator is added, and the stirring is continued for 1 minute before stopping. The high-performance guar gum base fluid is obtained and placed for use. When the cross-linking performance, heat and shear resistance, sand carrying performance, and filtration loss performance of the fracturing fluid need to be tested, a certain amount of base fluid is added in proportion to multiple cross-linking agents and a gel breaker, and stirred evenly; when the gel breaking performance of the fracturing fluid needs to be tested, a certain amount of base fluid is added in proportion to multiple cross-linking agents and a gel breaker, and stirred evenly.

[0092] Example 1 The system components are shown in Table 1:

[0093] Table 1 Example 1 Fracturing fluid components and proportions

[0094]

[0095] Example 2

[0096] The implementation of this embodiment is basically the same as that of Example 1, except that the components of the fracturing fluid system in step (3) are as shown in Table 2:

[0097] Table 2 Example 2 Fracturing fluid components and proportions

[0098]

[0099]

[0100] Example 3

[0101] The implementation of this embodiment is basically the same as that of Example 1, except that the components of the fracturing fluid system in step (3) are as shown in Table 3:

[0102] Table 3 Example 3 Fracturing fluid components and proportions

[0103]

[0104] Example 4

[0105] The implementation method of this embodiment is basically the same as that of embodiment 3, except that the remaining water in step (3) is salt water with a total mineralization of 30,000 ppm, and the functional additive is 0.3%.

[0106] Example 5

[0107] The implementation of this embodiment is basically the same as that of Example 1, except that the components of the fracturing fluid system in step (3) are shown in Table 4:

[0108] Table 4 Example 5 Fracturing Fluid Components and Ratios

[0109]

[0110] Example 6

[0111] The implementation of this embodiment is basically the same as that of embodiment 1, except that the components of the fracturing fluid system in step (3) are as shown in Table 5:

[0112] Table 5 Components and proportions of fracturing fluid in Example 6

[0113]

[0114]

[0115] In order to better illustrate the technical effects of the present invention, corresponding characterization and performance evaluation are provided for relevant embodiments below.

[0116] 1. Comparison of performance between grafted modified guar gum and common guar gum

[0117] The grafted modified guar gum SHJ-1 prepared in step (1) of Example 1 was compared with several other guar gums in terms of swelling performance, moisture content and water-insoluble matter content in clear water. The results are shown in Table 6:

[0118] Table 6 Comparison of the properties of several guar gums

[0119]

[0120] Note: JK101 is the hydroxypropyl guar gum produced by Sinopec Kunshan Company, model JK101; GHPG is the super guar gum produced by Sinopec Kunshan Company, model GHPG.

[0121] It can be seen from Table 6 that the grafted modified guar gum SHJ-1 prepared by the present invention has the highest viscosity at a dosage of 0.6%. At 0.30%, its apparent viscosity exceeds 40 mPa·s, and SHJ-1 has a fast swelling speed, with a 3-min viscosity increase rate of more than 85%, which is suitable for online mixing and fracturing construction; secondly, the water-insoluble content of SHJ-1 after modification is greatly reduced, by nearly 90%.

[0122] 2. Crosslinking state and performance test of multiple crosslinking agents and grafted modified guar gum

[0123] The grafted modified guar gum SHJ-1 prepared in step (1) of Example 1 was used to prepare a guar gum base liquid, and the multiple cross-linking agent prepared in step (2) was used to cross-link the guar gum base liquid, and the cross-linking time and the viscosity of the cross-linking liquid were measured. The strength of the cross-linked jelly (hanging property) was observed, and the cross-linking agent samples prepared from different raw material components shown in Table 7 were used to cross-link SHJ-1 respectively, and the properties of the cross-linked products were compared. The cross-linking performance test results are shown in Table 8:

[0124] Table 7 Experimental formulas with different component ratios when optimizing multiple cross-linking agents

[0125]

[0126]

[0127] Table 8 Crosslinking performance test results of multiple crosslinking agents

[0128]

[0129] From the results of Table 7 and Table 8, we can see that:

[0130] ① The multiple cross-linking agent has good delayed cross-linking performance. The cross-linking time can be optimized by adjusting the proportion of each component of the multiple cross-linking agent and the amount of the multiple cross-linking agent in the fracturing fluid;

[0131] ② According to the characteristics of deep coal-rock gas volume fracturing technology, under high-displacement construction conditions, the time for the fracturing fluid to reach the bottom of the well or even pass through the blasthole is more than 2 minutes. Therefore, the delayed cross-linking time of the gel should be controlled to be greater than 2 minutes as much as possible to meet the technical requirement that the fracturing fluid is basically not cross-linked before entering the formation in the wellbore during construction, and avoid the high friction caused by high-viscosity gel;

[0132] ③ The nano-modified matrix, chemical cross-linking component and synergistic enhancer in the multiple cross-linking agent need to be used simultaneously to maximize the viscosity of the fracturing fluid and the gel strength. Without any one of them, the other two cannot fully play their role.

[0133] ④ Compare the viscosity reduction values ​​when each component is missing with SH-JL2 (baseline value 507mPa.s) (D1# lacks nanomaterial matrix, the jelly viscosity is 72mPa.s low; D2# lacks borax, the jelly viscosity is 105mPa.s low; D3# lacks synergistic enhancer, the jelly viscosity is 126mPa.s low), and the performance is greatly improved when the three components act at the same time, realizing the design concept of 1+1+1 far greater than 3.

[0134] ⑤ Increasing the dosage of nanomaterial matrix, titanium-containing organic matter, borax, synergistic enhancer and other components will increase the apparent viscosity of the gel to a certain extent, but the corresponding delayed cross-linking time will be reduced, which is not conducive to the friction control of fracturing construction.

[0135] The cross-linked gel of the fracturing fluid provided in Example 1 of the present invention was subjected to electron microscopy scanning to observe the gel structure and compare it with the cross-linked gel structure of conventional guar gel fracturing fluid. The electron microscopy scanning structures of the two gels are as follows: Figure 1 As shown, it can be seen that the conventional guar gum cross-linked jelly is a relatively regular layered structure, with a fine connecting skeleton and loose connections between layers; the grafted modified guar gum cross-linked jelly provided by the present invention is a complex three-dimensional network structure, with tight connections between molecular chains, and the provided cross-linked jelly has higher strength, which is beneficial to the improvement of heat resistance and shear resistance, sand carrying performance, etc.

[0136] It can be seen from the macroscopic data of the cross-linking effect of the fracturing fluid and the microscopic structure of the cross-linked gel that the graft polymerization modified guar gum of the present invention is successful, and the design and optimization of the multiple cross-linking agent is reasonable and effective.

[0137] 3. Evaluation of Friction Performance of Fracturing Fluid System

[0138] Based on the formulations of Examples 1, 5, and 6, the friction performance of the formulation products was evaluated after removing the breaker. Among them, the formulation of Example 5 obtained low-viscosity slippery water, and the formulation of Example 6 obtained linear glue.

[0139] According to the method in the standard "SY / T 5107-2016 Water-based fracturing fluid performance evaluation method", a multifunctional flow loop instrument or similar products is used to measure the stable pressure difference when clean water, Example 5, and Example 6 pass through the pipeline. When measuring the friction resistance of the fracturing fluid, it is necessary to wash it with clean water before changing the liquid, and calculate the resistance reduction rate of Example 5 and Example 6. The results are as follows: Figure 7 shown.

[0140] Depend on Figure 7 It can be seen from the indoor test that within a certain range, as the flow rate increases, the drag reduction performance of the fracturing fluid becomes better, and the drag reduction rates of low-viscosity slick water and linear glue are both above 70%.

[0141] Then, according to the formula of Example 1, the fracturing fluid base liquid was first prepared and poured into the base liquid tank of the multifunctional flow loop instrument. The multifunctional flow loop instrument was turned on and the flow rate was set to 40 L / min (according to the previous experiment, the fracturing fluid resistance reduction rate was close to the maximum value at this flow rate). The multiple cross-linking agents were immediately added to the base liquid tank in proportion, and the timing was started. The pressure difference changes at different times were recorded and the resistance reduction rate was calculated. The test results are shown in FIG. Figure 6 This is used to simulate the friction change during the cross-linking process of the fracturing fluid to verify the great contribution of delayed cross-linking to the resistance reduction performance of the fracturing fluid.

[0142] from Figure 6It can be seen from the experimental data that the present invention adopts a multi-stage chelated titanium / boron composite crosslinking agent with delayed crosslinking performance. The delayed crosslinking time of Example 1 is about 4 minutes, and the drag reduction rate does not change much within 4 minutes. This reduces the friction resistance of the fracturing fluid as much as possible, controls the fracturing fluid not to crosslink in the wellbore, and will inevitably not cause high friction resistance to the construction.

[0143] 4. Evaluation of filtration performance of fracturing fluid system

[0144] The formulations of Examples 2 and 3 were selected to perform a static filtration performance test with reference to "SY / T 5107-2005 Water-Based Fracturing Fluid Performance Evaluation Method" when the breaker was removed.

[0145] Comparative formula 1 is 0.3% EM30S, and comparative formula 2 is 0.4% EM30S, wherein EM30S is a commonly used fracturing fluid thickener in Changqing Oilfield. The specific results are shown in Table 9:

[0146] Table 9 Static filtration performance test data and results of each fracturing fluid formulation

[0147]

[0148]

[0149] It can be seen from the test results in Table 9 that the fracturing fluid provided by the present invention has a small initial filtration loss and a low filtration coefficient, has excellent filtration reduction performance, and can significantly improve the liquid efficiency. In comparison, the polyacrylamide fracturing fluid has poor filtration performance (the filtration coefficient is one order of magnitude larger), which fully demonstrates the great advantages of the present fracturing fluid system in coal rock gas volume fracturing.

[0150] 5. Evaluation of temperature and shear resistance of fracturing fluid system

[0151] The formulations of Examples 1 to 4 were selected and the heat and shear resistance tests were carried out with reference to "SY / T 5107-2005 Water-based Fracturing Fluid Performance Evaluation Method" after removing the breaker.

[0152] Simulate the online mixing fracturing construction mode, prepare the fracturing fluid base fluid, add the crosslinking agent to the base fluid for 3 minutes, mix it thoroughly, and then transfer it to the high-temperature rheometer for temperature and shear resistance test. The test temperatures are 60℃, 90℃, and 140℃, and the test time is 60min, 60min, and 120min respectively; the test data statistics are shown in Table 10, and the test rheological curves are shown in Figures 2 to 5 As shown:

[0153] Table 10 Rheological test results of different formulations of fracturing fluids

[0154] formula Base fluid viscosity, mPa.s Complete cross-linking time, s Viscosity after test, mPa.s Example 1 27 143 84.3～93.8 Example 2 33 134 104.2～115.1 Example 3 48 126 92.5～102.3 Example 4 39 121 76.8～83.9

[0155] From Table 10 and Figures 2 to 5 It can be seen that the apparent viscosity of the fracturing fluid provided by the present invention increases slowly during the heating process, and secondary (or multiple) cross-linking occurs during the process. The time for complete cross-linking of fracturing fluids with different formulations is different, indicating that the fracturing fluid has good delayed cross-linking performance and the online cross-linking time is controllable and adjustable. After 170s -1 After continuous shearing, the viscosity of the fracturing fluid is finally greater than 80 mPa·s, indicating that the fracturing fluid of this embodiment has good heat resistance and shear resistance, and is suitable for reservoirs below 140°C within the formulation range. The high-performance fracturing fluid provided by the present invention can also be prepared with brine, has good heat resistance and shear resistance, and can meet the requirements of 120°C reservoirs within the formulation range.

[0156] VI. Evaluation of sand carrying performance of fracturing fluid system

[0157] The formulations of Examples 1 to 3 were selected to perform sand carrying performance tests with reference to "SY / T 5107-2005 Water-based Fracturing Fluid Performance Evaluation Method" when the breaker was removed.

[0158] Prepare the fracturing fluid base liquid according to the formula, take 200ml of the base liquid and pour it into the Wu Yin mixer, control the speed of the mixer so that the liquid can form a vortex, add multiple cross-linking agents in proportion, and stir for more than 3 minutes. When the fracturing fluid begins to slowly cross-link, the viscosity increases and the vortex slowly closes, weigh 96g of 30-50 mesh ceramsite (30% sand ratio) and slowly disperse and add it to the fracturing fluid, and adjust the stirring speed appropriately to make the ceramsite evenly dispersed in the fracturing fluid, pour it into a 250ml measuring cylinder, and then move the measuring cylinder into a 90℃ constant temperature oven and let it stand for 1h, and record the volume V of the clear liquid chromatographed from the upper layer, and calculate the proppant sedimentation rate. The experimental records and calculation results are shown in Table 11, among which the sand carrying performance of the cross-linked gel in Example 3 is shown in Figure 8 As shown:

[0159] Table 11 Test results of suspended sand performance of several groups of high performance guar gel fracturing fluid gels

[0160] Group Clear liquid V, ml Sedimentation rate, % Experimental phenomenon Example 1 5 2.5 Almost no proppant settlement Example 2 0 0 No proppant settling Example 3 0 0 No proppant settling

[0161] From the data in Table 11 and Figure 8 It can be seen from the specific performance that the cross-linked gel of the high-performance fracturing fluid provided by the present invention has excellent sand carrying performance, and the proppant has almost no sedimentation in the gel, which can greatly reduce the difficulty of adding sand during fracturing construction, and is of great significance for high-intensity sand adding in coal rock gas volume fracturing.

[0162] VII. Evaluation of gel breaking performance of fracturing fluid system

[0163] The formulations of Examples 1 to 6 were used for testing. Evaluation of the fracturing fluid debonding performance The debonding fluid surface tension and residue content of several groups of fluids were tested. The test results are shown in Table 12.

[0164] Table 12 Fracturing fluid degelling fluid performance test

[0165]

[0166] The results in Table 12 show that the fracturing fluid provided by the present invention has a short gel-breaking time and low viscosity of the gel-breaking fluid; functional additives are added to Examples 1 to 6, and the surface tension of the gel-breaking fluid is reduced, but the surface tension of Examples 1, 2, 3, and 4 is reduced to below 28 mN / m. The difference from Examples 5 and 6 is that multiple cross-linking agents are added, and as the amount of the multiple cross-linking agents increases, the surface tension of the gel-breaking fluid gradually decreases, indicating that surface-active substances are also introduced into the multiple cross-linking agents, which further reduces the surface tension of the gel-breaking fluid; at the same time, the residue content of the fracturing fluid gel-breaking fluid is as low as below 70 mg / L, which is far lower than the national standard (600 mg / L), indicating that when the guanidine collagen powder is modified and the dosage is reduced, the residue content is significantly reduced, and the damage of the fracturing fluid to the reservoir can also be significantly reduced.

[0167] 8. Test on the damage of degelling liquid to coal rock adsorption and coal rock gas desorption

[0168] Conventional guar gum fracturing fluid and the guar gum fracturing fluid provided by the present invention were selected to prepare degumming fluids respectively for adsorption damage and desorption performance test comparison.

[0169] The test method of the adsorption capacity of degelling liquid on coal rock is as follows: take two coal samples and dry them at 105℃ to constant weight, weigh them and get W 0 , respectively, and immersed in the prepared degelling solution for 48 h, and then the coal samples were taken out and dried to constant weight, and weighed to obtain W 1 , the adsorption amount is calculated based on the weight difference and the weight of the coal block.

[0170] The coal-rock gas desorption damage test method is: using the coal-rock gas adsorption-desorption test system to conduct experiments, adding a certain amount of dry coal powder into the adsorption-desorption container, saturating methane at a certain temperature and pressure, desorbing methane by reducing the pressure, and recording the dry coal powder analysis amount V 0 Then add dry coal powder and saturated methane under the same conditions, inject the test liquid, reduce the pressure and drain the liquid for desorption, and record the desorption volume V of coal powder after the test liquid damages 1 , the desorption damage rate of the test fluid to the coal rock is calculated by formula (1).

[0171]

[0172] The test formula and test results are shown in Table 13.

[0173] Table 13 Test of damage of different fracturing fluids to coal and rock

[0174]

[0175] The test results show that, compared with the HPG fracturing fluid system, the fracturing fluid system provided by the present invention has reduced the content of cationic groups due to the grafting modification of guar gum, so that the adsorption of polymer on coal rock after degelling is reduced, and the matching of functional additives further reduces the adsorption of degelling fluid, which is reduced by about 71% compared with the HPG fracturing fluid, thereby significantly reducing the damage to the permeability of the coal rock matrix; at the same time, this system also greatly reduces the desorption damage of coal rock gas, which is reduced by about 69% compared with the HPG fracturing fluid, and can significantly enhance the desorption effect of coal rock gas after fracturing and increase production.

[0176] IX. Field Application

[0177] In December 2024, Jishen** Well completed 12 sections of fracturing construction with a construction displacement of 10-16m 3 / min, the average sand addition in a single construction section is only 400m 3 After the construction was completed, a 12 mm oil nozzle was used to spray for production, with a maximum daily gas production of 105,000 cubic meters, demonstrating good gas production potential. The well fully utilized the high-performance guar gum fracturing fluid system proposed in the present invention (the system formula is the formula in Example 2: 0.25% grafted modified guar gum + 0.2% multiple cross-linking agent + 0.2% functional additive + 0.1% regulator + 0.04% breaker) to carry out online mixing (viscosity) fracturing construction, and finally completed the well's high-efficiency seam creation and high-strength sanding construction tasks with high quality. The successful application of the present invention on site also shows that the system effectively solves the sanding construction difficulties faced by coal gas volume fracturing construction. Compared with the conventional guar gum fracturing fluid system, various construction parameters have been greatly improved (the construction displacement reaches 16m 3 / min, the highest sand ratio during construction reached 35%, and the average sand addition in a single section during construction reached 420m 3 ), the typical construction curve is shown in Fig. 9 Field practice has also confirmed that the high-performance guar gum fracturing fluid provided by the present invention can fully meet the construction requirements of such coal rock gas volume fracturing.

[0178] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing, characterized in that: In terms of mass fraction, it includes the following components:

2. A high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 1, characterized in that: The grafted modified guar gum is prepared from the following components by mass fraction: The preparation method comprises the following steps: Step S1: fully dispersing guanidine collagen powder in a dispersion medium until uniform, adding an alkalizing agent, stirring and alkalizing at a speed of 200 to 300 r / min for 60 to 90 minutes at 35 to 40° C. to obtain an alkalized solution; Step S2: adjusting the temperature to 65-70° C. and the stirring speed to 500-600 r / min, slowly adding the functionalizing agent to the alkalized solution within 40-50 min, and adjusting the speed to 200-300 r / min after the addition to react at a constant temperature for 90-120 min; Step S3: adjusting the temperature to 40-45° C., adding the graft polymerization modifier under nitrogen protection, stirring until completely dissolved, adding a neutralizer according to the pH value of the solution, adjusting the solution pH to 7±0.2, passing nitrogen for 45-60 minutes, and then adding a 5% mass concentration of an initiator aqueous solution to the solution after adjusting the pH within 10 minutes; Step S4: stop nitrogen flow, adjust stirring speed to 300-400 r / min, react for 210-300 min until the temperature is constant, then stop heating and stirring, wait for the temperature to cool to below 50° C., filter, dry and pulverize to obtain.

3. A high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 2, characterized in that: The alkalizing agent is one of sodium hydroxide or sodium methoxide; The functionalizing agent is one of propane sultone, p-toluene sulfonate, diisopropyl phosphate, trimethyl phosphate, methyl sulfonate, diethyl sulfate, methyl sulfate, sodium 3-chloro-2-hydroxypropyl sulfonate, and propylene oxide; The graft polymerization modifier is a combination of a hydrophilic monomer and a hydrophobic modification monomer, wherein the hydrophilic monomer is acrylic acid and maleic acid; the hydrophobic modification monomer is one of 2-(trifluoromethyl)acrylic acid, trifluoropropylene, trifluoroacetic acid vinyl ester, trifluoroethyl acrylate, and trifluoroethyl methacrylate; The neutralizing agent is one of dilute hydrochloric acid or sodium hydroxide; The initiator is a combination of ammonium cerium nitrate and potassium persulfate, or one of benzoyl peroxide; The dispersion medium is one of methanol (99.5%), ethanol (99%) and isopropanol (99%).

4. A high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 3, characterized in that: The ratio of acrylic acid, maleic acid and hydrophobic modifier is 21:3:1 by weight. The ratio of the ammonium cerium nitrate to potassium persulfate is 1.5:

1.

5. The high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 1, characterized in that: The multiple cross-linking agent is prepared from the following components by mass fraction: The preparation method comprises the following steps: Step 1): The nanomaterial matrix, the titanium-containing organic matter and isopropanol are stirred and reacted at 65-73° C. and 300-400 r / min for 1-2 hours, and then the chelating agent No. 1 is added and the reaction is continued for 0.5-1 hour to obtain a primary chelating intermediate; Step 2): keeping the temperature constant, adjusting the stirring speed to 600-650 r / min, adding chelating agent No. 2 to the primary chelating intermediate and reacting for 1 hour to obtain a secondary chelating intermediate; Step 3): Under the same conditions, a portion of chelating agent No. 3 is added to the secondary chelating intermediate, and after dissolving and mixing, the reaction temperature is adjusted to 75±1° C. and the reaction is carried out at 0.8-1 MPa for 1-1.5 h to obtain a tertiary chelating intermediate; Step 4): Control the temperature to 70-75°C, the pressure to 0.5-0.8 MPa, set the stirring speed to 800-900 r / min, add water and borax to the tertiary chelating intermediate in sequence, add the remaining chelating agent No. 3, adjust the stirring speed to 600-650 r / min, continue the reaction for 1.5h-2h, obtain the quaternary chelating final product, reduce the pressure, and cool; Step 5): Add the synergistic enhancer into the cooled final product of the fourth-stage chelation, stir and mix, and discharge the product.

6. A high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 5, characterized in that: The nano matrix material is hydrophilic fumed silica; The titanium-containing organic substance is one of tetrabutyl titanate, tetraethyl titanate, and isopropyl titanate; The chelating agent No. 1 is one of triethanolamine, acetylacetone, ethylenediamine, ethylenediaminetetraacetic acid, and aminotriacetic acid; The chelating agent No. 2 is one of methanol, ethanol, ethylene glycol, glycerol, or a combination of any two of equal weight parts; The chelating agent No. 3 is one of xylitol, sorbitol, sodium gluconate, and citric acid; The synergistic enhancer is one of N,N-methylenebisacrylamide, N,N-(1,2-dihydroxyethylene)bisacrylamide and polyethylene glycol monomethyl ether monomethacrylate.

7. The high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 5, characterized in that: In terms of mass fractions, the ratio of the chelating agent No. 3 added to the secondary chelating intermediate in step 3) to the remaining chelating agent No. 3 added in step 4) is 28:2-5.

8. The high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 1, characterized in that: The regulator consists of the following components by mass fraction: Triethanolamine 40~45% Sodium bicarbonate 55-60% The functional additives are composed of a system synergist and a damage inhibitor in equal weight ratios, wherein the system synergist is a silicone synergist or a nonionic perfluorooctyl polyoxyethylene ether surfactant, and the damage inhibitor is a member selected from the group consisting of ethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol butyl ether, propylene glycol phenyl ether, and sodium lauryl sulfate; The gel breaker is one of ammonium persulfate and potassium persulfate.

9. The on-site preparation method of the high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: In a mixing vehicle, the grafted modified guar gum is sucked into water in a suction cycle using a jet technology and mixed; Step 2: After the grafted modified guar gum is absorbed, add the regulator according to the formula ratio and continue to circulate and stir for 10 minutes before stopping. The viscosity is tested to be up to standard and the fracturing base fluid is obtained for standby use; Step 3: Add functional additives and multiple cross-linking agents to the fracturing base fluid in the sand mixing truck according to the formula ratio, and then add the degumming agent in the formula ratio, and mix well in the sand mixing truck.

10. The application method of the high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing according to claim 9, characterized in that: The application scenario of the high-performance guar gum fracturing fluid system for deep coal-rock gas volume fracturing is the volume fracturing construction of deep coal-rock gas.

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