Oil-phase-free resistance reducing agent for fracturing fluid and preparation method of oil-phase-free resistance reducing agent

Abstract

The invention relates to an oil-phase-free resistance reducing agent for fracturing fluid and a preparation method of the oil-phase-free resistance reducing agent. The resistance reducing agent comprises the following components in parts by weight: 38-58 parts of a suspending agent, 1-2 parts of a dispersing agent, 1-2 parts of a thixotropic agent, 1-2 parts of an emulsifying agent, 4-8 parts of a cross-linking agent and 35-50 parts of a thickening agent. The preparation method of the resistance reducing agent comprises the following steps: (1) sequentially and slowly adding the dispersing agent, the thixotropic agent and the emulsifying agent into the suspending agent under the stirring condition at the rotating speed of 300-600rad / min, and stirring for 15-30 minutes to obtain a mixed solution I; (2) sequentially and slowly adding a thickening agent and a cross-linking agent into the mixed solution I under the stirring condition of the rotating speed of 200-500rad / min, and stirring for 5-15 minutes to obtain a target product. The prepared resistance reducing agent uses a non-oil suspending agent, so that the generation of oil pollutants is reduced from the source, the pollution to a reservoir and the environment is reduced, and the subsequent treatment cost of oily sewage and oily sludge is reduced; the cross-linking agent is introduced into the resistance reducing agent, resistance reducing and cross-linking are integrated, the cross-linking agent does not need to be independently added in the fracturing process, and the fracturing construction technology can be simplified.

Description

Technical Field

[0001] The invention relates to the field of fracturing fluid drag reducing agents, and more specifically to an oil-free phase drag reducing agent for fracturing fluid and a preparation method thereof. Background Art

[0002] Unconventional oil and gas reservoirs such as shale oil and gas, tight sandstone, and coalbed methane have huge resources, accounting for about 80% of the total oil and gas resources, and have great development potential. Hydraulic fracturing is the key to realizing the development of unconventional reservoirs; and fracturing fluid, as the "blood" of hydraulic fracturing, is a key factor affecting the fracturing effect; drag reducers, as the core additives of fracturing fluids, directly determine the performance and application effect of fracturing fluids. Since 2000, synthetic polymer drag reducers have become the mainstream products of fracturing fluids. According to the appearance, polymer drag reducers are divided into powder drag reducers and emulsion drag reducers. Emulsion drag reducers are further divided into W / O inverse emulsion drag reducers and suspended drag reducers. Suspended drag reducers have the characteristics of rapid dissolution, fast viscosity increase rate, and good salt resistance. With supporting auxiliary agents such as cross-linking agents, drainage aids, and clay stabilizers, they can achieve full online mixing of slippery water, linear glue, and glue liquid (suspended drag reducers with good salt resistance can be mixed online with 100% return water). Since 2018, suspended drag reducers have become the most widely used drag reducer product for unconventional reservoirs such as shale gas.

[0003] At present, the dispersing medium or suspension agent used in the suspended drag reducer is mainly chlorinated paraffin, diesel, liquid paraffin and other oil suspension agents. These oil suspension agents will form emulsions in the presence of emulsifiers, causing damage to the reservoir. Oil-containing return water will have a great impact on the environment, such as polluting the soil and interfering with plant production, polluting water quality and causing biological death. The existing suspended drag reducer only has the function of reducing drag, and no cross-linking agent is introduced. When preparing the gel fracturing fluid, an additional cross-linking agent needs to be added, which makes the construction complicated, the performance of the gel cannot be guaranteed, and the packaging, transportation and labor costs are wasted. At the same time, the existing suspended drag reducers generally have problems such as easy stratification after long-term storage and cannot be stored and transported for a long time. Therefore, it is necessary to further improve the performance of the suspended drag reducer. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an oil-free phase drag reducer for fracturing fluid and a preparation method thereof, which adopts a fully water-soluble material and can realize the integration of drag reduction and cross-linking.

[0005] The technical solution adopted by the present invention to solve the technical problem is: construct an oil-free phase drag reducing agent for fracturing fluid, comprising the following components, calculated by weight: 38-58 parts by weight of suspending agent, 1-2 parts by weight of dispersing agent, 1-2 parts by weight of thixotropic agent, 1-2 parts by weight of emulsifier, 4-8 parts by weight of cross-linking agent and 35-50 parts by weight of thickener.

[0006] According to the above scheme, the dispersant is one or more of methanol, ethanol, propylene glycol methyl ether, and N,N-dimethylformamide.

[0007] According to the above scheme, the thixotropic agent is a mixture of 10-15 parts by weight of sodium carboxymethyl cellulose, 30-50 parts by weight of nano-cellulose and 30-50 parts by weight of sodium alginate.

[0008] According to the above scheme, the emulsifier is two or more of AES, OP-10, T-70, Tween-60, and TX-10.

[0009] According to the above scheme, the cross-linking agent is a mixture of 3-5 parts by weight of organic zirconium and 1-3 parts by weight of urotropine.

[0010] According to the above scheme, the organic zirconium is one or more of zirconium citrate, zirconium lactate, zirconium acetate, zirconium acetate and zirconium citrate.

[0011] According to the above scheme, the thickener is anionic modified polyacrylamide with a molecular weight of 20 million, 25 million or 30 million and a particle size of 100-120 meshes.

[0012] The present invention also provides a method for preparing an oil-free phase drag reducing agent for fracturing fluid, comprising the following steps:

[0013] (1) slowly adding 1-2 parts by weight of a dispersant, 1-2 parts by weight of a thixotropic agent and 1-2 parts by weight of an emulsifier to 38-58 parts by weight of a suspending agent in sequence under stirring at a speed of 300-600 rad / min, and stirring for 15-30 minutes to obtain a mixed solution I;

[0014] (2) Under the stirring condition of a rotation speed of 200-500 rad / min, 4-8 parts by weight of a cross-linking agent and 35-50 parts by weight of a thickener are slowly added to the mixed solution I in sequence, and stirred for 5-15 minutes to obtain the target product, an oil-free environmentally friendly integrated drag reducing agent.

[0015] The mechanism of the present invention is as follows:

[0016] The stability of the drag reducing agent is the key to the preparation of integrated drag reducing agent. According to the Stokes sedimentation formula, the sedimentation velocity of the particle is related to the particle radius and the density and viscosity of the medium. The smaller the particle radius, the greater the medium density and viscosity, and the slower the particle sedimentation velocity.

[0017] In order to improve the stability of the integrated drag reducing agent, the present application adopts the following measures:

[0018] First, a mixture of polyethylene glycol 400 and propylene glycol is used as a suspending agent, which not only improves the density and viscosity of the system but also has better fluidity.

[0019] The second is to use a small-particle thickener, which is determined to be an anionic modified polyacrylamide of 100-120 mesh. The inventors found in practice that if the thickener particle size is less than 120 mesh, its molecular chain will be destroyed, resulting in reduced temperature and salt resistance.

[0020] Third, a thixotropic agent is added to form a metastable structure in the system to slow down the sedimentation rate of the thickener particles. The present invention uses a mixture of sodium carboxymethyl cellulose, nano-cellulose and sodium alginate as a thixotropic agent, and the three act synergistically to improve the stability of the system.

[0021] At the same time, in order to further improve the dispersibility of the thixotropic agent in the alcohol suspension, a dispersant with a large polarity difference is added. In order to achieve the integration of drag reduction and cross-linking, and to improve the solubility and temperature resistance of the drag reduction agent, an organic zirconium cross-linking agent, hexamethylenetetramine and a composite emulsifier are added respectively. The raw materials used in the present invention are all environmentally friendly water-soluble materials, which improves the environmental performance of the product.

[0022] The oil-free phase drag reducing agent for fracturing fluid and the preparation method thereof of the present invention have the following beneficial effects:

[0023] 1. The drag reducing agent of the present invention has good rapid solubility. Since no oil phase material is used and a composite emulsifier is used, the drag reducing agent can be quickly dispersed, dissolved and thickened in water within 15 seconds, and the prepared fracturing fluid is clear and transparent without "fish eyes".

[0024] 2. The drag reducing agent of the present invention has low damage to the reservoir. Since water-soluble materials are used, the prepared fracturing fluid is clear, transparent and free of residue. At the same time, the suspending agent polyethylene glycol has certain anti-swelling properties, which can inhibit the expansion of clay and particle migration. It has the characteristics of low core damage rate, which is helpful for protecting the production layer during the fracturing construction process and promoting the purpose of fracturing production increase construction.

[0025] 3. The drag reducing agent of the present invention can realize the integration of drag reducing and cross-linking by introducing the cross-linking component. When preparing the gel fracturing fluid, there is no need to add additional cross-linking agent, which simplifies the construction process and saves packaging, transportation and labor costs.

[0026] 4. The drag reducing agent of the present invention does not contain oil, thereby reducing the generation of oil pollutants from the source, reducing the pollution to the reservoir and the environment and the cost of pollutant treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0028] Figure 1 This is a comparison chart of the cleanliness of the drag reducing agent prepared in Example 1 and the reference sample after dissolution;

[0029] Figure 2 This is a comparison diagram of the residue after gel breaking between the drag reducing agent prepared in Example 1 and the reference sample;

[0030] Figure 3 This is a graph showing the heat and shear resistance of the drag reducing agent prepared in Example 1.

[0031] Figure 4 This is a test chart of the drag reduction rate of the drag reducing agent prepared in Example 1 and the reference sample. DETAILED DESCRIPTION

[0032] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0033] Embodiment 1:

[0034] An oil-free phase drag reducing agent for fracturing fluid and a preparation method thereof, comprising the following steps:

[0035] (1) slowly adding 2 parts by weight of a dispersant, 2 parts by weight of a thixotropic agent and 2 parts by weight of an emulsifier to 43 parts by weight of a suspending agent in sequence under stirring at a speed of 600 rad / min, and stirring for 20 minutes to obtain a mixed solution I;

[0036] (2) Under the stirring condition of a rotation speed of 500 rad / min, 6 parts by weight of a cross-linking agent and 45 parts by weight of a thickener were slowly added to the mixed solution I in sequence, and stirred for 15 minutes to obtain the target product, an oil-free environmentally friendly integrated drag reducing agent.

[0037] In the preparation scheme, the suspending agent is 97 parts by weight of polyethylene glycol 400 and 3 parts by weight of propylene glycol; the dispersing agent is N,N-dimethylformamide; the thixotropic agent is a mixture of 15 parts by weight of sodium carboxymethyl cellulose, 40 parts by weight of nanocellulose and 45 parts by weight of sodium alginate; the emulsifier is 1 part by weight of TX-10 and 1 part by weight of AES; the cross-linking agent is 4 parts by weight of zirconium lactate and 2 parts by weight of hexamethylenetetramine; and the thickener is an anionic modified polyacrylamide with a molecular weight of 30 million and a particle size of 120 meshes.

[0038] Figure 1 This is a comparison chart of the cleanliness of the integrated drag reducing agent prepared in this example and the reference sample after dissolution. Figure 1(a) is a slippery water fracturing fluid formed by adding 0.4g of the drag reducing agent of this embodiment to 400mL water and stirring and dissolving for 15s; (b) is a slippery water fracturing fluid formed by adding 0.4g of the reference oil-based drag reducing agent to 400mL water and stirring and dissolving for 40s. The composition and proportion of the reference oil-based drag reducing agent are: 53 parts by weight of suspending agent, 1 part by weight of thixotropic agent, 1 part by weight of emulsifier and 45 parts by weight of thickener; the suspending agent is No. 5 white oil, the thixotropic agent is organic modified bentonite, the emulsifier is 40 parts by weight of Tween60 and 60 parts by weight of Span80, and the thickener is an anionic modified polyacrylamide with a molecular weight of 30 million and a particle size of 120 mesh. It can be seen that the slippery water fracturing fluid 15s prepared with the drag reducing agent of this embodiment is uniformly dispersed and clear and transparent, while the slippery water fracturing fluid 40s prepared with the reference oil-based drag reducing agent is uniformly dispersed. Due to the presence of white oil, a turbid water-in-oil liquid will be formed under the action of the emulsifier, resulting in turbidity of the prepared slippery water solution.

[0039] Figure 2 This is a comparison of the residues after the drag reducing agent prepared in this example and the reference sample were broken. Figure 2 (a) is a slippery water gel-breaking liquid prepared by the drag reducing agent of this embodiment, and the specific ratio is: by mass percentage, 0.1% drag reducing agent + 0.005% ammonium persulfate is placed at room temperature after breaking at 90°C for 2h; (b) is a slippery water gel-breaking liquid prepared by the reference drag reducing agent, and the specific ratio is: by mass percentage, 0.1% drag reducing agent + 0.005% ammonium persulfate is placed at room temperature after breaking at 90°C for 2h. It can be seen that the slippery water gel-breaking liquid prepared by the drag reducing agent of this embodiment is clear and transparent, and the residue content is 7mg / mL by measurement; the slippery water gel-breaking liquid prepared by the reference drag reducing agent is turbid, and the residue content is 63mg / mL by measurement. This is because the drag reducing agent of this embodiment uses a fully water-soluble material, and there is no oil phase residue in the prepared fracturing fluid after breaking; while the reference sample drag reducing agent contains water-insoluble white oil, and the prepared fracturing fluid contains oil phase residue after breaking. In addition, the thixotropic agent used in the drag reducing agent of this embodiment is a mixture of sodium carboxymethyl cellulose, nano-cellulose and sodium alginate, which has good water solubility and the prepared fracturing fluid has a small residue content after gel breaking; while the thixotropic agent used in the reference sample drag reducing agent is organic modified bentonite, and the prepared fracturing fluid has a high residue content after gel breaking.

[0040] Figure 3 This is the heat and shear resistance performance diagram of the drag reducing agent of this embodiment. 0.8g of the drag reducing agent of this embodiment is added to 100mL of water and stirred to dissolve, and heated in a 50℃ water bath for 3min to obtain a crosslinking liquid. 43mL of the crosslinking liquid is taken and put into the drum of a Haake rheometer for rheological experiment. -1 , sheared for 1h at 120°C, the viscosity of the fracturing fluid is >50mPa·s. This indicates that the adhesive prepared with the drag reducing agent of this embodiment has good heat and shear resistance.

[0041] Figure 4 It is a comparison chart of the drag reduction rate of the drag reducing agent of this embodiment and the reference sample. The average drag reduction rate of the drag reducing agent of this embodiment is 76.1%, and the drag reduction rate change rate is 2.7%; the average drag reduction rate of the reference drag reducing agent is 74.3%, and the drag reduction rate change rate is 3.1%.

[0042] Embodiment 2:

[0043] An oil-free phase drag reducing agent for fracturing fluid and a preparation method thereof, comprising the following steps:

[0044] (1) slowly adding 1 part by weight of a dispersant, 1 part by weight of a thixotropic agent and 2 parts by weight of an emulsifier to 51 parts by weight of a suspending agent in sequence under stirring at a rotation speed of 500 rad / min, and stirring for 30 minutes to obtain a mixed solution I;

[0045] (2) Under the stirring condition of a rotation speed of 300 rad / min, 5 parts by weight of a cross-linking agent and 40 parts by weight of a thickener were slowly added to the mixed solution I in sequence, and stirred for 15 minutes to obtain the target product, an oil-free environmentally friendly integrated drag reducing agent.

[0046] In the preparation scheme, the suspending agent is 96 parts by weight of polyethylene glycol 400 and 4 parts by weight of propylene glycol; the dispersing agent is 1 part by weight of N,N-dimethylformamide and 1 part by weight of propylene glycol methyl ether; the thixotropic agent is a mixture of 15 parts by weight of sodium carboxymethyl cellulose, 40 parts by weight of nano-cellulose and 45 parts by weight of sodium alginate; the emulsifier is 1 part by weight of TX-10, 1 part by weight of Tween-60 and 1 part by weight of T-70; the cross-linking agent is 4 parts by weight of zirconium acetate and 1 part by weight of hexamethylenetetramine; and the thickener is a modified polyacrylamide with a molecular weight of 25 million and a particle size of 100 meshes.

[0047] Embodiment 3:

[0048] An oil-free phase drag reducing agent for fracturing fluid and a preparation method thereof, comprising the following steps:

[0049] (1) slowly adding 1 part by weight of a dispersant, 1 part by weight of a thixotropic agent and 2 parts by weight of an emulsifier to 39 parts by weight of a suspending agent in sequence under stirring at a rotation speed of 400 rad / min, and stirring for 30 minutes to obtain a mixed solution I;

[0050] (2) Under the stirring condition of a rotation speed of 500 rad / min, 7 parts by weight of a cross-linking agent and 50 parts by weight of a thickener were slowly added to the mixed solution I in sequence, and stirred for 15 minutes to obtain the target product, an oil-free environmentally friendly integrated drag reducing agent.

[0051] In the preparation scheme, the suspending agent is 98 parts by weight of polyethylene glycol 400 and 2 parts by weight of propylene glycol; the dispersing agent is 1 part by weight of N,N-dimethylformamide, 1 part by weight of propylene glycol methyl ether and 1 part by weight of ethanol; the thixotropic agent is a mixture of 15 parts by weight of sodium carboxymethyl cellulose, 40 parts by weight of nano-cellulose and 45 parts by weight of sodium alginate; the emulsifier is 1 part by weight of OP-10 and 1 part by weight of Tween-60; the cross-linking agent is 5 parts by weight of zirconium citrate and 2 parts by weight of hexamethylenetetramine; and the thickener is a modified polyacrylamide with a molecular weight of 30 million and a particle size of 120 meshes.

[0052] Test example

[0053] The oil-free environmentally friendly integrated drag reducing agent product prepared by the present invention meets the requirements of the industry standard (NB / T14003.2-2016 Shale Gas Fracturing Fluid Part 2: Drag Reducing Agent Performance Indicators and Test Methods), and the test results of each indicator in each embodiment are shown in Table 1.

[0054] Table 1 Test results of various indicators of various embodiments and reference samples

[0055]

[0056] As shown in Table 1, the performance indicators of the oil-free environmentally friendly integrated drag reducing agent provided by the present invention meet the requirements of the drag reducing agent industry standards, and its residue content and continuous mixing and dissolution time indicators exceed the requirements of the industry standards.

[0057] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. An oil-free phase drag reducing agent for fracturing fluid, characterized in that: The invention comprises the following components, calculated by weight: 38-58 parts by weight of a suspending agent, 1-2 parts by weight of a dispersing agent, 1-2 parts by weight of a thixotropic agent, 1-2 parts by weight of an emulsifier, 4-8 parts by weight of a crosslinking agent and 35-50 parts by weight of a thickener.

2. The oil-free phase drag reducing agent for fracturing fluid according to claim 1, characterized in that: The dispersant is one or more of methanol, ethanol, propylene glycol methyl ether, and N,N-dimethylformamide.

3. The oil-free phase drag reducing agent for fracturing fluid according to claim 1, characterized in that: The thixotropic agent is a mixture of 10-15 parts by weight of sodium carboxymethyl cellulose, 30-50 parts by weight of nano-cellulose and 30-50 parts by weight of sodium alginate.

4. The oil-free drag reducing agent for fracturing fluid according to claim 1, characterized in that: The emulsifier is two or more of AES, OP-10, T-70, Tween-60 and TX-10.

5. The oil-free phase drag reducing agent for fracturing fluid according to claim 1, characterized in that: The cross-linking agent is a mixture of 3-5 parts by weight of organic zirconium and 1-3 parts by weight of hexamethylenetetramine.

6. The oil-free drag reducing agent for fracturing fluid according to claim 6, characterized in that: The organic zirconium is one or more of zirconium citrate, zirconium lactate, zirconium acetate, zirconium acetate and zirconium citrate.

7. The oil-free drag reducing agent for fracturing fluid according to claim 1, characterized in that: The thickener is anionic modified polyacrylamide with a molecular weight of 20 million, 25 million or 30 million and a particle size of 100-120 meshes.

8. A method for preparing the oil-free drag reducing agent for fracturing fluid according to claim 1, characterized in that: The following steps are involved: (1) slowly adding 1-2 parts by weight of a dispersant, 1-2 parts by weight of a thixotropic agent and 1-2 parts by weight of an emulsifier to 38-58 parts by weight of a suspending agent in sequence under stirring at a speed of 300-600 rad / min, and stirring for 15-30 minutes to obtain a mixed solution I; (2) Under the stirring condition of a rotation speed of 200-500 rad / min, 4-8 parts by weight of a cross-linking agent and 35-50 parts by weight of a thickener are slowly added to the mixed solution I in sequence, and stirred for 5-15 minutes to obtain the target product, an oil-free environmentally friendly integrated drag reducing agent.

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