CN104559997A - Slippery water for shale gas fracturing and preparation method thereof - Google Patents

Abstract

The invention provides slick water for shale gas fracturing. The slick water consists of 0.03-0.2 wt% of drag reducing agent, 0.3-1.0 wt% of clay stabilizer, 0.3-1.0 wt% of drainage aid, and 0.5 wt% of potassium chloride. ～2.0wt%, fungicide 0.05～1.0wt% and the rest are composed of water. Specifically, the drag reducing agent of the present invention is an acrylamide copolymer, which is obtained by copolymerizing acrylamide as the main structural unit, adding ionic structural units and functional monomers. The viscosity-average relative molecular mass of the drag reducing agent is 4 million to 6 million, and the intrinsic viscosity is 1300 to 1600 mL·g ^-1 . The slick water system of the present invention has a fast dissolution rate and uniform dispersion, and can be continuously mixed or mixed with an online mixing device in field application to meet the technical requirements of high displacement and large fluid volume fracturing in shale gas reservoirs.

Description

A kind of slick water for shale gas fracturing and preparation method thereof

technical field

The invention belongs to the field of petroleum engineering, and in particular relates to the formula composition, preparation method and main performance evaluation of slick water fracturing fluid used in large-scale fracturing reconstruction of shale gas.

Background technique

Domestic conventional oil and gas resources are limited, and unconventional oil and gas resources such as shale gas will surely become their alternative energy sources. With the increasing development of shale gas in China, the slick water fracturing technology will develop rapidly, and the research and development, optimization and optimization of additives in the slick water fracturing fluid system, as well as the evaluation of system performance, will be advanced rapidly and deeply.

The effective development of shale gas in the United States has changed the world's energy pattern. The exploration and development of shale gas resources is the focus of my country's "Twelfth Five-Year Plan" and one of the research hotspots. Many domestic research institutions are gradually carrying out research on shale gas.

The concept of "slippery water fracturing fluid" was proposed by American researchers. It was originally a new type of fracturing fluid jointly developed by Halliburton, Schlumberger and Messina for the Barnett shale area in eastern Texas. The definition of slickwater fracturing is "a fracturing method that uses a large amount of water and a small amount of additives as fracturing fluid to form fractures with a certain geometry and conductivity in order to obtain commercial value." Using slick water fracturing can reduce the cost of fracturing by 65% compared with conventional large-scale hydraulic fracturing.

The uniqueness of shale gas reservoirs, the type of gas reservoirs and the sensitivity of rocks are very different from those of ordinary sandstone gas. Its special geological conditions determine that conventional development technologies cannot be directly applied to the production of shale gas reservoirs. The key to the successful development of shale gas reservoirs lies in the advancement of large-scale fracturing technology for horizontal wells, and slick water is a commonly used fracturing fluid for fracturing shale gas reservoirs.

Drag reducer is the most important additive in slippery water. Its performance has a direct impact on the success of shale gas fracturing. It increases the flow rate at the same pump pressure by reducing frictional resistance, thereby increasing the pumping pressure of the pump truck and injection rate. Drag reducers are generally cationic, anionic and nonionic. The resistance reduction rate of polyacrylamide type drag reducer in the Barnett shale area of the United States is generally 50-70%.

my country's shale gas fracturing is still in the exploratory stage. The slick water fracturing fluid used in the early stage is mainly the technology provided by foreign oil service companies. There are few reports on domestic slick water systems with excellent performance, especially suitable for shale gas pressure. The research and development and evaluation of additives such as cracking drag reducers, clay stabilizers, and surfactants have just started. Additives such as clay stabilizers and surfactants used in conventional fracturing fluids are not completely suitable for shale fracturing, and targeted research is needed for screening and evaluation.

The slick water provided by foreign companies has the following problems: First, there are few studies on the adaptability to domestic formations. No matter what additives are added, it will be used without damage to the formations; The fracturing equipment is advanced, and there is little concern about the friction loss of the pipe string. However, due to the deep burial of shale gas in my country, the friction loss of the pipe string is very large, and the friction-reducing performance of slick water has a great impact on fracturing; Therefore, it is necessary to carry out adaptability research on the slick water fracturing fluid system for key areas of domestic shale gas reservoirs.

At present, the slick water system used in the domestic field has problems such as low resistance reduction rate, poor sand-carrying performance, and large amount of polymer additives adsorbed in the formation, causing great damage. It is necessary to develop a high resistance reduction rate that is compatible with the fracturing target formation. In the slick water system, under the premise of the same operation scale, the amount of drag reducing agent is reduced, which reduces the cost of slick water fracturing fluid.

During the fracturing construction of shale gas wells in mountainous or hilly areas, due to the inconvenience of transportation, powder additives have more advantages than liquid additives. The drag reducing agent used in the present invention is a dry powder additive.

Contents of the invention

The invention provides a low-cost and low-damage slick water formulation system adapted to the geological characteristics of domestic shale gas reservoirs. The additives are conveniently transported, dissolve quickly, have high friction reduction rate, low damage to shale rocks, and are convenient to use on site. Provide technical support for high-displacement and large-fluid-volume construction of gas fracturing.

Therefore, the present invention provides a kind of slick water for shale gas fracturing. Potassium 0.5-2.0wt%, bactericide 0.05-1.0wt%, and the balance are composed of water.

Preferably, the drag reducing agent in slippery water is 0.03wt%, the clay stabilizer is 0.3wt%, the drainage aid is 0.3wt%, potassium chloride is 1.0wt%, and the fungicide is 0.05wt%.

In a specific embodiment of the present invention, the drag reducing agent is an acrylamide copolymer, which is obtained by copolymerizing acrylamide as the main structural unit, adding ionic structural units and functional monomers. Wherein, the ionic structural unit is selected from 2-acrylamido dimethyl propane sulfonic acid, 2-acrylamido dodecyl sulfonic acid, 2-acrylamido tetradecyl sulfonic acid and 2-propene One or more of amidohexadecyl sulfonic acid; the functional monomer is selected from the group consisting of azobisisobutylamidine dihydrochloride, diethylene glycol monovinyl ether, acrylic acid and methyl One or more of glycidyl acrylate. The viscosity-average relative molecular mass of the drag reducing agent is 4 million to 6 million, and the intrinsic viscosity is 1300 to 1600 mL·g ^-1 .

The drag reducing agent used in the present invention is preferably disclosed in the applicant's previous application: an acrylamide-based drag reducing agent for slick water fracturing and its preparation method and application (201210265047.1), an acrylamide-based drag reducing agent for slick water fracturing Acrylamide-based drag-reducing agent and its preparation method and application (201210265039.7), an acrylamide-based drag-reducing agent for slick water fracturing, its preparation method and application (201210265032.5), an acrylamide-based terpolymer and its Preparation method and application (201210265136.6), an acrylamide-based copolymer and its preparation method and application (201210421047.6), an acrylamide-based drag reducer for slick water fracturing and its preparation method and application (201210422133.9), a Acrylamide drag reducing agent for slick water fracturing and its preparation method and application (201210421155.3), an acrylamide drag reducing agent for slick water fracturing and its preparation method and application (201210420912.5), a slick water fracturing Using acrylamide-based drag-reducing agent and its preparation method and application (201210421124.8), an acrylamide-based terpolymer and its preparation method and application (201210409930.3), in the above ten patent applications, as long as its content is consistent with this application If there is no conflict in the contents of these ten applications, these ten applications are all incorporated in the present invention by reference.

In a specific embodiment of the present invention, the clay stabilizer is selected from poly N-methylol acrylamide, polyisopropanol dimethyl ammonium chloride, acrylamide and ethyl acrylate trimethyl chloride One or more of ammonium copolymers, epichlorohydrin and dimethylamine copolymers.

In a specific embodiment of the present invention, the drainage aid is one or more selected from nonionic fluorocarbon surfactants, anionic fluorocarbon surfactants, methanol, ethanol, isopropanol kind.

Described potassium chloride is industrial product KCl.

In a specific embodiment of the present invention, the bactericide is one or more selected from formaldehyde, glyoxal, and quaternary ammonium salts; preferably, the quaternary ammonium salts are dodecyltrimethyl ammonium chloride.

The water can be clear water, lake water, river water, or effectively treated fracturing fluid flowback fluid.

In a specific embodiment of the present invention, the drag reducing agent is a dry powder type drag reducing agent, and the drag reducing agent is obtained through liquid phase polymerization.

The slick water fracturing fluid of the present invention has the characteristics of high resistance reduction rate, high surface activity, less damage to shale gas reservoir cores, low cost, and convenient on-site preparation, which can not only meet the needs of large-volume fracturing construction but also be suitable for shale The characteristics of gas reservoirs play an important role in promoting the development of shale gas in my country.

The present invention also provides a preparation method of the above-mentioned slick water, which comprises firstly adding potassium chloride into the water and stirring to dissolve it, then adding a drag reducing agent therein and stirring to dissolve it, and then adding a clay stabilizer, a drainage aid and The fungicide is stirred and dissolved to obtain the slippery water.

Effects of the invention: 1) The dry powder type drag reducer has a fast dissolution rate, and the dissolution time is less than 5 minutes. The molecular weight of the resist agent is moderate, the viscosity-average relative molecular mass is 4-6 million, the adsorption on shale rock is small, the damage is low, and the flowback fluid after fracturing can be recycled; 3) The slick water system of the present invention is low in cost and convenient in transportation , it has transportation advantages for the construction of shale gas wells with inconvenient transportation such as mountainous or hilly areas, and can also meet the technical requirements of low-cost slick water for shale gas fracturing.

Detailed ways

1. Composition of slick water: Drag reducer 0.03%, clay stabilizer 0.3%, drainage aid 0.3%, potassium chloride 1.0%, fungicide 0.05%. The drag reducing agent is a copolymer of acrylamide, 2-acrylamide dimethylpropanesulfonic acid, glycidyl methacrylate and acrylic acid, which belongs to anionic polyacrylamide drag reducing agent, and its viscosity-average relative molecular The mass is 5.6 million, and the intrinsic viscosity is 1490mL·g ^-1 ; the clay stabilizer is a quaternary ammonium cationic copolymer synthesized by polymerization of epichlorohydrin, dimethylamine and ethylenediamine; the drainage aid It is an aqueous solution of anionic fluorocarbon surfactant and methanol; the bactericide is formaldehyde.

2. Preparation of slippery water:

According to the above composition, weigh the required clear water, accurately weigh and record the types and amounts of each additive.

Add potassium chloride first: add KCl solid powder under stirring conditions, stir for 2 minutes to completely dissolve; then add drag reducing agent: add dry powder type drag reducing agent under stirring conditions, fully stir for 5 minutes to completely dissolve; then add other Additives: Add liquid clay stabilizer, drainage aid and bactericide according to the formula design, stir for 3 minutes to fully dissolve, stop stirring, and the preparation is complete.

3. Slippery water fracturing fluid performance test:

1) Stability experiment:

Place the prepared slippery water at room temperature (23°C), and observe the changes of the liquid at 2 hours, 4 hours, 6 hours, 8 hours, 12 hours, 24 hours and 48 hours. The experimental results show that the prepared slippery water The water has always been a uniform liquid, without stratification, suspension, flocculation, or precipitation, which shows that the liquid has good stability, and it will not affect the use after 2 days of storage.

2) Thermal stability experiment:

Place the prepared slick water in a water bath at 75°C, and observe the changes of the slick water at 2 hours, 4 hours, 6 hours and 8 hours respectively. The experimental results show that the prepared slick water has always been a uniform liquid without precipitation There is no floc, no delamination phenomenon, indicating that the thermal stability of the liquid is good.

3) Resistance reduction performance:

Use a tube type friction measuring instrument to test the pressure drop of the slippery aqueous solution in the present invention at room temperature, in a straight pipe with a diameter of 15mm, and at different flow rates, and compare it with the pressure drop of clear water at the same flow rate to determine the "shear rate" and the relationship curve between the resistance reduction rate" and the experimental results are listed in Table 1.

Table 1

The experimental results in Table 1 show that: under the condition of an average flow velocity of 8.29 (m/s), the drag reduction rate of slick water is 65.81%. It shows that the slick water prepared with dry powder drag reducing agent in the present invention has a high drag reducing rate and a good friction reducing effect, which can meet the requirements of large-volume fracturing fluid construction at a high displacement of 8-20m ³ /min.

4) Surface active properties:

The surface tension of the slick water system is 23.61mN/m and the interfacial tension is 1.18mN/m measured by the K100 interfacial tensiometer; the contact angle of the slick water system is 69° measured by the dynamic contact angle meter. It shows that the slick water in the present invention has high surface activity, which is helpful for rapid flowback after fracturing construction, and reduces the damage of fracturing fluid to ultra-low permeability tight shale reservoirs.

5) Anti-expansion performance:

Using a shale dilatometer to evaluate the anti-swelling performance of slick water on 2 shale cores, the results show that the anti-swelling rate is greater than 80%, indicating that the slick water in the present invention has a good anti-swelling effect, which can prevent clay in the fracturing process Mineral expansion and particle migration damage to shale gas reservoirs.

6) Dynamic damage performance:

Use the fracturing fluid damage evaluation instrument to measure the damage experiment of the slick water system to the permeability of the shale core matrix. Matrix permeability impairment experiments are performed. The experimental results show that the average damage rate of slick water to shale cores is 9.46%. It shows that the slick water in the present invention has little damage to the core of the shale gas reservoir.

4. Field application of slick water fracturing fluid:

The slick water additive of the present invention is cost-effective, the dry powder type drag reducing agent is convenient to transport, the dissolution speed is fast, and the dispersion is uniform. Continuous mixing or on-line mixing equipment can be used for liquid mixing in field application, which can meet the large displacement of shale gas reservoirs. Technical requirements for hydraulic fracturing construction.

Claims (10)

1. A slick water for shale gas fracturing, the slick water is composed of 0.03～0.2wt% drag reducing agent, 0.3～1.0wt% clay stabilizer, 0.3～1.0wt% drainage aid, 0.5～0.5wt% potassium chloride 2.0wt%, 0.05-1.0wt% fungicide and the rest are composed of water. 2. The slippery water according to claim 1, characterized in that the drag reducing agent is 0.03wt%, the clay stabilizer is 0.3wt%, the drainage aid is 0.3wt%, potassium chloride is 1.0wt%, and the fungicide 0.05wt%. 3. The slippery water according to claim 1 or 2, characterized in that, the drag reducing agent is an acrylamide copolymer, which uses acrylamide as the main structural unit, adding ionic structural units and functional monomers for copolymerization And get. 4. The slick water according to claim 3, characterized in that, the viscosity-average relative molecular mass of the drag reducing agent is 4 million to 6 million, and the intrinsic viscosity is 1300 to 1600 mL·g ^-1 . 5. slippery water according to claim 3, is characterized in that, described ionic structure unit is selected from 2-acrylamido dimethyl propane sulfonic acid, 2-acrylamido dodecyl sulfonic acid, 2 - one or more of acrylamido tetradecyl sulfonic acid and 2-acrylamido hexadecyl sulfonic acid, the functional monomer is selected from azobisisobutylamidine dihydrochloride , one or more of diethylene glycol monovinyl ether, acrylic acid and glycidyl methacrylate. 6. according to claim 1 and 2 described slippery waters, it is characterized in that, described clay stabilizer is selected from poly-N-methylol acrylamide, polyisopropanol dimethyl ammonium chloride, acrylamide and One or more of the copolymer of ethyl acrylate trimethylammonium chloride, the copolymer of epichlorohydrin and dimethylamine. 7. The slick water according to claim 1 or 2, characterized in that, the drainage aid is selected from nonionic fluorocarbon surfactants, anionic fluorocarbon surfactants, methanol, ethanol, iso One or more of propanol. 8. The slick water according to claim 1 or 2, characterized in that, the bactericide is one or more selected from formaldehyde, glyoxal, and quaternary ammonium salts; preferably the quaternary ammonium salts It is dodecyltrimethylammonium chloride. 9. The slick water according to any one of claims 1-8, characterized in that, the drag reducing agent is a dry powder type drag reducing agent, and the drag reducing agent is obtained by liquid phase polymerization. 10. A preparation method for slick water as described in any one of claims 1 to 9, comprising adding potassium chloride in water and stirring to dissolve it, then adding drag reducing agent therein and stirring to dissolve it, and then The slick water is obtained by adding clay stabilizer, drainage aid and bactericide and stirring to dissolve them.