A shale gas composite slickwater fracturing fluid and preparation method thereof

Abstract

The invention discloses a shale gas composite slick water fracturing fluid and a preparation method thereof, which comprises, by weight percentage: 0.01-0.2% drag reducing agent, 0.2-1% clay stabilizer, 0.1-0.8% drainage aid, 0.01-0.15% gel breaker, 25-40% self-suspending proppant, and the rest is water; the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1-3:3-5. The slick water fracturing fluid has high dissolution efficiency, strong temperature resistance, and strong sand carrying capacity, and can effectively solve the problems existing in the existing fracturing fluid.

Description

Technical Field

[0001] The invention belongs to the technical field of fracturing fluids, and in particular relates to a shale gas composite slick water fracturing fluid and a preparation method thereof. Background Art

[0002] Shale gas refers to unconventional natural gas that is found in reservoir rock systems dominated by organic-rich shales. It is a continuously generated biochemical gas, thermogenic gas, or a mixture of the two. It can exist in a free state in natural cracks and pores, in an adsorbed state on the surface of kerogen and clay particles, and a very small amount is stored in a dissolved state in kerogen and asphaltene. The proportion of free gas is generally between 20% and 85%.

[0003] For tight shale reservoirs, increasing production through fracturing is the most effective means, and hydraulic fracturing is an important means to increase the oil and gas production of the target reservoir. In the process of using slick water fracturing fluid for shale gas development, in order to improve the performance of slick water fracturing fluid, a certain amount of additives such as drag reducers and clay stabilizers are usually added to it. 98.0% to 99.5% of the slick water fracturing fluid is mixed sand water. The drag reducer is the core additive of the system. The drag reducer increases the viscosity of the slick water system, thereby increasing the sand carrying capacity of the system and the conductivity of the hydraulic fractures, thereby achieving the purpose of increasing production. The drag reducers commonly used in the current slick water fracturing fluid include components such as polyacrylamide and guar gum, but polyacrylamide is easily adsorbed on the surface of clay minerals in the reservoir, forming The guar gum can form filter cakes, change the soil structure, and affect the survival of microorganisms in the soil. At the same time, the residual acrylamide monomer is also toxic to a certain extent, which will also affect the survival of microorganisms. Guar gum, due to its large molecular weight, will leave a large amount of residue on the fracture wall after use, resulting in reduced formation seepage capacity and production capacity, which directly affects the fracturing effect. Reducing the amount of guar gum can reduce the content of solids entering the formation, reduce the damage of fracturing fluid and residues to fractures and reservoirs, but reducing the concentration of guar gum will lead to a decrease in the temperature resistance and shear resistance of the fracturing fluid, affect the viscosity of the system, and then cause the proppant to settle, reducing the support effect on the fracture.

[0004] Moreover, the sand-carrying capacity of existing fracturing fluid systems is generally weak. After the sand-carrying fluid enters the fracture, its viscosity decreases, and the proppant settles rapidly under the action of gravity and cannot be transported to the far end of the fracture, resulting in a small effective supporting volume in the horizontal and vertical directions, which affects the shale gas extraction effect. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a shale gas composite slickwater fracturing fluid and a preparation method thereof. The slickwater fracturing fluid has high dissolution efficiency, strong temperature resistance, and strong sand carrying capacity, and can effectively solve the problems existing in the existing fracturing fluid.

[0006] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0007] A shale gas composite slickwater fracturing fluid comprises, by weight percentage, 0.01-0.2% of a drag reducing agent, 0.2-1% of a clay stabilizer, 0.1-0.8% of a drainage aid, 0.01-0.15% of a gel breaker, 25-40% of a self-suspending proppant, and the remainder is water; the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1-3:3-5.

[0008] Furthermore, the mass ratio of guar gum to sesbania gum is 1-2:4-5.

[0009] Furthermore, the clay stabilizer includes at least one of potassium chloride and ammonium chloride; the breaker includes at least one of ammonium persulfate, potassium persulfate, hydrogen peroxide and magnesium hypochlorite.

[0010] Furthermore, the drainage aid includes at least one of ethanol, methanol, decanol, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate.

[0011] Furthermore, the self-suspending proppant is prepared by the following method: guar gum powder and fiber powder are mixed to prepare mixed powder, then the coupling agent solution is used to wet the proppant, and finally the mixed powder is sprayed on the proppant surface in a stirring state and dried to obtain the self-suspending proppant.

[0012] Furthermore, the proppant includes at least one of quartz sand and ceramsite, and the particle size of the proppant is 20-60 meshes.

[0013] Furthermore, in the mixed powder, the mass ratio of guar gum powder to fiber powder is 1-3:1-3.

[0014] Furthermore, the fiber is at least one of polyester fiber, polyurethane fiber and polyvinyl alcohol fiber.

[0015] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water into a container, sequentially adding a drag reducing agent, a clay stabilizer, a drainage aid, a gel breaker and a self-suspending proppant into the container under stirring conditions, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0016] The beneficial effects produced by the present invention are:

[0017] The drag reducing agent used in the present application can be naturally degraded into sugar compounds under reservoir conditions, without long-term diversion damage to the reservoir, and can effectively improve the production capacity of unconventional oil and gas; the larger the molecular weight of the drag reducing agent, the greater the viscosity, the higher the drag reducing performance, but the difficulty of degradation increases. Guar gum has a large molecular weight, and sesbania gum is relatively small. In the present application, a small amount of guar gum and a large amount of sesbania gum are used as drag reducing agents at the same time, which can not only ensure that the fracturing fluid base fluid has a certain viscosity and a good degradation effect, but also shorten the degradation time of the fracturing fluid, and reduce the residue in the cracks, thereby reducing damage to the reservoir;

[0018] In the present application, a coupling agent is first used to wet the proppant, and then the mixed powder is sprayed on the surface of the proppant, and the coupling agent is used to adhere the fibers and guar gum in the mixed powder to the surface of the proppant, so as to obtain a proppant with a self-suspending effect. When the proppant is placed in the base fluid of the slick water fracturing fluid, the fibers and guar gum on the surface of the proppant absorb water and swell, forming a layer of "swelling gum layer" on the surface of the proppant, so that the proppant is suspended in the base fluid of the fracturing fluid, thereby improving the suspension effect of the proppant; and the long chain structure of the fiber can form a three-dimensional network structure with a supporting effect in the base fluid of the fracturing fluid, which can also further improve the suspension effect of the proppant in the base fluid of the fracturing fluid, so that the proppant is not easy to settle during the pumping process, thereby improving the supporting effect on the cracks.

[0019] Guar gum and fiber are adhered to the proppant surface, so that the "swelling rubber layer" formed on the proppant surface is not easily separated from the proppant, which can improve the suspension effect of the proppant; the use of proppant with a "swelling rubber layer" can reduce the requirements for the shear resistance of the fracturing fluid base fluid. Even if the fracturing fluid base fluid is degraded by shear during pumping, the suspension effect of the proppant can still be guaranteed due to the presence of a "swelling rubber layer" on the proppant surface.

[0020] A small amount of drag reducing agent is used in the present application to prepare the fracturing fluid base fluid, which can reduce the damage of the drag reducing agent to the reservoir and reduce the residue in the reservoir; although the amount of drag reducing agent in the fracturing fluid base fluid of the present application is small, it can still improve the suspension effect on the proppant by using it in conjunction with the developed self-suspending proppant, and there is no problem of suspension agent sedimentation. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments.

[0022] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0023] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0024] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0025] Example 1

[0026] A shale gas composite slickwater fracturing fluid comprises, by weight percentage: 0.01% drag reducing agent, 0.2% potassium chloride, 0.1% methanol, 0.01% hydrogen peroxide, 25% self-suspending proppant, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1:3;

[0027] The self-suspending proppant is prepared by the following method: guar gum powder and polyester fiber powder are mixed in a mass ratio of 1:2 to prepare a mixed powder, and then a silane coupling agent KH560 solution is added to quartz sand, and the mixture is stirred to allow the silane coupling agent KH560 solution to wet the quartz sand, the particle size of the quartz sand is 20 mesh, and finally the mixed powder is sprayed on the surface of the quartz sand in a stirring state, the amount of the silane coupling agent KH560 solution accounts for 1% of the weight of the quartz sand, and the weight of the mixed powder accounts for 3% of the weight of the quartz sand, and the mixture is dried to obtain the self-suspending proppant.

[0028] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a degumming agent and a self-suspending proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0029] Example 2

[0030] A shale gas composite slick water fracturing fluid, comprising, by weight percentage: 0.05% drag reducing agent, 0.5% potassium chloride, 0.6% ethanol, 0.05% potassium persulfate, 30% self-suspending proppant, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 2:1;

[0031] The self-suspending proppant is prepared by the following method: guar gum powder and polyvinyl alcohol fiber powder are mixed in a mass ratio of 2:1 to prepare a mixed powder, and then a silane coupling agent KH560 solution is added to quartz sand, and the mixture is stirred to allow the silane coupling agent KH560 solution to wet the quartz sand, the particle size of the quartz sand is 60 mesh, and finally the mixed powder is sprayed on the surface of the quartz sand in a stirring state, the amount of the silane coupling agent KH560 solution accounts for 1% of the weight of the quartz sand, and the weight of the mixed powder accounts for 3% of the weight of the quartz sand, and the mixture is dried to obtain the self-suspending proppant.

[0032] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a degumming agent and a self-suspending proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0033] Example 3

[0034] A shale gas composite slick water fracturing fluid comprises, by weight percentage: 0.1% drag reducing agent, 0.8% potassium chloride, 0.8% sodium dodecyl sulfate, 0.1% ammonium persulfate, 35% self-suspending proppant, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1:4;

[0035] The self-suspending proppant is prepared by the following method: guar gum powder and polyester fiber powder are mixed in a mass ratio of 2:5 to prepare a mixed powder, and then a silane coupling agent KH560 solution is added to quartz sand, and the mixture is stirred to allow the silane coupling agent KH560 solution to wet the quartz sand, the particle size of the quartz sand is 40 meshes, and finally the mixed powder is sprayed on the surface of the quartz sand in a stirring state, the amount of the silane coupling agent KH560 solution accounts for 1% of the weight of the quartz sand, and the weight of the mixed powder accounts for 3% of the weight of the quartz sand, and the mixture is dried to obtain the self-suspending proppant.

[0036] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a degumming agent and a self-suspending proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0037] Example 4

[0038] A shale gas composite slick water fracturing fluid comprises, by weight percentage: 0.15% drag reducing agent, 0.6% ammonium chloride, 0.7% decanol, 0.15% magnesium hypochlorite, 30% self-suspending proppant, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1:4;

[0039] The self-suspending proppant is prepared by the following method: guar gum powder and polyurethane fiber powder are mixed in a mass ratio of 2:4 to prepare a mixed powder, and then a silane coupling agent KH560 solution is added to quartz sand, and the mixture is stirred to allow the silane coupling agent KH560 solution to wet the quartz sand, the particle size of the quartz sand is 40 meshes, and finally the mixed powder is sprayed on the surface of the quartz sand in a stirring state, the amount of the silane coupling agent KH560 solution accounts for 1% of the weight of the quartz sand, and the weight of the mixed powder accounts for 3% of the weight of the quartz sand, and the mixture is dried to obtain the self-suspending proppant.

[0040] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a degumming agent and a self-suspending proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0041] Example 5

[0042] A shale gas composite slickwater fracturing fluid comprises, by weight percentage: 0.2% drag reducing agent, 1% potassium chloride, 0.5% methanol, 0.1% hydrogen peroxide, 30% self-suspending proppant, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1:4;

[0043] The self-suspending proppant is prepared by the following method: guar gum powder and polyester fiber powder are mixed in a mass ratio of 2:4 to prepare a mixed powder, and then a silane coupling agent KH560 solution is added to quartz sand, and the mixture is stirred to allow the silane coupling agent KH560 solution to wet the quartz sand, the particle size of the quartz sand is 40 meshes, and finally the mixed powder is sprayed on the surface of the quartz sand in a stirring state, the amount of the silane coupling agent KH560 solution accounts for 1% of the weight of the quartz sand, and the weight of the mixed powder accounts for 3% of the weight of the quartz sand, and the mixture is dried to obtain the self-suspending proppant.

[0044] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a degumming agent and a self-suspending proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0045] Comparative Example 1

[0046] A shale gas composite slickwater fracturing fluid comprises, by weight percentage: 0.1% drag reducing agent, 0.8% potassium chloride, 0.8% sodium dodecyl sulfate, 0.1% ammonium persulfate, 35% quartz sand, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1:4; the particle size of the quartz sand is 40 mesh;

[0047] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a gel breaker and a proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0048] Comparative Example 2

[0049] A shale gas composite slickwater fracturing fluid comprises, by weight percentage: 3% guar gum, 0.8% potassium chloride, 0.8% sodium dodecyl sulfate, 0.1% ammonium persulfate, 35% quartz sand, and the remainder is water; the particle size of the quartz sand is 40 meshes;

[0050] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a gel breaker and a proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0051] Comparative Example 3

[0052] A shale gas composite slick water fracturing fluid comprises, by weight percentage: 0.1% drag reducing agent, 0.8% potassium chloride, 0.8% sodium dodecyl sulfate, 0.1% ammonium persulfate, 35% self-suspending proppant, and the rest is water; wherein the drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of guar gum to sesbania gum is 1:4;

[0053] The self-suspending proppant is prepared by the following method: guar gum powder and polyester fiber powder are mixed in a mass ratio of 2:5, water is added to dissolve the mixture to prepare a mixed solution, quartz sand with a particle size of 40 mesh is added to the mixed solution, and the mixture is dried to obtain the self-suspending proppant.

[0054] The preparation method of the shale gas composite slick water fracturing fluid comprises the following steps: adding water to a container, adding a drag reducing agent to the container in sequence under stirring conditions, and after the drag reducing agent is fully dissolved, continuing to add a clay stabilizer, a drainage agent, a degumming agent and a self-suspending proppant thereto, stirring and mixing to obtain the shale gas composite slick water fracturing fluid.

[0055] Test example

[0056] 1. Detection of friction performance

[0057] The slick water fracturing fluids in Examples 1-5 and Comparative Examples 1-3 were used as samples, and the friction properties of the slick water fracturing fluids were tested using a fracturing fluid friction tester. The test was performed at a flow rate of 10 m / s and a pipe diameter of 10 mm. The specific results are shown in Table 1.

[0058] Table 1: Friction test results

[0059]

[0060]

[0061] It can be seen from the results in the above table that the slick water fracturing fluid in the present application and the slick water fracturing fluid in Comparative Examples 1-3 both have a relatively high drag reduction rate.

[0062] 2. Shear performance testing

[0063] The slick water fracturing fluids in Examples 1-5 and Comparative Examples 1-3 were used as samples, and a shear test was performed on each group of fracturing fluids using a rheometer. The test temperature was 180° C. and the shear rate was 170 s -1 , the specific test results are shown in Table 2-3.

[0064] Table 2: Viscosity test results

[0065]

[0066] It can be seen from the data in the above table that after the shear test, the viscosity of the slick water fracturing fluid in the present application and the comparative example decreased, proving that the shear operation caused a certain degree of degradation of the drag reducing agent.

[0067] Table 3: Proppant suspension test results

[0068]

[0069] It can be seen from the data in the above table that after the shear test, the viscosity of the slick water fracturing fluid in the present application decreases, and the suspension rate of the proppant in the slick water fracturing fluid also decreases, but the suspension rate is still high and will not cause the problem of suspension agent sedimentation.

[0070] Comparing Comparative Example 1 with Example 3, the modification operation of adhering guar gum powder and fiber powder on the proppant surface is cancelled. It can be seen from the experimental results that the drag reduction rate of the fracturing fluid in Comparative Example 1 is slightly lower than that of the fracturing fluid in Example 3, and the modification operation of the proppant has little effect on the drag reduction rate; however, the suspension rate of the proppant in the fracturing fluid after shearing in Comparative Example 1 is significantly lower than that of the proppant in Example 3, which proves that the proppant after the modification treatment in the present application can be more stably dispersed in the fracturing fluid, thereby improving the suspension rate of the proppant.

[0071] Comparing Comparative Example 2 with Example 3, the modification operation of adhering guar gum powder and fiber powder on the proppant surface is cancelled. At the same time, the drag reducing agent in the fracturing fluid is adjusted to a single guar gum component. It can be seen from the experimental results that the drag reduction rate of the fracturing fluid in Comparative Example 1 is slightly lower than that of the fracturing fluid in Example 3, and the modification operation of the proppant has little effect on the drag reduction rate; and it can be seen from the suspension rate data that the use of guar gum as a drag reducing agent has little effect on the suspension rate of the proppant; however, it is found in practice that the solubility of guar gum is poor, and the use of guar gum as a drag reducing agent has the problem of long dissolution time.

[0072] Comparing Comparative Example 3 with Example 3, the use of silane coupling agent was eliminated in the process of proppant modification. The experimental results show that the suspension rate of the proppant also decreases after the shearing operation. It is speculated that the possible reason is that there is no adhesion effect of the silane coupling agent, resulting in a weak connection between the drag reducing agent and the proppant. After shearing, the proppant and the drag reducing agent are separated, resulting in a certain degree of sedimentation.

Claims

1. A shale gas composite slickwater fracturing fluid, characterized in that: The composition includes, by weight percentage: 0.01-0.2% drag reducing agent, 0.2-1% clay stabilizer, 0.1-0.8% drainage agent, 0.01-0.15% gel breaker, 25-40% self-suspending proppant, and the rest is water; The drag reducing agent comprises guar gum and sesbania gum, and the mass ratio of the guar gum to the sesbania gum is 1-3:3-5; The self-suspending proppant is prepared by the following method: guar gum powder and fiber powder are mixed to prepare mixed powder, then the coupling agent solution is used to wet the proppant, and finally the mixed powder is sprayed on the surface of the proppant in a stirring state and dried to obtain the self-suspending proppant.

2. The shale gas composite slick water fracturing fluid according to claim 1, characterized in that: The mass ratio of the guar gum to the sesbania gum is 1-2:4-5.

3. The shale gas composite slick water fracturing fluid according to claim 1, characterized in that: The clay stabilizer includes at least one of potassium chloride and ammonium chloride; the breaker includes at least one of ammonium persulfate, potassium persulfate, hydrogen peroxide and magnesium hypochlorite.

4. The shale gas composite slickwater fracturing fluid according to claim 1, characterized in that: The drainage aid includes at least one of ethanol, methanol, decanol, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate.

5. The shale gas composite slickwater fracturing fluid according to claim 1, characterized in that: The proppant comprises at least one of quartz sand and ceramsite, and the particle size of the proppant is 20-60 meshes.

6. The shale gas composite slick water fracturing fluid according to claim 1, characterized in that: In the mixed powder, the mass ratio of guar gum powder to fiber powder is 1-3:1-3.

7. The shale gas composite slickwater fracturing fluid according to claim 1, characterized in that: The fiber includes at least one of polyester fiber, polyurethane fiber and polyvinyl alcohol fiber.

8. The method for preparing the shale gas composite slickwater fracturing fluid according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: adding water into a container, sequentially adding a drag reducing agent, a clay stabilizer, a drainage aid and a gel breaker into the container under stirring conditions to obtain a fracturing fluid base fluid, then adding a self-suspending proppant into the fracturing fluid base fluid, stirring and mixing to obtain the fracturing fluid.

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