Self-suspending proppant containing nanofiller and preparation method of self-suspending proppant

Abstract

The invention relates to the technical field of fracturing proppants, and discloses a self-suspending proppant containing nanofiller and a preparation method thereof, the proppant comprises a proppant particle base material, a bonding layer and a composite coating layer, and the weight ratio of the proppant particle base material to the bonding layer to the composite coating layer is 100: (0.1-1): (2-13); the preparation method comprises the following steps: S1, uniformly mixing a water-soluble monomer, deionized water and an organic solvent to prepare an aqueous solution; s2, uniformly mixing the porous nano filler with the aqueous solution to prepare a mixed solution; s3, preheating a proppant particle base material, pouring the proppant particle base material into a sand mixer, cooling, and adding a binder to obtain a proppant coated with a bonding layer; and S4, cooling to 60-100 DEG C, and sequentially adding the mixed solution and an initiator to obtain the self-suspending proppant containing the nanofiller. The proppant can automatically suspend in clear water, and the porous nanofiller contained in the proppant can reduce the density of the proppant, effectively slow down the dissolution time of a surface wrapping layer and prolong the suspension time.

Description

Technical Field

[0001] This invention relates to the field of fracturing proppant technology, specifically to a self-suspending proppant containing nanofillers and its preparation method. Background Technology

[0002] Fracturing proppant is a solid filler used to fill fractures in fractured rock formations during oil and gas extraction. During fracturing, the proppant is usually carried into the formation by the fracturing fluid and used to support the fractures after fracturing, thereby creating artificial fractures with a certain conductivity in the formation, providing seepage channels for oil and gas extraction, maintaining high conductivity of oil and gas, improving resource extraction efficiency, and extending the service life of oil and gas wells.

[0003] Currently, fracturing fluids used both domestically and internationally are typically mixed with appropriate additives to form a proppant mixture with a certain viscosity. To enhance its proppant-carrying capacity, various high-molecular-weight thickeners (such as guar gum and polymer systems) are generally added to increase the viscosity of the mixture and ensure that the proppant remains in a stable suspension. However, when the proppant enters the fracture and the fluid velocity decreases, if the mixture still maintains a high viscosity, it can easily become trapped at the end of the reservoir fracture network. This residue can damage the reservoir, such as clogging formation porosity, affecting oil production efficiency, or polluting the subsurface environment. On the other hand, fracturing fluids require pre-preparation, a complex process that can lead to uneven dissolution of thickeners and reduced cross-linking effects.

[0004] The search revealed the following patent documents related to this application, the specific disclosures of which are as follows: 1. A method for preparing a low-friction self-suspended proppant for fracturing (CN105754580B) involves preparing a surface treatment liquid through a heating and heat preservation process and preparing a thickener fine powder through a drying and crushing process. Finally, the surface treatment liquid and the thickener fine powder are mixed with proppant particles. However, this method is complex and requires strict control of the reaction temperature when preparing the surface treatment liquid and the thickener fine powder.

[0005] 2. A self-suspending proppant and its preparation method (CN106675548A) involves sequentially adding reinforcing resin, curing agent, secondary resin, crosslinking agent, thickening polymer material, polymer curing agent, dispersant, etc. during the mixing of proppant aggregate. The process is complex, and the thickening polymer material is easily soluble in water, which makes it impossible to form a stable swollen resin layer on the surface of the proppant particles, resulting in poor suspension effect. The given suspension time is only 1 hour.

[0006] 3. A self-suspending proppant and its preparation method (CN 114437707B) involves mixing engineering plastic powder with thermosetting resin and azoaminobenzene solution, and then stacking multiple layers on the surface of proppant particles to form a low-density, high-strength coating layer. Its porous structure is mainly composed of pores formed by the stacking of plastic powder, and the size cannot be precisely controlled.

[0007] Therefore, based on existing research on self-suspension proppants, there is an urgent need for a proppant with long suspension time, high compressive strength, applicable to water fracturing, simple process, convenient operation, and suitable for large-scale industrial production. Summary of the Invention

[0008] This invention proposes a self-suspending proppant containing nanofillers and its preparation method. The proppant can automatically suspend in clear water without the need to add polymer compounds as thickeners for carrying sand. Moreover, the porous nanofillers contained in the proppant effectively slow down the dissolution time of the surface coating while reducing the density of the proppant, thereby prolonging the suspension time.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A self-suspending proppant containing nanofillers includes a proppant particle substrate, an adhesive layer, and a composite coating layer, wherein the composite coating layer is fixed to the proppant particle substrate by the adhesive layer; the proppant particle substrate, adhesive layer, and composite coating layer are in a weight ratio of 100:0.1-1:2-13. The substrate material of the proppant particles is natural quartz sand with a silica content of more than 90%. The adhesive layer is at least one of epoxy resin, phenolic resin, acrylic resin, and unsaturated polyester resin adhesive; The composite coating layer is composed of a water-soluble polymer and uniformly dispersed nanofillers, with the nanofillers accounting for 3%-15% of the total weight of the composite coating layer and the water-soluble polymer accounting for 85%-97% of the total weight of the composite coating layer.

[0010] Preferably, the nanofiller is one or a mixture of two-dimensional porous nanomaterials, three-dimensional porous nanomaterials, or other similar materials.

[0011] Preferably, the two-dimensional porous nanomaterial is one or a mixture of porous nanosheet-like graphitic carbon nitride and graphene, with two-dimensional mesopores of 2-50 nm uniformly distributed on the sheet-like structure; the three-dimensional porous nanomaterial is one or a mixture of hierarchical porous activated carbon, biomass-derived hierarchical porous carbon, and carbon aerogel, containing macropores of 50-100 nm and mesopores of 2-50 nm distributed on the walls and gaps of the macropores.

[0012] Preferably, the water-soluble polymer is polymerized from water-soluble monomers, organic solvents, and initiators.

[0013] Preferably, the water-soluble monomer is one or a mixture of acrylamide, starch-grafted sodium acrylate, and sodium alginate.

[0014] Preferably, the organic solvent is one of N,N'-methylenebisacrylamide, ethylene glycol diglycidyl ether and its polymers, and glyoxal.

[0015] Preferably, the initiator is one or a mixture of ammonium persulfate, potassium persulfate, hydrogen peroxide, sodium metabisulfite, and sodium bisulfite.

[0016] Preferably, in the composite coating layer, the content of water-soluble monomer is 0.5-8%, the content of organic solvent is 0.002-0.2%, and the content of initiator is 0.002-0.5% relative to the weight of the proppant particle substrate.

[0017] A method for preparing a self-suspending proppant includes the following steps: S1. Mix the water-soluble monomer, deionized water, and organic solvent evenly to prepare an aqueous solution with a mass fraction of 30-50%. S2. Mix the porous nanofiller with the above aqueous solution to prepare a mixed solution containing the nanofiller; S3. Preheat the proppant particle substrate to the preheating temperature and pour it into the sand mixer. When it cools down to 120-160℃, add the binder to obtain the proppant that encapsulates the adhesive layer. S4. When the proppant encapsulating the adhesive layer cools down to 60-100℃, a mixed solution containing porous nanofillers and an initiator are added sequentially to obtain a self-suspending proppant containing nanofillers.

[0018] Preferably, the preheating temperature is 180-220℃.

[0019] This invention provides a self-suspending proppant containing nanofillers and its preparation method, which has the following beneficial effects: 1) In this invention, water-soluble polymers and porous nanomaterials are co-coated on the surface of proppant particles. The water-soluble polymers have high water absorption and water absorption swelling characteristics, while the porous nanomaterials have ultra-low density characteristics. Through the synergistic effect of the two, the average density of the proppant is effectively reduced, which is lower than the density of the proppant coated with water-soluble polymer alone, thus having better self-suspension properties. 2) The self-suspended proppant prepared in this invention has a high specific surface area and a large number of active sites in its porous nanofiller. On the one hand, it enhances the interfacial interaction and binding force between the polymer and the nanofiller. On the other hand, it prevents the agglomeration of the nanofiller in the polymer, so that it is uniformly dispersed in the composite coating layer, thereby improving the overall compressive strength of the proppant. At the same time, it delays the hydrolysis process of the polymer, resulting in a longer suspension time and better conductivity. Experimental data show that the self-suspended proppant of this invention has a breakage rate of <0.3% at 52MPa and a suspension retention time of more than 50h. 3) The self-suspending proppant provided by this invention does not require the addition of a large amount of thickener to the water during use, and the viscosity of the sand mixing liquid is <1.3 mpa·s, thereby increasing the transport distance and oil and gas production while avoiding damage to the formation and clogging of the channels and throats in the fractures; the water-soluble polymer can achieve complete debonding, is environmentally friendly, has less pollution, and at the same time, the process is simple, the cost is low, and it is easy to scale up production. Detailed Implementation

[0020] The embodiments described below are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] A self-suspending proppant containing nanofillers includes a proppant particle substrate, an adhesive layer, and a composite coating layer, wherein the composite coating layer is fixed to the proppant particle substrate by the adhesive layer; the proppant particle substrate, adhesive layer, and composite coating layer are in a weight ratio of 100:0.1-1:2-13. The substrate material of the proppant particles is natural quartz sand with a silica content of more than 90%. The adhesive layer is at least one of epoxy resin, phenolic resin, acrylic resin, and unsaturated polyester resin adhesive; The composite coating layer is composed of a water-soluble polymer and uniformly dispersed nanofillers, with the nanofillers accounting for 3%-15% of the total weight of the composite coating layer and the water-soluble polymer accounting for 85%-97% of the total weight of the composite coating layer. The nanofiller is one or a mixture of two-dimensional porous nanomaterials, three-dimensional porous nanomaterials, or other similar materials. The two-dimensional porous nanomaterial is one or a mixture of porous nanosheet graphitic carbon nitride and graphene, with two-dimensional mesopores of 2-50 nm uniformly distributed on the sheet structure; the three-dimensional porous nanomaterial is one or a mixture of hierarchical porous activated carbon, biomass-derived hierarchical porous carbon, and carbon aerogel, containing macropores of 50-100 nm and mesopores of 2-50 nm distributed on the walls and gaps of the macropores.

[0022] The water-soluble polymer is polymerized from water-soluble monomers, organic solvents, and initiators; the water-soluble monomers are one or a mixture of acrylamide, starch-grafted sodium acrylate, and sodium alginate. The organic solvent is one of N,N'-methylenebisacrylamide, ethylene glycol diglycidyl ether and its polymers, and glyoxal. The initiator is one or a mixture of ammonium persulfate, potassium persulfate, hydrogen peroxide, sodium metabisulfite, and sodium bisulfite; Preferably, in the composite coating layer, the content of water-soluble monomer is 0.5-8%, the content of organic solvent is 0.002-0.2%, and the content of initiator is 0.002-0.5% relative to the weight of the proppant particle substrate.

[0023] A method for preparing a self-suspending proppant containing nanofillers includes the following steps: S1. Mix the water-soluble monomer, deionized water, and organic solvent evenly to prepare an aqueous solution with a mass fraction of 30-50%. S2. Mix the porous nanofiller with the above aqueous solution to prepare a mixed solution containing the nanofiller; S3. Preheat the proppant particle substrate to the preheating temperature and pour it into the sand mixer. When it cools down to 120-160℃, add the binder to obtain the proppant that encapsulates the adhesive layer. S4. When the proppant encapsulating the adhesive layer cools down to 60-100℃, a mixed solution containing porous nanofillers and an initiator are added sequentially to obtain a self-suspending proppant containing nanofillers.

[0024] Preferably, the preheating temperature is 180-220℃.

[0025] Example 1 1) Acrylamide and starch-grafted sodium acrylate are mixed at a mass ratio of 2:1 to obtain a mixed powder with a particle size of 2-10 μm; N,N'-methylenebisacrylamide is dissolved in deionized water to obtain a 1% transparent solution; 30 parts of the mixed powder and 2 parts of the transparent solution are added to 60 parts of deionized water and stirred until completely dissolved to obtain a 33% aqueous solution. 2) Add 6 parts of graded porous activated carbon to 100 parts of the above aqueous solution and mix evenly to obtain a mixed solution containing nanofillers; 3) Add 5 parts of potassium persulfate to 95 parts of aqueous solution and mix well to obtain an initiator solution with a mass fraction of 5% for later use; 4) Heat 100 parts of quartz sand to 200℃ and then pour it into a sand mixer. When the temperature of the quartz sand drops to 160℃, add 1 part of phenolic resin and stir quickly until uniform. Then add 0.15 parts of hexamethylenetetramine and 0.1 parts of ionic surfactant to obtain the support agent for the bonding layer. 5) When the temperature of the proppant covering the adhesive layer drops to 90°C, add 12 parts of the mixed solution containing nanofillers and continue to stir until homogeneous. Then add 1 part of 5% initiator solution to ensure that all components are completely dispersed, and the final self-suspending proppant containing nanofillers is obtained.

[0026] Example 2 1) Acrylamide and starch-grafted sodium acrylate are mixed at a mass ratio of 5:1 to obtain a mixed powder with a particle size of 2-10 μm; glyoxal is dissolved in deionized water to obtain a crosslinking agent solution with a mass fraction of 1%; 40 parts of the mixed powder and 2 parts of the crosslinking agent solution are added to 60 parts of deionized water and stirred until completely dissolved to obtain an aqueous solution with a mass fraction of 40%. 2) Add 8 parts of porous nanosheet graphitic carbon nitride to 100 parts of the above aqueous solution and mix evenly to obtain a mixed solution containing nanofillers; 3) Add 3 parts potassium persulfate and 2 parts sodium bisulfite to 95 parts aqueous solution and mix well to obtain an initiator solution with a mass fraction of 5% for later use; 4) Heat 100 parts of quartz sand to 200℃ and then pour it into a sand mixer. When the temperature of the quartz sand drops to 150℃, add 1 part of epoxy resin and stir quickly until uniform. Then add 0.1 parts of polyamide and 0.1 parts of ionic surfactant to obtain the support agent for the bonding layer. 5) When the temperature of the proppant covering the adhesive layer drops to 100℃, add 10 parts of the mixed solution containing nanofillers and continue to stir evenly. Then add 1 part of 5% initiator solution to ensure that all components are completely dispersed, and the final self-suspending proppant containing nanofillers is obtained.

[0027] Example 3 1) Acrylamide and sodium alginate are mixed in a mass ratio of 3:1 to obtain a mixed powder with a particle size of 2-10 μm; N,N'-methylenebisacrylamide is dissolved in deionized water to obtain a 1% transparent solution; 30 parts of the mixed powder and 2 parts of the transparent solution are added to 60 parts of deionized water and stirred until completely dissolved to obtain a 33% aqueous solution. 2) Add 2 parts graphene and 2 parts graded porous activated carbon to 100 parts of the above aqueous solution and mix evenly to obtain a mixed solution containing nanofillers; 3) Add 3 parts ammonium persulfate and 2 parts sodium bisulfite to 95 parts aqueous solution and mix well to obtain an initiator solution with a mass fraction of 5% for later use; 4) Heat 100 parts of quartz sand to 200℃ and then pour it into a sand mixer. When the temperature of the quartz sand drops to 160℃, add phenolic resin and stir quickly until uniform. Then add 0.15 parts of hexamethylenetetramine and 0.1 parts of ionic surfactant to obtain a support agent for the bonding layer. 5) When the temperature of the proppant covering the adhesive layer drops to 100℃, add 10 parts of the mixed solution containing nanofillers and continue to stir evenly. Then add 1 part of 5% initiator solution to ensure that all components are completely dispersed, and the final self-suspending proppant containing nanofillers is obtained.

[0028] Example 4 1) Dissolve N,N'-methylenebisacrylamide in deionized water to obtain a 1% (w / w) transparent solution; add 30 parts acrylamide and 2 parts transparent solution to 60 parts deionized water and stir until completely dissolved to obtain a 33% (w / w) aqueous solution. 2) Add 2 parts of graded porous activated carbon and 2 parts of biomass-derived graded porous carbon to 100 parts of the above aqueous solution and mix evenly to obtain a mixed solution containing nanofillers; 3)-5) The process is the same as in Example 3.

[0029] Comparative Example Comparative Example 1: The same quartz sand, binder, coating layer and water-soluble polymer treatment steps were used, but no porous nanofiller was added to the coating layer.

[0030] Comparative Example 2: The same treatment steps were used with quartz sand and a composite coating layer containing nanofillers, but without the addition of a bonding layer.

[0031] Comparative Example 3: The same quartz sand, bonding layer, and composite coating treatment steps were used, but the porous nanofiller accounted for 20% of the total mass of the composite coating.

[0032] Comparative Example 4: The same treatment steps of quartz sand, binder layer, and mixed solution containing nanofiller were used, but when mixing sand, the mixed solution containing nanofiller and initiator solution were added when the temperature of the proppant covering the binder layer dropped to 130°C.

[0033] The self-suspending proppants obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were tested according to industry standard SY / T 5108-2014. The test results are shown in Table 1: Table 1: Performance Test Results

Claims

1. A self-suspending proppant containing nanofillers, comprising a proppant particle substrate, an adhesive layer, and a composite coating layer, wherein the composite coating layer is fixed to the proppant particle substrate by the adhesive layer; the proppant particle substrate, adhesive layer, and composite coating layer are in a weight ratio of 100:0.1-1:2-13. The substrate material of the proppant particles is natural quartz sand with a silica content of more than 90%. The adhesive layer is at least one of epoxy resin, phenolic resin, acrylic resin, and unsaturated polyester resin adhesive; The composite coating layer is composed of a water-soluble polymer and uniformly dispersed nanofillers, with the nanofillers accounting for 3%-15% of the total weight of the composite coating layer and the water-soluble polymer accounting for 85%-97% of the total weight of the composite coating layer.

2. The self-suspending proppant containing nanofillers according to claim 1, characterized in that: The nanofiller is one of two-dimensional porous nanomaterials, three-dimensional porous nanomaterials, or a mixture thereof.

3. The self-suspending proppant containing nanofillers according to claim 2, characterized in that: The two-dimensional porous nanomaterial is one or a mixture of porous nanosheet graphitic carbon nitride and graphene, with two-dimensional mesopores of 2-50 nm uniformly distributed on the sheet structure; the three-dimensional porous nanomaterial is one or a mixture of hierarchical porous activated carbon, biomass-derived hierarchical porous carbon, and carbon aerogel, containing macropores of 50-100 nm and mesopores of 2-50 nm distributed on the walls and gaps of the macropores.

4. The self-suspending proppant containing nanofillers according to claim 1, characterized in that: The water-soluble polymer is polymerized from water-soluble monomers, organic solvents, and initiators.

5. The self-suspending proppant containing nanofillers according to claim 4, characterized in that: The water-soluble monomer is one or a mixture of acrylamide, starch-grafted sodium acrylate, and sodium alginate.

6. The self-suspending proppant containing nanofillers according to claim 4, characterized in that: The organic solvent is one of N,N'-methylenebisacrylamide, ethylene glycol diglycidyl ether and its polymers, and glyoxal.

7. The self-suspending proppant containing nanofillers according to claim 4, characterized in that: The initiator is one or a mixture of ammonium persulfate, potassium persulfate, hydrogen peroxide, sodium metabisulfite, and sodium bisulfite.

8. The self-suspending proppant containing nanofillers according to claim 5, characterized in that: In the composite coating layer, the content of water-soluble monomers is 0.5-8%, the content of organic solvents is 0.002-0.2%, and the content of initiator is 0.002-0.5% relative to the weight of the proppant particles substrate.

9. A method for preparing a self-suspending proppant as described in any one of claims 1-8, characterized in that: Includes the following steps: S1. Mix the water-soluble monomer, deionized water, and organic solvent evenly to prepare an aqueous solution with a mass fraction of 30-50%. S2. Mix the porous nanofiller with the above aqueous solution to prepare a mixed solution containing the nanofiller; S3. Preheat the proppant particle substrate to the preheating temperature and pour it into the sand mixer. When it cools down to 120-160℃, add the binder to obtain the proppant that encapsulates the adhesive layer. S4. When the proppant encapsulating the adhesive layer cools down to 60-100℃, a mixed solution containing porous nanofillers and an initiator are added sequentially to obtain a self-suspending proppant containing nanofillers.

10. The method for preparing the self-suspending proppant containing nanofillers according to claim 9, characterized in that: The preheating temperature is 180-220℃.

Images