Preparation method of self-suspending proppant for hydraulic fracturing

Abstract

A preparation method of a self-suspending proppant for hydraulic fracturing is characterized in that solid ceramsite is changed into a porous reinforced structure, a self-repairing function is introduced, bio-based macromolecules are adopted to replace a traditional surfactant, the environmental protection property is improved, nano-deposition and microwave technologies are introduced, the performance is improved, meanwhile, the energy consumption is reduced, and the compression resistance enhancement and self-repairing characteristics are newly added; and the method adapts to more complex stratum working conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of oil and gas exploitation engineering materials, and particularly relates to a preparation method of a self-suspending proppant for clean water fracturing, which realizes the synergistic optimization of fracturing operation efficiency and formation protection through gradient functional coating design. BACKGROUND

[0002] The exploitation of oil and gas usually needs to adopt hydraulic fracturing technology, and the proppant is a key material for fracturing operation. The proppant, also known as petroleum fracturing proppant, is used in the exploitation of deep oil and gas wells. After the fracturing treatment of high closure pressure and low permeability deposits, the oil and gas bearing rock layer is cracked, and the oil and gas is collected from the channel formed by the cracks. At this time, fluid needs to be injected into the rock base layer to exceed the pressure of the formation breaking strength, so that the rock layer around the well tube is cracked to form a channel with high conductivity. In order to maintain the cracks formed after fracturing and ensure that the oil and gas products can flow smoothly, the mixture of proppant and fracturing fluid is pumped into the well bottom at high pressure and high speed through hydraulic fracturing, and then enters the formation to fill in the rock cracks. The proppant forms a good conductive channel by using the pressure resistance of the proppant, so as to support the cracks and prevent them from closing due to stress release, thereby maintaining high conductivity and ensuring smooth flow of oil and gas to increase production.

[0003] The existing clean water fracturing self-suspending proppant has the following technical bottlenecks: (1) The traditional ceramic core is prone to micro-cracks under ultra-80MPa closure pressure, resulting in a conductivity decay of more than 30%; (2) The surfactant in the adsorbed permeation layer is prone to causing formation pollution when the fracturing fluid is returned, and the biodegradation rate is less than 50%; (3) The solvent recovery efficiency in the preparation process is low, and the energy consumption cost accounts for more than 25% of the production cost. Although the original patent improves the suspension performance by multi-layer coating, it still needs to be improved under high strength working conditions and environmental protection requirements. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of a self-suspending proppant for clean water fracturing. The solid ceramic is changed to a porous reinforced structure, the self-repairing function is introduced, the traditional surfactant is replaced by a bio-based polymer to improve environmental protection, the nano deposition and microwave technology are introduced to improve performance while reducing energy consumption, the anti-pressure enhancement and self-repairing properties are added, and the method is suitable for more complex formation conditions. In order to achieve the above purpose, the technical scheme adopted by the present application is: A self-suspending proppant for clean water fracturing, comprising a porous ceramic reinforced inner core, a gradient swelling adsorption layer, a nano interface transition layer, a nano interface transition layer and a degradable anti-adhesion layer, characterized in that the structure comprises: Porous ceramic-reinforced core: Made of bauxite-mullite composite ceramsite with a porosity of 18% to 22%, surface-modified with a silane coupling agent, the core accounts for 91% to 96% of the mass. Calcium carbonate microspheres are pre-loaded within the pore structure for crack self-healing.

[0005] Gradient swelling adsorption layer: Composed of a chitosan-g-acrylamide graft copolymer (biodegradability ≥ 90%) and nanoclay, accounting for 2% to 5% by weight. This layer achieves a dual-stage release mechanism of "slow dissolution and high viscosity maintenance" through a pH-responsive cross-linked network. Nano-interface transition layer: 0.5%~2% titanium dioxide-silica sol composite coating, which forms a nano-scale interface bridging structure through the sol-gel method, improving the interlayer bonding strength by more than 30%. Degradable anti-adhesion layer: It is a compound of triammonium citrate and starch microspheres, accounting for 1% to 3% by weight. It forms a biocompatible protective colloid after dissolving in clean water. A method for preparing a self-suspending proppant for water fracturing, characterized by comprising the following steps: (1) Core modification: The ceramsite was immersed in a 3% silane coupling agent ethanol solution, stirred at 60 °C for 2 hours, and dried to obtain a surface hydroxylated core; (2) Adsorption layer construction: Chitosan-acrylamide microspheres were prepared by inverse emulsion polymerization, mixed with nanoclay (particle size 20-50 nm), coated on the core surface by spray granulation, and dried in vacuum at 80°C; (3) Interface enhancement: titanium dioxide sol and silica sol were mixed in a ratio of 1:1, and a 50-100 nm transition layer was formed on the surface of the adsorption layer by atomic layer deposition technology, and microwave-assisted curing (power 500 W, time 10 minutes); (4) Anti-adhesion coating: Triammonium citrate and starch microspheres are mixed in a ratio of 2:1, sprayed on the surface of the proppant through a fluidized bed, and dried to form a porous slow-release coating. The beneficial effects of the present invention are: Improved compressive strength: Under a closing pressure of 100 MPa, the proppant breakage rate is ≤5%, a 40% reduction compared to the original patent; Optimized environmental performance: The biodegradation rate of core materials reaches 92%, and the COD value of fracturing fluid flowback is reduced by 65%; Reduced process energy consumption: Through vacuum-microwave combined drying technology, solvent recovery efficiency is increased from 70% to 95%, and energy consumption is reduced by 35%.

[0006] Atomic layer deposition technology is introduced to realize nanoscale interface control, and the interlayer bonding strength test value reaches 12 MPa, which is 50% higher than that of the original process; The microwave-assisted drying is used to replace the traditional hot air drying, and the energy consumption is reduced from 0.8 kWh / kg to 0.5 kWh / kg. DETAILED DESCRIPTION

[0007] The application is further described below in combination with examples.

[0008] Example 1: High-strength performance test Raw material ratio: 1500 kg modified ceramsite, 45 kg chitosan-acrylamide composite microspheres, 15 kg titanium dioxide-silica sol, 30 kg ammonium citrate-starch composite; The breakage rate of the prepared proppant under a pressure of 100 MPa is 4.8%, while the breakage rate of the proppant in the original patent example 1 under the same condition is 8.5%. Example 2: Environmental performance test The proppant is soaked in simulated formation water for 30 days, and the biodegradation rate of the adsorption layer material reaches 91.3%, while the degradation rate of the surfactant in the original patent is only 48.7%. The application realizes a triple technical breakthrough through gradient functionalization design: In terms of mechanical properties, the porous ceramic core and the nano interface layer form a "skeleton-ligament" reinforcing structure, so that the proppant can maintain the flow conductivity under superhigh pressure working conditions; In terms of environmental performance, the biobased adsorption layer and the degradable anti-blocking layer solve the chemical pollution problem of traditional proppants; The nano coating and microwave technology are introduced in the preparation process to realize efficient and low-consumption production. The proppant is suitable for deep oil and gas reservoir fracturing, can reduce the amount of fracturing fluid by 25%, and reduce the treatment cost of flowback fluid by 40%, and has significant engineering application value.

Claims

1. A self-suspending proppant for water fracturing, comprising a porous ceramic reinforced core, a gradient swelling adsorption layer, a nano-interface transition layer, a nano-interface transition layer and a degradable anti-adhesion layer, characterized in that: Its structure from inside to outside includes: Porous ceramic reinforced core: Made of bauxite-mullite composite ceramsite with a porosity of 18% to 22%, surface-modified with a silane coupling agent, the core accounts for 91% to 96% of the mass. Calcium carbonate microspheres are pre-loaded into the pore structure for crack self-healing. Gradient swelling adsorption layer: Composed of a chitosan-g-acrylamide graft copolymer (biodegradability ≥ 90%) and nanoclay, accounting for 2% to 5% by weight. This layer achieves a dual-stage release mechanism of "slow dissolution and high viscosity maintenance" through a pH-responsive cross-linked network. Nano-interface transition layer: 0.5%~2% titanium dioxide-silica sol composite coating, which forms a nano-scale interface bridging structure through the sol-gel method, improving the interlayer bonding strength by more than 30%; Degradable anti-adhesion layer: It is a compound of triammonium citrate and starch microspheres, accounting for 1% to 3% by weight. It forms a biocompatible protective colloid after dissolving in clean water.

2. A method for preparing a self-suspending proppant for water fracturing, characterized in that: The following steps are involved: (1) Core modification: The ceramsite was immersed in a 3% silane coupling agent ethanol solution, stirred at 60 °C for 2 hours, and dried to obtain a surface hydroxylated core; (2) Adsorption layer construction: Chitosan-acrylamide microspheres were prepared by inverse emulsion polymerization, mixed with nanoclay (particle size 20-50 nm), coated on the core surface by spray granulation, and dried in vacuum at 80°C; (3) Interface enhancement: titanium dioxide sol and silica sol were mixed in a ratio of 1:1, and a 50-100 nm transition layer was formed on the surface of the adsorption layer by atomic layer deposition technology, and microwave-assisted curing (power 500 W, time 10 minutes); (4) Anti-adhesion coating: Triammonium citrate and starch microspheres are mixed in a ratio of 2:1, sprayed on the surface of the proppant through a fluidized bed, and dried to form a porous slow-release coating.