Damage Evaluation Of Fracturing Fluid In Coal And Gas Reservoir And Modification Of Nanoparticles

As a high quality clean energy, Coalbed methane (CBM) has a huge amount of resources, by economic and effective development and utilization of it, there are three advantages to improve mine safety, protect the environment and make up the shortage of conventional energy sources. CBM which mainly exists under adsorption state occurs in the coal seam, and the output of CBM goes through three processes:desorption-diffusion-seepage. Due to the special characteristic of coal, fracturing technology of it is different from conventional fracturing, its key is to control the output of pulverized coal and the damage to coal by fracturing fluid. Meanwhile, coalbed reservoir is a gas-liquid-solid interaction system, the interaction of coal and fracturing fluid, which not only causes the reduction of permeability of coal, and also makes changes happen to the surface properties, which thus affects adsorption/desorption and diffusion capacity of coal.This thesis focuses on the No.9coal seam in Ningwu Basin, based on the analysis of coal mineral composition, physical properties, pore structure properties and surface properties, studies the influence of fracturing fluid to permeability, adsorption/desorption and diffusion of coal. Comprehensively analyze the damage and its damage mechanism of coal which is given by fracturing fluid, and optimize the fracturing fluid of coal by taking use of nanometer technology.Understand the mineral composition and pore structure characteristics of No.9coal. By using experimental means of X-ray diffraction, scanning electron microscopy (SEM), CT scans, nitrogen adsorption, etc. comprehensively characterize the mineral composition, pore size distribution and spatial distribution of crack of coal. Studies have shown that the inorganic minerals in coal are given priority to quartz, and clay minerals are mainly composed of montmorillonite; the pores in coal matrix are mainly nanoscale pores, pore size distribution of peak appeared in4nm; the pore structure in coal is quite complex, micro-fractures are developed, but spatial connectivity is poor.Make the surface properties of coal before and after the effect of fracturing fluid clear. Coal infrared spectroscopy (IR) observations indicate that the soak of coal by fracturing fluid changes coal intermolecular and intramolecular action forces type and size, impacts the-OH,-COOH groups greater, and prompts the transformation between the free and associated states. Wetting contact angle experiments of coal with formation water and fracturing fluid shows that, the wetting contact angle of fracturing fluids with coal are smaller than the wetting contact angle of formation water with coal, have better wettability of fracturing fluid to coal, and easy to adsorb on the surface of coal.Comprehensively evaluate the damage of fracturing fluid to desorption-diffusion-seepage of coalbed reservoir. Carry out the experiment of the change of coal permeability, adsorption/desorption and diffusion capacity before and after the effect of fracturing fluid, studies indicate that, the damage of coal permeability by fracturing fluid is the most significant; in the adsorption experiment of coal effect by fracturing fluid, due to the competitive adsorption between gas-liquid-solid three phase, the fracturing fluid decreases the adsorption quantity of coal; while in the desorption and diffusion experiment, on account of a series of problems such as coal matrix expansion and pore blockage caused by fracturing fluid, make the desorption and diffusion capacity reduced to different content. Among the damages, the weakest of the damage degree is the clean fracturing fluid.Propose the new method to modify fracturing fluid by adding nanoparticles and control the output of pulverized coal. Making use of the SEM characterized particle size of nanoparticles used by experiment is roughly in the range of10-100nm. Carried out the experiment of fracturing fluid performance evaluation and the control ability of pulverized coal before and after adding nanoparticles, the results show that the performance of fracturing fluid adding nanoparticles is improved, and the effect of fracturing fluid adding SiO2nanoparticles is significant. Through adsorption, nanoparticles can effectively control, as a result, make the pulverized coal output decreased over50%.Comprehensively evaluate the damage of fracturing fluid to coal can more accurately predict fracturing effect, meanwhile control the output of pulverized coal by nanoparticles can improve the effect of fracturing operation, and promote efficient development of CBM.