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Effect of fracturing fluid treatment on pore structure of coal
KANG Yili, CHEN Defei, LI Xiangchen
(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation in Southwest Petroleum University, Chengdu 610500, China)
Abstract:
Fracturing fluid and the coal seam will touch each other during fracturing operation of coal. The developed micro-fractures and high capillary pressure of coal make it easy for fracturing fluid intrude into coal seam and therefore cause serious damage to the pore structure, which affects further the adsorption capacity of coal bed methane. Using the NO.9 coal sample from Ningwu Basin and three fracturing fluid samples on site, the characterization of pore structure of coal, which was treated with fracturing fluid, was analyzed with nitrogen adsorption method. Combined with the analysis results of scanning electron microscopy (SEM), the influence of different fracturing fluid on pore structure of coal was investigated. Methane isothermal adsorption experiments were also carried out using the treated coal. The results show that pore size distribution, specific surface area and pore fractal dimension of coal change after treated by fracturing fluid. The results also indicate that gel fracturing fluid has the most impact on pore structure of coal, followed by activated water fracturing fluid, and clean fracturing fluid having the least. The larger the increase of specific surface area and pore fractal dimension of coal treated by fracturing fluid, the stronger its ability of methane adsorption. Therefore, the change of pore structure in coal will change its adsorption ability of methane.
Key words:  coalbed methane  fracturing fluid  pore structure  nitrogen adsorption  isothermal adsorption