Damage mechanism and countermeasures of reservoir with abnormal pickup of CBM flow pressure in well

The reasonable control of the casing pressure and the bottom-hole pressure and the reasonable depressurization of reservoir pressure is the key technology for the CBM development. The pickup of the bottom-hole flow pressure(BHFP) will restrain CBM' desorption, lead to reservoir permeability damage and reduce the production of CBM wells. Based on production practice of Fanzhuang block in Qinshui basin, this paper puts forward the cause of a CBM abnormal well type, pickup of the BHFP, clarifies the damage mechanism of the pickup of the BHFP through theoretical research and field data analysis, and puts forward the evaluating method of the damage degree of reservoir and the countermeasures of the pickup of the bottom-hole flow pressure. The results of research show that in general if the submergence degree of coal seam increases, the casing pressure will decrease and the faster the decrease of the casing pressure becomes, the faster the decrease of the bottom-hole flow pressure is. If the submergence degree of coal seam increase faster, the bottom hole flow pressure will rise. The pickup of the BHFP results in the increase of the gas output resistance and the decrease of output power, so some gas content is blocked in the pores by capillary pressure and hard to produce, which is the damage mechanism to the reservoir caused by the pickup of the BHFP. The damage index can indirectly represent the damage degree of reservoir caused by the pickup of the BHFP. The valve leakage and air lock of the displacement pump are the main reasons for the pickup of the BHFP, which result in the drainage amount of water less than the supply amount of water from coal seams to bottom hole. The treatment of wells with abnormal BHFP pickup is hydraulic flush to remove the coal powders to deal with fixing valve leakage, mechanical vibration to remove coal powders to deal with floating valve leakage and the combination of permanent-submerged-technology and pumping-unit-intermittent-working technology to deal with gas lock.