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水平井分段压裂是页岩气藏开发的主要技术手段。然而,页岩纳米孔与微裂缝的毛管自吸作用往往导致压裂液返排困难,滞留压裂液对页岩气解吸—扩散—渗流过程潜在损害严重。为深化页岩气藏压裂液返排与及其水相圈闭损害动态变化的认识,利用川东龙马溪组页岩样品,在岩心柱尺度上实验模拟增产改造时压裂液自吸—返排过程,讨论了孔隙结构、裂缝发育情况、返排压差及时间影响自吸—返排效果的机理。结果表明:孔隙半径越小,毛管力越大,页岩自吸速率越大,水相返排效果越差;自吸诱发页岩产生裂缝,增大了气相渗流通道,促进了滞留水相返排;返排压差、返排时间与水相返排效果呈正相关关系,在返排压差0.2MPa和1.0MPa条件下先后各返排12h,水相最大返排率约为46%,最大渗透率恢复率约为67%。分析表明:页岩气藏潜在水相圈闭损害严重,滞留水相的返排有利于增强页岩气渗流能力。
Horizontal well fracturing is the main technical means for the development of shale gas reservoirs. However, capillary self-priming of shale nanopores and micro-fractures often results in difficulties in returning the fracturing fluid, and the potential damage of the fracturing fluid to the desorption-diffusion-percolation of shale gas is serious. In order to deepen the understanding of the dynamic changes of fracturing fluid flowback and its trapping damage in shale gas reservoirs, the shale samples of Longmaxi Formation in East Sichuan Basin were used to simulate the effects of self-priming- Back to the process, discussed the pore structure, crack development, return pressure and time-dependent self-priming-back row effect of the mechanism. The results show that the smaller the pore radius is, the larger the capillary force is, the larger the self-priming rate of shale is and the worse the water-returning effect is. The self-priming induces fractures in shale and increases the gas-phase seepage channel, Pai; back row pressure difference, return time and the water phase return effect was positively correlated, return flow pressure 0.2MPa and 1.0MPa conditions have returned to each row 12h, the maximum water back to about 46%, the maximum Permeability recovery rate is about 67%. The analysis shows that the potential water phase trap of shale gas reservoirs is seriously damaged, and the return flow of the retained water phase is favorable for enhancing the shale gas seepage ability.