压裂液返排液对页岩储层裂缝的损害实验评价

Experimental Evaluation on Damage of Fracturing Flow-back Fluid to Shale Reservoir Fractures

页岩气井经过大规模体积压裂施工后会有大量的压裂液返排液滞留在储层裂缝中,这会对页岩储层造成一定的损害。因此,选择涪陵地区某页岩气井压裂液返排液和储层页岩为研究对象,开展了压裂液返排液对页岩储层裂缝的损害实验评价,并分析了其损害机理。结果表明:页岩储层岩心经过压裂液返排液污染后,渗透率明显下降,使用线性胶和滑溜水压裂液返排液污染并烘干后的岩心渗透率损害率分别在31.30%~84.59%和13.97%~61.69%之间,滑溜水压裂液返排液的损害程度稍微弱些。岩心驱替前后压裂液返排液中的固相颗粒粒径分布发生了明显变化,有大量固相颗粒在驱替过程中堵塞在了岩心孔隙和裂缝中。使用线性胶和滑溜水压裂液返排液污染后的页岩导流板导流能力值显著下降,导流板烘干后的导流能力相比初始阶段下降幅度分别为61.48%和31.32%,说明压裂液返排液对页岩储层裂缝造成了严重的损害。建议通过优化压裂液体系性能和建立合理的返排制度来降低压裂液返排液对页岩储层裂缝的损害程度。

After large-scale volume fracturing, a large number of fracturing flow-back fluid will remain in the reservoir fractures, which will cause certain damage to the shale reservoir. Therefore, choosing a shale gas well fracturing flow-back fluid and reservoir shale in Fuling area as the research object, the experimental evaluation of fracturing flow-back fluid damage to shale reservoir fracture was carried out, and the damage mechanism was analyzed. The results showed that the permeability of shale reservoir cores polluted by fracturing flow-back fluid obviously decreased. The permeability damage rates of cores polluted and dried by linear glue and sliding water fracturing flow-back fluid were between 31.30%~84.59% and 13.97%~61.69%, respectively. The damage degree of sliding water fracturing flow-back fluid was slightly weaker. The particle size distribution of solid particles in fracturing flow-back fluid before and after core displacement changed significantly, and a large number of solid particles were blocked in core pore and fracture during displacement. The fracture conductivity of shale diversion plate contaminated by linear glue and slip water fracturing flow-back fluid was significantly reduced. The decline rates of fracture conductivity of the diversion plate after drying were 61.48% and 31.32% respectively compared with the initial stage, which indicated that the fracturing flow-back fluid caused serious damage to shale reservoir fractures. It was suggested that the damage degree of fracturing flow-back fluid to shale reservoir fracture should be reduced by optimizing the performance of fracturing fluid system and establishing reasonable flow-back system.