考虑流固耦合影响的页岩力学性质和渗流规律

Effect of fluid–solid coupling on shale mechanics and seepage laws

为了研究页岩气藏在生产过程中外来水对页岩力学和渗流规律的影响,以四川盆地宜宾地区的下志留统龙马溪组黑色页岩露头及页岩岩心为样本进行了分析。首先,利用VHX-5000超景深显微镜观察了饱和水后岩心裂缝的发育情况;其次,通过单轴压力试验机、应变测试分析系统,研究了水、地层水及滑溜水与饱和水岩心、未饱和水岩心压裂后的破坏形式和抗压强度的变化;最后,通过DYQ-1型多功能驱替装置,研究不同含水条件下流固耦合对页岩气渗流特征影响。岩心成分分析结果表明:龙马溪组页岩脆性矿物含量高,属于可压性较高的储层,有利于压裂改造。页岩抗压强度实验结果表明:去离子水、地层水和滑溜水对页岩的作用效果不同,导致页岩饱和前后的抗压强度差距较大,水的存在会降低页岩的抗压强度,更容易被压裂,产生更多的裂缝,从而提高页岩的渗流能力。含水条件对页岩气渗流特征实验结果表明:流固耦合条件下,含水饱和度越大,页岩微裂缝在压力作用下,扩展发育效果和渗流能力越好,水的存在有助于页岩气藏压裂改造,达到了增加产量的目的。

In this paper, the cores of outcropped black shale of Lower Silurian Longmaxi Fm in the Yibin area, Sichuan Basin, were taken as samples to investigate the effects of extraneous water on shale mechanics and seepage laws during the production of shale gas reservoirs. Firstly, the development of fractures in water saturated cores was observed by using a VHX-5000 optical superdepth microscope. Secondly, water, formation water and slick water, as well as the damage form and compression strength of water saturated/unsaturated cores were investigated by means of a uniaxial compression testing machine and a strain testing ＆ analysis system. Finally, the effects of fluid-solid coupling on shale gas flowing performance in different water saturations were analyzed by using a DYQ-I multi-function displacement device. Analysis on core components shows that the Longmaxi shale is a highly crushable reservoir with a high content of fragile minerals, so fracturing stimulation is suitable for it. Shale compression strength test reveals that the effects of deionized water, for- mation water and slick water on shale are different, so the compression strength of shale before being saturated is quite different from that after being saturated. Due to the existence of water, the compression strength of shale drops, so the shale can be fractured easily, more fractures are generated and thus its seepage capacity is improved. Experiments on shale gas seepage under different water saturations show that under the condition of fluid-solid coupling, the higher the water saturation is, the better the propagation and seepage capacity of micro-fractures in shale under the effect of pressure. To sum up, the existence of water is beneficial to fracturing stimulation of shale gas reservoirs and helps to achieve the goal of production improvement.