气体在页岩储层中运移受解吸、扩散及渗流多种机制共同作用,同时也受储层的应力敏感效应等因素影响。综合考虑解吸、扩散及应力敏感效应,基于线性流模型,构建了符合页岩储层改造特点及流体渗流特征的分段压裂水平井多重复合流动模型。利用Laplace变换和Stehfest数值反演,得到封闭边界定产量下无因次井底拟压力和无因次产量半解析解。研究了页岩气在基质-微裂缝-压裂缝多重孔隙介质的复合流动,认识流体特性参数与压裂缝网参数对产气量的影响规律,并利用北美页岩气井生产数据进行拟合,验证了模型可靠性。研究结果表明:吸附气的解吸扩散使井底压力响应曲线出现明显“下凹”阶段;解吸系数增大,解吸气量越大,气井日产气量越高;窜流系数越大,基质与裂缝间的流体交换时间越早,但持续时间越短;压裂改造体积大,储层流体流动性强,但存在最优值;对比拟合结果,考虑改造带宽有限性更符合矿场实际。研究结果旨在为页岩储层分段压裂水平井多重复合流动规律研究提供理论基础。
Gas flow in shale reservoir is affected by the interaction of desorption, diffusion, seepage mecha- nisms and formation stress sensitivity. Based on the trilinear model, a composite flow model for multistage fractured horizontal well was established with consideration of multiple mechanisms,which can reflect the characteristics of stimulation and fluid flow in shale gas reservoirs. Applying Laplace transform and Stehlest numerical inversion,the semi-analytical solutions of non-dimensional bottom-hole pseudo-pressure and productivity in closed reservoir were obtained. The analysis of gas flow in multi-scale porosity and the effects of different factors on productivity were carried out. The presented model was validated by the production data of gas well in North America. The results show that gas adsorption results in an obvious "dip" in pressure response curves. The larger desorption coefficient is, the higher desorption gas and production are. The larger channeling factor is,the earlier fluid exchange between matrix and fracture appears but the shorter it lasts. Larger stimulated volume would increase formation conductivity, while an optimistic value exists due to the fractures interference. The limited stimulated bandwidth are more accord with the practice by comparing matching results. The presented model and results enrich the pressure and rate analysis mod- el for the multistage fractured horizontal wells in shale reservoirs.