考虑多重运移机制耦合页岩气藏压裂水平井数值模拟

页岩作为典型的微纳尺度多孔介质,游离气与吸附气共存,传统的达西定律已无法准确描述气体在页岩微纳尺度的运移规律.基于双重介质模型和离散裂缝模型构建页岩气藏分段压裂水平井模型,其中基岩中考虑气体的黏性流、Knudsen 扩散以及气体在基岩孔隙表面的吸附解吸,吸附采用Langmuir等温吸附方程;裂缝中考虑黏性流和Knudsen扩散,在此基础上建立基岩-裂缝双重介质压裂水平井数学模型并采用有限元方法对模型进行求解.结果表明,基岩固有渗透率越小,表面扩散和Knudsen扩散的影响越大,反之则越小;人工裂缝的性质包括条数、开度、半长以及间距,主要影响压裂水平井生产早期,随着人工裂缝参数值的增加,压裂水平井产能增加,累产气量也越大.其次,页岩气藏压裂诱导缝和天然裂缝的发育程度对页岩气藏的产能有很大的影响,水平井周围只有人工裂缝,周围天然裂缝不开启或不发育时,页岩气藏的水平井的产能较低. 

NUMERICAL SIMULATION OF MULTI-FRACTURED HORIZONTAL WELL IN SHALE GAS RESERVOIR CONSIDERING MULTIPLE GAS TRANSPORT MECHANISMS

Shale is a typical micro-nano-scale porous media, in which free gas and absorbed gas coexist, so traditional Darcy's law is unable to describe gas transport mechanisms of micro-nano-scale accurately. Based on double porosity model and discrete fracture model, the fractured horizontal well numerical model has been built in shale gas reservoir. Viscous flow, Knudsen di usion and surface di usion have been considered in shale matrix, while viscous flow and Knudsen di usion are considered in the natural fracture. The finite element method is applied to solve the model. The results show that the smaller intrinsic matrix permeability, the greater the e ect of surface di usion and Knudsen di usion. The properties of hydraulic fractures including fracture number, aperture, half-length and spacing, mainly a ect the early production. With the augment of those parameter values, the production rate and cumulative gas of multi-fractured horizontal well increase. Then the development of induced fractures and natural fractures has a significant e ect on the shale gas production and the production will be low when the natural fractures surrounding the horizontal well are closed or not developed.