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裂缝网络是页岩气有效开发的基础,为研究页岩裂缝渗透率在有效应力作用下的变化规律,选取具有代表性的四川盆地龙马溪组页岩样品,通过实验考察了基质、微裂缝和人工裂缝渗透率对应力的敏感程度,总结了孔渗幂指数模型、Gangi模型和Walsh模型对裂缝渗透率的拟合和修正结果,并探讨了支撑裂缝和裂缝滑移降低应力敏感性的作用机理。研究结果表明,微裂缝和人工无填充裂缝的渗透率的应力敏感最强,随着有效应力的增加呈指数式递减,Gangi模型和Walsh模型的拟合精度都在97%以上,参数分析结果表明可通过增加裂缝面的粗糙度和向裂缝加入支撑剂来降低其应力敏感系数。有支撑和滑移裂缝的应力敏感性最低,仅仅在一定应力范围内满足Walsh模型。高应力状态下,优选强度较高、耐压性好的陶粒支撑剂有利于提高裂缝的导流能力,而裂缝滑移在一定程度上比裂缝支撑剂更能增加裂缝渗透率,因此在水力压裂模型中应该考虑设计裂缝滑移来降低裂缝的应力敏感性。
Fracture network is the basis for the effective development of shale gas. In order to study the variation law of shale fracture permeability under effective stress, a representative sample of Longmaxi Formation shale in Sichuan Basin was selected to investigate the effects of matrix, The sensitivity of artificial fracture permeability to stress is summarized. The results of fitting and correction of fracture permeability by pore infiltration index model, Gangi model and Walsh model are summarized, and the mechanism of action of supporting fracture and fracture slippage to reduce stress sensitivity is also discussed . The results show that the permeability of micro-cracks and artificial unfilled cracks is the most sensitive to stress, exponentially decreasing with the increase of effective stress, the fitting accuracy of Gangi model and Walsh model is above 97%, and the result of parameter analysis The stress sensitivity coefficient can be reduced by increasing the roughness of the fracture surface and adding proppant to the fracture. The stress sensitivity of the supported and slip cracks is the lowest, and the Walsh model is satisfied only within a certain stress range. High stress state, the preferred high strength, good pressure resistance ceramic proppant helps to improve the conductivity of the fracture, and crack slip to some extent than the crack proppant to increase fracture permeability, so in the hydraulic Fracture design should consider the design of crack slip to reduce the stress sensitivity of the crack.