水力压裂页岩激电特征与各向异性实验研究

IP characteristics and anisotropy experiment of hydraulic fracturing shale

水力压裂是改善非常规储层物性、实现非常规油气资源有效开发的核心技术。与微地震监测不同,电磁监测方法以压裂液与围岩的复电阻率差异为基础,具有更好的物性基础。对于致密页岩等非常规储层,水力压裂形成的裂隙储层结构复杂,多种激发极化机理复合作用,给实际地层的激电建模带来一定的困难,限制了压裂电磁监测的储层评估能力。为此,开展了裂隙介质双重孔隙介质理论建模,结合五峰组致密储层页岩的压裂前、后激发极化特征实验,分析了储层样品在不同压力、压裂前后不同饱和度、填充不同支撑剂等状态下的激电参数变化及各向异性特征。研究结果表明:压裂后裂隙储层的激电物理特征受裂隙面影响较大,储层孔隙结构连通性增强是引起电阻率下降的主要原因;支撑剂的定向分布有利于增强裂隙储层的各向异性。该研究成果为储层激电建模提供了理论与实验基础。

Hydraulic fracturing is the core technology to improve the physical properties of unconventional reservoirs and effectively develop unconventional oil and gas resources.Different from microseismic monitoring,the electromagnetic monitoring method has a better physical basis based on the complex resistivity differences between fracturing fluids and surrounding rocks.The fractured reservoirs formed by hydraulic fracturing of tight shale and other unconventional reservoirs have complex structures and often have various induced polarization(IP)mechanisms,which causes certain difficulties in IP modeling of actual formations and limits the evaluation of electromagnetic fracturing monitoring.Therefore,this paper carries out IP modeling based on dual pore media and combines the IP characteristics of tight shale in Wufeng Formation before and after fracturing with the experiment.The differences in IP parameters and anisotropy characteristics of reservoir samples before and after fracturing are analyzed in the condition of different pressure,saturation,and proppant filling.The results show that the IP physical features of fractured reservoirs after fracturing are greatly affected by the fracture surface,and the enhanced pore connectivity of reservoirs is the main reason for the resistivity decrease.Meanwhile,the directional distribution of proppants is beneficial to enhance the anisotropy of fractured reservoirs,which provides a theoretical and experimental basis for IP modeling of reservoirs.