基于三维CT重构的页岩裂缝定量表征及可压裂性评价

CT scan-based quantitative characterization and fracability evaluation of fractures in shale reservoirs

页岩油气储层自然产能低,需利用水平井分段体积压裂技术进行储层改造,储层压后裂缝定量表征是评价压裂效果的关键参数.本次研究对龙马溪组泥页岩样品进行恒速应变法破裂压力实验,使用微米CT扫描实验前后岩心样品并三维重构.综合利用分形维数、集中程度值表征裂缝复杂度,使用层次分析法构建了基于裂缝改造率、抗压强度、围压的新型可压裂性评价模型.研究结果表明该模型可较好反映实验前后裂缝的空间展布特征差异,可压裂性评价结果与微地震事件能够较好的对应.该方法能够克服传统弹性参数法、矿物组分法等评价储层可压裂性的不足,丰富了现有的储层可压裂性评价方法.

Natural production capacity of shale oil and gas reservoirs is low,and horizontal well staged volumetric fracturing technology is required for reservoir stimulation.Quantitative characterization of fractures after reservoir fracturing is a key parameter for evaluating fracturing effects.In this study,the constant-rate strain method fracture pressure experiment was carried out on the mud shale samples of the Longmaxi Formation,and the core samples before and after the experiment were scanned by micro-CT and three-dimensionally reconstructed.A new fracability evaluation model based on fracture reconstruction rate,compressive strength,and confining pressure was constructed by using the fractal dimension and concentration value to characterize the complexity of fractures.The results show that the model can better reflect the difference in the spatial distribution characteristics of fractures before and after the experiment,and the results of fracability evaluation and microseismic events can better correspond.This method can overcome the deficiencies of the traditional elastic parameter method and mineral composition method in evaluating reservoir fracturability,and enriches the existing reservoir fracability evaluation methods.