页岩储层脆性评价分析及可压裂性定量评价新方法研究

Probability study of formation brittleness and new quantitative evaluation of fracability for shale reservoirs

目前绝大部分可压裂性模型以弹性参数脆性指数法为基础评价页岩储层可压裂性,然而通过岩石应力应变特性、岩石力学测试统计结果和矿场压裂实例分析可知,通过弹性参数评价页岩脆性缺乏理论依据,且与实验测试、压裂效果等相悖.针对页岩储层可压裂性定义不统一、不全面的问题,综合分析了影响页岩体积压裂过程中压碎难度、缝网的复杂度、获得较高改造体积的概率以及压裂后导流能力等方面,给出了新的且全面的可压裂性定义.基于可压裂性科学内涵,综合考虑页岩脆性、围压、天然裂缝发育程度、断裂韧性和抗压强度,建立了页岩可压裂性评价新模型及归一化指数模型,此模型通过室内试验测试和现场测井数据可分别实现室内和矿场储层可压裂性的定量表征.本文所建立地可压裂性模型在页岩典型井中开展了应用分析,并与已有可压裂性评价模型进行了对比,其评价结果与压后产能监测数据相一致,验证了本文模型的准确性.

Currently,the majority of fracability evaluation models are characterized by brittleness index which is developed from elastic properties.While,this evaluation method of using elastic properties are lack of theoretical foundations from the analysis of stress-strain deformation,geomechanics tests and hydraulic fracturing cases.Additionally,it disagrees with the results from laboratory tests,and hydraulic fracturing applications.From literature review,there is no uniform or complete definition of the fracability of shale reservoirs.In this way,this paper develops a quantitative method of evaluating fracability which includes the level of formation crushing ability,fracture complexity,the probability of obtaining large stimulated reservoir volume and post-fracture conductivity.This method comprises detailed evaluation criteria which is a new and complete definition of fracability.A new fracability evaluation model and a normalized fracability index model are built up by the combination of brittleness,confining pressure,natural fracture,fracture toughness and unconfined compressive strength following the definition of fracability.These models can be developed and quantitatively characterized by laboratory tests and field logs.This model has been applied in the evaluation of hydraulic fracturing in shale wells and compared with other existing models.Its results match well with production data.