页岩储层水力裂缝网络多因素耦合分析

为优化压裂设计、提高页岩储层的改造效果,基于室内真三轴水力压裂模拟实验、现场压裂实践和理论分析的方法,从页岩绪层岩石的脆性指数、水平应力差、天然裂缝的力学特征和发育程度、液体黏度和施工参数等方面分析了页岩储层压裂形成缝网的受控因素。结果表明:页岩储层的水力裂缝网络发育程度受到地质因素和工程因素的双重作用;从储层地质因素上看,岩石的脆性指数越高、天然裂缝越发育、天然缝胶结程度越差,越有利于形成缝网;从压裂作业的因素看,压裂液黏度越低以及压裂规模越大,越有利于形成充分扩展的缝网。在分析单个因素的基础上,建立了多因素耦合的缝网发育指数来表征页岩储层水力裂缝网络发育程度,并用于评价页岩储层压裂后水力裂缝的复杂程度。

Multi-factor coupling of hydraulic fracture network in a shale gas reservoir

In order to optimize fracturing design and improve shale reservoir stimulation effect, according to the results of indoors true triaxial hydraulic fracturing simulation experiments and the methods for analyzing field fracturing practices and theories, this paper systematically discussed the controlling factors of fracture network induced by shale reservoir fracturing, including the brittleness index of shale reservoir rocks, horizontal stress difference, mechanical characteristics and expansion of natural fractures, fluid viscosity, and construction parameters. The analysis results showed that the expansion of hydraulic fracture network of a shale reservoir is influenced by both geological and engineering factors. From the perspective of geological attributes, higher rock brittleness resulting in better natural fracture development and worse natural fracture cementation, will facilitate the formation of fracture network. From the perspective of the engineering factors of fracturing operation, lower fluid viscosity and larger fracturing scale will be more conducive to the formation of fully expanded fracture network. On this basis, the multi-factor coupling network growth indexes were established to represent the expansion of hydraulic fracture network of a shale reservoir and evaluate the complexity of hydraulic fractures induced by shale reservoir fracturing.