页岩储集层脆性研究进展

Research Progress on Brittleness of Shale Reservoirs

脆性是选择页岩储集层有利压裂层段的关键指标,常用评价方法包括矿物法和弹性参数法。中国南方海相页岩具有沉积环境多样、岩相类型复杂、埋深范围大等特点,通过实例分析了现有评价方法存在的理论缺陷和适用性限制。根据页岩岩石力学性质的研究认识,重点总结了矿物组成、有机质、层理和围压对脆性的影响,并阐释了页岩脆性与可压裂性的关系。综合分析指出:矿物法有更强的实用性,但是对脆性矿物的界定模糊,弹性参数法可以有效实现测井和地震预测,但是无法反映围压的影响,难以表征深层和浅层页岩脆性差异。结合中国南方海相页岩的岩相类型和埋深范围,基于不同矿物组分的脆性差异,提出以石英、白云石和黄铁矿作为脆性矿物;基于围压对脆性的影响,提出在弹性参数的基础上增加强度或断裂韧性作为围压指示因子,以适应深层页岩脆性评价。深入认识矿物组成、有机质、层理和围压对脆性的影响,以及脆性与可压裂性的关系,有助于页岩岩相的精细表征和"甜点"优选。

Brittleness is a key indicator to select favorable fracturing intervals. Mineral-based method and elastic parameter-based methodare generally used to evaluate shale brittleness. The marine shales in South China are characterized by various sedimentary environment,complex lithofacies and large range of burial depth. The paper analyzes the theoretical defects and the limitations during application on thebasis of case study. Based on the research results on shale mechanical properties, the paper summarizes the influences of mineral composi-tion, organic matter, bedding and confining pressure on shale brittleness, and demonstrates the relationship between brittleness and fraca-bility. The comprehensive analysis shows that mineral-based method is more applicable but has a detect that there is not a unified defini-tion for brittle minerals yet. Elastic parameter-based method can perform logging and seismic prediction effectively, but this method can＇treflect the influence of confining pressure and it is difficult to characterize the brittleness differences between deep and shallow shales withthe method. Combined with the lithofacies and burial depth range of marine shales in South China and based on the differences among dif-ferent mineral components, quartz, dolomite and pyrite are proposed to be considered as brittle minerals; based on the influence of confin-ing pressure on brittleness, the paper suggests that strength or fracture toughness should be added to the elastic parameter-based indices asa confining pressure-indicator to apply to the deep-burial shale brittleness evaluation. Profound understandings on the influences of mineralcomposition, organic matter, bedding and burial depth on brittleness and the relationship between brittleness and fracability can promotedetailed lithofacies characterization of shales and sweep-spot optimization.