基于岩石物理与矿物组成的页岩脆性评价新方法

泥页岩的脆性决定其压裂改造的效果，开展页岩的脆性评价研究，可为压裂设计提供技术支撑，压裂改造的效果对提高页岩产能意义重大。鄂尔多斯盆地东南部下寺湾地区延长组长7段张家滩页岩层系内大量发育粉砂质泥页岩条带，矿物组成复杂，岩性非均质性强，对页岩气产量影响显著。针对目前矿物脆性评价中存在的脆性矿物不明确的问题，为了明确复杂矿物组成对页岩脆性的影响，通过对21块样品(页岩15块,粉砂质泥页岩6块)分别开展页岩总有机碳、全岩矿物X-射线衍射和地层条件下的三轴压缩应力试验，系统分析矿物组成及岩石力学特征，并以实验结果为基础分析矿物与岩石物理参数表现的关系，定量模拟岩石弹性参数随矿物组分变化的特征，明确了石英和黄铁矿是张家滩页岩的脆性矿物，并提出基于岩石物理模型的陆相页岩矿物组分脆性评价新方法。以YY22井为例，应用矿物脆性评价方法，计算其页岩层段的矿物脆性指数，为高脆性有利压裂目的层的识别及增产方案设计提供了参数依据。

A new shale brittleness evaluation method based on rock physics and mineral compositions

Hydraulic fracturing effect in shale is decided by the brittleness.The research on brittleness evaluation provides technical support for stimulation treatment design,and successful hydraulic fracturing increases the wells’ production rate.Continental Zhangjiatan shale in the member 7 of Yanchang Formation in Xiasiwan area of southeast Ordos Basin,which is featured with complex mineral compositions,plenty of silty mudstone is developed,strong lithological heterogeneities make significant impact on shale gas production.Currently brittle mineral and the influence of complex mineral compositions on shale brittleness are not clear in mineral brittleness evaluation.The mineral compositions and rock mechanics characteristics of rock samples (15 shale,6 silty shale) were systematically analyzed by the TOC,XRD,and triaxial compressive stress test under formation condition.On the basis of experimental results,the relationship was analyzed between the mineral compositions and the rock physical parameters.Quartz and pyrite as brittle minerals in Zhangjiatan shale was confirmed by quantitative simulation of the rock elasticity characteristics with different mineral composition.A new brittleness evaluation method of continental shale was put forward based on rock physics model and mineral compositions.The shale mineral brittleness index was calculated by the method in Well YY22,which provided geological basis for identifying fracturing target bed in quality brittleness shale and designing stimulation treatment.