深层致密砂岩储层脆性指数评价新方法

储层岩石脆性评价是储层压裂改造方案设计的重要基础工作，对储层压裂改造效果有着重要影响。以准中地区深层致密砂岩储层为研究对象，开展了0~90 MPa多级围压下的岩石三轴试验，分析了围压变化对于岩石脆性的影响。针对现有脆性指数对目标储层岩石脆性评价效果不理想的情况，基于应力-应变曲线中的能量转化关系建立了新的脆性指数模型，包括岩石峰前峰后脆性指数和综合脆性指数。研究结果表明:试验围压对岩石脆性评价有着显著影响；岩石峰前脆性随围压增大先增加后减小，峰后脆性和综合脆性随围压增大而递减；研究区储层含砾细砂岩的脆性较细砂岩的脆性小，脆性差异主要表现在峰后脆性。 

A NEW METHOD FOR EVALUATING BRITTLENESS INDEX OF DEEP TIGHT SANDSTONE RESERVOIR

Reservoir rock brittleness evaluation is important foundation work for the design of reservoir fracturing reconstruction scheme, which has great influence on reservoir fracturing reconstruction effect. Taking the deep tight sandstone reservoir in the central part of the Junggar Basin as the research object, the rock triaxial test under 0~90 MPa multilevel confining pressure was carried out and the influence of confining pressure variation on brittleness rock was analyzed. In view of the unsatisfactory effect of the existing brittleness index on the evaluation of rock brittleness in target reservoirs, based on the energy conversion relationship in the stress-strain curve, a new brittleness index model, which includes the pre-peak brittleness index, post-peak brittleness index and the comprehensive brittleness index, is established. The results show that the confining pressure has a significant influence on the evaluation of rock brittleness; the pre-peak brittleness increases first and then decreases with the increase of confining pressure, while the post-peak brittleness and comprehensive brittleness decrease monotonously with the increase of confining pressure. The study shows that the brittleness of the reservoir gravel fine sandstone is poorer than that of the fine sandstone, and the brittleness difference is mainly manifested in post-peak brittleness.