基于全应力—应变曲线的盖层岩石脆性评价改进方法

An improved method to evaluate brittleness of cap rock based on complete stress-strain curve

地下储气库储气能力与其盖层岩石的脆性有着密切的关系,较脆的盖层在注气过程中容易产生破裂,可能会导致油气渗漏。为合理准确地评价盖层岩石的脆性,通过归纳总结并分析现有的基于硬度或坚固性、强度、矿物组成、应力应变曲线等脆性指标的局限性,提出一种基于全应力—应变曲线的岩石脆性评价改进方法,综合考虑塑性屈服特征、应力状态及屈服阶段对岩石脆性进行评价,并与已有的脆性指标对比以验证方法的有效性。将方法应用于实际储气库评价工程,评价了X9、D5盖层岩石的脆性,得到X9盖层岩石脆性比D5强的结论,即D5盖层岩石塑性变形能力较X9好。研究结果解决了现有评价方法对存在相同屈服平台高度但屈服平台长度不同的岩石脆性评价的不足之处,对储气库盖层岩石脆性评价具有指导意义。

Capacity of gas storage is closely related to brittleness of its cap rock. An over brittle cap rock may bring cracks and lead to leakage of oil and gas during gas injection. In order to evaluate brittleness of cap rock reasonably and accurately,existing indices of brittleness based on hardness and sturdiness, strength, mineral composition and stress-strain curve were summarized and investigated,and their limitations were analyzed. An improved method for rock brittleness evaluationbased on complete stress-strain curve is proposed. Influences of plastic yielding,stress state and yield stage are comprehensively taken into account. Validity of the proposed method is proved by comparing the method with the existing brittleness indices. With the method being applied to evaluate brittleness of X9 and D5 in a practical project,a conclusion that X9 is more brittle than D5 can be drawn,namely D5 has a better plastic deformation performance. The research findings solve the deficiencies of existing brittleness evaluation methods with a same yielding platform height but a different length,and the findings are directive on brittleness evaluation of cap rock of gas storage.