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储层砂岩破坏特征及其脆性评价对油气田开采工程具有重要意义,针对胜利油田某油井隔层和油层砂岩岩芯,开展压缩条件下的物理试验及数值模拟。研究结果表明:储层岩芯在三轴压缩条件下的破坏模式以剪切破坏为主,同种围压的隔层岩芯脆性高于油层岩芯,脆性指数B较好地描述了岩芯脆性的变化趋势;分析了储层岩芯主要力学参数与脆性指数B的相关性,即在围压压缩条件下,岩芯峰值强度、扩容点、弹性模量、泊松比、残余强度及残余强度系数随脆性指数B的增加而降低,且用线性关系拟合各参数与脆性指数B的相关性较好;油层砂岩黏土矿物含量大于隔层砂岩是造成其脆性较高的内因,单轴压缩条件下的岩芯断面CT扫描图从细观上反映了2种岩芯脆性破坏特征的不同;在单轴压缩条件下,数值岩芯脆性随弹性模量、压拉比、内摩擦角的增加而增加,随泊松比、残余强度系数的增加而降低,与峰值强度之间的关系不大;在声发射模式上,储层砂岩以前震–主震–后震型和群震型为主,根据物理试验和数值计算结果,总结了脆性指数B与岩芯破裂声发射模式之间的内在关系,即在相同加载速率条件下,低脆性区、中脆性区和高脆性区岩芯声发射模式分别为群震型、前震–主震–后震型及主震型,通过对灰岩试样和不同种类煤体声发射模式的对比,验证了机制讨论的正确性。
The characteristics of reservoir sandstone damage and its brittleness evaluation are of great significance to the exploitation of oil and gas fields. A physical test and numerical simulation of a sandstone core in an oil well of Shengli Oilfield under compressive conditions are carried out. The results show that the failure mode of reservoir core under triaxial compression is dominated by shear failure, and that of the same type of confining pressure is higher than that of reservoir core. The brittleness index B better describes the core The relationship between the main mechanical parameters and the brittleness index B of the reservoir core is analyzed. That is to say, under the confining pressure conditions, the core peak strength, expansion point, elastic modulus, Poisson’s ratio, residual strength and residual The strength coefficient decreases with the increase of brittleness index B, and the correlation between each parameter and the brittleness index B is better fitted by linear relationship. The content of clay mineral in sandstone is larger than that of sandstone, which is the internal factor causing higher brittleness, uniaxial compression Under the condition of the core section of the CT scan shows a microcosm of the two kinds of core brittle failure characteristics of different; under uniaxial compression, numerical core brittleness with the elastic modulus, pressure ratio, internal friction angle increases But decreases with the increase of Poisson’s ratio and residual strength coefficient, and has little to do with the peak intensity. In the acoustic emission model, the pre-earthquake-mainshock-post-earthquake type and the group earthquake type are dominant in reservoir sandstone , According to the physical test and numerical calculation, The intrinsic relationship between brittleness index B and rock burst acoustic emission modes is concluded. Under the same loading rate, the rock acoustic emission modes of low-brittleness zone, medium-brittleness zone and high-brittleness zone are respectively group earthquake type, foreshock- The main shock, the post-earthquake type and the main shock type verify the correctness of the mechanism discussion by comparing the acoustic emission modes of limestone samples with those of different types of coal.