超深层砂岩储层岩石力学特性实验研究

Experimental study on mechanical properties of ultra-deep sandstone

为研究超深层砂岩储层岩石力学特性及其与浅层砂岩的重要区别,通过开展砂岩在超深环境下的形变破坏实验,得到埋藏深度对其力学参数的影响规律。采用室内岩石力学实验方法,获取超深层砂岩单轴压缩、三轴压缩、巴西实验、抗剪实验、脆性指数等岩石力学参数,系统研究砂岩单轴抗压强度、三轴抗压强度、抗拉强度、抗剪强度、内摩擦角、黏聚力、弹性模量、泊松比、脆性指数、裂纹数量及破坏方式等随埋藏深度或围压的变化规律,同时分析埋藏温度对砂岩强度和力学行为的影响。研究表明,超深层砂岩本体在力学强度、抗变形破坏能力、破坏方式等方面与浅层砂岩有显著差异,前者强度更高,脆性表现更差,压剪破坏的难度也更大。超深层砂岩的主要岩石力学参数均随围压的升高而得到强化,岩石强度、脆性等随温度增加而降低,延性特征随围压和温度的升高而显著增强。围压、温度、物性及胶结效果等是影响超深层砂岩力学表现的关键因素。

In order to study the mechanical properties of sandstone in ultra-deep reservoirs and their difference from those of sandstone in shallow reservoirs,research of deformation and failure mechanism of sandstone under ultra-deep in-situ conditions was conducted to obtain influence rules of the burial depth on the mechanical parameters of sandstone. Laboratory rock mechanical experiments including uniaxial compression, triaxial compression, Brazil and shear tests were conducted, and variation laws of uniaxial and triaxial compressive strengths,tensile strength,shear strength,internal friction angle,cohesion,elastic modulus,Poisson’s ratio,brittleness index,fracture amount and failure modes with depth were systematically analyzed. Effects of formation temperature on sandstone strengths and mechanical behaviors were also studied. The results show that there are significant differences of mechanical strength,anti-deformation failure and failure mode between ultra-deep and shallow sandstones. Ultra-deep sandstones have higher strength and lower brittleness index and hence,are notably difficult in shear compression failure. Increasing of the confining pressure strengthen major rock mechanical parameters of sandstone. With increasing the temperature,the strength and the brittleness index decrease while the ductility rises. The confining pressure,temperature,physical properties and diagenesis are critical factors affecting the mechanical properties of ultra-deep sandstone.