泥质岩盖层前期名义固结压力及封闭特性研究

APPARENT PRECONSOLIDATION STRESS AND SEALING CHARACTERISTICS OF ARGILLACEOUS CAP ROCKS

在油气勘探实践中逐渐认识到,仅仅研究盖层当前封闭性能是不够的,还要研究盖层在地质历史中的演化特征及应力状态与脆性–延性匹配关系,从而为盖层封闭的有效性做出评价。以鄂西–渝东地区的不同地质历史及成岩演化程度的泥质岩盖层为研究对象,采用厚壁钢制容器对试样的径向进行约束来模拟单轴应变试验,根据厚壁圆筒理论建立侧向压力和竖向压力之间的关系,获得其前期名义固结压力;并在此基础上,研究前期名义固结压力与单轴抗压强度、声波波速、孔隙率以及黏土矿物含量等因素的关系以及侧压系数的变化规律;初步探讨泥质岩脆性–延性转化特征及相应封闭临界条件,并对几类泥质岩在各种地质条件下封闭能力给出评级。研究对评价不同演化程度泥质岩盖层的封闭性具有重要的指导意义,为下一步建立盖层动–静封闭评价模型奠定基础。

It has been gradually recognised in oil and gas exploration that it is not adequate to study only the current sealing properties of cap rocks. The geological history and the relationship between the stress state and the brittleness-ductility of the cap rock should also be understood for proper assessment of the sealing properties. A uniaxial strain test was carried out for argillaceous rocks at different diagenesis states from the western Hubei-eastern Chongqing area, using a thick-walled steel drum as a lateral restrainer. The relationship between lateral stress and axial stress was established based on the theory of thick-walled cylinders, and the apparent preconsolidation stress was calculated. Subsequently, the relationships between the apparent preconsolidation stress and the uniaxial compressive strength, the ultrasonic velocity, the porosity, the clay mineral content, and the changes in lateral stress coefficients were investigated. Preliminary assessments of the characteristics of the brittleness to ductility transfer of argillaceous rocks are given with the corresponding onset threshold conditions, as well as the sealing capacity under various geological conditions. This work lays the foundation for subsequent work in establishing the dynamic-static sealing model for argillaceous cap rocks. © 2015, Science Press. All right reserved.