多场耦合作用下泥页岩地层强度分析

STRENGTH ANALYSIS OF FORMATION ROCK FOR POROUS MEDIA COUPLED WITH MECHANICAL-CHEMICAL EFFECTS

研究多场耦合作用下井眼围岩的强度变化问题。在石油钻井环境中,钻井液中存在多种化学成分,钻井液时刻与井壁发生作用,导致井眼周围岩石力学参数为时间的函数。在实验基础上得到岩石强度参数与含水量的关系,基于渗流力学理论,建立孔隙压力与岩石黏聚力及内摩擦角的关系,为研究化学作用对强度参数的影响提供前提,进而进行多孔介质多场耦合作用下的应力分析,建立化学作用对岩石强度参数影响的关系模型。所得结论可深化对泥页岩井壁稳定性的认识,具有一定的工程实用价值。

The strength changing for fully coupled mechanical-chemical behavior of shale formation is studied. The drilling fluid in which there are many chemical reagents which exchange water and ions with rock nearby borehole while drilling： as the result that the strength parameters of shale nearby the borehole are depend on time and position. To analyze the strength changing affected by chemical effect of drilling fluid, a new model is presented. Based on experiment, the relation between strength parameters and water content is obtained; and based on hydrodynamics, the relation between pore pressure and strength parameters is obtained. At the same time, a new model that calculating pore pressure for fully coupled hydraulic-chemical behavior of the shale formation is developed. So using these models, the pore pressure profile and strength profile at different times and positions are investigated. Some conclusions are found that for given poison, with the water content increasing, the pore pressure increases, but the cohesion decreases that will induce the wellbore instability. However, the chemical effect can restrain the increase of water content, so that restrain the increase of pore pressure, and restrain the decrease of cohesion that will be of benefit to enhance the borehole stability. This paper will be of benefit to engineering application for analyzing borehole stability and borehole reinforcing.