泥页岩地层水化后井眼周围应力的计算模型

A MODEL OF CALCULATING THE STRESS DISTRIBUTION NEAR THE BOREHOLE UNDER HYDRATION

由于泥页岩中含有水敏性黏土矿物,当与钻井液接触时,泥页岩与钻井液相互作用,产生水化膨胀,不仅改变了井眼周围的应力分布,而且由于吸水使得泥页岩的强度降低,这就使得泥页岩地层的井壁失稳问题非常严重。水化作用后的围岩,在假定泥页岩为线弹性的条件下,建立了均匀地应力作用下泥页岩水化后井眼周围应力分布的计算模型。对该模型利用差分方法进行了求解,可以编制程序,该程序可以计算出泥页岩水化后井眼周围岩石的含水量分布、井眼周围的应力分布及保持井壁稳定所需的坍塌压力。

Shale usually contains a significant amount of water-sensitivity clays. When in contact with drilling fluid, shale and drilling fluid interact with each other, which lead to swelling due to hydration. This not only alters the stress distribution near the borehole, but also reduces the strength of the shale. So, the problem of the borehole instability in shale becomes very serious. While the shale is linear elasticity under the assumption condition, a model was established to calculate the stress distribution near the borehole under hydration. The model was discriminated by using difference method to carry out programming. The program can calculate the distribution of the water content, the stress distribution and the collapse pressure that is necessary for keeping the borehole stable.