水敏性泥页岩地层临界坍塌时间的确定方法

A Method for Determining the Critical Time of Wellbore Instability at Water-sensitive Shale Formations

钻井过程中,井眼的形成打破了地层原来的力学和化学平衡,水敏性泥页岩地层不同程度的水化膨胀改变了井周围岩应力,同时也改变了地层的材料特性。这些改变具有时空分布的特点,给井壁地层失稳预测带来了盲目性。从泥页岩的本构关系出发,结合地层的水化特性,预测了不同钻井液密度和滤失条件下地层的临界坍塌时间,结果对实际钻井有指导意义。

The process of drilling a well results in the change of the original mechanical and chemical balance of formations, with the developm ent of a stress concentration and hydration stresses induced by volume dilation because of the water-sensitive shale formations absorbing mud filter. In additi o nal, the material properties of formations are changed. All these changes vary f rom time and space, so the prediction for wellbore stability becomes troublesome issue. In this paper, the relationship among the critical time of wellbore inst ability, mud weight and filter loss is established on the basis of the constitut ive relationship of the shale and the hydration characteristics of formations. T he results can guide drilling practices.