龙马溪组页岩地层井壁坍塌周期预测

Prediction of Borehole Wall Collapse Cycle in Longmaxi Shale

针对页岩层理结构和水化特性易导致钻井过程中井壁坍塌的问题,开展岩石三轴力学实验,以确定不同钻井液作用时间下的页岩力学参数;综合考虑层理产状和水化作用对页岩强度的影响,建立页岩地层井壁稳定性分析模型,预测页岩地层坍塌周期。计算分析表明:层理产状变化使得坍塌压力分布更为复杂,水化作用使得坍塌压力在钻井初期迅速升高;层理和水化作用导致的坍塌压力增量分别为0.26~0.38 g/cm^3和0.60~0.79 g/cm^3,缩短了页岩地层的坍塌周期。该模型能准确预测坍塌周期,对优化钻井液性能,调整钻井液密度,保证井壁稳定有重要意义。

The shale bedding architecture and hydration performance will easily result in borehole wall collapse during well drilling operation. Tri-axial mechanical test is used to determine the mechanical parameter values under different mud action times. The bedding occurrence and hydration are comprehensively considered to establish a model to analyze shale formation borehole wall stability and predict shale formation collapse cycle. Analysis shows that the variation of bedding occurrence results in more complex distribution of collapse pressure and hydration rapidly increases the collapse pressure in the early stage of drilling operation. The shale formation collapse pressures are increased by 0. 26-0. 38 g / cm^3 and 0. 60-0. 79 g / cm^3 respectivelydue to bedding occurrence and hydration,which reduce the shale formation collapse cycle. This model could precisely predict collapse cycle,which is of great significance to mud performance optimization,mud density adjustment and improve borehole wall stability.