适用于硬脆性泥页岩的钻井液井壁稳定性评价方法

Evaluation Method for Wellbore Stability of Drilling Fluid Applying to Hard-brittle Shale

陈金霞

CHEN Jinxia

为了提高硬脆性泥页岩的井壁稳定效果， 通常强调钻井液的封堵能力， 而未考虑钻井液水化作用对泥岩力学强度的影响。在传统钻井液封堵性能评价方法的基础上， 重点考察了钻井液对岩石力学强度的保持能力， 开展了钻井液水化作用对岩石抗压强度、 抗张强度以及地层坍塌压力增量影响等评价实验， 形成了一套适用于硬脆性泥页岩的井壁稳定性评价方法。结果表明， 优良的井壁稳定性能不仅要具备较低的渗透封堵滤失量、 良好的延缓压力传递能力， 对岩心裂缝较高的封堵率， 而且要具有较强的岩石力学强度保持能力 （钻井液作用后岩石力学强度降幅最小， 且地层坍塌压力增量最低）。建议初步开展 PPT渗透封堵实验、 压力传递实验及岩心裂缝封堵实验等， 初选性能较好的钻井液配方， 再进行钻井液作用对岩石力学强度的影响实验， 结合钻井液作用对坍塌压力、 破裂压力的影响分析， 进一步确定井壁稳定钻井液最佳配方。该套评价方法从岩石力学角度全面评估了钻井液的井壁稳定性能， 为体系的优化提供了借鉴。图 12表3参 15

In order to improve the wellbore stability of hard-brittle shale，the plugging ability of drilling fluid was usually emphasized，but the effect of drilling fluid hydration on mechanical strength of shale was not considered. Based on traditional drilling fluid plugging performance evaluation method，the rock mechanical strength retention ability of drilling fluid was investigated. The effect of hydration of drilling fluid on rock compressive strength，tensile strength and pressure increment of formation collapse was carried out. And a set of evaluation method for wellbore stability of hard-brittle shale was developed. The results showed that the excellent wellbore stability should have a low penetration plugging filter loss，excellent ability to delay the delivery of pressure，high plugging rate for core cracks，and strong rock mechanical strength retention ability，i. e. ，the decrease of rock mechanical strength was minimum，and the increment of collapse pressure was the lowest after drilling fluid immersion. It was suggested that PPT permeability plugging test，pressure transfer test and core fracture plugging test should be carried out initially， the drilling fluid formula with better performance should be selected，and then the influence experiment of drilling fluid on rock mechanical strength should be carried out，combined with the impact analysis of drilling fluid on collapse pressure and fracture pressure. Finally，the optimum formula of drilling fluid with good wellbore stability could be further determined. From the perspective of rock mechanics，this set of evaluation methods comprehensively estimated the wellbore stability performance，and provided reference for the optimization of drilling fluid.