微观地质特征对硬脆性泥页岩井壁稳定性影响与对策研究

STUDY ON THE INFLUENCE OF MICROSCOPIC GEOLOGIC CHARACTERISTICS ON WELLBORE STABILITY OF BRITTLE SHALE

硬脆性泥页岩引起的井壁失稳是钻井过程中经常遇到的一个十分复杂的难题。利用扫描电镜、压汞、X-衍射、比表面分析仪等岩矿测试手段研究硬脆性泥页岩的微观地质特征,根据研究结果分析其对硬脆性泥页岩井壁失稳的影响,并提出保持硬脆性泥页岩井壁稳定的措施,为硬脆性泥页岩井壁稳定性研究提供一种新思路。研究结果表明,硬脆性泥页岩中发育的一部分微裂缝是导致井壁失稳的重要原因。在钻井过程中,钻井液滤液沿着泥页岩中的微裂缝进入到地层内部,导致粘土矿物的水化膨胀,使孔隙压力增加,泥页岩强度降低,最终发生井壁失稳。最后根据研究结果提出在钻井液中加入一部分和泥页岩孔喉相匹配的封堵粒子,期望它能降低或阻止钻井液滤液在泥页岩中的漏失,达到稳定井壁的目的。

Wellbore instability caused by brittle shale is a very complex problem during drilling.This paper studied the microscopic geologic characteristics of brittle shale by mineral testing ways such as SEM,mercury injection,X-ray diffraction and specific surface area analyzer.According to the studying results,the influence of the microscopic geologic characteristics of brittle shale on wellbore instability has been analyzed,and the measures to stabilize side wall have been proposed.This paper provided one kind of new way to study wellbore stability of brittle shale.The studying results showed that wellbore instability of brittle shale is mainly caused by the micro-fracture in the brittle shale.During drilling,filtrate of the drilling fluids invades the brittle shale through micro-fracture,resulting in swelling of the clay minerals,increase of pore pressure,and decrease of brittle shale's intensity,finally leads to wellbore instability.Finally,the paper put forward a new way to stabilize wellbore of brittle shale.It is suggested that putting some particles compatible with pore size distribution of brittle shale into drilling fluids to plug micro-fracture,thereby decrease or prevent filtrate of drilling fluids to leak into inside of brittle shale,and attain the goal of wellbore stabilization.