钻井液浸泡对库车组泥岩强度的影响及应用研究

 通过岩石三轴抗压实验研究包含在用钻井液体系在内的多套钻井液体系对库车组泥岩强度特性的影响。在已有钻井液性能评价方法的基础上，结合泥岩受不同钻井液体系浸泡24 h后所表现出的应力–应变规律及浸泡前后岩石力学性能、岩石变形和破坏规律，对现用钻井液体系进行筛选和优化研究，获得对该泥岩地层具有更好稳定作用的钻井液体系；通过对不同钻井液体系浸泡前后岩石的强度测试结果，计算分析不同体系下的地层坍塌压力变化，成果应用到现场钻井，稳定井壁及提速效果显著。研究表明：通过优化钻井液体系可以调整和改变泥岩地层的强度特性，最佳状态下的钻井液应该使泥岩浸泡前后表现出基本相同的应力–应变规律；在现有钻井液评价技术中引入岩石强度特性研究成果，不仅将泥岩与钻井液的化学力学耦合作用主动地引到钻井液体系的优化设计当中，而且为从源头上遏制钻井液与目标泥岩地层之间可能出现的化学力学耦合作用对泥岩地层井壁稳定带来的不确定影响奠定了理论基础和方法基础；把钻井液体系设计与优化和井壁力学稳定性相结合，为获得钻井目标泥岩地层坍塌压力，实现低密度钻井液安全、高效钻井奠定了基础；泥岩与不同钻井液体系接触后表现出的变形破坏规律是泥岩地层钻井液稳定井壁性能优化的重要依据，根据泥岩浸泡前后应力–应变特征的研究可以实现对钻井液性能的评价和优选。

RESEARCH ON EFFECT OF DRILLING FLUID ON KUQA SHALE STRENGTH BEHAVIOR AND ITS APPLICATIONS

The effect of different drilling fluids on the strength behavior of Kuqa shale is studied based on triaxial rock mechanical test. Combined with existing drilling fluid performance evaluation methods,stress-strain curve shown by shale after immersion in different drilling fluids for 24 hours and the rock mechanical performance,rock deformation and failure laws,the existing drilling fluid is selected and optimized. One drilling fluid with better stabilization to this kind of shale formation is obtained. Besides,the formation collapse pressure change in different drilling fluids is also calculated and analyzed by testing rock strength before and after immersion in those systems. The findings achieve remarkable wellbore stabilization and speedup effect when they are applied to drilling field practice. Results show that present drilling fluid will remarkably decrease rock strength,and the shale strength performance can be regulated and changed by optimizing the drilling fluid. Rock strength performance research is applied to existing shale drilling fluid evaluation. It can not only induce the chemo-mechanical coupling between shale and drilling fluid initiatively into the optimization procedure of drilling fluid system,but also can establish theoretical and methodological basis to restrain the uncertain effect to shale wellbore caused by coupling chemo-mechanical radically. The research combines the optimization procedure of drilling fluid with wellbore stability. It establishes the basis to obtain collapse pressure of target shale formation and achieve safe,effective drilling with low density drilling fluid. Deformation failure law showed by shale after contacted with different drilling fluid is the important criteria to shale formation drilling fluid stabilization and wellbore performance optimization. The stress-strain curve of shale before and after being immersed by different drilling fluids can lead to achieve evaluation and optimization of drilling fluid performance. The shale strength behavior and collapse pressure are adjustable by optimizing drilling mud components.