裂缝性漏失封堵屏障再破坏机理与稳态重构理论研究

Plugging barrier is used to prevent drilling fluid loss in fractured formations, which is a formally complete wellbore composed of rock mass-fracture-plugging zone. The existing control theories of fluid loss in fractured formations mainly study the mechanism of fluid loss and the formation of the plugging zone, with less consideration of the destruction and reconstruction process of plugging barrier, which makes it difficult to achieve effective plugging. In this project, the repeated fluid loss of fractured formations is taken as the research object. The main factors affecting the control of fluid loss are obtained by analyzing the oilfield data of fluid loss and failure causes of the fluid loss control. Based on laboratory experiments and theoretical analysis, the redestruction mechanism of the plugging barrier influenced by the multi-factor coupling of external factors-rock-fracture-drilling fluid-plugging zone is proposed. Combined with the differences between re-forming and the forming a barrier for the first time, a relational model of the formation-redestruction-reconstruction of plugging barrier is established, and the steady state reconstruction mechanism of the plugging barrier is investigated. Based on the true characterization of rock-fracture-drilling fluid-plugging material, a coupled model used to prevent fluid loss in fractured formations with considering the continuous process of formation-redestruction–steady state reconstruction of plugging barrier is established. Steady-state plugging theory of plugging barrier used to prevent fluid loss is formed with considering the impact of rock-fracture-plugging zone-drilling fluid. The research results provide a theoretical basis for the effective control of repeated fluid loss in fractured formations, and have important theoretical and practical significance to improve the drilling efficiency of fractured formation.

裂缝性漏失封堵屏障是由岩体-裂缝-封堵区构成的形式上的完整井周，现有裂缝性漏失控制理论主要研究裂缝性漏失和封堵区形成机理，较少考虑封堵屏障的再破坏和重构过程，难以实现有效封堵。本项目以裂缝性地层反复漏失为研究对象，拟通过现场裂缝性漏失资料和漏失控制失败成因进行分析，明确裂缝性漏失控制的主控影响因素；基于室内实验和理论分析，揭示封堵屏障在在外界条件-岩体-裂缝-钻井液-封堵区多因素耦合作用下的再破坏机理，结合重构和首次形成封堵屏障的差异，建立封堵屏障形成-再破坏-重构的关系模型，明确封堵屏障的稳态重构机理；基于岩体-裂缝-钻井液堵漏材料的真实表征，建立裂缝性漏失封堵屏障形成-再破坏-稳态重构连续过程耦合模型，形成考虑岩体-裂缝-封堵区-钻井液耦合作用的裂缝性漏失封堵屏障稳态封堵理论。研究成果为有效实现裂缝性地层反复性漏失控制提供了理论基础，对提高裂缝性地层钻井效率具有重要的理论和现实意义。

裂缝性漏失是钻井工程的重大技术难题之一，项目以裂缝性地层反复漏失为研究对象，开展了裂缝性漏失封堵屏障破坏及重构机制研究，并取得了以下成果：（1）基于多类型地层漏失案例，明确了裂缝性地层反复性漏失的主控影响因素；（2）基于漏失封堵屏障的形成和再破坏的过程角度，利用实验和数据分析，厘清了多因素耦合作用条件下裂缝漏失封堵屏障的形成-再破坏的过程和机理；（3）基于多类型堵漏的复合评价过程，考虑裂缝的稳态平衡要素，揭示裂缝性漏失封堵屏障的稳态重构机理；（4）室内建立一套裂缝性漏失封堵屏障形成-再破坏-重构的连续过程物理模拟方法，建立基于有限元-离散元的数值模拟方法，结合破坏与稳态重构机理、物模实验与数值模拟，建立一套裂缝性漏失稳态封堵的堵漏体系，形成裂缝性漏失封堵屏障再破坏机理与稳态重构理论及稳态封堵堵漏技术。项目研究成果具有较好的推广和应用价值，为提高裂缝性地层的堵漏成功率提供了参考。