钻井液致密承压封堵裂缝机理与优化设计

针对钻井液防漏堵漏技术难题，借鉴微观颗粒物质力学“强力链”基本原理，提出了评价防漏堵漏材料的颗粒强度、颗粒弹性、颗粒表面摩擦等主要精细化技术指标，建立了相应的实验表征方法，揭示了基于微纳米尺度的钻井液致密承压封堵机理，给出了钻井液强化致密承压封堵优化设计方法，即通过合理的颗粒类型、粒度级配与浓度控制，刚性颗粒、弹性颗粒、纤维材料等协同封堵裂缝，可形成具有“强力链网络”的致密承压封堵层，显著提高地层承压能力。研制了钻井液封堵特性评价动态模拟实验装置，可模拟不同地层温度、压力条件下不同开度裂缝的漏失与封堵过程，为致密承压封堵机理及钻井液防漏堵漏效果评价提供了实验方法。采用所研制的封堵动态模拟实验装置，优化了不同开度楔形裂缝的强化致密承压封堵钻井液配方。实验结果表明，其具有良好的自适应裂缝开度致密封堵特性，承压能力达8 MPa以上，可显著提高地层承压能力。

Tight fracture-plugging mechanism and optimized design for plugging drilling fluid

According to the basic principle of "force-chain" in micro-granular matter mechanics, the key fine technical indices were proposed to evaluate the particle strength, particle elasticity and surface friction of loss protection and sealing materials, so as to solve the technical difficulties in loss protection and sealing of drilling fluid. Meanwhile, the corresponding experimental characterization method was established to reveal the pressure containment and tight plugging mechanism of drilling fluid at the micro-nano scale and put forward the optimization method of tight plugging drilling fluid, i.e., using reasonable particle types, particle size gradation and concentration control, rigid particles, elastic particles and fibers were synergized to plug fractures, so as to form tight pressure containment and sealing zones with a strong force chain network and greatly improve the formation pressure containment ability. The newly-developed experimental apparatus for evaluation and dynamic simulation on the plugging characteristics of drilling fluid can simulate the loss and plugging process of fractures with different widths under different formation temperatures and pressures, providing a experimental method for pressure containment and tight plugging mechanism and plugging effect evaluation. Using this novel plugging dynamic simulation equipment, the strengthened tight-plugging formulas are also optimized for drilling fluid at the wedge fractures with different widths, which exhibits the tight plugging characteristics self-adapting to fracture widths with pressure resistance up to 8 MPa, thus improving the pressure containment ability of formations significantly.