裂缝性漏失桥接堵漏颗粒动力学行为细观模拟研究

Lost circulation in fractured formation has always been a major technical problem during the oil & gas well drilling. The most common cure of this problem is introduction of granular lost circulation material (LCM) into the drilling fluid system. The fact that the acquired information from laboratory experiments is limited, and that theoretical models don’t fully consider the effect of particle properties on the dynamics characteristics of bridging particle, which causes the present studies can’t in depth reveal the mechanism of fracture sealing by bridging particle material. The project intends to establish a dynamics model of bridging particle based on DEM-CFD numerical coupling method at a particle scale, which consider a series of less studied properties of granular LCM, such as particle shape irregularity, particle surface friction properties and particle breakage. The morphology and physical properties parameters of bridging particle will be finely characterized using the digital image analysis and some modern testing technology. The dynamic evolution processes, such as particle migration, bridging, filtration, packing and breaking, can be simulated by considering the coupling effects between bridging particle and drilling fluid. It will solve scientific issues of unclear understanding of the dynamics behavior of the bridging particle in fracture in mesoscale. What’s more, it has important academic value for understanding the mechanism of the loss control technology, and would expand and supplement particle dynamics.

桥接堵漏是解决油气钻井中裂缝性漏失的重要方法，明晰桥接颗粒动力学行为特性是科学利用桥接法堵漏的核心基础。长期以来，室内堵漏模拟实验所获得的颗粒动力学信息有限，桥接理论模型也无法描述颗粒动力学演变过程，难以深入认识桥接堵漏颗粒动力学行为特性。本项目拟采用离散元-计算流体动力学（DEM-CFD）耦合数值模拟方法，考虑桥接颗粒外形非规则性、表面摩擦特性、主体破碎及其尺寸效应等因素，运用数字图像分析及CT扫描等现代测试技术对桥接颗粒的细观形貌、内部结构及物性特征精细表征，建立非规则可破碎颗粒分级离散元模型；考虑颗粒与流体相互作用，建立桥接颗粒-钻井液双向耦合数值模型，模拟桥接堵漏颗粒的运移、架桥、过滤堆积及挤压破碎等动态演化过程，揭示细观尺度下裂缝性漏失桥接堵漏颗粒的动力学行为特性。研究成果对认识裂缝性桥接堵漏作用机理具有重要科学价值，同时也是对颗粒物质力学的丰富与发展。

桥接堵漏技术是解决裂缝性漏失的重要方法，清晰认识桥接堵漏颗粒运移-阻塞机理及其动力学过程是其科学核心基础。项目考虑桥接堵漏颗粒材料外形非规则、内部可能存在缺陷，利用图像处理技术采集、分析了桥接堵漏颗粒形貌细观特征；为了精细表征桥接颗粒物的物性特征，量测了各类桥接颗粒材料的物性特征控制参数，并采用虚拟实验标定了关键细观参数；利用加长裂缝堵漏模拟实验装置，开展了天然裂缝性桥接堵漏模拟实验，量测了堵漏实验滤失量、堵塞层位置、厚度及颗粒体积分数等参数；验证了现有桥接堵漏材料粒度设计准则（规则），提出了裂缝性桥接堵漏颗粒粒度设计方法；对含有桥接堵漏颗粒的钻井液非牛顿流场进行建模，重点考虑流体对颗粒的浮力、拖曳力及压力梯度力等作用力，流体与颗粒间的作用力及动量双向交换，建立了裂缝性漏失桥接堵漏颗粒-非牛顿流体双向耦合数值模型,追踪桥接颗粒的位置、速度及接触力（力链）等动力学参数的时空演变过程，揭示了桥接堵漏颗粒运移-阻塞机理及其动力学过程。研究成果丰富和发展了颗粒封堵理论，为裂缝性地层安全高效钻井提供了理论支撑。