深部应力敏感裂缝性地层漏失封堵力学机理研究

In the process of oil and gas drilling, lost circulation posed great challenge to the whole industry both in technique and economic aspects. In particular, when encountered the stress sensitive and naturally fractured formation in the deep drilling process, lost circulation is more serious. Since the traditional plugging technique evaluation method with fractured plates cannot simulate the stress sensitivity and pore structure characteristics of the real core, this project proposed to develop large size true triaxial lost circulation control simulation evaluation device, in order to realize the loss circulation control simulation research close to the real situation in laboratory. Only in this way, it is possible to analyze the mechanical mechanism of the plugging confined structure failure and study the mechanism of the lost circulation path initiation and propagation in stress sensitive and naturally fractured formation. In view of the above objectives, the true triaxial loss circulation control simulation experiments will be done with artificial fractured core samples and a comprehensive study will be conducted using rock mechanics, fracture mechanics, experimental mechanics and other theoretical approaches. To this end, the corresponding relationship between the geometry of laboratory core and the true formation, experimental parameters, field operational parameters will be study based on the similarity theory. Considering the stress sensitivity difference due to fractures and pore features, microscopic mechanism of plugging material used in naturally fractured formation will be studied. Mechanical mechanism of lost circulation path initiation and propagation in stress sensitive and naturally fractured formation will be discussed and efficiency evaluation method for formation fracturing capacity will be established. The whole study can provide a theoretical basis for the realization of safe drilling under a narrow density window.

在油气钻井过程中，井漏问题给石油工程界带来极大挑战，尤其在深井钻井过程中遇到应力敏感裂缝性地层时，漏失问题更加突出。利用裂缝性钢板评价封堵的传统方法无法模拟应力敏感性及真实岩心孔隙结构等特征。本项目提出开发大尺寸真三轴钻井堵漏模拟评价装置，实现接近真实环境的室内裂缝性地层的漏失封堵模拟研究，分析封堵承压结构体破坏的力学机理，解决漏失通道开启与扩展的力学问题。鉴于以上目标，只有通过对人造裂缝性岩心试样进行真三轴的漏失封堵模拟实验，并运用岩石力学、断裂力学、实验力学等理论方法进行综合研究。为此，将根据相似理论，研究室内岩心几何尺寸与真实地层、实验参数、与现场施工参数的对应关系；考虑裂缝和孔隙特征造成应力敏感行为的差异，研究堵漏材料封堵裂缝性地层的微观机理，揭示堵漏过程中裂缝性漏失通道封堵开启与扩展的力学机理，建立裂缝性漏层承压能力的时效性评价方法。本项目为现场窄密度窗口下安全钻井提供理论支撑。

在油气钻井和地质勘探钻井过程中，井漏问题给石油工程界带来了极大的挑战，尤其在深井钻井过程中遇到应力敏感裂缝性地层时，漏失问题更加突出，由于地层压力变化异常，裂缝存在形态复杂多样，漏失引起的事故和危害呈多样化。. 根据应力敏感裂缝性地层的漏失特点，采用模拟地层条件下的岩心浸泡试验和常规岩石力学试验，测试了裂缝性和基质性灰岩在基浆和堵漏浆中作用不同时间后的岩石力学强度参数。通过实验结果对比，探讨了基浆和堵漏剂对于裂缝性和基质性灰岩的强度弱化效应。利用扫描电镜观察浸泡后的岩心，从微观角度分析了堵漏材料对裂缝性和基质性灰岩的封堵机理。. 由于堵漏颗粒架桥堆积形成的封堵区域具有明显的离散特征，利用颗粒流离散元方法模拟堵漏颗粒的承压作用机理，分析了颗粒间接触力分布特征及影响因素，结果表明颗粒受力非常不均匀，粗颗粒间接触力高于细颗粒，单颗粒架桥承压效果优于多颗粒架桥。承压封堵裂缝时缝内压力分布分为井内压力段、封堵区域压降段和缝尖压力段，封堵长度和钻井液粘度增加、封堵渗透率降低，裂缝易于满足止裂条件；裂缝长度、井内压力增加，裂缝不易止裂；封堵位置由裂缝尖端逐渐靠近裂缝入口时，裂缝越易满足止裂条件。. 利用真三轴承压堵漏模拟实验装置开展了颗粒粒径、堵漏材料类型、堵漏材料浓度、水平应力差和裂缝形态对堵漏承压效果影响的实验研究，结果表明堵漏配方中必须含有架桥颗粒，堵漏材料易于堆积在裂缝扭曲变形、分叉转向位置，而纤维可快速形成封堵且易于堆积在裂缝入口处。对裂缝内堵漏材料封堵渗透率进行了评价，细颗粒含量越高，封堵渗透率越低；多种堵漏材料复配使用可有效降低封堵渗透率。