构筑井周坚韧屏障:井漏控制理论与方法

Constructing a tough shield around the wellbore:Theory and method for lost-circulation control

分析了低承压能力地层致漏机理,概括出应力笼、阻渗带和强固环3种地层强化理论,建立了不同理论指导下的地层承压能力强化模型,总结了理论的适用条件及对材料的要求,并通过现场实例分析了各理论的应用效果。裂缝扩展与延伸、渗流效应和地层压力衰竭是导致地层承压能力降低的主要因素。应力笼理论适用于裂缝欠发育的低渗—致密地层,要求材料具有足够的抗压强度和合理的硬度、粒度级配;阻渗带理论适用于孔隙型和裂缝性地层,要求材料具有高表面摩擦系数、弹性变形量、体积分数和强度,合理匹配刚性颗粒、纤维和弹性颗粒可提高封堵承压能力;强固环理论适用于裂缝/孔洞性地层,要求材料胶结岩体软弱结构面或形成稳定的高强度结构体。现场应用实例表明,3种理论具有良好的地层承压能力强化效果。

According to the mechanism analysis of drilling fluid loss in the formation with low pressure-bearing capacity, three basic theories, including stress cage, plugged zone, and strength ring for wellbore strengthening, were summarized and the corresponding models were established. The application conditions for the three theories and their requirements on the material properties were determined based on the models. Fracture propagation, filtration effect of drilling fluid and depleted formation pressure are the major factors that lead to low formation pressure-bearing capacity. The stress cage theory strengthens the wellbore by establishing the balance between wellbore pressure and formation stress. It is applied in the formation with low-development fracture. It demands that the material has enough compressive strength and reasonable size distribution to sustain certain fracture width and low fracture pressure. The plugged zone theory works by establishing the balance between wellbore pressure and formation pressure. It is suitable in pore an fractured formation and demands that the plugging material has the properties of high surface friction coefficient, resilient deformation, volume fraction and strength to create the synergy effect of rigid granule, fiber and resilient particle. The strength ring theory applies to fracture-vug formation and it requires that the material can cement the weak structural plane or form a high strength body to separate the pressure propagation from wellbore to formation. The effect and guiding significance of the three theories were further confirmed by field applications.