裂缝封堵失稳微观机理及致密承压封堵实验

Microcosmic mechanism of fracture-plugging instability and experimental study on pressure bearing and tight plugging

裂缝性地层堵漏过程中,桥接堵漏材料形成的封堵层受力学因素影响易发生失稳破坏,导致封堵层承压能力较低,产生重复性漏失。基于裂缝封堵层微观结构受力分析,探讨了挤压破碎失稳、摩擦滑动失稳、剪切错位失稳、渗透漏失失稳等4种封堵失稳破坏形式,提出了粒度降级率、表面摩擦系数、剪切强度、堆积孔隙比等评价封堵失稳的特征参数;给出了裂缝致密承压封堵物理模型,即通过合理的堵漏材料类型和粒径级配优化控制,有利于在裂缝入口端附近形成致密承压封堵层。研制了长裂缝封堵模拟实验装置,开展了致密承压封堵模拟实验研究。实验表明,不同类型堵漏材料优化协同作用,可增大封堵层抗压强度、表面摩擦系数和抗剪切强度,形成紧密堆积结构,易在裂缝入口端附近形成致密承压封堵层,提高裂缝封堵突破压力,预防井漏。

While plugging fractured formations,the sealing zone formed by loss circulation materials are prone to instability due to the effects from mechanical factors,resulting in low pressure bearing ability of sealing zone and repetitive loss.Based on the micro-structural stress analysis of fractured sealing zone,this study explores the compressive-crush instability,friction-sliding instability,sheardislocation instability and seepage-loss instability pattern of sealing zone,and then proposes the characteristic parameters for evaluating plugging instability,such as granularity degradation rate,surface friction coefficient,shear strength and packing pore ratio.The pressure bearing and tight plugging physical model is put forward,i.e.,by controlling the reasonable loss circulation material types and particle size gradation optimization,it is favorable to form pressure bearing and tight sealing zone near the inlet end of fracture.The experimental apparatus with long fracture slot is newly developed to carry out pressure bearing and tight plugging simulation experiment and the experiment indicate that different loss circulation materials are synergized to improve compressive strength,surface friction coefficient and shear strength for forming tight packing structure,prone to generate pressure bearing and tight sealing zone near the inlet end of fracture and improve plug breaking pressure to prevent loss.