裂缝性地层防漏堵漏力学机制研究

Leakage prevention and control in fractured formations

井漏是制约安全、快速、高效钻井的技术瓶颈。为了提高防漏堵漏效率,基于断裂力学理论,采用理论分析和数值模拟方法,研究堵漏材料在裂缝内不同位置架桥及考虑不同封堵效率的裂缝尖端应力强度因子、井周有效切向应力及裂缝宽度大小。研究表明,井筒压力一定时,裂缝越长,裂缝宽度和裂缝尖端应力强度因子越大;堵漏材料在裂缝开口处架桥时,井周有效切向应力提高最多,裂缝尖端应力强度因子最小,承压堵漏效果越好;缝内压力越低,井周有效切向应力提高越多,裂缝尖端应力强度因子越小。钻井中应根据裂缝宽度变化范围,选择合理的颗粒尺寸,使架桥位置靠近井筒,并随钻加入防漏堵漏材料,及时封堵微裂缝,防止裂缝持续扩展;同时使用优化的粒度分布及高性能的堵漏材料,形成致密封堵层,可以提高地层承压能力,有效预防井漏。通过现场试验验证,研究结果对现场防漏堵漏工作具有很好的指导意义。

Leakge is a big problem for the safety and efficiency of drilling. The fracture aperture,circumferential stress and stress intensity factor of fracture tip were studied in the case of bridging or sealing in different fracture locations with the numerical method. The results show that,when the wellbore pressure is constant,the longer the fracture,the larger the stress intensity factor and the fracture aperture. The bridging location in the fracture opening has the best effect,with the circumferential effective stress enhanced the most and the stress intensity factor the lowest. The lower the fracture pressure,the more enhanced the circumferential effective stress and the smaller the stress intensity factor. Suitable particle size should be chosen in accordance with the fracture aperture while drilling. Sealing micro-fractures quickly and efficiently by constantly adding LCMs and using high-performance LCMs can prevent the occurrence of pernicious mud loss effectively,and improve the pressure bearing capacity of the formation.