费尔干纳盆地井壁失稳机理研究

STUDY OF BOREHOLE INSTABILITY MECHANISM IN FERGANA BASIN

井壁失稳是制约费尔干纳盆地油气勘探开发的重要因素之一。地质工程资料的综合分析表明,费尔干纳盆地由于受到构造运动的挤压,地应力高、地层破碎,特别是地层裂缝发育且存在多个压力层系,钻井过程中井下垮塌、井涌、漏失等复杂事故频繁发生。费尔干纳盆地多种井壁失稳机理共存、互相作用,以裂缝性地层的井壁失稳为主,选择合理的钻井液密度和良好的封堵性可有效防止费尔干纳盆地钻井过程中的井壁失稳问题。在深入分析井壁失稳力学机理的基础上,建立了费尔干纳盆地合理钻井液密度的确定方法,研究结果在吉达4井应用获得良好效果,卡钻等事故大大减少,钻井周期缩短了32%。

Borehole unstablility is one of the major problems that hamper the exploration and development of oil & gas in Fergana Basin in Central Asia. Comprehensive analysis of geological and engineering data indicated that,due to the extrusion of tectonic movement,the features of Fergana Basin were high in- situ stress and fractured formation with strong water- sensitive and abnormal overpressure generating which caused frequently borehole collapse and lost circulation problems. Borehole stability in Fergana Basin was influenced by many interactive mechanisms with the unstability of fractured formation. The key to prevent the unstability of fractured formation was proper drilling fluid density and better fluid sealing characteristics. The mechanisms of borehole unstablility in Fergana Basin were studied,a method for properly determining drilling fluid density was presented,and its application in Well JIDA4 got good results,the drilling cycle was decreased by 32%.