Abstract: In order to prevent stick accidents caused from plastic deformation of salt-bed creep during drilling,the density of drilling fluids in salt formation is commonly calculated using the established constitutive equation and the parameters obtained from experiments,which cannot meet the real requirement of drilling fluid.A new approach for controlling the dilatancy damage and deformation at the nearside of borehole was presented and used to calculate the density of drilling fluid for deep big-thickness salt formation.The acoustic emission signal generated from salt rock damage and deformation was analyzed in laboratory to determine the dilatancy border in the damaged salt-formation.The borehole of deep salt formation is stable only when the octahedral shear stress is below the dilatancy boundary.A comparison of the density of drilling fluid designed by the new method with that of the real drilling indicates that the density window for designing drilling fluids can be simply and effectively applied in the course of drilling in the big-thickness salt formations.

Key words: deep big-thickness salt formation, damage mechanism, dilatancy damage border, borehole stability, density of drilling fluids, design method

摘要： 为防止钻井过程中盐层蠕变发生塑性变形而导致卡钻等事故,传统的方法是建立蠕变本构方程及用实验确定蠕变参数,但是得到的控制盐层蠕变的钻井液密度不能很好地反映实际钻井情况.因而提出一种控制近井筒盐岩不产生扩容损伤变形的新方法,并利用该方法设计了深部巨厚盐层钻井液密度.通过室内试验分析了盐岩损伤变形过程中的声发射信号,确定了盐岩的扩容损伤边界.对于深部盐岩钻井工程中的井壁稳定性问题,根据八面体剪应力准则,井壁盐岩的应力状态控制在扩容损伤边界以内,设计了深部盐层安全钻井液密度窗口.与实际钻井对比分析表明,用该方法设计的钻井液密度窗口能够保证盐层安全钻井,且方法简单而有效,便于现场应用.

关键词: 深部巨厚盐层, 损伤机理, 扩容损伤边界, 井壁稳定性, 钻井液密度, 设计方法