为了解决深层蠕变性硬石膏岩地层钻井液密度难确定的问题，为套管类型选择及油气高效钻探提供依据。通过设计三轴实验对蠕变性硬石膏岩应力-应变曲线变化特征进行分析，对扩容点进行了定义。利用扩容准则描述了最大八面体剪应力分布特征。硬石膏岩三轴测试中扩容边界的八面体剪应力与平均应力间满足指数关系，钻进中若要地层维持稳定，最大八面体剪应力应位于扩容边界以内。利用扩容准则及Mogi-Coulomb准则确定了单井目的层钻井液安全密度，并与实际值进行对比，结果表明：基于扩容准则方法确定的钻井液安全密度与实际值极为相符，且纵向离散度小。由于常规Mogi-Coulomb准则方法所需待定参数较多，参数非确定性较强，因而最终确定的钻井液安全密度与实际值偏差较大。扩容准则方法可作为备选方案，对指导油气高效钻探具有重要参考价值。%In order to solve the problem that the drilling fluid density is hard to determain in creep anhydrite rock strata , and provide reference for oil and gas efficient drilling and selection of casing type .the stress-strain curve phase variation characteristics of creep anhydtite rock were analyzed by designing triaxial experiment .At the same time, the expansion point was defined .Using the capacity criterion to describe the distribution characteristics of the largest octahedral shear stress .The expansion boundary of anhydrite rock in triaxial tests shows that there ’ s index relationship of the octahedral shear stress and the average shear stress ,for stability of the formation,the big-gest octahedral shear stress should be located in the border of expansion boundary .Dertermine the safe drilling fluid density of single well of the purpose layer using the expansion criterion and Mogi-Coulomb criterion,compared with the actual values,it shows that,there’s well accords with the actual values when using the expansion criterion ,and the longitudinal dispersion degree is small .Because it needs a lot of input parameters of conventional Mogi-Coulomb criterion,the uncertain of these parameters are strong ,so there’ s large difference for the detainmined safe drilling fluid density compared with the actual value .The expansion criterion method put forward can be used as an alterna-tive plan,there’ s a certain reference value to guide the effective oil and gas drilling.
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