鄂尔多斯盆地大牛地气田下石盒子组高分辨率层序地层分析

下石盒子组是鄂尔多斯盆地大牛地气田的主要产气层位,沉积分布特征复杂,常规的小层对比方法难以准确识别其地层层序。在对测井、钻井及地震资料的基准面旋回识别标志进行分析的基础上,运用高分辨率层序地层学原理,在下石盒子组识别出3个中期旋回(MSC3—MSC5)和15个短期旋回(SSC13—SSC27)。中期旋回和短期旋回均可分为对称和非对称两种类型,其中对称型均细分为3个亚类:上升半旋回大于下降半旋回型(C1)、下降半旋回大于上升半旋回型(C3)两种不完全对称型及两半旋回近于相等的近完全—完全对称型(C2)。建立了中、短期旋回等时地层格架,并在此基础上进行了砂体追踪对比与分布模式分析,提高了储集层预测的准确性。图7表1参18

High-resolution sequence stratigraphic analysis of Lower Shihezi Formation of Daniudi Gasfield in Ordos Basin

The Lower Shihezi Formation is a main gas producing formation,which is so complex in deposition that it is difficult to identify its stratigraphic sequences using conventional sublayer correlation.Based on the analysis of datum cycle markers in logging,drilling and seismic data,3 moderately-long-term(MSC3-MSC5) and 15 short-term cycles(SSC13-SSC27) were identified in the formation using the concept of high resolution sequency stratigraphy.The moderately-long-term and short-term cycles can be subdivided into symmetric and asymmetric types.The former type can be subdivided into 3 subtypes,i.e.C1 with the uplifting semi-cycle more than the subsiding semicycle,C3 with the uplifting semi-cycle less than the subsiding semi-cycle,both of which are incomplete symmetric,and C2 with two equal semicycles.The isochronous stratigraphic framework was established for moderately-long-term and short-term cycles.Tracing and correlation of sand bodies were conducted,with the accuracy of reservoir prediction improved.