双饱和度法在三湖地区低饱和度气层识别中的应用

Application of dual saturation method in the low saturation unconsolidated gas-bearing sandstone in Sanhu area

(长江大学油气资源与勘探技术教育部重点实验室,湖北荆州434023)

Chen Xian,Key Laboratory of Exploration Technologies for Oil and Gas Resources,Ministry of Education,Yangtze University,Jinzhou 434023,China

柴达木盆地三湖地区第四系地层沉积疏松、储层泥质含量高、低饱和度气层发育。低饱和度气层的三孔隙度曲线“镜像”不明显,地层电阻率低,难以识别。由于高泥质含量的影响,利用阿尔奇公式计算含水饱和度效果较差,因此采用了可以消除泥质影响的印度尼西亚公式。影响束缚水饱和度的因素有很多,三湖地区主要受泥质的影响。基于纯气层处含水饱和度等于束缚水饱和度的原理,建立了束缚水饱和度与泥质含量的定量关系,以此确定束缚水饱和度。在较准确地计算含水饱和度和束缚水饱和度的基础上,结合录井和试气等资料,利用交会图技术建立了双饱和度法识别和区分低饱和度气层的解释标准。实际应用证明,双饱和度法能较好地区分低饱和度气层以及水层。

The Quaternary of Sanhu area in Chaidamu Basin develops loose sedimentary gas reservoir with low-saturation and high shale content.In low-saturation gas reservoir,the “mirror image” of tri-porosity curve is not obvious and the resistivity is low,so the reservoir is difficult to identify.For the impact of high shale content,bad result will be obtained by using Archie equation to calculate water saturation.Therefore,we utilized Indonesia equation that can reduce the impact of shale content.There are many factors influencing the irreducible water saturation,and the main impact factor in Sanhu area is shale.Based on the principle that the water saturation of pure gas layer is equals to irreducible water saturation,the quantitative relationship between irreducible water saturation and shale content has been established to determine irreducible water saturation.Along with the accurate calculation of water saturation and irreducible saturation,combining with the log data and gas testing data,the crossplot analysis was used to establish the interpretation standard of identifying and distinguishing low-saturation gas layer by dual saturation method.Actual application results indicate that the dual saturation method can well distinguish low-saturation gas layer and water layer.