致密砂岩储层“四性”特征及有效厚度下限值的确定——以鄂尔多斯盆地陇东地区山1段为例

Four-property characteristics of tight sandstone reservoirs and determining their minimum effective thickness:An example from Shan 1 Member,Longdong area,Ordos Basin

下二叠统山西组1段(以下简称“山1段”)气藏为鄂尔多斯盆地陇东地区的主力气藏,为了研究山1段储层的岩性特征、物性特征、电性特征及含气性特征,即“四性”特征,明确“四性”关系,深化气藏地质认识,确定储层有效厚度下限值,为优化试气层段及储层改造参数提供依据,进一步提高天然气开发效果。以岩心分析资料、岩心孔隙度、岩心渗透率、测井参数为研究对象,利用岩心观察、薄片鉴定、高压压汞法、密闭取心法、核磁共振实验法等手段,通过孔隙度—渗透率交会、多元回归方法分析了储层的“四性”特征并指出了其相互关系。研究结果表明:①山1段含气储层岩性为石英砂岩、岩屑石英砂岩;②电性参数下限值分别为电阻率30Ω·m,声波时差206μs/m,密度2.59 g/cm^3,泥质含量15%;③物性下限值分别为渗透率0.36 mD,孔隙度4.1%,含气饱和度46%。结论认为:①山1段砂岩物性较差,属于典型的致密砂岩储层;②“四性”特征相互关联,岩性特征是“四性”特征的基础,决定了储层的电性、物性及含气性特征;③对建立的孔隙度、渗透率、含气饱和度解释模型分别进行验证,精度高,取值合理;④以确定的储层有效厚度下限值预测试气结果,与实际结果对比验证,符合率高,能满足开发需求;⑤目前陇东地区天然气处于开发初期,物性下限值对于储层改造参数的确定具有重要影响,需要根据开发进度及时调整优化。

Most gas reservoirs of Lower Permian Shanxi 1 Member is the principal target in Longdong area,Ordos Basin.In order to investigate four characteristics including lithological,electric,physical,and gas-bearing properties(so-called four-property characteristic)of Shan 1 reservoirs,clarify a four-property relationship,deepen geological understanding,determine the minimum effective thickness,provide basis for optimizing test intervals and reservoir-reforming parameters,and further increase an development effect,this paper took core analysis data,core porosity and permeability,and welllogging parameters as objectives to analyze their four-property characteristics by means of two methods of both porositypermeability crossplot and multiple regression,core observation,thin-section identification,high-pressure mercury injection,sealed coring,and NMR experiments.In addition,the relationship among four-property characteristics were presented.Results show that these gas-bearing reservoirs of Shan 1 Member are lithologically composed of quartz sandstone and lithic quartz sandstone;the lower limits of electric parameters are individually resistivity 30Ω·m,interval transit time 206μs/m,density 2.59 g/cm^3,and shale content 15%;and the lower limits of physical properties are permeability 0.36 mD,porosity 4.1%,and gas saturation 46%,respectively.It's concluded that(1)Shan 1 Member may be classified as typical tight sandstone reservoirs because sandstone is featured by poorer physical property;(2)the fourproperty characteristics are correlative,and lithological one are the essential of"four-property"characteristics and dominates other three ones;(3)several established interpretation models of porosity,permeability,and gas-saturation are verified respectively,showing that they are of high precision and reasonable valuing;(4)some results from gas test are predicted by the determined minimum effective thickness and compared with actual ones,and their verification illustrates a high coincidence rate enough to meet a development demand;and(5)at present,gas development in Longdong area is still in an initial stage,and the lower limits of physical properties have an important influence on determining reservoirreforming parameters,so they should be adjusted and optimized in time according to development progress.