岩相角度的五峰组页岩小尺度沉积构造系统分类与解析——兼论对深层页岩精细评价的影响

Systematic classification and characterization of small-scale sedimentary structure of the Wufeng Formation shale based on lithofacies——Influence for the evaluation of deep shale reservoirs

深层页岩储层勘探开发高度依赖对页岩储层精细特征的认知,对小尺度沉积构造的精细解析可以为深层页岩储层勘探开发提供重要数据支撑。该研究以川南渝西地区大足区块五峰组页岩代表性钻孔的深层储层样本为例,通过手标本研究、岩石薄片观察、显微成像分析及地球化学测井数据分析等方法,对页岩储层小尺度沉积构造开展了系统分类研究和精细解析。结果表明,研究区内五峰组宏观非均质性相对较弱,但微观非均质性极强,可以从岩相角度将常见小尺度沉积构造划分为10个类型,其中包含4类粉砂质泥质纹层沉积构造、3类富硅质沉积构造以及3类组合类型沉积构造;五峰组页岩可以划分出多个精细小层,具有不同的石英等矿物来源以及沉积构造特征,反映了沉积条件的差异。在实际应用方面,对小尺度沉积构造的精细解析与认知可以为深层页岩优选提供一项关键指标。以上成果认识,对深层页岩精细选层具有一定的指导作用。

The exploration and development of deep shale reservoir highly depends on the cognition of fine characteristics of shale reservoir,and the characterization of small-scale sedimentary structure provides important data support for the exploration of deep shale reservoirs.Taking the deep reservoir samples from the representative wells of the Wufeng Formation shale from the Dazu block in the western Chongqing,southern Sichuan area as an example,the small-scale sedimentary structures of shale reservoirs are systematically classified and analyzed by methods of hand specimen research,thin-section observation,microscopic imaging analysis and geochemical logging data analysis.The results show that the macro-heterogeneity of the Wufeng Formation in the study area is relatively weak,but the micro-heterogeneity is extremely strong.The common small-scale sedimentary structures can be divided into ten types,including four types of silty argillaceous laminar deposits,three types of silicon-rich sedimentary structures and three types of combinatorial sedimentary structures.The Wufeng Formation shale can be divided into several sub-layers with different mineral sources such as quartz and sedimentary structural characteristics,reflecting the differences of sedimentary conditions.In practical application,the characterization and cognition of small-scale sedimentary structures can provide a key index for the optimization of deep shale.According to the above results,it has a certain guiding role for the optimization of layer evaluation of deep shale reservoirs.