昭通东北地区五峰组—龙马溪组龙一1亚段页岩岩相类型及其储层特征

Shale lithofacies types and reservoir characteristics from Ordovician Wufeng Formation to the first sub⁃member of the first member of Silurian Longmaxi Formation,northeast Zhaotong area

页岩岩相对页岩储层有着重要的影响,一定程度上控制着页岩的生烃能力、储集和压裂性能。基于岩心、薄片、X射线衍射及各类地化测试数据,对昭通东北地区上奥陶统五峰组—下志留统龙马溪组页岩岩相特征、储层特征和评价进行了研究。研究区主要发育含灰/硅混合质页岩相、混合质页岩相、含黏土/硅混合质页岩相、混合硅质页岩相、含黏土硅质页岩相,南部与北部岩相纵向分布存在差异,南部五峰组—龙一_(1)亚段岩相呈现出从黏土质页岩相组合向硅质页岩相组合再向混合质页岩相组合过渡的特征,北部呈现出从混合质页岩相组合向硅质页岩相组合再向混合质页岩相组合的过渡趋势;横向上岩相展布非均质性强,连续性差。不同岩相储层特征存在差异,硅质页岩储层性能较好,具有有机碳(TOC)含量高、含气量高、脆性矿物含量高的特征;黏土质页岩TOC含量和含气量较高,但脆性矿物含量极低;混合质页岩储层性质复杂,总体上硅质含量高的混合质页岩储层性质较好。基于TOC含量、含气量、脆性矿物含量,利用层次分析法和熵值法相结合的方法,建立了页岩岩相评价标准,确定了优势岩相,研究区混合硅质页岩相、含灰硅质页岩相和含灰/硅混合质页岩相为I类优势岩相;含黏土硅质页岩相、混合质页岩相和含黏土/硅混合质页岩相为Ⅱ类优势岩相;混合黏土质页岩相和含硅黏土质页岩相为非优势岩相。

Shale lithofacies has an important influence on shale reservoirs.It controls the hydrocarbon generation capacity,storage performance and fracturing performance of shale to a certain extent.In order to study the shale lithofacies characteristics,reservoir characteristics and evaluation of Wufeng-Longmaxi formations in the northeast Zhaotong area,a detailed research was carried out based on core,thin section,X⁃ray diffraction and various geochemical test data.Calcareous/siliceous mixed shale lithofacies,mixed shale lithofacies,clayey/siliceous mixed shale lithofacies,mixed siliceous shale lithofacies,clay⁃rich siliceous shale lithofacies are developed in the study area.There is a difference in the vertical distribution of lithofacies between the south and the north of the study area.The lithofacies from Wufeng Formation to the first sub⁃member of the first member of Longmaxi Formation(Long1⁃1 submember)presents the characteristics of transition from clayey shale lithofacies associa⁃tion to siliceous shale lithofacies association and then to mixed shale lithofacies association in the southern area,while the northern area shows a transition trend from mixed shale lithofacies association to siliceous shale lithofacies association and then to mixed shale lithofacies association.Horizontally,the lithofacies distribution is highly heterogeneous and has poor continuity.The reservoir characteristics of different lithofacies are different.Siliceous shale has good reservoir properties,with the characteristics of“high TOC content,high gas content and high brittle mineral content”.The TOC content and gas content of clayey shale are high,but the content of brittle minerals is very low.The properties of mixed shale reservoirs are complex,and generally,the mixed shale reservoirs with high siliceous content have better properties.Based on TOC content,gas content and brittle mineral content,the shale lithofacies evaluation standard is established by combining analytic hierarchy process and entropy method,and the dominant lithofacies are determined.Mixed siliceous shale lithofacies,calcium⁃rich siliceous shale litho⁃facies,calcareous/siliceous mixed shale lithofaciesis are classⅠdominant lithofacies;clay⁃rich siliceous shale lithofacies,mixed shale lithofacies and clayey/siliceous mixed shale lithofacies are classⅡdominant lithofacies;mixed clayey shale lithofacies and silicon⁃rich clayey shale lithofacies are non⁃dominant lithofacies.