Identification and Applications of Micro to Macroscale Shale Lithofacies.

Systematic research and evaluations of shale gas reservoirs are critical in shale gas exploration and development. Previous studies in this field mainly depend on experimental analysis that is often overly simplified. Here, we report an integrated geological and engineering method that combines the lithofacies division system with an identification and evaluation technology from the micro to macroscale. This method has been successfully applied in field sites. The key achievements of this method include the following: 1 Lithofacies refers to the rock or rock assemblage formed in a specific depositional environment that has experienced a certain degree of diagenesis, which is a comprehensive term that contains information about the lithology, physical properties, gas content and fracturability. With the main rock type or several rock types combined as the basic name, the shale lithofacies are classified and named by highlighting particular characteristics such as total organic carbon (TOC) and content of brittle minerals. 2 Based on the lithofacies classification and constrained by the equivalent sequence interfaces or thin layer interfaces, the organic matter-rich shales in the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in the Fuling gas field are longitudinally divided into 7 shale lithofacies. Furthermore, the organic carbonrich, high-silicon lithofacies is identified as the most favorable type for shale gas reservoirs. 3 A set of marine shale lithofacies identification technologies was created using cross-referenced scales of conventional logging and image logging, as well as logging summarization. Lastly, 4 the lithofacies technologies reported here have been successfully applied in multiple areas, including in the south and southeast of the Sichuan Basin and the Pengshui area. Applications in these areas include shale formation comparison and analysis, monitoring and analysis of horizontal well drilling, and assessment of fracturing stages in horizontal sections. The lithofacies technology is proven to be efficient and applicable for comprehensive shale gas reservoir evaluation.