Shale gas detection practice based on the BMT method: A case study of the Xujiahe Formation in the Muchuan area, southwestern Sichuan Basin

The Upper Triassic transitional shale of the Xujiahe Formation is characterized by organic-rich materials and large continuous thickness. It is expected to become a new target layer for shale gas exploration in the Sichuan Basin. However, the disturbances of dense cities and towns, large population, and the large burial depth of 2000m to 3000m challenges the traditional geophysical exploration method of shale gas in the region. Based on the analysis of existing data, this paper takes the Xujiahe Formation in the Muchuan area of southwest Sichuan as the research object. Combined with geological conditions, a theoretical electrical model of shale gas detection based on BMT method was established. Its applicability and validity were verified by forwarding simulation and known shale gas boreholes. By deploied BMT profiles in key shale gas exploration areas to explore the deep electrical structure of the study area, and processing and analyzing the obtained BMT data in combination with geological data. We found that the Xujiahe Formation in the study area is continuous and complete, with poorly developed faults. The organic-rich shale of the Upper Triassic Xujiahe Formation has a large thickness and displays a very good shale gas potential, which may become a new layer for shale gas exploration in this area. It is concluded that the BMT method can effectively identify the scale and spatial distribution of organic-rich shales, which is a quick, economic, and effective geophysical exploration method for shale gas detection at a depth of 3000m underground.