Comparison of biogenic gas fields in the Western Canada Sedimentary Basin and Qaidam Basin: implications for essential geological controls on large microbial gas accumulations

Abstract Compared to conventional thermogenic petroleum, the exploration for large biogenic gas accumulations is more challenging because the gas occurs commonly at shallow depths in a petroleum system with weak top and lateral seals. In addition to fundamental environmental requirements, such as temperature and formation water composition, microbial gas generation and retention require adequate petroleum system elements in order to form economic accumulations. The geological characteristics of Southeast Alberta Gas Field (SAGF), a giant biogenic gas accumulation located in southeastern Alberta and southwestern Saskatchewan within the Western Canada Sedimentary Basin (WCSB), are compared to those of Sanhu Sag, Qaidam Basin in northwestern China, to provide insight into the critical geological controls for economic biogenic gas accumulations. It was found that multilayered reservoirs, consisting of multiple layers of thin porous units and interbedded with source rocks, provide a most efficient storage mechanism. Low relief structural and stratigraphic traps with lateral permeability seals, commonly of stratigraphic or diagenetic origin, are the most effective trapping mechanisms. The recognition of these common constraints provides insight for future exploration of other biogenic gas fields and prospects in the basins studied elsewhere.