Fault systems characteristics of cratonic basins and their control on tight sandstone gas migration: a case study from Shenmu Gas Field, Ordos Basin

The fault systems in structurally stable, cratonic basins, such as the Ordos Basin in central China, can be difficult to identify and map, which has important implications for basin-scale natural gas prospecting. Limited research has focused on strike-slip fault systems from the Late Carboniferous to the Late Permian of Upper Paleozoic in the Ordos Basin and their control on tight sandstone gas migration. The characteristics of the fault systems in the Shenmu Gas field were comprehensively studied using various datasets, and theirs control on the tight sandstone gas migration was assessed. Analyses of six outcrop profiles adjacent to the gas field revealed fault displacements ranging from 2 to 5 m within the fault systems. Image logs showed that most of the fractures were unfilled and open. Carbon isotope compositions of natural gas and laser Raman data indicated gas migration along the fault systems. Fault systems exerted a stronger control on far-source gas-bearing assemblages than on near-source and in-source gas-bearing assemblages. Fault-type and diffusion-type migration modes for the far-source gas-bearing assemblage were established. This study advances understanding of the controlling role of fault systems in tight sandstone gas, which is conducive to the exploration of the Upper Paleozoic in the Ordos Basin.