Characterization of fault-fracture system for tight sandstone reservoirs in Sichuan Basin, China

Abstract:

Fault damage zones and associated fractures are crucial for the migration of subsurface fluids, which is challenging due to the lack of subsurface data. Based on integration of seismic data, well logging, core samples, and field observations, we have investigated the fractures at various scales for the Xujiahe tight sandstone in the northeast Sichuan Basin, China.

The core samples show mostly opening-mode microfractures that can be subcritically generated under low tectonic stress fields since the Late Triassic-Middle Jurassic. These opening-mode microfractures in such ultra-low permeability sandstone are likely to provide a storage volume for coal gas to accumulate. Macro-fractures from image logging and outcrop display well-developed joint networks within the sandstone. The basin-wide distribution of such macro-fractures implies potential conduits for gas migration during basin uplift in the Cretaceous. The seismic attributes are used to demonstrate the structure and distribution of damage zones that are formed and controlled by a system of reverse faults. We speculate that the multi-scale fractures and damage zones are likely to control the gas migration and accumulation within the tight sandstone of the Xujiahe Formation during the tectonic transformation from the Late Cretaceous to Quaternary Period. The approach and data lead to a more in-depth understanding of the fault-fractures on a regional scale, which controls the migration and accumulation of the gas in low-permeable and low-porosity sandstones.