Factors controlling the structures and physical properties of deformation bands in high-porosity sandstones

High-porosity sandstones are highly susceptible to the development of deformation bands under tectonic stress. However, limited studies have been conducted on factors controlling the structures and physical properties of these bands. By combining a systematic literature review and experimental analysis, we investigate the macro- and micro-structural characteristics and deformation mechanisms of these bands in high-porosity sandstones. Furthermore, we analyze the primary and secondary factors governing the structural and physical property evolution of these deformation bands, as well as the mechanisms by which these factors operate. The results indicate that effective normal stress and shear displacement serve as the primary factors controlling the structural and permeability evolution of the deformation bands. Specifically, the effective normal stress significantly reduces the permeability by intensifying grain breakage and modifying the boundary morphologies of shear zones. In contrast, shear displacement predominantly governs the thickening and structural stratification of the deformation bands. Notably, such controlling effect exhibits a pronounced nonlinear evolutionary trend, with a critical displacement threshold observed. The secondary controlling factors include the mineral composition, initial porosity, grain size, sorting degree, clay content, and strain rate of surrounding rocks. Under certain geological conditions, these factors modulate the structural morphology and physical property parameters of the deformation bands. The evolution of the deformation bands consists of five stages: non-deformation, initial deformation, initial stratification, stratification transition, and stable formation. Each stage exhibits regular variations in the microstructural parameters of the deformation bands, including band thickness, grain-size distribution, grain roundness, and grain orientation. With increasing stress level and displacement, the deformation bands experience significantly intensified grain breakage and pronounced enrichment of fine-grained matrix. This leads to porosity reduction of up to a maximum of 70% and permeability decreases of two to three orders of magnitude. The evolutionary patterns of the structures and physical properties of the deformation bands derived from laboratory tests are highly consistent with data from field outcrops. Future research on the of deformation bands should focus on computed tomography (CT)-based three-dimensional structural modeling, thermal-hydrological-mechanical-chemical (THMC) multi-field coupling simulations, and machine learning-based modeling for predicting structures and permeability.