Kinematic and Geological Significance of Contractional Deformation Bands in Oil-Bearing Sandstones: Example from Youshashan Anticline, China

The contractional deformation bands developed in oil-bearing sandstones of the fold related to the thrust fault in Qaidam basin, China. Deformation bands are organized as distributed and conjugated networks. The offsets of the deformation bands which are characterized by reverse-sense displacement is about 1mm-20mm. The dihedral angles of deformation bands vary in the range of 47–73°, and they bands are characterized by low S/C ratios in the range of 3.9–22.3. In comparison that of the host rock, the porosity of deformation bands decreased by approximately 11.0%–19.7%, the permeability decreases by 1–2 orders of magnitude. Deformation bands show grain “cataclasis” deformation, and can be categorized as contractional CSBs. The period of CSBs formation in the Youshashan anticline is consistent with or slightly later than the period of Youshashan anticline formation. The burial depth of the formation of deformation bands is approximately 2.5km–1.0km. The ability to store fluid of CSBs is worse than host rock, and oil-bearing content within CSBs is less than host rock. CSBs has a negative effect on hydrocarbon migration, resulting in higher oil saturation in the CSBs than the host rock.