Subsurface observations of deformation bands and their impact on hydrocarbon production within the Holstein Field, Gulf of Mexico, USA

Abstract

AbstractThe Holstein Field consists of poorly lithified turbidite sands deposited during the Pliocene Epoch. Dense arrays of cataclastic deformation bands have been observed in all cores from wells that penetrate the K2 reservoir sand, the highest density of which are located near the hinge of a monocline. The predominant set of deformation bands strikes parallel to the fold axis, and dips at both high and low angles with respect to bedding. Deformation band orientation and offset of marker beds indicate reverse shear and are consistent with a flexural slip origin during folding. Restorations suggest that the monocline and associated deformation bands formed early during the burial process with high pore pressure.Reservoir permeability estimates from well tests indicate a bulk permeability approximately one-third of the reservoir core permeability in regions with deformation bands, whereas other areas are unaffected. Bulk permeability estimated from the permeability of the reservoir and deformation band network is lower than the reservoir permeability alone, but exceeds the permeability observed in the well tests by a factor of 2. A reduction in permeability of oil relative to water for both the fault and host sand is required to match the well-test permeability with that measured from core.