Relationship between fractures, stress, strike-slip fault and reservoir productivity, China Shunbei oil field, Tarim Basin

Abstract

It is becoming widely recognized that a relationship exists between stress, stress heterogeneity, and the permeability of subsurface fractures and faults. We present an analysis of the Shunbei oil gas field, developed mainly in fractured carbonate, where active deformation has partitioned the reservoir into distinct structural and stress domains. These domains have differing geomechanical and structural attributes that control the permeability architecture of the field. The field is a composite of Caledonian contractional elements that have been modified by Hercynian contraction to produce basement-rooted strike-slip faults. Reservoir scale faults were interpreted in detail. Bulk reservoir performance is governed by the local stress architecture that acts on existing faults and their fracture damage zones to alter their permeability and, hence, their access to distributed oil. Reservoir potential is most enhanced in areas that have large numbers of fractures with high ratios of shear to normal stress. This occurs in areas of the field that are in a normal stress style. Comparatively, reservoir potential is lower in areas of the field that are in a strike-slip stress style where fewer fractures with high shear-to-normal stress ratios exist. Achieving the highest well productivity relies on tapping into critically stressed faults and their associated fracture damage zones. One wellbore has been drilled based on this concept, and shows an obvious improvement in petroleum productivity.