Fault and fracture characteristics of a major fault zone in the northern North Sea: analysis of 3D seismic and oriented cores in the Brage Field (Block 31/4)

Abstract

Abstract Based on three-dimensional (3D) seismic and core data, an analysis of fault geometry and fracture distribution related to a normal fault in the Brage Field, northern North Sea, has been achieved. The fault has a vertical throw of 200–300 m, and exhibits a steep ramp-flat-ramp geometry. Most of the deformation related to this fault is concentrated within a narrow zone in the hangingwall. Both extensional and compressional antithetic structures have been identified. The most intensive fracturing is associated with areas of change in the fault plane orientation. Correspondingly, these areas represent locations where questions regarding sealing capacity arise. The complexity of the fault zone caused difficulties in an exact pick of the fault plane. Oriented cores from one of the production wells in the area include a continuous 120 m long interval across the fault zone itself. Detailed measurements of fracture and bedding orientations were carried out using an automated goniometer as well as manual measuring techniques. Biostratigraphic data show that two faults can be identified within the narrow fault zone, with the main displacement recorded across the upper one. Fracture orientations and fracture distribution pattern versus core depth indicate, however, that the deformation is associated with the lower fault. Based on the core material which exhibits an asymmetrical distribution of deformation in relation to the fault zone, an exact determination of the depth of the fault plane has been possible. It is concluded that the lower interval is the initial main fault. The largest slip has, however, been taken up across the upper interval, representing a hangingwall splay fault.