Seismic interpretation and 2D restoration of F-A gas field, Bredasdorp Basin south coast of South Africa

Abstract

Seismic interpretation is always somewhat an uncertainty and questions on whether the horizons picked are properly correlated across faults and or the structures mapped are geologically or geometrically sensible always raise a concern as it provides the principal source of subsurface information used commonly in exploration by the oil and gas industry. In this study an attempt of delineating what are or not geological features has been done by validating the seismic structural interpretation using the restoration technique which also provided information about the extensional history of the study area. The seismic data, horizon and fault interpretation have been depth converted in 2DMove software followed by a sequential restoration and decompacting workflow. Simple shear was used as the restoration algorithm based on the deformation style of the basin (extensional basin). The seismic interpretation is valid and studies on tectonics interplay in basin development (gas field scale) during the Late-Jurassic- Early Cretaceous are based on the results of the four balanced cross-sections. They indicate that the Basin is not a simple extensional rift Basin but was rather formed through an alternation of extensional and compressional phases. The area understudy has undergone extension since rifting onset (break-up of Gondwana) with two intervening minor inversion episodes further NW and SE showing no significant shortening on the central part. A maximum extension is noted within the central part of the study area along the XL_1248 thus more accommodation space and subsequently thicker sediment accumulations are encountered in this region.