Application of Structural Analogs to Enhance Understanding of Tectonically Inverted Settings

Reynolds, David J.¹, John R. Underhill² (1) ExxonMobil Exploration Company, Houston, TX (2) The University of Edinburgh, Edinburgh, United Kingdom

Integration of field and subsurface data from the Wessex Basin (UK) and Doseo Basin (Chad) has provided important new insights into petroleum prospectivity in structurally inverted settings. Using these data it has proved possible to refine models of inversion anticline development and recognition criteria for a variety of polyphase deformation scenarios. In the Wessex Basin, structures are exposed that are typically difficult to image seismically, such as the steeply dipping, highly deformed forelimb of inversion anticlines. These regions are particularly important to resolve when mapping trap geometry, field extent, and fault displacement for fault seal analyses. In all cases the inversion anticlines are related one-for-one with early rift faults, regardless of their trend and that relaying normal faults produce en-echelon inversion anticlines. Thus, en-echelon folds do not indicate strike-slip faulting a priori. In addition, maximum inversion is coincident with the center of the fault segment where maximum subsidence occurs during extension. As a result, much can be interpreted about the pre-inversion structure by mapping the inversion anticlines themselves. Application of these observations has aided in the interpretation of subsurface data from the Cretaceous Central African rift system (Doseo and Doba Basins) in Chad, which contain up to 10 km of non-marine sediments and record a complex tectonic history from the Early Cretaceous to the present. Combining results of the seismic interpretation, structural analysis and direct field observations leads to the construction of a new, unifying, generic model for inversion and criteria for differentiating inversion anticlines from strike-slip fault zones which can be used to improve our understanding of trap geometry and risk.