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Rock-Physics Guided Seismic Exploration

Abstract

The history of exploration demonstrates that new data, new concepts and new interpretations can lead to the discovery of new plays and prospects in mature basins. In the Dampier Sub-Basin, north-west Australia, a re-processed regional 3D seismic volume has prompted a rock-physics guided seismic interpretation study to provide a different perspective on exploration prospectivity. Rock physics is a critical link between seismic data (and their derivatives) and geology. Statistical rock physics models have been constructed from well log data across the sub-basin to capture and quantify the inherent scatter in rock properties of key stratigraphic units. Stochastic forward modelling has then been used to derive the most likely ranges of seismic amplitude responses as a function of key variables such as lithology type, depth, fluid content and reservoir quality. The parallel seismic data workflow is focussed on identifying broad stratigraphic units and incorporating these into a sequence stratigraphy framework. Working within a stratigraphic framework guides understanding of expected lithologies and ensures the appropriate rock physics models are used when interpreting specific seismic amplitude-versus-angle (AVA) behaviour. The subsequent full integration of rock-physics modelling and seismic amplitude interpretation relies on iterative collaboration between the interpreter and the petrophysicist. It is essential that both basin-wide trends and local anomalies observed in the rock physics models are considered when interpreting seismic AVA responses. Application of this rock-physics guided seismic exploration workflow has generated new ideas on depositional systems and identification of additional prospectivity in mature areas, in addition to providing the more traditional assessment of charge risk on previously identified structural closures. The critical factors that make the workflow successful have been the recognition of geological trends within the basin architecture and stratigraphic framework of the sub-basin, and the ability to forward model seismic responses of hypothetical seal / reservoir pairs at different depths. This approach to an exploration prospectivity refresh has enabled integration of a large amount of existing well log data with new 3D seismic data, and facilitated a creative and multi-disciplinary review of a mature sub-basin.