Exploring the Predictive Power of Seismic Geomorphology to Assess Reservoir Quality of Gravity-Flow Sandstones.
Advances in computational power have allowed acquiring and processing of increasingly large subsurface datasets which have the potential to bolster exploration over large portions of sedimentary basins. It is envisaged that soon automated seismic interpretation processes will be paramount for unleashing the full potential of such extensive seismic datasets. However, the success of this approach relies on training these processes so for them to recognise valuable subsurface assets. With this research, we test the hypothesis that the rheology of gravity-flows dictates the planform geometry of the associated fan deposits. If this control exists, seismic geomorphology has the potential to predict the sedimentary characteristic, hence the reservoir quality of these sedimentary bodies. We analysed the occurrence of hydrocarbon bearing reservoirs with total porosity in excess of 20% and multi-Darcy permeability from the Neogene section of basins in East Africa. The overall external geometry of the reservoirs was described at the seismic scale integrating seismic amplitude extractions, structure and isochron maps. The maps were generated from detailed interpretation of the top and base reservoir reflections. Core photos from these reservoirs were integrated into the seismic project. Examination of cores allowed identification of dominant sedimentary facies that enabled to propose a classification of the deposits in terms of dominant flow processes. The research so far has shown that confinement of flows exerts a great control in the shape of the deposits and resulted in sedimentary bodies with marked elongation at the seismic scale. The analysis of the reservoirs at the core scale indicated that these are dominated by massive, poorly sorted, medium- to coarse-grained sandstones, commonly with with floating oversize clasts, as well as beds with disrupted laminae and sandy conglomerates. These characteristics may indicate 'depositional freezing' from high-density flows with yield strength, which may have also contributed to the limited lateral spreading of the deposits analysed. Additional examples of gravity-flow sandstones from other basins would validate the value of these general trends. This research is funded by the Natural Environment Research Council UK. The data utilised in this project is kindly provided by Ophir Energy.
AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018