SLOPE 2 Project Final Report (sponsors only)

This report details the results from Phase 2 of the SLOPE research project undertaken by the Stratigraphy Group of the Earth and Ocean Sciences Department of the University of Liverpool. Slope Phase 2 was an outcrop-based study that lasted for 3 years and was conducted in the exceptionally well exposed Permian deepwater reservoir analogue deposits of the Karoo basin, South Africa. The project team involved 2 full-time Post-Doctoral researchers (Rufus Brunt and Claudio Di Celma), a PhD student (Willem van der Merwe) and several graduate research assistants, supervised by David Hodgson and Stephen Flint. PhD students Carlos Oliveira, Jorge Figueiredo and Amandine Prélat also assisted in the field, alongside their own research. The purpose of the research was to develop predictive models for the sub-seismic scale architecture, net:gross distribution and connectivity of submarine slope deposits, within a hierarchical structure that could be applied to subsurface datasets. The starting point was that in many deepwater plays, 3-D seismic allows good imaging of the larger scale channel complexes, external levees and overall systems but not adequate description of lithologies and connectivity. In other plays such as the ultra-deep Gulf of Mexico and sub-basalt Atlantic margin, seismic quality is inadequate for good definition of larger geometries, requiring more reliance on well data and 3-D architectural scenarios derived from outcrop analogues. This project built on aspects of Phase 1 and focuses on the slope channel/interchannel successions in the Laingsburg depocentre. A unique aspect of the Laingsburg study area is the potential to trace and document different slope channel and marginal architectural elements within a single stratigraphic unit downslope, from bypass-dominated upper slope to depositional lower slope/basin floor positions (Fig 1.1.3). The analysis has been based on detailed sedimentology coupled with the interpretation of key surfaces and stacking patterns in order to understand the spatial/temporal variability in geometry, architecture and connectivity in slope channel complexes and between these and the deposits lateral to them. A hierarchical approach has been adopted through the study. A database has been developed for shale types, bed lengths and connectivity of sands, channel dimensions and trends in thickness, facies and net:gross, both locally and semi-regionally. The 3-D architecture of a high net:gross and a low net:gross slope channel complex set have been captured in PETREL static reservoir models. Full analysis of the Vischkuil Formation, the deepwater initiation unit, has been a major aim of Phase 2 because it provides a powerful outcrop analogue to similar debrite/MTC complex initiation phases recognized in West Africa and other subsurface examples. We have analysed the down-slope translation of the MTDs into turbidites, to capture their runout distances. Our current understanding of the Vischkuil system is detailed in this report but sponsors will also receive an electronic copy of the PhD thesis of Willem van der Merwe in approximately 1 year’s time (Dec 2008). Deliverables 1) A facies scheme and a hierarchical classification of the building blocks of reservoir and non-reservoir deposits in interpreted high to low gradient, mid to base of slope settings. Detailed examples are given of different styles of channel, channel complex and complex set and associated inner and outer levee, overbank and distributive frontal lobe deposits from different positions along and across the slope profile. 2) Capture of specific architectural changes within selected stratigraphic intervals traceable for 30 km plus downslope. 3) A high resolution sequence stratigraphic framework for the deepwater systems. 4) A quantitative database of geometries and architecture, within the hierarchical scheme and sequence stratigraphy. 5) Detailed study of the early muddy basin floor, emplacement of early debrites and associated deformation deposits. Capturing the effect of these mass transport deposits on the architecture of overlying sands in Fan A. 6) PETREL model of a high net:gross channel complex.