Depositional Systems Response to Dynamic Slope Profile Evolution in Deepwater Margins with Mobile Substrates

Ciaran O'Byrne, Brad Prather, Carlos Pirmez, Gary Steffens, and Scott Sumner
Shell International Exploration and Production Company, Houston, TX

Integrated studies and research over the last two decades on deepwater depositional processes and slope profile evolution have allowed us to better understand the dynamic interaction between depositing flows and syn-depositional topography. This in turn has led to an enhanced understanding of the structural and stratigraphic controls on the creation and healing of slope accommodation space and resultant impact on reservoir architecture, distribution and preservation for hydrocarbon exploration and appraisal. Slope accommodation can be classified with respect to an ideal graded profile. Above grade slopes, typical of margins with mobile substrates, comprise both closed or ‘ponded' and open or ‘healed' slope accommodation. Fluctuations in the rates of subsidence, uplift and sedimentation result in complex temporal and spatial development of these accommodation types on above grade slopes. Ponded accommodation space may be more prevalent on substrates underlain by mobile salt. Stepped slope profiles appear to be more dominant on shale cored mobile substrates where stepped slope profiles preferentially develop. However it is important to realize that no accommodation type is unique to a specific mobile substrate and thus related depositional models can have universal application. Depositional process models presented here represent some of the more significant advances in our understanding of reservoir distribution in these systems and are a critical component of regional to sub-regional studies of slope evolution which have proven to be of particular importance in assessing deliverability of discoveries with complex deepwater reservoir facies architectures.