Source-to-Sink at Continental Margins: A Novel Approach to Reservoir Prediction in Offshore Deep-Water Settings

Abstract

Deep-water settings are prevalent in many of the world’s frontier basins. To better focus exploration spend in today’s challenging environment and predict reservoirs, a novel approach to close the loop between onshore denudation and offshore sediment deposition is required. Sedimentary flux measurements, regional subsidence patterns, tomographic models and simple isostatic calculations are combined to constrain the history of offshore solid sedimentary flux and sub-plate support of the Mauritanian Basin. Predictions of solid sedimentary flux to the Mauritanian Basin calculated by inversion of continental drainage are compared to observations in the Chinguetti field of the Mauritanian Basin.

We explore the relationship between onshore uplift and erosion and solid sedimentary flux in the Mauritania Basin. Backstripping of 8 wells and mapping of 53,000 line-km of 2D seismic reflection data show that rapid Neogene-Recent subsidence occurred in the center of the Mauritanian Basin during the last 23 Ma. The history of sedimentary flux to the basin was determined by depth-converting and decompacting biostratigraphically-dated isopachs. Compaction and velocity errors, determined using check-shot data, were propagated into calculated sedimentary flux history. Solid sedimentary flux rates of 0.2_-0.1^+0.2 ×10³ km³ /Ma between 23.8-5.6 Ma, and 1.9_-1.4^+2.0 ×10³ km³ /Ma from 5.6-0 Ma are observed. A calibrated stream power erosional model was used to invert 14700 river profiles for a history of continental uplift rate. Incision rates were integrated along best-fitting theoretical river profiles to predict sedimentary flux at mouths of the rivers draining NW Africa. Our predicted history of sedimentary flux increases in two stages towards the present, in agreement with our offshore measurements. Predicted fluxes are indistinguishable if precipitation rate varies with a period < 1 Ma or drainage area varies by < 50%.

Salt withdrawal, thin-skinned tectonics, glacio-eustasy and flexure of the lithosphere due to the emplacement of Cape Verde cannot explain the timing or magnitude the observed Neogene-Recent subsidence. Conversion of shear wave velocities into temperature and isostatic calculations indicate that asthenospheric temperatures determine bathymetry from Cape Verde to W Africa. We suggest that the history of Cenozoic epeirogeny in the Fouta Djallon swell and growth of the Atlas Mountains determined the rate of Neogene sediment delivery to NW Africa’s passive margin.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018