Gravity and Magnetic Investigation of the South-Central Atlantic Margin of the USA (Offshore Florida to South Carolina) and its West African Conjugate Margins (The Gambia to Mauritania)

Abstract

The outer continental shelf of the US East Coast, and northwest Africa are two underexplored conjugate margins with predicted reserves for the US East coast to be 3.3 billion barrels of oil and 32 TCF of gas within Cretaceous and Jurassic carbonate reservoirs charged by Jurassic carbonate source rocks. Predictions for the less studied conjugate margin of NW Africa vary widely for inferred source rocks ranging from in age Triassic to Oligocene sandstones and reservoir rocks ranging in age from Triassic to Late Cretaceous. In order to better estimate the hydrocarbon potential of both conjugate margins, crustal geometries of both conjugates have been compared to assess which margin is more favorable for hydrocarbon accumulation - or if both margins have equivalent potential. Margins with more favorable potential are generally considered those with wider rift zones with overlying sag basins and a thicker passive margin section. In the parlance of asymmetrical rifting, the margin with a wider rift zone is called here the footwall block, and the margin with a more narrow rift zone is called the hangingwall block. A series of 8 2D gravity profiles were created using 722 refraction stations gathered from literature constrained with 20 DSDP, IODP and ODP wells, as well as previously interpreted seismic data, and is integrated with the most recent satellite-derived worldwide gravity grid, to model the outer continental shelf basins up to 40 kms deep using gravity modelling software. Previous works established hangingwall/footwall geometry across the margins, with offshore east coast USA acting as the hanging wall, and offshore west Africa acting as the footwall. This new gravity study indicates the wider, rifted margin of the east coast USA may be more favorable for hydrocarbons than the more narrow margin of NW Africa.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016