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Structural Deformation, Traps and Reservoir Distribution in Deep-water Southern Equatorial Guinea: A Tale of Two Basins

Scott Thornton
PanAtlantic

Abstract

The area of Block K in the southernmost part of Equatorial Guinea is an emerging exploration province, with proven plays to the north and south. The area straddles two basins, the Rio Muni Basin and the North Gabon Basin within the block. In the northern part, reservoirs and structures are typical of the adjacent Rio Muni Basin. Paleocene and Turonian reservoirs consist of relatively flat-lying, undeformed toe of slope submarine fans analogous to the deepwater Campos Basin of Brazil. Play extension of channelized Senonian reservoirs from producing fields such as Ceiba and Okume to the north is focused on analogous compressional anticlines formed by sliding on salt. Uplift events in the platform and onshore in the Middle Eocene tilted the basin, and caused sliding and thrusting. As much as 2-4 km of overthrusting of undeformed Upper Cretaceous section is evidenced. The southern half of Block K is radically different than the north. It is actually an extension of the North Gabon Basin, with much more movement of salt nappes than within Gabon. Multiple uplifts in the platform and onshore have driven a radial pattern of downslope movement of two spectacular salt nappes, which have been transported 20-40 km into the deepwater emerging exploration area from a source area on the present-day continental shelf. Upper Cretaceous marine as well as Lower Cretaceous rifted sequences below the salt nappes never had autochthonous salt. Sub-salt structural traps in the Upper Cretaceous represent a new deepwater play for the country, and could provide significant volume potential. Traps in the Lower Cretaceous rift sequence, which one would normally call "pre-salt", are, in fact, beneath allochthonous salt and an Albian-Turonian marine sequence. These "pre-salt" traps differ from pre-salt traps in northern and central Gabon, which are overlain by autochthonous salt. Gamba and pre-Gamba fluvial-lacustrine sandstone reservoirs are present in nearby wells and represent potential reservoirs in southern Equatorial Guinea. In this untested area of Block K, Equatorial Guinea, the diversity of trap types, reservoirs and salt tectonics are quite different that the rest of the Rio Muni Basin, as well as the Northern Gabon Basin. It is an untested deepwater emerging play area.

AAPG Search and Discovery Article #90200 © AAPG Geoscience Technology Workshop, Fifth Annual AAPG-SPE Deepwater Reservoir, January 28-29, 2014, Houston, Texas