Print this pageBarremian Basin Floor Fan Complex: From Untested Gas Play Within the Northern Pletmos Basin
The Pletmos Basin, offshore South Africa, shows a history of strong strike-slip movement during the Late Jurassic-Early Cretaceous breakup and separation of Gondwana. It consists of a series of en echelon depocentres, each of which comprises a complex of rift half-grabens separated by horst structures and overlain by thick drift succession. The east-west striking Northern Pletmos Basin is similarly sub-divided by a 40 km long regional arch, a potentially prospective prominent feature with up to 4000 m structural relief. This Transfer Zone Arch is the natural paleographic focal point for high-energy sand-channels crossing between the adjacent basins. Good 2D data reveal several bright anomalies overlying the Barremian unconformity (9At1). The 9At1 unconformity eroded an arenacous shelf with a feeder point on the northern rim of the Pletmos Basin. A massive sandstone, 25 m thick and interpreted to be channel fill, has been intersected in a nearby well and has porosities of 21 - 24%. This channel feature is highly erosive, and follows a steep course down the northern flank of the Pletmos Basin, ensuring high-energy mass-flow deposits into the basin. It was intersected off-target at a base of slope setting. The associated mounded channel infill is easily identified and the top of channel infill is marked by a high impedance contrast. This sinuous channel feature can be followed along its entire course from its feeder point on the shelf, arcuating down the slope and flattening out at base of slope. This is interpreted to be the major sediment source which resulted in the formation of the Barremian age deep-marine basin floor fan and channel complex. Its presence becomes more visual over the arch where channel and fan features combined with structure allow for traps resulting in bright spots. Charge is expected to come from deep-seated (possibly Kimmeridgian age) marine and lacustrine source rocks developed in the deepest parts of the Pletmos Basin. Its presence is supported by deep-seated gas-shows within three of the nearest wells, as well as the Superior High gasfields 40 km to the southwest. Up to six leads have been delineated, each with GIIP estimate (P50) ranging between 260 to 550 Bscf. A most likely deterministic resource estimate for the untested Barremian bff channel and fan complex is calculated at 2.44 Tcf.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil