A Coastal Barrier-Spit System: An Alternative Depositional Model for the Kudu Gas Field, Namibia

Abstract

The 1.3tcf Kudu gas field located in SW Namibia has long been considered as a coastal aeolian deposit that is interbedded with lava flows. The evidence for this is based largely on steep dips (22-24 degrees) recorded in dip meter logs, the presence of anhydrite and well sorted grains. In the actual core the dips are however not readily apparent. In the core there is evidence for marine bioturbation at certain levels and there are associated marine units with fossils. The presence of these marine fossils has given rise to some uncertainty in the aeolian interpretation but no reasonable alternative has previously been proposed. Recent field work in the well exposed Namibe Basin of SW Angola has identified a possible alternative analogue for Kudu. In the marine Maastrichtian interval a unit occurs with steep cross beds but is clearly shallow marine. The marine nature is given by the presence of abundant shark teeth and other marine fossils. The maximum observed thickness is about 10-12m, the same order of magnitude as the 8m thick, steeply dipping unit in the core. Recently portion of the Troll Field has been reinterpreted as a barrier-spit system. This is a well sorted, well stratified system with dips poorly preserved in the core. Thickness of the spit portion is about 4m. It has been shown that longshore drift systems have been active in Angola since the Albian and are still strongly active on the Namibian coast today. It is highly likely that the Kudu sands may be a product of a coastal spit system. This model will help explain the steep cross beds, the presence of anhydrite, texture, close association with other marine sediments and the north-south elongation of the reservoir. This has implications for future exploration for similar reservoirs to Kudu on the Namibian margin. Similarly production models need to be reassessed in the light of the new model.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018