Environmental Setting of the Chela Formation in the Onshore of Cabinda Province, Republic of Angola

Abstract

The Chela Formation is a silicoclastic unit of Aptian age commonly assigned to a continental setting. Although several authors have related it to a marine environment, especially because of its glauconitic content, in this study a new depositional model, focusing on its facies distribution, is proposed for this unit in Cabinda Province, Republic of Angola (Figure 1). As a conclusion, this study intends to predict the better reservoir zones for future exploration. This “pre-salt” interval has a wide distribution, developing all around the Lower Congo Basin margin and changing its name according to its geographical location. It is covered by a main regional salt seal called Loeme Formation (Figure 2) and has a thickness that varies from a few meters to 90 meters (Figure 3). This unit consists of fine light grey to brown sandstones, very micaceous at the top and interbedded with conglomerates toward the base. According to its lithology and its geographical distribution, the Chela Formation in Cabinda South Block, can be divided into three main units. The basal section was deposited in a coarse grain fluvial system. Above this rocks, and separated by a regional flooding surface, there is a sandstone unit which contains the main reservoirs of the area and was settling in a deltaic system. At the top of both sequences, a brackish unit related with a salty and partially closed lacustrine marginal system is found. This last interval represents the transition between Chela and Loeme Formations in a marine setting partially closed by the Walvis/Rio Grande Ridge. Considering that there are not outcrops in the study area, this analysis was principally made from subsurface data: mud loggings, electric logs, side wall cores, cores and seismic interpretation. The information was taken since the sixties but the last few years Pluspetrol intensified the data acquisition in the Chela Formation because of the hydrocarbons discoveries that took place in Cabinda area. (This abstract was sent to me with graphics included. The system does not allow for graphics at this time. Just wanted the reviewers to know the abstract did have additional information. - Terri Dunan)

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015