Evaluation of the Petroleum Potentials and Prospect of the Chad Basin Nigeria from Heat Flow and Gravity Data

Abstract

An integrated study of the Chad Basin Nigeria has been carried out using heat flow, Bouguer gravity anomaly, depth to basement maps and interpreted seismic reflection data of the area. The seismic reflection data show two main structural elements: faults and folds whose primary structural orientation is northeast–southwest. Other features such as grabens and horst which are formed as a result of tensional stress and magnetic intrusive are also identified in the sections. The Bouger gravity anomaly ranges from -10 to -50 mgal with a northeast to southwest trend while the heat flow values ranges from 63.63 to 105.4 m Wm-2 with an average of 80.6 m Wm-2. The result shows that areas with relatively low heat flux in the southwest and northeast is associated with Bouguer gravity values ranging from -30 to -50 mgal. These parts of the basin also have a higher depth to basement and are associated with low sediment, buried hills and crest of folds. The range of heat flow values computed for this study shows that the basin sediments are thermally mature and therefore has high prospects for oil and gas generation. The graben in the basin is associated with low heat flow and very low negative Bouguer gravity anomaly. The study reveals that a decrease in heat flow is observed with an increasing sedimentary thickness. Thus, by studying the heat flow map, regions of gravity highs and lows can be identified within the Chad basin. Moreover, areas of gravity lows have greater thickness of sediments than areas of gravity highs. Low geothermal gradient causes the formation of oil to begin at fairly deep subsurface levels, but makes the oil window to be quite broad. The heat flow, Bouguer gravity values and seismically determined structural features suggest that the Chad Basin Nigeria has good prospects for hydrocarbon plays in Cretaceous rocks, with high potentials for both structural and stratigraphic traps. The southwestern and northeastern axis of the basin is therefore recommended for further drilling to deeper depth based on the results of this study.

Keywords: Heat flow, Gravity, Depth to basement, Hydrocarbon potential, Chad Basin