Subsurface temperatures obtained from continuous temperature logs in 260 wells allowed to stabilize for several months were used in determining the geothermal gradients in the Niger Delta. Regional gradients are lowest (0.82oC/100m) at the central part of the Delta and increases both seaward and northward up to 2.62oC/100m and 2.95oC/100m respectively in the continental sands of the Benin formation. In the marine paralic deposition, geothermal gradients range from 1.83oC/100m to 3.0oC/100m at the central portions. The highest values of 3.5oC/100m to 4.6oC/100m are seen northwards while intermediate values of 2.0oC/100m to 2.5oC/100m are recorded seaward. The thermal gradients are clearly influenced by the lithology or rate of sedimentation in the area. Regions of low thermal gradients correspond with areas of high sand percentage, primarily because sands are better conductors than shale and therefore show as low thermal gradients. There is a continuous but non-linear relationship between geothermal gradients and depth, from less than 1.0oC/100m in the continental sands through 2.5oC/100m in the marine paralic section to 5.0oC/100m in the continuous shaly section.
Key words: Geothermal gradient, temperature, sand percentage, heat flow
(Global Journal of Pure and Applied Sciences: 2003 9(2): 265-272)