| Abstract |
The Geology of Nigeria is dominated and made up of two main rock types: basement complex and the sedimentary basins, which are equally dispersed. Minor formations are the volcanic plateaus and the river alluvium.The sedimentary rocks overlying the basement complex of Cretaceous to Tertiary ages, comprise the Niger Delta, the Anambra Basin, the Lower, Middle and Upper Benue Trough, the Chad Basin, the Sokoto Basin, the Mid-Niger (Bida-Nupe) Basin and the Dahomey Basin. Oil exploration activities, especially in deep basins of the Niger Delta and the Chad Basin, has resulted in acquiring subsurface geo-information including well-log data in which some borehole temperature data have been recorded among others. Research studies and analysis of data from the oil exploratory wells indicate potentials for geothermal energy in some of the basins. The geothermal gradients of the Eastern Niger Delta obtained from bottom hole temperature vary from 13.46°C/km to 33.66°C/km with an average of 23.56°C/km. Other studies in the Niger Delta indicate geothermal gradient in the basin ranges from 1.2°C to 7.56°C/100m. More than ten authors working in the Chad Basin over the last three decades had reported an established regional average geothermal gradient of 3°C/100m and above, in some places the gradient is up to 5.88°C/100m. Temperatures of 100°C to 175°C were obtained at 1200 to 2600 metres below ground level (mb.g.l.) in some part of the Nigerian sector of the Chad Basin, the results also indicate temperature of up to 250°C at the top of the basement complex, up to 85°C at the Cenozoic unconformity, up to 200°C at depth of 3000m b.g.l. and up to 320°C at the depth of 5000m b.g.l. A geothermal gradient value of about 5.5°C/100m was also reported in the Anambra Basin. In the Sokoto Basin geothermal gradient reported varies between 20.84 and 52.11 °C/km with an average of 33.99 °C/km. The subsurface temperature analyses let to assess some geothermal resources, especially for the Nigerian sector of the Chad Basin. The Cenozoic formation contains the unit geothermal resources ranging from 5GJ/m2 to 85GJ/m2 and the subsurface rock interval down to the accessible depth of 3000m b.g.l. contains resource value of 400GJ/m2 to about 1200GJ/m2. The geothermal resources in the Chad Basin area stored in the rock mass down to the deepest considered level (5000m) were estimated at 1.908E+23J. This paper presents the status of knowledge as for geothermal energy exploration and potential in some Nigeria’s deep sedimentary basins. The geothermal analysis based on geothermal gradients indicated geothermal anomalies within sedimentary basins. The areas of geothermal anomalies with gradients above 5°C/100m might be prospective for geothermal energy utilization. |