Assessment of geothermal resources in the Nigerian sector of the Chad Basin, NE-Nigeria

Abstract

Nigeria, with a population of over 200 million people, has been a slave to the energy conundrum. The need for alternative and cleaner energy sources is imperative to ensure Nigeria´s energy growth and energy mix (fossil fuel and renewables). The Nigerian sector of the Chad Basin has been the location of intense petroleum exploration in the 1980s and early 1990s with 23 oil wells drilled and oil and gas found in some of them. These wells can also shed light on the presence of exploitable geothermal resources in the basin. Temperature logs from 22 wells were analysed to determine the geothermal gradient in the area and wells in anomalous areas were selected for further studies. Reservoir temperatures below 120°C are suitable for direct use, including space-heating, while temperatures above 120°C can be utilized for electricity generation. The Bima sandstone was identified as a potential reservoir and wells with temperatures above 120°C at the top of the Bima sandstone were selected. Five wells, that is Ga1, Kn1, Kr1, Wd1 and Kt1 met these criteria with temperatures in the range of 120-152°C. These wells are within the sub-basinal structure in the southern part of the basin. A conceptual model of the resource showed that a geothermal system exists with the sandstone layers of the Bima providing the best geothermal reservoir conditions in the area. Monte Carlo volumetric assessment was performed indicating a P90 result of 285 MWe (90% likelihood that this can be achieved). Sustainable utilization of the geothermal resource in the area will depend on further investigation, and how well the reservoir is understood. The reservoir management, particularly the re-injection planning as well as the exploitation technology play an important role. The best mode of production is to adopt a step-wise increase in production for sustainable utilization