Analytical Estimation of Geotherm for Multi Layer Model from Heat Flow Equation: A Case Study of Parts of Chad Sedimentary Basin, Nigeria

Abstract

The subsurface temperature distribution of part of Chad sedimentary basin has been determined by applying analytical solution for multi-layer-model in solving the 1-D steady state conductive heat flow equation. Four-layer model was adopted because the Chad basin is made up of four lithostratigraphies. In this model, equilibrium geotherm of the four layers was computed by considering each layer separately while the temperature and heat flow are matched across the boundaries. The solution was used for generating temperature for each of the formation. Computed minimum, maximum and average thermal conductivity and surface heat flow of the basin were used as the input parameters for the analytical solution. The estimated temperatures increase with depth within the sedimentary column. The estimated temperatures were compared with measured bottom hole temperatures from four deep wells in the basin and the result shows very good match for the following different scenarios; (1) when maximum thermal conductivities of each formations are combined with the maximum heat flow of 100 mWm-2, (2) when the average thermal conductivities of each formation and the average heat flow of 85 mWm-2 are used as input for the model and (3) when the minimum thermal conductivities of each formation and the minimum heat flow of 65 mWm-2 are used as input for the model. The thermal structure of the sediment depends on its thermal conductivity, radiogenic heat sources, basal heat flow and surface temperature. The results of this research work have been used to effectively characterize the thermal structure of the study area.