Lithostratigraphic Interpretation, Geotemperature Analysis, and Hydrocarbon Windows Determination in Seloken Field, Chad Basin, Northeastern Nigeria

Abstract

The aim of this study is to interpret the lithostratigraphic units, analyze geotemperature and determine the hydrocarbon windows in the Seloken Field. Gamma-ray logs and formation tops were used to interpret the lithostratigraphic units. Corrected bottom hole temperature (BHT) data from the wells were used to calculate the geothermal gradients. A formular was derived from the geothermal gradient equation to analyze the geotemperature. Another formular was derived from the geotemperature equation to obtain the hydrocarbon windows. Five major lithostratigraphic units were interpreted. They are: Bima and Gongila Formations, Fika Shale, Kerri-Kerri and Chad Formations…The calculated geothermal gradients range from 3.4oC/100m to 4.0oC/100m, with an average of 3.65oC/100m and the standard deviation of 0.01oC/100m. The temperature of shale units of the formations at various depths calculated from the geotemperature equation range from 30.99oC to 202.45oC. This shows that some of the shale units are thermally mature to cook petroleum The oil window calculated from the derived geomathematical equation is between 1178.1m and 2457.95m, while the gas window is from 2457.95m to 5424.7m. The boundary between the two windows is at 2457.95m. The results above were used to generate a hypothetical model for the hydrocarbon windows. The model indicates that the shale units are within the diagenesis and catagenesis phases. This work provides mathematical methods of source rock thermal maturity evaluation to complement geochemical methods. The outcome is a very important tool, which can be applied to other fields and sedimentary basins in hydrocarbon exploration.