Integration of Sequence Stratigraphy, Facies, and Geotemperature Analyses in the Study of Hydrocarbon Prospectivity of Bornu Basin in Northeastern (Nigeria)

As Nigerian drilling operations expand into more challenging and costly operating environments of deep frontiers, there is a need for critical analyses of facies, stratigraphy, depositional environments, prospects, leads, geotemperature, and abundant hydrocarbon windows of the inland basins. In this study, the hydrocarbon prospectivity of Bornu Basin has been determined by integrating the above studies and reassessing the key petroleum play elements and prospects in the Seloken field. The facies interpreted from gamma ray and resistivity logs are sandy shale, shale/sand heterolithic, hemipelagic shale, shaly sandstone/coarse-grained sandstone, and sandy shale/coarse-grained sandstone facies, which are associated with Bima and Gongila Formations, Fika Shale, Kerri–Kerri, and Chad Formations, respectively. The log also interpreted the depositional environments, and the result shows that the sedimentary facies were deposited in various settings ranging from fluvial through transitional to shallow marine environments. Seismic and log data were used to analyze the sequence stratigraphy, and a genetic model was used to delineate the sequence boundaries. Three depositional sequences, including three maximum flooding surfaces (MFS), were identified. Three significant reservoirs corresponding to the sand members of the Gongila, Kerri–Kerri, and Chad Formations were placed, and these lie within the lowstand system tracts (LST) and highstand system tracts (HST). Fika Shale and shale members of the Gongila Formation found within the transgressive system tracts (TST) constitute the source rock. In contrast, the shale members of the Gongila, Kerri–Kerri, and Chad Formations, which lie within HST, are the seal. Depth surface maps were generated from seismic data, and two prospects and eight leads were identified across the maps. Seismic facies were interpreted from seismic data. The facies identified are named D, E, and Bh, which correspond to continuous high/low amplitude, low amplitude/high impedance, and high amplitude discontinuous, respectively. As E facies ranks highest, the Bh facies ranks lowest. The root mean square (RMS) and the sum of the negative amplitude attributes were run on the generated surfaces. The results show localized amplitude anomalies within the surfaces of the formations. The map generated from the above results shows clusters of bright amplitude which indicates traces of hydrocarbons within the shapes. These amplitudes are highest in the Kerri–Kerri Formation and are identified as prospective zones. Geothermal gradients of the field were calculated from the bottom hole temperature data, and they range from 3.4 °C/100 m to 4.0 °C/100 m with an average of 3.65°/100 m and a standard deviation of 0.01 °C/100 m. Temperature values of shale units of the formations calculated from geotemperature equation range from 30.99 to 202.45 °C. This shows that some shale units of some formations are thermally mature to cook petroleum. The hydrocarbon window model generated from the mathematical equation indicates that the oil window is between 1178.1 and 2547.9 m, while the gas window is between 2547.9 and 5424.7 m. This study shows a hydrocarbon prospect in Seloken Field, Bornu Basin, because most of the petroleum system elements are in place.