Determination and distribution of Formations thickness in Baga/Lake sub-basin using seismic imaging and well data, Chad Basin Nigeria

Abstract

The Borno Basin is located in North-Eastern Nigeria, formed in the Early Cretaceous. Deposition of sediments in the basin occurred during rifting. The sediments are mainly lacustrine shales and sandstones. This work was undertaken by the integration of 3D seismic interpretations and the well data analysis of eight wells fairly distributed in the study area to determine the thickness of the formations within the sub-basin. Da-1 well used in this study was subdivided into stratigraphic units based on the regional stratigraphic subdivision of the Chad basin and was later correlated with other wells using the similarity of observed log responses. Density and sonic logs were used to generate synthetic seismograms for seismic to well ties. Five horizons were interpreted, representing the tops of the formations on the 3D seismic data covering the block, average velocity function with a maximum residual of 0.48% was used for the time to depth conversion in all the generated maps. There is a general thickening of sediments from the west to the east and the estimated thicknesses of the various Formations in the Baga/Lake sub-basin are; Chad (400-750 m), Kerri-Kerri (300-1200 m), Fika (300-1000 m) and Gongila (100-1300 m). The thickness of the Bima Formation could not be established because the deepest well terminates within the Formation. This is a modification to the previous and widely referenced studies of over fifty decades that based the estimation of formation thickness within the study area on the observed outcrops and the use of a few water boreholes.