EVALUATION OF THERMAL MATURITY OF SOURCE ROCKS IN THE BORNU BASIN USING GEOCHEMICAL AND STATISTICAL METHODS

Abstract

ABSTRACT In this study, statistical analysis of Rock Eval pyrolysis data derived from shale cuttings of some wells in the Bornu Basin was carried out. The aim is to test source rocks availability of the Bornu basin that is believed to have high prospective potential for hydrocarbon generation. The pyrolysis data are; total organic carbon (TOC%), generating source potential (S2), production index (PI), oxygen and hydrogen indices (OI, HI) and (Tmax). Graphical evaluation of these data shows that sediments of both early and late Cretaceous have poor, fair and good potential for hydrocarbon generation. They are, characterized by Kerogen type III and type II/III that are capable of generating mainly gas and mixed gas and oil, respectively. The result also shows that the organic matter, are immature to mature thermally. In addition, cluster analysis reveal that the source rock in the Bornu Basin can be separated into two major clusters. Cluster I are source rocks characterized by HI of 10 to 162 (mg/g), TOC from 0.17 to11.83 wt%, S1 from 0.04 to 0.58 (mg/g) and S2 from 0.11 to 1.53 (mg/g) indicating poor to good source rocks with kerogen of type III–II and type II and are capable of generating oil and gas; this occur in shale sample of Coniacian to Turonian of late Cretaceous in Kinasar 1 well. Cluster II are source rocks characterized by HI from 50 to 280 (mg/g), TOC from 1.62 to 3.80 wt%, S1 from 0.08 to 0.3 (mg/g) and S2 from 1.90 to 7.38 (mg/g) indicating fair to very good source rocks with kerogen of type II and are capable of generating oil and limited gas; this occur in shale sample of Albian and older age in faltu 1 well and one shale sample of upper Santonian to Campanian in Ngor 1 well. Moreover, Pearson’s correlation analysis shows a moderate correlation between TOC and S2, indicating S2 is a moderate explainable variable for TOC. A weak positive correlation between TOC and S1, TOC and HI and TOC and Tmax indicating that S1, HI and Tmax are very weak explainable variable for TOC. Furthermore, very weak positive correlation between TOC and S1, HI, Tmax and OI indicate that the maturity of source rocks is independent of the amount of organic matter in the Bornu Basin.