Lorna C. Chesir*, Peter O. Ongoma*

Department of Chemistry, Egerton University, P.O. Box 536-20115, Egerton, Kenya 

Abstract

Understanding the association of organic matter and minerals in petroleum source rocks is a vital component of the hydrocarbongeneration process, especially in unconventional reservoirs, which are the targets of hydrocarbon exploration today. In this study, five source rock samples selected from three wells namely, Chalbi-3, Sirius-1, and Ndovu-1wells from the Anza basin, were investigated to characterise the thermal decomposition process using differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG) with a heating rate of 10 °C min−1 in an oxidizing atmosphere. The Anza basin is a sedimentary basin located in the north-eastern part of Kenya. The source rocks displayed variable degrees of organic richness, with TOC contents ranging from 0.54 to 1.99 wt. %, at subsurface depths ranging from 1067–3100 m. The Ndovu-1 (H) sample had the highest TOC value, while Sirius-1 (F) had the lowest. In all the analyses, the TG/DSC curves allowed three distinct decomposition regions of organic matter and inorganic matter decomposition identified as i) low-temperature oxidation of bitumen (temperature ranging from 257 °C to 350 ° C), ii) thermooxidation of the kerogen (between 430 and 560 °C), and iii) high-temperature decomposition of calcite mineral (between 723 and 747 °C), and clay minerals in the temperature range 907 and 923 °C. There was also a strong correlation between the mass loss and combustion of organic matter in the source rocks

Keywords:

source rocks, TG/DTG/DSC analysis, Thermo-oxidative decomposition, Anza basin

Chesir, L.C & Ongoma, P.O. JKCS 16-1 (2023), 13-19