This research project describes an unconventional gas source and carbon sequestration interplay in Mui basin, located approximately 180 Km north-east of Nairobi in Kitui County, Kenya. The area is bound by geographic coordinates 38.16° and 38.24° East and 0.87° and 1.475° South and is approximately 532.45 square kilometers. 400 million tonnes of coal were discovered by the Government of Kenya through its Ministry of Energy in Mui basin in 2010.The research was carried out in partial fulfillment for the award of Bachelor of Science in Geology. The main objective of the research project was to evaluate the natural gas (methane) resource in Mui basin coal and its potential recovery through enhanced coal bed methane recovery by carbon dioxide (CO2-ECBM). In relation to this the geological suitability of Mui basin for carbon storage and the risks associated with injection of CO2 were assessed. The estimated capital gains from applying this process versus conventional coal extraction were calculated and compared. The role of this research is to provide a framework of utilizing the fossil fuel resources in Mui basin with minimal greenhouse gas emissions.
Electric resistivity data was used to delineate the sediment thickness in block A of Mui basin. The sedimentary sequence was found to be thin and therefore unsuitable for the application of CO2-ECBM recovery. Core log data was used to compile the stratigraphy of block C of Mui basin by drawing and interpreting cross-sections. 5 coal seams were identified in block C that are interbedded with mudstones, shales and sandstones between the depths of 80 and 330 meters. Coal seam 5 occurring between 300 and 330 meters with an average thickness of 3 meters was the only one identified as suitable for CO2- ECBM recovery. Geochemical data was used to calculate the gas content in coal seam 5 of block C using an adsorption isotherm equation. The calculated methane resources were found to be 6.938 × 108 m3 and based on a 2 to 1 sorption selectivity of CO2 over CH4 by coals; the coal seam has a 13.8760 × 108 m3 storage capacity for CO2. Cross-sectional analysis revealed seal pairs for the reservoir that are laterally extensive and continuous. Porosity and permeability analyses were used to define the gas flow mechanisms in coal. Faulting was identified as playing a major role in the distribution of the coal seams as seen in the central and southern part of block C where coal seams have been downthrown. Stratigraphic and structural traps, and well design mechanisms were identified as controls to risks associated with CO2- ECBM application by acting as seals preventing leakage from the reservoir and contamination of groundwater resources. The calculated revenue that can be acquired from conventional coal mining was found to outweigh revenue from CO2- ECBM recovery. Deeper coal seams probably lie at the central and southern parts of block C and in block B of Mui basin. Exploration and exploitation of these resources for CO2-ECBM recovery could prove to be more profitable than conventional coal mining in block C of Mui basin. At the current state the CH4 content in Mui basin coal will be a potent greenhouse gas and fire hazard during coal mining. Carbon dioxide should be co-injected with an inert gas like nitrogen to recover as much more methane as possible. The extracted methane could be marketed as liquefied petroleum gas to offset the cost of CO2 injections. Geophysical and geochemical methods are used to monitor the gas migration mechanisms in the coal seam.
