Loading...
Effects of igneous intrusions on gas content, composition, and origin in coalbed gas play in Central Kalahari Karoo Basin, Botswana
Zhumazhanova, Aigerim
Zhumazhanova, Aigerim
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2023
Date Submitted
Keywords
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
2024-04-18
Abstract
Numerous studies revealed that igneous intrusions could have positive, negative or negligible effect of on coal bed methane plays.
In Botswana, magmatic intrusions are largely present in the form of dolerite sills and play important role in CBM development.
Previous studies of igneous intrusions in the area suggested that the rank, characteristics, and thermal maturity of Permian coals were dramatically impacted by the sills' intrusion.
This study attempts to understand the influence of igneous intrusions on gas content, composition, and origin of the CBM play in Botswana. The results received indicated a positive effect of dolerite intrusions on total gas content. Total gas content increase towards dolerite contacts. In addition, a considerably larger vertical influence of thinner sills (with thickness below 5.2 m) on TGC per sill thickness is noted.
Another finding of the study is a negligible effect of dolerite sills on gas composition. Heat- affected and non heat-affected gases are dominated by methane (CH4 >96 mole %). Heat-affected gases have a slightly lower content of C2 and C3, and CO2 compared to non-heat-affected samples, but the difference is minor.
Additionally, data analysis did not demonstrate any noticeable influence of dolerite sills on isotopic composition. Carbon isotope values for methane and carbon isotope values for carbon dioxide in heat-affected and non-heat-affected samples are in the same rage. Also, no significant changes in isotopic composition are established with the proximity to the dolerite contact.
Analysis of isotopic composition indicated biogenic gas origin with the mixture of early mature thermogenic gas. Despite the data showing that dolerite sills positively affected coal's thermal maturity and rank, it did not show any evidence that dolerite intrusions cause more thermogenic gas generation, as would generally be anticipated.
Dolerites demonstrated the ability to control the ash, volatile matter, and moisture content: Ash content increased while volatile matter and moisture levels reduced as one got closer to the dolerite contact. Additionally, the presence of the dolerites causes changes in the maceral composition: the vitrinite and liptinite content is decreased, while the inertinite concentration is increased in heat-affected samples.
Understanding how intrusions affect CBM's gas content, composition, and origin is essential knowledge that could benefit CBM play exploration, prospecting, assessment, and geological and economic risk mitigation in the area.
Associated Publications
Rights
Copyright of the original work is retained by the author.