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Title: The geochemistry of oil in fractured basement rocks
Author: Baba, Mas'ud Umar
ISNI:       0000 0004 7972 5345
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2019
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The occurrence of hydrocarbons in basement reservoirs has been attracting much interest from oil companies and researchers alike due to the increasing demand for exploring unconventional hydrocarbon resources. Most of the oils found in basement reservoirs are biodegraded due to the presence of microbial communities introduced by circulating water along fractures. In this research, I assess the occurrence of bitumen in fractured basement rocks across the United Kingdom using organic geochemistry, petrography and thermal history techniques. Organic geochemical studies reveal the presence of biodegraded oils. I use isoprenoids, hopanes, 25-Norhopanes and diasteranes ratios to rank the oils in terms of degree of biodegradation, and to distinguish between recent and ancient biodegradation. Results reveal that almost all bitumen occurrence in fractured basement rocks were biodegraded and solidified in the past. Biomarkers also correlate the bitumen to their original source, as well as constrain their level of maturity. The biomarker data used in this study offer an additional type of evidence for basement-hosted microbial activity. Petrographic studies using scanning electron microscopy (SEM) reveal that bitumen was emplaced as a viscous liquid before been solidified as a result of biodegradation in the subsurface. In most cases, multiple stages of fracturing facilitated the emplacement of hydrocarbons and the circulation of mineralising fluids which led to the precipitation of ore minerals in the basement. Pyrite occurs in abundance in association with bitumen and is concluded to be a probable consequence of microbial sulphate reduction. Thermal maturity from biomarkers and fluid inclusion analysis from minerals constrained the level of heating experienced by the rocks and revealed that temperatures were suitable for microbial activity. The biomarkers also reveal that the source rock has reached the oil window and therefore, was able generate and expel hydrocarbons.
Supervisor: Parnell, John ; Bowden, Stephen Sponsor: Petroleum Technology Development Fund (PTFD) ; Nigeria
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Hydrocarbon reservoirs ; Bitumen ; Biodegradation ; Microorganisms ; Biochemical markers