Petroleum geochemistry of oil and gas from Barbados:Implications for distribution of Cretaceous source rocks and regional petroleum prospectivity

摘要

Petroleum produced from the Barbados accretionary prism (at Woodbourne Field on Barbados) is interpreted as generated from Cretaceous marine shale deposited under normal salinity and dysoxic conditions rather than from a Tertiary source rock as previously proposed.Barbados oils correlate with some oils from eastern Venezuela and Trinidad that are positively correlated to extracts from Upper Cretaceous La Luna-like source rocks.Three distinct groups of Barbados oils are recognized based on thermal maturity,suggesting petroleum generation occurred at multiple levels within the Barbados accretionary prism.Biodegradation is the most significant process affecting Barbados oils resulting in increased sulfur content and decreased API gravity.Barbados gases are interpreted as thermogenic,having been co-generated with oil,and show mixing with biogenic gas is limited.Gas biodegradation occurred in two samples collected from shallow reservoirs at the Woodbourne Field.The presence of Cretaceous source rocks within the Barbados accretionary prism suggests that greater petroleum potential exists regionally,and perhaps further southeast along the passive margin of South America.Likewise,confirmation of a Cretaceous source rock indicates petroleum potential exists within the Barbados accretionary prism in reservoirs that are deeper than those from Woodbourne Field.