Geochemical characterization of lithofacies and organic facies in Cretaceous organic-rich rocks from Trinidad, East Venezuela Basin

Shelf petroleum system of the Columbus basin, offshore Trinidad, West Indies. I. Source rock, thermal history, and controls on product distribution

“…Ranges of average TOC and HI of the organic-rich samples in the Naparima Hill and Gautier Formations obtained from eight wells in the basin are 1.9 -7.9 wt% TOC and 191 -596 mg HC/g TOC, and 1.6-4.2 wt% TOC and 114-538 mg HC/g TOC, respectively. Requejo et al (1994) also showed that the source rocks belong to carbonate, siliceous, and siliciclastic lithofacies, with the latter two tending to be localized in south-central Trinidad.…”

“…All of these units show indications of deposition in deep neritic (outer shelf to upper slope) to bathyal environments (Koutsoukos & Merrick, 1986). The organic-rich Gautier and Naparima Hill formations, which constitute a stratigraphic thickness in excess of 3000 ft (915 m) in southern Trinidad (Ablewhite & Higgins, 1968), are considered the source rocks for the majority of petroleum in Trinidad (Requejo, Wielchowsky, Klosterman, & Sassen, 1994;Rodrigues, 1987). These units are broadly agecorrelative to the La Luna, Querequal and other upper Cretaceous source rock sequences in Venezuela and adjacent areas (Talukdar, Gallango, & Ruggiero, 1987;Zumberge, 1984).…”

“…Observed variations in kerogen type, quality, GC, and biomarker characteristics of the Naparima Hill and Gautier source rocks led Rodriguez (1987) to conclude that substantial variation in organic facies exists within the Upper Cretaceous section. Requejo et al (1994) made a detailed geochemical characterization of the Cretaceous organic-rich rocks from the Southern Basin of Trinidad and attempted to correlate organic facies with lithofacies. Variations in lithofacies and organic facies occur both stratigraphically and regionally, with the best-quality oil source rocks existing in the Cenomanian to Campanian age strata.…”

“…Cretaceous formations in the Trinidad area have been studied in considerable detail for source rock evaluation (Requejo et al, 1994;Rodrigues, 1987). Rodrigues (1987) performed geochemical analysis on a large number of shale and marl samples from the Southern Basin.…”

Geochemistry and possible origin of the hydrocarbons from Wells Zhongshen1 and Zhongshen1C, Tazhong Uplift

“…They both demonstrate dominant pregnanes, which is probably related to their high maturity (Eglinton et al, 1988;Requejo et al, 1994;Wingert and Pomerantz, 1986), along with C 27 > C 28 <C 29 normalized relative abundance of regular steranes. However, a distinct difference is also observed.…”