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Source Rock Analysis in the Western Caribbean Region

Abstract

Abstract

An integrated approach of geological and geochemical analysis of the Western Caribbean Region identified the existence of seven source rocks of Cretaceous and Tertiary ages. Each source rock has distinctive organic facies, aerial distribution, and petroleum generative potential. The evaluated data came from samples of hydrocarbon fields, oil and gas seeps, cuttings and cores from exploration and scientific wells, and outcrops. The seven source rocks identified are: 1) middle Eocene Yellow Limestone Group located on Jamaica Island. TOC content in this sequence is good to excellent; Kerogen varies from type II to III but mainly is type III. This source rock is poorly constrained and immature with very limited distribution; 2) lower-middle Eocene Punta Gorda and Touche formations along the Nicaraguan Rise. Source rock distribution in this area is characterized for drastic organic facies changes from a typical marine source rock with good potential type II kerogen to an extremely poor or lean sequence; 3) upper Cretaceous Cenomanian-Campanian Loma Chumico Formation is found mainly in the northwestern side of the Chorotega Block. This unit is an excellent potential source rock with a TOC average value of 15% and a kerogen type I/II; 4) middle Miocene Gatun Formation in Costa Rica and Panama containing good to excellent TOC and kerogen Types II and III; 5) upper Cretaceous, Coniacian-Campanian Cansona Formation found only in the Sinu-San Jacinto folded belt. This source rock has good to excellent TOC, type II organic matter, and excellent potential to generate oil; 6) Oligocene to early Miocene Cienaga de Oro and Lower Porquero formations in the Lower Magdalena Valley Basin. This sequence has fair to good potential to generate gas and some oil, but the huge thickness of the sequence compensates the moderate potential; 7) upper Cretaceous Coniacian-Santonian strata in the Colombian and Venezuelan deep basins associated with the upper Cretaceous Oceanic Anoxic Event in the region. Thin layers, just meters thick in the best of the cases, with high TOC and fair quality organic matter values have been identified in some of the DSDP/ODP wells. Despite the presence of very thin organic-rich layers in the DSDP/ODP wells along the Colombian and Venezuelan basins, this Coniacian-Santonian sequence could have a higher petroleum potential near the continental margin, where thicker sedimentary package has been interpreted.