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Geochemical Assessment and Petroleum Systems in the Sinú-San Jacinto and Sinú-San Jacinto Offshore Basins, Northwestern Colombia

Abstract

The Sinú-San Jacinto (S-SJ) and Sinú-San Jacinto offshore (S-SJOFF) Basins have abundant oil and gas manifestations, of diverse characteristics, giving evidence of the existence of various petroleum systems. The oils can be separated into two or three oil families. The first oil family is derived from Upper Cretaceous source rocks deposited in anoxic marine environment. The second oil family were derived from rocks of tertiary age (Oligocene), deposited in deltaic marine environments with high input of terrestrial organic matter. The third group includes oils possibly related with mixing processes or derived from other tertiary source rocks. Regarding source rock correlations, Cansona Formation extracts exhibit positive correlation with the oil Family I, and extracts from Ciénaga de Oro Formation of Plato Subbasin exhibit good correlation with the second oil family. Ciénaga de Oro Formation is the main reservoir in the basin with an average thickness ranging from 300 to 500 feet, and porosity of 15 %. Also there are less well known reservoirs in the Paleocene and Eocene sequences and in younger intervals, in particular related to Tubará and Porquero formations. The presence of Pre-Cansona Sequence could be inferred and in this case could not be ruled out the existence of source rock intervals in it. In Sinú-San Jacinto and Sinú-San Jacinto offshore basins three (3) kitchens or pods of generation are postulated, with oil generation and expulsion determined by geochemical modeling at depths greater than 12,000 feet. Associated with each of the three kitchen, there are three active petroleum systems: Pre-Cansona – Pre-Cansona (?), Cansona - San Cayetano (.), and Ciénaga de Oro - Ciénaga de Oro (.). This paper evaluates the characteristics of the oils, classify the oil families and source rock correlations, assess the petroleum systems's elements and processes, and proposes some areas of exploratory interest according the petroleum charge.