Geochemical evaluation of southern Tampico-Misantla Basin, Mexico: Oil-oil and oil source rock correlations.

摘要

The bulk of the oil in the southern Tampico-Misantla Basin is in Upper Cretaceous reservoirs of the Golden Lane and Poza Rica Trend, with additional production from Upper Jurassic and Eocene reservoirs. The nature of the source rocks that gave rise to these oils is not known. This study presents results of geochemical characterization of oils and possible source rocks from the Tertiary, Cretaceous, and Upper Jurassic formations of the study area. Oil-oil and oil-source rock correlations are based on analyses of n-alkanes, isoprenoids, stable carbon isotopes, and biomarkers in oils and rock extracts.;The data indicate that the Tertiary formations are thermally immature and poor source rocks. Cretaceous formations have entered the oil window and are fair source rocks, whereas Upper Jurassic formations, namely, the Santiago, Taman, and Pimienta Formations, are good source rocks in the early stage of oil generation. Upper Jurassic Formations in the study area consist of shales and carbonates, and were deposited in environments from suboxic to anoxic.;Analyses of the oils suggest that they have a common origin and that they were generated from an organic carbon-rich carbonate source rock containing algal and bacterial organic matter deposited in an anoxic environment. The physical and chemical differences among oils are explained by migration effects, thermal maturation differences, changes of organic facies of the source rock, and contamination during migration through younger rocks. Oils display geochemical similarities to Upper Jurassic carbonate source rocks. However, it is difficult to correlate oils and rocks in the study area. Therefore, it is possible that the studied Upper Jurassic-Cretaceous section has not contributed significantly to the oils entrapped locally. These data and geological considerations imply that oils have migrated from deeper facies downdip of the study area, most likely from offshore Gulf of Mexico.