--> Pre-Oxfordian Source Rocks on the Western Margin of the Gulf of Mexico

2020 AAPG Hedberg Conference:
Geology and Hydrocarbon Potential of the Circum-Gulf of Mexico Pre-salt Section

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Pre-Oxfordian Source Rocks on the Western Margin of the Gulf of Mexico

Abstract

Geochemical data on the origin of oil and gas around the western Gulf of Mexico are mainly focused on the Upper Jurassic or younger rocks (González and Holguin, 2001; Guzmán, et al., 2001), and only a few studies are available to evaluate older rocks. Some data from outcrops in Peregrina region in Tamaulipas show that the Silurian Cañón de Caballeros Formation is composed of limestone and black shale, with woody and aquatic macerals (AM), Total Organic Carbon (TOC) of 0.59% to 0.53%, and Thermal Alteration Index (TAI) values of 4-/4 for thermal maturity. The Mississippian Vicente Guerrero Formation consists of sandstone and black shale containing AM kerogen, 0.5% or less of TOC, and TAI 4-/4. The Pennsylvanian limestone Del Monte Formation and the turbiditic siliciclastic succession of the Permian Guacamaya Formation have similar values of AM kerogen, 0.5% or more TOC, and TAI 4-/4 (Sandoval-Cambranis, 1980). In the Tampico-Misantla Basin the Tepehuaje 1, González 101 and Zamorina 1 wells drilled the Guacamaya Formation without showing hydrocarbons. The Pennsylvanian Upper Santa Rosa Formation, in the Comalapa region in Chiapas, is a thick succession of shale and sandstone which is structurally deformed, and some samples of carbonaceous slate have values from 0.18% to 0.29% TOC. The data of all these rocks suggests that in the Paleozoic sedimentary deposits the predominant organic matter is of type I and II, with poor TOC, and high thermal evolution, resulting in poor gas-prone potential. Elements of the Petroleum System of pre-Oxfordian in Mexico suggest that favorable conditions exist for storing hydrocarbons in carbonates and siliclastic fractured rocks, and stratigraphic and structural traps. The regional seal is salt or anhydrite, which migrated in space and time, with wedges onlaping paleogeographic highs. Recognition of sequence boundaries is crucial to separate a pre-salt sedimentary prism. It is convenient to obtain more geochemical data and modeling the migration and synchrony to predict evolution of possible accumulation and evolution of hydrocarbons.