Diagenetic studies of the Eagle Ford and Indidura Formations in the Sabinas basin: Implications for source rock maturation

Abstract

We analyzed the dynamics of interacting fluids within the Cenomanian-Turonian source rocks associated with hydrocarbon generation. Diagenetic alterations, authigenic minerals, isotopic data (δ13C and δ18O) of the matrix and carbonated cement, fluid inclusions, and fluorescence of hydrocarbons present were examined. Three thermal episodes related to diagenetic cements were defined, but only one is associated with gas production with temperatures of 99° and 168 °C. The isotopic data of the cements and segregations of calcite indicate that their generation is associated with the production of CO2 derived from organic matter. Therefore, they must have been formed during the interaction of hot fluids, organic acid, and meteoric waters. Due to the increased compaction and deepening of the succession, these fluids migrated through the dissolution, re-crystallization, and fracture zones, with a mainly lateral direction until reaching the large faults. For this, we can observe how the hottest fluids are expelled closer to the limits of the basin. The presence of light and intermediate hydrocarbons in permeable zones indicates that the Eagle Ford and Indidura Formations are also acting as reservoir rock due to the fracture system that allowed fluid circulation. Finally, a thermal convection model is proposed in the Sabinas basin with the microthermometric data of fluid inclusions, observing the wet gas and dry gas production zones through stratigraphy.