DIAGENETIC STUDIES IN THE SABINAS BASIN: IMPLICATIONS FOR SOURCE ROCK MATURATION

This study comprehensively examines the fluid dynamics within Cenomanian-Turonian source rocks, which are crucial for understanding hydrocarbon generation processes. We investigated diagenetic alterations, the formation of authigenic minerals, and collected isotopic data (δ13C and δ18O) from both the matrix and carbonate cement. Additionally, we analyzed fluid inclusions and hydrocarbon fluorescence to gain insights into the thermal history and fluid interactions.

Three distinct thermal episodes related to diagenetic cement formation were identified. Among these, only one-episode correlates directly with gas production, characterized by temperatures ranging between 99°C and 168°C. Isotopic analyses of the cements and calcite segregations revealed that the genesis of these minerals is closely tied to CO2 production derived from organic matter decomposition. This indicates that their formation occurred during the interaction of hot fluids, organic acids, and meteoric waters.

As the geological succession experienced increased compaction and deepening, these fluids migrated through zones of dissolution, recrystallization, and fractures. The migration predominantly followed a lateral trajectory until reaching major fault systems. This migration pattern underscores how the hottest fluids are expelled near the basin boundaries. Furthermore, the presence of light and intermediate hydrocarbons in permeable zones suggests that the Eagle Ford and Indidura Formations function as reservoir rocks. This is facilitated by a fracture system that enabled extensive fluid circulation.

To better understand these processes, a thermal convection model for the Sabinas Basin was developed using microthermometric data from fluid inclusions. This model delineates the zones of wet gas and dry gas production within the stratigraphic framework. The insights gained from this model highlight the critical role of thermal convection in hydrocarbon generation and migration.

Overall, this study provides a detailed understanding of the diagenetic processes, fluid interactions, and thermal history within Cenomanian-Turonian source rocks. These findings are essential for improving hydrocarbon exploration strategies and enhancing our knowledge of subsurface fluid dynamics.