Enhanced Reservoir Characterization of Complex Carbonates by Integrating Diagenesis with Petrophysical Properties

Abstract

Carbonate reservoir characterization is often challenging due to variable mineralogy, pore-geometry, texture, and diagenetic processes that modified the rock fabric and its petrophysical properties affecting rock typing, reservoir-potential evaluation, and deliverability prediction. This work implements a multidisciplinary petrophysical discrimination scheme that draws upon the diagenetic history of the rock to resolve such characterization challenges and optimize field development practices. This study integrates sequence stratigraphy, core description, petrography, diagenetic analysis, mineralogy, routine core analysis (RCA), mercury injection capillary pressure (MICP) and wireline logs to define Diagenesis-Integrated Reservoir Rock Types (DI-RRT). The DI-RRT are established by delineating the continuous mineral phase, flow-dominant pore types, and main diagenetic processes. The data integration facilitated DI-RRT predictions, DI-RRT-constrained permeability and saturation-height modeling in all wells across the field. This rock typing scheme effectively classifies reservoir potential and delineates the contrast in the reservoir's flow and storage properties. Diagenesis, linked to lithological and pore attributes, serves as an effective discriminant for rocks of similar depositional and lithological settings but contrasting reservoir behavior. This is evident in reservoir intervals of high-energy depositional facies, which showed distinct petrophysical trends due to post-depositional modifications. Calcitic DI-RRT of mainly grain-dominated fabric and moldic porosity exhibits consistently low-to-modest potential that varied in response to the intensity of leaching, cementation and compaction. On the contrary, dolomitic DI-RRT manifest six distinctive behaviors distinguished by pore-type, texture, replacive dolomitization, dissolution and cementation. The reservoir quality is significantly enhanced where replacive dolomitization accompanied intensive dissolution, even with patchy anhydrite cementation. This scheme enabled the identification and mapping of these high-productivity zones in wells across the field. It further granted a good match between log- and core-based predictions of permeability and saturation. Integrating diagenesis with petrophysical rock types, wireline logs and field observations enhances reservoir characterization in complex carbonate reservoirs. It boosts current intellection of reservoir performance, identifies porosity-permeability and saturation trends with higher precision, and capitalizes on reservoir-quality zones during the field-development cycle. It further provides a roadmap to distribute petrophysical properties in uncored wells and 3D models optimizing subsequent static and dynamic models.