Improved Massive Dolomite Mapping and Stratigraphic-Diagenetic Traps Opportunity

Abstract

Objective: Stratigraphically discordant massive dolomite bodies have long been documented in the study area because it strongly affects the reservoir quality. Dolomite may behave as either a conduit or a barrier to flow depending on the original depositional texture, the chemistry of dolomitizing fluid, previous diagenetic stages, the timing and type of dolomitization. In this paper, we discussed the potential of stratigraphic-diagenetic traps within these dolomite bodies using geological and seismic data. Methods: This study integrates geological and forward diagenetic modeling focusing on the following aspects: (1) developing an improved diagenetic-lithofacies classification based on dolomite content and porosity, (2) detailed 3D geological modeling to better delineate the spatial distribution of the massive dolomite, (3) Porosity and permeability modeling to predict reservoir quality, (4) integrating seismic attribute analysis, 3D geological and forward diagenetic modeling to investigate the dolomitization mechanisms and their impact on reservoir quality, and (5) proposing stratigraphic-diagenetic trapping models and predicting the regional reservoir/seal sets. Results: Five main conclusions have been derived from this study: (1) a classification of four diagenetic-lithofacies types was established with porous limestone and porous dolostone being the main reservoirs and tight limestone and tight dolostone the main lateral seal; (2) the distribution of massive dolomite varies but is developed mainly in the northeastern part of the study area, with a southward decrease in dolomite content; (3) partial dolomitization improves, but over-dolomitization reduces reservoir quality; (4) two episodes of dolomitization are likely, supported by core, thin-section, geochemistry and seismic data. The first episode was driven by tectonic compression which developed adjacent to the Gotnia salt basin. The second episode of late hydrothermal dolomitization resulted in overprinting of early dolomite. It may have been related to structural reconfiguration and associated fracture systems; and (5) the dolomite front area holds the best potential for stratigraphic-diagenetic traps two of which were identified. These traps may include porous limestone and dolostone sealed by tight limestone or against tight dolomite. General results: an improved lithofacies-diagenetic classification is proposed based on calculated porosity changes from dolomitization. This integrated study significantly improves the understanding of the two dolomitization mechanisms and their impact on stratigraphic-diagenetic trap generation. Therefore, it opens more opportunities for exploration and production.

AAPG Datapages/Search and Discovery Article #90364 © 2019 AAPG Middle East Geoscience Technology Workshop, Integrated Emerging Exploration Concepts: Challenges, Future Trends and Opportunities, Dhahran, Saudi Arabia, December 2-4, 2019