Abstract

Depositional facies, diagenetic overprints, and fracturing all have an impact on the quality and architecture of carbonate reservoirs and frequently result in complex, multi-pore systems that are intricately connected and difficult to predict. These processes are coupled and impact to varying degrees subsurface storage capacity and fluid flow characteristics. Yet, the low resolution of seismic data, combined with the wide spacing typically found between hydrocarbon wells, makes the quantification of reservoir properties in interwell volumes challenging. Reservoir equivalent rock sequences that are exposed at the earth’s surface are invaluable field laboratories as they enable 3D mapping of facies architecture, diagenetic overprints, and structural elements at the interwell scale. This dissertation aims to illuminate the interwell region blindspot by conducting an advanced three-dimensional outcrop analog investigation and paleohydrodynamic modeling to better understand the processes that control depositional systems and diagenetic overprints in Saudi Arabia's late Jurassic reservoir sequences. The reservoir-prone sediments of the Oxfordian Hanifa and Kimmeridgian Arab Formations were deposited primarily in shallow marine lagoons and consist of a diverse range of facies, including barren to bioturbated wackestone, peloidal/foraminiferal grainstone, sponges (stromatoporoid and cladocoropsis), corals, and oncoidal grainstone. The findings reveal that hydrodynamics has a significant impact on the spatial distribution and vertical stacking of carbonate facies, especially the architecture and connectivity of stromatoporoid-coral buildups. Drone-based hyperspectral data of the investigated outcrops of the Arab Formation combined with petrographic, geochemical, burial history, and fracture analysis indicates three stages of diagenetic alteration that resulted in the formation of dolomite with a unique vertical and lateral architecture and textural distribution. Cyclic dolomitization started with slightly evaporated seawater during the shallowing-up phases, then recrystallized upon burial, and was finally overprinted by hot fluids channelled by the NW-SE regional fracture trend. An improved understanding of depositional and diagenetic processes, as well as their impact on the vertical and lateral distribution of reservoir properties, in particular the porosity and permeability, is crucial for the development of geologically realistic reservoir models, fluid flow heterogeneity scenarios, and optimal subsurface management strategies.

This thesis establishes the value of the investigated surface rock exposures for providing a valuable process-based understanding of depositional systems and diagenetic overprints for the most important reservoir sequence of Arabia.  The new techniques developed for arriving at these conclusions have the potential for wide application beyond the Jurassic rock sequences investigated for this dissertation.