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Title: Controls on fracture abundance in gently deformed carbonates
Author: Al-Fahmi, Mohammed M.
ISNI:       0000 0004 7430 6969
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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Fractures can profoundly affect the capacity of carbonate reservoirs to store and permeate fluids, depending on the properties and abundance of fractures. Fractures exist abundantly in carbonate outcrops; however, their abundance in subsurface carbonates is obscure because of the data shortages and uncertainties about the factors that drive fracturing in sedimentary basins. The objective of this research is twofold. The first is to study abundance of fractures in gently deformed carbonates, which were generally overlooked. The second is to address measuring fracture abundance using electrical borehole imaging, which is the mostly used method to describe reservoir fractures. Fractures were studied from areas in the gently folded and shallowly (less than 2 km depth) buried interiors of the Arabian Platform. The study areas include outcrops and reservoirs of the Late Jurassic Arab carbonates in the sprawling homocline of Central Arabia and a low-relief dome in Eastern Arabia. The Cenozoic Rus carbonates in the dome outcrops were also studied. Fracture abundance was measured from the outcrops using scanlines and from the reservoirs using core and borehole images of extended-reach drilling. Many systematic properties were drawn on mineralization, orientation, and abundance of fractures. The fractures were found to be opening mode, mostly barren, and exist with subvertical dips, and some regional trends. The fractures display significantly differing ranges of abundance that were controlled by the subtle structural bending of the dome and homocline, carbonate lithofacies, and paucity of fracture mineralization. The borehole imaging was found to significantly lower fracture abundance. The detection of fractures was subject to several factors including size of fracture widths, nature of fracture roughness, and present-day stress field. The results have implications for modeling of fracture systems and tectonic regimes. For example, finding that fracture abundance varies drastically in such gently deformed regions indicates that carbonates are very sensitive to fracturing processes. Moreover, the borehole imaging limitations influence the models of fracture abundance and orientations, which are often used to deduce paleo tectonic regimes and present-day geodynamics in carbonate reservoirs.
Supervisor: Cartwright, Joe ; Walker, Richard Sponsor: Saudi Aramco
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geology, Structural ; Stress ; Arabia ; Fractures ; Carbonate reservoirs ; Arab Reservoirs