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Title: Genesis of natural fracture systems in mudrocks (Upper Cretaceous-Eocene), Jordan
Author: Abu-Mahfouz, Isra'a Salem
ISNI:       0000 0004 7654 6915
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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Organic-rich mudrocks are of great importance to the petroleum industry, potentially acting as source rocks, cap rocks or unconventional reservoirs. The analysis of natural fractures in mudrocks is crucial for the evaluation of their impact on fluid storage and flow. This research focuses on the investigation of natural fractures in organic-rich mudrocks, using integrated core, borehole image, field, petrographic, and geochemical techniques. The aim is to obtain a better understanding of the development of natural fracture systems in mudrocks, regarding their stratigraphic distribution, timing and formation mechanism. Natural fractures are abundant in the Upper Cretaceous-Eocene Belqa Group of Jordan. Distribution analyses of fractures resulted in an informal division of the stratigraphic section into three units; upper and lower highly fractured units and a middle weakly fractured unit. The host lithology represents an important factor influencing fracture distribution and formation; calcite-filled veins were observed in calcareous mudstone and carbonate intervals, and silica-filled veins were observed in chert intervals. Bitumen is present within natural fractures, either as macroscopic deposits, or as inclusions in the fracture cement, suggesting that hydrocarbons were present throughout and after the opening of fractures. Fractures are commonly associated with concretions in the Upper Cretaceous strata, implying that fracturing is sensitive to diagenesis. Open fractures in the succession are often confined to specific beds minimizing the potential leakage risk due to the high fracture intensities within the upper and lower caps which can be posed where fracture networks are connected. Mechanical stratigraphic controls on fracture distribution, relationship to compaction and early cementation, as well as the presence of bitumen within fractures, suggest that fracturing was affected by different processes and has different timings. Fracture formation mechanisms can be summarized as fluid pressuring (bedding-parallel veins), early diagenesis (folded calcite veins and silica veins) and late tectonic processes (planar calcite veins and joints, and gypsum veins). Petrographic and geochemical analyses show that fractures have developed at two main stages; (1) early diagenesis (calcite veins, ~40-30 Ma, were folded by sediment compaction), followed by fracturing during burial diagenesis, and (2) late fractures (~25-20 Ma) formed during uplift and extension, or fault reactivations.
Supervisor: Cartwright, Joe ; Hooker, John Sponsor: Shell-Oxford Collaboration
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Petroleum Geology ; Geology, Structural--Research