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Title: Timing reservoir quality enhancement at the Shuaiba/Nahr Umr Boundary, Oman
Author: Al Hajri, Aisha Ali Hamood
ISNI:       0000 0004 5358 0483
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2015
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Despite the fact that both depositional and diagenetic processes control pore geometries and hence reservoir complexity, there is a tendency to underestimate the impact of diagenesis on petrophysical reservoir properties. Moreover, there is a lack of published data on the geometry of carbonate pore systems, despite the fact that pore shape and size can highly affect permeability. Seismic and core data of the Shuaiba Formation in northern Oman oil fields highlight the occurrence of large fractures within this formation, yet only few published studies focus on the diagenesis and how it enhances the heterogeneity of the Shuaiba Formation as a reservoir. Integrated depositional and diagenetic study (i.e. petrographic, geochemical, and structural evaluation) is essential if the heterogeneity observed in these carbonate rocks in Oman and elsewhere is to be understood. This thesis presents the first regional, integrated analysis of the upper 10 m – 15 m of the Shuaiba Formation in North Oman, where a noticeable modification in porosity, mostly by solution-enhancement, is documented below the Albian-Aptian unconformity in a number of oil fields. Different hypotheses were tested to justify this modification, including dissolution during sub-aerial exposure, corrosion by burial fluids, and dissolution by fluids sourced from compacted overlying shales of the Nahr Umr Formation. Detailed characterization of the Shuaiba Formation pore system and associated pore- filling cements was accomplished, including classification of pore types and their regional distribution within lithofacies, identification and geochemical characterization of the main diagenetic cement phases and the timing of pore modification relative to the main tectonic events that postdate the deposition of the Shuaiba Formation. Finally, 2D and 3D characterization of the pore system was conducted via multi-scale image analysis. The results of this study show that negligible volumes of porosity were formed at the top of the Shuaiba Formation during sub-aerial exposure. No evidences for clay compaction- related dissolution was found. The majority of the pores are interpreted to have formed from the up-dip migration of fluids during hydrocarbon charge in the Late Cretaceous, largely enhancing microporosity, mainly within the matrix. A phase of dissolution in telogenetic setting possibly occurred at the end of the Late Cretaceous along with precipitation of euhedral, sulphur isotope –depleted pyrite. Breaching of the deeper seals is believed to cause recharge of hydrocarbon in the Late Tertiary which might have contributed to the overall pore system of the Shuaiba Formation in the fields with mixed oils.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available