Carbonate facies, diagenesis and sequence stratigraphy of an eocene nummulitic seservoir interval (jdeir formation), offshore NW Libya

• Main Author: Alhnaish, Abdelhakim S.
• Format: Thesis
• Language: unknown
• Published: 2006
• Subjects: Planktonic foraminifera
• Online Access: http://etheses.dur.ac.uk/2332/; http://etheses.dur.ac.uk/2332/1/2332_342.pdf

This study investigates the sedimentology, petrology and depositional environments of a major Early Eocene nummulitic reservoir unit: the Jdeir Formation, from offshore NW Libya in the Mediterranean Sea. This formation is a prolific hydrocarbon-producing unit that was deposited as part of the Mesozoic-Cenozoic stratigraphic fill of the Sabratah Basin. The Sabratah Basin is an elongate ESE/WNW trending fault-bounded basin that originated as a left lateral pull-apart basin during the Late Triassic-Early Jurassic. Presented in this thesis is a review of the tectonostratigraphic setting of the Jdeir Formation, an evaluation of the facies and an interpretation of the depositional environment of the platform. During this Master project, diagenesis was also evaluated with the aim of better understanding reservoir development of the Jdeir Formation. On the basis of detailed core description and petrographic study eight facies have been distinguished. These are: (1) Planktonic Foraminifera Fades, (2) Discocyclina-Nummulitc Facies, (3) Nummulite Facies, (4) Alveolina Facies, (5) Peloidal-Bioclastic Facies, (6) Mollusc Facies, (7) Echinoderm Facies and (8) Sandy- Bioclastic Facies. These are interpreted as having been deposited in open-marine, fore-bank, bank, lagoonal (back-bank) and restricted lagoonal environments. Nummulitic rudstones, dominated by B-forms with minor A-forms, comprise the upper part of bank, and float/rudstones form the lower part of the bank. Abrasion and fragmentation of bioclasts resulted from the transport of sediment from palaeohighs and their reaccumulation into intra-, or back-bank environments. Discocyclina and planktonic foraminifera-rich facies formed in open-marine environments, with the former accumulating towards the base of the photic zone. The back-bank or lagoonal deposits are highly variable, were sometimes affected by siliciclastic influx, and may be dominated by molluscs, echinoderm debris or imperforate foraminifera. Facies and thickness variations between the three wells were ...