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Syn-Tectonic Sedimentation Over a Miocene Gas-Bearing Structure – Sequence Stratigraphy Case Study of the Aphrodite Field, Levant Basin


The Aphrodite gas field located in the western Levant basin is a large four-way dip closure segmented by a series of NW trending layer-bound faults. The reservoir is comprised of stacked deep marine turbidite sandstones with interbedded mudstones and siltstones of Oligocene - Miocene age, sealed by Late Miocene, Tortonian marls and in turn by the Messinian salt. Sequence stratigraphic analysis was used to constrain timing of structural development and provides a consistent basis for correlation of the reservoir interval. The field was discovered in 2011 by Noble's Cyprus A-1 well. An appraisal well, Aphrodite-2 drilled by the Pelagic Group discovered gas on the eastern flank of this structure in 2012, and in 2013 a further appraisal well, Cyprus -A2a was drilled by Noble to evaluate the northern part of the structure. All three wells proved columns of dry gas in Early Miocene (Aquitanian) - Late Oligocene (Chattian) sandstones equivalent to the "Tamar Sands". Prior to the drilling, the field was covered by few 2D data and by 3D surveys of various vintages. A well -log sequence stratigraphic analysis of well Aphrodite -2 (RPS 2014) constrains the timing of structural development observed from 3D seismic data. The deep water setting during the Oligocene and Miocene makes such study challenging in contrast to study of coastal onlaps in shallow water environments. A biostratigraphic framework based on occurrence of diagnostic species together with the patterns of abundances and diversity of micro and nannofossils was integrated with wireline log data and lithofacies. Peaks in nanno and microfossil abundance were used as indicators of condensed sedimentation which when integrated with lithofacies and wireline information enabled discrimination and dating of maximum flooding events and sedimentary processes such as gravity flow deposition. Changes in microfossil assemblage and abundance minima were associated with sequence boundaries. Each depositional sequence defined in this way was calibrated to published zonation schemes and to the sea level curve of Haq et al 1987. The seismic data indicate that the structure began to develop during the Early Miocene (Burdigalian) and that deformation continued to the Middle Miocene (Tortonian). The structure is not recognized at the base of the Messinian salt layer. Onset of structural development coincided with cessation of sand deposition at Aphrodite suggesting an over riding tectonic control on sand distribution within the Levant basin. It was also found that few, low confidence biostratigraphic events could be identified in the Middle Miocene owing to extensive reworking and this may also reflect active tectonism. The development of the Aphrodite structure appears to be simultaneous with the other gas-bearing structures in the Levant Basin. Its exact timing as revealed in the Aphrodite-2 well can be used as a benchmark for a basin-wide study if and when information from more wells is released in the future. Using Pelagic's 3D data it can be observed that structural development at the western flank of Leviathan closely matches Aphrodite. The mechanism that formed these contemporaneous "Syrian Arc II" structures is interpreted in the majority of studies as oblique compression induced by the on-going plate collision between the Africa and Eurasia plates along the Cyprus Arc and the Latakia Ridge but the reasons for deformation being mainly confined to the Middle Miocene remain unclear.