New insights on the Lower Lekhwair Formation (Offshore Abu Dhabi): understanding the key role of Lithocodium/Bacinella floatstones on large scale reservoir quality variations
Anthony Tendil, Laura Galluccio and Catherine Breislin
The Lower Cretaceous Lekhwair Formation is one of the most prolific oil reservoirs in onshore and offshore UAE, yet the available literature on this interval remains limited. Based on a recent study carried out in collaboration with ADNOC Offshore, the present paper provides new insights into the comprehension of the interplay between primary depositional and secondary diagenetic controls on the reservoir performance, which is of crucial importance for the refinement of the static and dynamic models.
A total of 28 wells (c.6000ft of core) and 728 thin-sections were described in detail to define the sedimentological framework and diagenetic overprint of the formation. Descriptive lithofacies and interpretative genetic elements formed the building blocks for the sedimentological understanding, together with the recognition of key stratigraphic surfaces and vertical stacking patterns, which helped in defining the sequence stratigraphic framework. In offshore Abu Dhabi, the Lower Lekhwair Formation is characterised by an alternation of relatively thick argillaceous (dense zones) and clean limestones (reservoir zones) organised into low-order sequences. Reservoir zones consist of basal, low to moderate energy inner ramp deposits, grading upward into thick inner and mid-ramp sediments. Lithocodium/Bacinella is the volumetrically dominant skeletal allochem and can form m-thick, stacked floatstone units. Such Lithocodium/Bacinella-rich floatstones are interpreted to originate from a mid-ramp depositional setting as a result of an increase in the accommodation space. By contrast, the contribution of Lithocodium/Bacinella floatstones is significantly reduced in inner ramp settings where these tend to form cm- to dm-scale, laterally discontinuous interbeds.
Tendil, A. J-B, Galluccio, L, Breislin, C, Alsabeai, J. A, Lavenu, A. P. C. and Obara, H. (2021) New insights on the Lower Lekhwair Formation (Offshore Abu Dhabi): understanding the key role of Lithocodium/Bacinella floatstones on large scale reservoir quality variations. Paper presented at the Abu Dhabi International Petroleum Exhibition & Conference, Abu Dhabi, 15-18th Nov, 2021. SPE-207692-MS
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New insights on the Lower Lekhwair Formation (Offshore Abu Dhabi): understanding the key role of Lithocodium/Bacinella floatstones on large scale reservoir quality variationsDownload PDF (0.18mb)