Field-Scale Reservoir Quality Variations and Predictability in Uncored Intervals within the Arab Formation, offshore Abu Dhabi (United Arab Emirates)
Meriem Bertouche and Andrea James
This field-scale study presents the results of integrated sedimentology and reservoir quality assessment of the Arab Formation Members A to D, offshore Abu Dhabi. The reservoir quality evaluation based on conventional core analyses data, thin-sections and logs highlighted that reservoir potential was initially closely related to facies variations. The distribution of reservoir quality within the limits of the stratigraphic cycles is investigated to understand the impact of the sedimentological and diagenetic influences on reservoir behaviour and distribution. The reservoir quality appears to be primarily related to the depositional fabric variations. The distribution of the good reservoir facies (mainly shoal/marginal shoal deposits) follows the sedimentological variations according to platform evolution and facies belt migration. The Arab D hosts well-developed shoal/margin shoal sections that have a good lateral extent, forming large, connected, high porosity/permeability horizons. The overlying Arab C, B and A are associated with a decrease in reservoir quality related to the development of large supratidal/intertidal/lagoonal deposits with fewer occurrences of coarse-grained, macroporous facies, creating only limited and poorly-connected patches of high reservoir potential deposits. Based on these observations the depositional model is likely to be an important guide to building the static reservoir model. However, Diagenesis also has a clear influence on the pore system and increases the complexity of the reservoir architecture: the main detrimental phases are early/late pore-filling calcite and dolomite precipitation, while the main enhancing phases include several dissolution events, of which the late phase is most significant for enhancing pore systems and leaching dolomite and anhydrite cement. As lithofacies associations appear to have a good correspondence with reservoir quality variations, a log characterisation of the deposits has been carried out using neutron/density logs. Results show that dense anhydrite-bearing facies and high porosity, poorly-cemented shoal/marginal shoal deposits can be easily identified in logs. Also, limestone and dolomite lithologies display different log signatures, allowing a good characterisation in uncored intervals. Finally, these different trends and cut-offs, which were first defined on cored intervals have been successfully blind-tested in uncored intervals, showing their predictability at reservoir scale.
Deville de Periere, M, Garrick, K, Davies, Q, Al-Jefri, G, Al-Menhali, H, Al-Tamimi, I, Bertouche, M and James, A. (2014) Field-Scale Reservoir Quality Variations and Predictability in Uncored Intervals within the Arab Formation, offshore Abu Dhabi (United Arab Emirates). Paper presented at the AAPG International Conference and Exhibition, Istanbul, 14-17th September, 2014
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