AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Facies and High-Frequency Sequence Stratigraphy of the Lower Fadhili Carbonate Reservoir, Khurais Field, Saudi Arabia
(1) RCD, Saudi Aramco, Dhahran, Saudi Arabia.
Middle Jurassic Lower Fadhili Member of the Dhruma Formation in Khurais Field is composed of three high-frequency sequences, with numerous small-scale fining-upward cycles that vertically partition the reservoir. The Lower Fadhili was deposited in a shallow marine intra-shelf basin. The reservoir is overlain and underlain by marls. The reservoir consists mainly of wackestones and packstones with several thin layers of grainstones capped by hardgrounds/firmgrounds.
The first sequence consists of argillaceous mudstone, beach intraclast-ooid grainstone and shoreface coated-grain, ooid grainstone. Chondrities burrows occurred only in argillaceous mudstone facies. Gastropods are common in the beach intraclast-ooid grainstone facies. The sequence is capped by an exposure surface (hardground). The beach intraclast, ooid grainstone facies was cemented by early ferroan calcite cement beneath the unconformity, with some reddened strata. Dissolution features include partially/totally dissolved grains, with meteoric calcite cement common.
Fining-upward small-scale cycles of the second sequence onlap the unconformity. These are dominated by open marine Pfenderina trochoidea wackestone facies and stromatoporoid packstone/wackestone facies. The maximum flooding surface can be traced across the field. Grain-rich lithofacies are common in the highstand systems tract.
The third sequence highstand was dominated by fining-upward cycles of stromatoporoid packstone/wackestone facies, shallow-marine lagoonal wackestone and shoreface coated-grain grainstone. Thaumatoporella and Cladocoropsis are abundant in the lagoonal wackestones. These are capped by thin cycles of shoreface coated-grain grainstone, beach grainstone and marginal marine green marl/argillaceous mudstone. Progradational and retrogradational stacking patterns of these lithofacies reflect a low relief carbonate ramp that dipped gently to the north.
High-resolution sequence stratigraphy of the Lower Fadhili reservoir has been beneficial to reservoir characterization and geological modeling.