Sedimentary Facies and Reservoir Architecture of the Gharif Formation Outcrops in the Southern Huqf Area, Sultanate of Oman
M. Al Ghammari1, D. Alsop1, A. Al Abri1, A. Al Mahrooqi1, and H. Al Rawahi1
The clastic sediments of the early-middle Permian Gharif Formation represent a major oil and gas reservoir in the Sultanate of Oman. The Upper Gharif Member is well exposed in the Southern Huqf area around Wadi Gharif where a detailed outcrop characterization was undertaken. Seven lithofacies and four facies associations and depositional environments were identified and interpreted in terms of sedimentary bodies, reservoir architecture, geometry and reservoir heterogeneity. Fluvial channel sandstones, inclined heterolithic stratification (IHS) and flood plain palaeosols are the dominant facies associations. Deposition was in a low to moderate sinuosity fluvial channel belt in humid tropical conditions with fluctuating water level and seasonal wet and dry periods. Such conditions allowed water retention in the channel while mud deposited on the upper portions of the point bar was exposed. Sandstone body geometries indicate relatively small channels stacked up to form amalgamated channel stories. The channel belt is estimated to be approximately 150 to 250m wide encased in oxidized red palaeosols. Palaeocurrent measurements indicate flowing in a northwest orientation. Four architectural elements were identified in the outcrop: 1) channel stories which are flat lying and laterally continuous, suggesting deposition in either low sinuosity rivers or potentially as braid plain deposits, 2) lateral accretion surfaces and channel fill deposits which are bounded by palaeosols in one end and merge laterally into channel facies association, 3) channel stories with incision, representing multiple cut and fill events, 4) flood plains with minor channel fill, representing chute channels or small crevasse channels. Generally, the reservoir architectures are indicative of cut and fill under relatively low accommodation conditions with potential claystone baffles in the IHS section. Differences in grain size between the coarse grained channel sandstones and the fine grained IHS sandstones potentially create a permeability contrast while the inclined surfaces will affect fluid movement for both vertical and lateral flow.
AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain