This study documents petrophysical changes in the Arab D reservoir in Qatar that affect trap configuration and hydrocarbon accumulation in subtle structures with approximately 100 ft (30m) of vertical relief. Two facies have been identified from well data as capable of sustaining producible oil saturations under these conditions. These are clean grainstones and massive permeable dolomites. Analysis of capillary pressure curves indicates that the interbedded packstones, wackestones and mudstones of the Arab D will act as waste zones with a 100 ft (30m) oil column. The distribution of the highly porous grainstone facies is controlled regionally by paleobathymetry, but is unpredictable from well control on the prospect scale. Areas of high porosity can be identified seismically using acoustic inversions. However, seismic data cannot be relied upon to delineate permeability trends.