A regional comparison of Khuff and Arab reservoir potential throughout the Middle East

S.N. Ehrenberg, P.H. Nadeau, and A.A.M. Aqrawi

Statoil, N-4035 Stavanger, Norway

Compilation of average porosity and permeability data for petroleum reservoirs in the Permian/Triassic Khuff (25 reservoirs in 7 fields) Jurassic Arab (36 reservoirs in 16 fields) confirms and quantifies the major differences known to exist between these units. Most Khuff reservoirs have average porosity <10%, while most Arab reservoirs have average porosity of 15-27% and correspondingly higher permeability. The average reservoir data are supported by a compilation of published porosity-permeability data from specific fields, where core and wireline log data provide insight into geologic controls. The above differences reflect a combination of depositional, diagenetic, and economic factors. Khuff strata were deposited on an extensive, poorly-circulated, very low-relief shelf and consist in large part of interbedded mudstone and grainstones having relatively fine grain size, with major amounts of depositional calcium sulphate present. Arab reservoirs were deposited under better-circulated conditions nearer to margins facing deep-marine basins and thus have coarser, more grain-dominated fabrics and lesser content of chemically precipitated grains. Overall deeper burial of Khuff reservoirs has also resulted in greater porosity loss by chemical compaction and cementation. Furthermore, Khuff deposits were likely composed of less stable mineralogy than Arab sediments because the Permian/Triassic was a time of "aragonite seas", whereas the Jurassic was a time of "calcite seas." The combined result of these factors is that Arab reservoirs are characterized by greater preservation of primary depositional pore types, more coarsely crystalline dolomite fabrics, and lesser plugging by anhydrite. In addition to the above factors, however, the main reason for lower average porosity and permeability in Khuff reservoirs could be that the Khuff is almost exclusively a gas play, whereas the fluid of interest in Arab reservoirs is oil. As a result, much lower permeabilities are required for production of Khuff reservoirs compared to Arab reservoirs.

EHRENBERG, S.N., NADEAU, P.H., and AQRAWI, A.A.M., 2005, A regional comparison of Khuff and Arab reservoir potential throughout the Middle East: (Abstract) International Petroleum Technology Conference.