Geologic And Seismic Attribute ModellingTo Aid Exploration In Complex Carbonates: Khuff (Permian-Triassic), Saudi Arabia

Harland, Tom¹, Abdel Fattah Bakhiet¹, A.E. Greg Gregory¹, David Tang¹, Abdel Ghayoum Ahmed¹ (1) Saudi Aramco, 31311 Dhahran, Saudi Arabia

The late Permian-early Triassic Khuff carbonates in Saudia Arabia and adjacent areas of the Middle East provide a series of giant gas fields with reserves currently estimated at 2.5 Qcf (BP 2006) and a potential 1.16 Qcf to find (USGS 2006). Deposition of these Khuff carbonates occurred on an extensive, shallow platform which was developing on the passive SW margin of the newly formed Tethys Ocean.

Lateral sedimentary patterns and sequential development were controlled by the interplay of carbonate and evaporite deposition, variable and differential subsidence, and eustatic fluctuations. Diagenetic overprinting of the sediments has been complex and prolonged, ranging from syn-sedimentary processes, particularly related to evaporitic environments, through early and later burial processes, to very late-stage, fault-conduit or charge related modifications.

Depositional architecture and diagenetic overprint were initially determined using a combination of detailed core work, associated petrography, extrapolation to well-logs, well correlations and analog modelling. Certain aspects of later diagenetic modification were additionally assessed by mapping compositional variations in reservoired gas and provided a further check on sequence architecture by indicating probable migration pathways.

Extrapolation onto seismic presented the means to develop a robust framework both within the area of closest well control and away from well control. Detailed iteration between all disciplines and mapping of seismic attributes (amplitude, impedance, facies) then provided reservoir fairway maps, which account depositional characteristics, predict diagenetic overprint, and anticipate probable composition of gas accumulations.