Seismic Characterisation of Permian Gharif Clastic Reservoirs in Oman

By

Zulkifli Haji-Ahmad¹, Glenn Williams¹, Edwin Quadt²

(1) Petroleum Development Oman llc, Muscat, Oman (2) Petroleum Development Oman llc,

 The Permian Gharif clastic reservoirs represent one of the Oman’s oldest producing hydrocarbon reservoirs with significant remaining upside hydrocarbon potential (more than 20% of the total scope volumes) locked in low-relief difficult stratigraphic traps. The application of seismic quantitative interpretation techniques plays a key role in helping to realise this potential. The delivery of high- fidelity seismic data through modern seismic acquisition and processing techniques has aided the Gharif exploitation efforts.

The Gharif fluvial and shoreface sand reservoirs are characterised by large spatial variations in rock properties and a small sand/shale acoustic impedance contrast. Variations in the pore-fill fluids have small effects on the seismic signature which can be difficult to identify in the presence of lithology changes and seismic noise. Hence feasibility studies indicate that using acoustic and elastic impedances from seismic inversion to predict gross reservoir property distribution will not necessarily be successful.

Multi-attribute seismic analyses including neural-network techniques showed some success in predicting gross sand reservoir distribution and properties (e.g Sadad field) on good quality seismic data. The results show good correlation between seismic predictions and known depositional patterns (e.g channel geometry) observed at well control. This technique becomes more effective with the use of additional well data and has yielded benefits for field appraisal and development well drilling campaigns by reducing risk in choosing well locations.

By applying multi-attribute analyses to the seismic data, meaningful predictions of Gharif reservoir properties have been obtained for the first time. This has allowed seismic data to play an important role in unlocking the untapped potential in the Gharif hydrocarbon play.