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The Gharif Formation was deposited in the early Permian and is one of the major producing oil and gas reservoirs in the Sultanate of Oman. The Upper Gharif Unit crops out at Wadi Gharif, where a detailed outcrop characterization was undertaken. Fluvial channel sandstones, inclined heterolithic stratification (IHS) and floodplain palaeosols are the dominant facies associations. Deposition was in a low to moderate sinuosity multistorey fluvial channel belt with fluctuating water levels, allowing water retention in the channel while mud deposited on the upper portions of the point bar was exposed. Sandstone-body geometries indicate ribbon-like channels flowing in a NW orientation. The channel belt is estimated to be between 150 and 250 m wide and encased in oxidized red palaeosols. The depositional units are stacked from east to west and the scour and erosional surfaces are indicative of cut and fill under relatively low accommodation conditions. The reservoir architecture highlights the presence of potential claystone baffles in the IHS section on the margins of the point bars. 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. A deterministic surface-based model was constructed to access static connectivity of the Gharif fluvial channels.

The Gharif Formation is one of the most prolific oil and gas producing clastic reservoirs in the Sultanate of Oman with production spanning five decades and thousands of wells. The depositional environment for the Gharif varies both vertically as well as spatially across Oman making identification of appropriate field analogues challenging. A thematic study of the Gharif Formation over the last few years has added new insights into the impact of these geologically complex reservoirs on connectivity and field development options. The objectives of the development catalogue is to utilize the geological, petrophysical and reservoir engineering knowledge and data to support the decision making process. The Gharif is divided into three main units with the depositional environments ranging from fluvio-deltaic, shoreface, tidal flats, semi-arid and humid tropical fluvial systems. Each environment has its own respective reservoir characteristics such as reservoir properties, body geometry, vertical and lateral connectivity and net to gross. These environments vary between units as well as regionally across Oman. Standardization of core facies and well picks with the application of sequence stratigraphy has enabled regional palaeogeography maps to be created at flow unit level. Production is often co-mingled with nine possible reservoir combinations and fluids range from heavy oil (<20 °API) to gas. Development areas have been identified based on regional palaeogeography maps, diagenetic trends and fluid properties. For each area and unit, an assessment of the rock and fluid properties has been undertaken and key uncertainties are identified and captured in a matrix. A review of development decisions and approaches resulted in an understanding of how optimal field development varies throughout the Gharif; the key development decisions were captured in a decision matrix. The distillation and analysis of the extensive Gharif dataset has resulted in specific tools and workflows that are available to aid better, and faster, decision making in Gharif field developments. Technical databases put the appropriate quality controlled data at the field developer's finger tips while development workflows utilizing uncertainty and decision matrices empower teams in their decision making process. We envisage field development studies benefiting from the consistent application of identified best practices resulting in significant multi-month time savings. This work has shown how formation specific data, covering a wide geographical area, can be integrated and analysed to quickly assess subsurface uncertainties and identify appropriate analogues. This in turn enables development teams to make better and faster decisions on development options. This approach will now be replicated for other formations in Oman.

An integrated geological study of the Rankin Trend of the North West Shelf, Australia, was undertaken to underpin the ongoing development of the giant gas fields it contains. The study applied an improved understanding ofthe regional stratigraphy in conjunction with interpretation of the regional-scale Demeter 3D seismic survey and focussed on existing fields, undeveloped discoveries, and exploration prospects. The study included a redescription of 1,500 m of core, a new facies-based petrological analysis, a revision of the well-based stratigraphy and palaeogeographic mapping, and a seismic stratigraphic analysis. Reservoir production and hydrodynamic data were also integrated. The stratigraphic framework was improved by implementing a broad range of depositional and facies analogues and a system-wide sequence stratigraphic approach to understanding lateral and vertical stacking patterns of the reservoir succession. Visualisation and modelling technologies were also employed to more adequately describe genetic reservoir packages.Specific outcomes include: improved correlation of reservoir sequences, application of appropriate subsurface depositional analogues to field descriptions, updated palaeogeographic maps and recognition of palaeosols as stratigraphic marker horizons—resulting in a more consistent regional interpretation framework. This forms the basis for seismic stratigraphic interpretation away from well control.The new regional geological model has enabled the linkage of exploration, development and production understanding across the North West Shelf assets as well as management of geological uncertainties.

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