The Gharif Development Catalogue: From Geoscience to Development Decisions

Abstract

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.

Matching of Water Breakthrough in Low Resistivity Oil Reservoir Using Permeability Anisotropy

“…Since then, a total of 32 wells have been drilled in the Haushi reservoirs of the Middle and Lower Gharif. The Haushi Group deposited during the Late Carboniferous to Early Permian time consists of the glaciogenic Al Khlata Formation and the marginal marine to fluvial Gharif Formation overlaid by the Khuff formation [13]. As the deposits are located close to the marine basin, the facies are transitional from marine to the west to basinal to the east.…”

Matching of Water Breakthroughs in a Low-Resistivity Oil Reservoir Using Permeability Anisotropy

“…Since then, a total of 32 wells have been drilled in the Haushi reservoirs of the Middle and Lower Gharif. The Haushi Group, deposited during the Late Carboniferous to Early Permian period, consists of the glaciogenic Al Khlata Formation and the marginal marine to fluvial Gharif Formation overlaid by the Khuff Formation [13]. As the deposits are located close to the marine basin, the facies are transitional from marine to the west to basinal to the east.…”