From Bureau of Economic Geology, The University of Texas at Austin (
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GEO 2004--6th Middle East Geosciences Conference and Exhibition, Kingdom of Bahrain, March 7-10, 2004

Integrated Reservoir Modeling of a Complex Carbonate Reservoir Al Huwaisah Field, North Oman

Amthor, Joachim, Huw A. Davies, John Keating, Mohammed Al-Mughairy, and Charles Kerans


The billion barrel Al Huwaisah oil field is a large, faulted dip-closure with locally significant fracture swarms, which produces from heterogeneous rudist-dominated limestones of the Aptian ShuÕaiba Formation. It is the most complex field within the ShuÕaiba of Oman in terms of facies distribution, stratal geometry and flow unit architecture, which is reflected in the historical well and field performance. To address the key uncertainties for long-term development of the Al Huwaisah field beyond its primary depletion phase, an integrated modeling approach was adopted. Improved 3-D seismic definition resulted in: (1) a reduction in top reservoir uncertainty; (2) improved imaging of faults and fractures; and (3) improvement in imaging the depositional geometry through the use of seismic facies and attribute analysis. Integration of 3-D seismic data with extensive borehole image log data led to the development of a fault/fracture model which greatly improved the understanding of the water movements in the field. Interpretation of the complex reservoir architecture is based on the integration of seismic and well data (cores, high-resolution image logs, dipmeter and conventional open-hole logs) with the available production performance data. Outcrop data and field analogs were reviewed and integrated into alternative geological models to account for the complex reservoir architecture. To address the range of uncertainty in reservoir architecture and to allow planning of uncertainty mitigation, a number of static reservoir models were constructed using a multiple realization approach. For each of the four field areas, different realizations were constructed to account for variable top structure, fault/fracture architecture, depositional architecture, porosity and permeability distribution and oil saturation models. These area models were then upscaled and exported for reservoir simulation. The simulation models suggest that further development of the Al Huwaisah field through infill drilling supported by waterflood-pressure maintenance can significantly increase oil rates in the next decade.