Core to Seismic-Scale Integrated Reservoir Characterization of a Permian Fluvio-Aeolian Gas Reservoir, Waqar Field, Eastern Saudi Arabia

Sprague, Ronald Allan, Saudi Aramco, Dhahran, Saudi Arabia

An integrated geological model of the Permian ‘Unayzah A fluvio-eolian g

as reservoir, Waqar Field, Eastern Saudi Arabia was constructed for reservoir characterization. Integrated reservoir characterization involves the combined analysis of geological, geophysical and production data at a variety of scales, to produce an accurate geological model for reservoir simulation. Whole core, core plug porosity and permeability, thin section, SEM, image log, and wireline log data were utilized. These were integrated with seismic structural and strati­graphic interpretations of amplitude and impedance. The geologic model includes analysis of fluid characteristics, drillstem tests and production pressure data.

Lineation analysis of seismic structure maps tied to wells suggests the existence of minor faulting that may create either reservoir baffles or potential reservoir compartments. The existing seismic structural interpretation was reexamined for subtle faults; subsequent image log interpretation and whole core description confirmed their existence. Facies analy­sis from whole core description tied to image log interpretation demonstrates a range of “arid” continental facies across the field, from lacustrine to fluvial to eolian, with paleosols possibly acting as reservoir baffles or barriers. Thin section, SEM, and core plug porosity and permeability data correlated to these environments suggest a strong facies control on reservoir porosity and permeability. Seismic amplitude and impedance data tied to whole core indicate a similar facies influence on the seismic expression of the distribution of reser­voir and non-reservoir intervals.

The resultant geological model explains existing gas well drillstem test and production pressure behavior, and demonstrates the necessity for a multi-scalar, multi-disciplinary modeling approach.