Full-Field Reservoir Modeling of Central Oman Gas-Condensate Fields

Abstract

Summary Gas reserves sufficient for a major export scheme have been found in Central Oman. To support appraisal and development planning of the gas and condensate fields, a dedicated, multidisciplinary study team comprising both surface and subsurface engineers was assembled. The team fostered a high level of awareness of cross-disciplinary needs and challenges, resulting in timely data acquisition and a good fit between the various work activities. A field-development plan was completed in March 1994. The foundation of the subsurface contributions was a suite of advanced full-field reservoir models that were used to do the following. Provide production and well requirement forecasts. Quantify the impact of uncertainties on field performance and project costs. Support the appraisal campaign. Optimize the field-development plan. Derive recovery factor ranges for reserves estimates. The models were constructed early during the study, initially with general data with large uncertainty ranges and gradually refined with new appraisal data. This ultimately resulted in more than 20 full scenarios, quantifying and ranking the remaining uncertainty ranges. Geological/petrophysical uncertainties were quantified by use of newly developed, 3D probabilistic modeling tools. An efficient computing environment allowed a large number of sensitivities to be run in a timely, cost-effective manner. The models also investigated a key concern in gas-condensate fields, well impairment caused by near-well condensate precipitation. Its impact was assessed by use of measured, capillary-number-dependent, relative permeability curves. Well-performance ranges were established on the basis of equation-of-state (EOS) single-well simulations and translated into the volatile-oil full-field models with pseudorelative permeability curves for the wells. The models used the sparse available data in an optimal way and, as part of the field-development plan, sustained confidence in the reserves estimates and the project, which is currently in the project specification phase.