Improvement of the Compositional Model to Represent a Complex Fluid System of a U.A.E. Carbonate Reservoir

Abstract: The studied field is located in Abu Dhabi and has been identified as faulted anticlines structure with associated local fractures. The reservoir is characterized by lateral and vertical variations in reservoir rock and fluid properties ranging from a gas condensate at the top of the structure to undersaturated black oil down the reservoir. A substantial compositional gradient has been identified from over 50 fluid samples taken at different depths over the thick fluid column of about 1500 feet. The field is presently under miscible hydrocarbon WAG (HC-WAG) injection, water injection and future consideration for CO₂-WAG injection. The field has been characterized using an Equation of State (EOS) model and compositional mapping with areal changes of saturation pressure. Therefore, the aim of this study is to improve the compositional model that can replicate the areal and vertical variation in the fluid thermodynamic. This presents a huge task considering the vast number of laboratory experiments. Hence, the updated EOS will be used to improve the reliability of reservoir modeling, production forecasts and operational requirements. All the fluids analyses studies were compiled and validated. These data were analyzed areally and vertically down the fluid column. Correlations of saturation pressure, gas-oil ratio, formation volume factor and compositions were generated with depths across the formation. The data showed a large variation of saturation pressure, all fluids parameters and composition with depth especially close to the gas oil contact. Then the compositions and saturation pressures were validated using a 1-D vertical model and obtained results were compared with the experimental values at various depth. The obtained result proved that a single EOS and fluid representation could model the complex thermodynamic behavior of all the reservoirs in the field. Considering that part of the field has been under HC-WAG injection and future consideration for other WAG processes, the generated EOS would allow the numerical simulation to have a better representation of the fluids and predict the impact of these processes on the ultimate oil recovery.

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