The Late Cretaceous Mishrif limestone is known locally in Bahrain as the "Rubble" due to extensive tectonic fracturing and karst brecciation which may have tens to hundreds of times the permeability of the tight matrix where most oil resides. If these secondary features are not properly managed, steam utilization during thermal heavy oil recovery is compromised, so heat transfer to viscous crude in the matrix is less effective. To address this challenge, field pilots are conducted across Awali field to apply customized thermal processes to varying geology.

Designing the thermal pilots uses 3D static and dynamic models representing the heterogenous reservoir to test various thermal processes (cyclic steam stimulation, forced imbibition, and steamflood). Initial geocellular models are multi-well secular models utilizing simplified erosional surface truncations and fault-fracture networks to optimize run times for multi-component thermal simulation. Reservoir properties are guided by well log data and geostatistics, whereas an effective permeability hierarchy accounts for historic well performance and observations. Additional inputs for simulation include thermal properties for rock and fluids, temperature-dependent relative permeability curves, temperature-viscosity relationships and vapor-liquid equilibrium ratios for each crude component, and injected steam quality.

Piloting in a sparsely fractured portion of Awali field gave unexpected results that required revisiting conceptual geologic models and testing new ideas with dynamic simulation. This effort was accelerated by multiple scenario playing with "pseudo-fractures" strategically relocated to honor dynamic data while remaining consistent with the known fault, fracture and karst trends.

This paper describes the results of this particular pilot and the versatile modeling approach taken to understand the outcomes. It recommends early quick multiple scenario playing to help guide subsequent time-intensive detailed fault-fracture-karst modeling.

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