The Third Sand Upper (3SU) is one of the three sub-reservoirs in the Third Sand of the Greater Burgan field, the world's largest sandstone oil field. Initial oil production begun in 1948 and 3SU field development has not been aggressive due to its poor reservoir quality and productivity. After 60 years of primary production, only 7.5% recovery has been achieved.

Infill drilling was identified as a key development strategy in 3SU. In 2008, a simulation study was initiated to investigate infill drilling potential and its impact on production and recovery. We opted for a sector model mainly due to practicality and time constraint. The 780,800 cells sector geological model was scaled-up to 421,632 cells for flow simulation. Due to the sand-to-sand contact with the lower Burgan sands, it is imperative to include these reservoirs in the model to achieve proper energy balance. Accordingly, four pseudo layers were added to the simulation model to allow fluid migration from the lower reservoirs. The 3SU sector simulation model has 100m X 100m areal cells and individual layers with 4-6 feet thickness. Overall, the sector model has 30 times refinement compared to previous 3SU models (Ambastha et al, 2006).

The history match has been carried out for 37 3SU historical wells with 60 years of production history. Detailed study of interactions among field permeability distribution, aquifer strength, fluid migration and fault transmissibility specifications on simulation results was key in developing meaningful history match. Water cut match was less than satisfactory for wells located in the dome area due to modeling deficiency introduced by the pseudo layers. Three infill drilling spacing scenarios were set up to evaluate prediction performance of 800-meter, 400-meter and 200-meter well spacing. Results of the 50-year prediction runs indicated that an incremental recovery of 11% can be achieved by reducing the current well spacing of 800-meter to 400-meter.

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