Development of a Full-Field Parallel Model to Design Pressure Maintenance Project in the Wara Reservoir, Greater Burgan Field, Kuwait

Abstract

Abstract The Wara reservoir is one of the four main reservoirs in the Greater Burgan field, the world's largest sandstone oil field. It has experienced significant pressure decline after 60 years of primary production. In 2005, design for a pressure maintenance project (PMP) via a peripheral waterflood was initiated to arrest pressure decline and improve oil recovery. A key building block of the Wara PMP is a stand-alone, full-field Wara simulation model. The 23-million cells geological model was scaled-up to 4 million cells for flow simulation. Four pseudo layers were added to the simulation model to allow fluid migration via faults from the lower reservoirs. The new model has 100 m x 100 m areal cells and individual layers with an average thickness of 6 ft. Overall, this new model has 18 times refinement compared to the previous model for the Wara reservoir. Thus, this model is suitable for evaluating PMP, infill drilling and pattern waterflood. This paper, however, focuses on PMP evaluation only carried out over the last four years. The final history-match has been carried out at three levels: Field, Gathering Centers (GC) and Key Wells. Detailed study of interactions among field permeability distribution, edge aquifer representation, and fault transmissibility specifications on simulation results was key in developing a meaningful history-match. PNC data for many wells around the periphery of the field provided useful insights for edge aquifer representation. Water cut match was less than satisfactory for wells located in the center due to modeling deficiency of pseudo layers as discussed in the body of the paper. Prediction runs have been set up to investigate various PMP designs. These runs include sensitivity with respect to number of injectors, number of producers, target injection rate per well, maximum bottom-hole injection pressure, voidage replacement ratio, injector-producer distances, and injector-producer rows along with various scenarios for dealing with production from existing Wara producers throughout the field. This flow simulation model will be used as an operating model to optimize process design and well location.