Implementation Study for Miscible Water Alternating Gas (WAG) EOR in a Giant, Offshore Field

Abstract

Abstract The WAG (water-alternating-gas) recovery process is a well-established process for enhanced oil recovery with several successful field applications. This process is evaluated for potential application in a giant, offshore Abu Dhabi field. This paper describes an evaluation approach of the WAG process application to the subject field. Many separate reservoir simulation models were created to evaluate various aspects of the WAG recovery process. The models addressed WAG operating parameters such as implementation timing, and the effect of WAG parameters (WAG ratio, cycle length). The models were also used to estimate the rate and recovery impact of WAG implementation using different injectants (off-site available hydrocarbon gas, associated gas, enriched gas). The evaluation process for the giant field started with a small 3D sector model derived from a full-field model of the most significant reservoir unit. This model was extensively used to test the operational parameters. The findings were then tested with larger-scale models for full-field evaluations. Finally, grid sensitivity studies were done using 2D cross-sectional models to calibrate the recovery results from the coarser gridded full-field models. Results show that WAG incremental recovery over the waterflood recovery for the situations studied is about 7 to 8% OOIP (original-oil-in-place). A WAG ratio of 4:1 appears to be optimal. Incremental WAG recovery is insensitive to cycle lengths and timing of WAG implementation. Miscible injectants provide higher recoveries than immiscible gas injection. Model derived recovery benefits were sensitive to the grid size with as much as twice the likely benefit shown with a coarser grid.