Gas and downhole water sink assisted gravity drainage (GDWS-AGD) is a promising gas-based enhanced oil recovery (EOR) process applicable for reservoirs associated with infinite aquifers. However, it can be costly to implement because it typically involves the drilling of multiple vertical gas-injection wells. The drilling and well-completion costs can be substantially reduced by using additional completions for gas injection in the oil production wells through the annulus positioned at the top of the reservoir. Multi-completion-GDWS-AGD (MC-GDWS-AGD) can be configured to include separate completions for gas injection, oil, and water production in individual wells. This study simulates the MC-GDWS-AGD process applied to the synthetic reservoir (PUNQ-S3, based on a real North Sea Field) by placing multiple completions in two wells, which include a gas injection loop, and 2-horizontal wells with a diameter of 2⅜ inch, first one for producing oil located above the oil/water contact and the second one for water sink placed below the oil/water contact. Hydraulic packers are positioned to isolate the multiple completions and an electric submersible pump are positioned to produce the water zone. These results compare to a base case involving no MC-GDWS-AGD wells, which achieved 55.5% oil recovery and 70% water cut.