Thesis (M.Eng.)--Chulalongkorn University, 2013

Gas injection into a dipping reservoir is one of the most efficient methods to recover residual oil left by water flooding. This process includes Double Displacement Process (DDP) which consists of injecting gas into waterflooded oil zones and Second Contact Water Displacement (SCWD) process which consists of submitting these gas-flooded zones to a new water displacement process. After gas breakthrough in DDP, gravity has a major effect on oil film flow so that the oil flow rate is very low. After the oil bank is produced, the oil production rate is very low, and then a very long time is needed to reach very low oil saturation. To shorten the period of low oil production, SCWD has been suggested. This process is considered an extension of the DDP. The effect of dip angles is studied. The results show that the less the dip angle, the better the SCWD performance. For stopping time for water and gas injection, water cut of 60% and gas-oil ratio of 5 is the best stopping criteria to provide the best SCWD performance. In term of water and gas injection rate, the best oil recovery is provided when using the 1st water injection rate of 2,000 STB/D, gas injection rate of 2,000 MSCF/D and the 2nd water injection rate of 4,000 STB/D. Using 4 vertical wells yields the highest oil recovery for reservoir with 0 and 15 degree dip angle while two horizontal wells works best for a reservoir with 30 degree dip angle. For sensitivity analysis, the oil recovery from ECLIPSE default and Stone 1 are insignificantly different but the oil recovery from Stone 2 is less than the others. A higher vertical to horizontal permeability ratio results in higher oil recovery, and smaller residual oil saturation yields higher oil recovery. Moreover, in term of wettability, water-wet system shows better overall performance than oil-wet system because oil can flow easily in the water-wet system.