Perpustakaan Digital ITB

The increasing of energy demand amid the continuously declining oil production demands additional oil recovery from existing reserves. Enhanced oil recovery (EOR) becomes an effective solution to this problem, and gas injection, with its advantages over other methods, is a promising EOR method for enhancing oil recovery. However, due to its very low density, several problems often occur during the implementation of this method, such as gas channeling or the tendency of gas to move to the upper part of the reservoir, that can reduce the sweep efficiency. By combining the advantages of gas injection and water injection, water-alternating-gas (WAG) is proposed to be the solution for this sweep efficiency issues. This study is conducted to examine the sensitivity of several parameters in WAG injection to the achieved oil recovery of this method. The study was carried out over 12 years, with the first 2 years of production occurred naturally and the following 10 years by performing WAG injection. Sensitivity analysis was performed by varying several parameter values; the sequence of WAG injection with either water or gas is injected first, WAG ratio of 5:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:5, WAG cycle with durations of 2 months, 4 months, 6 months, 8 months, and 12 months per cycle; as well as well-completion pattern including normal five-spot pattern, normal seven-spot pattern, and normal nine-spot pattern. The simulation showed that WAG injection preceeded by water injection resulted in higher oil recovery, WAG ratio with a larger gas portion produced the highest oil production, WAG cycle with a longer cycle durations yielded the highest oil recovery factor, and the normal five-spot pattern performed better compared to the two other well pattern.