Perpustakaan Digital ITB

One of the most applicable EOR techniques is Water-Alternating-Gas (WAG). WAG injection is an oil recovery method initially intended to improve sweep efficiency during gas injection. Water is used to control the mobility of the gas to achieve higher sweep efficiency, while gas injection provides higher microscopic displacement efficiency. As provision for maximizing recovery and reducing cost, optimization of the WAG injection process is an important part of this effort. Reservoir simulation is executed on field X during 20 years of production period to forecast how effective WAG injection to improve the oil recovery. Thence, a series of sensitivity studies were conducted to find the optimum WAG injection technical condition by varying operational parameters (i.e., WAG starting time, water injection rates, CO2 injection rates, injection duration, bottom-hole injection pressures, tapering starting time, and tapering duration). This study also analyzed the impact of WAG injection in improving oil recovery compared with several EOR methods: waterflooding, CO2 Injection, and immiscible Water Alternating Gas injection. Following the analysis and sensitivity of technical parameters of the WAG injection method, a simple economic evaluation is performed. A sensitivity study elucidates the technically best operational scenario for the WAG injection. The scenarios consist of the first 5 years efforts to increasing reservoir pressure to come close to the minimum miscibility pressure (MMP) by injecting water with rate of 16.775 Mbbl/d for 1825 days, followed by water injection rate of 15 Mbbl/d, a CO2 injection rate of 15 MMscfd with a cycle of 2-month water half-cycle and 2-month CO2 half-cycle, and tapering method after 20% Hydrocarbon Pore Volume Injected (HCPVI) with a 6-month water half-cycle and 2-month CO2 half-cycle. The result prove that by utilizing the technical optimum WAG injection scenario gives 66.4% of the oil recovery factor, better than other EOR method. The most profitable WAG injection scenario is acquiring when the WAG injection method in field X is developed as a different business entity with the CO2 sources. For this particular set of data, the WAG injection scenario could give the Net Present Value at a 10 percent discount rate of $ 1,168,452.69, and IRR of 10.63%.