Publications

With the current low oil price, efforts must be directed toward optimizing current production and looking for appropriate and cost effective EOR method. One of the most cost effective alternative methods compared to thermal/chemical, is utilization of available water and gas. Produced hydrocarbon gas is often flared/vented because uneconomic for sale or own produce. This practice has positive impact for production by reducing bacpressure, however this practice is now systematically reduced due to stringent environmental regulation that limits gas flaring/venting from well/ surface facilities. Moreover, CO2 is also a growing concern and its release to atmosphere needs to be reduced. Those concerns motivate efforts to inject back hydrocarbon gas and CO2 into reservoir in form of EOR or CO2 storage. Gas injection is among the oldest EOR method and particularly effective for reservoir with high relief where gravity drainage is dominant. However continuous gas injection mode still inherit drawbacks due to density difference between gas and displaced oil with recovery factor typically in range of only 10-20% OOIP after waterflood. The problem is more pronounced in heterogeneous formation and medium to heavy oil and where permeability contrast exist, leading to much lower recovery efficiency. This study’s objective is to compare Gas Injection method and its variant, Water-Alternating-Gas Injection in term of oil recovery. Simulation work in this study is a modification of work by Killough and Cossack (1987) with modification to better reflect reservoirs condition in Indonesia (shallow, layered). Two conceptual geologic (homogeneous and heterogeneous) models and an 11-component fluid models were built for this purpose. Impacts of injection parameters such as slug size, WAG ratio and injection rate, are reviewed using sensitivity study. The simulation study shows that WAG significantly improves sweep efficiency, delays breakthrough and thus increase recovery compared to continuous gas injection. Use of N2 can provide viable alternatives in case CO2 and Hydrocarbon gas sources are not geographically close to support economics of the project. N2 can be produced onsite and stripped from sales gas with low cost.