The purpose of this study is to investigate the geological and engineering factors that affect the compressor power requirement of the gases (CH4, N2, Air, and CO2) injected into reservoirs pores to displace trapped oil. This gas -oil displacement process is called Gas Enhanced Oil Recovery (GEOR) and it is a well developed research area. However, little is known about the power requirement and competitiveness of the respective gases. Power requirement in reservoir management has economic and technical implications, and gas compression/injection cost is a significant unit in the power cost centre , hence low compression power demand is desired in GEOR processes. Granted the gases have different fluid properties such as viscosity, density, specific heat capacity. It is hypothesised that the gases distinctive characteristics might couple with the reservoirs geological settings differently, such that the power required to achieve certain compression and displacement magnitude would differ from gas to gas and from one reservoir layer to another. This study aims to identify the gas and geological settings that enable compression power optimisation in the gas EOR process. The study used two empirical methods, that is, data mining and experimental. Data mining of field data from over 450 oilfields were analysed to qualitatively discover patterns for power characterisation of Gas EOR processes. Subsequently, an experimental method was conducted to quantitatively evaluate the respective gases competitiveness. The minimum power required for a steady-state permeation is estimated from the respective threshold displacement pressures (TDP), which were calculated from Darcy flow rates for several analogous core samples with varying structural parameters such as porosity, permeability, number of pores and thickness . The experimental results implicated reservoir structural parameters as the major determining factors for the power requirement of GEOR processes. A scatter plot of gas TDP for the respective EOR gases as a function of their injection power requirements or ratings was presented in the study. The mean values of the gas TDP suggest N2 requires a relatively high compressor rating, while CO2 requires the least ratings. Therefore, CO2 is the most competitive gas. The coefficient of variation (CV) analysis shows N2 gas injection power rating is the most affected by structural variability or reservoir heterogeneity. The competitive ranking for power requirement is experimentally determined as CO2, >Air, > CH4, > N2. The information from this study can be directly applied in selecting gas and screening reservoirs for GROR processes. It can also find application in gas separation processes such as the separation between CO2 and CH4 in biogas production
