Modelling Gas Based EOR Injection Schemes – The Interplay Between Compositional Effects, Relative Permeability Hysteresis

摘要

Gas injection is a proven enhanced oil recovery method especially for light oil reservoirs. Gas has the ability to enhance hydrocarbon recovery beyond levels possible with primary and secondary recovery methods and leads to high displacement efficiency. However, the sweep efficiency of all gas based EOR schemes including CO2 could be suboptimal due to channelling, fingering and gravity segregation of the injected gas. This poses a serious challenge for all gas injection EOR schemes. This challenge has long been recognized and possible solutions have been proposed in the literature, mainly implementing water alternating gas (WAG), simultaneous injection of water and gas (SWAG) and a newly proposed EOR option of simultaneous injection of miscible gas and polymer (SIMGAP). In this study we performed a systematic analyses of the interplay between compositional effects, relative permeability hysteresis, interfacial tension dependent relative permeability and three phase relative permeability models for different gas based EOR schemes. The simulation runs were performed using 2D and 3D fine scale sector models. The simulation study was also extended to investigate gas injection processes in reservoirs with large transition zone. To the best of our knowledge, there is no commercial simulator which has implemented the combination of relative permeability hysteresis, IFT dependent and three phase models in compositional mode. Therefore, the study presented in this paper is the first in the literature which investigates the combination of all these effects on the performance of gas injection EOR schemes. The study shows that proper representation of relative permeability hysteresis, compositional effects and three phase models is essential in order to assess the performances of all gas based EOR processes and it provides a tool to investigate the effect of these effects in the absence of laboratory data and provides a basis for acquiring any additional experimental data. The study also shows that before embarking on very expensive laboratory work for EOR studies under three-phase flow, simulations should be used to help design the laboratory program in order to focus on the most important parameters that affect fluid flow and hydrocarbon recovery.