Mechanistic Modeling of CO2-Foam Processes in Fractured Chalk Rock: Effect of Foam Strength and Gravity Forces on Oil Recovery

摘要

Recent laboratory and mechanistic modeling studies have demonstrated that CO2-foam has the potential to recover additional oil in fractured water flooded chalk rock with low matrix permeability. The CO2-foam processes were carried out in short core plugs by injecting pre-formed foam at 340 bar and 55oC. The fractured model was represented by core plug with a 0.3 cm diameter hole drilled though the centre, and packed with monodispersed glass beads. Calculated mobilities also indicated that CO2-foam is highly effective in decreasing the mobility of CO2 and increasing the apparent viscosity of CO2 in fractured chalk rock. In this work, mechanistic simulation studies based on history-matched foam models tuned to laboratory data are used to investigate the effect of the strength of pre-formed foam and the role of gravity forces on oil recovery in long fractured chalk models. Pre-formed foam was injected either horizontally or vertically (from the bottom) at 340 bar and 55oC. Pure CO2 injection was also injected in fractured chalk models and used as base cases. The foam qualities and water saturation were varied. Results indicate that decreasing the foam quality increases the rate of oil production with both horizontal and vertical injection of pre-formed foam. However, the oil recovery efficiency with horizontal injection of pre-foamed foam was higher than with vertical injection. The simulation results show that molecular diffusion is an important oil recovery mechanism in chalk fractured rock with low matrix permeability and should be taken into account, and that considerable gravity effect can affect the oil recovery in horizontal injection of pre-formed foam. The mechanistic models can be used to study CO2-foam processes in fractured chalk reservoirs with multiple fractures.