The Stability of Pre-formed Foam and the Effect of Gravity Forces During CO2-foam Processes in Fractured Chalk Rock

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. The CO2-foam process was carried out in a short core plug by injecting pre-formed foam at 340 bar and 55oC. The fractured model was simulated by drilling a 3 mm hole through the centre of the plug and packing it with 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 modeling studies based on the successfully history-matched experiments in fracture chalk rock have been carried out to investigate the stability of pre-formed foam and the role of gravity forces on oil recovery in long fractured chalk models. Pre-formed foam was injected horizontally at 340 bar and 55oC. Foam qualities and water saturation have been varied. Results indicate that increasing the foam quality decreases the rate of oil production but increases the ultimate oil recovery with horizontal injection of pre-formed foam. The simulation results also show that molecular diffusion is an important recovery mechanism in chalk fractured rock and should be taken into account, and that even in horizontal injection there is considerable gravity effect. The mechanistic models can be used to study CO2-foam processes in fractured chalk reservoirs with multiple fractures.