Effect of HS and Pressure Depletion on the CO MMP of Zama Oils

Phase behaviour and minimum miscibility pressure measurements were carried out to evaluate the potential of applying miscible CO 2 /H 2 S flooding in the Zama reefs of NE Alberta, Canada. Since there is some variability in the properties of oils from different wells or reefs, the measurements were carried out on recombined reservoir fluids from two different wells. The injection solvent will be supplied from a nearby gas plant that is expected to produce CO 2 /H 2 S streams with a range of compositions due to a number of operational factors. Accordingly, three solvent injection gases were considered: pure CO 2 and CO 2 containing 20 and 40 mol% H 2 S. Minimum miscibility pressure (MMP) measurements were carried out using the rising bubble apparatus (RBA). The MMP decreased almost linearly with the amount of H 2 S in the injection gas in the range of compositions studied. Some evidence of precipitation of solids was observed. Measurements were also carried out to determine the CO 2 MMP of these reservoir fluids as they were depleted of gas through a differential liberation procedure. The results show that the MMP decreased with decreasing liberation pressure. Key properties of the liberated reservoir fluids were also measured and compared with those of the recombined reservoir fluids. The results show that miscible flooding with sour acid gas is feasible in this case, and could provide an excellent means of storing/sequestering these gases while improving oil recovery.