ADDITION OF CONDENSABLE OR NON-CONDENSABLE GAS TO STEAMFLOOD PROCESSES FOR IMPROVED HEAVY OIL RECOVERY BY GRAVITY DRAINAGE
This research focused on quantifying the advantages of adding condensable and noncondensable gases to steamflooding for heavy-oil recovery governed by gravity drainage in naturally fractured carbonate reservoirs. The work consists of numerical and immature physical modeling. The numerical modeling investigates the effects of gas addition on recovery through a series of sensitivity studies in order to develop a clear behavior prediction of the roles the gases play on recovery. The numerical investigation proceeds, afterwards, to include the construction of two synthetic models that mimic actual rock properties for two physical core plugs used in the laboratory. The first model has a short length of 3.5 inches, prototype model, and the second model has a long length of 28 inches. The development of both models in the numerical analysis is made by a thermal reservoir simulator, STARS CMG© . The numerical results compare between the three injection schemes, steam, steam/N2 and steam/CO2, and between the recovery behavior of the prototype and original experiments. The work, also, sheds light on the physical aspects of the study. This includes the modeling and preparation of the short and long core plugs in the laboratory.
The research work concluded that, numerically, the addition of non-condensable gas to steamflood processes increases the cumulative oil recovery slightly over steam injection but more importantly accelerates oil production at early time of the process. The injection of condensable gas accelerates the production to some extent at early time of production but the rate drops afterwards. The cumulative oil recovered by the co-injection of condensable gas is slightly less than steam alone injection. The main differences between the two gases are attributed to the solubility factor of CO2 in oil and water phases and the better steam propagation profile in the N2 injection case.