Nitrogen Foam Flooding Test for Controlling Water Cut and Enhance Oil Recovery in Conventional Oil Reservoirs of China Offshore Oilfield

Abstract SZ oilfield was put on production in China Bohai Bay in 1993, characterized by huge thickness, high permeability, severe heterogeneity and high oil viscosity (24-452cp). There are many challenges during water injection because high oil-water viscosity ratio leads to quick breakthrough of injected water, high increasing rate of water cut, and so on. In order to solve these problems, nitrogen foam flooding was conducted in SZ oilfield during 2010 to 2011. Before pilot test, laboratory experiments and reservoir numerical simulation study under field conditions were conducted to evaluate the performance of different foaming agent and foam stabilizing agent, blocking performance of foam systems with different gas-liquid ratio and injection method, the influences of reservoir heterogeneity, connectivity, water cut time on nitrogen foam flooding efficiency. The study shows that the rational gas-liquid ratio in SZ oilfield is 1:1-3:1, the optimum concentration of foam agent is 3000- 5000mg/L, the optimum foam stabilizing agent concentration is 700-1000mg/L, and the injection method should be mixed injection. The more heterogeneous, more connective, higher water cut the porous media is, the higher the increment of oil recovery and the better the efficiency of foam displacement. The Hall curve analysis was used to evaluate the effectiveness of injection well and to calculate the resistance factor (RF) & residual resistance factor (RRF) (RF from 1.22 to 2.88, RRF from 1.06 to 2.00). The decline curve analysis was also used to obtain net incremental oil. Results from two well patterns conducted nitrogen foam flooding in 2011 indicate that water cut reduction ranged from 3.2 to 14.5%, accumulative oil production increases 30283m3 in a year and enhanced the oil recovery of the pilot about 0.5%, which suggests that nitrogen foam flooding has good prospect in conventional heavy oil reservoirs of china offshore oilfield.