Optimization of transitional steam injection mode in mid-late stage of steam flooding for shallow thin heavy oil reservoirs: A case study of Block Pai 612, Chunfeng Oilfield

Some problems, such as low heat utilization rate and unsaturated steam chamber, often occur during the transition from continuous to intermittent steam flooding of heavy oil reservoirs. Based on the reservoir engineering theory, the transitional steam injection modes in the mid-late stage of steam flooding were compared by way of numerical simulation. The results show that the pulse steam injection and rate-variable steam injection deliver higher heat utilization rates than continuous steam injection and effectively displace residual oil. As per the geological conditions of Block Pai 612 in the Chunfeng Oilfield, a numerical model was built for control of the shut-in of some high steam channeling wells in the early stage of steam flooding. The optimal steam injection parameters of two transitional steam injection modes in the mid-late stage were clarified. For the pulse steam injection, the best performance is achieved when the injection is performed at 100 m³/d for 5 d and suspended for 1 d. For the rate-variable steam injection, the best performance is realized when the rate-variable injection interval is 50 d at 50, 80 and 110 m³/d, respectively. The comparison suggests that the rate-variable steam injection is the optimal transitional steam injection option for the target block. This mode can effectively improve the recovery of reserves and restore the formation pressure to provide energy for subsequent intermittent steam injection and further enhance the recovery efficiency of the target block.