Keshang formation in Karamay oil field belongs to typical conglomerate reservoirs. It is characterized by high water cut, poor sweep efficiency, high heterogeneity and inefficient oil recovery during the end-period of water flooding. The selection of EOR technique is very important for future development of such reservoirs. Foam flooding can improve macroscopic sweep efficiency, which may increase oil recovery for highly heterogeneous reservoirs particularly. In this study, systematic laboratory studies on foam flooding for Keshang formation have been performed.
Both the foamability and stability are the key factors to ensure high incremental oil recovery. The nitrogen foam formulas were optimized which had good performance of foamability and stability. The operating parameters including foam injection modes and gas liquid ratio were investigated by core flooding experiments at reservoir conditions.
The results show that: 1. Injection mode is an important factor and the direct injection of foam is better than co-injection of gas and solution obviously. 2. The gas liquid ratio is another important parameter. The optimized gas liquid ratio was proposed as 3:1-5:1 for direct injection mode. EOR effect evaluation indicated that foam flooding could contribute 40.00% OOIP recovery even if the recovery after water flooding was 41.50% under good operating protocols. The remarkable increasing of injection pressure during the foam flooding indicated that nitrogen foam flooding had excellent profile control ability.
Foam flooding integrates both properties of gas injection technique and chemical flooding. It is a candidate EOR method for highly heterogeneous conglomerate reservoirs.