Low Salinity Cyclic Water Floods for Enhanced Oil Recovery on Alaska North Slope

Abstract

Abstract With low salinity waterflooding already implemented, cyclic waterflooding is under extensive research for increased oil recovery than conventional waterflooding. Low salinity cyclic water injection (CWI) is an interesting combination that offers the effects of both, with notably high oil recovery and less usage of water. Careful evaluation might promote the application of cyclic injection in the fields, especially on Alaska North Slope (ANS). Two phase flow experiments were conducted on representative sandstone cores. After establishing initial water saturation, Amott-Harvey Wettability tests were performed with spontaneous and forced displacement of the fluids by one another. Cyclic water floods were conducted to calculate oil recovery from the volume of produced fluids. Pulsed cyclic floods were programmed in the injection pump. The experiments were repeated with cores of different permeability and lab reconstituted brines of 22000, 11000 and 5500 ppm salinity. Results were compared with available data from continuous injection performed on the same cores. Cyclic floods were also tested for two symmetric on-off time intervals. With the dead oil experiments, it is observed that residual oil saturation (Sor) is achieved as early as 3-4 pore volumes (PV) of injected water in cyclic injection as compared to 6-7 PV’s in continuous injection. Additional oil recovery is observed in cyclic injection’s idle time, when the already flooded water spreads smoothly within the pores to displace oil out of the core. Better recovery was obtained with lower salinity brines. Within cyclic injection, shorter pulse intervals yielded better results. To conclude, low salinity CWI with shorter pulse intervals yield better oil recovery and early Sor. This is an attractive option for ANS operators.