Over the past two decades, low salinity waterflooding has emerged as a successful tertiary recovery method. Several mechanisms have been suggested to contribute to the effect of the low salinity waterflooding. Fines migration in clay containing sandstones is amongst the main reasons attributed to the success of this technique. The effect resulting from the migration of fines helps homogenize the flow pattern of the waterfront, thus achieving better displacement efficiency. Little or no attention has been given to the effect of water blockage on multilayered reservoirs. The present work aims to study the effect of low salinity waterflooding on multilayered clay-rich sandstone reservoirs.
Parallel coreflood experiments were used to investigate the effect of low salinity waterflooding on multilayered reservoirs. Clay-rich Bandera sandstone cores were used for the experiment. Cores from two different blocks were used to obtain a contrast in the absolute permeability. All cores were saturated with the same high salinity formation water and then displaced with oil to reach initial water saturation. The cores were then aged at the reservoir temperature for 21 days. Three parallel coreflood experiments were used to compare the high salinity waterflooding to the low salinity waterflooding in both secondary and tertiary modes. Core effluent and CT scan were used to evaluate the recovery from all experiments.
The high salinity waterflooding shows heterogeneous water invasion, and more oil was recovered from the higher permeability core. Alternatively, the low salinity waterflooding in secondary mode showed a more homogeneous recovery regime, as the water blockage kept the waterfront advancement even between cores. Finally, the application of low salinity waterflooding in tertiary mode slightly improved the recovery from both cores equally.
This work is the first to emphasize the benefits of low salinity waterflooding in multilayered clay-rich sandstones. The conclusions from this work suggest a diversion effect to occur allowing for higher displacement efficiencies in multilayered clay-rich reservoirs.