Experimental Study of Low Salinity Waterflooding and its Effect on Wettability

Abstract

Many low salinity waterflooding studies have been performed, both in the laboratory and on the reservoir scale, over the last decades. These studies have proven that, under the right conditions, it is possible to get an enhanced oil recovery by reducing the salinity of the injecting water.

This report presents laboratory core sample experiments on low salinity waterflooding and its effect on wettability, along with a literature study of low salinity waterflooding and rock wettability.

Two set of Berea sandstone of four cores each, one set of high clay content and low permeability and the other with low clay content and high permeability, were cleaned measured for porosity and saturated with formation brine. Initial water saturations were established by the porous plate method. The cores were saturated and aged in Heidrun crude oil. The wettability was measured by the Amott-Harvey method on one core from each set after aging, after flooding with high salinity brine (3.5 % NaCl), after flooding with high salinity brine and diluted brine (1500 ppm Na+) and after flooding with high salinity brine and two diluted brines (1500 ppm Na+ and 350 ppm Na+, respectively). The purpose was to look on the effect low salinity waterflooding had on the wettability of the cores. Produced volumes and pH were measured regularly and differential pressure drop across the cores was recorded continuously during the floodings.

All the wettabilities measured on both sets of cores came out on the water-wet side. As a result of this, little or no enhanced recovery was observed when flooding with diluted brines. An exception was core 14D which had an increase in recovery of 7.75 % OOIP when flooded with the most diluted brine. This recovery was likely due to migration of fines since it was seen in connection with severe spikes in the differential pressure.

A characteristic increase in the differential pressure across the cores was observed for all floodings when injection of diluted brine was initiated.

No clear tendency of increased water-wetness as a result of low salinity waterflooding was observed for any of the two core sets, except for core 14D. The increased water-wetness seen for this core is likely a result of the fines migration.