Influence of Crude Oil Components on Recovery by High and Low Salinity Waterflooding

This study presents an investigation on the effects of various polar components of a crude oil on its recovery by high and low salinity waterflooding and correspondingly on some of the suggested mechanisms in the literature. Coreflooding experiments were performed on several Berea core plugs aged in four different variants of the same crude oil with relative amounts of acids; bases, and asphaltenes. The oils labeled as acid-free, base-free, asphaltenes-free (deasphalted), and original or normal crude oil were expected to initiate varying wetting conditions during aging. The results of high salinity waterflood showed that the plug aged with base-free oil provided the highest whereas that with acid-free oil provided the lowest final oil recoveries. A reduction in residual oil saturation (S-orw) by 1.4% to 2.9% PV for normal, base-free, and asphaltene-free crude oils after low salinity waterflooding (LSW) in tertiary recovery mode was observed. For the case of acid-free crude oil, the S-orw was reduced marginally. A 2-3-fold increase in differential pressure was observed during injection of low salinity brines. The effluent brine pH was also increased by 1 pH unit during LSW. The observations from the present work indicate that different oil components initiate varying wetting conditions and that the initial wetting conditions influence the performance of a tertiary low salinity flood. In particular, a low salinity flood seems favorable when the initial wetting conditions are not water-wet.