Laboratory studies along with field tests conducted over the decade reveal that reducing the salinity of water injected into reservoirs improves the oil recovery. Different phenomena e.g. increase in pH (alkalinity), fines migration, multi-component ionic exchange, etc., have been proposed by researchers for improved oil recovery during low salinity waterflooding (LSW). Though LSW has attracted attention among reservoir engineers as tertiary recovery process, limited studies have reported the potential of LSW as secondary recovery process. Also, the relationship between reservoir rock parameters such as wettability, rock minerals, etc. and oil recovery is not well established for LSW. The objective of this paper was to investigate the relationship between rock wettability and oil recovery with low salinity water injection as secondary recovery process. Coreflooding experiments have been performed at room conditions on Berea cores with four different wettabilities ranging from water- to oil- wet. Brines and n-decane were used as displacing and displaced phases, respectively. The results showed that, for all the salinities, oil recovery increases as wettability changes from water- to neutral- wet conditions. Further change in rock wettability from neutral- to oil-wet condition resulted in decreased oil recovery. It was also interesting to observe that oil recovery is higher for LSW as compared to high salinity waterflooding when used as secondary recovery process. Increase in pressure drop and hence decrease in effective permeability was also observed during LSW process in most of the cases considered.

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.

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CO2 dissolution is considered as one of the most promising mechanisms for trapping of free-phase CO2 into brine. It causes an increased density of the brine and initiation of gravitational instability that eventually leads to density-driven natural convection in saline aquifers. Correct estimation of the onset time for convection and the rate of dissolution of CO2 into brine is important because the timescale for dissolution corresponds to the timescale over which free-phase CO2 has a chance to leak out. The gravitational instability of a diffusive boundary layer in porous media has been studied in several papers in recent years, but there are few works about the behavior of density-driven natural convection mechanism in heterogeneous saline aquifers. Barriers such as shales and calcites layers are common types of heterogeneities in geological formations that are important in the fluid flow. Despite the recognized importance of convective dissolution in these heterogeneous geological formations, there is no experimental data available for studying the accelerated mass transfer rate of CO2 into these media.In this paper, we investigated the effect of the regular distribution of barriers on the rate of dissolution of CO2 into water and geometries of convection fingers. A series of experiments were performed using a precise experimental set-up with barrier heterogeneous Hele-Shaw cell geometries and by using CO2 and water. The approach and procedure for performing the experiments give us this opportunity to have both qualitative (images and movies) and quantitative (amount of the dissolved CO2 into water) data at the same time. The behavior of convection pattern after onset time and the effect of system properties on the behavior of convective mixing process will be presented and discussed. Moreover, some speeded-up movies from the experiments that are suitable for improving public awareness of the problem have been uploaded on the internet platform. Lastly, the relationships between dissolution flux after onset time for convection and barrier properties are discussed.

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