Impact of Electrical Surface Charges and Cation Exchange on Oil Recovery by Low Salinity Water

Abstract

Low salinity water is a promising technique for improving oil recovery in sandstone reservoirs. However, the mechanisms of low salinity water are still uncertain; that makes the optimum conditions are unknown. In this paper, we study the effect of cation type and concentration in the injected water to identify the optimum salinity. Coreflood experiments of waterflooding and cation exchange tests were conducted to investigate the impact of cations on oil recovery, and understand the rock/brine interactions. In addition, zeta potential at oil/brine and rock/brine interfaces were measured to examine how the cation type and concentration change the electrical surface charges, and relate these measurements to the oil recovery obtained from coreflood.Berea sandstone cores were used for waterflooding and cation exchange experiments; all coreflood experiments run at HPHT. Three concentrations of NaCl, CaCl 2 , and MgCl 2 were tested with two crude oils of different compositions and properties. ICP-OES, and a spectrophotometer were used to analyze the ions concentrations in the effluent fluids for both waterflooding and cation exchange tests. Zeta potential was measured for solutions of oil/brine, and solid/brine; the solids used were Berea sandstone and four types of clays.This work contributes to the understandings of the impact of electrical surface charge and cation exchange on oil recovery by low salinity waterflooding. Zeta potential results showed that Na + changes the electrical charge at both oil/brine and rock/brine interface to highly negative, which results in repulsion forces between the two interfaces, and hence wettability alteration and improvement in oil recovery. Moreover, waterflood experiments of NaCl solutions improved oil recovery significantly compared to CaCl 2 , and MgCl 2 . Analysis of core effluent fluid proved the interaction between brine and rock; injection of single cation brine leached some of the ions from the rock surface by exchanging cations, which could contribute to improvement of oil recovery. Results demonstrate that the existing cations in the injected water brine have more dominant effect on the recovery factor than the water salinity. These findings can help in defining the brines that have higher potential for oil recovery improvement.

Extended DLVO-based estimates of surface force in low salinity water flooding

“…In contrast, 0.2 wt.% MgCl 2 and CaCl 2 generate negative disjoining pressure for all the clays. A similar conclusion was reported by Nasralla Ramez et al from core-flooding experiments and contact angle tests [32,[42][43][44]. It is worth noting that although we did not pronouncedly observe the effect of clay types on disjoining pressure, these clays may play different roles in low salinity effect from perspective of pore surface chemistry and surface complexations, despite the effect of such interactions on low salinity effect are not yet fully understood.…”

“…9). To better understand the mechanism behind the incremental oil recovery from coreflooding experiments in the literature [43], we used three different sets of zeta potential data to calculate the disjoining pressure using the formation brine provided in the literature [43]. However, we did not observe the difference of disjoining pressure using the three different sets for zeta potential (Fig.…”

“…Disjoining pressure of the crude Oils A and B/electrolytes/Berea sandstone system was simulated to determine the correlation of disjoining pressure simulation and coreflooding experiments by injecting various electrolytes, whose details are provided in the literature [43]. Figs.…”

Thin liquid films in improved oil recovery from low-salinity brine

“…Nasralla et al have compared the brine/oil zeta potential for two crude oils and three types of brines (NaCl, CaCl 2 , MgCl 2 ) with each brine type at three different weight fractions of salt [34]. At the same weight fraction, NaCl displays the most negative zeta potential with both oils.…”

Effect of Ca2+, Mg2+ and SO42− ions on the zeta potential of calcite and dolomite particles aged with stearic acid

“…The wettability of a reservoir is directly related to the surface electrical properties of the rock/water/oil interfaces [14][15][16]. Strand et al [17] used zeta potential measurements to investigate the relative affinity of Ca 2+ and SO 4 2− ions towards a chalk surface in order to support their findings from spontaneous imbibition and chromatographic adsorption experiments.…”