Drivers of Low Salinity Effect in Carbonate Reservoirs

Abstract

Wettability alteration appears to be the main mechanism of low salinity water flooding in carbonate reservoirs. However, what factor(s) controls the wettability alteration is not clearly defined. We hypothesized that zeta potential at interfaces of oil/brine and brine/rock controls the wettability alteration in carbonate reservoirs. To test our hypothesis, we removed SO4 2– ions from the aqueous ionic solutions because SO4 2– ions likely adsorb at the pore surface, triggering desorption of carboxylic materials. We examined the zeta potential of interfaces of crude oil/brines and brines/rock. We also measured the contact angle and conducted two core-flooding experiments. Moreover, we performed a geochemical study to examine the potential of calcite dissolution by low salinity water using PHREEQC software. Our work demonstrates that contact angle strongly correlates with polarity of the zeta potential of interfaces of oil/brine and brine/rock, showing that the same polarity of zeta potential for oil/brine and brine/rock triggered a strongly water-wet carbonate surface in the presence of formation brine. The opposite polarity of zeta potential of oil/brine and brine/rock, on the other hand, yielded an intermediate or slightly oil-wet surface in the presence of 10 times diluted formation brine. However, incremental recovery of 5.8–18.1% was observed under tertiary mode, implying that low salinity water likely shifts the reservoir wettability from strongly water-wet to intermediate-wet. In addition, geochemical modeling revealed a negligible amount of calcite was dissolved in the presence of low salinity water, confirming that calcite dissolution is not a contributing factor to the low salinity effect. Moreover, we demonstrate that the contact angle on the carbonate substrate decreases linearly with increasing Z parameter, Z p = (|Zeta oil/brine + Zeta brine/rock |). We therefore argue that manipulating the Z parameter (polarity of zeta potential of brine/rock and oil/brine) is of vital importance to shift the reservoir wettability and improving oil recovery. We suggest that the Z parameter may be used as an interpolant to model the low salinity effect, rather than using salinity level or individual ions in the solution.

Enhanced oil recovery from carbonate reservoirs by spontaneous imbibition of low salinity water

“…Sari et al (2017) observed a linear relation between contact angle and f-parameter (a combination of rock-brine and oil-brine f-potential), stating that f-potential is a more reliable means of wettability alteration prediction rather than brine salinity because different salinities of different ions may result in the same oil recovery. However, what seems to be the main cause of wettability alteration is a shift in f-potential (Sari et al 2017).…”

“…Shariatpanahi et al (2016) used dolomite outcrops to perform spontaneous imbibition tests and concluded that sea water did not act as a strong wettability modifier for dolomites at 70°C, but using 10 times diluted sea water could increase the oil recovery by 10%-15% of original oil in place (OOIP) compared with the results from imbibition results with sea water (Shariatpanahi et al 2016). Sari et al (2017) observed a linear relation between contact angle and f-parameter (a combination of rock-brine and oil-brine f-potential), stating that f-potential is a more reliable means of wettability alteration prediction rather than brine salinity because different salinities of different ions may result in the same oil recovery. However, what seems to be the main cause of wettability alteration is a shift in f-potential (Sari et al 2017).…”

Effect of salinity on oil production: review on low salinity waterflooding mechanisms and exploratory study on pipeline scaling

“…For example, clay dispersion is found to be minimized at low pH conditions and increasing pH is considered to amplify the fine releasing phenomenon from the rock wall and cause drastic permeability reduction [74]. Surface complexation modeling was performed in [27,[75][76][77][78] to quantitatively describe the effect of pH on wettability. Bond product sum, which is calculated by the summed products of the oppositely charged surface species locating on the brine/ mineral interface or the oil/brine interface, is introduced to indicate the wettability as a measurement of the oilmineral electrostatic attraction [76,77].…”

“…The sample age has been considered as a factor affecting other mechanisms in recent years [75,78]. It can be concluded from their results that contact angle will increase much faster in aged samples (35°?…”

Carbon Storage and Enhanced Oil Recovery in Pennsylvanian Morrow Formation Clastic Reservoirs: Controls on Oil–Brine and Oil–CO2 Relative Permeability from Diagenetic Heterogeneity and Evolving Wettability

“…Even with an individual mineral, wettability experiments in an oil-brine-calcite system have demonstrated a range of oil-wet to water-wet responses that depend on pH, mineral surface composition, dissolved ion composition, and whether samples were aged with oil [22][23][24][25]. Still, efforts continue to improve our fundamental understanding of wettability controls.…”