Electrokinetics of Limestone and Dolomite Rock Particles

Abstract

High-salinity water such as seawater, or formation brines, is frequently injected in carbonate reservoirs. Ion interactions between injection water, reservoir fluids, and rock surface are quite complex. It has recently come to be believed that the chemistry of injection water can significantly enhance oil recovery. Several reaction mechanisms were suggested, including rock dissolution, change of surface charge, and/or sulfate precipitation.This study attempts to characterize the electrokinetics of limestone and dolomite suspensions at 25 and 50°C. In addition, reaction mechanisms at the water/rock interface were established. Synthetic formation brine, seawater, and aquifer water were chosen from Middle East reservoirs. Carbonate particles were soaked in high-and low-salinity water. A phase-analysis-light-scattering (PALS) technique was used to determine the zeta potential (surface charge) of carbonate particles over a wide range of pH, ionic strength, and temperature.Zeta potential of limestone particles was significantly affected by calcium ion. Low-salinity water created more negative charges on limestone and dolomite particles by expanding the thickness of the diffuse double layer. Individual divalent cations decreased the zeta potential of limestone particles in sodium chloride solutions, while sulfate ions showed a negligible effect. Limestone particles in high-salinity water had decreased zeta potential. The solubility of calcium ions increased as temperature was increased and thus created additional negative charges. The absence of sulfate in aquifer water strongly influenced the dolomite surface charge. In summary, surface-charge adjustment from positive to negative can alter the wettability of carbonate rock from preferentially oil-wet to waterwet. As a result, residual-oil saturation should be decreased. IntroductionInterfacial phenomena at carbonate/water interfaces are controlled by the electrical-double-layer 1 (EDL) forces. Therefore, it is necessary to understand the behavior of the ions' interactions with the rock surface. Charged species 2 are transferred across any solid/liquid interface only until reaching equilibrium. The interface can be visualized as a semimembrane 3 that allows the common charged species between solid and solution to pass through. These species are called potential-determining ions. As a result of the relative motion between the charged dispersed phase and the bulk liquid, the EDL is sheared. The potential, at this shear plane, is commonly called electrokinetic or zeta potential (). Various methods are applied to measure the potential at the shear plane. However, the most commonly used technique is the electrophoresis method (Pierre et al. 1990).

Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs

“…Because all aqueous ions potentially exchange at calcite-surface sites, a large number of surface complexes is possible. Fortunately, considerable information is available on the calcite/water interface (Somasundaran and Agar 1967;Möller and Werr 1972;Siffert and Fimbel 1984;Thompson and Pownall 1989;Van Cappellen et al 1993;Pokrovsky et al 2000;Nystrom 2001;Wolthers et al 2008;Hiorth et al 2010;Alotaibi et al 2011;Heberling et al 2011;Alshakhs and Kovscek 2015). We adopt the five preliminary surface reactions listed in Table 2, where the symbol > denotes surface species.…”

“…In particular, sodium and chloride ions are dominant species at high brine concentrations and may participate in ion-exchange equilibria. It is commonly accepted, however, that sodium and chloride ions are inactive at the calcite/water interface (Somasundaran and Agar 1967;Möller and Werr 1972;Siffert and Fimbel 1984;Thompson and Pownall 1989;Van Cappellen et al 1993;Pokrovsky et al 2000;Nystrom 2001;Wolthers et al 2008;Hiorth et al 2010;Alotaibi et al 2011;Heberling et al 2011;Austad et al 2015;Puntervold et al 2015). Unfortunately, no direct evidence is available to confirm or refute this view.…”

“…The surface charge of the mineral interfaces appears to play a critical role. This last observation engendered a large number of ancillary studies on silica, clay, and calcite/water interfaces and their ion-exchange behavior, especially recently (Lager et al 2008a;Sorbie and Collins 2010;Nasralla and Nasr-El-Din 2012;Alotaibi et al 2011;Alotaibi and Yousef 2015;Alshakhs and Kovscek 2015;Brady Myint and Firoozabadi 2015;Puntervold et al 2015;Qiao et al 2016). Fundamental studies (Ricci et al 2013;Alshakhs and Kovscek 2015;Brady et al 2015;Lashkarbolooki et al 2016;Mugele et al 2016) of the calcite/water interface, including molecular simulation (Kerisit and Parker 2004;Sakuma et al 2014;Qiao et al 2016), also garnered attention.…”

Calcite Dissolution Behaviour During Low Salinity Water Flooding in Carbonate Rock

“…The surface charge is strongly pH dependent, because H + and OH − are potential determining ions in many solids [Alotaibi et al 2011]. surface charge of the particles was measured over a pH range of 3 to 12 (adjusted with HCl or NaOH).…”

“…These clay particles are lacking in Carbonate porous media. The suggested recovery mechanism for carbonates is wettability alteration [Aladasani et al 2012;Yousef et al 2011], due to ion exchange [Al Shalabi et al 2013;Brady et al 2012], electric double layer expansion [Alotaibi et al 2011], Calcite dissolution [Hio 2008;Yousef et al 2011;Zhang and Sarma 2012] and pH increase. Other mechanisms are insitu surfactants generation, emulsion formation [Emadi and Sohrabi 2013;Mahzari and Sohrabi 2014], salting-in effect [RezaeiDoust et al 2009] and fines migration [Zahid et al 2012].…”