Wettability Assessment and Surface Compositional Analysis of Aged Calcite Treated with Dynamic Water

Abstract

The following study investigates the effect of brine ionic composition and salinity (a mixture we call dynamic water) on calcite surface wettability alteration using atomic force microscopy (AFM) and surface compositional analysis using X-ray photoelectron spectroscopy (XPS) in addition to contact angle measurements. Three ions are particularly varied (Mg 2+ , Ca 2+ , and SO 4 2−) to examine their role for surface alteration. Dissolution, adsorption, and precipitation are among the processes competing at the interface in the calcite/crude oil/brine system. Dissolution takes place according to a specific path with reiteration of etched pits deepening, steps retreat, and material removal from the surface. Aging calcite in crude oil causes adsorption and precipitation phenomena, especially asphaltene and carboxylic acids. The AFM topographic images of calcite saturated in deionized water and NaCl brine show that calcite dissolution occurs rapidly but maintains its crystal rhombohedral shape. Surface wettability measurements of aged calcite surfaces showed that sulfate has a dominant effect on altering surface wettability to strongly water-wet followed by diluted seawater. Nonetheless, when magnesium ions were removed from the brine, surface wettability alteration was weak, which indicated the need for such an ion in the brine. AFM topographic images show clear indication of surface morphology changes in all studied surfaces, although less features were observed when treated with SWME*0Mg (brine without any magnesium ions). All other surfaces showed some magnesium surface adsorption, while in the case of SWME*4S (brine with 4 times sulfate concentration compared to seawater), round-shape and vermicular features were also observed. An increase in the magnesium/ calcium ionic ratio in the brine will enhance surface dissolution and favor the presence of nucleation pits and growth of round-shape features. An increase in the sulfate/calcium ionic ratio alters the calcite surface by enhancing the formation of platelets and round-shape features. The effect of determining ions (most effective surface alteration ion) on altering calcite wettability is not a single ion because there are affinities between sulfate, calcium, and magnesium that will change surface morphology at certain ratios. Surface compositional analysis using XPS indicates the presence of sulfur on each treated calcite surface, but that by itself does not explain the wettability alteration results. However, the data provide clear evidence that magnesium ions need to be present in the brine mixture.

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

“…The effect was almost similar for the case of the aged dolomite as indicated by the plateau of zeta potential trends for the aged dolomite. In the study done by Abdallah and Gmira [43], it showed that the absorbability of Mg 2+ ions could be enhanced by the presence of Ca 2+ or SO 4 2− ions in the same solution. However, no strong conclusion can be made on such effect based on the obtained zeta potential due to the slight changes in zeta potential of the aged calcite and the aged dolomite as discussed here.…”

“…Smith et al [42] also showed similar rhombohedral shapes caused by dissolution on a calcite chip immersed in NaCl brine. Very recently, Abdallah and Gmira [43] demonstrated a rapid development of rhombohedral structures on Iceland spar calcite chips immersed in deionized water and NaCl brine.…”

“…6f). Abdallah and Gmira [43] reported an increase in the Ca 2+ and Mg 2+ ions adsorption on calcite surfaces treated with twice-diluted Arabian Gulf seawater with increased SO 4 2− ions concentration using X-ray photoelectron spectroscopy (XPS). Comparing Fig.…”

Mechanisms of Surface Charge Modification of Carbonates in Aqueous Electrolyte Solutions

“…Low Salinity Waterflooding (LSW) is an enhanced oil recovery strategy that injects water, of a controlled ionic concentration and composition, into oil reservoirs [1][2][3], potentially yielding up to 40% extra hydrocarbon, depending on conditions and crude oil properties [1,4]. Even though LSW has been demonstrated as a promising approach to improve oil recovery factors, the principal mechanisms involved are not fully understood.…”

Quantifying mineral surface energy by scanning force microscopy

“…In this case, water imbibition into pores is supported by the positive capillary pressure, which improves the oil recovery. It is widely accepted that carbonate rock formations are moderately to strongly oilwet [2,3]. This is attributed to the adsorption of polar compounds contained in crude oil such as carboxylic acids and asphaltenes, onto the carbonate surface, which results in the rock surface changing from hydrophilic to hydrophobic [2,4].…”