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

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• 作者：Wael Abdallah ; Ahmed Gmira
• 刊名：Energy & Fuels
• 出版年：2014
• 出版时间：March 20, 2014
• 年：2014
• 卷：28
• 期：3
• 页码：1652-1663
• 全文大小：1071K
• 年卷期：v.28,no.3(March 20, 2014)
• ISSN：1520-5029

文摘

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 (Mg²⁺, Ca²⁺, and SO₄^{2鈥?/sup>) 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.}