Interactions of crude oil and salt solutions with mineral surfaces

Abstract

Understanding the fundamental interaction of liquids with mineral surfaces and their relation to larger scale mechanisms and phenomena in porous media is relevant to wide range of applications in oil recovery, soil remediation etc. Most previous imaged-based studies related to these applications were limited to two-dimensional space and rarely included multi-scale observations. Idealised systems, comprising monomineralic model porous media, simple liquids such as salt solutions and model oils have been successful in demonstrating predictable and reproducible trends. However, once the system is set closer to real environmental conditions, using realistically complex porous media with several minerals, and including variable aqueous conditions (e.g. salinity, ion valency or pH) and complex oils (e.g. crude oil), the results become too difficult to interpret. This thesis aims to unravel some of these complexities associated with the physics and chemistry of aqueous and hydrocarbon phases and mineralogy. The studies show the importance of interfacial interactions for industrial processes in porous media, which include carbonate and/or silicate minerals. In the first part of the thesis, sandstone cemented with dolomite and anhydrite was the porous medium for a case study of the effect of salinity on particle mobilization. Rock samples were imaged with micro-CT, and analysed digitally. This study was complimented by Atomic Force Microscopy (AFM) measurements of the adhesion forces between carbonate and quartz surfaces to better understand initial attraction between dolomite particles and quartz grain. The second part of the thesis was devoted to systems relevant to silicate minerals, in particular kaolinite and quartz, in contact with both salt solutions and crude oil. The focus was on the wettability alteration of such minerals, and its dependence on salinity, ion valency, pH and waterflooding. Wettability alteration was characterised by contact angle measurements and imaging of adsorbed/deposited crude oil polar compounds by scanning electron microscopy (SEM) and AFM. To study kaolinite wettability, a special procedure for kaolinite substrate preparation was developed, giving thin and smooth kaolinite coats, which remained stable in contact with liquids. The results showed that the wettability alteration of kaolinite by crude oil was generally similar to quartz, displaying a decrease in oil-wetness with increase in salinity and pH of the aqueous phase. The effect of subsequent waterflooding on wettability alteration was studied on glass and sandstone substrates. The preparation procedures developed showed that initial wettability alteration towards oil-wetness decreases, and its flooding-induced reversal towards water-wetness increases, with rising salinity and pH of the aqueous phase. Oil deposits after flooding were distributed as nano-blobs, with their substrate coverage and size similarly dependent on salinity and pH. It was found that the use of organic solvents to remove the bulk oil to inspect the deposits introduce preparation artefacts, which result in overestimation of deposit coverage. Analogous experiments on sandstone rock samples supported all findings for the glass model substrates. The final part of the thesis unified these new methodologies for wettability analysis with micro-CT analysis to study the pore-scale distribution of residual crude oil in plugs after waterflooding and relate this to the wettability state.--provided by Candidate.