Molecular-level modelling of complex liquid interfaces

  • Sean O'Connor

Student thesis: Master's Thesis

Abstract

In a world with ever-increasing energy demands, it is important that the oil industry continually adapts and innovates in order to ensure maximum possible yield of oil recovery. Enhanced Oil Recovery, (EOR), is being increasingly applied to optimise oil recovery. One method of EOR is through the use of water injection. Water injection involves flooding an oil reservoir with water. This helps maintain the pressure during the extraction of oil and can also be used to move the oil to a more favourable position in the reservoir. The competitive interaction between oil and water at the reservoir wall is better understood through analysis of several interfacial properties, such as partial density distribution, interfacial tension, adsorption energy and contact angle. Researching these interfacial properties will allow prediction of the optimum characteristics of water injected into a reservoir based on its interaction with the hydrocarbon fluid and the sedimentary rock surface. At the same time it will be determined whether or not Molecular Dynamics is a useful tool to assist and improve EOR. Molecular Dynamics simulations were employed to explore several interfacial properties of water and dodecane at the {1014} surface of calcite. A series of different initial water configurations were investigated at two different temperatures. Partial density analysis demonstrated a significant increase in the density distribution of water at the surface of calcite. It was found that the partial density distribution of water is lower for the simulations carried out at the higher temperature at the calcite surface. An investigation into the interfacial tension between water and dodecane resulted in a value of 50.05 mN/m. This result was comparable to those found in both experimental and other computational studies.Use of the Radial Distribution Function yielded adsorption free energy results of -33.4 kJ mol⁻¹ and -39.4 kJ mol⁻¹ for at 298K and 353K respectively. Potential of Mean Force analysis yielded an adsorption energy result of -44.0 kJ mol⁻¹ for water at the {1014} calcite surface. Several studies carried out in recent years have produced results comparable to this, though a portion of the scientific community believe this result to be too low. It has been shown that the value for adsorption energy is dependent on the Ca - Owater distances for computational studies. However the results in this study do not follow this trend. Contact angle analysis showed that the addition of dodecane inhibited the spreading of water on the {1014} calcite surface, but not entirely. A new computational method was also developed for measuring the contact angle for GROMACS coordinate files which, whilst producing efficient results for uniform spreading, is generally than the more traditional method. However for non-uniform spreading it could be argued that the traditional method is less reliable. Analysis of a water droplet system proved unequivocally that the {1014} surface of calcite is water-wet.
Date of Award1 Oct 2014
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsSchlumberger Middle East S.A.
SupervisorMaxim Fedorov (Supervisor) & (Supervisor)

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