Molecular Dynamics Simulations of Clay-Oil-Brine Interfaces: Understanding Low-Salinity Enhanced Oil Recovery

Abstract

In an age of increasing energy demand it is clear that we must utilise our energy resources as efficiently as possible. Current oil extraction methods only recover in the region of a third of the oil in a reservoir. Presently oil is recovered through primary methods (pressure differentials) and secondary methods (water-flooding). However, it has been shown that incremental oil recovery beyond secondary methods can be achieved via using water floods of decreased salinity. The aim of this research is to bring clarity to the fundamental mechanisms behind low-salinity enhanced oil recovery (EOR), a technique where sea water, partially desalinated, is used to push increasing amounts of crude oil from existing, and future, oil reservoirs, increasing the reservoir lifetime and overall production. In this thesis, the key mechanisms driving low-salinity EOR have been examined with atomic resolution using classical molecular dynamics (MD) simulations. Simulations have focussed on modelling the three-phase properties of clays (montmorillonite and kaolinite) with model oil compounds (containing decane, decanoic acid and decanamine) at varying salt concentrations of brines (NaCl and CaCl2). The key result presents that clay minerals play an important role in the phenomenon of low-salinity EOR. The oil-wettability of a clay mineral surface is dictated by several factors, including: (a) the surface charge density of the mineral; (b) the nature of the charge balancing cation (monovalent vs divalent); (c) the amount of polar components within the oil phase; (d) the salt concentration of the surrounding flood.