Characterization of Crude Oil-Water and Solid -Water Interfaces and Adsorption / Desorption Properties of Crude Oil Fractions: The Effect of Low Salinity Water and pH

Abstract

The reservoirs of conventional oil are rapidly depleting because of increased production and consumption of crude oil in the world. Mature and mostly depleted oil reservoirs require advanced recovery techniques to sustain the production rates. During the past years, a variety of enhanced oil recovery (EOR) methods have been developed and implemented to increase the oil recovery from mature reservoirs.

Low Salinity Waterflooding (LSW) is an emerging EOR process of injecting water containing low concentrations (<4000 ppm) of total dissolved solids into the reservoir. This moderatecost process yields relatively higher incremental recoveries than other water based recovery methods. Investigation of mechanisms for increased recovery is quite challenging because this process depends upon complex crude oil/water/rock properties. This work was done to study the surface chemistry of typical reservoir surfaces where LSW can be used for EOR. The oilwater and solid-water interfaces were characterised in low salinity aqueous solutions and investigated how the electrolytes and pH of solutions affect the interfacial and surface properties. The influence of low saline aqueous solution on the desorption behaviour of different fractions (acid-free oil and base-free oil) of crude oils was also explored.

Reservoir minerals are sensitive to small changes in solution properties and therefore model, outcrop and reservoir particles were characterized in low salinity aqueous solutions. Theextent of ionic adsorption on the mineral surfaces was found by various techniques. Particles were also characterized with respect to their elemental compositions. Asphaltene adsorption/desorption on reservoir rock surfaces play an important role in EOR processes. Various injection sequences of low saline aqueous solution of Na&nbsp;+, Ca2+ and sea water were considered to study the desorption of asphaltenes from silica surfaces. Composition of the aqueous phase influenced the interfacial properties of crude oil. Acids, bases and asphaltenes were selectively removed from crude oils and demonstrated the significance of each component on the interfacial behaviour in the aqueous phase under various electrolyte concentrations, type of electrolytes and pH ranges. It was determined that the crude oil acids and electrolyte type played an important role for interfacial properties at high pH conditions. Adsorption/desorption properties of various crude oil fractions on silica coated quartz surfaces were also studied. The influence of electrolyte types and pH conditions of low salinity aqueous solutions on desorption behaviour of different oil fractions was considered. Finally, the dynamic interfacial behaviour of two different crude oils and their fractions were evaluated in different aqueous solutions. The effects of mono and divalent ionic concentrations on interfacial properties were compared.