Interfacial Tensions And Aging Behaviour of Some Crude Oils Against Caustic Solutions
Authors: McCaffery Frank G. 
Published: March 2010

Interfacial tensions between sodium hydroxide solutions and four crude oils were measured as a preliminary step in the investigation of caustic waterflooding possibilities. Based on these initial results and some laboratory caustic flood tests reported in the literature; the Wainwright and Viking Kinsella Wainwright B heavy oil reservoirs are possible candidates for improved oil recovery by caustic waterflooding. Core displacement measurements or pilot floods will, however, be required to evaluate actual benefits from the process. A minimum interfacial tension between these heavy oils and caustic solutions occurs with about O.25wt. % NaOH injection water.

The interfacial tension between the erode oils and sodium hydroxide solutions was found to release with the age of tire interface. This behaviour suggests that many of the sodium soap products, which are formed when acidic compounds in the crude oil react at the interface with sodium ions in the aqueous phase, subsequently migrate away from the oil-water interface.

Introduction

The current upswing in improved recovery research has resulted in several recent reports of laboratory studies and field trials of caustic waterflooding processes. This work has been discussed in detail by Johnson(1) and Ehrlich et al.(2). Several controlling mechanisms all relying on changing the properties of some of the interfaces involved, have been identified or suggested as being responsible for improving the recovery aver that of a conventional waterflood. Reisberg and Doscher(3) indicated that interfacial tension lowering and the elimination of rigid films at oil/water interfaces were responsible for an improved ultimate recovery in laboratory displacement experiments, Others(2, 4–6) have tested relatively high NaOH concentrations for alkaline waterflooding in light oil reservoirs where the controlling mechanism appeared to be a wettability change from oil-wet to water-wet. A caustic process has also been used with saline water, in which there was a wettability change from water-wet to oil-wet and the production of a water-in-oil emulsion(7). Workers at Chevron Oil Field Research (8, 9) found significant increases in viscous oil recovery before water breakthrough, and have attributed this to a reduction in water channelling- which results from residual oil being emulsified in situ at low interfacial tensions (oil-in-water emulsion) and then becoming trapped again in small pare throats, Johnson's recent paper(1) also discusses the emulsification and entrainment mechanism, in which emulsified oil is produced rather than becoming trapped. A mobility-controlledaustic flooding process has been outlined by Sarem(10) and is currently being field tested(11). Friedman recently suggested using polyethylenimine, a polybasic polymer, for the recovery of viscous acidic crudes(12).

The present study was concentrated on interfacial tension determinations between four Canadian crude oils and caustic solutions. Most of the measurements were with heavy oil of 21–22 º API gravity" from the Wainwright and Viking Kinsella Wainwright B pools in Alberta. Scott et al.(13) and Dranchuk et al.(14) have reported a number of alkaline waterflood tests with heavy ail primarily from the Lloydminster area.