Low Salinity Oil Recovery–Increasing Understanding of the Underlying Mechanisms

Abstract

Abstract Water injection has been used to increase oil recovery since the late 19th century. For over 100 years, the mechanisms behind this incremental oil recovery have been thought of as physical, i.e. the injection of water maintains reservoir pressure and sweeps the mobilised oil to the producing well. In the last decade this premise has been questioned and through the development of BP's LoSal™ EOR technology, it is now recognised that oil recovery through waterflooding also involves chemical processes and that modifying the brine chemistry of the injection water can significantly impact the observed recovery. Several hypotheses regarding the mechanism involved with low salinity waterflooding have been discussed in the literature. In 2006, BP published a proposed mechanism for this phenomenon based upon multicomponent ion exchange (MIE) triggered by expansion of the electric double layer at the mineral surfaces that bind the oil. This paper describes on going research studies focused on advancing the understanding of these mechanisms using sophisticated physical chemistry techniques such as Small Angle Scattering using neutrons from the ILL facility in Grenoble, France and the ISIS facility at the Rutherford Appleton laboratory, UK and X-rays at the DIAMOND Light source, Oxon. These techniques are capable of measuring the thickness of any water layer at the mineral surface down to the Angstrom level. Results to date provide some support for the BP published mechanism. They have shown the presence of a thin water layer and its variation with changes in the salinity of the water medium at model silica and clay-like surfaces, with attached (model) polar oil components, suspended in oils. Furthermore, the impact of cation-type on the water-layer thickness has also been demonstrated.