LoSal Enhanced Oil Recovery: Evidence of Enhanced Oil Recovery at the Reservoir Scale

Abstract

Abstract For over 10 years research has been carried out on the impact of low salinity waterflooding on oil recovery. Data derived from corefloods, single well tests, and log-inject-log tests have shown that injecting low salinity water into an oil reservoir should result in a substantial increase in oil recovery in many cases. The results varied from 2 to 40% increases in waterflood efficiency depending upon the reservoir and composition of the brine. In 2005, a hydraulic unit was converted to inject low salinity brine into an Alaskan reservoir, by switching a single injection pad to low salinity water from high salinity produced water. An injector well and 2 close production wells were selected within a reasonably well constrained area. A surveillance programme was devised which included capturing produced water samples at regular intervals for ion analysis and the capturing of production data. Detailed analysis of the production data, and the chemical composition of the produced water, demonstrated an increase in oil production and provided direct field evidence of the effectiveness of LoSal™ at inter-well scales. Additionally, the response of the reservoir to low salinity water injection was confirmed by single well chemical tracer test. In parallel, laboratory studies have led to mechanistic understanding of LoSal™ in terms of multiple-component ionic exchange (MIE) between adsorbed crude oil components, cations in the insitu brine and clay mineral surfaces. The results clearly show that the enhanced oil production and associated water chemistry response was consistent with the MIE mechanism proposed. The oil production data have been modeled using an in-house developed modification to Landmark's VIPTM reservoir simulation package. An excellent match for the timing of the oil response was obtained which provides a good basis for predicting the result for large scale application of LoSal™ flooding. Introduction It has been more than 10 years since Yildiz and Morrow (1996) pushed forward the research started by Jadhunandan(1990; 1991; 1995) and published their paper on the influence of brine composition on oil recovery. This paper showed that changes in injection brine composition can improve recovery. Since then, Tang & Morrow (1999) have progressed the research on the impact of brine salinity on oil recovery, followed by other researchers such as Webb et al. (2004) and McGuire et al. (2005); these authors performed an extensive research programme on low salinity injection (LoSal™). This programme included numerous core flood experiments performed at ambient and reservoir conditions (at high temperature and pressure, with 'live' fluids) both in secondary and tertiary mode, single well tracer tests (SWCTT) and log inject log tests, showed a significant increase in oil recovery due to low salinity brine injection.