Improving The Oil Recovery Efficacy of Lignosulfonate Solutions

Abstract

Abstract Potential cosurfactants for use with lignosulfonate-based surfactant solutions were tested for their ability to improve the oil recovery efficacy of pure lignosulfonate solutions. A procedure involving a sequence of strategies was developed and used to screen various additives for their effectiveness. The key parameter was the magnitude of the interfacial tension obtained against the crude oil, but measurements of surface tension, pH, density and viscosity of the lignosulfonate formulations were also used for characterization purposes. The oil employed throughout the study was a light Ontario crude. In the formulation studies, interfacial tension values below 1.0 dyne/cm were obtained upon the addition of caustic soda to various aqueous lignosulfonate solutions. The most effective of the organic additives tested was butanol-1, for which interfacialtensions as low as 1.7 dynes/cm were obtained at a 10% butanol-1 concentration. The addition of brine to the lignosulfonate-caustic systems produced no further improvement in interfacial activity. However, with the lignosulfonatebutanol systems, as much as 50% further reduction in interfacial tension was obtained upon the addition of brine. The interfacial tension between pure brine (1.5% NaCI) and the crude was 4.5 dynes/em, while tensions in the range of 1 to 2 dynes/em were obtained in the presence of various Iignosulfonates. In actual displacement tests using this crude oil, the final oil recovery after 2. 7 PV injection of brine was 83%. Additional recoveries of between 2% and 4% were obtained when using 3% and 6% lignosulfonate solutions respectively, while a I% solution produced no additional recovery. Introduction This work is concerned with the use of a new class of surface-active agents, known as lignosulfonates, in enhanced oil recovery operations. Lignosulfonates are wood-based chemicals made from the sulfite liquors generated during the sulfite process of wood pulping, and are at least four times cheaper than the well-known petroleum sulfonates which are currently popular in many micellar recovery strategies. Although de Groote and Monson(l) proposed the use of sulfite spent liquors in secondary water-flooding in 1931, no field test using this material has yet been reported. However, Kalfoglou(2) did recently patent a process involving the use of lignosulfonates as sacrificial agents in tertiary oil recovery operations (either as a pre-flush or as an integral part of the micellar slug). Felber and Dauben(3) have found lignosulfonate gels useful for improving sweep efficiency in highly heterogeneous reservoirs. Increasing amounts of lignosulfonates are also being used in the formulation of emulsion-based drilling muds. A preliminary study of the oil recovery efficacy of lignosulfonates using various refined oils has recently been published by Bansal(4) and Bansal, Hornof and Neale(Sl. Although interfacial tension (IFT) values only as low as 10 dynes/cm were obtained with Fuel Oil No.4, additional oil recoveries of 1.3% and 8.5% (relative to those obtained using waterflooding) were obtained at 1 PV injection in laboratory displacement tests using 1% and 10% lignosulfonate solutions respectively. The lignosulfonate employed was commercially available Marasperse N-22. The American Can Company(6,7), manufacturers of Marasperse products, has suggested the addition of caustic soda, sodium chloride or methanol in order to lower the IFT of lignosulfonate solutions.