Effect of the Addition of Certain Chemicals On Oil Recovery During Waterflooding

Abstract

Abstract A laboratory study was conducted to determine the recovery of high-viscosity crude oil from natural unconsolidated sand by wate1flooding with a number of chemical solutions. Displacement tests were run using chemical solutions to displace a high-viscosity crude oil from artificial packs of unconsolidated core sand. Results of the displacement tests showed that oil recovery was increased by a number of chemical solutions. Sodium hydroxide in bTi.ne at concentrations less than 0.01 per cent by weight had little effect on recovery as compared to brine floods. Sodium hydroxide concentrations of 0.1 per cent OT greater increased recovery significantly. The interfacial tension between Lloydminster crude oil and various aqueous solutions was greatly reduced by the addition of a number of chemicals to the aqueous solutions. The presence of sodium chloride in the aqueous solution reduced the a1nount of chemical required for the reduction of the interfacial tension between crude oil and the solution to a given level. The reduction in interfacial tension influenced the recovery of oil. The production of a very stable emulsion and evidence of reduced water mobility during displacement tests suggested that emulsification may have occurred within the core. The formation of an emulsion may have increased oil recovery. Introduction THERE ARE large known reserves of heavy oil in Western Canada. However, the nature of the reservoirs and oils involved are such that primary recovery is estimated at 5 to 6 per cent(l), with a possibility of increasing total recovery to about 10 per cent of the oil in place by means of conventional water-flooding. In order that these recoveries be increased to a more acceptable value) new secondary recovery techniques must be developed. This study represents a continuation of a series of investigations conducted at the University of Alberta(2,3) into the effect of chemical additives on water-flood recovery from heavy oil reservoirs. It is well known that the preferential wettability of the solid surfaces in porous media influences their relative permeability, capillary pressure and waterflood ability characteristics. These properties can be altered by introducing any one of a variety of liquids which alter the contact angle. However, if a surface is oil-wet, the contact angle (conventionally measured through the denser phase) cannot be reduced below 90 degrees, so that further reductions in adhesion tension and therefore energy requirements for oil displacement can only be realized through reductions in interfacial tension. Reductions in interfacial tension also serve to reduce capillary forces, thereby further reducing the amount of energy required for oil displacement. Similarly, changing a system from an oil-wet to a water-wet state improves the relative permeability to oil and increases the efficiency of the oil displacement process. Several investigators(4,5,6) have reported obtaining higher waterflood recoveries from preferentially water-wet systems than from corresponding oil-wet systems. The ability of some oils to preferentially wet silica sand surfaces has been noted and the use of chemicals or "flooding agents" to increase recovery from such sands has been considered by a number of investigators.