The effect of alkali on crude oil/water interfacial properties and the stability of crude oil emulsions

The alkaline-surfactant-polymer (ASP) flooding using sodium carbonate as the alkali component to enhance oil recovery in the on shore oil fields at Daging and Shengli in China has brought new problems to the oil industry. The alkali added forms stable water-in-crude oil emulsion and de-emulsification process is necessary to separate oil and water. The problems related in the enhanced oil recovery using the alkaline-polymer-surfactant flooding technique have been investigated in the laboratory using the fractions of Gudong oil from the Shengli oil field. The oil was separated into aliphatic, aromatic, resin and asphaltene fractions. These fractions were then used in an additive free jet oil to form model oils. The emulsion stability of each of the water-in-model oil emulsions formed between water or 1.2% sodium carbonate solution and a model oil was investigated. The interfacial properties, such as interfacial tension and interfacial pressure of the systems were also measured. These in combination with the molecular parameters of the fractions were used to get insight into the problem related in the enhanced oil recovery method. The study reveals that the sodium carbonate solution reacts with the acidic hydrogen in the fractions of the crude oil and form soap like interfacially active components. These accumulate at the crude oil/water interface and contribute to the stability of the water-in-oil emulsion. (c) 2005 Elsevier B.V. All rights reserved.