Correlation between foam stability and electrokinetic signal in foam assisted water alternate gas process

Abstract

Foam is purposely used in some of the Enhanced Oil Recovery (EOR) displacement processes in order to control the mobility ratio, hence improving the volumetric sweep efficiency. The efficiency of a foam displacement process in EOR depends largely on the stability of the foam films. In laboratory, foam stability is usually measured through physical observation of the foam bubble in a glass tube. Unfortunately, this direct observation is not possible in the reservoir. Therefore, indirect measurement such as the measurement of electrokinetic signal would be a better alternative. This study aimed to determine the correlation between the foam stability and the associated streaming potential signals which resulted from the flowing fluid in foam assisted water alternate gas (FAWAG) process. The downhole monitoring of streaming potential which uses electrodes mounted on the outside of an insulated casing is a promising new technology for monitoring fluid movement processes in real time. In this study, the experiments were divided into two: Foam stability test and electrokinetic signal measurement. The electrokinetic signals were measured using five non-polarizing Cu/CuCl electrodes, installed along a sand pack model and measurement was recorded continuously using NIDAS and the LabView software. Surfactant alternate gas was used to produce foams inside the porous media using five different Sodium Dodecyl Sulphate (SDS) concentrations, namely 2500, 5000, 7500, 10000 and 12500 ppm. The result from the experiment showed that 10000 ppm was an optimum concentration of SDS. Thus, the voltage (electrokinetic signal) decreased with an increase in foam stability up to optimum SDS concentration. While for 12500 ppm SDS concentration the electrokinetic signal increased as foam stability decreased. The burst of the foam bubbles had changed the pattern of electrokinetic signals. Although the voltage was small, i.e., ranging from 0 to 1 mV, it was still measureable. These results present new findings in the relationship between foam stability and electrokinetic signals generated in the FAWAG process. This fundamental knowledge can lead to developing a new approach in monitoring FAWAG processes in making the EOR process more efficient.