Effects of connate water on chemical flooding processes in porous media

Abstract

This work examines the effects of connate water on the unstable displacement patterns and fractional oil recoveries observed when simulated secondary and tertiary oil displacement processes are conducted in the laboratory. Three displacement systems were investigated; a non-reacting system without surfactant (water displacing non-acidic paraffin oil), a non-reacting system with externally added surfactant (sodium dodecyl sulfate solution displacing non-acidic paraffin oil), and a reacting system with internally generated surfactant (sodium hydroxide solution displacing acidified paraffin oil). A consolidated porous medium constructed of fused glass beads was used to simulate the underground oil reservoir. Each of the three basic displacement processes was conducted both in the absence and presence of connate water, and at three different flow rates. The results obtained indicate that the presence of connate water can exert a significant influence on the displacement pattern with the non-reacting systems, particularly at low flow rates. Some of these effects include an increase in the number of fingers and/or much thinner fingers with many tiny branches. At low flow rates, the presence of connate water tends to decrease the breakthrough oil recovery for the non-surfactant system, but increases the breakthrough recovery for the surfactant-containing systems. At high flow rates, connate water has a much less pronounced effect due to the dominance of viscous forces.