Enhanced Gas Recovery by CO2 Injection and Sequestration: Effect of Connate Water Salinity on Displacement Efficiency

Abstract

Abstract As natural gas continues to gain widespread usage as a source of cleaner and efficient fossil fuel, while greenhouse gas emission is attracting environmental consequences, the need for a viable method to enhance gas recovery and curtail greenhouse gas emissions, is paramount. The technique of injecting CO2 for Enhanced Gas Recovery (EGR) is deemed one of the efficient methods for simultaneously storing CO2 emissions and improving additional natural gas recovery from depleted gas fields, provided that the gas mixing in situ can be reduced. This can be achieved by an understanding of the mechanisms of displacement and the factors that affect them. This provides vital information for further studies aimed at a robust field scale application to establish the economic viability of the process. Connate water saturation and salinities are vital properties of the reservoir and their influence on the displacement efficiency cannot be overemphasised. This experimental study determines the effect of connate water salinity, in sandstone sample, on the displacement efficiency during EGR. This study presents the first novel experimental measurement of dispersion of CO2 in CH4 as a function of salinity in consolidated porous media. A laboratory experiment depicting the detailed process of the CO2-CH4 displacement in sandstone core samples at a temperature a temperature of 40°C and at a pressure of 1,300 psig, was carried in the investigation, at a CO2 injection rate of 0.25 ml/min to evaluate the displacement efficiency. The findings indicated that salinity of the connate water tends to decrease the dispersion of CO2 in CH4 at the stated conditions. This can be attributed to the increase in density of the connate water with increase in salinity, which occupies smaller pore channels within the porous medium thereby making the core sample more homogeneous. Also, grain diameter measurements were carried out from Scanning Electron Microscopy (SEM) images of the porous media using image analysis to establish the characteristic length scale of mixing of the medium.