Enhanced Gas Recovery by CO2 Injection and Sequestration: Effects of Temperature, Vertical and Horizontal Orientations on Dispersion Coefficient

Abstract

Enhanced gas recovery (EGR) by CO2 injection and sequestration is receiving increased attention within the research community. This is as a result of its potential to be an avenue for the simultaneous additional recovery of natural gas from the reservoir and provide a safe CO2 sequestration site. However, the major problem with this technology lies in the excessive mixing of the injected CO2 and the nascent natural gas (CH4) during the displacement process. This excessive mixing is the reason why the technology has not been widely patronised, given that the recovered CH4 will be heavily contaminated with the injected CO2 thereby making it "lacking" as sales gas after recovery. This hinders the market value of the recovered CH4 and eventually renders it not viable economically. Hence, highlighting the factors responsible for the mixing could provide technical solution to minimise the mixing phenomenon during EGR. This research focuses on the temperature effects and the orientation of the injection pattern of the technique. An experimental core flooding simulation was carried out at a temperature of 50°C and a pressure of 1300 psig and varying injection rates of 0.2 - 0.5 ml/min on Grey Berea sandstone core sample with the sample situated in both vertical and horizontal orientations. It was observed that at higher temperature (50°C) suitable for many gas reservoirs, the disperstion coefficient increased significantly compared to our earlier work (Abba, Abbas, & Nasr, 2017) at 40°C by a factor of 2.3. This trend was due to the increased energy of the gas molecules at the observed conditions, thereby increasing their mobilities. Conversely, the dispersion coefficient also increased significantly by a factor of 3.4 in the horizontal orientation at lower injection rates compared to the vertical core flooding with the concentration profiles showing significant capillary tailing effects at higher flowrates. This signified the effect of gravity in the horizontal orientation was more pronounced at lower injection rates during the injection of CO2 and this will have tremendous effect on the flow behavior of supercritical CO2 during the gas-gas displacement process.