Carbonated water injection (CWI) is a CO
2-augmented water injection strategy that leads to increased oil recovery with added advantage of safe storage of CO
2 in oil reservoirs. In CWI, CO
2 is used efficiently (compared to conventional CO
2 injection) and hence it is particularly attractive for reservoirs with limited access to large quantities of CO
2, e.g. offshore reservoirs or reservoirs far from large sources of CO
2. We present the results of a series of CWI coreflood experiments using water-wet and mixed-wet Clashach sandstone cores and
a reservoir core with light oil (
n-decane), refined viscous oil and a stock-tank crude oil. The experiments were carried out to assess the performance of CWI
and to quantify the level of additional oil recovery and CO
2 storage under various experimental conditions. We show that the ultimate oil recovery by CWI is higher than the conventional
water flooding in both secondary and tertiary recovery methods. Oil swelling as a result of CO
2 diffusion into the oil and the subsequent oil viscosity reduction and coalescence of the isolated oil ganglia are amongst
the main mechanisms of oil recovery by CWI that were observed through the visualisation experiments in high-pressure glass
micromodels. There was also evidence of a change in the rock wettability that could also influence the oil recovery. The coreflood
test results also reveal that the CWI performance is influenced by oil viscosity, core wettability and the brine salinity.
Higher oil recovery was obtained with the mixed-wet core than the water-wet core, with light oil than with the viscous oil
and low salinity carbonated brine than high-salinity carbonated brine. At the end of the flooding period, an encouraging amount
of the injected CO
2 was stored in the brine and the remaining oil in the form of stable dissolved CO
2. The experimental results clearly demonstrate the potential of CWI for improving oil recovery as compared with the conventional
water flooding (secondary recovery) or as a water-based EOR (enhanced oil recovery) method for watered out reservoirs.
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