![]() ![]() Recent research has suggested that supercritical CO 2–brine systems are not strongly water-wet which could imply a much lower trapping capacity than presented here ( Chiquet et al., 2007 Plug, 2007). However, to date, most of the experiments have been performed on oil–water or gas–water systems for application to hydrocarbon recovery further work is needed that focuses on supercritical CO 2–brine displacement to confirm the degree of trapping in these cases. Potentially, this concept could be applied to CO 2 storage, where trapped CO 2 in aquifers and oil fields could be safely stored, even in the absence of a good caprock. The conclusion of this section is that at the small scale between 3 and 8% of the total rock volume can be filled with a residual non-wetting phase. The plot indicates that within the considerable scatter of the data – caused by taking results from different rock types and fluid systems – there appears to be an optimal porosity of around 0.2–0.3 that provides the maximum trapping capacity. Capillary trapping capacity C trap (maximum residual saturation times porosity) as a function of porosity for different measurements in the literature, using the data in Fig. 6.2. In oilfield applications, long-term contact between the grain surface and the crude may lead to wettability alteration, which may have a significant impact on the trapping of both oil and gas (or CO 2).Ħ.3. In this discussion we will focus on experiments that have studied water-wet systems, where the trapped oil (or gas, or CO 2) is the non-wetting phase. The residual saturation increases with initial saturation while it usually decreases with increasing rock porosity ( Jerauld, 1997 Suzanne et al., 2003). This could be caused by natural groundwater flow, buoyancy-driven upwards migration of the CO 2 plume or deliberate injection of brine (chase brine) to trap the CO 2. The same flooding sequence is of relevance in CO 2 storage applications: CO 2 is injected into an aquifer and will locally reach some saturation – which may be well below the maximum possible, since the CO 2 may channel through the formation at low saturation – followed by its displacement by water after the initial injection phase. The saturation at the end of the displacement is recorded. In core-flood experiments on rock samples a few cm long, an initial saturation of displaced fluid (typically oil) is first established and then the displacing fluid (water) is injected. In petroleum engineering applications, the residual saturation – the fraction of the pore space occupied by a trapped phase – is important, since this determines how much oil cannot be recovered during waterflooding to recover oil. ![]() Blunt, in Developments and Innovation in Carbon Dioxide (CO2) Capture and Storage Technology, 2010 6.2 Experiments of capillary trapping Carbon dioxide (CO2) injection design to maximise underground reservoir storage and enhanced oil recovery (EOR)
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