An Experimental Study of CO2 Exsolution and Relative Permeability Measurements During CO2 Saturated Water Depressurization

Abstract

Dissolution of CO 2 into brine is an important and favorable trapping mechanism for geologic storage of CO 2 . There are scenarios, however, where dissolved CO 2 may migrate out of the storage reservoir. Under these conditions, CO 2 will exsolve from solution during depressurization of the brine, leading to the formation of separate phase CO 2 . For example, a CO 2 sequestration system with a brine-permeable caprock may be favored to allow for pressure relief in the sequestration reservoir. In this case, CO 2 -rich brine may be transported upwards along a pressure gradient caused by CO 2 injection. Here we conduct an experimental study of CO 2 exsolution to observe the behavior of exsolved gas under a wide range of depressurization. Exsolution experiments in highly permeable Berea sandstones and low permeability Mount Simon sandstones are presented. Using X-ray CT scanning, the evolution of gas phase CO 2 and its spatial distribution is observed. In addition, we measure relative permeability for exsolved CO 2 and water in sandstone rocks based on mass balances and continuous observation of the pressure drop across the core from 12.41 to 2.76 MPa. The results show that the minimum CO 2 saturation at which the exsolved CO 2 phase mobilization occurs is from 11.7 to 15.5%. Exsolved CO 2 is distributed uniformly in homogeneous rock samples with no statistical correlation between porosity and CO 2 saturation observed. No gravitational redistribution of exsolved CO 2 was observed after depressurization, even in the high permeability core. Significant differences exist between the exsolved CO 2 and water relative permeabilities, compared to relative permeabilities derived from steady-state drainage relative permeability measurements in the same cores. Specifically, very low CO 2 and water relative permeabilities are measured in the exsolution experiments, even when the CO 2 saturation is as high as 40%. The large relative permeability reduction in both the water and CO 2 phases is hypothesized to result from the presence of disconnected gas bubbles in 123 460 L. Zuo et al. this two-phase flow system. This feature is also thought to be favorable for storage security after CO 2 injection.

Experimental Observation of Permeability Changes In Dolomite at CO2Sequestration Conditions

“…Inset (b) Calculated CO 2 saturation (S CO 2 ), k rw , and k rCO 2 as a function of time for the 50°stage. 24,37 At steady state, the calculated values for free-phase CO 2 saturation of the pore space (S CO2 ), k rw , and k rCO 2 reach ∼0.5, ∼0.1, and ∼0.0065, respectively. Inset (a) in Figure 1 shows the relative permeabilities as a function of pore space water saturation, S w , which are in general agreement with values measured in similar exsolution experiments.…”

Physics of Porous Media: Fluid Flow Through Porous Media

“…Case (b) shows a nonwetting liquid. For example, a gas initially dissolved in the saturating pore liquid may come out of solution if the thermodynamic conditions are changed and bubbles of a second phase are formed (e.g., Zuo et al, 2011). If the pressure is released, the nonwetting fluid is spontaneously expelled, although a portion of it may remain trapped in the porous medium.…”

Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene

“…Internal drainage has been discussed in the context of solution gas drive, carbon dioxide sequestration and geothermal reservoir applications. It can result in different distributions of gas, and different constitutive relationships, than during external drainage due to gas which nucleates and becomes trapped in pores that are not part of the most conductive channel network (Counsil and Ramey, 1979;Egermann and Vizika, 2001;Jang and Santamarina, 2014;Kamath and Boyer, 1995;Poulsen et al, 2001;Sheng et al, 1999;Zuo et al, 2012).…”