Scaling the impacts of pore-scale characteristics on unstable supercritical CO2-water drainage using a complete capillary number

Abstract

Geological carbon storage in deep aquifers involves displacement of resident brine by supercritical CO (scCO), which is an unstable drainage process caused by the invasion of less viscous scCO 2. The unstable drainage is greatly * = −4.0 using the complete capillary number (! *) that considers pore characteristics. For the hexagonal and the high-anisotropy elliptical micromodels, a monotonic increase in scCO 2 saturation with increasing ! * (without crossover) was observed. It appears that the complete capillary number is more appropriate than the 3 classic capillary number when characterizing flow regimes and CO 2 saturation in different pore networks.

Impacts of Mixed‐Wettability on Brine Drainage and Supercritical CO2 Storage Efficiency in a 2.5‐D Heterogeneous Micromodel

“…We assume that (1) at the field, CO 2 is injected at a volumetric rate ( Q ) of 10,000 m 3 /day over a screen length of 15 m, and (2) scCO 2 density ( ρ ) from reservoir pressure and temperature is close to that at experimental conditions and CO 2 velocities in the formation is radially uniform. This volumetric rate corresponds to an annual injection of one million metric tonnes of CO 2 at 8.5 MPa and 45 °C (this study), and 1.8 million metric tonnes of CO 2 at 9 MPa and 40 °C (Chang, Kneafsey, et al, 2019; Wang et al, 2012). The distance from the injection well can then be calculated as follows: where d refers to the (radial) distance from the injection well, h is the screen length of the injection well, and is the CO 2 velocity that equals to the lab values listed in Table 1.…”

“…Results from Wang et al (2012) and Chang, Kneafsey, et al (2019) in Micromodels #R1, #R2, #R3, and #R4 were also included in Figure 8, with estimated CO 2 saturations from their published figures. #R4 refers to an anisotropic and homogeneous micromodel that consists of elliptical silicon posts with estimated transverse‐to‐longitudinal permeability ratio of 6.86 (see Figure S5 for more details).…”

“…The nonuniform displacement and preferential CO 2 flow in micromodels and rock cores subject to pore and subcore scale heterogeneity has been extensively reported (Berg & Ott, 2012; Berg et al, 2013; Chang et al, 2014, 2013; Chen et al, 2018; Krevor et al, 2011; Pini et al, 2012; Shi et al, 2011). In a previous study, we presented in 4 cm‐scale micromodels the change of CO 2 saturations by a factor of ~10 at similar imposed displacement rates, depending on the heterogeneity and anisotropy of pore networks (Chang, Kneafsey, et al, 2019). We show here the importance of mixed‐wettability and its effect on displacement efficiency and CO 2 saturation, particularly at low displacement rates.…”

“…One of the major reasons for inefficient CO 2 storage in the subsurface is unstable displacement characterized by fingering flow due to the low viscosity of scCO 2 relative to formation brine (typical ratio ~ 1:20) (Berg & Ott, 2012; Wang et al, 2012; Wietsma, et al, 2011, Zhang, Oostrom, Grate, et al, 2011; Zhang, Oostrom,). The unstable displacement and fingering flow of scCO 2 will also increase leakage potential through caprock (Tsang et al, 2008), nonequilibrium CO 2 dissolution (Chang et al, 2013, 2014, 2016, 2017; Chang, Kneafsey, et al, 2019; Chang, Zhou, et al, 2019), and mineral trapping (Huq et al, 2015; Sanchez‐Vila et al, 2007) after injection ceases.…”

Dynamic Processes of CO2Storage in the Field: 1. Multiscale and Multipath Channeling of CO2Flow in the Hierarchical Fluvial Reservoir at Cranfield, Mississippi

“…Dynamic CISB from centimeter to meter scale was imaged in laboratory studies of CO 2 flood or injection using digital cameras or computerized tomography (CT) scans. The channeling of CO 2 flow at centimeter scale was studied using 2-D horizontal micromodels with layered (Zhang et al, 2011), normally distributed (Liu et al, 2016), and sandstone analog pore size distributions (Chang et al, 2016(Chang et al, , 2017(Chang et al, , 2019. The studies showed that channelized CO 2 flow through large pores was often followed by CO 2 invasion into smaller pores, leading to higher CO 2 saturation.…”