Coupled supercritical CO2 dissolution and water flow in pore-scale micromodels

Dissolution trapping is one of the most important mechanisms for geological carbon storage (GCS). Recent laboratory and field experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and coupled scCO2 dissolution and water flow, i.e., scCO2 dissolution at local pores/pore throats creating new water-flow paths, which in turn enhance dissolution by increased advection and interfacial area. However, the impacts of pore-scale characteristics on these coupled processes have not been investigated. In this study, imbibition and dissolution experiments were conducted under 40 °C and 9 MPa using a homogeneous/isotropic hexagonal micromodel, two homogeneous elliptical micromodels with low or high anisotropy, and a heterogeneous sandstone-analog micromodel. The four micromodels, initially saturated with deionized (DI)-water, were drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at different rates with logCa (the capillary number) ranging from −6.56 to −4.34. Results show that bypass of scCO2 by displacing water is the dominant mechanism contributing to the residual CO2 trapping, triggered by heterogeneity in pore characteristics or pore-scale scCO2-water distribution. Bypass can be enhanced by pore heterogeneity or reduced by increasing transverse permeability, resulting in relatively low (<2% of CO2 solubility) or high (9–13% of CO2 solubility) dissolved CO2 concentration in displacing water. The overall dissolution of residual scCO2 increases with decreasing Ca, and approaches to their solubility at low Ca value with sufficient residence time. This main trend is similar to a capillary desaturation curve that represents the relationship between the residual saturation and Ca. Spatially, dissolution initiates along the boundary of bypassed scCO2 cluster(s) in a non-equilibrium manner, and the coupling of water flow and dissolution occurs which fragments the bypassed scCO2 clusters and enhance scCO2 dissolution

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

Geological carbon storage in deep aquifers involves displacement of resident brine by supercritical CO2 (scCO2), which is an unstable drainage process caused by the invasion of less viscous scCO2. The unstable drainage is greatly complicated by aquifer heterogeneity and anisotropy and regarded as one of the key factors accounting for the uncertainty in storage capacity estimates. The impacts of pore-scale characteristics on the unstable drainage remain poorly understood. In this study, scCO2 drainage experiments were conducted at 40 °C and 9 MPa using a homogeneous elliptical micromodel with low or high anisotropy, a homogeneous/isotropic hexagonal micromodel, and a heterogeneous sandstone-analog micromodel. Each initially water-saturated micromodel was invaded by scCO2 at different rates with logCa (the capillary number)ranging from −7.6 to −4.4, and scCO2/water images were obtained. The measured CO2 saturations in these centimeter-scale micromodels vary considerably from 0.08 to 0.93 depending on the pore-scale characteristics and capillary number. It was also observed that scCO2 drainage follows the classic flow-regime transition from capillary fingering through crossover to viscous fingering for either of the low-anisotropy elliptical and heterogeneous micromodels, but with disparate crossover zones. The crossover zones of scCO2 saturation were then unified with the minimum scCO2 saturation occurring at logCa*=-4.0 using the complete capillary number (Ca*)that considers pore characteristics. For the hexagonal and the high-anisotropy elliptical micromodels, a monotonic increase in scCO2 saturation with increasing Ca* (without crossover)was observed. It appears that the complete capillary number is more appropriate than the classic capillary number when characterizing flow regimes and CO2 saturation in different pore networks

Heavy Grazing Significantly Reduced the Temporal Stability of Aboveground Biomass

The stability of a plant community is the embodiment of the dynamic balance achieved by the interaction between populations in the form of competition or mutual benefit. Temporal stability refers to the ratio of the average value to the variance of the biomass of the population or community. For grassland ecosystems, the stability of the grassland plant community is the basis for its survival and functional performance, and is the key factor affecting its structure and function. In order to study the impact of grazing on the temporal stability of aboveground biomass of desert steppe, this study used a completely randomized block design to study the relationship between the temporal stability of Stipa breviflora desert steppe vegetation communities and functional groups under different grazing intensities and their influencing factors, and then explored the relationship between temporal stability and species richness and species asynchrony. The results showed that heavy grazing significantly reduced temporal stability, species richness and species asynchrony of grassland communities. In terms of plant functional groups, grazing significantly reduced the stability of shrubs, semi-shrubs and perennial miscellaneous grasses. There were significant positive correlations between species richness and species asynchrony and community stability. Therefore, understanding changes in community asynchrony, richness and functional group stability is of great significance to further understanding of the temporal stability of desert grassland plant communities

The polymorphisms of κ-casein gene and their associations with milk production traits and expression analysis in Chinese Holstein cattle

The polymorphisms of exon 4 and 5 of κ-casein (CSN3) gene and their associations with milk production traits and expression pattern in Chinese Holstein cattle were investigated. Nine mutational sites, of which seven were novel mutational sites, were identified and genotyped by polymerase chain reactionrestriction fragment length polymorphism (PCR-RFLP), created restriction site-PCR (CRS-RFLP) and sequencing methods in 398 cows. Linkage disequilibrium analysis showed that SNP-1 (g.10891 T > C rs 43703015, g.10927 C > A rs 43703016, g.10988 G > A ss 256302464 and g.10966 A > T ss 256302465) and SNP-2 (g.12907 A > G ss 256302466, g.12950 G > A ss 256302468, g.12989 C > T ss 256302469 and g.13028 A > G ss 256302470) were completely linked, respectively. Correlation analysis showed that SNP-1, SNP-2 and SNP-3 (g.12980 T > C ss 256302467) markers were closely correlated to the fat content. The SNP-3 marker had a remarkable effect on the protein content (P < 0.05). 16 combined genotypes of the three SNPs were found. Fat and protein content in combinations of genotypes were varied significantly (P < 0.05). Genotypes BBCCEE and ABTCDD individuals had the highest fat and protein content, respectively, which may be useful for marker assisted selection program in dairy cattle. The expression of CSN3 mRNA in the mammary tissue was higher than that of in the liver tissue (P < 0.05) and the expression in the spleen of BB genotype was higher than that of AA genotype in the SNP-1 (P < 0.05) by fluorescent quantitation real-time PCR (Q-PCR) assay.Key words: SNPs, CSN3 gene, combined genotype, Q-PCR, milk production traits