Decarbonizing the Coal-Fired Power Sector in China via Carbon Capture, Geological Utilization, and Storage Technology.

Carbon capture, utilization, and storage (CCUS) is a critical technology to realize carbon neutrality target in the Chinese coal-fired power sector, which emitted 3.7 billion tonnes of carbon dioxide in 2017. However, CCUS technology is often viewed as an "alternative technology" option owing to common perceptions of relatively high cost and potential risks. This study indicates that coal power CCUS is likely to be a cost-effective and key technology for helping China reach the ambitious goal of carbon neutrality. This comprehensive, national-scale assessment of CCUS deployment on coal power in China is based on a unique bottom-up approach that includes site selection, coal plant screening, techno-economic analysis, and carbon dioxide source-sink matching. Analysis indicates that, based on 2017 costs and assumptions, more than 70% of coal power plants in this study could be cost-competitive with natural gas-fired power plants, and 22-58% would be cost-competitive with onshore wind generation. These insights suggest that the commercialization of CCUS technology in the coal power sector in China is a viable route toward decarbonizing the economy if a grid price policy similar to that of renewables and natural gas power is applied.

Gas-partitioning tracer test to quantify trapped gas during recharge.

Dissolved helium and bromide tracers were used to evaluate trapped gas during an infiltration pond experiment. Dissolved helium preferentially partitioned into trapped gas bubbles, or other pore air, because of its low solubility in water. This produced observed helium retardation factors of as much as 12 relative to bromide. Numerical simulations of helium breakthrough with both equilibrium and kinetically limited advection/dispersion/retardation did not match observed helium concentrations. However, better fits were obtained by including a decay term representing the diffusive loss of helium through interconnected, gas-filled pores. Calculations indicate that 7% to more than 26% of the porosity beneath the pond was filled with gas. Measurements of laboratory hydraulic properties indicate that a 10% decrease in saturation would reduce the hydraulic conductivity by at least one order of magnitude in the well-sorted sandstone, but less in the overlying soils. This is consistent with in situ measurements during the experiment, which show steeper hydraulic gradients in sandstone than in soil. Intrinsic permeability of the soil doubled during the first six months of the experiment, likely caused by a combination of dissolution and thermal contraction of trapped gas. Managers of artificial recharge basins may consider minimizing the amount of trapped gas by using wet, rather than dry, tilling to optimize infiltration rates, particularly in well-sorted porous media in which reintroduced trapped gas may cause substantial reductions in permeability. Trapped gas may also inhibit the amount of focused infiltration that occurs naturally during ephemeral flood events along washes and playas.

Hydrogeologic controls on induced seismicity in crystalline basement rocks due to fluid injection into basal reservoirs.

A series of Mb 3.8-5.5 induced seismic events in the midcontinent region, United States, resulted from injection of fluid either into a basal sedimentary reservoir with no underlying confining unit or directly into the underlying crystalline basement complex. The earthquakes probably occurred along faults that were likely critically stressed within the crystalline basement. These faults were located at a considerable distance (up to 10 km) from the injection wells and head increases at the hypocenters were likely relatively small (∼70-150 m). We present a suite of simulations that use a simple hydrogeologic-geomechanical model to assess what hydrogeologic conditions promote or deter induced seismic events within the crystalline basement across the midcontinent. The presence of a confining unit beneath the injection reservoir horizon had the single largest effect in preventing induced seismicity within the underlying crystalline basement. For a crystalline basement having a permeability of 2 × 10(-17) m(2) and specific storage coefficient of 10(-7) /m, injection at a rate of 5455 m(3) /d into the basal aquifer with no underlying basal seal over 10 years resulted in probable brittle failure to depths of about 0.6 km below the injection reservoir. Including a permeable (kz = 10(-13) m(2) ) Precambrian normal fault, located 20 m from the injection well, increased the depth of the failure region below the reservoir to 3 km. For a large permeability contrast between a Precambrian thrust fault (10(-12) m(2) ) and the surrounding crystalline basement (10(-18) m(2) ), the failure region can extend laterally 10 km away from the injection well.