The heat energy resource in the deep earth (3 ∼10 km), which is carried by Hot Dry Rocks (HDR), has a huge capacity for geothermal power generation. As a type of conductive geothermal energy, HDR has low rock permeability, so that Enhanced/Engineered Geothermal System (EGS) is developed to artificially increase the heat exchange area and further extract the deep geothermal energy with the connected natural fractures and hydraulic stimulated fracture network. The coupled Thermal-Hydrological-Mechanical (THM) processes largely control the heat recovery efficiency from HDR, and thus real 3D reservoir scale investigations that account for the multiphysics coupling mechanisms are needed to inform geothermal energy recovery from HDR.In this work, we built a three-dimensional THM model for the EGS of Qiabuqia HDR (Zhang et al. 2018, Gonghe Basin, China) by taking advantage of the novel simulation framework, GEOSX (Settgast et al. 2022). As a rapidly growing open-source multi-physics simulator, GEOSX has highly scalable algorithms for solving complex fluid flow, thermal, and geomechanical coupled systems. Preliminary geological data of the targetarea has been acquired by exploratory wells (e.g., GR1, GR2, DR3, DR4). There is also a trial production well GH-01. In our model, we considered a dual-well utilization system. Our 3D model focuses on reservoir-scale THM coupling, and takes into consideration the geostress directions in configuring the faults and (hydraulic)fractures, which are explicitly handled with EDFM (Embedded Discrete Fracture Model) method. The simulated results of heat recovery efficiency under different production scenarios provide guidance information for engineering practices.
Teflon bag chambers have long been used for investigating atmospheric chemical processes, including secondary organic aerosol formation. The wall-loss process of gas-phase species in Teflon bag chambers has typically been investigated at around room temperature. Recent laboratory studies started employing Teflon bag chambers at sub-273 K conditions for simulating wintertime and upper-tropospheric environments. However, temperature dependence in vapor-wall-loss processes of semi-volatile organic compounds (SVOCs) in a Teflon bag chamber has not been well investigated. In this study, we experimentally investigated wall-loss processes of C14–C19 n-alkanes in a 1 m3 Teflon bag for the temperature range of 262 to 298 K. Enhanced wall losses of the tested n-alkanes were observed following the decrease in temperature. For instance, 65 % of C14 n-alkane was lost to the wall 15 h after injection at room temperature, while the corresponding value was 95 % at 262 K. The experimental data were analyzed using a two-layer kinetic model, which considers both absorption of gas-phase species to the surface layer of the Teflon wall and diffusion to the inner layer. The experimental data demonstrated that absorption of gas-phase species by the surface layer was enhanced at lower temperatures. The temperature dependence in absorption was well accounted for using the equilibrium-dissolution model of organic compounds to the Teflon surface by considering reduced saturation vapor pressure at lower temperatures. On the contrary, diffusion of n-alkanes from the surface to the inner layer slowed down at reduced temperatures. Mechanistic studies on these processes will need to be conducted in the future to quantitatively predict the influence of temperature-dependent wall-loss processes of SVOCs on laboratory experimental results.
The reactions between CO2 slugs and crude oil induce a substantial amount of asphaltene precipitation and adsorption on the rock surface during the CO2 alternative water flooding process. When the subsequent water slug passes through the core pores after asphaltene adsorption, it will displace the previous CO2 slug. The wettability of water and CO2 on the asphaltene-adsorbed rock surface will directly determine the magnitude and direction of the capillary force of the two media, which in turn affects their flow resistance and flow pattern analysis. In this paper, the systems of CO2/water/sandstone and CO2/water/asphaltene adsorption sandstone were established by molecular dynamics simulation technology. The effects of asphaltene adsorption, thickness of the asphaltene adsorption layer, CO2 density, mass fraction and type of salt in water on the wettability of water on sandstone surfaces were studied. The results reveal that asphaltene adsorption significantly reduces the wettability of water on the original powerful water-wetting sandstone surface, making it easier to see how CO2 density affects the wettability of water on the asphaltene-adsorbed sandstone surface. The increased CO2 density will continue to lower the wettability of water on the asphaltene-adsorbed sandstone surface, even causing it to become wet with CO2. The adsorption thickness of asphaltene does not affect the wettability of water and CO2 on the asphaltene-adsorbed sandstone surface, and just a layer of 5A-thick asphaltene adsorption can significantly reduce the wettability of water on sandstone surfaces. Furthermore, a rise in salinity in water has a detrimental impact on the wettability of water on the asphaltene-adsorbed sandstone surface, with divalent salts having a stronger negative effect than monovalent salts.