The interfacial property of H2O+CO2+oil three-phase systems is crucial for CO2 flooding and sequestration processes but was not well understood. Density gradient theory coupled with PC-SAFT equation of state was applied to investigate the interfacial tension (IFT) of H2O+CO2+oil (hexane, cyclohexane, and benzene) systems under three-phase conditions (temperature in the range of 323–423 K and pressure in the range of 1–10 MPa). The IFTs of the aqueous phase+vapor phase in H2O+CO2+oil three-phase systems were smaller than the IFTs in H2O+CO2 two-phase systems, which could be explained by enrichment of oil in the interfacial region. The difference between IFTs of aqueous phase+vapor phase in the three-phase system and IFTs in H2O+CO2 two-phase system was largest in the benzene case and smallest in the cyclohexane case due to different degrees of oil enrichment in the interface. Meanwhile, CO2 enrichment was observed in the interfacial region of the aqueous phase+oil-rich phase, which led to the reduction of IFT with increasing pressure while different pressure effects were observed in the H2O+oil two-phase systems. The effect of CO2 on the IFTs of aqueous phase+benzene-rich phase interface was small in contrast to that on the IFTs of aqueous phase+alkane (hexane or cyclohexane)-rich phase interface. H2O had little effect on the interfacial properties of the oil-rich phase+vapor phase due to the low H2O solubilities in the oil and vapor phase. Further, the spreading coefficients of H2O+CO2 in the presence of different oil followed this sequence: benzene > hexane > cyclohexane.
Frost heave can have a very destructive impact on infrastructure in permafrost regions. The complexity of nanoscale ice-mineral interactions and their relation to the macroscale frost heave phenomenon make ice lens growth modelling an interesting but ch allenging task. Taking into account the limiting assumption of the constant segregation temperature in the segregation potential model, we propose here a new quasi-static model for ice lens growth under a time varying temperature based on the water activity criterion. In this model, the conventional pressure potential gradient in Darcy's law is replaced by a water activity based chemical potential gradient for the calculation of water flow velocity, which provides a better prediction of ice lens growth and is useful to describe the ice nucleation and the state of water at a specific temperature. M oreover, based on the analysis of the new developed model, a mathematical description of the segregation potential is provided here. The modified Kozeny-Carman equation is applied to determine the water permeability of a given soil. In our new model, the effects of the equivalent water pressure are taken into account to modify the freezing characteristic function. Hence, the temperature-and equivalent water pressure-dependent hydraulic permeability in the frozen fringe is mathematically determined and improved. By coupling the quasi-static model with the modified hydraulic permeability function, the numerical calculation of ice lens growth is validated based on the experimental data of the temperature of the ice lens measured in the laboratory. The prediction of ice lens growth using the proposed method contributes and facilitates the simplified calculation of frost heave in the field and/or laboratory scenarios at a quasi-static state, and thus enables a better understanding of phase change and fluid flow in partially frozen granular media (soils).
Hydraulic fracturing is widely used to exploit unconventional hydrocarbon sources, to enhance exploitation of geothermal energy and to aid in carbon sequestration through underground storage of captured CO 2 . The hydraulic fracturing fluids, which are commonly acidic, cause dissolution of minerals and desorption of elements which can lead to groundwater contamination. Batch reactor experiments were conducted to explore the interaction of simulated fracturing fluids with two end member compositions of basinal shales of the Bowland-Hodder unit (Carboniferous, UK) whereby the impact of temperature, fluid acidity, and rock/fluid ratio conditions were investigated. The results demonstrate that the fluid acidity is mainly controlled by the oxidative dissolution of pyrite and the dissolution of calcite, impacting mobilisation and fate of major and trace elements. The dissolution of calcite and pyrite significantly dominates the leaching of Sr and As, respectively. Generally, increased fluid acidity and temperature facilitate element mobilisation due to enhanced mineral dissolution and ion desorption, whereas higher rock/fluid ratio (higher mass of carbonate minerals) raises the buffering capacity and may promote the immobilisation of some metal ions by adsorption and precipitation (e.g. Ba, Pb, Fe, Al, and Mn). Moreover, the surface topography of different minerals in polished shale sample sections after fluid-rock interaction indicates that mineralogical compositions may play an important role in determining the pore structure. This research identifies chemical reaction pathways of geochemical elements (including contaminants) in fracturing fluids over a range of fluid chemistries and environmental conditions, and helps to evaluate element mobilisation from shale reservoirs with differing mineralogies.
With the rapid development of transmission line engineering in the west of China, the uplift problem of the tower foundation affected by extreme weather has provoked increasing concerns. Based on Balla rupture surface assumption and limit equilibrium method, a simplified calculation method of uplift bearing capacity of rock-socketed pedestal pile is derived. According to the results of the centrifugal model test and in situ field test, it is verified that the Balla rupture surface hypothesis is suitable for describing the failure mode of rock and the reliability of the calculation method. Furthermore, by combing the PLAXIS 3D numerical simulation results, the influence factors of uplift bearing capacity are compared and analyzed. Results show that the failure mode of rock is a trumpet-shaped surface, and it can be expressed by Balla rupture surface equation. The undetermined parameter N of rupture surface shape presents a negative correlation with mechanical integrity and uniaxial compressive strength (UCS) of the rock. The complete soft rock (5 MPa < UCS ≤ 6 MPa) should be N = 0.6, the strongly weathered soft rock (5 MPa < UCS ≤ 6 MPa) should be N = 1.5, and strongly weathered extremely soft rock (UCS = 2.6 MPa) should be N = 3.0. Additionally, the method provides a good reference for the calculation of uplift bearing capacity of tower foundation in similar regions.
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