Analysis of coupled thermo-hydro-mechanical behavior of unsaturated soils based on theory of mixtures I

This paper analyzes a coupled thermo-hydro-mechanical behavior of unsaturated soils based on the theory of mixtures. Unsaturated soil is considered as a mixture composed of soil skeleton, liquid water, vapor, dry air, and dissolved air. In addition to the mass and momentum conservation equations of each component and the energy conservation equation of the mixture, the system is closed using other 37 constitutive （or restriction） equations. As the change in water chemical potential is identical to the change in vapor chemical potential, a thermodynamic restriction relationship for the phase transition between pore water and pore vapor is formulated, in which the impact of the change in gas pressure on the phase transition is taken into account. Six final govern- ing equations are given in incremental form in terms of six primary variables, i.e., three displacement components of soil skeleton, water pressure, gas pressure, and temperature. The processes involved in the coupled model include thermal expansions of soil skeleton and soil particle, Soret effect, phase transition between water and vapor, air dissolution in pore water, and deformation of soil skeleton.     

储层含水条件下致密砂岩/页岩无机质纳米孔隙气相渗透率模型

页岩及致密砂岩储层富含纳米级孔隙,且储层条件下页岩孔隙(尤其无机质孔隙)及致密砂岩孔隙普遍含水,因此含水条件下纳米孔隙气体的流动能力的评价对这两类气藏的产能分析及生产预测具有重要意义.本文首先基于纳米孔隙内液态水及汽态水热力学平衡理论,量化了储层孔隙含水饱和度分布特征;进一步在纳米孔隙单相气体传质理论的基础上,考虑了孔隙含水饱和度对气体流动的影响;最终建立了含水饱和度与气相渗透率的关系曲线. 基于本文岩心孔隙分布特征,计算结果表明:储层含水饱和度对气体流动能力的影响不容忽视,在储层含水饱和度20%的情况下,气相流动能力与干燥情况相比将降低约10%;在含水饱和度40% 的情况下,气相流动能力将降低约20%.      

Effect of Interphase Heat Transfer on the Stability of a Turbulent Multicomponent Flow in a Vortex

The parameters of an axisymmetric turbulent two-phase swirling flow of a viscous heat-conducting gas containing a liquid dispersed phase in the presence of water vapor condensation on the particles are calculated. For the dispersed phase, a model taking into account the variation of the vapor concentration and the particle size due to condensation or evaporation is proposed. The distributions of the parameters of the basic unperturbed flow obtained numerically are used in the numerical solution of the linear problem of hydrodynamic stability within the time-dependent formulation. The parameters of small-amplitude harmonic perturbations propagating along the vortex axis are investigated in the linear formulation. A significant effect of heat release in the gas due to water vapor condensation on the parameters of the neutral perturbations and the neutral-stability curves is detected.     

The influence of thermodynamic gas parameters on laser-induced bubble dynamics in water

The oscillating properties of laser-induced cavitation bubbles in water are investigated by means of a fiber-optic sensor based on optical beam deflection. The experimental results show two important points. One is that the smaller the bubble radius the more quickly the bubble surface moves. Thus, the variations of the temperature and the pressure inside the bubble will be close to those of an adiabatic process. The other is that the high-energy vapor inside the newborn bubble diffuses and coagulates rapidly through violent expansion and thermal conduction. Thus, the gas content of the bubble reduces significantly in the first oscillation. Numerical simulation is made for the bubble model with consideration of liquid viscosity, surface tension, and gas content. Through modification of the polytropic index and the gas content parameter, two parameters of this model, the numerical results fit the experimental results well.     

Drying Rate Measurements in Convection- and Diffusion-Driven Conditions on a Shaly Sandstone Using Nuclear Magnetic Resonance

Carbon Capture and Storage (CCS) is one of the solutions studied to reduce greenhouse gas accumulation in the atmosphere. Depleted oil and gas reservoirs have been studied for potential storage sites but also saline aquifers that have the advantages of much larger pore volume. In this latter case, injection of large volume of anhydrous carbon dioxide will lead to a strong water desaturation of the near wellbore region because of evaporation mechanisms. Even the capillary trapped water can be removed by thermodynamical transfer of water vapor in the CO₂ phase. The extension in time and space of the dry zone will be controlled by the drying rate induced by the gas flow. Consequences of drying may induce alteration of the injectivity by salt precipitation and/or alteration of the rock fabric itself, especially for shaly sandstones in the case of clay drying. The context of CCS has raised new interests in the understanding of drying kinetic where the water vapor is evacuated by gas convection. In this study, we investigated experimentally the drying rate evolution with time on a shaly sandstone sample in two conditions of drying: convective and diffusive. In convective conditions, air is injected at different flow rates through the porous media in conditions of drying representative of a CO₂ injection site at one million ton per year. In diffusive conditions, no flow is imposed and the water vapor escape by diffusion. Drying rates dynamics in both conditions were measured by Nuclear Magnetic Resonance (NMR) and compared. We varied the temperature and the salinity in diffusive-driven drying and the gas flow rate in convective-driven drying. The water distribution in the pore network and the water saturation profiles were monitored continuously using T₂ relaxation and 1D imaging NMR techniques. For the range of temperature and air flow rate used, we show that drying rates in the two drying conditions are similar but not identical. They both present different periods characteristic of the main mechanisms for water mass transfer. Drying rate has a power law dependence on the temperature, as predicted by thermodynamic, and drying rate was found proportional to the flow rate in convective drying. Presence of salt has a complex effect: an increase of the drying rate at early stage of drying followed by a strong decrease for the remaining time of drying.     

Method for calculating the dynamics of vapor bubbles when a liquid boils in a centrifugal force field

The specific feature of the study of the dynamics of vapor bubbles during boiling of a liquid in a centrifugal force field is the fact that the velocity of a bubble is much greater than the rate of change of its radius, and its movement occurs in fields of variable pressure and underheating that have to be determined in the solution of the problem. In addition, when investigating processes occurring when liquid helium boils in a centrifugal force field, its thermodynamic parameters may be close to the critical values, and the dependences of the thermophysical properties of the liquid and vapor on the temperature and pressure must be taken into consideration. The equation of state of a substance close to its critical thermodynamic point cannot be an approximation to the equation of state of an ideal gas, as has been suggested in a series of articles. The nonequilibrium nature of the phase transition must be taken into consideration in the case of substances existing at near-critical parameters and substances with a low coefficient of accommodation. A marked deformation of the bubbles, which also has to be taken into account, will be observed in strong centrifugal force fields. Such studies have not appeared in the specialist journals. Equations of the two-temperature and two-velocity hydrodynamics of two-phase media in a one-dimensional form for substances obeying the equation of state for an ideal gas were discussed in [1, 2] with allowance for the dependence of the thermophysical properties on the temperature and pressure. In strong centrifugal force fields the one-dimensional approach is unacceptable and the flow of liquid around a buoyant bubble must be taken into account. A joint examination of the change in the temperature field with time in the vicinity of a vapor bubble with changes in its dimensions and position was made for the first time in [3–8]. The present article is an extension of the latter work and takes the aforementioned factors into account.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 66–71, July–August, 1984.