5 research outputs found
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A study of vapor-liquid flow in porous media
We study the heat transfer-driven liquid-to-vapor phase change in single-component systems in porous media by using pore network models and flow visualization experiments. Experiments using glass micromodels were conducted. The flow visualization allowed us to define the rules for the numerical pore network model. A numerical pore network model is developed for vapor-liquid displacement where fluid flow, heat transfer and capillarity are included at the pore level. We examine the growth process at two different boundary conditions
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A pore network model for adsorption in porous media
Using a pore network model to represent porous media we investigate adsorption-desorption processes over the entire range of the relative pressure, highlighting in particular capillary condensation. The model incorporates recent advances from density functional theory for adsorption-desorption in narrow pores (of order as low as 1 nm), which improve upon the traditional multi-layer adsorption and Kelvin's equation for phase change and provide for the dependence of the critical pore size on temperature. The limited accessibility of the pore network gives rise to hysteresis in the adsorption-desorption cycle. This is due to the blocking of larger pores, where adsorbed liquid is allowed to but cannot desorb, by smaller pores containing liquid that may not desorb. By allowing for the existence of supercritical liquid in pores in the nm range, it is found that the hysteresis area increases with an increase in temperature, in agreement with experiments of water adsorption-desorption in rock samples from The Geysers. It is also found that the hysteresis increases if the porous medium is represented as a fractured (dual porosity) system. The paper finds applications to general adsorption-desorption problems but it is illustrated here for geothermal applications in The Geysers
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An experimental study of adsorption in vapor-dominated geothermal systems
We report results of steam adsorption experiments conducted for rock samples from vapor-dominated geothermal reservoirs. We examine the effect of the temperature on the adsorption/desorption isotherms. We find that the temperature effect is only important on the desorption such that the hysteresis becomes more pronounced as the temperature increases. The scanning behavior within the steam sorption hysteresis loop is also studied to investigate the behavior during repressurization. Collection of sets of data on the sorption behavior of The Geysers geothermal field in California is presented
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A study of relative permeability for steam-water flow in porous media
We report on continuing experimental and numerical efforts to obtain steam-water relative permeability functions and to assess effect of heat transfer and phase change. To achieve these, two sets of steady-state flow experiments were conducted: one with nitrogen and water and another with steam and water. During these experiments, a mixture of nitrogen-water (or steam-water) was injected into a Berea sandstone core. At the onset of steady state conditions, three-dimensional saturation distributions were obtained by using a high resolution X-ray computer tomography scanner. By identifying a length of the core over which a flat saturation profile exists and measuring the pressure gradient associated with this length, we calculated relative permeabilities for nitrogen-water flow experiments. The relative permeability relations obtained in this case were in good agreement with those reported by other investigators. Another attempt was also made to conduct a steam-water flow experiment under adiabatic conditions. This experiment was completed with partial success due to the difficulties encountered during the experiment. The results of this experiment showed that a flat saturation profile actually developed over a substantial length of the core even at a comparatively modest injection rate (6 grams per minute) with low steam quality (4% by mass). The completion of this set of experiments should yield steam-water relative permeability relations in the near future
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Adsorption characteristics of rocks from vapor-dominated geothermal reservoir at the Geysers, CA
This paper reports on a continuing experimental effort to characterize the adsorption behavior of rocks from The Geysers steam field in California. We show adsorption results obtained for 36 rock samples. All of the adsorption isotherms plotted on the same graph exhibit an envelope of isotherms. The minimum and the maximum values of the slope (or rate of adsorption) and of the magnitude within this envelope of isotherms belonged to the UOC-1 (felsite) and NCPA B-5 (serpentine) samples. The values of surface area and porosity, and pore size distribution for 19 of the samples indicated a very weak correlation with adsorption. An interpretation of the pore size distributions and the liquid saturation isotherms suggests that the change in the slope and the magnitude of the adsorption isotherms within the envelope is controlled primarily by the physical adsorption mechanism instead of capillary condensation. Grain-size and framework grain to matrix ratio are found to be insufficient to characterize this adsorption behavior. An accurate identification of the mineralogy of the samples will be essential to complete this analysis