Liquid-phase Relative Permeability Research Articles

Impact of experimentally measured relative permeability hysteresis on reservoir-scale performance of underground hydrogen storage (UHS)

Underground Hydrogen Storage (UHS) is an emerging large-scale energy storage technology. Researchers are investigating its feasibility and performance, including its injectivity, productivity, and storage capacity through numerical simulations. However, several ad-hoc relative permeability and capillary pressure functions have been used in the literature, with no direct link to the underlying physics of the hydrogen storage and production process. Recent relative permeability measurements for the hydrogen-brine system show very low hydrogen relative permeability and strong liquid phase hysteresis, very different to what has been observed for other fluid systems for the same rock type. This raises the concern as to what extend the existing studies in the literature are able to reliably quantify the feasibility of the potential storage projects. In this study, we investigate how experimentally measured hydrogen-brine relative permeability hysteresis affects the performance of UHS projects through numerical reservoir simulations. Relative permeability data measured during a hydrogen-water core-flooding experiment within ADMIRE project is used to design a relative permeability hysteresis model. Next, numerical simulation for a UHS project in a generic braided-fluvial water-gas reservoir is performed using this hysteresis model. A performance assessment is carried out for several UHS scenarios with different drainage relative permeability curves, hysteresis model coefficients, and injection/production rates. Our results show that both gas and liquid relative permeability hysteresis play an important role in UHS irrespective of injection/production rate. Ignoring gas hysteresis may cause up to 338% of uncertainty on cumulative hydrogen production, as it has negative effects on injectivity and productivity due to the resulting limited variation range of gas saturation and pressure during cyclic operations. In contrast, hysteresis in the liquid phase relative permeability resolves this issue to some extent by improving the displacement of the liquid phase. Finally, implementing relative permeability curves from other fluid systems during UHS performance assessment will cause uncertainty in terms of gas saturation and up to 141% underestimation on cumulative hydrogen production. These observations illustrate the importance of using relative permeability curves characteristic of hydrogen-brine system for assessing the UHS performances.

Simulating gas-water relative permeabilities for nanoscale porous media with interfacial effects

AbstractThis paper presents a theoretical method to simulate gas-water relative permeability for nanoscale porous media utilizing fractal theory. The comparison between the calculation results and experimental data was performed to validate the present model. The result shows that the gas-water relative permeability would be underestimated significantly without interfacial effects. The thinner the liquid film thickness, the greater the liquid-phase relative permeability. In addition, both liquid surface diffusion and gas diffusion coefficient can promote gas-liquid two-phase flow. Increase of liquid surface diffusion prefer to increase liquid-phase permeability obviously as similar as increase of gas diffusion coefficient to increase gas-phase permeability. Moreover, the pore structure will become complicated with the increase of fractal dimension, which would reduce the gas-water relative permeability. This study has provided new insights for development of gas reservoirs with nanoscale pores such as shale.

Thermally induced evolution of dissolved gas in water flowing through a carbon felt sample

Carbon felts are widely used as flow through porous electrodes in great variety of electrochemical devices due to their superior electrochemical properties and low price. In plant-scale electrochemical reactors stacked with large carbon felt electrodes, uniformly and efficiently feeding liquid electrolytes to the entire area of individual electrode is frequently challenged by the complicated gas bubble evolution phenomena induced by dissolved gas exsolutions or/and gassing side reactions. To explore the hydraulic characteristics of this locally generated two-phase flow in fibrous porous media, thermally induced evolutions of dissolved air in water flowing through a carbon felt sample are experimentally studied. When 20°C air-saturated water is started to be pumped through the felt and simultaneously heated up to 30°C at the outlet, evolved gas bubbles are observed to emerge several minutes later and accumulate to considerable amount after a few hours. The correspondingly increasing average gas saturations in the felt are measured by a weighing method, maximum values of which fall in the range from 6% to 14% at different liquid velocities. The most surprising finding is that although the volume evolution rate of gas bubbles is only 0.36% of the liquid flow rate, the resulting liquid-phase relative permeability drops significantly and continuously for a couple of hours and down to 0.42 at the lowest liquid velocity.

Impact of PTFE content and distribution on liquid–gas flow in PEMFC carbon paper gas distribution layer: 3D lattice Boltzmann simulations

A 3D multiphase lattice Boltzmann model (LBM) was established and employed to study the impact of polytetrafluoroethylene (PTFE) content and distribution on the liquid–gas transport in proton exchange membrane fuel cell (PEMFC) carbon-paper gas distribution layer (GDL). In the computer-generated carbon paper GDL, part of the fibers’ surface was randomly specified as PTFE to achieve a desired PTFE content and distribution. For non-uniform PTFE distribution cases, a GDL sub-region neighboring to gas channel (GC) was set to have higher PTFE content. PTFE content and distribution show important influence on the liquid–gas flow and on the relationship of relative permeability versus phase saturation. The GDL sub-region of more PTFE acts like a capillary barrier and raises the liquid saturation level in the rest part of GDL. The simulated liquid saturation level in GDL diminishes with the increase of PTFE content in GDL. The liquid phase relative permeability is larger in the GDL of lower PTFE content if the (overall) liquid saturation is lower than a threshold value, whereas it becomes smaller if the liquid saturation is higher than this threshold value. The liquid phase relative permeability in the GDL with non-uniform PTFE distribution is reduced when the liquid saturation in GDL is lower than a certain value, but when the liquid saturation is higher than this value, it is larger compared with that in the GDL with uniform PTFE distribution. The gas phase relative permeability in the GDL of lower PTFE content is larger than tat in the GDL of higher PTFE content and the non-uniform distribution of PTFE in GDL slightly reduces the gas phase relative permeability value.

Injection, Flow, and Mixing of CO2 in Porous Media with Residual Gas

Geologic structures associated with depleted natural gas reservoirs are desirable targets for geologic carbon sequestration (GCS) as evidenced by numerous pilot and industrial-scale GCS projects in these environments world-wide. One feature of these GCS targets that may affect injection is the presence of residual CH4. It is well known that CH4 drastically alters supercritical CO2 density and viscosity. Furthermore, residual gas of any kind affects the relative permeability of the liquid and gas phases, with relative permeability of the gas phase strongly dependent on the time-history of imbibition or drainage, i.e., dependent on hysteretic relative permeability. In this study, the effects of residual CH4 on supercritical CO2 injection were investigated by numerical simulation in an idealized one-dimensional system under three scenarios: (1) with no residual gas; (2) with residual supercritical CO2; and (3) with residual CH4. We further compare results of simulations that use non-hysteretic and hysteretic relative permeability functions. The primary effect of residual gas is to decrease injectivity by decreasing liquid-phase relative permeability. Secondary effects arise from injected gas effectively incorporating residual gas and thereby extending the mobile-gas plume relative to cases with no residual gas. Third-order effects arise from gas mixing and associated compositional effects on density that effectively create a larger plume per unit mass. Non-hysteretic models of relative permeability can be used to approximate some parts of the behavior of the system, but fully hysteretic formulations are needed to accurately model the entire system.

Mathematical modelling of solvent drying from a static particle bed

Distributed-parameter models of vacuum contact drying of a static particle bed have been formulated and a numerical solution of the resulting set of partial differential equations describing heat and mass transfer in the particle bed has been carried out. Systematic parametric study of the effect of jacket temperature, head-space pressure, bed depth, and gas- and liquid-phase relative permeability has been performed. Trends observed in vacuum contact drying experiments, namely the independence of drying rate on the mode of driving force realisation (by jacket temperature or head-space pressure), linear scaling of heat-transfer rate with bed depth during the constant-rate period, independence of drying rate on particle size above a certain critical size, and disappearance of the constant-rate period below a certain particle size, have been reproduced by the model both qualitatively and quantitatively. A study of the effect of gas-phase permeability on drying kinetics revealed an interesting phenomenon–a reversal of the direction of drying front propagation. The drying front was found to originate from the heat source (heated walls) for large permeability, and from the mass sink (head-space) for low permeability.

Relative Permeability Modification in Gas/Liquid Systems Through Wettability Alteration to Intermediate Gas Wetting

Summary The wettability of Berea and chalk samples for gas/oil and gas/ water fluids were altered from strong liquid wetting to intermediate gas wetting. Two polymers, FC-722 and FC-759, were used to alter the wettability. FC-759 is soluble in water and 120 as expensive as FC-722. Gas and liquid relative permeabilities were measured before and after wettability alteration. The results demonstrated a significant increase in liquid-phase relative permeability. Gas-phase relative permeability for a fixed saturation may increase or decrease; however, because of the very high liquid mobility and reduced liquid saturation, the gas mobility also increased for a fixed pressure drop. A number of liquid injectivity tests were also carried out. The results revealed that the liquid-phase mobility could increase significantly when the wettability of rocks was altered from strong liquid wetting to intermediate gas wetting. All the results show clearly that the application of wettability alteration to intermediate gas wetting may significantly increase deliverability in gas condensate reservoirs.

Experimental study of air-water two-phase flow through a fracture (narrow channel)

Two-phase (air-water) flow experiments were conducted in artificial horizontal fractures (narrow channels). Two experimental set-ups were utilized. One set of experiments was performed by using two glass plates (1 × 0.5 m) with a gap width of 1 mm. The second set of experiments was performed using two bricks made of baked clay (28 × 14 cm) for which three gap widths of h 1 = 0.54 mm, h 2 = 0.40 mm and h 3 = 0.18 mm have been tested. Air and water were injected separately, through alternating capillary tubes for the first set-up and through a porous medium for the second. For each experiment, the fracture was initially saturated at constant water flow-rate, and air injection was then started. When steady state was reached, pressure drop and liquid volume fraction were measured. Then, air injection was increased stepwise and the experiment was repeated at different liquid flow rates. By varying the flow rates of each fluid phase, different flow structures were observed for the glass channel experiment: bubbles, fingering bubbles, complex, annular and droplet flow. These flow structures show more similarity to those observed in pipes than to those expected in porous media. Using the formalism developed for two-phase flow in pipes, and by taking experimental observations into account, a theoretical relationship for the two-phase pressure gradient is proposed. This relationship is evaluated with experimental data. Then, the results are analyzed with three models. First, the Lockhart & Matinelli model gives a good fit for both pressure drop and liquid volume fraction against the Martinelli parameter. Second, by considering the two phases flowing in the fracture as a single phase with averaged properties, the appropriate friction factor and Reynolds number of the mixture are defined. This model, which is similar to the homogeneous model, permits the selection of the experimental data corresponding to laminar flow. Finally, by using the generalized Darcy model, it was found that for laminar flow, the liquid-phase relative permeability is equal to the liquid volume fraction, while the gas-phase relative permeability is not a linear function of the liquid volume fraction.

The hydrodynamics of trickling flow in packed beds. Part I: Conduit models

AbstractThe hydrodynamics of trickling flow in packed beds is modeled by representing the porous medium as an array of parallel conduits of circular cross section.First, a straight tube model is developed and analytical solutions are obtained for the relative permeabilities of the gas and liquid phases. Then a periodically constricted tube model is proposed and the equations of motion are solved numerically to determine the effect that surface tension forces have on the relative permeabilities. The constricted tube model predicts that the relative permeabilities of the phases are appreciably sensitive to surface tension forces, a prediction that seems at odds with experimental observations. This discrepancy may be caused by the assumption of fully wetted surface area of particles employed in the model.The straight tube model confirms experimental results indicating that the liquid phase relative permeability is, for practical purposes, insensitive to the gas flow rate and to the gas‐to‐liquid density and viscosity ratios. Both conduit models show that the gas phase relative permeability curves are strong functions of the gas phase Reynolds number when this parameter is small. For large gas Reynolds numbers, a single curve for the relative permeability as a function of saturation is obtained. These trends are observed in previous experimental studies.

The hydrodynamics of trickling flow in packed beds. Part II: Experimental observations

AbstractThe liquid holdup and the pressure drop for two‐phase trickling flow in a packed bed were measured experimentally. Different values of those parameters were obtained as the liquid flow rate was increased and then decreased, indicating a multiplicity in hydrodynamic states. This behavior was observed even when the gas flow rate was zero in the bed. It was determined that the hysteresis exhibited by the process is due to imperfect wetting of the packing and to the difference between advancing and receding contact angles at the gas‐liquid‐solid contact lines. The reduced wetting conditions are also the cause of the increase in liquid holdup observed when the surface tension of the liquid is decreased. In this case, the amount of liquid retained in the bed is controlled by the extension of the wetted regions due to the more favorable contact angles as the surface tension decreases. The transition from the trickling to the pulsing flow regime was also dependent on the history of the process.A new correlation for predicting liquid holdups and pressure drops for trickling flow in packed beds is proposed for the decreasing liquid flow rate operating mode. This correlation is based on the experimental determination of the liquid phase relative permeability as a function of the the liquid phase reduced saturation and the determination of the gas phase relative permeability as a function of the gas phase saturation and the gas phase Reynolds number. The new data are analyzed in the light of the theory developed in the first part of this paper.