Role of Relative Permeability Hysteresis in Numerical Simulations for Hydrogen Geostorage

Hydrogen (H2) is increasingly being seen as a viable way to transport excess energy generated by renewable sources, preventing imbalances in energy supply. H2 storage is the barrier that we must overcome because current surface facilities are unable to meet the large-scale storage demands. Underground porous media such as confined seem to be the most feasible option to store H2. Our contribution to underground hydrogen storage is related to the modeling of multiphase flow in porous media. In the present work, we focus on the processes of capillary trapping and spatial heterogeneities in the hydraulic properties of the porous medium. To evaluate the spreading of the saturation front due to spatial heterogeneities, we model the immiscible displacement of brine by hydrogen. We simulate multiple cycles of H2 injection/production in a test volume, incorporating hysteresis in the relative permeability to study how this condition impacts hydrogen dissolution, purity, and recoverability. We compare cases with and without hysteresis to investigate the role of viscous forces and heterogeneities alone. These cycles also help us understand the balance between fingering stability and gravity override. Finally, we perform a dynamic reservoir simulation on a realistic reservoir geometry, taking into consideration the elements already discussed.Peer reviewe

Preliminary Field Trails and Simulation Results on Performance of Hybrid Positioning Based on GNSS and 5G Signals

From 1G to 4G, different advances on network-based localization have been developed and included. The 3rd-Generation Partnership Project (3GPP) has being working on these standards defining localization features, such as the Positioning Reference Signals (PRS) and the Long-Term Evolution (LTE) Positioning Protocol (LPP). However, network-based localization has been always considered an optional feature for cellular networks due to its low accuracy, and its methods have been focused mainly on assistance data for GNSS and cell ID enhancement. Now, a new perspective came up in the latest releases of 4G LTE and 5G due to the introduction of high-accuracy positioning services. 3GPP is moving towards including localization for a new range of markets, which has been translated in specific 3GPP activities, aiming at providing high accuracy GNSS for LTE and 5G technologies and designing Radio Access Technology (RAT)- dependent technologies to meet more stringent targets than in previous generations. For high-accuracy positioning, for instance tosupport autonomous driving or industrial automation, the integration of GNSS (augmented with precise or differential corrections), terrestrial (RAT-dependent) technologies and complementary sensors is expected to play a key role on 5G localization. The goal of GINTO5G project is to support the design of PNT solutions in the context of 5G applications by carrying out extensive experiments and simulation campaigns, as well as theoretical assessment of possible disruptive techniques. For downlink TDoA using 5G SRS signal, the field trials of one campaign shows that sub-meter accuracy can be achieved with 100 MHz bandwidth in the 3.7 GHz band. At the same time the evaluation shows a significant discrepancy between achieved TOA accuracy, and the overall positioning performance, especially for the outdoor tests. Based on CEP95 and SEP95 values, it can be stated that a 2D accuracy of sub 3 meter can be achieved an outdoor area where transmitting points have been deployed and optimized for positioning purpose. Similar performance could be seen in the results of the tests carried out in indoor spaces; what is more, half of all measured indoor positions even show a significantly lower error (sub 1 meter for 2D, and sub 3 meters for 3D). Another set of outdoor trials, conducted this time on a set of transmitting points deployed more randomly, revealed a mean 2D positioning error ranging from sub metre to several hundreds of metres

Saturation overshoot and hysteresis for twophase flow in porous media

Saturation overshoot and hysteresis for two phase flow in porous media are briefly reviewed. Old and new challenges are discussed. It is widely accepted that the traditional Richards model for twophase flow in porous media does not support non-monotone travelling wave solutions for the saturation profile. As a concequence various extensions and generalizations have been recently discussed. The review highlights different limits within the traditional theory. It emphasizes the relevance of hysteresis in the Buckley–Leverett limit with jump-type hysteresis in the relative permeabilities. Reviewing the situation it emerges that the traditional theory may have been abandoned prematurely because of its inability to predict saturation overshoot in the Richards limit

Diffusion‐to‐Imbibition Transition in Water Sorption in Nanoporous Media: Theoretical Studies

The ability to predict multiphase fluid transport in nanoporous rocks such as shales is critical for many geoscience applications, for example unconventional hydrocarbon production, geologic carbon sequestration, and nuclear waste disposal. When the pore sizes approach nanoscales, the impact of the molecular interaction forces between fluids and solids becomes increasingly important. These forces can alter macroscopic fluid phase behavior and control transport. Recent experimental studies have shown that capillary condensation and subsequent imbibition of liquid water can occur in hydrophilic nanoporous media even if the vapor phase is at a critical relative humidity (rhcrit) well below vapor saturation. This study presents a theoretical investigation of the processes controlling adsorption, capillary condensation and imbibition in nanoporous media, using the square-gradient classical density functional theory. The proposed theoretical model explicitly includes the relevant interaction forces among fluids and solids in macroscopic porous media. Application of the model to a relative-humidity-controlled water adsorption experiment is presented to demonstrate the impact of water-pore wall attractive forces on multiphase water behavior in a hydrophilic silicon nanoporous medium. The model represents well the measured time-dependent evolution of the water imbibition front inside the nanoporous medium and also explains the diffusion-like water transport regimes observed at rh < rhcrit and the imbibition-like flow regimes observed at rh > rhcrit. The study furthermore gives an insight on hysteresis phenomenon in adsorption and desorption isotherms