Trapping, hysteresis and Ostwald ripening in hydrogen storage: a pore-scale imaging study

Green hydrogen, produced from surplus electricity during peak production, can be injected into subsurface reservoirs and retrieved during high-demand periods. In this study, X-ray tomography was employed to examine hysteresis resulting from repeated hydrogen injection and withdrawal. An unsteady state experiment was performed to evaluate the distribution of hydrogen and brine after drainage and imbibition cycles: images of the pore-space configuration of fluids were taken immediately once injection had stopped and after waiting for a period of 16 h with no flow. A Bentheimer sandstone sample with a length of 60 mm and diameter of 12.8 mm was used, and hydrogen was injected at ambient temperature and a pore pressure of 1 MPa. The gas flow rate was decreased from 2 ml/min to 0.08 ml/min over three cycles of gas injection followed by water flooding, while the brine injection rate was kept constant. The results showed the presence of capillary pressure hysteresis and hydrogen migration through Ostwald ripening due to the diffusion of gas dissolved in the brine. These phenomena were characterized through analysis of interfacial curvature, area, connectivity and pore occupancy. The hydrogen tended to reside in the larger pore spaces, consistent with water-wet conditions. 16 h after flow had stopped, the hydrogen aggregated into larger ganglia with a single large connected ganglion dominating the volume. Moreover, the Euler characteristic decreased after 16 h, indicating an improvement in connectivity. The work implies that Ostwald ripening – mass transport of dissolved gas – leads to less hysteresis and better connectivity than would be assumed ignoring this effect, as done in assessments of hydrocarbon flow and trapping

Short Oxygen Plasma Treatment Leading to Long-Term Hydrophilicity of Conductive PCL-PPy Nanofiber Scaffolds

Electrically conductive scaffolds are of significant interest in tissue regeneration. However, the chemistry of the existing scaffolds usually lacks the bioactive features for effective interaction with cells. In this study, poly(ε-caprolactone) was electrospun into aligned nanofibers with 0.58 µm average diameter. Electrospinning was followed by polypyrrole coating on the surface of the fibers, which resulted in 48 kΩ/sq surface resistivity. An oxygen plasma treatment was conducted to change the hydrophobic surface of the fiber mats into a hydrophilic substrate. The water contact angle was reduced from 136° to 0°, and this change remained on the surface of the material even after one year. An indirect cytotoxicity test was conducted, which showed cytocompatibility of the fibrous scaffolds. To measure the cell growth on samples, fibroblast cells were cultured on fibers for 7 days. The cell distribution and density were observed and calculated based on confocal images taken of the cell culture experiment. The number of cells on the plasma-treated sample was more than double than that of sample without plasma treatment. The long-lasting hydrophilicity of the plasma treated fibers with conductive coating is the significant contribution of this work for regeneration of electrically excitable tissues

Electroactive nanostructured scaffold produced by controlled deposition of PPy on electrospun PCL fibres

The electrical conductivity of biodegradable polymeric scaffolds has shown promising results in tissue engineering, particularly for electrically excitable tissues such as muscles and nerves. Herein, we demonstrate a novel processing approach to produce electroactive nanofibres. Electrically conducting, robust nanofibres comprising both a biodegradable component using poly(ε-caprolactone) (PCL) and a conducting component, polypyrrole (PPy), have been produced by electrospinning and vapour phase polymerization. The PCL/PPy nanofibres were characterised in terms of morphology, electrical conductivity, and dimensional stability. The as-prepared nanofibres were found to be cytocompatible with good electrical conductivity and mechanical properties. It was found that electrical conductivity of the PPy coated PCL nanofibre was 1.9 S/cm, which is much higher than that of PCL mixed with PPy in other studies. Cell viability on the scaffolds were firstly examined by in vitro culturing the L929 fibroblast cells for 24 h, revealing viability of 97.6 ± 2.7 %. Then PC12 cells differentiation observed by neurite outgrowth which occurred after 4 days of culture on the scaffolds. Significantly larger areas of the PPy coated PCL were covered by cells compared to PCL without coating. The obtained results from filament staining suggested the high potentials of the conducting scaffold for use in neural tissue engineering

<b>Estaillades Carbonate: High-Resolution X-ray Imaging of Steady-State Oil-Brine Flow in Microporous Rock</b>

Experimental Details:Objective: This experiment aims to investigate fluid flow behavior within a microporous Estaillades carbonate rock with significant sub-resolution pore space under steady-state conditions using high-resolution imaging techniques.Rock Sample: The experiment utilizes a sample of Estaillades carbonate rock, characterized by its microporous nature, which is known to influence fluid flow dynamics.Flow Rate: The flow rate is controlled at a constant value of 0.02 mL/min throughout the experiment. This controlled flow rate ensures steady-state conditions. The low flow rate results in capillary-dominated flow.Fractional Flow Measurement: The co-injection of phases allows for the adjustment of fractional flows by changing the flow rates of phases during the experiment, while maintaining a constant total flow rate. This measurement is used to analyze the evolving flow behavior as the experiment progresses. Measurements are taken at fractional flow values of 0.0, 0.15, 0.3, 0.5, 0.7, 0.85, and 1.0, which are indicated in the image's name.Imaging: High-resolution X-ray imaging is employed to capture images of the rock sample and the flowing fluids. These images are taken at the final stage of each fractional flow, once a steady state is achieved. The high contrast provided by a 30wt% KI brine aids in differential imaging and characterizing sub-resolution pore space, a significant fraction of pore space in this rock, that cannot be fully resolved with micro-CT.Purpose and Significance:This experiment is conducted to gain insights into the fluid flow characteristics, displacement mechanisms, and pore-scale interactions within the microporous Estaillades carbonate rock. The study of such phenomena is essential for understanding reservoir behavior, enhancing hydrocarbon recovery processes, and optimizing fluid injection strategies in carbonate reservoirs.This heterogeneous rock in which a significant fraction of pore space can not be resolved with micro-CT and identifying unresolved pore space is possible through differential imaging. This feature makes the experiment an ideal case for testing multi-scale pore network modeling.Note: In the segmented image, label 0 is out of the domain, label 1 represents grain voxels, labels 2 and 3 correspond to voxels with sub-resolution porosity, and label 4 corresponds to resolved pore voxels. This information was obtained based on the segmentation of a dry scan and differential imaging. Please check here for all files.Keywords: Steady state core-flooding, Estaillades carbonate rock, microporosity, fluid flow, fractional flow, X-ray imaging, high contrast brine, differential imaging, sub-resolution pore space.</p