Search Results (31)

Conventional liquid springs enable storage of energy in the form of interfacial tension at forcibly wetted lyophobic surfaces. The pressure–volume work performed to compress the liquid into a poorly wettable porous medium is recovered during spontaneous expulsion when pressure falls below the capillary pressure characteristic of a given system. Our study explores generalizations to easily wettable materials where liquid infiltration is opposed solely by steric hindrance exerted on liquid molecules in micro-sized pores. The concept is exemplified in molecular simulations of prototypical model systems with methanol intruding narrow slits between hydrocarbon or graphene surfaces. While these materials show significant wetting propensities at macroscopic interfaces with liquid methanol, substantial compression is required to wet molecular-sized pores barely accommodating a monolayer of liquid molecules. The observed O(10³) bar intrusion pressures secure stored energy densities competitive with supercapacitors and amenable to improvement. Wall–liquid attraction and small pore diameters lead to intrusion–expulsion pathways along cooperative-adsorption isotherms. The process avoids abrupt liquid/vapor transitions and associated nucleation barriers, responsible for cycle hysteresis in experiments with water in hydrophobic capillaries. Using open ensemble (Grand Canonical) Monte Carlo sampling, we identify the range of porosities supporting reversible energy storage/recovery operation in lyophilic media; the results can assist with the design of molecular spring devices with competitive storage and power capacities in pragmatic contexts. Full article

Recently, a substantial quantity of oil and gas has been discovered in the pre-salt Lower Cretaceous microbialite successions of Brazil’s Santos Basin, thereby prompting a global surge in research related to microbialites. It has been demonstrated that microbial shoal reservoirs yield the highest hydrocarbon production, with optimal reservoir properties, as evidenced by experience in the field of oilfield production. However, as research progresses, it has become increasingly evident that significant heterogeneity exists in both the lithology and physical properties within microbial shoal bodies. In order to address the identified knowledge gap, the present study employs systematic petrological and petrophysical datasets. These include 30-m continuous core samples, thin-section analyses, routine petrophysical tests and mercury injection capillary pressure (MICP) measurements. The aim is to characterize the internal microfacies architecture and reservoir heterogeneity of microbial shoals. It is imperative to ascertain the principal factors that govern the heterogeneity observed in these reservoirs. This critical step is essential for a comprehensive understanding of the subject matter. The results of the study demonstrate that: the Barra Velha Formation microbial shoals in the Santos Basin can be subdivided into three microfacies, which are delineated from base to top. The foundation of the shoal is the shoal base. The rock composition is dominated by the presence of spherulites, with intracrystalline pores functioning as the primary reservoir spaces. The compositional rocks of the shoal flank are poorly sorted microbial debris, with intergranular and intragranular pores formed by penecontemporaneous dissolution. The sedimentary succession of the shoal core is characterized by well-sorted microbial debris rocks displaying multiple shallowing-upward sequences, with reverse-graded textures. The primary storage space is constituted by fabric-selective pores from penecontemporaneous dissolution, though these are subject to local disruption by destructive silicification. Meanwhile, the microbial shoals demonstrate wide porosity (8.8–26.4%, mean 16.8%) and permeability (0.13–839 mD, mean 169 mD) ranges, thus classifying them as medium-porosity, high-permeability reservoirs. The superimposition of microfacies and diagenetic processes gives rise to considerable reservoir heterogeneity. It is evident that the shoal core microfacies exhibits robust energy and substantial grain size, characteristics that facilitate its exposure above lake level during periods of high-frequency lake-level oscillation. This exposure is further compounded by the influence of atmospheric water dissolution, which remodels the microfacies during the quasi-contemporaneous period. The reservoir quality is optimal, exhibiting the highest proportion of large pores. The reservoir properties of the shoal flank are closely followed by medium and large pores, and those of the shoal base are the worst, with micro and medium pores. Full article

Water saturation is a key factor influencing the mechanical behavior and stability of tunnel rock masses in water-bearing strata. However, current research based on physical model tests has yet to systematically reveal its intrinsic relationship with rock failure modes. To address this gap, this study systematically investigated the effects of water saturation levels (0%, 33%, 58%, and 100%) on the failure mechanisms of four typical tunnel cross-section models: wall-arch, horseshoe, circular, and square. The results indicate the following: (1) Water saturation exerts a significant deteriorating effect on the mechanical properties of tunnel models. As saturation increases, peak stresses generally decrease across all models, but the extent of deterioration varies markedly by tunnel shape: at low saturation (≤58%), peak stress follows the order Wall-Arch > Horseshoe > Circular > Square; at high saturation (>58%), this relationship reverses to Circular > Square > Wall-Arch > Horseshoe. (2) The failure mechanism is significantly controlled by saturation, exhibiting distinct transition characteristics: At low saturation, capillary effects dominate, with matrix suction enhancing material strength, resulting in brittle failure with crack concentration. At high saturation, pore water pressure effects prevail, reducing effective stress and leading to plastic failure dominated by distributed shear slip. Notably, square tunnels consistently exhibit pronounced flexural failure characteristics across all saturation levels. (3) Energy evolution analysis indicates the following: as saturation increases, the total energy U of specimens decreases, the dissipation rate of dissipated energy U_d accelerates, the energy inflection point advances, and failure precursors manifest earlier. The energy dissipation factor n of high-saturation specimens decreases more significantly with increasing strain, confirming that moisture accelerates energy dissipation and promotes premature material instability. (4) Significant differences exist in the response characteristics to moisture effects among tunnel types: Square tunnels consistently exhibit pronounced flexural failure; Circular tunnels demonstrate optimal stress distribution properties under high water content conditions; Wall-arch and horseshoe-shaped tunnels are most sensitive to saturation changes, with their failure modes transitioning from tensile-dominated to shear failure as water content increases. This study reveals the coupled mechanism between water saturation and tunnel cross-sectional shape in influencing rock mass stability. Full article

High-pressure intrusion of water and LiCl aqueous solutions at different concentrations in hydrophobic STT-type zeosil was studied for possible applications in absorption and storage of mechanical energy. The water is intruded at a pressure of 35 MPa and remains trapped in the pores after pressure release, which corresponds to bumper behavior with total energy absorption. The use of LiCl solution leads to a change in system behavior, regardless of the concentration investigated (10, 15, or 20 M). Its intrusion is mainly reversible, but a small part of the intruded liquid remains in the pores after the first intrusion–extrusion cycle, which corresponds to a mixed behavior of bumper and shock absorber. The intrusion pressure rises strongly with an increase in salt concentration and reaches 227 MPa for a LiCl 20 M solution; the stored energy of 27 J/g can be achieved. The characterization of STT-type zeosil before and after intrusion–extrusion tests by structural and physicochemical methods shows that silanol defects are formed both under the intrusion of water and LiCl solutions. The relationship between zeosil structure and intrusion–extrusion characteristics is discussed by comparing the results obtained with those of other structural types of zeosils. Full article

Per- and polyfluoroalkyl substances (PFASs), used since the 1940s, are persistent and carcinogenic pollutants. Water is a major exposure route; effective removal is essential. While nanofiltration (NF) and reverse osmosis (RO) are effective but costly, ultrafiltration (UF) membranes offer advantages such as lower cost and higher flux, but their relatively large pore size makes them ineffective for PFAS compounds like perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). Since PFAS removal depends on both pore size and surface properties, this study investigates the effect of polyelectrolyte multilayer coatings using poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) on the zeta potential of UF membranes. Pristine UF membranes showed limited performance (UP150: ~2% for both PFOS and PFOA; UP020: 34.4% PFOS, 24.1% PFOA), while coating significantly enhanced removal (coated UP150: 45.3% PFOS, 43.4% PFOA; coated UP020: 77.8% PFOS, 73.3% PFOA). The modified UF membranes achieved PFAS removal efficiencies significantly closer to NF membranes, though still below those of RO (e.g., BW30XLE: up to 91.0% PFOS, 88.3% PFOA; NP030: up to 81.0% PFOS, 79.3% PFOA). Findings emphasize the importance of membrane surface charge and suggest that modified UF membranes offer a promising, low-cost alternative for PFAS removal under low-pressure conditions. Full article

During the waterflooding recovery process, water is injected into the hydrocarbon reservoirs and displaces a portion of the oil and gas, thereby improving oil and gas recovery rates and extending the production life of the reservoir. The macro benefits of waterflooding technology are widely recognized; however, the micro-scale effects of water on the reservoir’s pore structure and fluid distribution during the injection process remain underexplored. Therefore, this study aims to analyze the micro-distribution characteristics of fluids in the reservoir during the oil–water displacement process. To further investigate the micro-mechanisms of waterflooding recovery and the factors influencing recovery efficiency, the study focuses on the impact of permeability, pressure gradient, injection volume, and reverse displacement on oil recovery efficiency. A combined qualitative and quantitative analysis approach was employed, using techniques such as nuclear magnetic resonance (NMR), CT scanning, and fluid distribution tomography to comprehensively analyze the fluid evolution patterns within the reservoir. The results show the following: (1) The movable fluids in the oilfield are primarily distributed within pores ranging from 0.1 to 40 μm; the remaining oil is mainly distributed within pores of 0.1 to 10 μm, accounting for over 85% of the total distribution, and these pores serve as the main space for extracting remaining oil in later stages. (2) Increasing the injection volume significantly improves the oil recovery efficiency in pores ranging from 0.1 to 10 μm. Increasing the displacement pressure gradient effectively reduces remaining oil in pores of 0.1 to 5 μm. However, for reservoirs with permeability greater than 10 mD, once the injection volume exceeds 1 PV or the displacement pressure gradient exceeds 1.8 MPa/m, the increase in oil recovery efficiency becomes marginal. (3) With increasing water injection multiples, the oil displacement efficiency of cores with varying permeability levels shows an overall upward trend. However, the extent of improvement varies significantly, with low-permeability cores exhibiting a markedly greater enhancement in displacement efficiency compared to high-permeability cores. (4) Reverse displacement can reduce the remaining oil in pores ranging from 0.1 to 10 μm, and the increase in oil recovery efficiency is more significant in cores with lower permeability than in those with higher permeability. Therefore, increased production cannot solely rely on improving the production pressure differential to develop remaining oil. Full article

This study investigates the mechanical behavior of fractured sandstone under various factors, including freeze–thaw cycles, fracture dip angle, roughness, grouting material, and confining pressure. Freeze–thaw and triaxial compression tests were conducted to analyze the effects of individual factors and their interactions on the mechanical properties of sandstone. The results indicate the following: (1) Under independent factor conditions, freeze–thaw cycles generate frost heave forces through the water–ice phase transition, leading to the expansion of microcracks and deterioration of the pore structure, which results in a weakening effect. Grouting material enhances the bonding strength and supporting capacity of the rock sample, roughness improves the anchoring effect of the grout, fracture dip angle improves stress transmission efficiency, and confining pressure increases rock sample density and restricts deformation, all of which exhibit strengthening effects. (2) Interaction analysis revealed three types of interaction mechanisms for the peak stress and elastic modulus of the rock samples: interaction enhancement mechanism, where peak stress or elastic modulus significantly increases when the related factors are at high levels, demonstrating a synergistic strengthening effect; interaction inhibition mechanism, where factors at high levels suppress each other’s strengthening or weakening effects; and interaction reversal mechanism, where the influence trend of certain factors reverses under different conditions. Specifically, the interaction enhancement mechanism for peak stress is observed in the interactions between grouting material and roughness, grouting material and confining pressure, and fracture dip angle and roughness. The interaction inhibition mechanism occurs between grouting material and freeze–thaw cycles and confining pressure and freeze–thaw cycles. For elastic modulus, the interaction enhancement mechanism is observed in the interactions between fracture dip angle and confining pressure, grouting material and roughness, and confining pressure and roughness; the interaction reversal mechanism appears in the interaction between freeze–thaw cycles and fracture dip angle. Full article

Forward osmosis (FO) technology, known for its minimal energy requirements, excellent resistance to fouling, and significant commercial potential, shows enormous promise in the development of sustainable technologies, especially with regard to seawater desalination and wastewater. In this study, we improved the performance of the FO membrane in terms of its mechanical strength and hydrophilic properties. Generally, the water flux (J_w) of polyisophenylbenzamide (PMIA) thin-film composite (TFC)-FO membranes is still inadequate for industrial applications. Here, hydrophilic polydopamine (PDA)@ zeolitic imidazolate frameworks-8 (ZIF-8) nanomaterials and their integration into PMIA membranes using the interfacial polymerization (IP) method were investigated. The impact of PDA@ZIF-8 on membrane performance in both pressure-retarded osmosis (PRO) and forward osmosis (FO) modes was analyzed. The durability and fouling resistance of these membranes were evaluated over the long term. When the amount of ZIF-8@PDA incorporated in the membrane reached 0.05 wt% in the aqueous phase in the IP reaction, the J_w values for the PRO mode and FO mode were 12.09 LMH and 11.10 LMH, respectively. The reverse salt flux (J_s)/J_w values for both modes decreased from 0.75 and 0.80 to 0.33 and 0.35, respectively. At the same time, the PRO and FO modes’ properties were stable in a 15 h test. The incorporation of PDA@ZIF-8 facilitated the formation of water channels within the nanoparticle pores. Furthermore, the J_s/J_w ratio decreased significantly, and the FO membranes containing PDA@ZIF-8 exhibited high flux recovery rates and superior resistance to membrane fouling. Therefore, PDA@ZIF-8-modified FO membranes have the potential for use in industrial applications in seawater desalination. Full article

Under the influence of the sedimentation process, the phenomenon of intraformational non-homogeneity is widely observed in low-permeability reservoirs. In the development process of water and gas replacement (WAG), the transport law of water and gas and the distribution of residual oil are seriously affected by the non-homogeneity of reservoir properties. In this paper, a study on two types of reservoirs with certain lengths and thicknesses is carried out, and a reasonable development method is proposed according to the characteristics of each reservoir. Firstly, through indoor physical simulation experiments combined with low-field nuclear magnetic resonance scanning (NMR), this study investigates the influence of injection rate and core length on the double-layer low-permeability inhomogeneous core replacement and pore throat mobilization characteristics. Then, a two-layer inhomogeneous low-permeability microscopic model is designed to investigate the model’s replacement and pore throat mobilization characteristics under the combined influence of rhythmites, gravity, the injection rate, etc. Finally, based on the results of the core replacement and numerical simulation, a more reasonable development method is proposed for each type of reservoir. The results show that for inhomogeneous cores of a certain length, the WAG process can significantly increase the injection pressure and effectively seal the high-permeability layer through the Jamin effect to improve the degree of recovery. Moreover, for positive and reverse rhythm reservoirs of a certain thickness, the injection rate can be reduced according to the physical properties of the reservoir, and the gravity overburden phenomenon of the gas is used to achieve the effective development of the upper layers. The effect of the development of a positive rhythm reservoir therefore improved significantly. These findings provide data support for improving the development effectiveness of CO₂ in low-permeability inhomogeneous reservoirs and emphasize the importance of the influence of multiple factors, such as injection flow rate, gravity, and rhythm, in CO₂ replacement. Full article

This study investigates the modification of polyethersulfone (PES) membranes with 1 wt% titanium dioxide (TiO₂), zirconium dioxide (ZrO₂) and a nanocomposite of TiO₂/ZrO₂. The aim was to efficiently remove Rhodamine B (RhB) from water using a threefold approach of adsorption, filtration and photodegradation. Among the modified membranes (TiO₂, ZrO₂ and TiO₂/ZrO₂), the TiO₂/ZrO₂-PES nanocomposite membrane showed a better performance in rejection of RhB than other membranes with the rejection efficiency of 96.5%. The TiO₂/ZrO₂-PES membrane was found to possess a thicker selective layer and reduced mean pore radius, which contributed to its improved rejection. The TiO₂/ZrO₂ nanocomposite membrane also showed high bulk porosity and a slightly lower contact angle of 69.88° compared to pristine PES with a value of 73°, indicating an improvement in hydrophilicity. Additionally, the TiO₂/ZrO₂-PES nanocomposite membrane demonstrated a relatively lower surface roughness (Sa) of 8.53 nm, which offers the membrane antifouling properties. The TiO₂/ZrO₂-PES membrane showed flux recovery ratio (FRR), total fouling (R_t), reversible fouling (R_r) and irreversible fouling (R_ir) of 48.0%, 88.7%, 36,8% and 52.9%, respectively. For the photocatalytic degradation performance, the removal efficiency of RhB followed this order TiO₂ > TiO₂/ZrO₂ > ZrO₂ (87.6%, 85.7%, 67.8%). The tensile strength and elongation were found to be compromised with the addition of nanoparticles and nanocomposites. This indicates the necessity to further modify and optimise membrane fabrication to achieve improved mechanical strength of the membranes. At low pressure, the overall findings suggest that the TiO₂/ZrO₂ nanocomposite has the potential to offer significant improvements in membrane performance (water flux) compared to other modifications. Full article

The wettability of coal is an important factor influencing hydraulic stimulation. Field-trial data has proven that high-pressure N₂ injection plays a positive role in increasing the coalbed methane (CBM) production rate. For the purpose of investigating the mechanism by which N₂ promotes the gas rate, multiple experiments were conducted sequentially on the wettability of anthracite under different N₂ pressures. Testing of the coal surface contact angle was conducted under 0.1–8 MPa nitrogen pressure using a newly built contact angle measuring device. The coal samples were collected from the Xinjing Coal Mine in the Qinshui Basin, China. The test results revealed that the contact angle increased with increasing N₂ pressure. That is, the contact angle was 77.9° at an N₂ pressure of 0.1 MPa and gradually increased to 101.4° at an infinite N₂ pressure. In contrast, the capillary pressure decreased with an increasing N₂ pressure, from 0.298 MPa to −0.281 MPa. The relationship between contact angle and N₂ pressure indicated that the wettability was reversed at a N₂ pressure of 5.26 MPa, with a contact angle of 90° and a capillary pressure of 0 MPa. The capillary pressure reversed to a negative value as the N₂ pressure increased. At the microlevel, a high N₂ pressure increases the surface roughness of coal, which improves the ability of the coal matrix to adsorb N₂, forming the gas barrier that hinders the intrusion of water into the pores of the coal matrix. The results of this study provide laboratory evidence that high-pressure N₂ injection can prevent water contamination and reduce the capillary pressure, thus benefiting coalbed methane production. Full article

In the last decade, the development of a new generation of membranes based on low-cost materials has been widely studied. These membranes demonstrate significantly higher performance than the conventional ceramic membranes currently used in membrane separation technology. This work is focused on the development of a low-cost flat UF ceramic membrane composed completely of sepiolite using a uniaxial pressing method with dimensions of 5.5 cm of diameter and 3 mm of thickness. The sintering temperatures used were from 650 to 800 °C. Several properties, such as morphology, porosity, permeability, mechanical strength, and chemical resistance, are investigated. The results show that the mean pore diameter is increased from 40 to 150 nm when the sintering temperature increases from 650 °C to 800 °C. At these temperatures, excellent mechanical strength of 18 MPa to 22 MPa and high chemical resistance were achieved. SEM results revealed a crack-free structure with a uniformly smooth surface. Permeability tests were conducted using dead-end filtration. The sepiolite membrane demonstrated an improvement in its water permeability from 18 to 41 L·m⁻²·h⁻¹·bar⁻¹ when the sintering temperature increased from 650 °C to 750 °C. The efficiency of the sepiolite membranes sintered at 650 °C and 700 °C were evaluated with the application of the removal of paracetamol (PCT) and indigo blue (IB) dye separately from two synthetic aqueous solutions representing the pharmaceutical and textile sectors. Excellent removal efficiency of almost 100% for both contaminants was observed at ambient temperature and a pressure of 3 bars. Membrane regeneration was achieved through simple rinsing with deionized water. According to this finding, the UF sepiolite membrane demonstrated reversible fouling, which is consistent with the fouling coefficient “FRR” value higher than 90%. Full article

Forcible wetting of hydrophobic pores represents a viable method for energy storage in the form of interfacial energy. The energy used to fill the pores can be recovered as pressure–volume work upon decompression. For efficient recovery, the expulsion pressure should not be significantly lower than the pressure required for infiltration. Hysteresis of the wetting/drying cycle associated with the kinetic barrier to liquid expulsion results in energy dissipation and reduced storage efficiency. In the present work, we use open ensemble (Grand Canonical) Monte Carlo simulations to study the improvement of energy recovery with decreasing diameters of planar pores. Near-complete reversibility is achieved at pore widths barely accommodating a monolayer of the liquid, thus minimizing the area of the liquid/gas interface during the cavitation process. At the same time, these conditions lead to a steep increase in the infiltration pressure required to overcome steric wall/water repulsion in a tight confinement and a considerable reduction in the translational entropy of confined molecules. In principle, similar effects can be expected when increasing the size of the liquid particles without altering the absorbent porosity. While the latter approach is easier to follow in laboratory work, we discuss the advantages of reducing the pore diameter, which reduces the cycling hysteresis while simultaneously improving the stored-energy density in the material. Full article

A 40 cm length Bis(triethoxysilyl)ethane (BTESE) membrane having different pore sizes was successfully prepared by changing the number of coating times for gas permeation (GP) and organic solvent reverse osmosis (OSRO) separation study. It was found that BTESE-6 membranes prepared through six-time coating consisted of small-sized pores in the range 0.56 to 0.64 nm estimated using modified Gas Translation (mGT) method and 0.59 to 0.67 nm estimated by nanopermporometry (NPP) method, respectively. These membranes demonstrated a high DMF rejection, R_DMF > 95% with total flux, J_{v total} > 5 kg m⁻² h⁻¹ at operating condition feed pressure, P_f: 8 MPa; feed temperature, T_f : 50 °C; and feed flowrate, Q_f : 30 mL/min; and they exhibited a high degree selectivity of He/SF₆ in the range of ~ 260–3400 at a permeation temperature 200 °C. On the other hand, the larger pore sizes of the BTESE-4 membranes (pore size estimates > 0.76 nm to 1.02 nm) exhibited low DMF rejection and a low degree selectivity of He/SF₆ around ~30% and 25, respectively, at the same operating condition as BTESE-6. Both GT and NPP methods can be considered as an indicator of the measurement membrane pore size. From this study, it was found that He and SF₆ gases can be some of the potential predictors for water and DMF permeance. Furthermore, by comparing our OSRO membrane with other PV membranes for DMF/H₂O separation, our BTESE-6 membranes still exhibited high flux in the range of 3–6 kg m⁻² h⁻¹ with a separation factor H₂O/DMF in the range of 80–120. Full article

A rapid change in the pore water pressure of unsaturated soil due to a wetting front is a crucial factor and may result in instabilities in layered slopes. This study presents preliminary research on such a change, which we define as the seepage hammer effect. Vertical infiltration with multiple soil layers by column test was implemented to investigate the mechanism of the seepage hammer effect and distinguish it from the well-known Lisse effect and reverse Wieringermeer effect. A two-phase flow model was utilized to understand the evolutions of pore water/air pressure and volumetric water content, and its result evolved into a layered infinite slope stability analysis. Thus, the impacts of the seepage hammer effect on slope stability can be analyzed. This study found that the seepage hammer effect was triggered when the wetting front reached the interface of multiple layers and impermeable layers, and the rising speed of pore water pressure was proportional to the air venting capacity of soil. Slope stability analysis showed that the safety factor may decline suddenly because of the seepage hammer effect. Its relationship with the factor of safety and the sliding velocity is proportional. The detection of the seepage hammer effect could be a potential application of the study of fast-moving landslides. Full article