Search Results (1,048)

Understanding the fluid storage and production mechanisms in sedimentary rocks is vital for optimising natural gas extraction and subsurface resource management. This study applies high-resolution X-ray computed tomography (≈15 μm) to digitise rock samples from onshore Cyprus, producing digital rock models from DICOM images. The workflow, including digitisation, numerical simulation of natural gas flow, and experimental validation, demonstrates strong agreement between digital and laboratory-measured porosity, confirming the methods’ reliability. Synthetic sand packs generated via particle-based modelling provide further insight into the gas storage mechanisms. A linear porosity–permeability relationship was observed, with porosity increasing from 0 to 35% and permeability from 0 to 3.34 mD. Permeability proved critical for production, as a rise from 1.5 to 3 mD nearly doubled the gas flow rate (14 to 30 fm³/s). Grain morphology also influenced gas storage. Increasing roundness enhanced porosity from 0.30 to 0.41, boosting stored gas volume by 47.6% to 42 fm³. Although based on Cyprus retrieved samples, the methodology is applicable to sedimentary formations elsewhere. The findings have implications for enhanced oil recovery, CO₂ sequestration, hydrogen storage, and groundwater extraction. This work highlights digital rock physics as a scalable technology for investigating transport behaviour in porous media and improving characterisation of complex sedimentary reservoirs. Full article

It is well known that the operation of a Borehole Heat Exchanger (BHE) can thermally induce groundwater convection in aquifers, enhancing the thermal performance of the BHE. However, the effect on the thermal performance of BHEs installed in low-permeable rock formations remains unclear. In this study, two BHEs were installed in a silty sandstone formation, one backfilled with high-permeable materials and the other grouted with sand–bentonite slurry. A Thermal Response Test (TRT) showed that the fluid outlet temperature of the high-permeable-material backfilled BHE was about 2.5 °C lower than that of the BHE refilled with sand–bentonite slurry, implying a higher thermal efficiency. The interpreted borehole thermal parameters also show a lower borehole thermal resistance in the high-permeable-material backfilled BHE. Physical model tests reveal that groundwater convective flow was induced in the high-permeable-material backfilled BHE. A test of BHEs with different borehole diameters shows that the larger the borehole diameter, the higher the thermal efficiency is. Thus, the thermal performance enhancement was attributed to two factors. First, the induced groundwater flow accelerates heat transfer by convection. Additionally, the increment of the thermal volumetric capacity of the groundwater stored inside a high-permeable-material refilled borehole stabilized the borehole’s temperature, which is key to sustaining high thermal efficiency in a BHE. The thermal performance enhancement demonstrated here shows potential for reducing reliance on fossil-fuel-based energy resources in challenging geological settings, thereby contributing to developing more sustainable geothermal energy solutions. Further validation in diverse field conditions is recommended to generalize these findings. Full article

This study examines the impact of physicochemical and geological factors on radon concentrations in groundwater throughout the Mexican Altiplano. Geological diversity, uranium deposits, seismic zones, and geothermal areas with high heat flow are all potential factors contributing to the presence of radon in groundwater. To move beyond local-scale assessments, this research employs spatial prediction methodologies that incorporate geological and geochemical variables recognized for their role in radon transport and geogenic potential. Certain properties of radon enable it to serve as an ideal tracer, viz., short half-life, inertness, and higher incidence in groundwater than surface water. Twenty-five variables were analyzed in samples from 135 water wells. Geostatistical techniques, including inverse distance weighted interpolation and kriging, were used in conjunction with multivariate statistical analyses. Salinity and geothermal heat flow are key indicators for determining groundwater origin, revealing a dynamic interplay between geothermal activity and hydrogeochemical evolution, where high temperatures do not necessarily correlate with increased solute concentrations. The occurrence of toxic trace elements such as Cd, Cr, and Pb is primarily governed by lithogenic sources and proximity to mineralized zones. Radon levels in groundwater are mainly influenced by geological and structural features, notably rhyolitic formations and deep hydrothermal systems. These findings underscore the importance of site-specific groundwater examination, combined with spatiotemporal models, to account for uranium–radium dynamics and flow paths, thereby enhancing radiological risk assessment. Full article

Groundwater seepage plays a critical role in the long-term safety of high-level radioactive waste (HLW) disposal, yet its characterization remains challenging due to the complexity of fractured rock media. This study introduces the Double-Layered Seismo-Electric Method (DSEM) for imaging groundwater seepage fields with enhanced sensitivity and spatial resolution. By integrating elastic wave propagation with electrokinetic coupling in a stratified framework, DSEM improves the detection of hydraulic gradients and preferential flow pathways. Application at a representative disposal site demonstrates that the method effectively delineates seepage channels and estimates hydraulic conductivity, providing reliable input parameters for groundwater flow modeling. These results highlight the potential of DSEM as a non-invasive geophysical technique to support safety assessments and long-term monitoring in deep geological disposal of high-level radioactive waste. Full article

Comprehension of spatio-temporal groundwater recharge (GWR) under climate change is imperative to enhance water resources availability and management. The main aim of this study is to examine climate change’s effects on spatio-temporal GWR. This study was done by ensembling five climate models and the physically-based WetSpass-M model to estimate GWR during baseline (1986 to 2015), mid-term (2031 to 2060), and long-term (2071 to 2100) periods for the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. In comparison to the Identification of unit Hydrographs and Component flows from Rainfall, Evaporation, and Streamflow (IHACRES)’s baseflow and direct runoff with corresponding WetSpass-M model outputs, the statistical indices showed good performance in simulating water balance components. Projected future temperature and rainfall will likely increase dramatically compared to the baseline period for RCP4.5 and RCP8.5. In comparison to the baseline period, the annual GWR had been projected to increase by 4.28 mm for RCP4.5 for the mid-term (MidT4.5), 15.27 mm for the long-term (LongT4.5), 2.38 mm for the mid-term (MidT8.5), and 13.11 mm for the long-term for RCP8.5 (LongT8.5), respectively. The seasonal GWR findings showed an increasing pattern during winter and spring, whereas it declined in autumn and summer. The mean monthly GWR for MidT4.5, LongT4.5, MidT8.5, and LongT8.5 will increase by 0.34, 1.26, 0.18, and 1.07 mm, respectively. The watershed’s downstream areas were receiving the lowest amount of GWR, and prone to drought. Therefore, this study advocates and recommends that stakeholders participate intensively in developing and implementing climate change resilience initiatives and water resources management strategies to offset the detrimental effects in the downstream areas. Full article

As metal resource extraction increases, heavy metal ion pollution in the saturated zone intensifies. Hence, research on the migration of heavy metal ions in aquifers and the efficacy of protective measures is essential to inform pollution prevention and control engineering. This study focuses on the slag pond and its surrounding area of a smelting plant. Utilizing field hydrological surveys and experiments, and data from previous studies, we employed FEFLOW7.0 simulation software to model the groundwater system of the boulder aquifer in this region. The model divides the domain based on natural topography: the eastern river serves as a constant-head boundary, while other areas are set as specified-flux boundaries. The impermeable layer at the bottom is treated as a no-flow boundary, with a maximum simulation period of 2500 days. The simulation examines the natural movement of zinc ions and how the construction of the wall impacts their migration, as well as the wall’s effectiveness in preventing seepage. Findings indicate that the movement of zinc ions is significantly influenced by the reaction coefficient. When the reaction coefficient exceeds 10⁻⁸ s⁻¹, zinc ions decrease rapidly in the area. After the construction of the cutoff wall, the maximum migration distance of zinc ions within 2500 days decreased from 220 m to 77 m, demonstrating its effectiveness in controlling zinc transport in groundwater. Full article

The Niland Moving Mud Spring, located near the southeastern margin of the Salton Sea, represents a rare and evolving geotechnical hazard. Unlike the typically stationary mud pots of the Salton Trough, this spring is a CO₂-driven mud spring that has migrated southwestward since 2016, at times exceeding 3 m per month, posing threats to critical infrastructure including rail lines, highways, and pipelines. Emergency mitigation efforts initiated in 2018, including decompression wells, containment berms, and route realignments, have since slowed and recently almost halted its movement and growth. This study integrates hydrochemical, temperature, stable isotope, and tritium data to propose a refined conceptual model of the Moving Mud Spring’s origin and migration. Temperature data from the Moving Mud Spring (26.5 °C to 28.3 °C) and elevated but non-geothermal total dissolved solids (~18,000 mg/L) suggest a shallow, thermally buffered groundwater source influenced by interaction with saline lacustrine sediments. Stable water isotope data follow an evaporative trajectory consistent with imported Colorado River water, while tritium concentrations (~5 TU) confirm a modern recharge source. These findings rule out deep geothermal or residual floodwater origins from the great “1906 flood”, and instead implicate more recent irrigation seepage or canal leakage as the primary water source. A key external forcing may be the 4.1 m drop in Salton Sea water level between 2003 and 2025, which has modified regional groundwater hydraulic head gradients. This recession likely enhanced lateral groundwater flow from the Moving Mud Spring area, potentially facilitating the migration of upwelling geothermal gases and contributing to spring movement. No faults or structural features reportedly align with the spring’s trajectory, and most major fault systems trend perpendicular to its movement. The hydrologically driven model proposed in this paper, linked to Salton Sea water level decline and correlated with the direction, rate, and timing of the spring’s migration, offers a new empirical explanation for the observed movement of the Niland Moving Mud Spring. Full article

To elucidate the hydrochemical characteristics and evolution mechanisms of shallow groundwater in the alluvial–coastal transitional zone of the Tangshan Plain, 76 groundwater samples were collected in July 2022. An integrated approach combining Piper and Gibbs diagrams, ionic ratio analysis, multivariate statistical methods (including Pearson correlation, hierarchical cluster analysis, and principal component analysis), and PHREEQC inverse modeling was employed to identify hydrochemical facies, dominant controlling factors, and geochemical reaction pathways. Results show that groundwater in the upstream alluvial plain is predominantly of the HCO₃–Ca type with low mineralization, primarily controlled by carbonate weathering, water–rock interaction, and natural recharge. In contrast, groundwater in the downstream coastal plain is characterized by high-mineralized Cl–Na type water, mainly influenced by seawater intrusion, evaporation concentration, and dissolution of evaporite minerals. The spatial distribution of groundwater follows a pattern of “freshwater in the north and inland, saline water in the south and coastal,” reflecting the transitional nature from freshwater to saline water. Ionic ratio analysis reveals a concurrent increase in Na⁺, Cl⁻, and SO₄²⁻ in the coastal zone, indicating coupled processes of saline water mixing and cation exchange. Statistical analysis identifies mineralization processes, carbonate weathering, redox conditions, and anthropogenic inputs as the main controlling factors. PHREEQC simulations demonstrate that groundwater in the alluvial zone evolves along the flow path through CO₂ degassing, dolomite precipitation, and sulfate mineral dissolution, whereas in the coastal zone, continuous dissolution of halite and gypsum leads to the formation of high-mineralized Na–Cl water. This study establishes a geochemical evolution framework from recharge to discharge zones in a typical alluvial–coastal transitional setting, providing theoretical guidance for salinization boundary identification and groundwater management. Full article

Groundwater–surface water interactions play a critical role in regulating river temperature and flow, particularly in northern regions affected by climate change. This study evaluates the influence of climate warming on groundwater discharge for two rivers in Quebec: the Sainte-Marguerite River, located in a humid continental zone without permafrost, and the Berard River, situated in a subpolar continental zone with discontinuous permafrost. Using two-dimensional hydrothermal modeling supported by field data, the analysis reveals that climate warming will increase groundwater seepage into both river systems. The effect is notably more pronounced in permafrost regions, where thawing accelerates subsurface flow. Model projections indicate that permafrost near the Berard River may vanish by 2040 under high-emission scenarios or by 2070 under low-emission scenarios. This transition is expected to result in more than a thirtyfold increase in groundwater discharge by the end of the century. These findings highlight the growing influence of groundwater in shaping river hydrology under changing climatic conditions and underscore the need to incorporate subsurface flow dynamics into future water resource management and habitat conservation strategies in northern environments. Full article

Southern Kazakhstan, particularly the Zhambyl Region, is facing increasing groundwater stress due to climate change, degradation of irrigation infrastructure, and unsustainable water use. Despite substantial renewable groundwater reserves (8.33 km³/year), irrigation still relies on ephemeral surface flow. This study delineates priority zones for Managed Aquifer Recharge (MAR) using a GIS-based Multi-Criteria Decision Analysis framework integrated with the Analytic Hierarchy Process (AHP). Nine hydrogeological criteria were incorporated: shallow aquifer depth, groundwater salinity, precipitation, terrain slope, soil texture, land use/land cover, Normalized Difference Vegetation Index (NDVI), drainage density, and lineament density. Each parameter was normalized to a five-class suitability scale and weighted through expert-informed pairwise comparisons. The MAR suitability map identifies about 19% of the region (27,060 km²) as highly favorable for implementation. Field investigations at eleven groundwater sites in 2024 corroborate model results, providing aquifer depth, quality, and infiltration data. The most suitable areas are concentrated on Quaternary alluvial–proluvial fans near the Kyrgyz Alatau foothills and the Talas-Assa interfluve. Three hydrostratigraphic settings were identified: unconfined alluvial aquifers, Neogene–Quaternary unconsolidated sediments, and fractured Carboniferous carbonates. Recommended MAR methods include infiltration galleries, check dams, and injection wells. The proposed approach, validated through consistency analysis (Consistency Ratio ≤ 0.1), demonstrates the applicability of integrated geospatial and field methods for site-specific MAR planning. Strategic MAR deployment could restore productivity to 37,500 ha of degraded irrigated lands and improve groundwater resilience. These findings provide a practical framework for policymakers and water management authorities to optimize groundwater use and enhance agricultural sustainability under changing climatic conditions. Full article

Accurately simulating immiscible counter-current flow is crucial for applications from geological ${\mathrm{CO}}_2$ storage to shale gas production, yet it remains a major challenge for conventional pore network models (PNMs), which are unable to handle the numerical instability of opposing flows. To address this critical gap, we developed a novel dynamic PNM that incorporates a ‘transition state’ algorithm. This method successfully eliminates the spurious meniscus oscillations that hinder traditional models, enabling robust simulation of the complete counter-current process. Using this model, we quantify the profound impact of pore structure on flow efficiency. Our results demonstrate that increasing the pore size distribution uniformity (Weibull shape factor k from 0.5 to 3.0) extends the persistence of continuous air outflow pathways by more than six-fold (from 359 to over 2300 simulation steps). This leads to a quantifiable increase in the initial fluid exchange rate by nearly 10 times (from ${10}^{-11}$ to ${10}^{-10}$${\mathrm{m}}^3$/s) and a reduction in final residual air saturation by 53% (from 0.91 to 0.43). This work provides a tool for predicting and optimizing counter-current flow efficiency in subsurface engineering applications. Full article

Compared to shallow geothermal systems, coaxial medium-deep and deep borehole heat exchangers (MDBHE and DBHE) offer higher temperatures and heat extraction rates while requiring less surface area, making them attractive options for sustainable heat supply in combination with ground-source heat pumps (GSHP). However, existing simulation tools for such systems are often limited in computational efficiency or open-source availability. To address this gap, we propose a rapid modeling approach using the open-source Python package “pygfunction” (v2.3.0). Its workflow was adjusted to accept the fluid inlet temperature as input. The effective undisturbed ground temperature and ground thermophysical properties were weight-averaged considering stratified ground layers. Validation of the approach was conducted by comparing simulation results with 12 references, including established models and experimental data. The proposed method enables fast estimation of fluid temperatures and heat extraction rates for single boreholes and small-scale bore fields in both homogeneous and heterogeneous geological conditions at depths of 700–3000 m, thus supporting rapid assessments of the coefficient of performance (COP) of GSHP. The approach systematically underestimates fluid outlet temperatures by up to 2–3 °C, resulting in a maximum underestimation of COP of 4%. Under significant groundwater flow or extreme geothermal gradients, these errors may increase to 4 °C and 6%, respectively. Based on the available data, these discrepancies may result in errors in GSHP electric power estimation of approximately ±10%. The method offers practical value for GSHP performance evaluation, geothermal potential mapping, and district heating network planning, supporting geologists, engineers, planners, and decision-makers. Full article

The precise and accurate use of aquifer hydraulic parameters for assessing local and regional recharge potential for enhancing groundwater allocation planning is vital for many hydrogeological studies. The conventional approach for allocating groundwater presents a challenging scenario, as it remains uncertain whether the applied recharge estimate is local or regional recharge. The approach does not account for the extent of the aquifer recharge in terms of local and regional scale; instead, it assumes that recharge is distributed across the catchment. This study aimed to demonstrate the use of aquifer hydraulic parameters (transmissivity and storativity) to explain areas of potential recharge (local and regional) for enhancing groundwater allocation planning with a specific case study of De Aar, Northern Cape, South Africa. It argues that not integrating local and regional recharge potentials in planning for groundwater allocations can result in over- or under-allocation of groundwater resources to users. A constant discharge pumping test and recovery test matching the duration of pumping were conducted for data collection. The Flow Characteristics method was used as a diagnostic tool to understand the different aquifer flow regimes in the study area. To develop an integrated understanding of the groundwater system, a hydrogeological conceptual model was used to visualize areas with higher or lower recharge potential across local and regional scales. Results showed significant variability in transmissivity, ranging from 213 to 596 m²/d, and storativity, ranging from 0.0000297 to 0.000185. The transmissivity values suggest that groundwater moves faster; meanwhile, the storativity values suggest that the aquifer system has high water storage capacity. These results will assist water resource planners in making informed decisions on how to allocate groundwater to users. This study demonstrated that aquifer hydraulic parameters are a valuable tool for improving groundwater allocations, thereby highlighting the importance of considering areas for potential recharge, both local and regional, in planning groundwater allocation. Full article

Electrical resistivity tomography (ERT) is one of the most commonly used geophysical methods for imaging the distribution of electrical resistivity in the subsurface. It is often employed to characterise heterogeneity in karst regions and locate cavities and conduits below the surface. The resistivity contrast between the host rock and the cavity depends on the material filling the cavity. Air has a high electrical resistivity and should therefore produce strong reflections and refractions off cavity walls. However, cavities are not always easily detectable. A decrease in resistivity contrast at the interface between rock and air may result from different physical conditions relating to pore saturation, fracturing and stress near the cavity walls. Our first goal is to understand how extensive fracturing and hydrogeological conditions in the first subsurface layers can affect electric current flow in the presence of a karst tunnel. We use the commercial Res2Dmod software 3.0 to simulate an ERT on several ground models. The results, which are based on hydrogeological models, are presented for several conditions of a karst conduit: empty; full of water within a homogeneous background; and below the groundwater level in the presence of extensive fractures in the shallow layer above it. Full article

A permeable reactive barrier (PRB) containing zero-valent iron (ZVI) is an in situ groundwater remediation technology that passively intercepts and treats contaminated groundwater plumes. Over time, secondary mineral precipitation within the PRB diminishes porosity and hydraulic conductivity, altering flow paths, residence times, and sometimes causing bypass of the reactive zone. This study utilizes the THMC software to simulate porosity reduction in a PRB, capturing the coupled effects of fluid flow and geochemical interactions. The simulation results indicate that porosity loss is most significant at the PRB entrance and stabilizes beyond 0.2 m. Porosity reduction is primarily caused by aragonite, siderite, and ferrous hydroxide precipitating in pore spaces. The model further elucidates the influence of groundwater chemistry, demonstrating that variations in bicarbonate concentrations significantly impact mineral precipitation processes, thereby leading to porosity reduction. Furthermore, the study highlights reaction kinetics, with anaerobic iron corrosion rates being critical in controlling porosity reduction via mineral precipitation. THMC software effectively simulates porosity reduction in PRBs, identifies key factors driving clogging, and informs design optimization for long-term remediation. Full article