Aquifer Formation Research Articles

Optimizing hydrogen storage in a heterogeneous aquifer considering hysteresis and dissolution

Hydrogen (H2) is a rising solution for carbon-neutral fuel transition. Saline aquifer, ubiquitous underground, is a competitive candidate for large-scale underground hydrogen storage (UHS). This study proposed to use a heterogeneous aquifer formation for probing the functioning of UHS and optimizing its operation. By integrating geological information with lithofacies from the Ordos Basin in China, a heterogeneous triplet aquifer model was built, upon which compositional simulations of UHS operations that consider two-phase flow, relative permeability hysteresis, hydrogen and water phase behavior, rock compressibility, and dissolution mechanisms were conducted. Orthogonal array L25 (56) with mixed levels was designed to optimize the H2 recovery. Results substantiate the feasibility of storing millions of cubic meters of H2 with over 95% recovery. Ignoring dissolution and relative permeability hysteresis will result in an overestimation of the hydrogen recovery factor, with the effect of relative permeability hysteresis being more significant. Provided equal cycle length, a lower injection-withdrawal rate is suitable for long-term operation of hydrogen storage, while a higher rate can achieve a higher recovery factor during the early cycles. Measures of lowering the skin factor and pre-extracting brine could improve storage capacity and reduce water production during injection and withdrawal. The optimized case is expected to achieve an average H2 recovery of 98.8% for 30 operation cycles with moderately low saline water production. These findings provide valuable insights for developing large-scale and cost-effective UHS in saline aquifers.

Uncertainty analysis of geomechanical responses: China’s first offshore carbon capture and storage project

Enping 15–1 project is China’s first Carbon Capture and Storage (CCS) project to store CO2 in the offshore deep saline aquifer formations. Due to the lack of detailed observed data, geomechanical responses are fraught with uncertainty, which can result in unanticipated risks during the implementation of CO2 injection. Thus, the uncertainty analysis of geomechanical responses shows great importance and necessity for CO2 storage projects. To bridge the gap, in this work, a Thermal-Hydraulic-Mechanical-Chemical (THMC) coupling model was built to study the uncertainty of geomechanical responses including surface uplift and rock damage. First, Monte Carlo sampling technology was used to create 616 cases. Then the sensitivity of 13 parameters (including reservoir, cap, and operating parameters) on geological responses was analysed using the Sobol sensitivity analysis method. The results show that 90.10 % of cases in the uncertainty analysis have a maximum surface uplift of less than 8 mm, and 80.84 % of cases have a safety factor higher than 0.5. However, it is the most likely to cause surface uplift over 100 mm and rock failure when the reservoir permeability is 1 mD. Therefore, the local low permeable zone is at more risk of rock damage and geological hazards. In addition, five parameters (i.e., reservoir permeability, reservoir Young’s modulus, initial horizontal/vertical stress ratio, cap cohesion, and well length) have large contributions to the surface uplift. Three parameters (i.e., Reservoir permeability, reservoir cohesion, and initial horizontal/vertical stress ratio) have considerable effects on the reservoir safety factor. Eventually, proxy models using Regression Trees (RTs) were proposed to predict the surface uplift and reservoir safety factor, which is efficient and saves computational resources. This work provides insights and suggestions into the geomechanical responses of CCS project.

CO2 geological storage in subsurface aquifers as a function of brine salinity: A field-scale numerical investigation

Subsurface aquifers demonstrate a broad range of salinities and salt compositions, affecting the physicochemical characteristics of the CO2/brine/rock systems, which in turn, influence the CO2 trapping of the aquifer formation. Available simulation studies generally focus on single NaCl systems and do not adequately account for the variations in salt types. In this study, the impact of salinity and salt type on several key parameters, including wettability, interfacial tension, brine properties, diffusion, and capillary pressure, were considered within the context of underground CO2 storage. We conducted pore network modeling to assess the impact of salinity (i.e., pure water, 1 M (molality), 3 M, and 5 M) and salt type (i.e., NaCl, CaCl2, and MgCl2) on the residual trapping behaviors. Subsequently, these findings were utilized in field-scale simulations to assess the influence of various salinities and salt types on the CO2 trapping capacity in a single salt brine system. The pore network modeling results showed that residual CO2 saturation decreases in higher salinity conditions, with the lowest value in MgCl2 brine system. In field-scale simulations incorporating residual trapping alone, the residual trapping capacity decreases in higher salinity NaCl brine systems. However, in high salinity MgCl2 brine, increased viscosity and density lead to a widespread CO2 plume, leading to an increased residual trapping capacity. This plume spread difference also influences the amount of dissolved CO2 in scenarios considering dissolution trapping alone. When considering both trapping mechanisms, our observations indicate that a decrease in dissolution trapping under high salinity and divalent cations conditions leads to enhanced residual trapping (e.g., ∼51.56% for 5 M MgCl2) - suggesting an interplay or codependency between these two mechanisms. The influences of diffusion and capillary pressure on the CO2 geo-storage trapping capacity are also investigated. Overall, an aquifer containing lower salinity brine composed of monovalent ions exhibits lower residual trapping, greater dissolution trapping, and lower mobile CO2. Especially, the pure water system exhibits the lowest percentage of mobile CO2 (∼13.72%). We also highlight that this impact is not governed by the corresponding wettability shift alone; rather, the physical properties of native brine (i.e., viscosity and density) play a part too. The findings help evaluate the CO2 storage potential of aquifers and thus assist in de-risking large-scale storage projects.

Review on the Impacts of the Samalas Eruption (1257 CE) to the Hydrogeological Conditions of Mataram, Lombok, Indonesia

This paper examines the local impacts of the 1257 CE Samalas eruption in the Mataram plain in relation to the hydrogeological conditions. Data from several previous studies in the Mataram plain is summarized and then reinterpreted. Data collected from new fieldwork is also presented. This review summarizes hydrogeological conditions into several categories, i.e. stratigraphy, aquifer formation, groundwater quality, and evolution. Two coring data were evaluated, which showed that Mataram plain has a relatively thick alluvial layer with a dominant material of sand mixed with pumice from the reworked deposit of the 1257 CE Samalas eruption. The sediment from this eruption formed a freshwater aquifer layer up to ~18 m deep. Using resistivity data, the aquifer layers in the studied area were characterized as unconfined aquifer, aquitard, and semi-unconfined aquifer. Seven water samples show that the groundwater in the studied area is in good condition, which indicates the bicarbonate water type. The results of the analysis show that the impact of the 1257 CE Samalas eruption on the hydrogeology of Mataram is considered a positive impact, i.e. forming an unconfined aquifer containing freshwater that is good for domestic uses.

Features of the formation of natural-technical systems within the injection areas of the Daldyn kimberlite field (Western Yakutia)

Relevance. Primary diamond deposits mined by PJSC ALROSA in Western Yakutia have widespread watering of varying intensity with sub-permafrost and inter-permafrost strong and very strong brines. Currently, the resulting drainage waters are pumped back into the depths of the permafrost, which leads to the formation of natural-technogenic aquifers that require constant control, monitoring and study. Aim. Identification of the features of the formation of natural-technogenic systems within the injection areas of the Daldyn kimberlite field, determination of the volume of permafrost waters involved in this process, as well as their characteristics to confirm the environmental friendliness of the method of handling drainage brines. Methods. Field work consisted of quarterly routine testing of observation and injection wells. Assessment of technogenic influence, as well as subsequent forecasting of the dynamics of changes in cryohydrogeological conditions and hydrodynamic regime, was carried out using modeling methods in Feflow software. An additional method was analytical balance calculation based on the parameter of changing mineralization. Results and conclusions. The interaction of drainage waters with permafrost waters leads to areal changes in mineralization without significant changes in the dominant anions and cations within the studied objects, forming an equilibrium natural-technogenic system in the peripheral parts relative to background temperature conditions. The volume of formed man-made aquifers will exceed 300 million m3. The process of involving cryogenic waters, despite the significant volumes, has a positive impact on the ecological state of the territory, because in the peripheral parts of the resulting aquifers, equilibrium cryohydrogeological conditions are formed, characteristic of natural cryopegs in the region of study.

Development of heat and mass transfer modulus to Feflow code for calculation of brine loaded to permafrost ground

The article discusses the application of FreezeThaw75 module, developed by one of the authors to calculate heat and mass transfer taking into account water–ice and ice–water–water phase transitions. Numerical simulations are compared with the analytical solution and other software codes. The module was tested at one of the injection sites in Daldino-Alakitskii district of Yakutia. FreezeThaw75 module was developed in relation to Feflow v7.4–7.5 model environment. The module was tested on a model of brine injection into frozen rocks. The model simultaneously takes into account the movement of groundwater flow, heat and mass transfer and phase transitions. A feature of the calculations in the developed model is the consideration of large injected volumes of highly mineralized brines.It influences the degradation of permafrost and takes into account the cryohydrogeological conditions of the site. Brines are injected into permafrost rocks with a high absorption capacity especially in areas confined to zones of tectonic disturbances. The developed module can adjust the predicted potential of the operated injection sites. It can also act as an additional element of control over the injection process and the formation of an artificial aquifer in the permafrost rocks.

Solar thermal energy and CO2 storage in saline aquifers for renewable energy space heating

There are a large number of abandoned oil and gas wells and corresponding depleted oil/gas reservoirs (DOGR) throughout the world, which are recognized as one of the best geological formations of saline aquifers for thermal energy storage and CO2 sequestration and however, the lack of innovative technique limits the efficient use of underground storage space. Here a novel scheme of storing solar thermal energy and concomitantly sequestrating CO2 in DOGR for renewable energy heating is proposed, which uses CO2 as thermal energy storage working fluid. The process of thermal energy storage and release as well as CO2 sequestration in DOGR are simulated, and thermal performance and CO2 dissolution in DOGR are analyzed. The results for twenty years of operation show that the thermal recovery efficiency reaches up to 82.93 %, which is 76 % higher than the traditional high temperature aquifer thermal energy storage. Energy storage capacity per heating season, energy storage density per unit volume of underground space and energy efficiency are respectively 57,222.27 GJ, 22,943.01 kJ/m3 and 96.19 %. Furthermore, the dissolved CO2 during thermal energy storage and extraction is 54.76 % larger than that of mere CO2 sequestration due to the repeated expansion and contraction of gas and water interface caused by the periodically injection and extraction of CO2, indicating that energy storage accelerates CO2 sequestration. To sum up, the new scheme is a high value-added technical route for solar thermal energy storage and CO2 sequestration as well as renewable energy heating.

Experimental simulation of H2 coinjection via a high-pressure reactor with natural gas in a low-salinity deep aquifer used for current underground gas storage.

If dihydrogen (H2) becomes a major part of the energy mix, massive storage in underground gas storage (UGS), such as in deep aquifers, will be needed. The development of H2 requires a growing share of H2 in natural gas (and its current infrastructure), which is expected to reach approximately 2% in Europe. The impact of H2 in aquifers is uncertain, mainly because its behavior is site dependent. The main concern is the consequences of its consumption by autochthonous microorganisms, which, in addition to energy loss, could lead to reservoir souring and alter the petrological properties of the aquifer. In this work, the coinjection of 2% H2 in a natural gas blend in a low-salinity deep aquifer was simulated in a three-phase (aquifer rock, formation water, and natural gas/H2 mix) high-pressure reactor for 3 months with autochthonous microorganisms using a protocol described in a previous study. This protocol was improved by the addition of protocol coupling experimental measures and modeling to calculate the pH and redox potential of the reactor. Modeling was performed to better analyze the experimental data. As in previous experiments, sulfate reduction was the first reaction to occur, and sulfate was quickly consumed. Then, formate production, acetogenesis, and methanogenesis occurred. Overall, H2 consumption was mainly caused by methanogenesis. Contrary to previous experiments simulating H2 injection in aquifers of higher salinity using the same protocol, microbial H2 consumption remained limited, probably because of nutrient depletion. Although calcite dissolution and iron sulfide mineral precipitation likely occurred, no notable evolution of the rock phase was observed after the experiment. Overall, our results suggested that H2 can be stable in this aquifer after an initial loss. More generally, aquifers with low salinity and especially low electron acceptor availability should be favored for H2 costorage with natural gas.

Numerical analysis of hydrogen storage in lined rock cavern under high pressure and its implications to hydrogen embrittlement

Underground hydrogen storage could provide buffer capacity to store the excess energy from renewable resources. A lined rock cavern (LRC) is one of the hydrogen geologic storage site options. It offers great flexibility because it does not rely on the existence of salt caverns, aquifer formations or depleted hydrocarbon reservoir fields. However, many important aspects have to be investigated before its full-scale implementation, among them (1) the effect of spatial variation of rock mass properties and (2) hydrogen embrittlement on the steel lining. We present a numerical study on these two aspects by simulating field tests at a pilot LRC project. For the effect of rock heterogeneity, we assign a spatial variation of elastic properties based on the Gaussian covariance model. The results show a good agreement with the field measurements. The spatial correlation length of rock mass elastic properties only has a minor impact on the cavern surface deformation. Regarding hydrogen embrittlement, our simulations predict a significant hydrogen diffusion in the low alloy steel (S355) lining after ∼2 months of operation. The fracture simulations show little fracture propagation even after 10 years of contact with hydrogen gas. However, the product loss may be too high for the low alloy steel (S355). We would recommend the use of stainless steel to inhibit the hydrogen diffusion. We show that advanced numerical models are powerful tools to ensure the safety of hydrogen storage in LRCs.

Control of paleoclimate and paleoweathering on chromium contents in a non-ultramafic aquifer hosting high chromium groundwater.

Cr(VI) is a carcinogen with proven mutagenic and genotoxic effects. The effects of the depositional environment (e.g., paleoweathering, paleoclimate, and paleoredox condition) on Crenrichment in non-ultramafic aquifer solids are unclear. In this study, we presented the sedimentary characteristics of a borehole from a typical non-ultramafic aquifer with high Cr groundwater in Jingbian, central Ordos Basin, China. Chromium was enriched in the K1h sandstone aquifer, especially at depths of 400-500m, with the highest value of mass transport coefficient (τAl,Cr) up to 92.13% and τAl,Fe up to 33.5%. The provenance of aquifer Cr was predominantly intermediate and felsic igneous rocks with a mafic rock mixture. This mafic source was inferred from Cr-rich granodiorite and mafic/ultramafic rocks in the Yinshan (Daqingshan-Wulashan) Block, northern Ordos Basin. The Cr-rich aquifer in K1h was developed due to a moderate chemical index of alteration (CIA) (mean, 56.7) under relatively warm and humid paleoclimate, as evidenced by high CIA-temperature (CIA-Temp) (mean, 6.79°C) and paleoclimatic index values (mean, 0.40). Fe-Mn redox cycling in the oxic to suboxic environments contributed to aquifer Cr accumulation. Using path analysis, we identified that paleoclimate created favorable weathering conditions and enrichment of Fe contributed to the formation of high-Cr aquifers. The study reveals the formation of positive Cr anomalies in non-ultramafic aquifers, which is the potential source of groundwater Cr, and highlights the effects of depositional factors on Cr accumulation during aquifer deposition or early diagenesis. It can provide new insights into the natural processes of high-Cr sediments occurring in non-ultramafic aquifers.

Hydrogeological analysis and remediation strategies for water inrush hazards in highway karst tunnels

Geological hazards, particularly water inrush, pose frequent challenges in tunnel constructions within karst regions. Drawing from the engineering experiences in addressing multiple large-scale water inrush hazards in the Dejiang tunnel, a combined method of field investigation and theoretical analysis was employed for qualitative and quantitative analyses of water inrush mechanisms. The regional geological investigation highlighted the formation of strong and weak aquifers due to alternating weak limestone and mudstone in the synclinal strata, creating favorable conditions for large-scale karst conduit. Atmospheric precipitation water connects karst cavities through groundwater-eroded karst conduit, establishing a recharge system for water inrush hazards. Three empirical formulas are adopted to investigate the influence of rainfall on the tunnel’s actual water inflow. Importantly, it was found that considering only the influence of rainfall or surface water cannot reasonably predict the inflow in this area. The disaster’s primary causes are attributed to the heavy rainfall, karst conduit, underground river, and weak strata, which have contributed to the persistent nature of water inrush events. The principle of “drainage and blockage” was used to address the issue of water inrush. Proposed remediation strategies during construction, including the innovative membrane bag high-pressure grouting, have proved to be effective in addressing the connected karst conduits. The drainage and blockage effects were achieved by installing drainage pipes during the grouting reinforcement process. Finally, the water pressure-resistant structure was employed to enhance the stiffness of the lining. As validated by monitoring data, the measures serve as crucial methods to guarantee the safety of tunnel structures, effectively prevent water inrush and amplify the ecological benefits of water-rich areas.

Hydraulic Conductivity Estimation: Comparison of Empirical Formulas Based on New Laboratory Experiments

Hydraulic conductivity (K) is one of the most important characteristics of soils in terms of groundwater movement and the formation of aquifers. Generally, it indicates the ease of infiltration and penetration of water in the soil. It depends on various factors, including fluid viscosity, pore size, grain size, porosity ratio, mineral grain roughness, and soil saturation level. Each of the empirical formulas used to calculate K includes one or more of the influencing parameters. In this study, pumping tests from an aquifer were performed by using a hydrology apparatus. Laboratory experiments were conducted on six types of soil with different grain sizes, ranging from fine sand to coarse sand, to obtain K. The experimental-based K values were compared with that of empirical formulas. The results demonstrate that Breyer and Hazen (modified) formulas adequately fit the laboratory values. The novelty of the present study is the comparison of the experimental formulas in completely similar conditions of the same sample, such as porosity, viscosity, and grain size, using the pumping test in a laboratory method, and the results show that the Hazen and the Breyer formulas provide the best results. The findings of this work will help in better development of groundwater resources and aquifer studies.

Reduction capacity in the transmissive zones fueled by the embedded low-permeability lenses: Implications for contaminant transformation in heterogeneous aquifers

Redox conditions play a decisive role in regulating contaminant and nutrient transformation in groundwater. Here we quantitatively described and interpreted the temporal and spatial variations of aquifer reduction capacity formation in lens-embedded heterogeneous aquifers in 1-D columns. Experimental results indicated that the aquifer reduction capacity exported from the low-permeability lens permeated into the downstream sandy zones, where it subsequently accumulated and extended. Reactive transport modeling suggested that reduction capacity within the lens preferentially diffused to the transmissive zones around the lens-sand interface, and was then transported via convection to downstream transmissive zones. A low-permeability lens of the same volume, but more elongated in the flow direction, led to less concentrated reduction capacity but extended further downgradient from the lens. The increased flow velocity attenuated the maintenance of aquifer reduction capacity by enhancing mixing and diluting processes in the transmissive zones. The reduction zones formed downstream from the low-permeability lens were hotpots for resisting the oxidative perturbation by O2. This study highlights the important role of low-permeability lenses as large and long-term electron pools for the transmissive zones, and thus providing aquifer reduction capacity for contaminant transformation and remediation in heterogeneous aquifers.

Effects of aquifer size and formation fracture pressure on CO2 geological storage capacity

Introduction: Carbon capture and storage (CCS) is important for achieving net-zero carbon emissions. However, although the current geological storage capacity stands at approximately 3,000 Gt-CO2, the formation pressure increases with CO2 injection, imposing severe constraints on capacity from a geomechanical perspective. This study numerically examined nine cases (combinations of three fracture pressures and three aquifer radius factors) through sensitivity analysis to quantify the effects of these parameters on CO2 injection mass and storage capacity.Methods: The CO2 injection mass was determined as the cumulative CO2 injected until the formation pressure reached a specified fracture pressure. Storage capacity was defined as the amount of CO2 enclosed within the reservoir based on a fill-and-spill analysis encompassing 200 years after the start of injection (2230).Results: Based on the sensitivity analysis, the aquifer radius had a greater impact on the CO2 injection mass and storage capacity than the fracture pressure. A sufficiently high aquifer radius factor can compensate for the capacity limitations imposed by a low fracture pressure. For the lowest fracture pressure (20.95 MPa), considering a safety factor of 0.8, the CO2 injection mass increased approximately 5.5 times, from 3.2 to 17.6 Mt-CO2, depending on the aquifer radius factor ranging from 2 to 7.Discussion: Therefore, geological sites with high aquifer radius factors and low fracture pressures were preferred over those with low aquifer radius factors and high fracture pressures. Nevertheless, when considering space-limited capacity, storage efficiency, defined as the ratio of injected to stored CO2, tends to be higher (approximately 80%) when both parameters are low. The scenario featuring the highest aquifer radius factor and fracture pressure reached an injection mass of 68.9 Mt-CO2. However, the storage efficiency was only 23% due to space constraints. This study provides key insights into two pivotal parameters from pressure- and space-limited perspectives, which must be collectively considered to reliably evaluate CCS projects.

Water Resources, Pollution, Integrated Management and Practices in Nigeria – An Overview

This paper provides a comprehensive overview of Nigeria’s water landscape, focusing on its abundant surface and underground water sources and the agencies responsible for water resources development and management. Findings reveals that the country boasts vast freshwater reserves, encompassing surface and groundwater, intricate river drainage systems, numerous dams, and managed aquifer formations, primarily overseen by River Basin Development Authorities. Despite these resources, Nigeria faces severe pollution challenges, especially in the Niger Delta, resulting from oil-related activities and causing environmental degradation, health crises, and enduring ecosystem consequences. Approximately 13 million barrels of oil spills have adversely impacted coastal wetlands, mangroves, and agricultural lands. Elevated levels of heavy metal pollution, exceeding recommended guidelines, pose significant threats to public health, emphasizing the lasting impact of persistent oil spillage on fishery production and aquatic organisms. River Basin Development Authorities have made substantial contributions, challenges persist in catchment management and the indiscriminate disposal of hazardous substances. The absence of effective environmental policies necessitates urgent, coordinated action from federal and state governments. Nigeria must prioritize integrated water management practices to strike a delicate balance between resource utilization and preservation for the benefit of current and future generations. This manuscript relies on secondary sources, utilizing key search terms such as “water resources in Nigeria,” “water pollution in Nigeria,” “water supply and demand in Nigeria,” “water management in Nigeria,” and “integrated water practices in Nigeria.” Data were sourced from reputable institutions, including the Federal Ministry of Water Resources, The World Bank, United Nations Environmental Protection (UNEP), USAID’s Sustainable Water Partnership, and various scientific publications, ensuring the reliability of the presented data.

Overburden failure and water–sand mixture outburst conditions of weakly consolidated overlying strata in Dananhu No.7 coal mine

This study presents a case of weakly consolidated strata developed in Dananhu No.7 coal mine. Using a combination of numerical simulation, field measurement comparison, and the critical hydraulic gradient criterion, we investigate the overburden failure and the risk possibility of water–sand mixture inrush during excavation. The following are the principal findings: (1) Weakly consolidated rocks have poor physical characteristics, particularly when they are mudded and disintegrated after encountering water, which may become a favorable source of water–sand inrush; (2) The water-conducting zone develops to a height of 160.5 m with a crack-mining ratio of 15.29 times, extending upward to Toutunhe Formation aquifer. The predictions are consistent with measurements in adjacent mines with similar geological conditions; (3) Cracks without larger subsidence are developed at the front edge of the mining direction, and some parallel stepped cracks behind the goaf could be easily observed. Ground subsidence along the goaf center finally displays a symmetrically wide-gentle U shape; (4) The critical hydraulic gradient of Toutunhe Formation aquifer, aquifer above 3# coal seam, and aquifer of 3#–7# coal seam in Xishanyao Formation is 1.314, 1.351, and 1.380, the actual value is 0.692, 2.089, and 7.418 accordingly. It is inferred water–sand mixture outburst will not occur in Toutunhe Formation aquifer, while the potential risk exists in the aquifers of Xishanyao Formation. Through drainage and depressurization projects, a water–sand mixture outburst accident does not occur during excavation. This study reveals the overburden failure characteristics and the initiation mechanism of water–sand inrush in weakly cemented strata, as well as the internal relationship between them, which provides new research ideas for safe operation in other mining areas with similar geological conditions. The research work has certain practical guiding significance.

Multivariate Statistics Applied to the Identification of Compositional Control Parameters for Groundwater

The objective of the present study was to identify the most influent parameters in the composition of groundwater in the municipality of Icapuí, Ceará - Brazil, seeking correlations with the composition of the percolating aquifer formations that can be associated with the sources of these components. For this purpose, multivariate statistical techniques were applied by means of a Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). The PCA allowed a reduction of physicochemical parameters and determined the two components responsible for approximately 86% of total variance in the data for both sampling periods (rainy and dry). The first component is represented by variables that indicate natural rock weathering processes, and the second comprises seasonality and pollution indicators. Samples were also correlated through HCA according to compositional similarities, which were associated with possible natural or human sources.

Underground Gas Storage in Saline Aquifers: Geological Aspects

Energy, gases, and solids in underground sites are stored in mining excavations, natural caverns, salt caverns, and in the pore spaces of rock formations. Aquifer formations are mainly isolated aquifers with significant spreading, permeability, and thickness, possessing highly mineralized non-potable waters. This study discusses the most important aspects that determine the storage of natural gas, hydrogen, or carbon dioxide in deep aquifers. In particular, the selection and characterization of the structure chosen for underground storage, the storage capacity, and the safety of the process are considered. The choice of underground sites is made on the basis of the following factors and criteria: geological, technical, economic, environmental, social, political, or administrative–legal. The geological and dynamic model of the storage site is then drawn based on the characteristics of the structure. Another important factor in choosing a structure for the storage of natural gas, hydrogen, or carbon dioxide is its capacity. In addition to the type and dimensions of the structure and the petrophysical parameters of the reservoir rock, the storage capacity is influenced by the properties of the stored gases and the operating parameters of the storage facility. Underground gas storage is a process fraught with natural and technical hazards. Therefore, the geological integrity of the structure under consideration should be documented and verified. This article also presents an analysis of the location and the basic parameters of gas storage and carbon dioxide storage facilities currently operating in underground aquifers. To date, there have been no successful attempts to store hydrogen under analogous conditions. This is mainly due to the parameters of this gas, which are associated with high requirements for its storage.

Statistical Evaluation of Dugwell Construction and Placement Parameters on Groundwater Contamination in the Sandstone Phreatic Aquiferous Formations in Garoua, North Region Cameroon: Seasonal Variations

Statistical Evaluation of Dugwell Construction and Placement Parameters on Groundwater Contamination in the Sandstone Phreatic Aquiferous Formations in Garoua, North Region Cameroon: Seasonal Variations

THE GUARANI AQUIFER IN SANTA CATARINA

This is a study about the Guarani Aquifer in the state of Santa Catarina. Groundwater is a very important source both for its economic and social value. It is known that drinking water is an essential natural resource for the maintenance of life on the planet, but that it is becoming scarce due to factors such as irregular rains, climatic conditions, combined with population growth and irrational use. Thus, a bibliographic research is carried out in order to deepen the knowledge about the Guarani Aquifer System, its location and its use in that State. This study addresses: water as a precious liquid; groundwater and aquifer formation and more specifically the Guarani Aquifer its characteristics, uses and vulnerability and its connection with the Serra Geral Aquifer System in Santa Catarina. It also points out the importance of the involvement of the countries that are part of the Guarani Aquifer (Brazil, Paraguay, Argentina and Uruguay) in the search for more effective and controlled ways to use these transboundary waters.