Geological Systems Research Articles

Perspective: Microbial hydrogen metabolism in rock-hosted ecosystems

Hydrogen (H2) is among the most common and widely utilized electron donors in microbial metabolism. This is particularly true for microorganisms that inhabit subsurface environments where H2 concentrations can be high due to H2 generation via one or more abiotic and biotic processes, such as serpentinization, radiolysis, cataclasis, and microbial fermentation. A surge in interest in the exploration for and exploitation of geologic (i.e., white and orange) H2 as a clean low carbon fuel therefore necessitates an evaluation of the influence of microorganisms on its flux and potential recovery from subsurface systems. The widespread application of high throughput metagenomic sequencing approaches to rock-hosted ecosystems now makes it possible to readily identify microorganisms that harbor the potential to metabolize H2 and to predict their mode of coupling H2 oxidation with available oxidants using comparative genomic data from natural samples alone. When combined with several recent reports of measured rates of net microbial H2 consumption in rock-hosted ecosystems, such information provides new perspective on the potential for microorganisms to impact the economics of H2 recovery from geologic systems. In this perspective, the different classes of enzymes that microorganisms use to reversibly oxidize H2 to fuel their energy metabolism are introduced and their distribution in several rock-hosted ecosystems is discussed. A compilation of net microbial H2 oxidation activities in rock-hosted ecosystems is also presented to enable estimates of potential H2 loss from natural or stimulated geologic reservoirs during mining activities, with an example provided from the Samail Ophiolite that indicates >90% of geologic H2 produced could be lost to microbial consumption. Finally, avenues to guide future microbial research in environments where geologic H2 mining is planned are discussed.

Geoscience for Cities: Delivering Europe’s Sustainable Urban Future

European Union (EU) policy is clear in its ambition to deliver a sustainable urban future for Europe. In this paper, we consider the role of urban geoscience to help achieve these ambitions. We highlight the relevance of geology to urban subsurface planning and wider EU policy and strategy. Despite the lack of explicit mention of urban underground space in key policy documents, we identify a significant number of priority urban issues for which geological characterisation is a pre-requisite and for which the geological system forms part of the solution, such as mitigation of climate impacts, delivering net zero energy, and implementing nature-based solutions. We reflect on the paradigm shift of urban geoscience as a geological discipline, rooted initially in engineering geology but which has moved towards an interdisciplinary, solution-focused science operating at the inter-section of environmental–social–built systems. In this regard, we highlight cutting-edge urban geoscience research aligned to current urban challenges and note, in particular, the significance of digital technologies to enable 3D urban characterisation, support data-driven decision-making for planning and development, and serve as a means to communicate geology to urban practitioners. The role of the urban geoscientist as an agent of change to enhance integrated science, improve the accessibility of geological issues, and accelerate the translation of national–regional geology to local settings and to urban policy drivers should not be underestimated.

Justification of the approach to searching for and exploring productive objects: a case study of the Krasnoleninsk and Angaro-Lena oil and gas regions

The article provides a rationale for the approach to the search and exploration of local productive zones based on the analysis of geographically distant objects of different geological structures: the Tyumen and Chora formations. The need for a joint study of the problem of localizing oil and gas deposits has been identified by comparing the patterns of location of local productive objects in remote territories that differ in their geological structure. The relevance of the study is determined by the significant degree of depletion of reserves of hydrocarbon deposits, characterized by the simplest development conditions and the need to find an approach to the study of deposits, within which the establishment and description of the patterns of deposit structure cause difficulties. The primary information for the study was drilling data, geophysical well survey results, description of core material, petrophysical survey data, information on testing and well performance dynamics, 2D seismic interpretation materials, as well as published articles. Methods of analysis and comparison were adopted as a basis in order to highlight common features of the distribution of hydrocarbon deposits in the studied areas. In the course of the study, the prerequisites were formed for the development of a comprehensive methodology for studying the structure of hydrocarbon deposits of Tyumen and Chora formations from the perspective of an approach to the exploration of complex objects, implying a joint study of the possibilities of processes described separately by both organic and inorganic hypotheses of oil and gas generation. The need to introduce an approach to geological modeling that takes into account the fractal structure of geological systems is formulated.

4D Neutron Imaging of Solute Transport and Fluid Flow in Sandstone Before and After Mineral Precipitation

AbstractIn many geological systems, the porosity of rock or soil may evolve during mineral precipitation, a process that controls fluid transport properties. Here, we investigate the use of 4D neutron imaging to image flow and transport in Bentheim sandstone core samples before and after in‐situ calcium carbonate precipitation. First, we demonstrate the applicability of neutron imaging to quantify the solute dispersion along the interface between heavy water and a cadmium aqueous solution. Then, we monitor the flow of heavy water within two Bentheim sandstone core samples before and after a step of in‐situ mineral precipitation. The precipitation of calcium carbonate is induced by reactive mixing of two solutions containing CaCl2 and Na2CO3, either by injecting these two fluids one after each other (sequential experiment) or by injecting them in parallel (co‐flow experiment). We use the contrast in neutron attenuation from time‐resolved tomograms to derive three‐dimensional fluid velocity field by using an inversion technique based on the advection‐dispersion equation. Results show mineral precipitation induces a wider distribution of local flow velocities and leads to alterations in the main flow pathways. The flow distribution appears to be independent of the initial distribution in the sequential experiment, while in the co‐flow experiment, we observed that higher initial local fluid velocities tended to increase slightly following precipitation. The outcome of this study contributes to progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface using the promising technique of neutron imaging.

Performance analysis of data-driven and physics-informed machine learning methods for thermal-hydraulic processes in Full-scale Emplacement experiment

This study centers on the critical aspect of thermal management in deep geological repositories, particularly concerning the heat induced by radioactive nuclear waste. It evaluates eight machine learning methods to analyze thermal-hydraulic processes, focusing on their accuracy in predicting temperature and relative humidity, computational efficiency, robustness, and sensitivity to parameters. These methods are applied to data from the Full-scale Emplacement experiment in the Mont Terri underground laboratory. Notably, the Physics-Informed Machine Learning approach incorporates the experiment's heater power output conditions. The results demonstrate the effectiveness of these methods, especially the Physics-Informed Machine Learning model, in simulating complex processes typical of deep geological repository systems. The study highlights the k-Nearest Neighbor model's efficacy due to its proximity-based decision-making and the superior performance of the Physics-Informed model, suggesting its broader applicability. Our findings offer valuable insights for enhancing the design, management, and safety of underground facilities, contributing novel tools for precision and computational efficiency in energy process simulations.

Fluid-mineral Equilibrium Under Nonhydrostatic Stress: Insight From Molecular Dynamics

The interpretation of phase equilibria and reactions in geological materials is based on standard thermodynamics that assumes hydrostatic and homogeneous stress conditions. However, rocks and minerals in the lithosphere can support stress gradients and nonhydrostatic stresses. Currently, there is still not an accepted macroscopic thermodynamic theory to include the effect of nonhydrostatic stress on mineral reactions, and the use of several thermodynamic potentials in stressed geological system remains under debate. In experiments under nonhydrostatic stress, it is often difficult to resolve the direct effect of differential stress on phase equilibria because pressure gradients may be developed. Such gradients can affect the metamorphic equilibria at the local scale. Here, we investigate the direct effect of a homogeneous, nonhydrostatic stress field on the solid-fluid equilibrium using molecular dynamics simulations at non-zero pressure and elevated temperature conditions. Our results show that, for simple single-component systems at constant temperature, the equilibrium fluid pressure of a stressed system is always larger than the value of fluid pressure at hydrostatic stress conditions. The displacement of the equilibrium value of the fluid pressure is about an order of magnitude smaller compared to the level of differential stress in the solid crystal. Thus, phase equilibria can be accurately predicted by taking the fluid pressure as a proxy of the equilibration pressure. On the contrary, the mean stress of the solid can deviate substantially from the pressure of the fluid in stressed systems at thermodynamic equilibrium. This has implications on the use of thermodynamic pressure in geodynamic models since the fluid pressure is a more accurate proxy for predicting the location of metamorphic reactions, while the equilibrium density of the solid has to be determined from its mean stress.

Evaluation method of agricultural environmental geological system state based on optimized particle swarm optimization algorithm

The conventional evaluation methods for the state of agricultural environmental geological system mainly use the support vector regression (SVR) model to process the evaluation samples, which is vulnerable to the influence of the sensitive loss function, resulting in the high difference of the evaluation entropy. Therefore, a new evaluation method for the state of agricultural environmental geological system needs to be designed based on the optimized particle swarm optimization algorithm. That is to say, combining with the evolution process of regional agricultural environmental geology, the accurate state evaluation target is selected, the state evaluation system of agricultural environmental geology system is constructed, and the state evaluation model of agricultural environmental geology system is designed combined with the optimized particle swarm optimization algorithm, so as to complete the state evaluation of geological system. The results demonstrated the suggested methodology assesses the state of an agricultural environmental geological system. Key factors included soil texture (0.254), soil nutrient (0.118), and soil pH (0.256). It showed that the designed evaluation method of agricultural environmental geological system state based on optimized particle swarm optimization algorithm has good evaluation effect, reliability and certain application value, and has made certain contributions to the formulation of reasonable agricultural ecological protection scheme.

Multidisciplinary monitoring of an in-situ remediation test of chlorinated solvents

Pollutions on and within the underground poses risks for groundwater contamination and is a widespread global problem. Common remediation methods based on digging and removal can be expensive and have limitations, while in-situ remediation is an attractive alternative. However, there is a need to develop tools to monitor the effectiveness both in terms of the successful injection of remediation fluids but also the effectiveness of the treatment, i.e., degree of degradation/removal of the pollutants and possible metabolites. This paper presents a methodology for monitoring the changes following an in-situ remediation treatment of a site contaminated with chlorinated solvents. The methodology consists of two different methods, where Direct Current resistivity and time-domain Induced Polarization (DCIP) was used to acquire daily data and geochemical analyses on water samples were collected approximately every three months. The geophysical results provide insights on how the injected fluids are spreading and assist in acquiring a better understanding of the geological and hydrogeological system. On the other hand, the geochemical sampling enhances our knowledge about the hydrochemistry of the system and the concentration of the pollutants. Our research highlights the challenges of monitoring in-situ bioremediation experiments in complex environments and in cases where pollutants are situated in low hydraulic conductivity formations. The joint interpretation of the data shows the importance of an interdisciplinary approach to understand complex systems.

Addressing quantum’s “fine print” with efficient state preparation and information extraction for quantum algorithms and geologic fracture networks

Quantum algorithms provide an exponential speedup for solving certain classes of linear systems, including those that model geologic fracture flow. However, this revolutionary gain in efficiency does not come without difficulty. Quantum algorithms require that problems satisfy not only algorithm-specific constraints, but also application-specific ones. Otherwise, the quantum advantage carefully attained through algorithmic ingenuity can be entirely negated. Previous work addressing quantum algorithms for geologic fracture flow has illustrated core algorithmic approaches while incrementally removing assumptions. This work addresses two further requirements for solving geologic fracture flow systems with quantum algorithms: efficient system state preparation and efficient information extraction. Our approach to addressing each is consistent with an overall exponential speed-up.

MODPATH-RW: A Random Walk Particle Tracking Code for Solute Transport in Heterogeneous Aquifers.

Random walk particle tracking (RWPT) is a discrete particle method that offers several advantages for simulating solute transport in heterogeneous geological systems. The formulation is a discrete solution to the advection-dispersion equation, yielding results that are not influenced by grid-related numerical dispersion. Numerical dispersion impacts the magnitude of concentrations and gradients obtained from classical grid-based solvers in advection-dominated problems with relatively large grid Péclet numbers. Accurate predictions of concentrations are crucial for reactive transport studies, and RWPT has been recognized for its potential benefits for this kind of application. This highlights the need for a solute transport program based on RWPT that can be seamlessly integrated with industry-standard groundwater flow models. This article presents a solute transport code that implements the RWPT method by extension of the particle tracking model MODPATH, which provides the base infrastructure for interacting with several variants of MODFLOW groundwater flow models. The implementation is achieved by developing a method for determining the exact cell-exit position of a particle undergoing simultaneous advection and dispersion, allowing for the sequential transfer of particles between flow model cells. The program is compatible with rectangular unstructured grids and integrates a module for the smoothed reconstruction of concentrations. In addition, the program incorporates parallel processing of particles using the OpenMP library, enabling faster simulations of solute transport in heterogeneous systems. Numerical test cases involving different applications in hydrogeology benchmark the RWPT model with well-known transport codes.

Dynamic behavior of sorption of europium onto biotite flakes under the condition of saline groundwater

This study discussed the interaction between Eu and biotite in flakes under the coexistence of Na ions, considering saline groundwater. The sorption experiments were conducted by mixing an Eu solution with Na or K ions and biotite flakes at pH 5. Resultantly, the sorption of Eu gradually increased because of the diffusion into the layered structure of biotite flakes. Thereafter, the sorption amount of Eu with Na ions was less than that without Na ions, and Eu was hardly sorbed with K ions. Additionally, the apparent diffusion coefficients were estimated to be in the order of 10−13 m2/s based on a two-dimensional diffusion model. These values were lower than the effective diffusion coefficients in plutonic rock, which are employed to assess the performance of geological disposal systems. This indicates that the sorption of Eu in plutonic rock is restricted by the diffusion process in biotite flakes.Graphical abstract

Phase diagram and permeability evolution for dissolving vertical fractures in a gravity field

Rock fractures always provide the main flow pathways in geological systems. When exposed to reactive flow, mineral dissolution causes different dissolution regimes and significantly impacts permeability change. Previous studies have examined dissolution regimes and permeability evolution in horizontal geometry, but dissolution dynamics and permeability changes of vertical fractures in a gravity field remain unexplored. Here, we conduct flow-dissolution experiments combined with a pore-scale modeling approach to investigate regime transition and permeability evolution in vertical fractures. We validate the modeling approach using experimental results and illustrate the importance of gravitational effects in dissolving vertical fractures. Our 3D numerical simulations reveal the regime transition, represented by a critical Richardson number Ri, from the forced convection regime to the buoyancy-driven convection regime as the importance of gravity increases. In the buoyancy-driven regime, gravitational effects promote the development of localized dissolution/flow channels. However, gravitational effects become negligible in the forced convection regime where wormholes and uniform patterns can be separated by the critical Pe number. Using the critical Ri and Pe numbers, we establish a phase diagram of dissolution regimes for vertical fractures in a gravity field, exhibiting good agreement with experiments. By correlating this phase diagram with permeability-aperture curves, we directly estimate the power law exponent of permeability evolution for each dissolution regime. This approach extends the classic phase diagram of dissolution regimes to consider gravitational effects on vertical fractures and provides a guide to directly estimate the parameters for permeability evolution, which is essential in reactive-transport modeling at the field scale.

Gas equilibrium membrane inlet mass spectrometry (GE-MIMS) for water at high pressure

Abstract. Gas species are widely used as natural or artificial tracers to study fluid dynamics in environmental and geological systems. The recently developed gas equilibrium membrane inlet mass spectrometry (GE-MIMS) method is most useful for accurate and autonomous on-site quantification of dissolved gases in aquatic systems. GE-MIMS works by pumping water through a gas equilibrator module containing a gas headspace, which is separated from the water by a gas-permeable membrane. The partial pressures of the gas species in the headspace equilibrate with the gas concentrations in the water according to Henry's Law and are quantified with a mass spectrometer optimized for low gas consumption (miniRUEDI or similar). However, the fragile membrane structures of the commonly used equilibrator modules break down at water pressures ≳3 bar. These modules are therefore not suitable for use in deep geological systems or other environments with high water pressures. To this end, the SysMoG® MD membrane module (Solexperts AG, Switzerland; “SOMM”) was developed to withstand water pressures of up to 100 bar. Compared to the conventionally used GE-MIMS equilibrator modules, the mechanically robust construction of the SOMM module entails slow and potentially incomplete gas–water equilibration. We tested the gas equilibration efficiency of the SOMM and developed an adapted protocol that allows correct operation of the SOMM for GE-MIMS analysis at high water pressures. This adapted SOMM GE-MIMS technique exhibits a very low gas consumption from the SOMM to maintain the gas–water equilibrium according to Henry's Law and provides the same analytical accuracy and precision as the conventional GE-MIMS technique. The analytical potential of the adapted SOMM GE-MIMS technique was demonstrated in a high-pressure fluid migration experiment in an underground rock laboratory. The new technique overcomes the pressure limitations of conventional gas equilibrators and thereby opens new opportunities for efficient and autonomous on-site quantification of dissolved gases in high-pressure environments, such as in research and monitoring of underground storage of CO2 and waste deposits or in the exploration of natural resources.

Properly shortening design time scale of medium-deep borehole heat exchanger for high building heating performances with high computational efficiency

The medium-deep borehole heat exchanger (MDBHE) is a clean solution for building heating with renewable geothermal energy. The long-term performance evaluation with the design time scale same as the life span of the MDBHE is generally adopted by the MDBHE design for high heating performances. However, the long-term performance evaluation largely increases the computational load of the MDBHE design, resulting in practical inconvenience. This study proposes the idea that properly shortening the design time scale could maintain the information of the long-term performance evaluation for the MDBHE design with high heating performances while reducing the computational load. The idea is verified by the MDBHE design for building heating in the severe cold zone of China. The multiple design parameters of the MDBHE are simultaneously optimized considering climate change. The results show that under different geological conditions, economic conditions, and system safety requirements, compared with the life span of the MDBHE of 30–50 years, the design time scale properly shortened to 10 years achieves similar high heating performances regarding the energy consumption, cost, and system safety, and reduces the computational load by 66.1 %–79.3 %. This study contributes to high computational-efficient and high-performance design of the MDBHE for building heating.

Mass-Balance-Consistent Geological Stock Accounting: A New Approach toward Sustainable Management of Mineral Resources.

Global resource extraction raises concerns about environmental pressures and the security of mineral supply. Strategies to address these concerns depend on robust information on natural resource endowments, and on suitable methods to monitor and model their changes over time. However, current mineral resources and reserves reporting and accounting workflows are poorly suited for addressing mineral depletion or answering questions about the long-term sustainable supply. Our integrative review finds that the lack of a robust theoretical concept and framework for mass-balance (MB)-consistent geological stock accounting hinders systematic industry-government data integration, resource governance, and strategy development. We evaluate the existing literature on geological stock accounting, identify shortcomings of current monitoring of mine production, and outline a conceptual framework for MB-consistent system integration based on material flow analysis (MFA). Our synthesis shows that recent developments in Earth observation, geoinformation management, and sustainability reporting act as catalysts that make MB-consistent geological stock accounting increasingly feasible. We propose first steps for its implementation and anticipate that our perspective as "resource realists" will facilitate the integration of geological and anthropogenic material systems, help secure future mineral supply, and support the global sustainability transition.

Re-evaluation of CO<sub>2</sub> storage capacity of depleted fractured-vuggy carbonate reservoir

<p>Confronting the dual crises of energy supply-demand imbalances and climate change, carbon neutrality emerges as a vital strategy for China in mitigating resource and environmental constraints, while fostering technological advancement and sustainable growth. In the context of extensive hydrocarbon exploitation, the CO<sub>2</sub> storage capacity within depleted oil fields could be significantly underestimated in comparison to the prevalent practice of saline aquifer sequestration. In this study, we employ both theoretical and computational models to investigate the temporal (from microseconds to millennia) and spatial (spanning pore, Darcy, and hybrid scales) dynamics of CO<sub>2</sub> trapping mechanisms in post-depletion carbonate reservoir with fractured-vuggy systems. The multiscale storage efficiency factor is obtained from simulation results and substituted into the existing analytical models for calculating CO<sub>2</sub> storage volume in field cases, reappraising the carbon sequestration potential of fracture-vuggy carbonate. Drawing from comparative results, we discern that depleted carbonate can dissolve and mineralize more CO<sub>2</sub> than saline layer, despite the storage volume can be considerably less. The annual storage capacity per well of two geological systems are comparable. Under unfavorable geological conditions, the minimum unit storage capacity of carbonate reservoir exceeds that of saline aquifer. The study's discoveries offer fresh perspectives on reliable and efficient CO<sub>2</sub> geological storage, contributing to the reduction of atmospheric carbon emissions and advancing the utilization of underground resources and global energy transformation.</p>

A two-step chromatographic purification method for Ni for its isotopic analysis by MC-ICP-MS

The new purification procedure for Ni isotope analysis presented here is both economical and time-efficient, improving the ability for further investigation of Ni isotope geochemistry in various geological and environmental systems.

Rapid determination of V isotopes with MC-ICP-MS: new developments in sample purification

The new purification procedure for V isotope analysis presented in this work is both economical and time-efficient, improving the ability for further investigation of V isotope geochemistry in various geological and environmental systems.

Sustainable development of geological resources: the Characteristics of Red Karst Landscape and Tourism Development in Tongren, Guizhou

<abstract> <p>China is rich in karst resources and famous for its karst landscape. As a part of karst, the popularity of red karst is obviously low and has received little attention; moreover, the related scientific research and tourism development are relatively immature. Therefore, this paper takes the red karst in Tongren, Guizhou as the research object, analyzes the characteristics and causes of the red karst, comprehensively evaluates its landscape value, and puts forward development strategies and protection suggestions. Through the above research, the following three research results are obtained. (1) On the basis of a field investigation and a literature review, the geographical situation, background, and landscape characteristics of the red karst landform and its surrounding areas in Tongren City were investigated in detail. It forms isolated peaks, rock walls, protruding rocks, stone pillars, and other forms. The most prominent features of the red karst landscape in Tongren City are that the color is red and white, and the shape is concave and convex in order. (2) Geochemical test and structural data collection and analyses of the collected samples were performed. The obtain concave layer rock is dolomitic limestone, and that convex lay rock is argillaceous dolomitic limestone. Because the convex layer rock sample is high in silicon element content, the convex layer rock sample is not easy to be weathered, is rich in clay mineral, and is not easy to be corrode; the convex layer rock sample gradually protrudes with the passage of time to form an uneven shape. The red karst landform is developed in either the rock stratum or tectonic zone with moderate tectonic deformation intensity. First, the formation of a single-layer honeycomb morphology requires that the rock stratum is subjected to a sufficient horizontal compressive stress at a certain burial depth. Second, it is necessary to widely exist in areas with relatively gentle rock formation occurrence; too strong of a structural deformation will make the rock formation occurrence steep, which is not conducive to the occurrence of differential dissolution between adjacent strata. (3) Through the construction of an evaluation index system, the red karst in Tongren City is evaluated, and it is concluded that the geological heritage value is high, and the development and utilization conditions are weak. The conclusion of this article is a supplement to the geological and geomorphological system characteristics of southern karst. From the perspective of world natural heritage, the study enriches the academic evidence of red karst and enables its exemplary role to be well played. From the perspective of the tourism development value, more people should be made aware of the diverse types of karst landforms, which provide experience and suggestions for the value of landforms, tourism resources, and tourism development in similar areas.</p> </abstract>

Mountain Steppes And Upland Xerophytes ― As an Element of Landscape Diversity in The Eastern Central Caucasus

Long-term observations of dynamic processes in the landscapes of intra-mountain basins on the territory of North Ossetia-Alania have shown that changes in them can be both progressive and regressive, which is associated with natural external factors that are imposed by anthropogenic influences. For a long time, arid landscapes in the eastern part of the Central Caucasus (within the North Ossetia-Alania) were intensively exploited as pasture (less often arable) land and underwent significant anthropogenic degradation. The situation began to change in the last decade of the 20th century due to the general crisis state of the country's economy, the collapse of collective farms and state farms, a sharp reduction in the number of cattle and small cattle. The removal of agricultural load on mountain landscapes led to the gradual restoration of their natural state. Currently, there is a trend towards a change in traditional nature management to recreational, and the problem of protecting natural geological systems is again emerging from recreational impact. The most vulnerable are arid dry-steppe and upland xerophytic formations, occupying a little more than 6 thousand hectares (8.4%) of the area of intracity basins, but are habitats included in the Red Book of North Ossetia-Alania, endemic and rare vascular plants (more than 20 species) and invertebrate animals (about 60 species).