Complex Geology Research Articles

Generating extremely low-dimensional representation of subsurface earth models using vector quantization and deep Autoencoder

Geological model compression is crucial for making large and complex models more manageable. By reducing the size of these models, compression techniques enable efficient storage, enhance computational efficiency, making it feasible to perform complex simulations and analyses in a shorter time. This is particularly important in applications such as reservoir management, groundwater hydrology, and geological carbon storage, where large geomodels with millions of grid cells are common. This study presents a comprehensive overview of previous work on geomodel compression and introduces several autoencoder-based deep-learning architectures for low-dimensional representation of modified Brugge-field geomodels. The compression and reconstruction efficiencies of autoencoders (AE), variational autoencoders (VAE), vector-quantized variational autoencoders (VQ-VAE), and vector-quantized variational autoencoders 2 (VQ-VAE2) were tested and compared to the traditional singular value decomposition (SVD) method. Results show that the deep-learning-based approaches significantly outperform SVD, achieving higher compression ratios while maintaining or even exceeding the reconstruction quality. Notably, VQ-VAE2 achieves the highest compression ratio of 667:1 with a structural similarity index metric (SSIM) of 0.92, far surpassing the 10:1 compression ratio of SVD with a SSIM of 0.9. The result of this work shows that, unlike traditional approaches, which often rely on linear transformations and can struggle to capture complex, non-linear relationships within geological data, VQ-VAE's use of vector quantization helps in preserving high-resolution details and enhances the model's ability to generalize across varying geological complexities.

Influencing Factors Analysis in Railway Engineering Technological Innovation under Complex and Difficult Areas: A System Dynamics Approach

The geological complexity, environmental sensitivity, and ecological fragility inherent in complex and difficult areas (CDAs) present new opportunities and challenges for technological innovation in railway engineering development in China. At the current stage in China, the process of technological innovation in railway engineering within CDAs still faces a series of pressing issues that need addressing. The paper identifies and determines 22 influencing factors for technological innovation in railway engineering within CDAs across five dimensions. Subsequently, a technological innovation model for railway engineering in such areas is constructed based on system dynamics (SD), which is followed by simulation and sensitivity analysis to identify the key influencing factors. The results indicate that key influencing factors for technological innovation in railway engineering within CDAs include technological innovation capability, the adaptability of technology to the environment, R&D funding investment, technological product requirements, technological innovation incentive mechanisms, and the level of technological development. The importance ranking of each dimension is as follows: technological factors > technical factors > management factors > resource factors > environmental factors. The paper provides new insights for promoting technological innovation and management development in complex and challenging railway engineering projects. It offers a fresh perspective to enhance the technological innovation efficiency of railway projects in complex and challenging areas.

Seeking sand origins on Mars: Towards testing the volcaniclastic hypothesis globally

Aeolian processes are a dominant cause of Martian surface modification today. Sand is pervasive, even while the contemporary transport of sand at high-threshold wind speeds implies sand breakdown. Thus, detecting the origin(s) of sand on Mars is an important open question in Mars science. One long-standing hypothesis for an origin of Martian sand is as volcaniclastic sediments, either epiclastic (from the breakdown of effusive volcanic rock) or pyroclastic (from explosive sedimentation). Recent analyses identified the most likely pyroclastic unit on Mars, the Medusae Fossae Formation (MFF) – mapped as the Hesperian and Amazonian-Hesperian transitional units (Tanaka et al., 2014) – as an origin of Martian sand, a genesis consistent with inferences from other work. On these bases, we continued in this work to test for a volcaniclastic origin of Martian sand elsewhere on Mars. We inspected the seven units from the global geologic map of Mars interpreted as possibly/partially volcaniclastic and six geographic terrains ascribed as likely volcanogenic in a more recent analysis. Of these units and geographic terrains, potential sand sources (PSSs) were detected only within two locales: 1) the remaining (central and eastern) extent of the MFF, and 2) Arabia Terra. Arabia Terra shows more numerous PSS, commonly characterized as having proximal dune fields. The explosive volcanic history of the region points towards a pyroclastic origin, though the geologic complexity of the region suggests complexity in the provenance of Arabia Terra PSSs. In contrast to PSS identifications in the western MFF, PSSs in the central and eastern MFF were clustered along the contact of the MFF with lava plains, indicating a potential epiclastic sand origin. Thus, these results indicate both pyroclastic and potentially epiclastic origins for sand on Mars. However, these sand origins as detected by this work are confined to limited locales and (for the MFF) in the amount of sand generated. To further evaluate the amount of sand production in these two study regions from volcanogenic processes, spectroscopic analysis of PSSs in comparison with sand deposits would be a means to test first whether the PSSs were indeed generating sand and secondly if that sand were of volcanic origin. Potential sand flux modeling would be a means to establish the source location(s) of the sand. The origin(s) of the pervasive sand on Mars remain(s) to be better understood, for which the work presented here provides a foundation.

Hydrological response of the largest inland tectonic basin in Japan

The Itoigawa-Shizuoka tectonic line formed the largest inland tectonic basin in Japan. Taking advantage of the characteristics of the large tectonic basin, this study aims to clarify the hydrological response related to groundwater recharge and discharge in this area from field measurements such as monthly spring discharge measurements in the spring belt, infiltration measurements of irrigation recharge in rice paddy fields and analysis of stable isotopic ratios of oxygen and hydrogen. Volumetric water flow measurements in the tectonic basin demonstrate that the hydrological response function (HRF) is expressed as a linear equation. Despite the complex topography and geology of the mountain catchment and artificial recharge within the basin, this HRF is maintained, except for forced artificial irrigation in August when the natural water supply is significantly reduced, and except in March and April when snowmelt flows into the river. This study clarifies that monthly fluctuations in total groundwater flow within a basin can be estimated by applying HRF to monitoring data of total surface flow at the farthest downstream. The field measurements demonstrate that the rainfall in the mountain catchment area and artificial irrigation recharge in the basin greatly influence the fluctuation of groundwater flow rate, especially on the fluctuation of the spring water in the spring belt. Field data inferred that the frequent depletion of the springs in the inland tectonic basin, where all groundwater emerges at the most downstream, depends on the rapid decline in annual rainfall in mountain catchment areas. These observations suggest that the total groundwater resource in this region was affected not only by reduced irrigation recharge due to the historical paddy acreage reduction program implemented in Japan from 1971 to 2018, and by excessive groundwater extraction, but also by rapid decline in annual rainfall in mountain catchments that occurs non-periodically.

Relatively stable pressure effects and time-increasing thermal contraction control Heber geothermal field deformation

Due to geological complexities and observational gaps, it is challenging to identify the governing physical processes of geothermal field deformation including ground subsidence and earthquakes. In the west and east regions of the Heber Geothermal Field (HGF), decade-long subsidence was occurring despite injection of heat-depleted brines, along with transient reversals between uplift and subsidence. These observed phenomena contradict current knowledge that injection leads to surface uplift. Here we show that high-yield production wells at the HGF center siphon fluid from surrounding regions, which can cause subsidence at low-rate injection locations. Moreover, the thermal contraction effect by cooling increases with time and eventually overwhelms the pressure effects of pressure fluctuation and poroelastic responses, which keep relatively stable during geothermal operations. The observed subsidence anomalies result from the siphoning effect and thermal contraction. We further demonstrate that thermal contraction dominates long-term trends of surface displacement and seismicity growth, while pressure effects drive near-instantaneous changes.

Chaotic behavior of geophysical logs for stratigraphic hiatuses: A case study from Upper Assam Shelf, India

We propose a novel fractal analysis-assisted approach for stratigraphic characterization to understand the in-situ subsurface geology of hydrocarbon reservoirs. By employing correlation dimension and multifractal detrended fluctuation analysis, we quantify the self-similarity and long-range dependencies in the geophysical logs, reflecting the unique sedimentation processes inherent in the stratigraphic formations of the Bhogpara oil field in the Upper Assam basin. The fractal properties of the logs associated with various stratigraphic units are used to establish a fractal-based stratigraphic signature. The hierarchy of the studied formations, based on the correlation dimension ranging from 1.98 to 1.13, is follows as: Girujan > Tipam > Barail > Kopili > Prang > Narpuh > Lakadong-Therria. Furthermore, the spectrum width values, was found to range from 0.70 to 2.04, reflecting the spatial correlation, geological complexity, and heterogeneity inherent in each formation as: Kopili > Prang > Narpuh > Barail > Girujan > Tipam > Lakadong-Therria. This method identifies common fractal patterns between wellbores and aids in determining the spatial continuity of stratigraphic units. Our approach effectively detects lateral variations in subsurface formations, linking well log fractality with depositional patterns through various transitional environments, such as lacustrine to shallow marine to fluvial, in presence of different fluids. The petroliferous formation exhibits lowest fractal dimension and weak multifractality. The research utilizes fractal analysis to improve stratigraphic correlation, enhancing subsurface characterization and reservoir delineation, particularly in complex geological environments, and enhancing reliability.

The Geomechanics of the Dangkhar Landslide, Himachal Pradesh, India

The Dangkhar Landslide is an extremely large landslide located in the Spiti Valley of Himachal Pradesh, India. The landslide is situated in a remote high mountain desert within the Tethys Himalaya at elevations between 3400 m and 5600 m. It is amongst the five largest continental landslides on earth, covering an area of approximately 54 km2 and having an estimated volume of 15–20 km3. Geomechanical evaluations based on the block theory indicate that the Dangkhar Landslide formed as a result of unfavorable combinations of structural geological features and complex surface morphology. A massive kinematically removable block is created by a regional synclinal flexure that is crosscut and kinematically liberated by bounding side valleys. Three-dimensional block kinematics are necessary to permit the release of the giant block and its sliding along the synclinal flexure. Pseudostatic slope stability sensitivity analyses incorporating estimates of site seismicity and shear strength parameters suggest that earthquake shaking could have triggered instability if the static factor of safety was less than or in the range of about 1.5–1.9. Considering the glacial history of the region, ice debuttressing represents an additional potential triggering mechanism.

Unraveling the role of dextral faults in the formation of pull-apart basin structures and their implications on the genesis of ophiolites and pluto-volcanics

Rhombic structures have been observed in the Qom-Zefreh-Nayin-Dehsheir-Baft region, specifically along the direction of the dextral faults, which have caused significant changes in strike length. This study investigates the geological features and fault interactions in the region through the examination of aerial images, fault-lithology correlations, petrology, crustal thickness, and seismic studies. The analysis of aerial photos and geological correlations revealed the presence of ophiolites and pluto-volcanics associated with faults and rhombic structures. By conducting field geology and combining various geological studies, a pull-apart basin was identified in the area, contributing to the formation of three rhombic structures. This basin played a crucial role in the genesis of the region’s ophiolites and pluto-volcanics. The research suggests that the initial tensional stress leading to the pull-apart basin was caused by the right step of a dextral fault within the Urumieh-Dokhtar magmatic arc. This fault formation occurred due to the oblique Arabian subduction towards the Iranian plateau. During the Zagros orogeny, the stretched area persisted, leading to the formation of oceanic crust in this location. The subduction angle changes from subduction to super-subduction, resulting in the classification of the region into two types: C and E genes. Different types of magma, including alkaline, subalkaline, shoshonite, calcalkaline, and adakitic, were identified in this region. The study highlights the significance of tholeiitic arcs, abyssal features, crust thickness, and seismicity in understanding oblique diagonal subduction models and tensional pull-apart basins, which are crucial in the transition from subduction to super-subduction. This research offers valuable insights into the geological complexities of the region and opens up opportunities for further exploration of similar models.

Review: Andesitic aquifers—hydrogeological conceptual models and insights relevant to applied hydrogeology

Research on the hydrogeology of andesitic volcanic aquifers in subduction areas is reviewed. Andesitic aquifers are of high interest in volcanic arc islands and subduction zones, where they constitute a strategic water resource. This review gathers a compilation of worldwide results and case studies to propose a generic hydrogeological conceptual model (GHCM). It is based on the geological conceptual model splitting the volcanic edifice, from upstream to downstream, into central, proximal, medial and distal zones. In this geological structure, the GHCM identifies where the main aquifer types (fractured lava, pyroclastic flows, and the volcano-sedimentary basins downstream) and the typical aquitards (lahars, fine pyroclastic falls and surges, indurated pyroclastic flow, and weathered rocks) are structured and organized. To integrate the evolution of volcanoes and some specific volcanic activities, a specific GHCM for old andesitic volcanoes or andesitic shield volcanoes is detailed. The paper also describes how the GHCM results are of use to hydrogeologists in terms of scale (from the lithological units to the regional scale), to effectively site water wells, and to sustainably manage groundwater resources in such aquifers. Among these various scales, the volcanic “flank continuum” is presented as the most adapted to support groundwater resources management. Several ways to improve this GHCM are suggested, notably to better consider the geological complexity of these aquifers.

Groundwater recharge sources and mechanisms in the Ethiopian central Afar rift: Insights from isotopic and hydrogeochemical tracers.

Groundwater flow and recharge mechanisms in the central Afar rift and the associated western marginal grabens and Northwestern Plateau (NWP) are poorly understood because of the complex geology and spatial heterogeneity in the aquifer systems. The major aquifers in the region include the Oligocene and Pliocene to recent volcanics and recent alluvio-lacustrine sediments. We employed hydrogeochemical, stable isotopes of water (18O and 2H), and geological structures insights to identify groundwater recharge sources and mechanisms, aiming to develop a representative conceptual groundwater flow model. Water samples from groundwater and surface water were collected based on lithological/aquifer variation and geomorphological setup for isotope and hydrochemical analysis. Findings reveal distinct isotopic differences between the deep (>350 m) and shallow groundwater systems of the Afar rift, with deep systems showing relative isotopic depletion, indicating varying recharge sources. The deep groundwater exhibited a similar isotopic signature to that of the marginal grabens and NWP. The distribution of major ion chemistry and electric conductivity (EC) of groundwaters from the western plateau to the Afar rift show significant spatial variability. However, in some corridors of western parts of the rift, there is a clear geochemical evolution along the flow paths inferring groundwater flow continuity between aquifers. The results revealed the existence of preferential deep groundwater recharge from the NWP through the highly fractured linking zones, interacting fault zones in between the marginal grabens, to the deeper volcanic aquifers of the central Afar rift. The proposed groundwater flow model of this study illustrates the deep groundwater flow from the NWP to the Afar rift is primarily directed by the orientations of the faulted marginal grabens and the highly fractured interacting zones. This model is pivotal for understanding groundwater dynamics in similar continental rift environments, offering insights for effective groundwater management.

Rapid profiling rock mass quality underneath tunnel face for Sichuan-Xizang Railway

The Sichuan-Xizang Railway is a global challenge, surpassing other known railway projects in terms of geological and topographical complexity. This paper presents an approach for rapidly profiling rock mass quality underneath tunnel face for the ongoing construction of the Sichuan-Xizang Railway. It adopts the time-series method and carries out the quantitative analysis of the rock mass quality using the depth-series measurement-while-drilling (MWD) data associated with drilling of blastholes. A tunnel face with 15 blastholes is examined for illustration. The results include identification of the boundary of homogeneous geomaterial by plotting the blasthole depth against the net drilling time, as well as quantification of rock mass quality through the recalculation of the new specific energy. The new specific energy profile is compared and highly consistent with laboratory test, manual logging and tunnel seismic prediction results. This consistency can enhance the blasthole pattern design and facilitate the dynamic determination of charge placement and amount. This paper highlights the importance of digital monitoring during blasthole drilling for rapidly profiling rock mass quality underneath and ahead of tunnel face. It upgrades the MWD technique for rapid profiling rock mass quality in drilling and blasting tunnels.

Physics‐reliable frugal local uncertainty analysis for full waveform inversion

AbstractFull waveform inversion stands at the forefront of seismic imaging technologies, pivotal in retrieving high‐resolution subsurface velocity models. Its application is especially profound when imaging complex geologies such as salt bodies, which are regions notoriously challenging, yet essential given their hydrocarbon potential. However, with the power of full waveform inversion comes the intrinsic challenge of estimating the associated uncertainties. Such uncertainties are crucial in understanding the reliability of subsurface models, particularly in terrains like subsalt regions. Addressing this, we advocate for a nuanced approach employing the Stein variational gradient descent algorithm. Through a judicious use of a limited number of velocity model particles and the integration of random field‐based perturbations, our methodology provides a local representation of the uncertainties inherent in full waveform inversion. Our evaluations, based on the Marmousi model, showcase the robustness of the proposed technique. Yet, it is our exploration into salt‐intensive terrains, leveraging data from the Sigsbee 2A synthetic model and the Gulf of Mexico, that emphasizes the method's versatility. Findings indicate pronounced uncertainties along salt boundaries and in the deeper subsalt sediments, contrasting the minimal uncertainties in non‐salt terrains. However, anomalies like salt canyons present unique challenges, potentially due to the interplay of multi‐scattering effects. Emphasizing the scalability and cost‐effectiveness of this approach, we highlight its potential for large‐scale industrial applications in full waveform inversion, while also underscoring the necessity for prudence when integrating these uncertainty insights into subsequent seismic‐driven geological and reservoir modelling.

Tomographic imaging of South Rewa basin, Central India: Implications of Gondwana rifting and Late Cretaceous volcanism

We have imaged thick (3.0–5.0 km) sub-trappean Gondwana sediments deposited in a typical rift-environment of the south Rewa basin in Central India masked by the Deccan basalts. The basalts intrude through the basin forming several dykes, sills, and other intrusions along with large-scale undulations of the basement showing complex geology and tectonic settings due to Late Cretaceous volcanism (∼65 Ma). To delineate complex subsurface geological structures and understand the tectonic settings, we use long-offset seismic reflection data along the N-S trending 127 km Kuvari-Shahdol profile of the basin. The conventional stack and pre-stack time migration techniques fail to image the complex subsurface structures dominated by steeply dipping faults. The steeply dipping faults with small-scale structures are influenced by strong lateral and vertical velocity variations that cause problems in imaging the basin. Hence, a robust tomographic inversion with pre-stack depth migration technique is adopted to image fine-scale subtle subsurface geological structures with smooth velocity variations. The tomographic velocity model and pre-stack depth migration seismic image could decipher basaltic trap thickness, numerous dyke intrusions, alternate horsts and grabens with deposition of thick hydrocarbon-bearing sub-trappean Gondwana rocks along with the basement configuration. The deep basinal faults with highly distorted basement structures represent the intense tectonic activity of this Gondwana rift-basin. The deep-seated hydrocarbon reservoir is discovered with an excellent trapping mechanism forming both pre-rift and syn-rift settings of the rift-basin. The seismic image is further constrained and corroborated by the inversion of residual Bouguer gravity anomaly data to obtain corresponding density model derived from tomographic velocity model. The large basement faults, horsts and grabens, several intrusives like dyke, sill, laccolith, and thick sub-trappean Gondwana formations with Deccan trap cover indicate complex geology and tectonic settings of south Rewa basin forming the Late Cretaceous Volcanic Province of India.

Surrogate numerical prediction method of TBM position via FEM simulation and machine learning

The position of the tunnel boring machine (TBM) during tunnel construction is critical and must be precisely controlled. Owing to the geological uncertainty and complexity of the interaction between the ground and the TBM, controlling the position of the TBM is challenging. Hence, a surrogate numerical method is proposed to predict the position of the TBM using the finite element method (FEM) and machine learning method. First, a refined three-dimensional FEM model was established. Different values of the property parameters of the ground and the thrust force of the TBM were input into the FEM model, generating a database that includes 1000 cases. Subsequently, the database is used to train a gradient boosting regression (GBR) model. The GBR model learns from the database and establishes the relationship between the construction parameters, ground parameters, and TBM position as a surrogate model. The surrogate model exhibited high accuracy on the test set. With a geological survey and a construction parameter monitoring system, the TBM position could be predicted quickly and precisely using a surrogate model. The construction parameters were adjusted if the TBM position did not satisfy the requirements.

Geological Structure and Possible Mineralized Zones in Ikungi – Manyoni Area, Tanzania: Delineated from High-resolution Aeromagnetic Data

Understanding geological structures is important in mineral exploration. Delineating subsurface geological structures, structural intersections, and complexities of potential geological settings for the formation of hydrothermal mineral deposits, such as gold requires using magnetic data, particularly, high-resolution aeromagnetic data. To define possible targets for mineral exploration, this study used linear detection and the Centre for Exploration Targeting (CET) techniques on high-resolution aeromagnetic data for structural delineation and interpretation. The study's conclusions indicate that the majority of geological features, such as faults, shears, fault intersections, and fracture systems, trend NE-SW, N-S, and occasionally NW-SE. These structures create potentially large areas that have a strong chance of becoming mineralized. The CET grid analysis technique defined mineralized zones, particularly the structural intersections which are potential targets in mineral exploration. The effectiveness of the CET technique in mineral prospecting was demonstrated by the correlation between the results and existing mineral occurrences (such as Shanta Gold Mine, abandoned pits, and the operating pits of small-scale miners in Muhintiri). Based on the findings reported herein, any sites that share characteristics with those that have demonstrated gold mineralization should be prioritized for ground follow-up

Characterization of a Metamorphosed Volcanic Stratigraphy and VMS Alteration Halos Using Rock Chip Petrography and Lithogeochemistry: A Case Study from King North, Yilgarn Craton, Western Australia

Despite countless advances in recent years, exploration for volcanogenic massive sulfide (VMS) deposits remains challenging. This is particularly the case in the Yilgarn Craton of Western Australia, where outcrop is limited, weathering is deep and extensive, and metamorphism is variable. At Erayinia in the southern Kurnalpi terrane, intercepts of VMS-style mineralization occur along ~35 km strike length of stratigraphy, and a small Zn (-Cu) deposit has been defined at King (2.15 Mt at 3.47% Zn). An extensive aircore and reverse circulation drilling campaign on the regional stratigraphy identified additional VMS targets, including the King North prospect. Through a combination of detailed rock chip logging, petrography (inc. SEM imaging), and lithogeochemistry, we have reconstructed the volcanic stratigraphy and alteration halos associated with the King North prospect. Hydrothermal alteration assemblages and geochemical characteristics at King North (Mg-Si-K enrichment, Na depletion, and high Sb, Tl, Eu/Eu*, alteration index, CCPI, and normative corundum abundance values) are consistent with an overturned VMS system. The overturned footwall stratigraphy at King North is dominated by metamorphosed volcanic rocks, namely the following: garnet amphibolite (tholeiitic, basaltic), biotite amphibolite (andesitic, calc-alkaline), chlorite–quartz schist (dacitic), and narrow horizons of muscovite–quartz schist (dacitic to rhyolitic, HFSE-enriched). The hanging-wall to the Zn-bearing sequence is characterized by quartz–albite schists (metasedimentary rocks) and thick sequences of amphibolite (calc-alkaline, basaltic andesite). An iron-rich unit (>25% Fe2O3) of chlorite–actinolite–quartz schist, interpreted as a meta-exhalite, is associated with significant Cu-Au mineralization, adjacent to a likely syn-volcanic fault. Extensive Mg metasomatism of the immediate felsic footwall is represented by muscovite–chlorite schist. Diamond drilling into the deep hanging-wall stratigraphy at both King North and King has also revealed the potential for additional, stacked VMS prospective horizons in the greenstone belt stratigraphy. The discovery of HFSE-enriched rhyolites, zones of muscovite–chlorite schist, presence of abundant sulfide-rich argillaceous metasedimentary rocks, and a second upper meta-exhalite horizon further expand the exploration potential of the King–King North region. Our combined petrographic and lithogeochemical approach demonstrates that complex volcanic lithologies and VMS alteration signatures can be established across variably metamorphosed greenstone belts. This has wider implications for more cost-effective exploration across the Yilgarn Craton, utilizing RC drilling to reconstruct the local geology and identify proximal halos, and limiting more costly diamond drilling to key areas of complex geology and deeper EM targets.

Developing meshing workflows in Gmsh v4.11 for the geologic uncertainty assessment of high-temperature aquifer thermal energy storage

Abstract. Evaluating uncertainties of geological features on fluid temperature and pressure changes in a reservoir plays a crucial role in the safe and sustainable operation of high-temperature aquifer thermal energy storage (HT-ATES). This study introduces a new automated surface fitting function in the Python API (application programming interface) of Gmsh (v4.11) to simulate the impacts of structural barriers and variations of the reservoir geometries on thermohydraulic behaviour in heat storage applications. These structural features cannot always be detected by geophysical exploration but can be present due to geological complexities. A Python workflow is developed to implement an automated mesh generation routine for various geological scenarios. This way, complex geological models and their inherent uncertainties are transferred into reservoir simulations. The developed meshing workflow is applied to two case studies: (1) Greater Geneva Basin with the Upper Jurassic (“Malm”) limestone reservoir and (2) the 5° eastward-tilted DeepStor sandstone reservoir in the Upper Rhine Graben with a uniform thickness of 10 m. In the Greater Geneva Basin example, the top and bottom surfaces of the reservoir are randomly varied by ± 10 and ± 15 m, generating a total variation of up to 25 % from the initially assumed 100 m reservoir thickness. The injected heat plume in this limestone reservoir is independent of the reservoir geometry variation, indicating the limited propagation of the induced thermal signal. In the DeepStor reservoir, a vertical sub-seismic fault juxtaposing the permeable sandstone layers against low permeable clay-marl units is added to the base case model. The fault is located in distances varying from 4 to 118 m to the well to quantify the possible thermohydraulic response within the model. The variation in the distance between the fault and the well resulted in an insignificant change in the thermal recovery (∼ 1.5 %) but up to a ∼ 10.0 % pressure increase for the (shortest) distance of 4 m from the injection well. Modelling the pressure and temperature distribution in the 5° tilted reservoir, with a well placed in the centre of the model, reveals that heat tends to accumulate in the updip direction, while pressure increases in the downdip direction.

Chemical and olfactometric inventory of gaseous spot vents in Mt. Amiata volcanic-geothermal area (Italy)

Geothermal areas are typically characterised by the presence of gases and odours in the background atmosphere, stemming from natural emissions and possible mining exploitation of the area. This study presents the first olfactometric investigation of endogenous gas emissions from natural and archaeo-industrial vents in a geothermal area. Mt. Amiata is known for its complex geology and historical cinnabar mining. This study offers an inventory of spot gas emissions, not only in terms of odour and chemical concentration but also including flux data, a ground-breaking achievement in this field. The primary challenge of this investigation was estimating the emitted flow from ground holes or mine entrances, posing the risk of hazardous anoxic conditions. To address this challenge, an innovative and adaptive approach was adopted. The main breakthrough method involved the adaptation of a balometer, typically employed for indoor ventilation systems, to measure the flow of endogenous gases. Field surveys revealed odour concentrations that can exceed 106 of ouE/m3, surpassing industrial emission level considerably. Chemical concentrations, primarily consisted of CO2 (80/90 %v/v) and CH4 (∼10%v/v), providing critical insights into the global warming potential (GWP) associated with natural emissions. Moreover, these spots, often located at ground level and lacking a substantial atmospheric dilution, pose potential risks to nearby individuals, with concentrations of gases such as H2S surpassing safety thresholds. Total emissive flux of the investigated spot vents in the Mt. Amiata area, showed that the emission rate of H2S is notably substantial (55 kg/h), roughly equivalent to emissions from approximately four 20 MW geothermal plants, as along with odour emission rates in the order of 107 ouE/s. Considering the GWP derived from emitted gases, the total inventory assessment of the spot vents resulted in 36 t/h or 23 t/h CO2eq, depending on the time horizon considered (GWP20 or GWP100 respectively).

3D pre-stack inversion constrained by spatial reflection features using the Sylvester's equation

Reflection feature-constrained inversion (RCI) is a multichannel strategy that can effectively improve the stability and continuity of seismic inversion in complex geology, especially for pre-stack inversion with higher uncertainty. To address the limitations of conventional RCI to 2D profiles and high computational costs, a 3D pre-stack seismic inversion constrained by spatial reflection features was developed. First, a new approach to characterize seismic reflection features by decomposing seismic events along the vertical and lateral directions was proposed, which significantly reduces the size of the reflection feature operators. Second, we constructed reflection feature regularization terms and designed a fast reflection feature-constrained inversion (FRCI) for 2D seismic profiles. Finally, the proposed FRCI was extended to 3D by considering the spatial reflection features in two mutually perpendicular directions. Fast spatial reflection feature-constrained inversion (FSRCI) was proposed by constructing spatial reflection feature operators in a 3D coordinate system. The key to this method is that the parameter estimation is transformed into solving the 3D Sylvester equation such that the model parameters can be estimated directly from 3D seismic data. The inversion results of the overthrust model and field data showed that the proposed method can improve efficiency while ensuring spatial continuity. In summary, this study developed a fast pre-stack seismic inversion constrained by spatial reflection features based on the characterization of stratum spatial features, which is effective in complex geology, such as high-dipping and faults.

Introducing a tailored site delineation approach to optimize the design of managed aquifer recharge surface spreading infrastructure

Managed aquifer recharge (MAR) is an emerging solution to effectively replenish overused groundwater resources, but high associated costs often hinder its uptake. There are several parameters to consider when determining the cost of MAR, including recharge types, scale of MAR schemes, land acquisition, operation and maintenance period, and the hydrogeological setting. Hydraulic conductivity and its spatial variability are the most significant hydrogeological parameters for predicting infiltration rates at MAR sites, but limited data availability makes accurate predictions often challenging. Hence, it is essential to increase data availability to optimize MAR efficiency and to better assess its economic performance. Therefore, a novel approach for MAR planning is presented in this article to efficiently enhance the data availability during the conceptual stage of MAR planning by combining site exploration, spatially resolved infiltration rate estimation, and cost analysis. The approach was applied at an actual MAR site in Vincenza, Italy, and incorporated an electromagnetic induction survey and direct push profiling as across-scale investigation methods to enhance site delineation and subsequent parameterization of the identified zones using laboratory analysis of collected samples. This MAR site is particularly suitable for its heterogeneous subsurface structure and potential to counteract groundwater depletion. The performed investigation resulted in an image of the lateral variation of subsurface conditions and allowed the delineation of three zones with different infiltration behavior, with 99.5% of infiltration occurring in just two zones, representing only 22.1% of the site. In this particular scenario, the overall cost per cubic meter of recharged water can be reduced by 59.1% by identifying and eliminating unfavorable zones. This study provides scientists and practitioners with a useful tool for MAR planning that can be applied to a wide range of sites with complex geology, thereby reducing water costs, minimizing the environmental impact of infrastructure construction, and reducing land use conflicts.