Subjects -> EARTH SCIENCES (Total: 771 journals)
    - EARTH SCIENCES (527 journals)
    - GEOLOGY (94 journals)
    - GEOPHYSICS (33 journals)
    - HYDROLOGY (29 journals)
    - OCEANOGRAPHY (88 journals)

GEOPHYSICS (33 journals)

Showing 1 - 31 of 31 Journals sorted by number of followers
Geophysical Research Letters     Full-text available via subscription   (Followers: 201)
GIScience & Remote Sensing     Open Access   (Followers: 57)
Reviews of Geophysics     Full-text available via subscription   (Followers: 50)
Journal of Remote Sensing & GIS     Full-text available via subscription   (Followers: 38)
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (Followers: 9)
Journal of the Earth and Space Physics     Open Access   (Followers: 7)
New Zealand Journal of Geology and Geophysics     Hybrid Journal   (Followers: 6)
Artificial Intelligence in Geosciences     Open Access   (Followers: 6)
Eos, Transactions American Geophysical Union     Open Access   (Followers: 6)
Geothermal Energy     Open Access   (Followers: 5)
Research in Geophysics     Open Access   (Followers: 5)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 4)
Journal of Earth Sciences and Geotechnical Engineering     Open Access   (Followers: 4)
Greenhouse Gases : Science and Technology     Hybrid Journal   (Followers: 4)
Journal of Environmental & Engineering Geophysics     Hybrid Journal   (Followers: 3)
Geodesy and Cartography     Open Access   (Followers: 2)
Geodesy and Cartography : The Journal of Committee on Geodesy of Polish Academy of Sciences     Open Access   (Followers: 2)
Geology, Geophysics and Environment     Open Access   (Followers: 1)
Contributions to Geophysics and Geodesy     Open Access   (Followers: 1)
Interpretation     Hybrid Journal   (Followers: 1)
Near Surface Geophysics     Open Access   (Followers: 1)
GEOMATICA     Hybrid Journal   (Followers: 1)
Chinese Journal of Geophysics     Full-text available via subscription   (Followers: 1)
Transportation Geotechnics     Full-text available via subscription   (Followers: 1)
Results in Geophysical Sciences     Open Access  
Energy Geoscience     Open Access  
Geomechanics and Geophysics for Geo-Energy and Geo-Resources     Hybrid Journal  
Geodesy and Geodynamics     Open Access  
Acta Geologica Polonica     Open Access  
Geofísica internacional     Open Access  
GeoScience Engineering     Open Access  
Similar Journals
Journal Cover
Geomechanics and Geophysics for Geo-Energy and Geo-Resources
Number of Followers: 0  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2363-8419 - ISSN (Online) 2363-8427
Published by Springer-Verlag Homepage  [2467 journals]
  • Effect of pore pressure magnitude on the frictional properties and
           permeability evolution of fractures in schist

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      Abstract: Abstract Fluid injection-triggered seismicity has increased dramatically over the last decade with elevated pore fluid pressures acting as a prime culprit. Thus, understanding the effect of pore fluid pressure on the mechanical and hydrologic behavior of fractures and faults will illuminate the contributing and dominant physical processes. We present concurrent measurements of shear displacement and flow to quantify the evolution of frictional strength, stability and permeability of schist during the full seismic cycle. We use a miniature double direct shear (mini-DDS) apparatus to conduct velocity stepping (VS for stability) and slide-hold-slide (SHS for frictional healing). Our results demonstrate that increasing pore fluid pressures can stabilize frictional slip under otherwise invariant effective stresses. This implies that elevated pressures favor stable slip as a material characteristic even in the absence of decreasing critical fault stiffness (thereby increasing stability) as a result of decreased effective stress. However, the magnitude of pore pressure does not control permeability evolution during velocity steps as pore pressure does not control aperture dilation/compaction for an invariant effective normal stress. During SHS tests, it is shown that the magnitude of normalized permeability change increases with hold time and that the rate of permeability change generally decreases with the increment of pore fluid pressure, suggesting that high fluid pressures may limit permeability change during interseismic response, although creep response may still dominate over the long term.
      PubDate: 2022-12-17
       
  • Pre-drill pore pressure prediction from 1D seismic velocity profile to 3D
           modeling using high resolution full waveform inversion velocity (FWI):
           deep water offshore, West Nile Delta

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      Abstract: Abstract Pore pressure prediction is one of the most critical steps while planning new well delivery activity in exploration fields in order to achieve the well target by delivering a safe well. It is very important to understand the structural and stratigraphic complexity that may influence formation pressure differences in the study area. Also, it is critical to have a range of uncertainty in prediction to mitigate any kind of drilling problems and operational risks. In this case study, the target is to predict the pore pressure gradient for four proposed exploration wells in West Nile Delta Raven field. The workflow has been applied utilizing tilted transverse isotropic seismic velocity and a high-resolution full waveform seismic inverted velocity. It is important as well to compare different methodologies where each one will have its own limitations. A manually picked normal compaction trend with the conventional Eaton pressure transform method was applied and compared with a BP internal normal compaction trend with a modified Eaton (Presgraf) pressure transform method in the Predrill prediction. The pre-drill pore pressure is finally compared with the actual measured pore pressure data that yields a good match.
      PubDate: 2022-12-10
       
  • Correction to: Energy dissipation mechanisms in fluid driven fracturing of
           porous media

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      PubDate: 2022-12-08
       
  • Pore morphology effect on elastic and fluid flow properties in Bakken
           formation using rock physics modeling

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      Abstract: Unconventional geo-resources are critical due to their important contributions to energy production. In this energy transition and sustainability era, there is an increased focus on CO2-enhanced oil recovery (CO2-EOR) and geological CO2 storage (GCS) in unconventional hydrocarbon reservoirs, and the extraction of hot fluid for energy through enhanced geothermal systems. However, these energy solutions can only be achieved through efficient stimulation to develop a complex fracture network and pore structure in the host rocks to extract heat and hydrocarbon, or for CO2 storage. Using Bakken formation well data and rock physics models, this study aimed to identify the post-depositional effect of pore structure on seismic velocity, elastic moduli, and formation fluid; and further predict the best lithofacies interval for well landing, and the implications for fluid (gas, oil, and water) recovery in naturally- and often systematically-fractured geosystems. The KT and DEM models' predictions show distinct formation intervals exhibiting needle-like pores and having higher seismic velocities (Vp and Vs) and elastic moduli (K and µ), relative to other formation intervals that exhibit moldic pores. At the same fluid concentration, the needle-like pores (small aspect ratios) have a higher impact on elastic moduli, Vp, and Vs than on the moldic spherical pores with all other parameters held constant. Vp is affected more than Vs by the properties of the saturating fluid (gas, oil, or water) with Vp being greater in Bakken formation when it is water-saturated than when it is gas-saturated. Vs exhibit the reverse behavior, with Vs greater in the gas-saturated case than in the water-saturated case. Further, analyses suggest that the middle Bakken formation will have a higher susceptibility to fracturing and faulting, and hence will achieve greater fluid (oil and water) recovery. Our findings in this study provide insights that are relevant for fluid production and geo-storage in unconventional reservoirs. Article highlights Integrated well log data and rock physics models. Investigated the effect of changes in pore structure on elastic properties and fluid flow in shale. Increase in porosity causes a reduction in elastic moduli and seismic velocities. Vp is more affected by pore geometry than Vs depending on density and properties of saturating fluid. Lithofacies with needle−like pores are more susceptible to fracturing than lithofacies with intragranular pores.
      PubDate: 2022-11-28
       
  • Hydraulic stimulation strategies in enhanced geothermal systems (EGS): a
           review

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      Abstract: Abstract In enhanced geothermal systems (EGS), the natural permeability of deep rocks is normally not high enough and needs to be increased. Permeability increase can be achieved through various stimulation methods, such as hydraulic, chemical, and thermal stimulation. Among these, hydraulic stimulation is the most commonly used technique to increase both reservoir permeability and the specific area for heat exchange. A comprehensive understanding of the underlying processes towards an optimization of hydraulic stimulation performance while minimizing the potential of unwanted induced seismicity is a critical prerequisite for a successful development of any EGS site. In this paper, we review the hydraulic stimulation strategies that have been developed and implemented for EGS. We begin with a description of the underlying mechanisms through which the permeability and heat exchange area increases are achieved. We then discuss the mechanisms of fluid injection-induced seismicity during and after a hydraulic stimulation operation. After that, alternative hydraulic stimulation strategies, namely conventional hydraulic stimulation, multi-stage fracturing, and cyclic soft stimulation, are reviewed based on current research in theoretical studies as well as, laboratory, and in-situ field experiments. Finally, some representative EGS projects are reviewed, focusing on fluid injection strategies, seismic responses, and reservoir permeability enhancement performance. The review shows the importance and need of (a) a comprehensive geological characterization of the natural fracture system including the nearby fault zones as well as the in-situ stress conditions, prior to the development of the site, (b) a proper design of the well arrangement, such as the positioning of the injection and production wells, and (c) the selection of an appropriate fluid injection strategy for the system at hand.
      PubDate: 2022-11-28
       
  • A novel three-directional servo control dynamic loading apparatus for
           geomechanics

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      Abstract: Abstract To more accurately determine the mechanical behavior of geomaterials exposed to different stress conditions, we developed a novel three-directional servo-controlled loading apparatus, the “DWZ-250”, which could apply static or dynamic loads in the two horizontal and one vertical directions. DWZ-250 system consisted of a loading frame, a servo-controlled system, and a PC console. The loading frame had three loading pistons, two in the horizontal direction and one in the vertical direction. The servo-controlled system had static and dynamic modules that supplied either static or dynamic forces of up to 250 kN or a positive or negative velocity for each piston of up to 50 mm/min. The forces were recorded by load cells, and the displacements were recorded by linear variable differential transformers (LVDTs). The PC console consisted of a terminal controller, which included an advanced bespoke control software package “Dex.MulTest.2020”, which performed all operations and met data storage requirements. The DWZ-250 system performed static/dynamic uniaxial compression, bi-directional compression, static/dynamic double shear, slide hold slide, velocity stepping tests, etc. This new system did not have the limitations of existing devices and provided new strategies for performing a geomechanical investigation.
      PubDate: 2022-11-24
       
  • Investigation of the effect of initial structure and loading condition on
           the deformation, strength, and failure characteristics of continental
           shale

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      Abstract: Abstract The study of the mechanical characteristics of lamellar continental shale is of great theoretical and application value for unconventional shale oil production. In this study, four cuboid continental shale specimens were subjected to true triaxial compression tests to investigate their deformation, strength, and failure characteristics. The initial structures were analysed at three observational scales using optical photography, three-dimensional microscopic and thin section observations. Specimens were tested under different intermediate stresses and the force–displacement data in three directions were monitored. The failure characteristics were studied using optical photography and non-destructive X-ray computed tomography (CT). It was found that the continental shale specimens had high heterogeneity and were composed of a large number of natural fractures and lamina with uneven thicknesses, and the macroscopic mineral bands were of two main types: those mixed with clay minerals and those mixed with quartz, feldspar and mica minerals. Under four applied stress conditions, the shale deformation stiffness increases with the increasing horizontal stress difference, and the peak strength of continental shale conforms to the Mogi-Coulomb criterion. The failure mode of continental shale interacts with natural horizontal fractures and new inclined/vertical fractures which develop along the direction of intermediate principal stress. With increasing horizontal stress differences, the inclined shear cracks are flatter, the horizontal crack and the connection between horizontal cracks with oblique/vertical cracks are more obvious. The initial structural characteristics and the stress conditions jointly affect the stress–strain curve response with stress fluctuation points and crack characteristics in "bricklaying" form, producing a stress–structure-controlled failure mode. These conclusions have value for engineering applications and provide theoretical guidance for the design of continental shale oil recovery schemes.
      PubDate: 2022-11-23
       
  • Development of blast vibration predictors based on K-Means and TwoStep
           clustering techniques and evaluation of site factors

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      Abstract: Abstract The paper investigates applicability of K-Means and TwoStep clustering techniques to create alternative predictor equations for blast vibrations. Site investigation was performed in a sandstone quarry. The blast data was divided into sub-groups by cluster analysis process. Twelve different classification models were created. Both K-Means and TwoStep techniques were applied successfully. TwoStep clustering seems to be more robust and efficient method for classification process. F test and Wilks’ lambda tests were successfully used to determine dominant parameters of classification. After grouping process, totally twenty-four alternative predictor equations were developed for each group. The predictor models were constructed based on square-root scaled distance concept. Models were compared by using six different accuracy metrics. The predictor equations forecast ground vibration with a mean error lower than two millimeter per second. It is proven that it is possible to develop different predictor models for a specific quarry or open pit. Site factors of the predictor equations were examined in detail. In our case, increase of model data results in formation of higher site factors. The variation in K factors of equations is relatively higher than β factors.
      PubDate: 2022-11-23
       
  • A hybrid DEM+SPH coupling method and its application in modeling water and
           mud inrush disasters

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      Abstract: Abstract Water and mud inrush disasters are among the most common geological disasters in tunnel construction, which are a complex hydromechanical coupling process of groundwater and geotechnical media. This study proposed a hybrid discrete element method–smoothed particle hydrodynamics (DEM+SPH) coupling method to simulate the two-phase flow process of a disaster. The basis of the DEM and SPH used to establish coupling method was firstly introduced. An unsolved coupling algorithm was adopted for coupling the two phases of the DEM (for solids) and SPH (for fluid). Two typical examples, including a rotating drum and a two-phase dam break, were simulated to validate the adequacy of the coupling method. Finally, the developed SPH+DEM method was used to simulate the whole process of water and mud inrush disasters. The solid particles are prone to deposit on the floor of the tunnel and the fluid covers the surface of the deposit after the disaster occurs. Most of the fluid can flow out of the tunnel, but the solid particles remain on the floor at the end of the simulation. This phenomenon agrees well with the actual situation of water and mud inrush disasters observed in tunnels. The study can provide an effective numerical tool for analysis of the disasters.
      PubDate: 2022-11-23
       
  • An analytical model of the initiation pressure for multilayer tree-type
           hydraulic fracturing in gas-bearing coal seams

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      Abstract: Abstract Hydraulic fracturing is able to effectively enhance the permeability of coal seams and thereby achieve the appreciable methane drainage effect. Tree-type fracturing technology is an advance method that is expected to solve the problems of high initiation pressures and fracturing blank areas of conventional fracturing technology. The existing fracture initiation pressure models cannot accurately predict the initiation pressure when multiple tree-type branch boreholes (TTBBs) interact. An analytical model of calculating the initiation pressure during hydraulic fracturing under the condition of multiple TTBB layers was established in this study. The model focuses on analyzing the mutual influence of TTBBs in different layers and considers the influence of coal seam bedding planes, joints and coalbed methane pressure on the initiation pressure. The circumferential stress distribution around TTBB T2 under different TTBB arrangement parameters was analyzed. It was found that under the influence of TTBBs in adjacent layers, the circumferential stress of T2 first increased and then decreased with the distance to the fracturing borehole, and finally approached the stress value of a single TTBB. Theoretical initiation pressures under different TTBB arrangement parameters and coal seam geological parameters were calculated. The theoretical initiation pressure decreased with increasing number of TTBBs and TTBB layers because of the induced stress caused by the water pressure in the TTBBs. Additionally, the tree-type fracturing initiation patterns under most parameters entailed tensile failure along coal bedding surfaces. These results could help advance the development of hydraulic fracturing and provide dependable assistance for tree-type fracturing site applications.
      PubDate: 2022-11-23
       
  • New permeability model of deep coal rock considering the structure and 3D
           stress compression-induced anisotropy

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      Abstract: Understanding the gas flow behavior in coal mining is conducive to the efficient production of coalbed methane. In coal mining, in-situ stress usually manifests as three-dimensional anisotropy in deep formations, and affects the gas permeability in reservoirs. In this work, a permeability model for anisotropic coal by combining gas sorption effects and the three-dimensional stress compression was proposed. Then, the effect of stress-induced fracture expansion on the fracture-matrix system was quantitatively analyzed, and this effect was incorporated into the permeability model. Combining the theoretical work, the seepage tests under conditions of true triaxial stress was conducted, and the permeability of coal, sandstone, and composite coal-rock were measured. Results showed that the stress first causes fracture compression, thus causing the permeability reduction. Because of the continuous increase of stress, the resulting fracture initiation and expansion increase the seepage channel of rock, and its permeability showed a sudden increase trend. In addition, the measured permeability test data is in good agreement with the model predicted. It also shows that the new model can describe the reservoir anisotropy permeability behaviors owing to stress compression induced damage and the initiation of new fractures. This work may provide an important theoretical reference for the evolution of rock permeability and reserve assessment of deep oil and gas reservoirs. Article highlights A permeability model for coal rock considering the effect of three-dimensional stress compression and sorption was proposed. Combined with the in-situ environment, the seepage test for coal rock under true triaxial stress was carried out. According to the new model, the permeability behavior of rocks under 3D stress was simulated.
      PubDate: 2022-11-22
       
  • Experimental investigation on the grouting characteristics of fractured
           sandstones under different confining pressures

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      Abstract: Abstract Grouting is an important technical method for anti-seepage reinforcement in underground projects, and it is important to study the strength and deformation characteristics of grouted rocks under different confining pressures (σ3). The time-varying characteristics of urea-formaldehyde resin slurry (UF-RS) with different oxalic acid concentrations and volume ratios were investigated for the selection of suitable ratios. The mechanical properties and damage characteristics of the yellow sandstone and its grouted rock were investigated, and their fractal dimension were studied. The results showed that for higher oxalic acid concentrations, the span of the low-viscosity stage was shorter and lesser time was required to reach the initial setting state of the slurry for the same volume ratio. The span of the low-viscosity stage was longer for a greater volume ratio of modified UF-RS to oxalic acid. The strength recovery ratio of grouted solids was found to be proportional to the σ3, and the cohesion of grouted solids had a larger gap than that of intact yellow sandstone. The fractal dimension and strength recovery ratio of the grouted solids showed an opposite trend with changes in σ3, and the fractal dimension showed a decreasing trend with increases in σ3.
      PubDate: 2022-11-21
       
  • Practical workflow for assessment of seismic hazard in low enthalpy
           geothermal systems

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      Abstract: It is of vital importance to be able to determine the seismic hazard in advance of any geothermal operation in the subsurface, especially in a densely populated area such as The Netherlands. The author aims to arrive at a practical assessment of the seismic hazard in low-enthalpy geothermal doublet systems specifically designed for heat exchange in porous and permeable aquifers operated on a volume balance, at a depth range of 1800 to 3300 m having temperatures in the range of 60 °C to 100 °C. The article presents a practical workflow aiming to determine the probability distribution for mechanical re-activation along pre-existing weak faults. After presenting the tectonic structural setting the criticality criterion based on shear mobilisation is introduced. Existing stress models are reviewed and a practical manner to estimate and limit all geomechanical input parameters is presented, including fault mechanical properties. The workflow is demonstrated both for early period operation times and at final thermal breakthrough. The uncertainty is addressed through probabilistic logic tree analysis quantifying the variation of the four most uncertain input parameters: fault cohesion and friction coefficient, the thermal stress parameter and the initial minimum Earth stress. The probabilistic hazard assessment is characterised by four output parameters: the expected value, the probability that unity is exceeded and two more probabilities. In case unity is exceeded the range of fault dips prone to mechanical re-activation is shown. Exceedance of this first necessary condition requires the assessment of the other two necessary conditions: seismogeneity and moment magnitude. Article highlights The article presents a practical workflow to assess the seismic hazard associated with geothermal operations. To be able to perform the necessary uncertainty analysis, four main input parameters are treated probabilistic. The first necessary condition for seismicity to occur is characterised by four probabilities: the expected probability, the probability that seismicity can occur and two higher probabilities.
      PubDate: 2022-11-21
       
  • Prediction and prevention of mining-induced water inrush from rock strata
           separation space by 3D similarity simulation testing: a case study of Yuan
           Zigou coal mine, China

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      Abstract: Abstract The prediction and prevention of water inrush from rock strata separation space (RSSS) is vital in preventing casualties and equipment damage.To research the mechanism of water inrush from an RSSS, a pressure sensor is used to analyze the rock pressure. And a change in water volume within the bag reflects the shift of RSSS under mining effects based on a similar 3D RSSS water-inrush simulation experiment. The test can accurately simulate the practical coal mining process by adopting similar rock materials, 3D stratum, reserved coal pillar, schedule mining, and water-bearing stratum simulation. The results of the experiments show that the RSSSs are distributed between sandstone strata with greater strength and stiffness, and claystone strata with a weak strength and greater deformability. It is evident that the shape of RSSS is irregular. Moreover, the water-conducting fissure zone destroys the RSSS and becomes the water gushing channel. The RSSS near the coal seam has a short development period and a small volume; therefore, there is no large water inrush disaster. The RSSS far away from the coal seam develops for a long time, and the volume is large, so the risk of a water inrush disaster is high. Furthermore, the persistent time and volume of separation are positively correlated with the thickness and strength of hard rock. The situ borehole video image investigation of RSSS indicates a significant RSSS between coarse conglomerate stratum in the Yijun zone and claystone stratum in the Anding zone, verifying the experimental results. In addition, the water level variation in the drill hole indicates that the water-conducting fissure zone developed to the bottom of the Yijun zone, which also confirms the experimental results. Finally, based on the results and analysis, the vertical diversion hole is proposed to prevent water inrush. The research proposes a new method for predicting and preventing RSSS water inrush disasters.
      PubDate: 2022-11-21
       
  • Fracture and fragmentation of granite specimen under high-voltage pulses

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      Abstract: Abstract The high-voltage pulse technique is considered as a promising method for rock fragmentation in rock engineering. Understanding the fracture modes and fragment distribution of rocks subjected to high-voltage pulses is thus essential. In this work, a circuit system for rock breaking by high-voltage pulses discharge was established. The fracturing effect on granite under high-voltage pulses was explored and changes in the median size of fragments with specimen size, charge voltage, and energy density were investigated. The results showed that a breakdown, radial crack, and circumferential crack zone are formed within granite specimens. With the growth of specimen sizes, the average breakdown voltage of granite shows only a marginal change, and the median size of fragments gradually increases. As the charge voltage increases, the median size of fragments is reduced. Additionally, the median size of the fragments attenuates exponentially with the energy density. Furthermore, microscopic analysis using a scanning electron microscope indicated that high-temperature melting and shock waves are the dominant factors in inducing rock fracturing.
      PubDate: 2022-11-21
       
  • Resistivity of granite and sandstone varies with frequency and water
           saturation

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      Abstract: Abstract Exploring the effects of excitation polarization and moisture saturation on rock resistivity is crucial for evaluating resistivity-related technologies and engineering, such as electrical exploration. This study selected granite and sandstone from Shandong and Wanzhou to evaluate the rock resistivity at various frequencies (0.1 ~ 200 kHz) and saturations (0 ~ 100%). Under conditions of low saturation of granite and sandstone, the results indicate that the resistivity of the rock sample will rise with increasing saturation due to the excitation polarization effect. As the saturation corresponding to the peak resistivity is approached, the influence of pore water on resistivity replaces the primary role of the excitation polarization effect, resulting in a fall in the resistivity of the rock sample with the increase in saturation. Furthermore, the exponential function relationship between peak saturation and frequency is positively correlated, and peak saturation increases rapidly with increasing frequency due to the disappearance of interface polarization at 104 ~ 105 Hz, with an increase of about 60%.
      PubDate: 2022-11-20
       
  • The strata movement and ground pressure under disturbances from extra
           thick coal seam mining: a case study of a Coal Mine in China

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      Abstract: The exploitation of extra thick coal seams (ETCSs) has been emphasized in the Chinese coal industry. However, the strata movement and ground pressure under the mining conditions of an ETCS constitute a complex problem that urgently requires comprehensive understanding and efficient solution. With the background of the working face of the Tashan Coal Mine (Shanxi, China), a physical simulation test and numerical study based on the discontinuous deformation analysis (DDA) are conducted to investigate the aforementioned problem. The movement of the overlying strata is first observed and discussed based on physical simulation. Next, a quantitative comparative analysis of the displacement field and stress field are carried out. The conclusions are as follows: (1) in the process of the ETCSs mining, the evolution of strata structure can be summarized into four patterns, namely, the simply supported beam pattern, the multi-simply supported beam pattern, the cantilever beam pattern, and the multi-cantilever beam pattern. (2) The fractal dimension can provide a quantitative expression for the structural evolution of the strata. The fractal dimension indicates that the fracture of the immediate roof and key stratum may significantly trigger the movement of the strata. (3) Based on the integration of DDA and physical simulation, the movement of the key stratum can be divided into three stages, namely, the stable stage, the fracture stage, and the compaction stage. The displacement of other strata is generally dominated by these three stages. (4) The mining disturbances and constraint reaction of the adjacent rock mass are responsible for the direction and magnitude evolution of stress in the key stratum. The gradual and full release of vertical stress of the key stratum indicates that the direction of the principal stress may change from horizontal and vertical to only horizontal. Moreover, the constraint reaction of the fractured rock mass causes a rapid increase in stress of the key stratum. (5) The movement of key stratum significantly impacts the pressure propagation. The stress in front of the working face accumulates sharply under such an effect and then shows a moderate increase with the sufficiency of the relative movement of the adjacent rock mass and release of the stress of the key stratum. These results indicate that the movement of the key stratum may be the underlying reason for the ground pressure. Article highlights The structure evolution of the overlying strata under the mining disturbances is qualitatively summarized and quantitatively described. The inherent relation and intrinsic influence between the key stratum movement and ground pressure during the mining process is revealed. The role of the key stratum for the pressure propagation and ground pressure behaviors is clarified and discussed.
      PubDate: 2022-11-20
       
  • Real-time monitoring of induced strain during multi-stage ad-/desorption
           of methane on coal

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      Abstract: The sorption-induced strain of coal is very important for the evaluation of coalbed methane productivity. Previous studies have focused on the strain properties of the equilibrium state, however, the time-dependent strain evolution behavior has been rarely considered. In this paper, to explore the time-dependent strain evolution behavior and the mechanism behind, we perform the real-time monitoring of induced strain during multi-stage sorption of methane on coal. The results show the multi-scale pore structure and the heterogeneous interface properties of coal determine the kinetics behavior of gas transport and sorption, which then dominates the time-dependent strain evolution properties. Single-stage sorption and multi-stage sorption are driven by high pressure and low pressure to complete continuous and discontinuous strain evolution, respectively. This differences in driving pressure and strain continuity have potential effects on strain kinetics. This study has potential implications for time-dependent production assessment of coalbed methane. Article Highlights Multi-stage ad-/desorption-induced strains are compared; Influence of multi-stage on strain kinetics is analyzed.
      PubDate: 2022-11-17
      DOI: 10.1007/s40948-022-00514-y
       
  • Coupled coal–gas interaction during CBM and CO2-ECBM recovery in
           coal seams: a critical review

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      Abstract: Coupled coal–gas interaction in coal seams is crucial to the efficient recovery of Coalbed methane (CBM), and carbon dioxide-enhanced CBM (CO2-ECBM). Coal is physically deformed and damaged during gas extraction/injection and permeability enhancement in coal seams, which might alter the reservoir properties of coalbeds in terms of coal diffusivity and permeability and thus affect gas desorption and transport. In turn, gas desorption and transport also change the geomechanical behaviors of the coal, including coal deformation and mechanical parameter alterations. In many cases, when investigating gas transport in coal, it is necessary to consider the coupling between stress, deformation and gas flow in coal. First, this review paper presents a comprehensive review of the mechanisms and properties of gas adsorption in coal, the geomechanical behavior of coal including mechanical deformation and mechanical property alterations, and mechanisms of gas transport in coal including gas diffusivity and permeability evolution in coalbeds under coupled coal–gas interactions. Next, several waterless fracturing techniques such as liquid N2 fracturing and supercritical CO2 fracturing are discussed for improving the permeability of coalbeds. Finally, an overview of the current knowledge and research gaps are identified. Article highlights Mechanical property alterations of coal during coupled coal-gas interactions are reviewed. Diffusion and permeability models during coal-gas interaction are reviewed. Several waterless fracturing techniques for enhancing coal permeability are reviewed.
      PubDate: 2022-11-17
      DOI: 10.1007/s40948-022-00477-0
       
  • DEM fluid–solid coupling method for progressive failure simulation of
           roadways in a fault structure area with water-rich roofs

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      Abstract: Abstract Faults are common large geological structures in underground coal mining, and roadways near faults are seriously damaged. When faults connect aquifer roofs, the roadway surrounding rock (RSR) softens in the long-term water invasion process, resulting in more serious deformation. In this paper, taking the Beixinyao Coal Mine as the research object, the UDEC-Voronoi numerical model is used to study the progressive failure process of the RSR when a roadway passes through the fault under the condition of rich-water roofs. Based on the quantitative relationship of water immersion weakening of rock samples in laboratory tests, a fluid–solid coupling simulation method and a damage quantitative index suitable for the engineering scale are put forward. On this basis, the progressive failure characteristics of the RSR under the roof aquifer are simulated. The result shows that the fault activates the aquifer to form a seepage channel under the action of roof water pressure and mining stress. After water immersion, the mechanical strength of the coal and rock mass decreases, resulting in the development of cracks. Under the primary support conditions, the damage ratio in the study area is 63.3%. Among them, the number of shear crack events is 4.5 times the number of tensile crack events in the failure process of the RSR. According to the progressive failure characteristics of the RSR from water-rich roofs, a control strategy of dewatering the roof aquifer near the fault and strengthening the roadway support is proposed. The subsidence of the headgate roof is reduced by 65.9%.
      PubDate: 2022-11-17
      DOI: 10.1007/s40948-022-00517-9
       
 
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