Gassy Coal Research Articles

Damage and permeability of gassy coal in loading – Unloading path

To effectively prevent dynamic gas disasters, the adding vertical and unloading radial stress were investigated in laboratory and numerical simulation experiments. The objective about the research was to ascertain how various gas pressures and loading rates affected permeability and damage deformation. The results conclude that shear failure predominates in gassy coal, a rise in loading rate causes the permeability to mutate more slowly, and the plastic strain gradually decreases at the yield, peak, and post-peak stable points in gassy coal. As well, a rise in gas pressure causes an earlier transition from compression to expansion state of specimens, enhances permeability, and rises the plastic strain at specified points. Furthermore, the study focuses on the meso-scale failure and permeability characteristics. During failure, the seepage channel within the coal body gradually transitions from a vertical orientation to irregular deformation. In addition, a damage model is formulated centered around energy consumption, demonstrating that damage evolution curves exhibit an ‘ S’ shape with vertical strain. Meanwhile, higher axial loading rates delay the onset of unstable crack propagation, but raising gas pressure quickens the pace of damage to specimens. The conclusions of this research hold significant practical implications for mitigating coal-rock gas dynamic disasters.

Influences of Different Factors and Sensitivity Analysis of Permeability of Gassy Coal

Influencing factors and sensitivity analysis of coal permeability are significant for reasonably setting coalbed methane (CBM) extraction parameters and increasing CBM output. Seepage tests were conducted on gassy coal using a seepage test system for damaged coal and rock mass under various conditions of axial pressure, confining pressure, and gas pressure. Moreover, the influences of different factors on the permeability of gassy coal and the sensitivity of permeability to these factors were analyzed. Research results show that under the same confining pressure, the relationship between permeability and axial pressure of gassy coal meets the quadratic polynomial function; under the same axial pressure, the permeability changes with the confining pressure as a power function. The permeability of gassy coal is far more sensitive to confining pressure than to axial pressure during axial seepage. Under the same axial pressure and confining pressure (same stress), the permeability of gassy coal reduces at first and then increases in a V-shaped trend with growing gas pressure. There is a turning point in the seepage tests, that is, the critical gas pressure. When the gas pressure is lower than the critical value, the slippage effect plays the leading role in the variation of permeability of the coal; on the contrary, effective stress plays the dominant role. In the non-isobaric deviatoric stress state, the permeability of gassy coal is most sensitive to the confining pressure, followed successively by gas pressure and axial pressure. The research results provide a theoretical basis for precise gas extraction and control in coal seams.

Effects of Coal Thickness on the Fractal Dimension of Gas Migration Channels: Laboratory and Field Study of a Gassy Coal Mine

Effects of Coal Thickness on the Fractal Dimension of Gas Migration Channels: Laboratory and Field Study of a Gassy Coal Mine

Conditions That Determine Changing the Function of Mine Shafts in a Gassy Coal Mine—A Case Study

Conditions That Determine Changing the Function of Mine Shafts in a Gassy Coal Mine—A Case Study

Elimination mechanism of coal and gas outburst based on geo-dynamic system with stress–damage–seepage interactions

Coal and gas outburst is a complex dynamic disaster during coal underground mining. Revealing the disaster mechanism is of great significance for accurate prediction and prevention of coal and gas outburst. The geo-dynamic system of coal and gas outburst is proposed. The framework of geo-dynamic system is composed of gassy coal mass, geological dynamic environment and mining disturbance. Equations of stress–damage–seepage interaction for gassy coal mass is constructed to resolve the outburst elimination process by gas extraction with boreholes through layer in floor roadway. The results show the occurrence of outburst is divided into the evolution process of gestation, formation, development and termination of geo-dynamic system. The scale range of outburst occurrence is determined, which provides a spatial basis for the prevention and control of outburst. The formation criterion and instability criterion of coal and gas outburst are established. The formation criterion F1 is defined as the scale of the geo-dynamic system, and the instability criterion F2 is defined as the scale of the outburst geo-body. According to the geo-dynamic system, the elimination mechanism of coal and gas outburst—‘unloading + depressurization’ is established, and the gas extraction by boreholes through layer in floor roadway for outburst elimination is given. For the research case, when the gas extraction is 120 days, the gas pressure of the coal seam is reduced to below 0.4 MPa, and the outburst danger is eliminated effectively.

An improved gas–liquid–solid coupling model with plastic failure for hydraulic flushing in gassy coal seam and application in borehole arrangement

Hydraulic flushing can increase the efficiency of gas extraction by artificially modifying the coal reservoir. Considering the plastic failure of coal mass, an improved gas–liquid–solid coupling model for hydraulic flushing and gas extraction is constructed. The parameter evolution in the hydraulic flushing process was numerically investigated to determine the optimal borehole arrangement of hydraulic flushing. The results show that the relative permeability of gas gradually increases with the initial dewatering. The gas rates of both regular extraction and hydraulic flushing enhanced extraction show an increasing–decreasing trend. An increased and delayed peak gas rate is observed comparing with the regular extraction, caused by the hydraulic flushing induced new fractures. The area around of borehole is divided into the failure zone, the plastic softening zone, and the elastic zone after hydraulic flushing. The failure zone has the greatest increase in coal permeability, followed by the plastic softening zone, while the elastic zone keeps no significant change. The larger difference between the horizontal stress and vertical stress, the more obvious the elliptical shape of the permeability change area near the borehole, as well as the pressure drop in the elliptical zone. With the increase in the hydraulic flushing radius, the permeability increasing zone and gas pressure decreasing zone gradually increase. Subsequently, the equivalent effective radius and equivalent influencing radius were obtained, as well as the optimal borehole spacing for hydraulic flushing by cross-layer drilling. Finally, the optimal borehole spacing is obtained for different borehole diameters and efficient extraction times. These provide a theoretical guidance for field application of hydraulic flushing in a low-permeable coal seam.

Experimental and theoretical study on the dynamic effective stress of loaded gassy coal during gas release

In the process of mining coalbed methane (CBM), an unsteady state often arises due to the rapid extraction, release and pressure relief of CBM. In this case, the effective stress of coal changes dynamically, affecting the stability of the gassy coal seam. In this paper, gas release tests of gassy coal under conventional triaxial compression were performed, and the dynamic effective stress (DES) during gas release was obtained indirectly based on a constitutive equation and deformation of coal. The results show that the maximum increases in DES caused by the release of free gas and adsorbed gas under the stress of 1.1 MPa were 0.811 and 5.418 MPa, respectively, which seriously affected the stress state of the coal. During the gas release, the free gas pressure and the adsorbed gas volume were the parameters that directly affected the DES and showed a positive linear relationship with the DES with an intercept of zero. The DES of the coal sample increased exponentially with time, which was determined by the contents of free and adsorbed gas. Based on the experimental results and theoretical analysis, an effective stress model was obtained for loaded gassy coal during gas release. The results of verification indicated accuracy greater than 99%.

Experimental research of the geo-stress evolution law and effect in the intact coal and gas outburst process

Coal and gas outbursts are a potentially fatal hazard that must be managed when mining gassy coal seams. Mining-induced stress plays an important role in outbursts, while elastic potential is accumulated to provide energy for an outburst. In this study, a large-scale true triaxial (LSTT) apparatus was developed to conduct experiments and to understand the outburst mechanism and mining-induced geo-stress evolution law. In the LSTT experiments, coal and gas outbursts resulted from both stress and gas pressure and occurred in a limited balance area. Under the action of mining-induced stress, surrounding rock and coal are compressed. Thus, a large amount of elastic potential is accumulated to provide energy for a coal and gas outburst. Mining-induced stress promotes the development and expansion of the fracture in the coal body, which results in coal wall deformation and damage. The four types of coal wall instability are bodily movement of coal wall, layered separation of coal wall, collapse of coal wall, and break of coal wall. This study develops a classification scheme and management strategies for outbursts.

Experimental Investigation on Mechanical and Acoustic Emission Characteristics of Gassy Coal under Different Stress Paths.

Coal mining leads to stress loading–unloading variation in front of the working face, which influences the occurrence of disasters. In order to study the influence mechanism of stress loading–unloading to the coal failure, a series of experiments of gas-bearing coal deformation and failure under triaxial stress were conducted and acoustic emission (AE) was monitored. In this study, the effect of gas pressure on the mechanical behavior of gas-bearing coal in conventional triaxial stress (CTS) experiments and fixed axial stress and unloading confining stress (FASUCS) experiments was analyzed, and the damage evolution rules of gas-bearing coal in the CTS experiments and FASUCS experiments were determined using AE. The results show that with the increasing of gas pressure, the peak strength and peak strain of gas-bearing coal in the CTS experiments and FASUCS experiments gradually decrease, and the peak of AE ring-down counts lags behind the peak strength. Compared with the CTS experiments, the strength of gas-bearing coal in the FASUCS experiments is lower and the precursor information appears later. The trends in calculated stress and damage coefficient D are consistent with the stress path during unloading, and both begin to rise sharply after the sample enters the plastic stage. Therefore, AE ring-down counts, damage coefficient D, and calculated stress can be used as precursor information for failure of coal and rock, which has great significance for the further study of coal-rock material and for early hazard warning.

Concurrent 5. Presentation for: Multiple tracers for dis-connectivity of shallow aquifers, alluvium, and coal seam gas wells in the Great Artesian Basin

Presented on Tuesday 17 May: Session 5 The potential for connectivity between water supply aquifers and gas reservoirs raises community, government, and scientific concerns. Methane can occur naturally, making it difficult to determine whether water bore methane levels are being influenced by nearby gas operations. This poses a challenge in the Surat Basin, where coal seam gas production operates alongside groundwater using industries (including feedlots, agriculture, mines). Water and gas samples were taken from water bores and coal seam gas (CSG) wells in the Walloon Coal Measures and from overlying aquifers (nominally, the Springbok, Gubberamunda, Orallo, and Mooga sandstones) and the Condamine Alluvium, for stable isotopes of gases, groundwater and dissolved inorganic carbon, as well as strontium isotopes. Most of the sampled water bores had isotopic signatures distinct from CSG wells, though a minority from gassy Springbok Sandstone and Walloon Coal Measure water bores could not be distinguished from CSG wells. In those few cases, neither connectivity or dis-connectivity could be confirmed. Alluvium and shallow aquifer samples have higher R36Cl values distinct from the older CSG production waters, as is the case with most 14C measurements. Waters from the Condamine River indicate potential surface water connectivity with the alluvium. The use of multiple tracers has shown that groundwater in some aquifers can be differentiated from groundwater in the coal seam gas reservoir and hence are useful tools in identifying where groundwater connectivity occurs. Understanding this connectivity forms another line of evidence to improve impact prediction models on a regional scale as well as providing information on connectivity in local groundwater investigations. To access the presentation click the link on the right. To read the full paper click here

Research on the Nonlinear Characteristics of Acoustic Emission and Damage Mechanism of Gassy Coal under Unloading Conditions

Coal mining and production activities lead to static loading and unloading changes of coal stress in front of the working face, and the stress change process has a significant influence on the occurrence and development of coal-rock gas dynamic disasters. In this paper, the macroscopic failure characteristics, acoustic emission timing characteristics, and acoustic emission nonlinear characteristics of coal with different gas pressures under true triaxial loading and unloading conditions were experimentally studied. The results showed that the macroscopic failure form of coal with different gas pressures under unloading conditions was tensile-shear composite failure, and the crack structure was formed near the unloading surface. The fractal dimension D and multifractal parameter Δ α of acoustic emission time series both could reflect the complexity of coal fracture process. With the increase of gas pressure, the fractal dimension D and multifractal parameter Δ α decreased, which indicated that the greater the gas pressure, the lower the complexity of coal fracture process. Under different gas pressures, the dynamic change trends of multifractal parameter Δ α were similar, taking the beginning of unloading as the dividing point, the change was roughly in the form of “W.” When the stress state and failure form of coal body changed, the multifractal parameter Δ α changed synchronously, indicating that the change of Δ α could reflect the transformation process of failure mechanism of coal body under load to a certain extent, which was of great significance for clarifying the occurrence and development mechanism of coal-rock gas dynamic disasters and ensuring the safe production in underground coal mines.

CO2 Gas Fracturing in High Dip Angled Coal Seams for Improved Gas Drainage Efficiency at Hashatu Coal Mine

Effective gas drainage for the gassy coal seam is a technological measure to prevent excessive gas outing and gas related mine hazards. CO2 gas fracturing (CO2-Frac) is a new technology for coal mine gas control, and its effectiveness has been proven from many coal fields across China. CO2-Frac has been successfully implemented for gas drainage in single gently inclined coal seam, but it has not been experimented in steeply inclined multicoal seam. In this study, a pilot CO2-Frac project was carried out in Hashatu coal mine, a steeply inclined multicoal seam formation. To attain an effective gas drainage, three different types of CO2- Frac boreholes were drilled and experimented for a long-period gas drainage. One borehole type is the penetrating borehole through two seams, and other two types of in-seam boreholes include strike borehole and up-dipping borehole. With continuous field gas drainage and observation results, the gas drainage efficiency was found to be significantly improved in in-seam borehole and penetration borehole with CO2 fracturing, and the maximum methane flow rate increased 2.4 times for a given borehole length and the efficient drainage radius increased 3–4 times. In addition, the drainage effect of original drainage boreholes within the CO2-Frac circle influenced region was also significantly improved due to the borehole interference. The fractures radius of CO2-Frac in the penetrating borehole was larger than the two types of in-seam boreholes in the steeply inclined seam formation. This may be closely related to the developing property of bedding and cleat system in coal seam. This study provides both theoretical and practical evidence for effectiveness CO2-Frac in the area with steeply inclined angle and multicoal seam formations.

Analysis of precursor information for coal and gas outbursts induced by roadway tunneling: A simulation test study for the whole process

The diversity of precursor information is significant for providing accurate early warnings of outbursts. However, the existing research mainly focuses on noncontact indicators, which cannot fully and accurately reflect the outburst risk. To capture the precursor information of the key contact indicators, a simulation test for the whole process of outbursts was carried out. In the test, the newly developed similar materials of gassy coal and ultralow permeability rock and a simulation system were used to simulate the occurrence environment and disturbance conditions of the coal mass. The results show that the outburst phenomenon and gas concentration evolution are similar to the real phenomenon on site, which proved the accuracy of the test results. The abnormal characteristics of a number of physical aspects before outburst were detected: an obvious relief stress zone appeared in the in situ stress curve for coal seam; the gas concentration in the roadway exceeded the safety standard (0.3%) and continued to increase to 3%; the pressure of coal seam and roadway surrounding rock changed from stable to declining, with a total amplitude of 10 kPa; the temperature in coal seam and roadway changed from steady to fluctuating up and down, with fluctuations reaching 3.4 °C and 4.7 °C, respectively. According to the abnormal occurrence time and identification level, the sensitivity priorities of the above information were temperature, gas concentration, in situ stress, and gas pressure. In addition, the moving average, deviation rate, and dispersion rate of the gas concentration, gas pressure, and temperature versus time curve had more advantages than the signal itself. This study provides guidance for the realization of accurate and effective real-time warnings.

Stress Relief and Stimulation of Coal Reservoir by Hydraulic Slotting

Coal seam permeability is one of the key factors influencing the gas extraction efficiency, which is of great significance to reduce coal and gas dynamic disasters in gassy coal mines. Hydraulic slotting technique is an effective method to stimulate the coal reservoir, but the selection of slotting key parameters has great impact on gas extraction efficiency. For this reason, the hydraulic slotting model was established by using FLAC3D software to analyze the stress distribution before and after slotting. Then, the influence of borehole diameter, slotting width, and slotting length on coal seam stress relief is also discussed. The results show that the slotting width has a great influence on the stress relief of the coal seam, while the borehole diameter and slotting length have no obvious influence on that. Based on the results of numerical simulation, field tests were carried out in Sangshuping NO.2 coal mine. The results show that the coal seam stress can be fully released, resulting in the improvement of coal seam permeability. The gas extraction efficiency can be highly enhanced by hydraulic slotting. This research achievement provides the guidance basis for high-stress water jet slotting technology with adaptive selection of slotting parameters in different geological conditions.

Numerical and Similarity Simulation Study on the Protection Effect of Composite Protective Layer Mining with Gently Inclined Thick Coal Seam

Protective layer mining, as a dominating method for preventing coal and gas outburst, is generally adopted in highly gassy coal mines. In the absence of a suitable thickness coal seam to serve as the protective layer, the rock‐coal composite protective layer was proposed in this paper. We conducted a series of simulations and engineering measurements to investigate the protective effect under the mining of the rock‐coal composite protective layer of the Zhongtai coal mine located in the Hebi area of Henan, China. The numerical simulation analysis showed that, after the completion of protective layer mining, the minimum vertical stress of the No. 2‐1 coal seam had been reduced to 3.46 MPa. The maximum vertical displacement of the No. 2‐1 coal seam is 455.01 mm. The maximum expansion deformation of the No. 2‐1 coal seam is 9.77‰; the effective pressure relief range is as long as 160 m. The similarity simulation experiment revealed that, after the completion of protective layer mining, the minimum vertical stress of the No. 2‐1 coal seam is 4.0 MPa. The maximum vertical displacement of the No. 2‐1 coal seam is 640 mm. The maximum expansion deformation of the No. 2‐1 coal seam is 26.37‰; the effective protection range reaches 130 m. The engineering measurements demonstrated that the variation law of gas drainage parameters in the protected layer corresponds to the protected layer′s vertical stress distribution law in numerical simulation and similarity simulation. With the exploitation of the composite protective layer, the protective layer’s pressure begins to release. The average gas drainage concentration is 2‐3 times of that before the composite protective layer mining.

Improving the capacity of mine degassing pipelines

Purpose. To identify features of methane-air mixture flow within the steel degassing pipelines as well as within those ones made of composite materials, to develop engineering solutions improving their reliability for actual use. Methodology. To solve the problem of increasing the capacity of mine degassing pipelines, an analysis of fundamental studies on the physical and mechanical properties of mine methane and the processes of its recovery in a mine environment is conducted. Schemes of operating gas-transmission systems and peculiarities of functioning of zonal vacuum gas pipelines in the conditions of intensive removal of rocks of the bottom of underground workings and deformations of the massif are considered. Based on the results of expert assessment of production situations, potential reserves for enhancing the efficiency of in-mine gas pipelines have been determined. Reliability indicators of traditionally applied steel pipes and their analogues from composite materials used abroad are established, innovative technological and technical solutions for their construction at Ukrainian mines are recommended. Findings. According to the expert evaluation of the operation modes of mine degassing lines and analysis of the world practices to apply pipes made of composite materials for mining industry, an engineering solution concerning the improvement of operating degassing systems as well as their capacity has been substantiated. Originality. Innovative engineering solutions as for the modernization of the underground degassing systems, which allow increasing the capacity of mine pipelines, and provide maintaining of the quality the captured methane-air mixture in the process of its transportation from wells to vacuum pump stations, have been substantiated. Practical value. Implementation of the research results to decrease hydraulic resistance within the degassing mains as well as introduction of innovative engineering solutions for the construction of main degassing pipelines from long links of composite pipes with a minimum number of butt joints has been scheduled for Ukrainian mines dealing with the development of gassy coal seams.

Thermos-Solid-Gas Coupling Dynamic Model and Numerical Simulation of Coal Containing Gas

Based on gas seepage characteristics and the basic thermo-solid-gas coupling theory, the porosity model and the dynamic permeability model of coal body containing gas were derived. Based on the relationship between gas pressure, principal stress and temperature, and gas seepage, the thermo-solid-gas coupling dynamic model was established. Initial values and boundary conditions for the model were determined. Numerical simulations using this model were done to predict the gas flow behavior of a gassy coal sample. By using the thermo-solid-gas coupling model, the gas pressure, temperature, and principal stress influence, the change law of the pressure field, displacement field, stress field, temperature field, and permeability were numerically simulated. Research results show the following: (1) Gas pressure and displacement from the top to the end of the model gradually reduce, and stress from the top to the end gradually increases. The average permeability of the Y Z section of the model tends to decrease with the rise of the gas pressure, and the decrease amplitude slows down from the top of the model to the bottom. (2) When the principal stress and temperature are constant, the permeability decreases first and then flattens with the gas pressure. The permeability increases with the decrease of temperature while the gas pressure and principal stress remain unchanged.

Influence of methane on the prediction index gases of coal spontaneous combustion: A case study in Xishan coalfield, China

Lean-oxygen environment caused by methane in high gassy coal mine goaf has a significant influence on the prediction index gases of residual coal spontaneous combustion. The coal sample from Xishan coalfield in China was used to conduct the low-temperature oxidation experiments under different lean-oxygen environments. The experimental results show that different lean-oxygen environments had a significant delay effect on the formation of CO, CO2, H2 and C2H6, and the lower the O2 concentration, the more obvious the delay effect, and the delay effect of methane was greater than that of N2. A lean-oxygen environment caused by methane also had a significant influence on the values of CO/ΔO2 ratio and CO2/ΔO2 ratio. However, when the temperature was < 170 °C, the change of O2 concentration had no significant influence on the value of CO/CO2 ratio, and the relationship between the value of CO/CO2 ratio and temperature T can be accurately expressed by exponential function. The absolute amount of CO, CO2 and C2H6 generated by 1kg residual coal (CCO, CCO2 and CC2H6), which can reduce the influence of air leakage and residual coal mass on prediction index gases, were introduced to predict the spontaneous combustion in high gassy coal mine goaf. Then, the distribution diagrams of CCO, CCO2 and CC2H6 with temperature and O2 concentration were obtained, so as to accurately predict the degree of spontaneous combustion in high gassy coal mine goaf. The research results are of great significance to the prevention of spontaneous combustion in goaf of high gassy mine.

Spatial non-linearity of methane release dynamics in underground boreholes for sustainable mining

The paper is devoted to the problem of increasing energy efficiency of coalmine methane utilization to provide sustainable development of geotechnologies in the context of transition to a clean resource-saving energy production. Its relevance results from the fact that the anthropogenic effect of coalmine methane emissions on the global climate change processes is 21 times higher than the impact of carbon dioxide. Suites of gassy coal seams and surrounding rocks should be classified as technogenic coal-gas deposits, while gas extracted from them should be treated as an alternative energy source. Existing practices and methods of controlling coalmine methane need to be improved, as the current “mine – longwall” concept does not fully take into account spatial and temporal specifics of production face advancement. Therefore, related issues are relevant for many areas of expertise, and especially so for green coal mining. The goal of this paper is to identify patterns that describe non-linear nature of methane release dynamics in the underground boreholes to provide sustainable development of geotechnologies due to quality improvement of the withdrawn methane-air mixture. For the first time in spatial-temporal studies (in the plane of CH4-S) of methane concentration dynamics, according to the designed approach, the parameter of distance from the longwall (L) is introduced, which allows to create function space for the analyzed process (CH4 of S-L). Results of coalmine measurements are interpreted using the method of local polynomial regression (LOESS). The study is based on using non-linear variations of methane concentration in the underground boreholes and specific features of their implementation to perform vacuum pumping in the most productive areas of the undermined rock mass in order to maintain safe aerogas conditions of the extraction block during intensive mining of deep-lying gassy seams. Identification of patterns in the influence of situational geomechanical conditions of coal mining on the initiation of metastable gas-coal solution transformation and genesis of wave processes in the coal-rock mass allows to improve reliability of predicting methane release dynamics, as well as workflow manageability of mining operations. Presented results demonstrate that development of high-methane Donbass seams is associated with insufficient reliability of gas drainage system operation at distances over 40 m behind the longwall face. Obtained results confirm a working hypothesis about the presence of spatial migration of methane concentration waves in the underground gas drainage boreholes. It is necessary to continue research in the area of estimating deviation angles of “advance fracturing” zone boundaries from the face line direction. Practical significance of research results lies in the possibility to use them in the development of scientific foundation for 3D gas drainage of a man-made coal-methane reservoir, taking into account spatial and temporal advancement of the production face.

Experimental simulation on mineral and hydrochemical evolution in response to water–coal–gas interaction of closed gassy coal mines

One ubiquitous environmental issue with the abandoned gassy coal mine is the potential of changes in water quality due to water–rock–gas action caused by high residual gas content. Therefore, a better understanding of how to accurately characterize the new multiphase system in the closed gassy coal mine is required. The gas in closed coal mine mainly includes CH $$_{4}$$ , CO $$_{2,}$$ N $$_{2}$$ , H $$_{2}$$ S, CO, etc., existing in the adsorbed, dissolved and free phases, which also leads to complex gas–water–rock interactions in the underground flooded pool. The recovery of the water level caused by the closure of the coal mine varied dramatically in hydrogeochemical conditions as well as gas flow performance in the flooded mine. Based on the nationwide investigation and case studies of high residual coal mine gas in abandoned coal mines in China, some sealed gassy coal mines have been experiencing the CO $$_{2}$$ inrush problems. Modeling experiments of mine water–rock (coal)–gas(CO $$_{2}$$ /N $$_{2}$$ ) reaction were conducted in closed coal mines. The results show that with the increasing reaction time, pH value increases gradually, and the relationship between Eh and pH is negative, by taking CO $$_{2}$$ /N $$_{2}$$ as gas phases in the water–rock reaction. The concentration of HCO $$_{3}^{-}$$ , SO $$_{4}^{2-}$$ , Ca $$^{2+}$$ , Mg $$^{2+, }$$ and SiO $$_{2}$$ increases with a different magnitude, and the level of total Fe decreases gradually, while the TDS of the solution increases. The reaction between typical minerals in coal and high SO $$_{4}^{2-}$$ and Fe $$^{3+}$$ mine water is simulated. The chemical composition of mine water and coal mineral compositions are modified in order to obtain the influence of particular reactions. The results show that in the mine water–rock–gas reaction with CO $$_{2}$$ as gas phase, the pH value of the solution increases, and the Eh decreases. The dissolution of mineral phases leads to an increasing trend in the content of HCO $$_{3}^{-}$$ , SO $$_{4}^{2-}$$ , Ca $$^{2+}$$ , Mg $$^{2+}$$ , and soluble SiO $$_{2}$$ in the water. The concentration of the total Fe in the solution gradually decreases, and the mineralization of the solution gradually increases. Each mineral has individual distinct dissolution reaction rate. The dissolution of kaolinite promotes the dissolution of quartz, while calcite dissolves along with the regeneration of new carbonate minerals. Pyrite dissolves accompanied by chlorite formation. For the N $$_{2}$$ gas phase, changes in hydrochemistry and mineral phases are mainly controlled by water–rock interaction.