Ordovician Limestone Research Articles

Water Storage Capacity of Ordovician Limestone Aquifer and Hydrogeological Response Mechanism of Deep Reinjection in North China

Mine water treatment and emissions have become important factors that restrict the comprehensive benefits of coal enterprises and local economic development, and the use of the deep well recharge method can address the specific conditions of mine surge water. This paper takes the actual situation of coal mine water treatment as an example and innovatively carries out dynamic tests for the Ordovician limestone aquifers deep in the mine. Intermittent reinjection test shows that under the same reinjection time, the water level recovery rate during the intermittent period is fast at first and then slow. Moreover, the recovery speed of the water level buried depth slows down with the increase in the reinjection time, which reveals the characteristics of the water level rising rapidly and recovering quickly during the reinjection of the reservoir. The average formation water absorption index is 420.81 m3/h·MPa. The water level buried depth of the long-term reinjection test showed three stages (rapid rise, slow rise, and stable stages), and the water level buried depth was raised to 1.52 m at its highest. Monitoring data from the surrounding 5 km area showed that reinjection did not affect aquifer water levels, verifying the excellent storage capacity of the deep Ordovician fissure-karst aquifer. The variability of well loss under pumping and injection conditions was comparatively analyzed, and the well loss produced by the recharge test was 4.06 times higher than that of the pumping test, which provided theoretical support for the calculation of hydrogeological parameters to eliminate the influence of well loss. This study deepens the understanding of Ordovician limestone aquifers in deep mine water, providing a reference for cheap mine water treatment and sustainable groundwater management in similar mine areas.

Spatiotemporal evolution mechanisms of groundwater seepage-chemical coupling fields in Pingshuo mining area

This study investigates the Jinggong No.1 Mine, Jinggong No.3 Mine, and Xiali Yuan Mine in the Pingshuo mining area. Through field sampling and hydrochemical-seepage coupled tests, we reveal the seepage-solute coupled dynamic behaviors of groundwater systems across different mines. By analyzing fluid pressure gradients, ion concentration fields, and permeability coefficients from multiple aquifers (surface water, goaf water, sandstone fissure water, and Ordovician limestone water), combined with Piper trilinear diagrams and solute transport models, we decipher the controlling mechanisms of groundwater seepage pathways on hydrochemical evolution. Key findings include: The high total dissolved solids (TDS) (>4000 mg/L) and SO42- dominance (>84%) in the goaf water of Jinggong No.1 Mine stem from evaporation-concentration effects in low-velocity seepage zones (permeability coefficient K = 1.2 × 10−6 m/s, significantly lower than other mines); hydrochemical differentiation in sandstone aquifers is governed by heterogeneous seepage fields (hydraulic gradient of 0.15 in Jinggong No.1 Mine induces mixing, while stable seepage in Jinggong No.3 and Xiali Yuan Mines maintains K = 5 × 10−5 m/s); the temporal increase in TDS of Ordovician limestone water (annual growth rate 18%) reflects accelerated vertical seepage along fault zones (Darcian velocity rising from 0.3 to 0.8 m/d), driving the migration of Ca-Mg-SO4-type hydrochemical fronts. This study establishes quantitative response relationships between hydrochemical indices and seepage parameters, providing theoretical support for groundwater hydrodynamic field regulation and water-inrush channel identification in mining areas.

Hydrogeochemistry and Heat Accumulation of a Mine Geothermal System Controlled by Extensional Faults

Given the high proportion of global fossil energy consumption, the Ordovician karst water in the North China-type coalfield, as a green energy source that harnesses both water and heat, holds significant potential for mitigating environmental issues associated with fossil fuels. In this work, we collected geothermal water samples and conducted borehole temperature measurements at the Xinhu Coal Mine in the Huaibei Coalfield, analyzed the chemical composition of regional geothermal water, elucidated the characteristics of thermal storage, and explored the influence of regional structure on the karst geothermal system in the northern region. The results indicate that the geothermal water chemistry at the Xinhu Coal Mine is of the Na-K-Cl-SO4 type, with its chemical composition primarily controlled by evaporation and concentration processes. The average temperature of the Ordovician limestone thermal reservoir is 48.2 °C, and the average water circulation depth is 1153 m, suggesting karst geothermal water undergoing deep circulation. The geothermal gradient at the Xinhu Coal Mine ranges from 22 to 33 °C/km, which falls within the normal range for ground-temperature gradients. A notable jump in the geothermal gradient at well G1 suggests a strong hydraulic connection between deep strata within the mine. The heat-accumulation model of the hydrothermal mine geothermal system is influenced by strata, lithology, and fault structures. The distribution of high ground-temperature gradients in the northern region is a result of the combined effects of heat conduction from deep strata and convection of geothermal water. The Ordovician limestone and extensional faults provide a geological foundation for the abundant water and efficient heat conduction of the thermal reservoirs.

Initiation mechanism of split grouting cracks at the top of the Ordovician limestone in a coal seam floor

Initiation mechanism of split grouting cracks at the top of the Ordovician limestone in a coal seam floor

Study on deformation failure and permeability resistance of large faults under mining

The deformation and failure of large faults during coal seam mining can result in channels being formed that are connected to aquifers, which can present a serious threat to the safe mining of coal seams. This study takes the Beigongcun No. 1 fault in the No. 7 mining area of the Dongtan Coal Mine as a case study, aiming to explore the deformation and permeability resistance of large faults. Through the establishment of an engineering geological model, FLAC3D software is used to simulate the fluid–solid coupling of the mining process. The results show that as the working face advances, the compressive stress within 40 m of the fault decreases significantly and is most affected by mining at 20 m below the coal seam after mining to the fault. The calculated fault permeability strength is lower than the Ordovician limestone water pressure. Further simulation of the fault mining with different dip angles shows that the failure modes are basically the same but the failure depth is different. In the dip angle range of 50°–80°, the fault failure depth is smallest for a dip angle of 65°, and the fault resistance strength is greatest for a dip angle of 60°. This shows that the depth of fault failure is greatest at a specific dip angle.

The Hydrodynamic Simulation of Karst Water Under Deep Coal Mining and Fault Conditions: A Case Study of the Zhuxianzhuang Mine in Northern Anhui

As shallow coal resources in China become increasingly depleted, deep coal mining in complex geological areas has become an inevitable trend. However, the technical challenges associated with deep mining are becoming more significant, particularly the issues related to mine water hazards. This study utilized hydrogeological data from the III3 Mining Area in the Zhuxianzhuang Coal Mine, Anhui Province, and employed GMS (Groundwater Modeling System) software to construct a numerical karst water flow model under deep mining conditions. By simulating variations in the flow field, the study verified the drainage potential of the limestone water at the base of Seam 10 and assessed the water conductivity and connectivity of the F22 fault. The following conclusions were obtained: The simulation effectively captured the formation process of the karst water drawdown cone in the study area. The observed water level variations in different monitoring wells aligned well with the engineering reality after validation. The limestone water at the base of Seam 10 in the III3 Mining Area exhibited good transmissivity, weak recharge, and high drainage potential. Although the F22 fault is a normal fault with a maximum displacement of 550 m, offsetting formations from Seam 3 to the Ordovician limestone, its connectivity and water conductivity are poor, exhibiting significant water-blocking properties. The specific capacity (q) ranges from 1.40 × 10−4 to 3.26 × 10−3 m3/(s·m), and the hydraulic conductivity (K) ranges from 2.10 × 10−5 to 6.80 × 10−5. Under deep coal mining conditions, the extraction of coal disturbs the underlying limestone, generally resulting in an increase in its permeability coefficient compared to pre-mining conditions. The permeability coefficient (K) from the measured data before mining impact ranged from 0.000067 to 0.0022, while the simulated values after mining impact ranged from 0.0021 to 0.09. Additionally, mining activities affect the hydraulic head, flow rate, and flow paths of the karst water; the floor karst water is easily drainable, effectively reducing water pressure and the inrush coefficient, thus lowering water hazard risks. Although the mining area is affected by the large F22 fault, its water-resisting properties under sufficient drainage conditions prevent direct connectivity between the coal seam and the aquifer, avoiding water hazards. As global coal resources continue to be exploited, deep mining will inevitably become a common trend in coal extraction worldwide. This study develops a hydrogeological model tailored to deep mining under fault conditions, offering a solid theoretical foundation and practical reference for the prevention and management of mine water hazards on a global scale. This advancement contributes to the development of sustainable mining practices across the global industry.

Late Ordovician Bentonites From the Southern Ordos Basin: Response to the Subduction of the Proto‐Tethys Ocean

ABSTRACTThe connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO2 (57.94–77.95 wt.%) and Al2O3 (9.21–14.33 wt.%), classifying them within the low‐potassium alkali basalt to medium‐potassium calc‐alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right‐dipping, with a more pronounced negative Eu anomaly (δEu = 0.48–0.67). The zircons in the bentonites yield two‐stage model ages ranging from 546 to 956 Ma, along with ε Hf(t) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto‐Tethys Ocean along the southern margin of the North China Block.

Hydrogeochemical Characteristics and Formation Processes of Ordovician Limestone Groundwater in Zhuozishan Coalfield, Northwest China

A comprehensive understanding of the characteristics and formation mechanisms of groundwater in mining areas is essential for the effective prevention of coal mine water and the rational management of groundwater resources. The objective of this study was to examine the hydrogeochemical characteristics and evolution of Ordovician groundwater in the Zhuozishan coal mine, located in the northwest region of China. A total of 34 groundwater samples were collected for hydrogeochemical analyses and the investigation of their evolution processes, with the aid of a piper trilinear diagram, a Gibbs diagram, and an ion ratio diagram. The results indicate that the concentration of sodium (Na+), potassium (K+), bicarbonate (HCO3−), chloride (Cl−), sulphate (SO42−), total dissolved solids (TDS), and pH increases from the recharge area to the discharge area, whereas the concentration of calcium (Ca2+) and magnesium (Mg2+) decreases. The hydrogeochemical characteristics of the runoff from Zhuozishan to Gongdeer coalfield and further southward display a notable north–south directional change. The groundwater process is primarily controlled by rock weathering action and cation exchange, with Na+ and K+ deriving primarily from cation exchange and only to a minor extent from halite dissolution. In conclusion, the northern part of the coalfield is characterised by a geological structure that creates a retention area with groundwater, resulting in an unordered runoff process with a complex formation mechanism. The middle region is devoid of geological constraints that would alter the flow direction, thus simplifying the process of groundwater formation. In contrast, the southern area experiences an increase in strata depth and fault blocking, which creates a retention zone, thereby rendering the groundwater formation process more complex. This research contributes to the effective management of groundwater resources in this coalfield and other mining sites.

Advancing Sustainable Geothermal Energy: A Case Study of Controlled Source Audio-Frequency Magnetotellurics Applications in Qihe, Shandong

Geothermal energy is a key part of sustainable and renewable energy strategies, especially for clean heating in northern regions. This study focuses on Qihe County in Shandong Province, applying a controlled source audio-frequency magnetotellurics (CSAMT) method to investigate deep karst geothermal reservoirs. This research addresses the complex geological conditions and electromagnetic interference in the region, aiming to improve sustainable geothermal resource development. The findings indicate that the geothermal reservoir in the study area primarily consists of Ordovician limestone, characterized by moderate burial depth, high water volume, and elevated water temperature. Integrating CSAMT with vertical electrical sounding (VES) and radiometric surveying has clearly defined the deep aquifer layers and major water-controlling fault structures. Drilling verification results demonstrate the significant effectiveness of the integrated geophysical methods employed, providing reliable technical support for deep geothermal exploration in similar regions. This study makes a significant contribution to the scientific and technical foundation necessary for the sustainable development and utilization of geothermal resources, supporting the broader goals of environmental sustainability and renewable energy.

Investigate on the mechanical properties and microscopic three-dimensional morphology of rock failure surfaces under different stress states

The macro and micro morphology of rock failure surfaces play crucial roles in determining the rock mechanical and seepage properties. The morphology of unloaded deep rock failure surfaces exhibits significant variability and complexity. Surface roughness is closely linked to both shear strength and crack seepage behavior. Understanding these morphology parameters is vital for comprehending the mechanical behavior and seepage characteristics of rock masses. In this study, three-dimensional optical scanning technology was employed to analyze the micromorphological properties of limestone and sandstone failure surfaces under varying stress conditions. Line and surface roughness characteristics of different rock failure surfaces were then determined. Our findings reveal a critical confining pressure value (12 MPa) that influences the damage features of Ordovician limestone failure surfaces. With increasing confining pressure, pore depth and crack formation connecting the pores also increase. Beyond the critical confining pressure, the mesoscopic roughness of the failure surface decreases, and the range of interval-distributed pore roughness diminishes. Additionally, we conducted a detailed investigation into the water conductivity properties of rocks under different stress states using Barton's joint roughness coefficient (JRC) index and rock fractal theory. The roughness features of rock failure surfaces were classified into three categories based on mesoscopic pore and crack undulation forms: straight, wavy, and jagged. We also observed significant confining pressure effects on limestone and sandstone, which exceeding the critical confining pressure led to increased water conductivity in both rocks, albeit through different mechanisms. While sandstone exhibits fissures running across it, limestone shows shear abrasion holes. Beyond the critical confining pressure, the rock failure surface becomes smoother, leading to decreased water flow blocking capacity. The fractal dimension of Ordovician limestone increases significantly under critical confining pressure, leading to a more complex mesoscopic crack extension route.

Geochemical Characterization and Prediction of Water Accumulation in the Goaf under Extra-Thick Fully Mechanized Top-Coal-Caving Mining

In multi-seam coal mining, the water accumulation in the goaf of the upper coal seam will seriously threaten the safety of the lower coal-seam recovery. How to accurately determine the water charging source in the goaf and predict the amount of water accumulation in the goaf after a certain time interval has become a major challenge that urgently needs to be solved in coal production. In this study, we consider the water-discharging goaf of the Tangjiahui Coal Mine as the object of research to investigate the problem of water accumulation in the goaf during the fully mechanized caving mining of extra-thick seams of top coal. We used geochemical methods, water-accumulation space methods, and large-well methods to analyze the hydraulic connections between goaf water and other aquifers, predict the amount of water accumulation in the goaf, and explore the characteristics of water level changes over time. We then used the results to discuss the relationship between the elevation of the accumulated water and the time taken for it to fill the goaf. The results showed that there is a hydraulic connection between the water in the airspace and the goaf water (GW), roof water (RW), floor water (FW) and Ordovician limestone water (OW); the volume of water in the goaf of the working face after mining was 2,106,838.496 m3. The average rate of water accumulation was 65.407 m3/h, and the goaf was expected to have been filled in 32,211.208 h. The derived relationship between the water level and time was H0=−10−12t3+10−7t2−0.0042t+814.61 (R2=0.9837). This study is of great significance for the sustainable development of the safety evaluation of water blocking coal pillars at the mine boundary.

The Feasibility of Heat Extraction Using CO2 in the Carbonate Reservoir in Shandong Province, China

CO2 is being considered as an effective alternative working fluid for geothermal applications due to its superior fluid dynamics and heat transfer properties compared to water. Utilizing sedimentary rocks for geothermal energy recovery through a CO2-plume geothermal system, especially in carbonate reservoirs, has been shown to be a practical approach that eliminates the need for hydraulic fracturing. However, uncertainties remain regarding the thermal and hydraulic behavior, particularly the chemical interactions between CO2 and carbonate rocks. This study develops a comprehensive wellbore–reservoir coupling reactive transport model based on specific information obtained from the Ordovician limestone geothermal reservoir in Shandong, China. The model aims to assess the feasibility of heat extraction in carbonate reservoirs by evaluating the heat extraction performance and fluid–rock interaction. The results indicate a rapid temperature drop after CO2 breakthrough due to the Joule–Thomson effect. Simultaneously, the fluid transitions into and maintains a two-phase state throughout the operation. Chemical reactions within the reservoir are not aggressive since complete mixing between unsaturated water and CO2 only occurs in the vicinity of the production well, highlighting the potential of utilizing carbonate reservoirs for efficient heat extraction in geothermal systems. Further research is needed to optimize the performance of CO2-based geothermal systems in carbonate reservoirs.

A two-dimensional model test system for floor failure during automatic roadway formation mining without pillars above confined water

A two-dimensional model test system for floor failure during automatic roadway formation mining without pillars above confined water

Application of Free Ball Check Valve Mixed Grouting Device

In recent years, due to the uneven water abundance of the aquifer and the complexity of the underground seepage field, the grouting reconstruction project of coal mining enterprises is more difficult. The previous method is to install a high-pressure ball valve before the grouting pipe connected to the grouting pump is connected to the mixing device, which can be manually adjusted when the number of grouting pumps needs to be changed. However, under certain pressure, the ordinary high-pressure ball valve often fails due to the influence of high-pressure mixed slurry, cement solidification and wear, and the number of grouting pumps cannot be increased or decreased in real time. In order to solve the problem that the mixing device of traditional grouting system is easy to fail by using ordinary high-pressure ball valve, the mixing device of free ball check valve was developed and applied in the process of treating the Ordovician limestone aquifer area on the floor of No.9 coal seam in Xipang Well. The practical results show that the pipeline can be automatically closed when a single grouting pump stops grouting, and there is no need to flush the grouting pipeline with a large amount of water, which can improve the grouting efficiency and quality, and the influence time of single hole section is reduced from 8.25h to 0.34h. The process performance can meet the requirements of efficient grouting.

Study on the Hydrochemical Characteristics and Evolution Law of Taiyuan Formation Limestone Water under the Influence of Grouting with Fly Ash Cement: A Case Study in Gubei Coal Mine of Huainan, China

The hydrogeological conditions of Huainan Coalfield are complex. The Taiyuan formation limestone water (Taihui water) in this area is a direct threat to the water source of the 1# coal mining floor. In order to prevent and control water disasters, Gubei Coal Mine adopted ground high-pressure grouting with fly ash cement to block the hydraulic connection between the Taiyuan formation limestone aquifer and the Ordovician limestone aquifer. However, the injected slurry will destroy the original hydrochemical balance of Taihui water and change its hydrochemical characteristics. Taking the influence area of the 2# karst collapse column in the Beiyi 1# coal mining area of Gubei Coal Mine as an example, a total of 25 Taihui water samples were collected. The hydrochemical characteristics and evolution law of Taihui water before and after grouting are studied via the multivariate statistical method. The research methods include constant index statistics, Piper diagram, correlation analysis, ion combination ratio, and saturation index analysis. The results show that after grouting, the concentrations of Na+ + K+, Ca2+, Mg2+, and Cl− in Taihui water decrease, while the concentrations of SO42− and HCO3− increase. The average values of PH and TDS become larger. The hydrochemical types of Taihui water are more concentrated, mainly HCO3-Na and Cl-Na. The correlations between conventional indicators decrease. According to the analysis of ion combination ratio, dissolution, cation exchange, and pyrite oxidation mainly occur in Taihui water, and these effects are enhanced after grouting. The saturation index results show that after grouting, the saturation index of dolomite, calcite, and gypsum is significantly reduced, and the saturation index of rock salt is slightly increased. The conclusion of this study is that the hydrochemical characteristics of Taihui water are greatly affected by fly ash cement. Moreover, because fly ash cement contains a lower calcium oxide content than ordinary Portland cement, the effect of fly ash cement on the ion concentration of Taihui water and the resulting hydrogeochemical effect are significantly different. Therefore, in the treatment of mine water disasters, the hydrogeochemical evolution law affected by fly ash cement grouting should be identified.

Study on precursor information and disaster mechanism of sudden change of seepage in mining rock mass

Abstract Changes in the stress field and seepage field of mining unloading are one of the important causes of deformation and destabilization of the rock body of the bottom slab. With the increase of mining intensity and depth, the disaster of water influx on the bottom plate under the dual action of mining unloading and pressurized water has become one of the main problems restricting the efficient and safe mining of coal. Based on the research background of confined water inrush from Ordovician limestone floor in North China Coalfield, the numerical analysis revealed that mining unloading concentrates stresses, increases deformation, and increases the plastic zone and permeability range. Based on laboratory acoustic emission and mechanical tests, it is found that the peak of acoustic emission ringing number can be one of the precursor information of limestone seepage mutation. This study reveals the evolution law of rock body deformation and permeability under the unloading path, and the research obtains the unloading seepage and water gushing disaster mechanism of the subgrade rock body.

Investigation on water inrush fracture mechanics model based on fracture mechanics and microseismic monitoring

Investigation on water inrush fracture mechanics model based on fracture mechanics and microseismic monitoring

Exploration and prediction of high pressure dynamic water hidden collapse column in coal mines

Hidden collapse column associated with high pressure dynamic water is a main cause of major water inrush accidents in North China type coal fields. Taking the structural abnormality area discovered in 11603 working face of Daizhuang Coal Mine as an example, underground three-dimensional high-density electrical method, advanced exploration of underground drilling and curtain grouting were used to detect the existence of collapse column, and analyzed the water conductivity of collapse columns based on the hydraulic connection analysis of the 13th limestone and Ordovician limestone aquifers. Finally, it is determined that this abnormal area is a strong water filling collapse column originating from the upper Ordovician strata runoff zone (inferred to be within a range of 30 to 100 m below the Ordovician limestone top interface), developed to a height of 12th limestone. Based on the fact that the water yield and water pressure of underground directional drilling, the grouting pressure of curtain grouting, and the amount of cement injected are external quantitative factors that reflect the existence of hidden karst collapse columns during the process of detecting hidden karst collapse columns, and in combination with the feature that deep learning can fully independently learn abstract knowledge expression, a prediction model based on convolutional neural networks is constructed. According to the established network model, it was found that among the 12 sets of actual measurement data, only one data point indicated the absence of a collapse column. The prediction accuracy reached 91.6%, which meets the practical needs.

Development characteristic and main controlling factors of the Ordovician karst caves in the Keping area, Tarim Basin

Development characteristic and main controlling factors of the Ordovician karst caves in the Keping area, Tarim Basin

Numerical simulation of the interaction between mine water drainage and recharge: A case study of Wutongzhuang coal mine in Heibei Province, China

Numerical simulation of the interaction between mine water drainage and recharge: A case study of Wutongzhuang coal mine in Heibei Province, China