Mine water source identification and water-inrush tracing in deep coal mines remain challenging due to the complex hydrogeological conditions. Coal-derived dissolved organic matter (Coal-DOM) has emerged as a potential organic tracer, yet its temperature-dependent release characteristics under deep mining conditions are poorly understood. This study investigates the release of Coal-DOM from coals of varying metamorphism (long flame coal, lean coal, anthracite) at 25 °C and 50 °C using DOC analysis, EEM spectroscopy, and FT-ICR MS. Results show that elevated temperature significantly enhances DOC release, most markedly in anthracite (from 9.1 to 13.5 mg-C/L). For low-rank coals, temperature promotes the release of polar, protein-like DOM, increasing molecular diversity (from 3877 to 7876 formulas) and oxidation state (O/C from 0.31 to 0.40). In contrast, anthracite releases DOM dominated by aliphatic compounds (>75%), a signature reinforced at higher temperatures. These rank-specific molecular fingerprints exhibit clear media-specificity, demonstrating their potential as supplementary organic tracers for discriminating mine water sources and tracing water-inrush pathways in complex deep mining environments.

Directional drilling machines are extensively employed in gas drainage, water exploration, and coalbed methane exploration in underground coal mines. The measurement while drilling (MWD) system collects the spatial orientation and depth parameters of the drill rod during the drilling process using a three-axis sensor, which guides the drill rod along the predefined trajectory, ensuring it reaches the designated drilling position for safe coal mining. Due to installation angle errors of the three-axis sensor and alignment discrepancies between sensors, the sensor produces complex three-dimensional spatial errors during measurement, complicating the identification of the physical plane correction axis needed for traditional installation error correction methods. To resolve this issue, a BP neural network-based correction algorithm for installation errors in the MWD system is proposed. The algorithm disregards installation errors of accelerometer and magnetometer sensors, does not necessitate additional parameter calculations, and directly predicts attitude angles through ellipsoid fitting of the measurement data, thereby effectively mitigating the impact of installation errors. The effectiveness and prediction accuracy of the algorithm are validated through numerical model experiments, ground experiments, and underground tests. The results demonstrate that the absolute azimuth error in the indoor experiment is less than 1 degrees, improving by approximately 5 degrees compared to the traditional scalar product constant method, with an absolute pitch angle error of 0.1 degrees, improving by approximately 1.5 degrees compared to the traditional plane-fitting method. The absolute azimuth error in the ground experiment is less than +/- 1.8 degrees, and the absolute pitch angle error is less than +/- 0.18 degrees, which meets the requirements of the while-drilling measurement system for underground coal mining projects.

Understanding the thermal behavior of coal-derived dissolved organic matter (DOM) is essential for assessing its environmental reactivity in deep mining environments. Accordingly, in this study, gas coal (GC) and anthracite, representing distinct coal ranks, were subjected to temperature-controlled static incubation experiments at 25 and 50 °C to investigate the temperature-induced release dynamics and molecular evolution of Coal-DOM under simulated subsurface conditions. A multianalytical strategy combining excitation-emission matrix spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and machine learning (XGBoost-SHapley Additive exPlanations [SHAP]) was applied to characterize the molecular-level transformations of Coal-DOM. The results indicated that elevated temperature substantially enhanced DOM release, with dissolved organic carbon concentrations increasing by approximately 54% (to 10.3 ± 0.3 mg-C/L) for GC-DOM and 52% (to 12.3 ± 0.2 mg-C/L) for ANT-DOM compared to 25 °C, and promoted the generation of more oxidized, aromatic, and nitrogen-rich compounds, particularly in GC-DOM. FT-ICR-MS analysis revealed significant molecular alterations: the number of assigned molecular formulas increased from 5,593 to 8,470 for GC-DOM and from 4140 to 8107 for ANT-DOM upon heating to 50 °C, accompanied by an increase in O/C ratio (from 0.264 to 0.285 for GC-DOM). Further, Van Krevelen analysis revealed a shift toward lipid- and lignin-like structures at 50 °C. Meanwhile, SHAP analysis identified the nominal oxidation state of carbon, modified aromaticity index and double bond equivalence per carbon atom as the most influential predictors of thermally generated compounds. Additionally, mass difference network analysis indicated that oxidation and dealkylation were the predominant transformation pathways, with +3O additions being the most frequent. Overall, this study elucidates the temperature-mediated release mechanisms and structural evolution of Coal-DOM across coal ranks, offering molecular-level insight into its reactivity, mobility, and potential environmental risks in subsurface mining settings.

Combining multiple monitoring methods can improve the accuracy of coal damage and fracture behavior detection. In this study, nine coal samples, each with similar P-wave velocities and masses, were subjected to joint monitoring experiments involving multiple physical parameters. The acoustic emission (AE) and resistance information of coal samples were assessed from the initiation of loading to eventual failure under diverse uniaxial loading rates. The characteristic electrical and acoustic parameters were analyzed in combination with coal damage conditions. The results show that, throughout the loading process, resistivity declined gradually with escalation of coal strain, followed by an abrupt nonlinear increase. Deformation before failure reduced coal resistivity by up to 11.39

矿井水害问题伴随着矿产资源开采深度的加深日益突出,富水体形态不易确定,位置不明,极易造成突水事故.本文基于煤矿瞬变电磁探测矿井富水体响应规律,采用有限元法对矿井采掘工作面顶板富水性进行多角度全空间数值模拟,分析不同角度矿井顶板富水体的感应电流密度响应特征.结果表明:(1)探测角度为9°和 18°时,整体模拟效果更佳,锲合工作面实际探测的需求.当富水体在高阻煤层时,富水体外部等值线密集,感应电流密度极大值在富水体轮廓中;当富水体位于顶板时,富水体上部等值线密集,感应电流密度极大值位于富水体内上部;(2)富水体感应电流密度等值线轮廓以椭圆形为主,随着探测角度的增大,感应电流密度等值线逐渐稀疏,但富水体的整体轮廓不变;(3)探测角度增大,感应电流密度极大值降低但不会影响感应电流密度极大值在富水体内部出现的现象,因此可根据感应电流密度极大值判断富水体的位置.本文通过对典型煤矿富水体分布规律研究,改进了矿用瞬变电磁仪的正演模拟方法,推动了新的反演解释算法及软件开发,为非煤矿山、金属矿山、隧道工程等井工或地下作业场景水害探测防治提供一种新的技术与方法.

A series of experimental geophysical methods with resistivity as the key parameter provide strong support for predicting and providing early warnings of geological disasters. In this study, coal samples with similar P-wave velocities and pore distributions were screened, and a weighing method was used to control the water content of the coal samples. A real-time test system was independently constructed to conduct uniaxial compression tests on these coal samples and synchronously monitor resistivity and acoustic emission (AE) data. The results show that resistivity obviously characterizes the process of coal failure under load. The development of microfractures causes fluctuations. The resistivity changes relatively smoothly before the development of fractures, and resistivity fluctuations are obvious during the development of fractures. The resistivity fluctuation range reaches the maximum when the whole fracture occurs at the stress peak, but the presence of water weakens the resistivity fluctuations during the whole process of failure. Water migration causes circuit reconnection and changes the fluctuations. With increasing water content, the uniaxial compressive strength (UCS), elastic modulus (E) and maximum AE amplitude decrease. The resistivity variation at the peak value also decreases. Under the condition of 9.2% water content, the resistivity variation at the peak stress is only 2.52%. The results prove that violent fluctuations of resistivity correspond to the development of microfractures in the sample, and the amplitude of the fluctuations is positively correlated with the degree of damage and fracture. The volatility index (Resistivity Standard Deviation, RSD) is established to describe the degree of resistivity fluctuation, and the peak value occurs when the AE energy increases sharply. The establishment of a volatility index aims to provide a new parameter for rock damage and dynamic disaster prediction technology.

To examine the influence of lithology on the microseismic response mechanism during the process of coal and rock hydraulic fracturing (HF), we selected four lithological samples of coal, sandstone, shale, and mudstone, which are commonly found in coal-measure strata. The acoustic emission (AE) cumulative counts, AE energy, crack classification, AE peak frequency, and AE position of the four samples under natural conditions were studied, and the laws of crack propagation and evolution in the process of coal and rock HF were explained. We discovered the phenomenon of “bimodal frequency bands” during the HF of coal and rock samples. The results showed that the pressure curves and AE cumulative counts of the coal samples exhibited the largest fluctuations. The power-law distribution of AE energy has a discrete effect in the high-energy region and a plateau effect in the low-energy region. The AE energy power-law indexes of the mudstone samples are the largest, with the values of 0.64 and 0.61, whereas those of the shale samples are the smallest, with the values of 0.44 and 0.45. The crack classification of the samples of coal is mainly shear cracks, and the crack classification of the samples of sandstone, shale and mudstone is mainly tensile cracks. It is proposed to regard frequency band II as the dominant frequency band for HF in the coal, sandstone, and mudstone samples and frequency band I as the dominant frequency band for HF in shale samples.

Due to advantageous sensitivity to low resistance and noncomplicated operation, transient electromagnetic methods are the most widely used geophysical methods for advanced detection of coal-mining-disaster water bodies. To realize real-time imaging, we developed a wireless antenna attitude angle measuring instrument based on an electronic compass, which measures antenna attitude angle real-time. According to attitude angle information sent through WiFi to the host of transient electromagnetic real-time imager instruments, current transmission, signal acquisition, and antenna rotation angle information are achieved for real-time imaging. We studied the direct algorithm of the apparent resistivity of the whole-space transient electromagnetic field in overlapping loop mode based on double-logarithmic-transform piecewise least-squares fitting, which not only ensures accuracy but also accelerates calculation. On-site detection was carried out in a coal mine, and the detection results are generally consistent with the drilling results.

Water disaster is one of the major disasters threatening the safety production of coal mine, which is rank only second to gas disaster. And Meisbluke Coal Mine is seriously affected by water disasters. In order to find out the scope and location of water-bearing areas in Meisbluke Coal Mine. The comprehensive geophysical exploration method combining transient electromagnetic method (TEM) and high-density resistivity method (HDRM) is used to carry out this research. Firstly, the measuring area is determined and the relevant measuring points are arranged, and 73 TEM survey lines and 10 HDRM survey lines were arranged according to the requirements. Then, the principle, data processing method and main parameters of TEM and HDRM are introduced. The TEM detection results show that the thickness of Quaternary inferred by TEM is consistent with the geological conditions revealed by boreholes, and the thickness is about 50–80 m. And the water enrichment of the bedrock is obviously recharged by the Quaternary aquifer. Besides, the water-enriched areas in each elevation are marked and the water inrush runoff channel is deduced based on the 3D scenario inverted by TEM. And the detection results of the water-bearing areas by the two methods are in good agreement with each other, which can confirm and complement each other, and the interpretation of the data is scientific and reasonable with high reliability. Besides, the detection depth of HDRM is larger than that of TEM.

Resistivity will have different response characteristics to the hydraulic fracture propagation process. In this work, a resistivity testing system for hydraulic fracturing specimens was established. Resistivity and acoustic emission (AE) information were jointly analysed to determine the dynamic response characteristics of resistivity during hydraulic fracture propagation. The results show that the water and fracture exert a competitive influence on the connection structure of the circuit, and there are two significant peak resistivity points in the curve, presenting a double peak therein. The peak resistivity data of the specimen with a larger fracture area are much different from the initial value. With the increase of the rate of injection, the range of variation of the highest value that can be reached with the specimen resistivity decreases. High resistivity rates or high resistivity fluctuations exhibit rapid a release of fracture energy. The fracture failure mode dominated by shear fractures makes the formation produce a “series+parallel” electrical connection structure; a calculation model of formation resistivity based on shear and tensile failure was proposed to characterize the proportion of different types of hydraulic fractures and elucidate the control effect of matrix resistivity on the electrical performance of the overall circuit structure.

井下瞬变电磁随掘探测技术是探测掘进面前方致灾水体的有效方法,从硬件方面评估仪器对致灾水体的分辨能力,是仪器能够在井下正确使用的重要手段.通过比较二次场绝对差和仪器分辨率、叠加后背景噪声之间的大小关系,分析含水致灾体识别的硬件条件和评估依据;提出从硬件方面评估井下瞬变电磁对致灾水体分辨能力的计算方法:根据致灾水体结构建立三维地质模型,推导梯形波关断与负阶跃波关断二次场感应电压的关系,在GPU上采用全空间三维有限差分并行算法计算了致灾水体二次场响应;测量某瞬变电磁仪的关断时间和综合噪声,根据致灾水体的硬件分辨依据,从硬件方面评估井下瞬变电磁仪对导水陷落柱、充水采空区的分辨能力.为井下瞬变电磁探测仪器的研制和现场准确探测提供技术参考,具有重大的研究意义.

地层电阻率是地球物理勘探考察的重要参数,不同结构煤体受载破坏过程中电阻率变化特征存在差异.建立受载煤样电阻实时测试实验系统,对所压制未分层及不同厚度、不同强度的2分层型煤试样进行了单轴压缩实验,得出试样破坏过程的力学强度及电阻率变化规律,研究分层界面影响下不同结构型煤的电阻率响应特征.实验结果表明:型煤单轴压缩破坏下的电阻率呈现阶段性变化,未分层试样在压密后存在“U”型变化过程,最低点接近试样应力应变曲线屈服点;不同强度分层试样破坏过程中电阻率曲线先增加后呈现“U”型,破坏后电阻率为初始状态的2～4倍;不同厚度分层试样破坏过程中电阻率表现为先增后减,两分层厚度差异大的试样厚分层破坏更为剧烈,整体表现出的宏观电阻率值更大.分层试样弹性模量及抗压强度均较未分层试样小,峰值应力处的电阻率变化率为1～2,未分层试样则小于0.5;试样两分层厚度及强度越接近,压缩破坏产生的剥离部分越均匀,更容易产生区域“串-并联”现象,破坏后电阻率变化率越大.煤样本身或分层面空隙骨架的挤压破碎会导致煤层电阻率的增加.分层型煤试样破坏后表现出表面剥离,裂隙均匀连通的破坏形式,根据型煤受载破坏过程得出试样存在“纵向裂隙”和“纵向+横向裂隙”影响下电阻率变化数学模型.两分层及贯通界面的裂隙使试样呈“串-并联”形式连通电路,试样整体电阻率与裂隙电阻率及裂隙体积占比呈正相关.对分层型煤单轴压缩规律的描述反映了部分煤矿区地层物探过程中的电学各向异性特征.

Acoustic emission (AE) is a popular technique to monitor the process of rock failure during hydraulic fracturing for unconventional natural gas production. It contains abundant information that will be useful to study in-depth the nature of hydraulic fracturing. In this study, we focused on the AE count, energy, peak frequency, crack classification, and location recorded from four rock specimens subjected to a specific triaxial stress condition. We found the multi-frequency-response phenomenon of AE, and proposed the multi-frequency-response index to indicate the moment of the macrohydraulic crack formation. Furthermore, it was found that the power law distribution index of AE energy of non-stratified specimen was bigger than that of stratified specimens during hydraulic fracturing. The tensile crack dominated in all hydraulic fracturing tests. Our results are of significance for understanding hydraulic fracturing in stratified rocks.

Hydraulic fracturing is an effective method to improve the permeability of coal seams and enhance extraction of coalbed methane (CBM). Evolution of cracks in coal seam becomes increasingly complex when one borehole is drilled through multiple coal seams. In this work, physical models with two coal seams having different uniaxial compressive strength (UCS) ratios and height ratios were prepared to study the competitive initiation and extension of cracks based on pump pressure, acoustic emission (AE) source location, and crack morphology. The results showed that, a competitive relationship exists between the two coal seams in terms of crack extension. The pump pressure curves of all specimens presented four stages: (I) fluid-filling stage, (II) pressure rise stage, (III) pressure drop stage, and (IV) pressure stabilization stage. Compared with the pure specimen, the crack initiation pressure of specimens with two coal seams reduced generally. The AE source locations were first generated and mainly distributed in the softer coal seam, resulting in the formation of a complex crack network, whereas only a few cracks were generated in the harder coal seam, as observed after cutting the specimens. In seams with different height ratios, the AE source locations and tracers indicated that cracks preferentially developed and extended in the thinner coal seam. The higher the height ratio of the two coal seams, the more difficult it was for cracks to extend simultaneously in two coal seams. The research results will help improve the permeability of CBM reservoirs when subjecting multiple coal seams to hydraulic fracturing.

Abstract Hydraulic fracturing can evidently improve the coalbed methane production in underground coal mines, but it is difficult to delimit the stimulated area accurately. In order to evaluate the stimulated area, microseismic (MS) monitoring technique is proposed to investigate the seismic responses of the induced fractures of hydraulic fracturing. Three coal seams were targeted to be treated in a coal mine. An array of geophones was set along the underground roadway to detect the MS signals caused by HF. In order to verify the result of MS monitoring, water content of each coal seam has been measured before and after HF treatment. The results showed that a series of MS events were detected during the entire HF process, and a sharp MS event usually occurred during the first hour of HF process. The energy of the sharp MS event had higher magnitude than others. The MS distribution exhibited complex morphological features. The directionless MS response was distributed over a radius of less than 40 m but tended to be significantly conjugated with a radius of more than 40 m. HF could stimulate both the coal seam and the rock layers nearby. The achievable stimulated area in the coal seam was determined to be 50 m × 50 m according to the MS density and water content. The stimulated area in terms of MS density was easily found to be broader than the area of water direct intrusion. The present study indicated that MS monitoring technique could potentially be used for evaluation of HF in underground coal mine.

Firstly the transient electromagnetic(TEM) field convolution was given,and change rate of turn-off current is taken as a impact function,the field component of vertical step pulse excitation as the input signal.The convolution result is TEM response of arbitrary shape turn-off current.The current excitation pulse is regarded as a superposition of many vertical step function.The transient electromagnetic response of arbitrary current pulse excitation is induced by the superposition of step function response.When the measured value of TEM field and the turn-off current form are known,whole-stage apparent resistivity can be calculated by the method of programming.The paper gives two examples on TEM vertical magnetic field of slope turn-off current excitation of electric dipole source,a response of uniform half-space and all-time apparent resistivity,a response to the three K-type geoelectric section and whole-stage apparent resistivity.

The small multiturn overlapping coil is always used in mine transient electromagnetic exploration. For the effect of turn-off, the first field dominates total field during the off-time of transmitting current and early after off-time. This may cause unresponsive for shallow low resistance anomaly. So we suggest that use cross coil for first field eliminating: Analyzes the distribution of first field inside and outside the transmitting coil during the off-time; Deduces the analytic expression of magnetic flow for first field inside the receiving coil; Worked out the coefficient of position for receiving coil is 0.93 when the magnetic flow for first field inside the receiving coil is 0. According to laboratory experiment for low resistance model and site detecting

由于瞬变电磁技术对水体反应灵敏,已被应用于煤矿井下水害探测.为提高探测精度,研究了恒流发射技术,采用脉冲宽度调制与功率场效应管结合,保证发射电流在探测过程中保持恒定;为提高二次场强度,采用了电感反向截断技术,利用电感中电流突然关断产生反向高压原理,缩短电流关断时间;通过外部中断与微控制器内部定时器配合,记录发射电流关断时间;采用隔爆兼本安型结构设计,保证仪器在井下安全使用.最后通过实验室测试和充水巷道探测,验证了仪器的准确性和有效性.更多还原

鉴于传统瞬变电磁探测系统同步方式不适用于半航空无人机瞬变电磁勘探系统,提出一种基于信号峰值检测的瞬变电磁同步技术,并利用Labview2012开发了信号峰值检测程序及双极性叠加程序,在实验室通过对模型实际探测来对算法进行检验:通过对单测点重复测量,验证同步叠加的稳定性;通过对单测线低阻模型的实际探测,验证算法的准确性.实验测试表明,基于二次感应电压峰值检测的同步方式,在不增加无人机起飞重量的同时,能够保证同步叠加的稳定性和探测的准确性,适用于无人机空地瞬变电磁探测.