Forecasting Fractures in Coal Seams by Using Azimuthal Anisotropy from P-Wave Seismic Data

If the thickness of coal seams and the lithology of both roofs and floors of coal seams have not changed at all or only a little, then it is thought that the elastic anisotropy of coal seams depends mainly on fractures and obeys the horizontally symmetric model of an azimuth anisotropy. For a fixed offset, the amplitude A of the reflection P-wave and the cosine of 2 φ has an approximately linear relation, （ φ is the source-detector azimuth with respect to the fracture strike. Based on this relationship, many things can be done, such as the extraction of macro bins, the correction of residual normal moveout, the formation of azimuth gather, the transformation and normalization of azimuth gathers and the extraction of reflection wave amplitudes of coal seams. The least squares method was used to inverse theoretically the direction and density of fractures of coal seams. The result is in good agreement with the regional geological structure, indicating that the azimuth anisotropic analysis of the P-wave is feasible in evaluating the density and direction of fractures in coal seams.     

Forward Modeling of the Relationship Between Reflection Coefficient and Incident Angle of the P Wave in a Coal Seam

1 Introduction The AVO (Amplitude versus Offset) method is one of the more recent seismic techniques for oil and gas exploration. Taking the elastic wave theory as its theoretical basis and the isotropic medium as the model, the AVO method has been successfully ap- plied in forecasting reservoir properties and their fluid contents and in some cases, it can also be used to forecast the special position of the gas/water and gas/oil interfaces[1]. The AVO method is also a basic means for fore…     

Characteristics of transmitting channel wave in a coal seam

An embedded underground coal seam carries channel waves of low seismic velocity along a stratigraphic rock-coal-rock sequence. In a homogeneous and isotropic seam, seismic waves propagate as trapped waves within the seam, which leads to propagation of channel waves. We describe how to set up a field test for transmission in order to acquire channel waves in a coal seam. Because channel wave signals are non-stationary in their frequencies and amplitudes, a necessary velocity spectrum and wavelet transformation analysis are applied to interpret the characteristics of channel waves. The advantage of using a wavelet transformation is that different resolutions can be obtained at different times and different frequencies. According to analysis of the seismic signals acquired in the S7 sensor hole, it was clearly shown that the characteristics of channel waves are lower frequencies and attenuation which can guide an effective wave for detecting voids, boundaries and faults in coal seams with strong roofs and floors.     

Prediction of Coal Seam Methane Enriched Areas Using Seismic Data

All coal mine disasters are dynamic geological phenomenon and affected by many factors. However, locating the enriched areas of CSM （coal seam methane） may be the precondition for the successful prediction of such disasters. Traditional methods of investigating CSM enriched areas use limited data and only consider a few important factors. Their success rate is low and cannot meet practical needs. In this paper, an alternative method is proposed. The procedure is given as follows： 1） fracture attributes derived from azimuth variations of P-wave data in coal seams and wall rocks can be extracted; 2） AVO attributes, such as the intercept P and gradient G parameters can be extracted from different azimuths from 3D seismic data; 3） seismic cubes can be inverted and the relative attributes of impedance cubes can be extracted; 4） using a GIS platform, multi-source information can be obtained and analyzed; these include fracture attributes of coal seams and wall rocks, the thickness of coal seams, the distribution of faults and structures, the depth of coal seams, the inclination and exposure of coal seams and the coal rank. Through this processing procedure, methane enriched areas can be systematically detected.     

Relationship between joint development in rock and coal seams in the southeastern margin of the Ordos basin简

To predict joint development characteristics of coal seams, joint characteristics of rock seams from 88 field stations were observed and comparisons were made between joint characteristics of coal and rock seams at 10 coal outcrops. Additionally, detailed joint measurements of underground coal seams were taken at two coal mines. This study investigated the effects of seam thickness, lithology, and structure on joint development and established the relationship between joint development of coal and rock seams, which allowed predictions of predominant joint densities for the No.5 coal seam in the southeastern margin of the Ordos basin. The results show that outcrop and underground coal seams exhibit the same joint systems as rock seams. The joints are mainly upright. Predominant joints strike 55° on average, followed by joints striking 320°. The joint density of the coal seam is 18.7–22.5 times that of the sandstone seam at the same thickness. The predominant joint density of the No.5 coal seam, controlled by the structure, is ∼4–20 joints per meter. Joint densities exhibit high values at intersecting areas of faults and folds and decrease values in structurally stable areas. The permeability increases exponentially with increasing density of the predominant joints.     

不同厚度煤层AVO特征及模型研究

由弹性波动力学理论可知，当一种岩层纵、横波速度与另一种岩层纵、横波速度之比明显不同时，反射系数随入射角的变化而变化．这是ＡＶＯ的理论基础，将其运用于不同厚度煤层ＡＶＯ特征研究中．设计几种不同厚度煤层模型，绘出厚度依懒于反射、透射系数的关系，找出变化规律．试图为煤层厚度预测提供新途径．     

Reservoir reconstruction technologies for coalbed methane recovery in deep and multiple seams

Multiple coal seams widely develop in the deep Chinese coal-bearing strata. Ground in situ stress and coal seam gas pressure increase continuously with the increase of the mining depth, and coal and gas outburst disasters become increasingly severe. When the coal is very deep, the gas content and pressure will elevate and thus coal seams tends to outburst-prone seams. The safety and economics of exploited firstmined coal seams are tremendously restricted. Meanwhile, the multiple seams occurrence conditions resulted in different methane pressure systems in the coal-bearing strata, which made the reservoir reconstruction of coal difficult. Given the characteristics of low saturation, low permeability, strong anisotropy and soft coal of Chinese coal seams, a single hydraulic fracturing surface well for reservoir reconstruction to pre-drain the coalbed methane(CBM) of multiple seams concurrently under the different gas pressure systems has not yet gained any breakthroughs. Based on analyses of the main features of deep CBM reservoirs in China, current gas control methods and the existing challenges in deep and multiple seams, we proposed a new technology for deep CBM reservoir reconstruction to realize simultaneous high-efficiency coal mining and gas extraction. In particular, we determined the first-mined seam according to the principles of effectiveness and economics, and used hydraulic fracturing surface well to reconstruct the first-mined seam which enlarges the selection range of the first-mined seam. During the process of mining first-mined seam, adjacent coal seams could be reconstructed under the mining effect which promoted high-efficiency pressure relief gas extraction by using spatial and comprehensive gas drainage methods(combination of underground and ground CBM extraction methods). A typical integrated reservoir reconstruction technology, ‘‘One well for triple use", was detailed introduced and successfully applied in the Luling coal mine. The application showed that the proposed technology could effectively promote coal mining safety and simultaneously high-efficiency gas extraction.     

Research on Full Space Transient Electro-magnetism Technique for Detecting Aqueous Structures in Coal Mines

Based on the transmitting theory of ＂smoke ring effect＂, the transient electromagnetism technique was used in coal mines to detect abnormal areas of aquiferous structures in both roofs and floors of coal seams and in front of excavated roadways. Survey devices, working methods and techniques as well as data processing and interpretation are discussed systematically. In addition, the direction of mini-wireframe emission electromagnetic wave of the full space transient electromagnetism technique was verified by an underground borehole for water detection and drainage. The result indicates that this technique can detect both horizontal and vertical development rules of abnormal water bodies to a certain depth below the floor of coal seams and can also detect the abnormal, low resistance water bodies within a certain distance of roofs. Furthermore, it can detect such abnormal bodies in ahead of the excavated roadway front. Limited by the underground environment, the full space transient electromagnetism technique can detect to a depth of only 120 m or so.     

上邻近层残存瓦斯压力的理论与应用

本文根据岩体力学与采场覆岩移动原理,探讨了煤层原始瓦斯压力、采场开采技术参数、覆岩岩性、煤层倾角等对上邻近层残存瓦斯压力的影响。指出了采场覆岩法向裂缝宽度是影响上邻近层残存瓦斯压力的关键因素,推导出了能够反映上述影响的上邻近层残存瓦斯压力计算公式。经过实际应用证明比已有的其它公式理论性强、精度高。据此还可以计算上邻近层瓦斯涌出量、可抽放瓦斯量及考察解放层的解放效果等。     

测井曲线在潘一矿13-1煤层识别构造煤中的应用

为预测未揭露区煤体结构,根据钻孔测井曲线信息,结合视电阻率电位曲线与伽马伽马曲线对煤层内不同结构分层物性差异所反映的形态特征,通过对煤层内部的各分层之间的比较、煤层与邻近钻孔中同一煤层的比较和煤层与钻孔内的上、下煤层之间进行比较绘制出煤层结构柱状图。又以矿井煤层底板等高线图作为底图绘制构造煤平面分布图,判识煤层内部的构造煤分布。     

Measurement of overburden failure zones in close-multiple coal seams mining

In the Kaiping Coal field, mining of five coal seams, located within 80 m in the Kailuan Group, #5, #7, #8,#9 and #12 coal seam, is difficult due to small interburden thickness, concentrated stress distributions,high coal seam metamorphism, and complex geological conditions. By using the ZTR12 geological penetration radar(GPR) survey combined with borehole observations, the overburden caving due to mining of the five coals seams was measured. The development characteristics of full-cover rock fractures after mining were obtained from the GPR scan, which provides a measurement basis for the control of rock strata in close multiple coal seam mining. For the first time, it was found that the overburden caving pattern shows a periodic triangular caved characteristic. Furthermore, it is proposed that an upright triangular collapsed pile masonry and an inverted triangular with larger fragments piled up alternately appear in the lower gob. The research results show that the roof structure formed in the gob area can support the key overlying strata, which is beneficial to ensure the integrity and stability of the upper coal seams in multiple-seam mining of close coal seams.     

地面群孔瓦斯抽采技术应用研究

为保证新集一矿突出煤层13-1煤北中央采区的安全开采,先后开采131103、131105等11-2煤层工作面作为保护层。首先在上述两个工作面共布置了6个地面钻孔,建立了地面群孔瓦斯抽采系统,预抽采动区被保护层13-1煤瓦斯。接下来对地面钻孔抽采瓦斯参数进行了考察,主要包括基于示踪技术考察了131105工作面采动卸压地面钻孔走向及倾向瓦斯抽采半径,统计分析被保护层瓦斯抽采率,同时就地面群孔与井下底板巷穿层钻孔瓦斯抽采两种方法进行了抽采率、工程费用等方面的对比。研究结果表明：新集一矿的地层条件下地面钻孔抽采煤层卸压瓦斯沿煤层倾向和走向的抽采半径分别不小于160m和240m;采动区地面群孔瓦斯抽采率达35%以上;地面钻孔相对比井下底板巷,在抽采瓦斯方面具有技术上可靠、安全、经济等优点。     

急倾斜煤层开采诱发地表裂缝数值模拟

为了研究急倾斜煤层开采诱发地表裂缝的演化过程,探讨急倾斜煤层开采诱发地裂缝分布规律.利用可描述拉张破裂的有限元方法,对地表裂缝演化过程进行数值模拟.结果显示:最大拉应力集中在地表,地表优先于采空区破裂,采空区下山方向对应的地表一侧形成裂缝.急倾斜煤层开采地表和采空破裂的顺序与水平、倾斜煤层的破坏顺序相反.煤层倾角很陡时,地表先破裂到一定程度后,采空区才开始破裂.煤层倾角很缓或水平时,采空区先破裂,之后地表才破裂.     

Comprehensive evaluation of water-inrush risk from coal floors

Lower groups of coal seams are presently being mined in the Yanzhou coal mining area. We need to evaluate the risk from water-inrush from coal floors in order to have safe production in the lower groups of coal seams in mines, Based on a systematic collection of hydrogeological data and some data from mined working faces in these lower groups, we evaluated the factors affecting water-inrush from coal floors of the area by a method of dimensionless analysis. We obtained the order of the factors affecting water-inrush from coal floors and recalculated data on depths of destroyed floors by multiple linear regression analysis and obtained new empirical formulas. We also analyzed the water-inrush coefficient of mined working faces of the lower groups of coal seams and improved the evaluation standard of the water-inrush coefficient method. Finally, we made a comprehensive evaluation of water-inrush risks from coal floors by using the water-inrush coefficient method and a fuzzy clustering method. The evaluation results provide a solid foundation for preventing and controlling the damage caused by water of an Ordovician limestone aquifer in the lower group of coal seams in the mines of Yanzhou. It provides also important guidelines for lower groups of coal seams in other coal mines.     

岱庄煤矿近距离煤层微量元素赋存特征研究

煤矿开采的主要对象是煤层,煤层对比清楚与否,直接影响煤矿安全生产和经济效益.岱庄煤矿3上1、3上及3下煤层相距较近,区分不明显,容易造成采掘巷道串层现象.对岱庄煤矿可采煤层中微量元素赋存特征开展研究,掌握不同煤层中微量元素的赋存状况,可很好地判断岱庄煤矿煤层层位,能有效避免地质构造等因素造成近距离煤层采掘串层现象,对合理设计开采方案和采掘进度有重大意义,从而为岱庄煤矿安全、高效生产提供科学依据和保障.     

Progress on the hydraulic measures for grid slotting and fracking to enhance coal seam permeability

A method of hydraulic grid slotting and hydraulic fracturing was proposed to enhance the permeability of low permeability coal seam in China. Micro-structural development and strength characteristics of coal were analysed to set up the failure criterion of coal containing water and gas, which could describe the destruction rule of coal containing gas under the hydraulic measures more accurately. Based on the theory of transient flow and fluid grid, the numerical calculation model of turbulence formed by high pressure oscillating water jet was used. With the high speed photography test, dynamic evolution and pulsation characteristics of water jet water analysed which laid a foundation for mechanism analysis of rock damage under water jet. Wave equation of oscillating water jet slotting was established and the mechanism of coal damage by the impact stress wave under oscillation jet was revealed. These provide a new method to study the mechanism of porosity and crack damage under high pressure jet.Fracture criterion by jet slotting was established and mechanism of crack development controlled by crack zone between slots was found. The fractures were induced to extend along pre-set direction,instead of being controlled by original stress field. The model of gas migration through coal seams after the hydraulic measures for grid slotting and fracking was established. The key technology and equipment for grid slotting and fracking with high-pressure oscillating jet were developed and applied to coal mines in Chongqing and Henan in China. The results show that the gas permeability of coal seam is enhanced by three orders of magnitude, efficiency of roadway excavation and mining is improved by more than 57%and the cost of gas control is reduced by 50%.     

煤层群煤与瓦斯安全高效共采体系及应用

提出了高瓦斯煤层群煤与瓦斯安全高效共采的概念：在煤层群开采条件下，首先开采瓦斯含量低、无突出危险的首采煤层，利用其采动影响使处在其上部和下部的煤层卸压，煤层透气性成百倍地增加，从而形成高效的瓦斯抽采条件．同时进行的卸压瓦斯高效抽采既解决了由卸压煤层向首采煤层涌出瓦斯问题，保障首采煤层实现安全高效开采，又大幅度地降低了卸压煤层的瓦斯含量，消除了煤与瓦斯突出危险性，为在卸压煤层内实施快速掘进与高效采煤方法提供了安全保障，从而实现了瓦斯与煤炭两种资源的安全高效共采．文中介绍了针对不同卸压瓦斯流动特点的近程、中程和远程卸压瓦斯抽采方法及工程应用实践，最后对高瓦斯煤层群煤与瓦斯安全高效共采体系的应用前景进行了分析．     

Technical scheme and application of pressure-relief gas extraction in multi-coal seam mining region

A pressure relief gas extraction technical model of a typical mining area is proposed based on coal and gas simultaneous extraction theory. Flac3 Dwas employed to model vertical stress and displacement contour plot characteristics of non-outburst coal seam(No. 4) on top of outburst coal seam(No. 2) along strike and incline directions. Field investigations were also conducted to verify the scientific nature of the simulation. The results demonstrate that gas pressure in No. 2 coal seam dropped to approximately 0.55 MPa in the pressure relief multi-coal seam. The highest expansion rate of the coal mine reached up to 2.58%.The pressure-relief angle was 76° along the incline direction and 60° along the strike direction. As the expansion rate and pressure-relief angle increased and the gas pressure decreased, a large amount of gas flowed into the gob of No. 4 from No. 2 coal seam and was later discharged through specific gas pipes,which eliminated No. 2 outburst risks. This study resulted in positive outcomes in that gas extraction time was reduced by 13.5 days, due to pressure relief, and drilling work load was reduced by 0.1161 m/t coal. This method ensures that gas is discharged from the outburst coal seam quickly and safely,demonstrating that the proposed technical model of pressure-relief gas extraction is effective in a multi-coal seam region.     

高瓦斯煤层群保护层开采卸压效果数值模拟

为合理选择保护层,针对高瓦斯突出煤层群安全开采问题,分析了保护层开采的保护作用机理,即保护层开采可对被保护层起到卸压增透作用,改善被保护层的瓦斯抽放效果是解决煤与瓦斯突出问题及瓦斯灾害的重要技术手段;卸压对煤与瓦斯突出及瓦斯问题的解决具有决定作用.针对某矿高瓦斯突出煤层群生产地质条件,采用FLAC3D数值软件模拟2个非突出煤层作为保护层开采时的卸压效果,并对其进行了分析比较,研究结果可为保护层的合理选择提供参考依据.     

新安煤田正村井田二叠系煤岩层对比

煤岩层对比工作对于煤田地质勘探、储量计算以及煤炭资源的开发利用都具有极其重要的意义,它是研究含煤地层层序、煤田地质构造、煤层厚度变化、煤层赋存规律的基础工作,是煤田地质勘探工作的主要任务之一.本文采用标志层法、层间距法、煤质特征分析法和测井响应,对本区的主要含煤层段二叠系山西组、上下石盒子组进行了系统的划分和对比,准确确定了主要可采煤层二1煤层和局部可采煤层二2煤层、七2煤层的层位,并对这些煤层的空间展布进行了对比,这一煤岩层对比方案已为煤田勘探和煤矿开采的揭露所证实.