Development of a reconstituted brown coal material using cement as a binder

Like any other coal, the highly heterogeneous nature of brown coal can sometimes make it difficult to interpret the results of laboratory experiments. More homogeneous samples with properties reproducible in the laboratory would provide significant advantage, especially in understanding the effects of various factors in the properties of coal. An attempt was made to develop reconstituted coal (RC) samples in the laboratory through an extensive material development and laboratory testing programme. The latter consisted of mainly uniaxial compression tests. The main objective in developing the RC material is to use it in future research on CO₂ sequestration in unmineable coal seams. A highly homogeneous coal sample would make it much easier to identify, for example, the effect of CO₂ sorption on the mechanical, flow and transport properties of coal. Uniaxial compression tests were conducted on some brown coal samples to determine the approximate mechanical properties. The results revealed an average uniaxial compressive strength of 1.46 MPa, an average elastic modulus of 77.43 MPa and a Poisson’s ratio of 0.16. The measured properties were used as a reference for the development of RC samples. An extensive laboratory experimental programme was conducted to develop RC samples with the desirable mechanical properties. Portland cement was used as the cementing agent for the RC. Different variables such as percentage of cement, water content, compaction load and curing time were taken into account when developing RC samples. Uniaxial compression tests were carried out to ensure that the RC samples were reasonably homogeneous and the properties were similar to those of natural coal. Percentages of cement by weight of coal such as 4, 6 and 8% were attempted and a 4% cement mix with 50% water was considered most suitable for the RC samples. Average compressive strength of 0.8 MPa (28-day strength) and an average elastic modulus of 34 MPa were achieved for the RC samples. Further efforts at improvement would involve better matching of the uniaxial compressive strength and elastic modulus of RC samples with the natural coal samples.     

Evaluation of coal bed methane potential of coal seams of Sawang Colliery,Jharkhand, India

The coal seams of Sawang Colliery, East Bokaro Coalfields are bituminous to sub-bituminous in nature and categorized as high gaseous seams (degree II to degree III level). These seams have the potential for coal bed methane (CBM) and their maturity increases with increasing depth, as a result of enhanced pressure-temperature conditions in the underground. The vitrinite maceral group composition of the investigated coal seams ranges from 62.50–83.15%, whereas the inertinite content varies from 14.93–36.81%. The liptinite content varies from 0.66% to 3.09%. The maximum micro-pores are confined within the vitrinite group of macerals. The coal seams exhibit vitrinite reflectance values (Ro% calculated) from 0.94% (sample CG-97) to 1.21% (sample CG-119). Proximate analyses of the investigated coal samples reveal that the moisture content (M%) ranges from 1.28% to 2.98%, whereas, volatile matter (VM%) content is placed in the range of 27.01% to 33.86%. The ash content (A%) ranges from 10.92% to 30.01%. Fixed carbon (FC%) content varies from 41.53% to 55.93%. Fuel ratio variation shows a restricted range from 1.53 to 1.97. All the coal samples were found to be strongly caking and forming coke buttons. The present study is based on the adsorption isotherm experiments carried out under controlled P-T conditions for determination of actual gas adsorption capacity of the coal seams. This analysis shows that the maximum methane gas adsorbed in the coal sample CG-81 is 17 m³/t (Std. daf), at maximum pressure of 5.92 MPa and experimental temperature of 30°C. The calculated Langmuir regression parameters P_L and V_L range from 2.49 to 3.75 MPa and 22.94 to 26.88 m³/t (Std. daf), respectively.     

The Effects of Operational Parameters on a Mono-wire Cutting System: Efficiency in Marble Processing

Mono-wire block cutting machines that cut with a diamond wire can be used for squaring natural stone blocks and the slab-cutting process. The efficient use of these machines reduces operating costs by ensuring less diamond wire wear and longer wire life at high speeds. The high investment costs of these machines will lead to their efficient use and reduce production costs by increasing plant efficiency. Therefore, there is a need to investigate the cutting performance parameters of mono-wire cutting machines in terms of rock properties and operating parameters. This study aims to investigate the effects of the wire rotational speed (peripheral speed) and wire descending speed (cutting speed), which are the operating parameters of a mono-wire cutting machine, on unit wear and unit energy, which are the performance parameters in mono-wire cutting. By using the obtained results, cuttability charts for each natural stone were created on the basis of unit wear and unit energy values, cutting optimizations were performed, and the relationships between some physical and mechanical properties of rocks and the optimum cutting parameters obtained as a result of the optimization were investigated.     

韩城矿区碎软煤层顶板梳状孔水力压裂瓦斯抽采工程实践

韩城矿区碎软煤层发育,煤层透气性差,本煤层钻孔钻进困难,瓦斯抽采效果差。顶板梳状孔水力压裂技术结合了水力压裂技术和定向钻进技术二者的优势,是解决碎软低渗煤层瓦斯抽采难题的有效技术途径。在韩城矿区王峰煤矿3号煤层顶板粉砂岩中施工长钻孔并向煤层开分支,采用套管+封隔器座封的整体压裂方式进行水力压裂工程试验。钻孔总长度344 m,有效压裂长度284 m,累计注水量874.79 m3,最大泵注压力9.4 MPa。试验结束后对钻孔瓦斯抽采相关参数连续监测86 d,钻孔瓦斯抽采体积分数27%~51%,平均42.11%,钻孔瓦斯抽采纯量8.25~21.41 m3/min,平均17.02 m3/min,钻孔累计抽采瓦斯量约210万m3。与常规的穿层钻孔水力冲孔技术相比,该技术百米钻孔瓦斯抽采量提高了11.48倍,初步证明了该技术在碎软煤层瓦斯强化抽采领域的适用性。      

Mechanical Behavior of Methane Infiltrated Coal: the Roles of Gas Desorption, Stress Level and Loading Rate

We report laboratory experiments to investigate the role of gas desorption, stress level and loading rate on the mechanical behavior of methane infiltrated coal. Two suites of experiments are carried out. The first suite of experiments is conducted on coal (Lower Kittanning seam, West Virginia) at a confining stress of 2 MPa and methane pore pressures in the fracture of 1 MPa to examine the role of gas desorption. These include three undrained (hydraulically closed) experiments with different pore pressure distributions in the coal, namely, overpressured, normally pressured and underpressured, and one specimen under drained condition. Based on the experimental results, we find quantitative evidence that gas desorption weakens coal through two mechanisms: (1) reducing effective stress controlled by the ratio of gas desorption rate over the drainage rate, and (2) crushing coal due to the internal gas energy release controlled by gas composition, pressure and content. The second suite of experiments is conducted on coal (Upper B seam, Colorado) at confining stresses of 2 and 4 MPa, with pore pressures of 1 and 3 MPa, under underpressured and drained condition with three different loading rates to study the role of stress level and loading rate. We find that the Biot coefficient of coal specimens is <1. Reducing effective confining stress decreases the elastic modulus and strength of coal. This study has important implications for the stability of underground coal seams.     

The verification of displacement methane effect caused by hydraulic fracturing in gassy coal seams

During hydraulic fracturing in gassy coal seams, the gas concentration in mining path ways is found to increase significantly. This phenomenon should be the displacement methane effect caused by hydraulic fracturing. Does this effect exist objectively? To this end, laboratory and field verification experiments were carried out. An experimental system integrated with true triaxial hydraulic fracturing, seepage, and displacement gas was developed. The largest sample size was 500?×?500?×?500 mm³. Proper sealing was assured in the experimental system, and the effects of coal bed methane were simulated effectively. Methane at a specific pressure was injected into a sealed coal sample. After pressure stabilization and the methane adsorption reached its equilibrium level, the high-pressure water was injected into the coal sample from the surface. Absorbed methane in the coal sample was displaced from the bottom of the coal by water pressure seepage. After the conduction of deep borehole hydraulic fracturing in a high gassy coal seam, the gas was displaced inward and outward from the main fracture section. The permeability, diffusion, and transfer of the gas resulted in a region of increased methane content in both sides of the main fracture section. And the methane content in the main fracture section was decreased. Along the length of the borehole, the methane content changed significantly. The existence of displaced methane caused by hydraulic fracturing in gassy coal seams was first verified by laboratory experiments and then field tests. The pore-pressure gradient provides power for driving methane by hydraulic fracturing. The amount of desorbed methane resulted from the competitive adsorption of water and methane is more than that of the absorbed methane resulted from increased methane pressure, which provides material guarantee for displacing methane by hydraulic fracturing. The displacement methane caused by hydraulic fracturing in gassy coal seams was also found to be time dependent.     

Review of Cuttability Indices and A New Rockmass Classification Approach for Selection of Surface Miners

Rock excavation is carried out either by drilling and blasting or using rock-cutting machines like rippers, bucket wheel excavators, surface miners, road headers etc. Economics of mechanised rock excavation by rock-cutting machines largely depends on the achieved production rates. Thus, assessment of the performance (productivity) is important prior to deploying a rock-cutting machine. In doing so, several researchers have classified rockmass in different ways and have developed cuttability indices to correlate machine performance directly. However, most of these indices were developed to assess the performance of road headers/tunnel-boring machines apart from a few that were developed in the earlier days when the ripper was a popular excavating equipment. Presently, around 400 surface miners are in operation around the world amongst which, 105 are in India. Until now, no rockmass classification system is available to assess the performance of surface miners. Surface miners are being deployed largely on trial and error basis or based on the performance charts provided by the manufacturer. In this context, it is logical to establish a suitable cuttability index to predict the performance of surface miners. In this present paper, the existing cuttability indices are reviewed and a new cuttability indexes proposed. A new relationship is also developed to predict the output from surface miners using the proposed cuttability index.     

Estimation of Rock Cuttability from Shore Hardness and Compressive Strength Properties

Summary Shore hardness has been used to estimate some mechanical and physical properties of rocks for many years. This study differs from previous studies in a way that it is directly oriented to rock cuttability. Two Shore hardness values (SH ₁ andSH ₂) and a coefficient of deformation value (K) have been measured for 30 different rock samples. In the first stage of the study, optimum specific energy values for 16 different rock samples obtained from full-scale cutting tests were correlated with the Shore hardness values of the same rock samples changingSH ₁ values from 9 to 66 andSH ₂ values from 25 to 83, with deformation coefficient values changing from 26 to 195. In the second stage, the performance of a roadheader used in the Kü?üksu (Istanbul) tunnel was recorded in detail and the instantaneous cutting rate of the machine was determined. Then, the relationship between Shore hardness values, deformation coefficient and the instantaneous cutting rate of the machine was determined for different formations encountered. It is concluded that there is a relationship between Shore hardness values, optimum specific energy and compressive strength, which may be used to estimate the rock cuttability and the instantaneous cutting rates of roadheaders within certain limits of reliability.     

Performance Prediction of Large-Diameter Circular Saws Based on Surface Hardness Tests for Mugla (Turkey) Marbles

Surface hardness tests such as Shore hardness (SH) and Schmidt hammer rebound hardness (SR) may provide a quick and inexpensive measure of rock hardness, which may be widely used for estimating the mechanical properties of rock material such as strength, sawability, drillability and cuttability. In the marble industry, circular sawing with diamond sawblades constitutes a major cost in the processing. Therefore, several models based on the relations between hourly slab production (P _hs), rock surface hardness (SH and SR) and mineral grain size (S _cr) were developed using the data obtained from field and laboratory measurements on five different marbles quarried in the Mugla Province of Turkey. The models which include surface hardness and crystal size may as well be used for the prediction of sawability (hourly slab production) of carbonate rocks using large-diameter circular saws.     

煤层气井合层开发层间干扰分析与合采方法探讨——以平顶山首山一矿为例

多煤层合层开发是提高煤层气井单井产量的关键技术,然而工程实践中大部分煤层合采存在层间干扰问题,致使合采产气量提升不明显。为了提高合层开发煤层气井的产气量与开发效率,以平顶山首山一矿煤层气合采四2煤层和二1煤层为例,基于煤层气赋存的地质条件,分析了合采层间干扰的影响因素及干扰规律,并提出了煤层合层开发层间干扰的控制方法。结果表明:造成四2煤层和二1煤层合层排采产量低的主要因素是储层压力梯度、临界解吸压力和渗透率。其中,两层煤的储层压力梯度分别为1.05 MPa/hm和0.519 MPa/hm;渗透率分别为0.25×10–3 μm2和1.4×10–5 μm2;临界解吸压力分别为1.16~1.69 MPa和0.40~0.46 MPa;另外,两煤层间距大,平均170 m左右。以上主要影响因素差异,造成两层煤合采时层间矛盾突出,干扰严重,总体产量低,井组煤层气开发效率低。基于现状问题,探索提出大间距多煤层大井眼双套管分层控制合采工艺方法,以实现两层煤分开控制达到合采产能叠加的目标,从而提高煤层气井合采产量和开发效果。研究认识将为平顶山及类似地质条件的矿区多煤层煤层气高效合层排采提供新的技术途径。      

淮南煤田刘庄煤矿深部煤层气地质特征

为了查明刘庄煤矿深部煤层气赋存及开发地质条件,在井田内实施了两口煤层气探井,并开展了系统的分析测试工作。结果表明:刘庄深部勘查区主要煤层孔隙度一般为4.14%~4.77%,比表面积集中在2.184~5.228m 2/g,13-1煤层、11-2煤层和8煤层试井渗透率分别为0.12mD、0.09mD和0.08mD,孔裂隙系统发育一般,属于渗透性差的储集层;储层压力梯度大于静水压力梯度,属高异常压力范畴;主要煤层兰氏压力平均为2.61MPa,兰氏体积平均为6.74m 3/t,吸附能力较低;LT-1井气测录井过程中共出现14层气测异常,异常层段全烃含量均较低,最大为3.701%(16-1煤);主要煤层的含气量分布在0.21~1.47m 3/t,平均0.65m 3/t,主要煤层含气饱和度均很低,最大值仅为18.0%。综合分析认为,刘庄煤矿深部主要煤层埋深大,孔裂隙系统发育差,渗透率低,而且具有低含气量和低饱和度的特征,煤层气勘探风险较高。     

豫东地区岩浆活动对煤层结构及煤质的影响

为指导豫东地区煤矿合理部署、高效生产,基于大量钻井和测试资料的综合分析和对比研究,探讨了豫东地区岩浆活动的基本特征及其对煤层结构和煤质的影响。研究结果表明:燕山中晚期的岩浆活动对豫东地区的煤层结构和煤层连续性造成影响,导致煤层变薄、分叉、尖灭和吞噬;同时,岩浆活动导致本区煤层变质程度普遍增高,煤质参数发生变化。煤层的原始赋存状态、岩浆侵入的初始温度、侵入岩体的厚度、岩浆侵入煤层的方式、岩体离煤层的距离、围岩和岩体上覆地层的岩性等是影响煤层结构和煤变质程度的主要控制因素。      

Effects of Rock Properties on Specific Cutting Energy in Linear Cutting of Sandstones by Picks

Summary. Specific cutting energy (SE) has been widely used to assess the rock cuttability for mechanical excavation purposes. Some prediction models were developed for SE through correlating rock properties with SE values. However, some of the textural and compositional rock parameters i.e. texture coefficient and feldspar, mafic, and felsic mineral contents were not considered. The present study is to investigate the effects of previously ignored rock parameters along with engineering rock properties on SE. Mineralogical and petrographic analyses, rock mechanics, and linear rock cutting tests were performed on sandstone samples taken from sites around Ankara, Turkey. Relationships between SE and rock properties were evaluated using bivariate correlation and linear regression analyses. The tests and subsequent analyses revealed that the texture coefficient and feldspar content of sandstones affected rock cuttability, evidenced by significant correlations between these parameters and SE at a 90% confidence level. Felsic and mafic mineral contents of sandstones did not exhibit any statistically significant correlation against SE. Cementation coefficient, effective porosity, and pore volume had good correlations against SE. Poisson’s ratio, Brazilian tensile strength, Shore scleroscope hardness, Schmidt hammer hardness, dry density, and point load strength index showed very strong linear correlations against SE at confidence levels of 95% and above, all of which were also found suitable to be used in predicting SE individually, depending on the results of regression analysis, ANOVA, Student’s t-tests, and R² values. Poisson’s ratio exhibited the highest correlation with SE and seemed to be the most reliable SE prediction tool in sandstones.     

“三软”煤层顶板力学性能对瓦斯保存条件的影响

针对豫西芦店滑动构造区＂三软＂煤层（软顶、软底、软煤）瓦斯突出问题的特殊性,通过大量野外地质调查、岩石力学试验和瓦斯地质灾害实例分析,探讨了滑动构造区煤层顶板力学性能与瓦斯保存条件的内在关系;明确指出强度低、变形大且塑性软化特征强的软岩顶板容易形成封闭条件好的盖层,下伏煤层瓦斯难以逸散,从而提出了构造软岩分布区即瓦斯地质灾害高发区的结论。这一研究成果对我国东部滑动构造区的矿井瓦斯地质灾害防治具有一定的示范意义。     

薄互煤层中透射槽波探测断层的正演模拟

为了研究西南地区矿井薄互煤层中透射槽波探测断层的可行性,选择具有代表性的攀枝花煤业集团某矿为研究对象,根据实际地质资料建立不含夹矸、含3层夹矸、含3层夹矸和断层的3个薄互煤层的地质模型,通过三维弹性波正演模拟分析槽波的波场特征和频散特征,总结振幅衰减系数成像在薄互煤层中槽波探测断层发育位置及延展方向的有效性;并结合实际应用,探讨了透射槽波在薄互煤层中的传播速度及频散特征,以及断层、夹矸对槽波传播的影响。结果表明:薄互煤层中透射槽波探测,断层在影响薄互煤层槽波传播中占主导作用;0.5 m以下夹矸对槽波的发育和能量成像影响不大;在煤厚相同的情况下,含夹矸层状模型相比不含夹矸层状模型的槽波主频低,槽波对煤厚2 m、夹矸厚度0.5 m以下的薄互煤层能够进行比较准确的探测。透射槽波可在薄互煤层中探测断距大于1/2煤厚的断层位置、走向及延展长度,可为西南地区薄互煤层中构造探查提供参考。      

Relationship between Net Subsidence and Coal Cycle Parameters—A Statistical Appraisal from Subsurface Logs of Damuda Group,Talchir Gondwana Basin,India

Total thickness of strata and coal cycle parameters of the three formations, i.e. Karharbari, Barakar, and Barren Measures of the Damuda Group of the Talchir Gondwana basin were subjected to bivariate and multivariate statistical analyses. Polynomial regression lines were fitted to data sets consisting of total thickness of strata, number of coal cycles, and average thickness of coal cycles of the three formations of the Damuda Group. A significant direct relationship is observed between total thickness (net subsidence) of strata and number of coal cycles, while a significant inverse relationship exists between the number of coal cycles and their average thickness. Principal component and multiple regression analyses suggest that lithological parameters of the coal bearing strata reflect the dynamic of the basin subsidence. The sedimentary distributive mechanism in the form of lateral migration of streams or drainage diversion caused in response to differential subsidence of the depositional surface seem to be appropriate mechanisms for the development of coal cycles and peat swamps in the Talchir basin. Often during Karharbari sedimentation, peat accumulated in abandoned channels was scoured away by high energy migrating channels. On the other hand, Barakar peat swamps developed in a distal part of the flood plain, as a result of which many of the coal seams could be of appreciable thickness. The advent of arid climatic condition retarded the growth of vegetation to a larger extent that prevented profuse development of coal seams during the Barren Measures Formation.     

Catagenesis of Humic Coals Inferred from the X-Ray Phase Analysis and Mathematical Modeling

Dynamics of catagenetic changes in the structure of humic coals in the Earth's interior can quantitatively be described using X-ray indices of components (phases), redistribution of which is determined by a system of differential equations in geological time. The system describes changes in the main formation parameters of coal seams in the Earth's interior (subsidence depth, temperature, pressure, and catagenesis index), on the one hand, and kinetics of catagenetic transformation of organic matter (OM), on the other. Such model makes it possible to establish regular changes in the phase composition of humic coals at different stages of coal basin formation. Using Paleozoic (Middle Carboniferous) coals of the Donets Basin as an example, it is established that main changes in the OM structure took place during the maximal subsidence of coal seams at maximal temperatures ranging from 110–15°C (for slightly metamorphosed coals of the L and G ranks) to 28°C (for anthracites) and pressures ranging from 55–74 to 146 MPa, respectively. Major processes leading to the observed X-ray phase composition of coals during the maximal subsidence of sedimentary sequences lasted approximately 40 Ma regardless of the geological age of sediments (Middle Carboniferous or Permian coal seams of the Donets or Kuznetsk coal basins, respectively).     

韩城地区煤储层孔渗应力敏感性及其差异

以韩城煤层气区块3号、5号和11号煤层为例,进行不同围压条件下的煤心孔渗实验,探讨了该区煤储层物性与应力之间的耦合关系,建立了相应的数学模型。结果表明,煤心孔渗随围压的增加而不断下降,渗透率应力伤害远强于孔隙度应力伤害,但各煤层的应力敏感性各不相同:在实验围压从4.14 MPa（600 psi）增加到12.42 MPa（1 800 psi）条件下,11号煤层孔渗应力敏感性最强,孔隙度应力伤害达76.5%,渗透率应力伤害达93.3%;3号煤层孔渗应力敏感性最弱,孔隙度应力伤害38.5%,渗透率应力伤害77.9%;5号煤层孔渗应力敏感性较强,孔隙度应力伤害约45%,渗透率应力伤害达83.9%。分析认为,裂隙发育状况是造成各煤层间孔渗应力敏感差异的主要原因。从实验数据的拟合情况看,幂函数模式比指数函数模式更能准确地获取测试围压范围内的孔渗内插值。      

Applications of Remote Sensing Techniques in Coal Geology

Through applied researches, the regularity of thermal infrared radiation of the coal seams has been found, a model of thermal radiation of the coal seams established, and the internal relations of the information extracted from remote sensing images with coal seams and coal measures revealed. Through a series of complete tests of remote sensing techniques such as multi-level (space, aerial and ground) synchronous remote-sensing and multi-directional, multiband and multitemporal remote sensing, the optimal procedure for applications of remote sensing techniques in coal geology has been determined. The theories and methods established in the applied researches have yielded apparent economic results and social benefits in respect to coal field prediction, coal reconnaissance, coal geological surveys and detection of geological hazards in coal mines.     

利用钻孔资料预测矿井未采区煤层瓦斯含量

利用矿井采掘区煤层瓦斯含量实测值,在瓦斯地质定性分析基础上,通过丰富翔实的钻孔资料建立井田未采区适用的煤层瓦斯含量预测公式,从而达到对井田煤层瓦斯含量预测的目的。为大型低瓦斯矿井煤层瓦斯含量预测提供了思路和方法。