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Yao Z.,China University of Mining and Technology | Cao D.,China University of Mining and Technology | Wei Y.,China University of Mining and Technology | Li X.,North China Institute of Science and Technology | And 2 more authors.
Journal of Petroleum Science and Engineering | Year: 2016

Solid fines generation in coalbed methane (CBM) development can cause serious formation damage and production breakdown. The anisotropy of coal reservoirs makes fines issue more complicated. In this study, the experimental analysis of the correlation between tectonically deformed coal types and fines generation characteristics was implemented. Two samples with different coal structure types, undeformed coal and granulated coal, were collected from the same coal seam. Under single-phase fluid flow, two sets of core flooding experiments were conducted to generate fines from these samples. The yields of fines produced at varying experimental conditions were analyzed quantitatively. The characteristics of these fines were microscopically observed through the use of a laser particle size analyzer, a scanning electron microscope, and a polarizing microscope. The results indicated that tectonically deformed coal types significantly influenced the generating intensities, particle sizes and morphological features of fines. Because of the varying degrees of structural destruction, compared with undeformed coal, granulated coal contained more original tiny fines in the fractures and was more sensitive to variations of fluid flow rates and reservoir effective stress, which could intensify the generation of fines. Undeformed coal could generate fines with wider particle-size distribution ranges and larger mean particle sizes than granulated coal could. The micromorphology of fines produced from undeformed coal was mainly angular. However, for granulated coal, most of the fines were subangular and even subrounded. No appreciable impact of the development of tectonically deformed coal on the compositions of fines was found. Because of the water sensitivity of clay minerals and the stress sensitivity of vitrinite, the produced fines contained more clay minerals and vitrinite with increases of displacement velocities and confining pressures under laboratory conditions. Through well logging interpretation, the development intensity of tectonically deformed coal in three CBM wells was identified. After analysis of the concentration and mean particle size of fines collected from these wells, it was concluded that the more developed the tectonically deformed coal, the higher the fines concentrations and the smaller the fines mean particle sizes, which was consistent with the experimental results. © 2016 Elsevier B.V. Source

Wang J.,China Coal Technology and Engineering Co. | Yu B.,Datong Coal Mine Group Co. | Kang H.,China Coal Technology and Engineering Co. | Wang G.,China Coal Technology and Engineering Co. | And 3 more authors.
International Journal of Coal Science and Technology | Year: 2015

Thick and ultra-thick coal seams are main coal seams for high production rate and high efficiency in Chinese coal mines, which accounts for 44 % of the total minable coal reserve. A fully mechanized top-coal caving mining method is a main underground coal extraction method for ultra-thick coal seams. The coal extraction technologies for coal seams less than 14 m thick were extensively used in China. However, for coal seams with thickness greater than 14 m, there have been no reported cases in the world for underground mechanical extraction with safe performance, high efficiency and high coal recovery ratio. To deal with this case, China Coal Technology & Engineering Group, Datong Coal Mine Group, and other 15 organizations in China launched a fundamental and big project to develop coal mining technologies and equipment for coal seams with thicknesses greater than 14 m. After the completion of the project, a coal extraction method was developed for top-coal caving with a large mining height, as well as a ground control theory for ultra-thick coal seams. In addition, the mining technology for top-coal caving with a large mining height, the ground support technology for roadway in coal seams with a large cross-section, and the prevention and control technology for gas and fire hazards were developed and applied. Furthermore, a hydraulic support with a mining height of 5.2 m, a shearer with high reliability, and auxiliary equipment were developed and manufactured. Practical implication on the technologies and equipment developed was successfully completed at the No. 8105 coal face in the Tashan coal mine, Datong, China. The major achievements of the project are summarized as follows: 1. A top-coal caving method for ultra-thick coal seams is proposed with a cutting height of 5 m and a top-coal caving height of 15 m. A structural mechanical model of overlying strata called cantilever beam-articulated rock beam is established. Based on the model, the load resistance of the hydraulic support with a large mining height for top-coal caving method is determined. With the analysis, the movement characteristics of the top coal and above strata are evaluated during top-coal caving operation at the coal face with a large mining height. Furthermore, there is successful development of comprehensive technologies for preventing and controlling spalling of the coal wall, and the top-coal caving technology with high efficiency and high recovery at the top-coal caving face with a large mining height. This means that the technologies developed have overcome the difficulties in strata control, top-coal caving with high efficiency and high coal recovery, and enabled to achieve a production rate of more than 10 Mtpa at a single top-coal caving face with a large mining height in ultra-thick coal seams; 2. A hydraulic support with 5.2 m supporting height and anti-rockburst capacity, a shearer with high reliability, a scraper conveyor with a large power at the back of face, and a large load and long distance headgate belt conveyor have been successfully developed for a top-coal caving face with large mining height. The study has developed the key technologies for improving the reliability of equipment at the coal face and has overcome the challenges in equipping the top-coal caving face with a large mining height in ultra-thick coal seams; 3. The deformation characteristics of a large cross-section roadway in ultra-thick coal seams are discovered. Based on the findings above, a series of bolt materials with a high yielding strength of 500–830 MPa and a high extension ratio, and cable bolt material with a 1 × 19 structure, large tonnage and high extension ratio are developed. In addition, in order to achieve a safe roadway and a fast face advance, installation equipment for high pre-tension bolt is developed to solve the problems with the support of roadway in coal seams for top-coal caving operation with a large mining height; 4. The characteristics of gas distribution and uneven emission at top-coal caving face with large mining height in ultra-thick coal seams are evaluated. With the application of the technologies of gas drainage in the roof, the difficulties in gas control for high intensive top-coal caving mining operations, known as “low gas content, high gas emission”, are solved. In addition, large flow-rate underground mobile equipment for making nitrogen are developed to solve the problems with fire prevention and safe mining at a top-coal caving face with large mining height and production rate of more than 10 Mtpa. A case study to apply the developed technologies has been conducted at the No. 8105 face, the Tashan coal mine in Datong, China. The case study demonstrates that the three units of equipment, i.e., the support, shearer and scraper conveyor, are rationally equipped. Average equipment usage at the coal face is 92.1 %. The coal recovery ratio at the coal face is up to 88.9 %. In 2011, the coal production at the No. 8105 face reached 10.849 Mtpa, exceeding the target of 10 Mtpa for a top-coal caving operation with large mining height performed by Chinese-made mining equipment. The technologies and equipment developed provide a way for extracting ultra-thick coal seams. Currently, the technologies and equipment are used in 13 mining areas in China including Datong, Pingshuo, Shendong and Xinjiang. With the exploitation of coal resources in Western China, there is great potential for the application of the technologies and equipment developed. © 2015, The Author(s). Source

Li Z.S.,University of Science and Technology Beijing | Zhang L.,CCTEG Shenyang Research Institute | Gao W.,China Academy of Building Research
Transit Development in Rock Mechanics-Recognition, Thinking and Innovation - Proceedings of the 3rd ISRM Young Scholars Symposium on Rock Mechanics, 2014 | Year: 2015

The body structure type of layered structure in II-B area of north slope was identified and classified based on the background of Shuichang Iron Mine high-steep slope. The generalized model of slope was established in this region and internal stress and displacement distribution features of reverse layered soil-rock aggregate dualistic structural slope were analyzed, through the main failure mode of this kind of slope was obtained and the high-steep slope stability in II-B area for dynamic excavation on condition of complex tectonic stress field was analyzed emphatically. The results indicated that: 1. The dual structure of earth-rock aggregate slope was classified according to the relationship between slope strike of dualistic bedrock structure and rock strata. It was helpful to improve the accuracy for generalized slope model identification. 2. On the slope surface and the top of the slope with reverse layered dualistic soil-rock structure, the maximum principal stress paralleled to its face and the minimum principal stress went perpendicular to its face. The minimum principal stress would change to tensile stress when it went beyond zero. The phenomenon of the stress concentration appeared at toe of the slope. The maximum principal stress value increased prominently along the tangent slope foot. The minimum principal stress value significantly reduced and even changed to the tensile stress along the radial direction. The maximum horizontal displacement occurred at top of slope surface. The landslide type was more prone to bending toppling destruction. 3. In the whole mining process, the influence range of slope excavation developed simultaneously along the slope surface direction and perpendicular to the slope surface direction, and formed a circular destruction at the bottom of slope surface. The slope can fail easily if it is covered with hard rock. Moreover, when shear outlet consisting of the mudstone and weak rock that are located near the slope edge, the overlying loose layers slides more easily. © 2015 Taylor & Francis Group, London. Source

Yao Z.,China University of Mining and Technology | Cao D.-Y.,China University of Mining and Technology | Xiong X.-Y.,Petrochina | Wei Y.-C.,China University of Mining and Technology | And 2 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

Coal fines generation can cause downhole failures during coalbed methane development, which include poor drainage, pump leakage and stuck pump. In order to prevent and control these failures, the research on the forecast of damage on production equipment caused by coal fines through monitoring dynamometer card was conducted. Based on the coalbed methane production in Hancheng, Ordos Basin, the load analysis and shape comparison of typical dynamometer cards of coal fines-related downhole failures were performed. Two quantitative parameters for indicating downhole failures by monitoring dynamometer card were proposed, which were R, unload line lag range and θ, load line deviation angle. According to the variation range of R and θ, the intensity of failures was divided into four grades respectively. The example analysis of poor drainage and stuck pump showed that the shape feature of dynamometer card could be indicative for the severity of coal fines aggregation and related downhole failures. The comprehensive analysis of the production data, such as the shape and load ratio of dynamometer card, the current fluctuation of inverter, and daily water yield change, can accurately identify the functional state of downhole equipment and the damage degree of coal fines. Adopting reinjection drainage, well washing and other control measures to the wells with failure symptom can effectively dilute coal fines concentration, disrupt coal fines aggregation, accelerate coal fines migration, and then mitigate coal fines damage and related downhole failures. ©, 2015, China Coal Society. All right reserved. Source

Xu L.,Henan Polytechnic University | He F.,China University of Mining and Technology | Wang J.,CCTEG Shenyang Research Institute | Wang Y.,CCTEG Shenyang Research Institute | And 2 more authors.
Caikuang yu Anquan Gongcheng Xuebao/Journal of Mining and Safety Engineering | Year: 2014

In response to the surrounding rock control problem of ultrahigh roadway, the ultrahigh segment of No. 5205 belt transportation roadway in a mine has been selected as research object, the distribution characteristics, development law and relative evolution tendency of fracture field have been researched by UDEC numerical simulation within the height from 3.5 m to 8 m. Results show that surrounding rock fracture field has three areas: fracture transfixion area, fracture development area and microfracture area are all distributed as semi-ellipse. With the height increasing, three fracture areas depth of roof, floor and two sides increases gradually. The transformation from the microfracture area to the fracture development area and from the fracture development area to the fracture transfixion area is strengthened in roof and floor. On the contrary, the transformation from the microfracture area to the fracture development area and from fracture development area to the fracture transfixion area is reduced gradually in the two sides. Equal-stress axial ratio with different height when side-pressure coefficient equals 1.0 is analyzed. The results show that floor void reinforced area height decreases as negative exponent and two sides void reinforced area thickness increases as positive exponent with the height increasing. It is believed that bolt can control fracture slip and delay surrounding rock bulking deformation; side diagonal cable and beam can be anchored to the no fracture region in the shoulder and floor. It has stable and reliable anchor foundation and can squeeze the fracture transfixion area in middle part of the side. Based on this, the combined support technology of high strength and high pre-stressing bolt net bar & diagonal cable and beam is proposed. Super-high roadway will reach self-stabilization after it was dig out after 10 days. Roof-to-floor relative convergence is 104 mm, with two sides relative convergence 150 mm and total roof separation 3.5 mm. Source

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