Geological Controls on Mineralogical Characteristic Differences of Coals from the Main Coal Fields in Shaanxi, North China

Shaanxi is among the provinces with abundant coal resources in North China. These enormous coal resources (approx. 4143 Gt) are widely distributed in the Ordos Basin and its marginal fold belts. The main coal-bearing strata consist of the late Carboniferous Taiyuan Formation, the early Permain Shanxi Formation, the late Triassic Wayaobao Formation, and the middle Jurassic Yan’an Formation, which were respectively deposited in coastal plains and a lagoon environment, a continental environment, an inland open lake and a confined lake environment. The Permo-Carboniferous coals are low volatile bituminous and characterized by relatively high vitrinite content, which decreases from south to north, and from the lower coal seams upwards. By contrast, the late Triassic and middle Jurassic coals are highly volatile bituminous, but are respectively characterized by relatively high vitrinite and high inertinite content. Minerals in the Permo-Carboniferous coals, the late Triassic coals, and the middle Jurassic coals, are respectively dominated by kaolinite and calcite, quartz and kaolinite, and quartz and calcite. Furthermore, contemporary coals deposited in different coal fields or even different mines of the same coal field present different mineral characteristics. The Permain Shanxi Formation coals from the Shanbei C-P coalfield in the north of Shaanxi Province are characterized by higher kaolinite and lower carbonate contents compared to those from the Weibei C-P coalfield in the south of Shaanxi Province. The distinctive mineralogical characteristics of coals formed in different coalfields and different geological ages were ascribed to integrated influences of different terrigenous detrital input from sediment provenance, sedimentary settings (e.g., subsidence rate, sea transgression, and regression process), and hydrothermal activities.

Numerical Simulation Study of the Strata Movement Rule of Deep Mining with the Super-Thick and Weak Cementation Overburden: A Case Study in China

As the national energy strategy is to mine westward, the deep coal resources under the super-thick and weak cementation overburden in the western mining area will play a critical role in China’s sustainable economic growth. The super-thick and weak cementation overburden has weaker lithology, thicker strata, no large joints, bedding development, and better integrity. Therefore, its movement rule is inevitably different from that of the weak overburden and the middle hard overburden in Central China and Eastern China. However, lack of studies on the movement of the super-thick and weak cementation overburden has led to severe constraints for the large-scale exploitation of coal resources under the super-thick and weak cementation overburden in the western mining area. This study explored the surface movement rule and the influence of overburden characteristics on strata movement with field measurement and numerical simulation. The findings indicate that the surface reaches full mining and the subsidence coefficient is about 0.9 when D1 (width in the dip direction) and D3 (length in the strike direction) are 3 times H0 (the mean mining depth) or more. The strike mining degree has a certain influence on the surface movement law, the maximum difference of the surface subsidence coefficient is 0.35, and the maximum difference of the horizontal movement coefficient is 0.05. In addition, the control effect of the Zhidan group sandstone is stronger. Thus, its first breaking results in surface sinking in a fractured manner when D1 is about 1.3 times H0 and D3 is 3 times H0 or more. The above results can provide reference for the safe mining and control of the super-thick weak cementation overburden.

Influence of deep magma-induced thermal effects on the regional gas outburst risk of coal seams

The thermal effect caused by deep magma intrusion can not only accelerate the metamorphism of coal body, but also bring additional thermal field that changes the mechanical environment of coal seams, thereby affecting the permeability of coal seams. Different from shallow coal resources, deep coal resources are in a mechanical environment characterized by limited stress and strain. Thus, the thermal effect has a more significant influence on the distribution and permeability characteristics of deep coal seams. In this study, the evolution history of highly metamorphic coal seams in Yangquan mining area was analyzed, and the main effect of magmatic activity on coal seams was obtained. Based on the determined vitrinite reflectance data of typical mines in Yangquan mining area, the maximum paleotemperature was calculated by adopting the Barker’s method. Furthermore, the paleotemperature distribution in Yangquan mining area was summarized, and its relationship with the metamorphic degree was acquired. Then, a new permeability model considering the thermal strain was proposed to analyze the permeability evolution in deep coal seams at different ground temperatures. Finally, through a combination of the results of gas pressure and outburst number in Sijiazhuang Mine, Yangquan No. 5 Mine and Xinjing Mine, the influence of ground temperature on the gas outburst risk in Yangquan mining area was explored. The following conclusions were drawn: The maximum paleotemperature in Yangquan area can be 303 °C. In addition, the paleotemperature in the south is higher than that in the north of Yangquan mining area. The various temperatures at different depths bring about different degrees of thermal stress to different coal seams, leading to different strains. Under the fixed displacement boundary conditions in the deep, the coal seam folds and bends to varying degrees. Moreover, the difference in the ground temperature raises the a value of coal seams and lowers the permeability, which promotes the formation of gas-rich zones and increases the risk of coal seam outburst. The research results can help mines to make proper gas disaster prevention plan for different zones.

Risk Assessment and Prevention of Surface Subsidence under Buildings by Cemented Paste Filling and Strip Mining Methods: A Case Study

Intensive and continuous mining of coal resources in China implies their gradual exhaustion, especially in the eastern regions. While some mines face closure, others have to extract residual coal resources under buildings, water bodies, and industrial sites. Thus, safe and efficient mining of the residual coal resources requires innovative techniques, which would account for the particular site’s geological conditions. In this study, two schemes of roadway mining with cemented paste backfilling (RMCPB) and strip mining are put forward. After analyzing the type, construction, and protection standard of the buildings, the probability integration method and the prediction model are used to assess the surface subsidence and deformation. The research results show that both schemes can control the surface deformation to a certain extent, but RMCPB combines the advantages of a high coal recovery rate and disposal of gangue waste. According to the surface subsidence predicted and measured data, the RMCPB method can effectively control the surface subsidence, deformation, and buildings’ safety. It also yields significant economic and environmental benefits.

CLASSSFICATION OF COAL RESERVES AT THE TYAGLIV AND LYUBELYA FIELDS OF THE SOUTH-WESTERN COAL-BEARING REGION OF THE LVIV-VOLYN BASIN BASED ON THE MAIN NATURAL INDICATORS

A geological-statistic analysis of commercial resources and the predictive coal-bearing potential of the fields of the South-Western coal region, the principal promising part of the Lviv-Volyn Coal Basin, has been carried out. Based on the detailed analysis and systematization of data from prospecting and exploratory-assessment works regarding the depth of occurrence and the thickness of coal seams, ash content, sulphur content and grade composition of coal, resources of the Tyagliv and Lyubelya fields has been re-evaluated. These characteristics have been studied by discrete intervals. Re-evaluation of resources and their classification were carried out for every coal seam, the mine field, the field, and the coal-bearing region on the whole. In total, the analysis was performed for 24 coal seams. By the depth of occurrence of coal seams the majority of coal reserves at the Tyagliv and Lyubelya fields belong to the group of 600-900 m. The majority of predictive resources of coal within the Lyubelya field (6.6%) falls to the group of 900-1200 m. According to the thickness of coal seams, the most of the balance and overbalance reserves at the Tyagliv field is attributed to the groups of 0.61-0.80; 0.81-1.00 m, and at the Lyubelya field to the groups of 0.81-1.00; 1.01-1.20; 1,21-1.50 and over 1.5 m. Within the Lyubelya field, the predictive resources of coal are contained in the group of 0.81-1.00 m. According to the value of ash content, 50 % of balance and overbalance reserves of coal at the Tyagliv field are related to the groups of the medium-ash and ash coal. At the Lyubelya field, the most of coal reserves (66.4%) also corresponds to the group of medium-ash coal, and predictive resources — to the groups of medium-ash (43.1%) and ash (53.1%) coal. According to the content of the mass fraction of sulphur, at the Tyagliv field the balance and overbalance reserves of high-sulphur coal prevail, with the amount of sulphur, low-sulphur and medium-sulphur coal being at the equal ratios. At the Lyubelya field, high-sulphur and low-sulphur coal prevail almost at the equal ratios. Regarding predictive resources, the group of high-sulphur coal prevails within the field. The coal seams within the Tyagliv and Lyubelya fields differ from analogous ones in the industrial part of the basin by the higher thickness and the area of distribution. The depth of occurrence of the seams increases for 15-300 m. Coal in the fields of the South-Western coal region has higher quality and the least ash content. According to brand composition of coal, the technologic groups of gas coal, gas-fat coal and fat coal (according to the Ukrainian classification) prevail at the Tyagliv field. It is proved that gas coal is suitable for coking. At the Lyubelya field, fat, coke-fat and coke coal prevail. Сoke coal comprises almost a half of the reserves. In the region, reserves and resources of coal are estimated to be over two billion tons, which exceeds in two times the residual reserves of the commercial part of the basin. The analysis of the raw material base of the Tyagliv and Lyubelya fields, estimation of reserves and evaluation of coal resources have a great importance for developing and working-out of the feasibility study for their commercial development.

The Resources of Oil-rich Coals in China

The resource characteristics of coal-rich, oil-deficient, and low-gas have determined the need to fully exploit the advantages of coal resources in China. China holds a large amount of low-rank coal with high volatile content and high tar yield. Based on the abundant oil-rich and low-rank coal resources, resource evaluation and research on its development and utilization are of great significance to the coal geology. According to the estimated reserves, the low-rank coal reserves are about 63.86 billion tons. Among the low-rank coals, the tar yield is greater than 7%, which is called oil-rich coal. Gas and semi-coke resources, which can greatly increase the application value of this type of coal resources. The oil-rich coal resources are widely distributed in the Carboniferous-Permian, Triassic, Jurassic, Cretaceous, and Neogene in China. They are mainly distributed in the three provinces of Inner Mongolia, Shaanxi, Xinjiang, and also Qinghai and Gansu in space. The Carboniferous-Permian oil-rich coal is mainly distributed in Shaanxi Fugu mining area, and the Triassic oil-rich coal is mainly distributed in the Zichang mining area of Shaanxi Province. It shows that the oil-rich coals are mainly lignite and long-flame coal with low metamorphism but also contains a small amount of gas coal and gas-fat coal. The tar yield and volatile content generally have a positive correlation. It has great significance to further study on the oil-rich coal resources.