Search Results (30)

The Lower–Middle Jurassic of the Kuqa Depression consists of terrestrial clastic deposits containing coal seams and thick lacustrine mudstones, and is of great significance for oil and gas exploration. Based on the comprehensive analysis of core, well-logging, outcrop, and seismic data, the sequence stratigraphy, depositional systems, and the controlling factors of the basin filling in the depression are systematically documented. Four primary depositional systems, including braided river delta, meandering river delta, lacustrine, and swamp deposits, are identified within the Ahe, Yangxia, and Kezilenuer Formations of the Lower–Middle Jurassic. The basin fills can be classified into two second-order and nine third-order sequences (SQ1–SQ9) confined by regional or local unconformities and their correlative conformities. This study shows that the sedimentary evolution has undergone the following three stages: Stage I (SQ1–SQ2) primarily developed braided river, braided river delta, and shallow lacustrine deposits; Stage II (SQ3–SQ5) primarily developed meandering river, meandering river delta, and extensive deep and semi-deep lacustrine deposits; Stage III (SQ6–SQ9) primarily developed swamp (SQ6–SQ7), meandering river delta, and shore–shallow lacustrine deposits (SQ8–SQ9). The uplift of the Tianshan Orogenic Belt in the Early Jurassic (Stage I) may have facilitated the development of braided fluvial–deltaic deposits. The subsequential expansion of the sedimentary area and the weakened sediment supply can be attributed to the planation of the source area and widespread basin subsidence, with the transition of the depositional environments from braided river delta deposits to meandering river delta and swamp deposits. The regional expansion or rise of the lake during Stage II was likely triggered by the hot and humid climate conditions, possibly associated with the Early Jurassic Toarcian Oceanic Anoxic Event. The thick swamp deposits formed during Stage III may be controlled by the interplay of rational accommodation, warm and humid climatic conditions, and limited sediment supply. Milankovitch cycles identified in Stage III further reveal that coal accumulation was primarily modulated by long-period eccentricity forcing. Full article

The eastern Junggar Basin in Xinjiang, China is a key coal-bearing region dominated by the Middle Jurassic Xishanyao Formation. Despite its significance as a major coal resource base, detailed paleoenvironmental reconstructions of its coal seams remain limited. This study investigates the B₁, B₂, B₃, and B₅ coal seams of the Xishanyao Formation using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) to assess geochemical indicators of the depositional environment during coal formation. The results show that the coal samples are characterized by high inertinite content and low vitrinite reflectance, indicative of low-rank coal. Slight enrichment of strontium (Sr) was observed in the B₁, B₂, and B₅ seams, while cobalt (Co) showed minor enrichment in B₃. Redox-sensitive elemental ratios (Ni/Co, V/Cr, and Mo) suggest that the peat-forming environment ranged from oxidizing to dysoxic conditions, with relatively high oxygen availability and strong hydrodynamic activity. A vertical trend of increasing paleosalinity and a shift from warm–humid to dry–hot paleoclimatic conditions was identified from the lower (B₁) to upper (B₅) coal seams. Additionally, the estimated atmospheric oxygen concentration during the Middle Jurassic was approximately 28.4%, well above the threshold for wildfire combustion. These findings provide new insights into the paleoenvironmental evolution of the Xishanyao Formation and offer a valuable geochemical framework for coal exploration and the assessment of coal-associated mineral resources in the eastern Junggar Basin. Full article

The Jurassic aquifer in Northwest China is the key aquifer for mine water filling, which is significant due to its loose structure, large porosity, strong rock permeability, and fracture development characteristics. In addition, the water richness in space is extremely uneven, and many coal mine roof water inrush events are closely related to it. A case of evaluation of water-richness of the roof sandstone in the 3-1 coal seam of the Bayangaole minefield was analyzed in depth, and the evaluation index system is established based on lithology and structural characteristics. Specifically, the evaluation indexes are under the influence of the influencing factors of lithology, the density of fault intersection endpoints, and the density of fault scale and the strength of folds as the influencing factors of structure. On this basis, the set pair analysis-variable fuzzy set coupling evaluation method is introduced to form a targeted water-rich evaluation model of a roof sandstone aquifer. By using the coupling method of set pair analysis and variable fuzzy set, a targeted evaluation model is formed to realize the organic integration of indicators. Through the comprehensive analysis of the relative zoning of water abundance and the data from the borehole pumping (drainage) test, the distribution of water abundance grade in the study area is clarified. Full article

The Dzungaria Basin is located north of Xinjiang and is one of the largest inland basins in China. The eastern coalfields in the Dzungaria Basin contain a large amount of coal resources, and the thickness of the coal seams is significant. Therefore, the aim of this study was to classify the paleovegetation types and develop paleoclimate succession models of the extra-thick coal seams. We conducted the sampling, separation, and extraction of spores and pollen and carried out microscopic observations in the Wucaiwan mining area of the eastern coalfields in the Dzungaria Basin. The vertical vegetation succession in the thick seam (Aalenian Stage) in the study area was divided into three zones using the CONISS clustering method. The results show that the types of spore and pollen fossils belong to twenty families and forty-five genera, including twenty-three fern, twenty gymnosperm, and two bryophyte genera. The types of paleovegetation in the study area were mainly Lycopodiaceae and Selaginellaceae herb plants, Cyatheaceae, Osmundaceae, and Polypodiaceae shrub plants, and Cycadaceae and Pinaceae coniferous broad-leaved trees. The paleoclimate changed from warm–humid to humid–semi-humid and, finally, to the semi-humid–semi-dry type, all within a tropical–subtropical climate zone. The study area was divided into four paleovegetation communities: the nearshore wetland paleovegetation community, lowland cycad and Filicinae plant community, slope broad-leaved and coniferous plant mixed community, and highland coniferous tree community. This indicates that there was a climate warming event during the Middle Jurassic, which led to a large-scale lake transgression and regression in the basin. This resulted in the transfer of the coal-accumulating center from the west and southwest to the central part of the eastern coalfields in the Dzungaria Basin. Full article

Due to the gradual depletion of traditional metallic mineral resources, the search for new potential sources is an important issue. One such source is coal deposits. The extraction of metals from coal is a way to produce clean energy. This study presents the results of detailed research on geochemical features and mineralogy to understand the processes of microelement enrichment in the coal-bearing deposit of Shubarkol, in Central Kazakhstan. Modern analytical techniques were used to obtain information about the conditions and processes of trace element accumulation in coal, as well as the modes of occurrence of these elements. Geochemical data were analyzed using multidimensional statistical methods, including correlation, clustering, and factor analysis, which allowed us to draw several scientific conclusions. Numerous factors indicate that the enrichment of trace elements in sediments is controlled by clastic terrigenous material and low-temperature hydrothermal solutions circulating in the coal basin. The main sources of removal of trace elements from coal are ancient igneous rock complexes located within deposits that were directly involved in coal enrichment through secondary geological processes. According to estimates, the degree of enrichment of Jurassic coals at Shubarkol was close to the average value for world coals (0.5 < CC < 2), and coal seams were enriched with lithophilic and chalcophilic elements such as Ba, U, Yb, Co, La, Nb, Hf, Sc, V, Sr, Cu, and Zn. A correlation analysis of coal deposits revealed a significant correlation between main oxides and rare earth elements (REEs). The strongest correlation was between Zr, Hf, Th/Ta, and REEs. The positive correlations between Zr and Al₂O₃, Nb and Al₂O₃ indicate that these elements (Zr, Hf, Nb, Ta, and REY) are probably related to Al. The results obtained make it possible to consider coal as a potential mineral resource for the production of rare metals and serve as a guide for the industrial processing of the most important elements found in coal. Full article

Accurate prediction of the height of water-conducting fissure zone (HWCFZ) is an important issue in coal water control and a prerequisite for ensuring the safe production of coal mines. At present, the prediction model of HWCFZ has some issues such as poor prediction accuracy. Based on the widely collected measured data of the HWCFZ in different coal mines in northern Shaanxi Province, China, the HWCFZ in shallow-buried coal seams is categorized into two types, i.e., typical shallow-buried coal seams and near-shallow-buried seams, according to the different depths of burial and base-loading ratios. On the basis of summarizing the research results of the previous researchers, three factors, namely, mining thickness, coal seam depth, and working length, were selected, and the data of the height of the water-conducting fissure zone in the study area were analyzed by using a multivariate nonlinear regression method. Subsequently, each group of the data was randomly divided into training data and validation data with a ratio of 70:30. Then, the training data were used to build a neural network model (BP), random forest model (RF), a hybrid integration of particle swarm optimization and the support vector machine model (PSO-SVR), and a hybrid integration of genetic algorithm optimization and the support vector machine model (GA-SVR). Finally, the test samples were used to test the model accuracy and evaluate the generalization ability. Accordingly, the optimal prediction model for the typical shallow-buried area and near-shallow-buried area of Jurassic coal seams in northern Shaanxi was established. The results show that the HWCFZ for the typical shallow-buried coal seam is suitable to be determined by the multivariate nonlinear regression method, with an accuracy of 0.64; the HWCFZ for near-shallow-buried coal seams is suitable to be predicted by the two-factor PSO-SVR computational model of mining thickness and the burial depth, with a prediction accuracy of 0.84; and machine learning methods are more suitable for near-shallow-buried areas, dealing with small-scale data and discrete data. Full article

Deep coalbed methane (CBM) resources are abundant in China, and in the last few years, the country’s search for and extraction of CBM have intensified, progressively moving from shallow to deep strata and from high-rank coal to medium- and low-rank coal. On the other hand, little is known about the gas content features of deep coal reservoirs in the eastern Junggar Basin, especially with regard to the gas content and the factors that affect it. Based on data from CBM drilling, logging, and seismic surveys, this study focuses on the gas content of Baijiahai Uplift’s primary Jurassic coal seams through experiments on the microscopic components of coal, industrial analysis, isothermal adsorption, low-temperature CO₂, low-temperature N₂, and high-pressure mercury injection. A systematic investigation of the controlling factors, including the depth, thickness, and quality of the coal seam and pore structure; tectonics; and lithology and thickness of the roof, was conducted. The results indicate that the Xishanyao Formation in the Baijiahai Uplift usually has a larger gas content than that in the Badaowan Formation, with the Xishanyao Formation showing that free gas and adsorbed gas coexist, while the Badaowan Formation primarily consists of adsorbed gas. The coal seams in the Baijiahai Uplift are generally deep and thick, and the coal samples from the Xishanyao and Badawan formations have a high vitrinite content, which contributes to their strong gas generation capacity. Additionally, low moisture and ash contents enhance the adsorption capacity of the coal seams, facilitating the storage of CBM. The pore-specific surface area of the coal samples is primarily provided by micropores, which is beneficial for CBM adsorption. Furthermore, a fault connecting the Carboniferous and Permian systems (C-P) developed in the northeastern part of the Baijiahai Uplift allows gas to migrate into the Xishanyao and Badaowan formations, resulting in a higher gas content in the coal seams. The roof lithology is predominantly mudstone with significant thickness, effectively reducing the dissipation of coalbed methane and promoting its accumulation. Full article

The development height of a water-flowing fractured zone is the key parameter to consider when carrying out mining under water pressure and coal mining with water conservation. In this paper, Jurassic coal seam 3-1 in the Menkeqing Coal Mine was taken as the research target, and a three-dimensional mining geological model was established by using FLAC^3D to study the deformation and failure rules of overburden. Three roof boreholes were drilled in the auxiliary transportation roadway of adjacent working faces for dynamic monitoring by the resistivity method, which can better observe the whole process from failure to stability of the overburden. The results show that due to the complex sedimentary environment and large buried depth of coal seams in western China, there is a large deviation between the calculation results of the empirical formula of the fractured zone height under the “Regulations of buildings, water, railway and main well lane leaving coal pillar and press coal mining” (three regulations) and the simulation and on-site measurement. Based on the comprehensive analysis, the influence range of mining advance abutment pressure is approximately 60 m. The height of the water-flowing fractured zone is approximately 106 m, and it is located at the interface between sandy mudstone and mudstone. The height of the caving zone is approximately 22 m, and it is located at the interface between fine sandstone and medium sandstone. The ratio of the fractured height and coal seam thickness (R_f) reached 24.4, which was basically consistent with the test result of the adjacent Yushenfu mining area (which was 26 on average). There is no obvious change in the development height of the caving zone and water-flowing fracture zone from the working face to the drilling borehole position of more than 120 m, which reflects that the height of the overburden failure zone is related to the control of lithological combination. Full article

The development height of the water-conducting fracture zone (WCFZ) is crucial for the safe production of coal mines. The back-propagation neural network (BP-NN) can be utilized to forecast the WCFZ height, aiding coal mines in water hazard prevention and control efforts. However, the stochastic generation of initial weights and thresholds in BP-NN usually leads to local optima, which might reduce the prediction accuracy. This study thus invokes the excellent global optimization capability of the Improved Radial Movement Optimization (IRMO) algorithm to optimize BP-NN. The influences of mining thickness, coal seam depth, working width, and hard rock lithology proportion coefficient on the height of WCFZ are investigated through 75 groups of in situ data of WCFZ heights measured in the Jurassic coalfield of the Ordos Basin. Consequently, an IRMO-BP-NN model for predicting WCFZ height in the Jurassic coalfield of the Ordos Basin was constructed. The proposed IRMO-BP-NN model was validated through monitoring data from the 4⁻²216 working faces of Jianbei Coal Mine, followed by a comparative analysis with empirical formulas and conventional BP-NN models. The relative error of the IRMO-BP-NN prediction model is 4.93%, outperforming both the BP-NN prediction model, the SVR prediction model, and empirical formulas. The results demonstrate that the IRMO-BP-NN model enhances the accuracy of predicting WCFZ height, providing an application foundation for predicting such heights in the Jurassic coalfield of the Ordos Basin and protecting the ecological environment of Ordos Basin mining areas. Full article

The macroscopic structural fractures (joints) and geostress distribution characteristics of coal reservoirs are important factors affecting the exploitation of coalbed methane (CBM). In this study, the joints in the sedimentary strata of the Dahebian block in Liupanshui area, Guizhou Province were investigated. Directional coal samples were collected for observation and statistical analysis of coal microfractures, the paleotectonic stress fields of the study area were reconstructed, and the tectonic evolution was elucidated. The geostress distribution characteristics of the target coal seam (coal seam No. 11, P₃l) in the study area were analyzed using the finite element numerical simulation method. The results indicate that the structural evolution of the Dahebian syncline in the study area can be divided into two stages. The Late Jurassic–Early Cretaceous stage (Early Yanshanian) is the first stage. Affected by the sinistral strike slip of the Weining–Ziyun–Luodian (WZL) fault zone, the derived stress field in the study area exhibits maximum principal stress (σ₁) in the NEE–SWW direction. The Late Cretaceous stage (Late Yanshanian) is the second stage. Affected by the dextral strike slip of the WZL fault zone, the derived stress field exhibits σ₁ in the NNW–SSE direction. The folds and faults formed in the first stage were modified by the structural deformation in the second stage. The dominant strikes of joints in the sedimentary strata are found to be in the NW–NNW (300°–360°) and NE (30°–60°) directions, with dip angles mostly ranging from 60° to 90°. The dominant strikes of coal microfractures are in the NW (285°–304°) and NE (43°–53°) directions. The distribution of geostress in the study area is characterized by high levels of geostress in the syncline center, decreasing towards the surrounding periphery. The overall trend of the geostress contour line is similar to the shape of the syncline and is influenced by folds and faults. The σ₁ of coal seam No. 11 is vertical stress. The prediction results show that the joint density of coal seam No. 11 in the block is 36–50 joints/m, and the shape of the joint density contour line is also affected by the axial direction of the Dahebian syncline and the surrounding faults. The variation in coal seam joint density and the control effect of geostress on joints opening or closing affects the permeability of coal reservoirs. The study results provide significant guidance for the exploitation of CBM. Full article

At present, coal accounts for more than 56% of China’s primary energy consumption and will continue to dominate for a long time in the future. With the continuous expansion of the mining intensity and scale of Jurassic coal resources in Northwestern China, the problem of mine roof water disasters is becoming increasingly serious. The degree of harm is related to the hydrogeological structure of the overlying strata of the coal seam. Reasonable and effective prediction and evaluation of the water abundance of the coal seam roof aquifer is conducive to making scientific decisions on the prevention and control of roof water disasters, so as to achieve safe mining. In order to solve the problem of water abundance evaluation in mining areas lacking hydrological holes, taking the Hongliulin coal mine in Shennan mining area as an example, four main control factors for water abundance were selected: sandstone thickness, core recovery ratio, brittle rock thickness ratio, and flushing fluid consumption. Combined with unit water inflow and multiple factor comprehensive analysis, a back propagation (BP) artificial neural network and support vector machine regression (SVR) were introduced into water abundance evaluation. The reciprocal variance method was used to predict the measured unit water inflow. Finally, according to the “Detailed Rules for Coal Mine Water Prevention and Control”, the water abundance of aquifers was classified to verify the accuracy of the model and partition the water abundance of the study area. The results indicate that, based on the predicted results of unit water inflow, out of 37 borehole data, 22 weak water abundance holes and 15 medium water abundance holes were evaluated correctly, verifying their applicability. The study area was generally weak in water abundance, with two grades of medium and weak. The medium water abundance area was mainly located in the north and south of the study area, and the weak water abundance area was mainly located in the east and west. It can be seen that this evaluation model has certain applicability for evaluating the water abundance of coal seam roofs. It is of great significance, especially for the evaluation of water abundance in mining areas where hydrological holes are lacking. Full article

The Jurassic Yan’an Formation in the Ordos Basin is one of the main coal seams mined in the basin, and the enrichment of water bodies in the upper part of this coal seam is closely related to the sand bodies in the Zhiluo Formation. This study is based on the use of core observations in the northern part of the Ordos Basin for studying the pore characteristics of the permeable sand layer of the Zhiluo Formation in the study area through testing methods such as ordinary thin sections, cast thin sections, scanning electron microscopy (SEM), mercury intrusions, and physical property analysis. The results indicate that the primary pores of the Zhiluo Formation sandstone in the study area include primary intergranular pores, residual intergranular pores, and interstitial micropores. The secondary pores are mainly intergranular pores, feldspar dissolution pores, and rock debris dissolution pores. The throat-type pores are mainly variable fault contractions, sheets, curved sheets, and bundle-shaped throats. The pore structures of the Zhiluo Formation sandstone in the research area are complex, and the permeability is influenced by the throat characteristics. The main controlling factors of the pore structure characteristics of the Zhiluo Formation sandstone in the study area are sedimentation and diagenesis. Compaction and cementation are the main factors that destroy the sandstone pore structure, while later dissolution plays a certain role in the improvement of the pores. Section 1 of the Zhiluo Formation is greatly affected by diagenesis, and section 2 is greatly affected by sedimentation. Full article

The bed separation water inrush disasters in the Jurassic coalfield of Huanglong, China occur frequently, and they seriously threaten the safety of coal mining. This study systematically collected data from multiple instances of bed separation water inrush (BSWI) in the Cuimu coal mine and summarized the characteristics of BSWI. Through the analysis of hydrogeological conditions, hydrochemical characteristics, field detection of a water-conducting fractured zone (WCFZ), and groundwater level monitoring, the water inrush source, water-conducting channel, and the dynamic response of the aquifer water level were studied. The results showed that the water inrush source was mainly Cretaceous groundwater. The height of WCFZ in the extra-thick coal seam mining in the study area was 239.62 m, forming a water-conducting channel of water accumulation in bed separation. There was a strong correlation between water level changes in the Luohe Formation and BSWI. On this basis, we have proposed that four conditions must be met simultaneously for BSWI, and a hydrogeological-mining coupling conceptual model was established to reveal the evolution process and the mechanism of BSWI. The research results are crucial for the prevention of BSWI disasters and for ensuring the safety of coal mine production. Full article

The 8# coal seam in the Benxi Formation of the southeastern margin of the Ordos Basin is a deep coal seam with abundant coalbed methane resources. Calcite veins are commonly developed within the 8# coal seam, and their formation processes and mechanisms have significant implications for the enrichment of deep coalbed methane. Genesis of the calcite veins was analyzed to reveal the impact of the calcite veins formation on coalbed methane accumulation, with an integrated application of petrographic study by thin section, cathodoluminescence analysis, carbon-oxygen isotope analysis, and homogeneous temperature measurements of fluid inclusions. The research findings indicate that the calcite veins in the 8# coal seam can be classified into three stages: C1, C2, and C3. The diagenetic fluids of C1 primarily originated from contemporaneous seawater. The fluids responsible for the formation of C2 primarily consist of organic fluids enriched in biogenic gas, whereas the fluids contributing to the formation of C3 are primarily associated with liquid hydrocarbons originated form decarboxylation of organic matter. Furthermore, the development of both C2 and C3 is influenced by deep hydrothermal fluids resulting from tectonic heating events during the Early Cretaceous. By combining analysis of the hydrocarbon accumulation history and burial history in the study area, it has been established that C2 formation occurred during the Late Triassic to Early Jurassic, while C3 formation took place during the Late Jurassic to Early Cretaceous. The exploration and production practices in the study area have firmly established the crucial significance of the formation and evolution of calcite veins within the 8# coal seam for the migration and accumulation of coalbed methane. The research outcomes provide valuable insights for the exploration of deep coalbed methane enrichment areas. Full article

Mine seismic events are an inevitable dynamic phenomenon occurring in deep mines. A scientific and rational method is needed to evaluate and understand mine seismicity and its induced disasters. In the Ordos mining area of North China, multiple groups of thick hard-bedded sandstone formations commonly exist in the overlying strata of Jurassic coal seams. In recent years, frequent mine seismic events in many large mines of Ordos have resulted in suspended or limited production, which seriously threatens the safe and efficient operation of 10-million-ton modern mines in China. Therefore, taking the frequent occurrence of mine seismic events in the mining process of goaf working face with a multi-layer thick hard roof in Ordos mine as the research background, this study investigated the mechanism and prevention of mine seismic in goaf working face with the methods of case study, theoretical analysis and field monitoring. The following conclusions are made: when the goaf working face is mined, an “advanced and lateral” L-form roof forms under the coupled influence of the lateral suspension plate formed above the upper working face and the roof of the working face. Due to the common influence from “advanced and lateral” L-form roof activation, the gradually breaking multi-layer thick hard roof, thick hard roof group bending and prying effects, in addition to excessively fast or uneven mining speed, mine seismic events will occur frequently when the exceedance warning index (EWI) is breeched. On this basis, coordinated blasting to break the roof along two roadways and within the working face is put forward as a measure with the purpose of preventing and controlling mine seismic events, and a robust effect on mine seismic reduction and disaster prevention is obtained in field application. The research results can serve as a reference for the development and application of mine seismic mechanism and blasting vibration reduction technology on the working face where there is a multi-layer thick hard roof, thereby supporting a strategy of promoting the resource development and energy security of deep mines. Full article