Jurassic Coal Seams Research Articles

Genesis and accumulation mechanism of external gas in deep coal seams of the Baijiahai Uplift, Junggar Basin, China

Coal seams are typically self-sourced reservoirs. However, in certain special cases, the coal seams also contain large amounts of external gas from other source rocks. Successful development strategies in relation to Jurassic coalbed methane (CBM) in recent years have confirmed the presence of large amounts of external gas within the coal seams of the Baijiahai Uplift, Junggar Basin, China, which has important exploration and development prospects. However, the genesis and source of Jurassic CBM in the area remain unclear, limiting our understanding of its formation and accumulation as well as the planning of further development strategies. Based on a comprehensive analysis of the geochemical characteristics of Jurassic CBM, combined with research on the burial and thermal evolution history of the Jurassic coal seams, this study discusses the production curves of typical wells as well as regional tectonic styles, genesis, source, and accumulation of Jurassic CBM in the Baijiahai Uplift. Depending on the genesis, Jurassic CBM in the study area is divided mainly into coal-type (humic-type) gas, oil-type (sapropelic-type) gas, and mixtures of them, all of which are thermogenic gases of medium to high maturity. There are two main sources of Jurassic CBM in the Baijiahai Uplift. On the one hand, it comes from the vertical migration of gas generated by Permian and Carboniferous source rocks in the Baijiahai Uplift directly. On the other hand, it comes from the regional lateral migration from the Dongdaohaizi and Fukang Sags. Gas generated by source rocks in the Dongdaohaizi and Fukang Sags is driven by pressure, migrates towards the Baijiahai Uplift through sandstone channels, and accumulates in the Jurassic coal seams through faults. Compared with common self-sourced coal seams, enrichment of the coal seams with large amounts of external gases requires two necessary conditions: (1) Other layers of gas-generating source rocks are present at levels deeper than those of the coal seams, constituting additional gas sources for the coal seams, and (2) an open fault system is developed regionally, providing pathways for gas from other layers to enter the coal seams.

Water-inrush mechanism from the head-on working face roof in a Jurassic coal seam in the Ordos Basin.

When Chinese coal mines are mining Carboniferous Permian coal seams, the mechanism of water inrush from the roof of the working face usually conforms to the "Upper Three Zones" or "Upper Four Zones" theory. The water inrush passageway is water-conducting fracture zone, and the water inrush position is located in the goaf. However, when mining Jurassic coal seams in Chinese coal mines, the location of water inrush often appears at the head-on working face, above the coal mining machine. Due to the support of the fully mechanized mining support, the roof rock layer cannot collapse and therefore cannot form water-conducting fracture zone. Therefore, the water inrush mechanism cannot be explained by the above two theories. This paper is guided by the Practical Mine Pressure Control Theory, and based on the explanation of the motion forms of bending (pulling) failure movement and shearing (cutting) failure movement, and combined with on-site examples, it is revealed that the passageways leading to from the head-on working face roof in a Jurassic coal seam in the Ordos Basin are splitting zones type, fracture line type and structural fracture type, respectively. Taking the changes in water inflow during the mining process of the 3301 and 3302 working faces in Zhujiamao Coal Mine as examples, this paper reveals the mechanism of water inrush from the head-on working face roof caused by splitting zones type, and proves the existence of this passageway through on-site 3D high-density electrical detection and tracing experiments. Taking two catastrophic water inrush accidents that occurred head-on in the 1309 working face of Guojiahe Coal Industry Co., Ltd. as examples, the water inrush mechanism of the fracture line type and the water inrush mechanism of the structural fracture type were respectively revealed. Based on mechanism of water inrush from head-on roof of working face and the analysis of the on-site water inrush process, a method for distinguishing the type of water inrush passageway from the front roof of the working face is proposed. The results indicate that the Jurassic coal seam mining in the Ordos Basin is prone to shearing (cutting) failure movement, resulting in the frequent formation of the three types of water inrush passageways mentioned above.

Influence of high-frequency lake level fluctuations on organic matter accumulation in the northern Qaidam Basin, NW China: Insights from spectral attribute analysis and geochemistry

Assemblages of multiple organic matter-rich sedimentary energy carriers are frequently found in Jurassic nonmarine basins of China. These basins are strongly influenced by high-frequency fluctuations in lake levels. A series of coal- and oil shale-bearing successions reflecting periodic lake level variations is also present in the Shimengou Formation, northern Qaidam Basin, NW China. These Middle Jurassic coal and oil shale seams provide an excellent basis for studying the effects of high-frequency lake level fluctuations on organic matter accumulation. Moreover, additional factors influencing the primary organic matter input (e.g., wildfires) and its preservation and later diagenetic transformation (e.g., processes during coalification) must be considered. In the present study, organic matter maturity, source potential, and paleoenvironmental conditions during source rock formation are investigated based on macro- and micropetrographic data, proximate analyses, bulk geochemical parameters, biomarker analyses, stable isotope geochemistry, and spectral attribute analysis to provide a sequence stratigraphic framework for the accumulation of organic-rich intervals. According to the established depositional model, the Shimengou Formation can be subdivided into four depositional sequences, including three organic matter-rich intervals. These include the thick mixed gas- and oil-prone Sq1 coal seam with a relatively high ash yield, which represents a highstand systems tract, the gas-prone Sq3 coal seam corresponding to a transgressive systems tract, and the Sq4 oil shale layers likely corresponding to a subsequent highstand systems tract, indicating a drowned mire. The results provide insights for the optimization of high-quality sedimentary mineral resource production in similar basins worldwide.

Source of inorganic components in the Middle Jurassic inertinite-rich coals of the Southern Ordos Basin, China: With emphasis on formation of Sr- and Ba-bearing minerals

The Middle Jurassic coal seams located in the southern Ordos Basin display notably high concentrations of barium (Ba) and strontium (Sr). To acquire a comprehensive understanding of the source and occurrence of the elevated contents of Ba- and Sr-bearing minerals and their formation mechanism in the coal, a suite of petrological, mineralogical, and geochemical analyses was conducted on the Middle Jurassic coals of the Gaojiapu mine (No. 4 Coal) from the Binchang mining area, using optical microscopy, field emission-scanning electron microscopy, X-ray diffraction, X-ray fluorescence, and inductively coupled plasma mass spectrometry. The results indicate that the No. 4 Coal is a high volatile B bituminous coal, which is characterized by low ash, medium sulfur, and high inertinite contents. The modes of occurrence of minerals identified in the coal, including calcite, dolomite, pyrite, quartz, kaolinite, anatase, barite, and celestine, indicate that the No. 4 Coal may have been subjected to multiple stages of solutions injection. Barium and Sr in the investigated coals are significantly enriched, exhibiting maximum values of 19738 μg/g and 9932 μg/g, respectively, while concentrations of other trace elements are generally depleted. Barite and celestine, generally coexisting with carbonate minerals, commonly occur as cell- and fracture-fillings. Furthermore, the strong correlation coefficients (r) for Ba vs. Ca + Mg and Sr vs. Ca + Mg (0.78 and 0.61, respectively) indicate that most barite and celestine have a close association with carbonate minerals of epigenetic origin. The highly elevated concentrations of Ba and Sr are thought to be primarily derived from solutions leaching barite deposits developed in the Qinling Orogenic Belt, which is located in the south of the Ordos Basin. When mapped spatially, the distributions of Ba and Sr concentrations are fan-shaped, decreasing from the NW to the SE of the mining area. Meteoric water containing dissolved CO2 induced partial dissolution of carbonate rocks, and during this process, selected metal ions (e.g., Ca2+, Mg2+, Al3+, Si2+, Fe2+, Ba2+, and Sr2+) were redistributed and subsequently migrated along fracture zones to the coal seam. The fracture systems and abundant cavities within inertinite in the coal provided sufficient space and conduits for solutions migration.

Astronomical forcing in the coal-bearing Middle Jurassic Dameigou Formation, Qaidam Basin, northwestern China

Coal seams, as a terrestrial carbon sink, are not only important sedimentary and energy mineral resources but also excellent recorders of paleoclimate change. The study of coal-bearing strata is particularly significant in exploring the relationship between geological records and orbital forcing. However, the understanding of the relationship between coal seams of different sources of organic matter and astronomical cycles is incomplete. This study focuses on the Dameigou Formation, a typical Jurassic coal seam in the Qaidam Basin, Northwestern China. Organic petrology analysis, biomarker analysis, and whole-rock mineral analysis were combined to reconstruct the vegetation types and paleolake water level changes during coal seam deposition. In addition, using a time-series analysis method and high-precision gamma-scanning data from Well D1, we established a floating astronomical timescale and a time-depth model for cyclostratigraphical analysis. The results show that the Dameigou Formation, as coal-bearing strata, preserves well-developed Milankovitch cycles, and the climatic conditions and vegetation types during coal formation vary among different coal seams. Different patterns of variation in eccentricity, obliquity, and procession determine the thickness of the coal seam. This study is of great significance for understanding the astronomical factors that influenced climate evolution and coal deposition during the Middle Jurassic.

Study on the Mechanism and Prevention of Frequent Mine Seismic Events in Goaf Mining under a Multi-Layer Thick Hard Roof: A Case Study

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.

A Study on Disasters Induced by Head-On Ejection in High-Speed Driving under the Influence of Roof Drainage

During the gob-side entry driving of the Jurassic coal seam in Western China, ejection disasters occur under the influence of roof drainage, which rarely appear in the eastern mining area. To address this problem, a method combining theoretical analysis, numerical simulation, and field monitoring was used to study the disaster induced by head-on ejection during speedy driving under the influence of roof drainage in the context of gob-side entry driving of the 2202 auxiliary haulage roadway in a mine. A calculation model for the critical energy conditions for disasters induced by head-on ejection was established. The relationships between the driving velocity and the dynamic and static loads on the driving face and the disasters induced by ejection were clarified under the influence of roof drainage. The results indicate that the energy threshold for ejection-induced disaster is 12.23 kJ, and the elastic energy of the driving face induced only by static load fails to reach the energy threshold. When the driving velocity exceeds 5 m/d, microseismic activity in front of the driving face increases in a stepwise manner, and the influence of dynamic load intensifies. The superposition of accumulated elastic energy induced by static load and the energy transmitted by microearthquake to the driving face exceeds the energy threshold, resulting in the risk of ejection-induced disaster. Based on this, measures such as microseismic monitoring in front of the driving face, advanced pulverized coal monitoring, driving speed adjustment, and advanced pressure relief of large-diameter boreholes are adopted to ensure safe driving.

Dynamic behavior of oxidative heat release of key active groups for different Jurassic coal seams in northern Shaanxi

Dynamic behavior of oxidative heat release of key active groups for different Jurassic coal seams in northern Shaanxi

Predicting the Height of the Water-Conducting Fractured Zone in Fully Mechanized Top Coal Caving Longwall Mining of Very Thick Jurassic Coal Seams in Western China Based on the NNBR Model

Predicting the Height of the Water-Conducting Fractured Zone in Fully Mechanized Top Coal Caving Longwall Mining of Very Thick Jurassic Coal Seams in Western China Based on the NNBR Model

A Prediction Method for Height of Water Flowing Fractured Zone Based on Sparrow Search Algorithm–Elman Neural Network in Northwest Mining Area

The main Jurassic coal seams of the Ordos Basin of northwest mining area have special hosting conditions and complex hydrogeological conditions, and the high-intensity coal mining of the coal seams is likely to cause groundwater loss and negative effects on the surface ecological environment. The research was aimed at predicting the height of the water-flowing fractured zone (WFFZ) in high-intensity coal mining in that area and gave instructions for avoiding water inrush accidents and realizing damage reduction mining during the actual mining procedure of the coal mine. In this study, 18 samples of the measured height of WFFZ in Jurassic coal seams were systematically collected. In the mining method, the ratio of the thickness of the hard rock to the thickness of the soft rock in the bedrock, buried depth, mining height, and working face length was selected as the input vectors, applied the sparrow search algorithm (SSA) to iteratively optimize the weights and thresholds of the Elman neural network (ENN), constructed an SSA-Elman neural network model. The results demonstrate that the improved SSA-Elman neural network model has higher accuracy in predicting the height of the WFFZ compared with traditional prediction algorithms. The results of this study help guide damage-reducing, water-preserving mining of the middle-deep buried Jurassic coal seams in the northwest mining areas.

Research on the Development Law of Water-Conducting Fracture Zone in the Combined Mining of Jurassic and Carboniferous Coal Seams

The accurate prediction of the height of the water-conducting fracture zone is essential for the prevention of roof damage by water disasters in coal mines. The development law of water-conducting fracture zone in combined mining of Jurassic and Carboniferous coal seams is different from that of previous research results. This study constructed an engineering geomechanics model to carry out material simulation and numerical simulation. The changes of stress, displacement, and fracture propagation were analyzed and compared with the results of formula calculation and field measurement, revealing the combined action of Jurassic and Carboniferous coal seams on the development law of water-conducting fracture zone. The results show that: (1) stress concentration is formed in the middle of the goaf in Jurassic coal seam, resulting in the high height of water-conducting fracture zone and the fracture “closed”; (2) the mining of Carboniferous coal seams caused the second subsidence of Jurassic goaf, and closed fracture “activated”; (3) the height of the water-conducting fracture zone obtained by the empirical formula is small, which is quite different from the actual situation. These research results are of significance for determining the height of the water-conducting fracture zone in Jurassic and Carboniferous coal seams during combined mining and the prevention of coal roof water hazards.

Prediction method and research on characteristics of surface subsidence due to mining deeply buried Jurassic coal seams

Prediction method and research on characteristics of surface subsidence due to mining deeply buried Jurassic coal seams

Trapezoidal collapse model to calculate the height of the overburden collapse zone in coal seam mining: An example from Guo'Jiahe Coal Mine, Western China

In view of the fact that water inrush often occurs from head-on roof of working face, on the identical time, sand-burst and mud-burst accidents even occur in the process of mining the Jurassic Coal Seam, which is formed in one of the three main coal forming periods in China. Guided by the practical theory of mine pressure control, taking the two disastrous water inrush accidents that occurred head-on in 1309 working face of Guojiahe Coal Industry Co., Ltd. as an example, the mechanisms of head-on water inrush in the working face are respectively revealed for fracture line type, i. e. Then deduced the roof overburden collapse zone's evolution law because of coal seam mining and the stress state of the roof settlement process. A trapezoidal collapse model was proposed to evolve the overburden collapse zone after coal mining to describe the overburden collapse and fissures' evolution and calculate the collapse zone's height. The model accuracy was verified using numerical simulation, 3D high-density electric prospecting and measured data of different coal mines.

Roof-Breaking Characteristics and Ground Pressure Behavior in Deep Jurassic Coal Seams: A Thick-Plate Model and Field Measurements

Roof-breaking characteristics and ground pressure behavior of the coalface are instrumental in guiding deep Jurassic coal seam mining, in particular in the Shaanxi and Inner Mongolia regions of China. A thick-plate mechanical model (TPMM) of the main roof was developed and applied to the case study of 21102 first-mined coalface (FMC) of the Hulusu Coal Mine (HCM) in the Hujirt Mining Area (HMA), China. A theoretical analysis performed via the developed model revealed that the first and periodic breaking intervals of the main roof were 40.6 and 25.0 m, respectively. The roof failure occurred in the tensile mode, was controlled by the internal stress σ x in the rock strata, and started from the center of the long side with the fixed support in the goaf. The field measurement of roof weighting was also performed for the coalface advance from zero to 400 m. The measurement results showed that the first weighting average interval was 41.4 m, and the average interval of periodic weighting was 22.0 m, which agreed with the theoretical calculation and proved the proposed model’s feasibility. Finally, the frequency distribution features of the hydraulic support working resistance in the FMC were analyzed statistically. The results showed that the ZY10000-16/32D supports could adapt to the mining geological conditions of the FMC. However, the margin of the rated working resistance of supports was still small. Thus, roof management enhancement during the mining process was strongly recommended. These research findings could offer theoretical guidance for safe and high-efficiency production in the coal mines under similar geological conditions.

Barium in coal and coal combustion products: Distribution, enrichment and migration

Coal triggering pollution caused by the emission of harmful substances in the process of coal combustion has been paid more and more attention. Barium is a ubiquitous heavy metal element in coal. During coal combustion, Ba in coal has been released into the environment in different forms, and coal-fired products with high Ba content can cause harm to the environment, human health and even pose a serious threat to life. By reviewing the literature, distribution, modes of occurrence, mobility of Ba in coal seams were summarized and studied in this paper. It is expected to provide information for controlling emission of Ba. The content characteristics of Ba in coal in some countries are introduced, and the content gradient of Ba in coal of Chinese different provinces is introduced in detail. And coal with Ba content greater than or equal to 5 times of the world average Ba content, namely, coal containing 750 μg/g Ba is called high Ba coal. Many studies have shown that Ba was extremely enriched in coal in some areas (up to 5,000 μg/g), particularly in the Jurassic coal seams of the Huanglong coalfield in China. There were various types of occurrences of Ba in coal, including witherite, barite, crandallite and other minerals. Meanwhile, Ba can combine with organic matter as well. According to existing studies, the enrichment mechanism of Ba in coal is mainly derived from soil, sediment and seawater erosion, with the later causal minerals Ba carbonate and strontium rhodochrosite being the main carriers of Ba. The migration and transformation pathways of Ba in coal and its combustion products are described. As a medium volatile element, Ba is prone to concentrate in products of coal combustion, particularly those small-grainsize particles in fly ash, which may induce more serious contamination.

A method for judging depositional environment of coal reservoir based on coal facies parameters and rare earth element parameters

Coal facies refers to the genetic type and coal rock type of coal formed in a certain depositional environment. Rare earth elements (REE) are not easily disturbed by metamorphism, which is used to determine the provenance characteristics of coal-forming materials and the depositional environment in the coal seam. A total 76 coal samples from Carboniferous, Permian and Jurassic in the southern Ordos Basin were selected to determine the content and distribution characteristics of maceral compositions and REE using microscope observation and ICP-MS analysis. Combining the traditional REE indicator parameters (La/Lu, La/Sm, Gd/Lu, δEu, δCe, and REY) of the sedimentary rocks with the unique facies parameters in coal (Vitrinite content/Inertinite content (V/I), Gelation Index (GI), Texture Preservation Index (TPI), Groundwater Flow Index (GWI), Vegetation Index (VI) and Framework Matrix Ratio (F/M)), we determine the depositional environment, oxidation-reduction condition, coal-forming plants, hydrodynamic conditions and provenance characteristics of coal seams in different periods. The depositional environment is performed with the GI-TPI crossplot. The oxidation-reduction environment is explored by δEu, δCe and GI. The coal-forming environment is judged by a comprehensive combination of GWI-VI crossplot, ∑REY, La/Lu, La/Sm and Gd/Lu. The judgment of provenance characteristics is limited by the diagram of ∑REY and La/Yb and REE parameters. • The petrological features and REE characteristics of Permo-Carboniferous and Jurassic coal seams were explored. • The coal facies parameters suitable for the coal seams were performed. • A method for judging depositional environment of coal seams was established. • The depositional environment and coal-forming environment of coal seams in the southern Ordos Basin were discussed.

Disastrous Mechanism of Water Discharge in Abandoned Gob above the Stope in Mining Extra-Thick Coal Seam

The Datong mining area is a typical double system coal seam mining area in China, where the Jurassic and Carboniferous coal seams are mined simultaneously. The upper Jurassic coal seam has been largely mined, leaving a large amount of gob area. Besides, a large amount of harmful water is accumulated. With the exploitation of the 3-5# extra-thick coal seam in the Carboniferous system, the scope of overburden damage is greatly increasing, and the mining fracture field is further developed. Once the mining-induced fractures connect with the overlying gob, it is easy to induce the water discharge disaster. With the mining geological conditions of the 8202 working face in the Tongxin coal mine as references, the disastrous mechanism of water discharge in the abandoned gob above the stope in the mining extra-thick coal seam is researched by numerical simulation with the UDEC numerical software, and the research results are obtained. The water in the overlying gob percolates through the mining-induced fractures in the higher key layer forming a “shower” seepage pattern. The water in the above gob converges in the key fracture channel, flowing into the working face. The seepage in the fractures in the high key stratum experiences the process of increase, decrease, and stabilization, related with the stretching and extrusion deformation between the high key stratum blocks. Compared with other fractures, the flow rates in the No.2 and No.4 fractures in the far field key lay are larger, because the fractures are in the tension state, forming the “saddle-shaped” flow pattern. The influencing distance of mining-induced seepage is about 80 m in front of the working face. The research results provide a guided reference for the prediction and prevention of water discharge disaster in an abandoned gob above the stope in a mining extra-thick coal seam.

Division of Methane Weathering Zones in the Middle and Lower Jurassic Coal Seams of Santanghu Basin

Division of Methane Weathering Zones in the Middle and Lower Jurassic Coal Seams of Santanghu Basin

Study on the Strata Movement Rule of the Ultrathick and Weak Cementation Overburden in Deep Mining by Similar Material Simulation: A Case Study in China

In the deep mining areas of western China, there exist ultrathick and weak cementation strata in the overburdens above the Jurassic coal seams, and the overburden lithology is generally moderately a little weaker than the medium-hard strata. Yet, the practical measurement indicates that the surface movement rule in this area displays the specialty that is apparently inconsistent with its lithology, which increases the uncertainty of safe production in coal mines. In this study, the similar material and numerical simulations were conducted to investigate the movement rule and failure pattern of the ultrathick and weak cementation overburden. In addition, the photographing scale transformation-time baseline parallax (PST-TBP) method was used to monitor the similar material model to makeup for the lacks of Xi'an Jiaotong University Digital Close-range Industrial Photogrammetry System (XJTUDP) software. The findings of this study can be summarized as follows. (1) To some extent, the PST-TBP method can makeup for the deficiency of the XJTUDP software because the measurement accuracy of the PST-TBP method is 0.47 mm. (2) The height of the caving zone is approximately 66 m, and the height of the water suture zone is about 112 m, which is obviously larger than that of the medium-hard and soft overburden in eastern-central China. (3) The first breaking span of the immediate roof reaches 120 m, the cyclic fracturing length is about 60 m, and the separation occurred at 43 m and 66 m above the coal seam. (4) The failure pattern of the ultrathick and weak cementation overburden is “beam-arch shell,” and the failure boundary is arch. (5) The Zhidan group sandstone and Jurassic sandstone formations have strong control effects. The Zhidan group sandstone is the main control stratum and the Jurassic sandstone formation is the secondary-control stratum. The research results provide an insight into guiding the safe mining of deep coal in the ultrathick and weak cementation overburden.

Molecular Organic Geochemical Characteristics and Coal Gas Potential Evaluation of Mesozoic Coal Seams in the Western Great Khingan Mountains

AbstractCoal‐bearing strata are widespread in the western Great Khingan Mountains. Abundant coal resources have been found in the Jurassic Alatanheli Groups, the Cretaceous Bayanhua Groups, the Damoguaihe Formation and the Yimin Formation. The organic geochemical characteristics were analyzed in combination with hydrocarbon source rock evaluation and molecular organic geochemistry experiments, and the coal gas potential of coal seams was evaluated. The source rock evaluation results indicated that the Mesozoic coal samples have the characteristics of high organic matter abundance (TOC>30%), low maturity (Ro values of approximately 0.6%), and type III composition. The hydrocarbon generation potentials of the Alatanheli Groups and Bayanhua Groups are high, while the generation potentials of the Damoguaihe Formation and the Yimin Formation are low. The results of geochemistry show that the depositional environment of the coal seam was a lacustrine, oxidizing environment with a low salinity, and the source of the organic matter was mainly higher plants. Affected by weak degradation, the coal seams mainly formed low‐maturity gas of thermal catalytic origin. The Cretaceous coal seams contain a large amount of phytoplankton groups deposited in a low‐stability environment affected by a transgression event, and the potential range varied widely. For the Jurassic coal seams, the depositional environment was more stable, and the coal seams feature a higher coal‐forming gas potential.