Major Coal Seams Research Articles

Petrophysical and Geochemical Investigation-Based Methodology for Analysis of the Multilithology of the Permian Longtan Formation in Southeastern Sichuan Basin, SW China

Against the backdrop of the national strategic goals of carbon peaking and carbon neutrality, the imperative for China’s low-carbon new energy transformation is evident. Emerging as an efficient and clean new energy source, the coal-based “three gases” (coalbed methane, tight sandstone gas, and shale gas) have gained prominence. Nevertheless, the current exploration of the coal-based “three gases” is limited to individual reservoirs, posing challenges to achieving overall extraction efficiency. The primary obstacle lies in the conspicuous disparities in gas content among different reservoirs, with the causes of such disparities remaining elusive. To address this issue, this study focused on the Permian Longtan Formation (coal, shale, and tight sandstone) in the southeastern Sichuan Basin. Through a comparative analysis of the mineral composition, organic geochemical features, and pore structure characteristics, this study aimed to delineate reservoir variations and establish a foundation for the simultaneous exploration and exploitation of the coal-based “three gases”. The research findings revealed that the differences in reservoir characteristics account for the variations in gas content among coal, shale, and tight sandstone. The mineral composition of the rock formations in the study area primarily consists of quartz, feldspar, clay minerals, pyrite, calcite, and dolomite. By comparison, the coal samples from the four major coal seams in the study area exhibited relatively large pore sizes, which are favorable for gas accumulation.

Prediction of velocity, gas content from neural network modeling and estimation of coal bed permeability from image log in coal bed methane reservoirs: Case study of South Karanpura Coalfield, India

P-wave velocity and gas content of major coal seams are predicted from three wells from the South Karanpura coalfield, India. Multilayered feed-forward neural network (MLFN) model is developed for prediction P-wave velocity from two wells using three input log parameters: gamma ray, resistivity and bulk density. The model is tested on coal seams: Sayal, Balkudra, Banasgarah and Argada of three wells namely; A, B and C with satisfactory goodness of fit (R2 = 0.77). The ratio of P-wave and S-wave velocities (Vp/Vs) ranges from 1.68 to 3.10 in the coal seams of this field. Cleat density using image log is obtained from four major coal seams namely; Balkudra, Kurse, Hathidari, Banasgarah varying from 1/m to 11/m. Ash content varies from 15 to 51% whereas gas content of major coal seams varies from 2.30 to 4.4 10−3 kg/m3. There is a good correlation between ash content and Vp/Vs of coal seams under the study area. MLFN model for prediction of gas content of the above-mentioned coal seams from two well is trained with input parameters such as: Vp/Vs, bulk density, cleat density and ash content. The model estimates gas content of other coal seams: Argada from well A, Hathidari from well B and Balkudra, Kurse, Banasgarah from well C with satisfactory R2 = 0.77. Maximum horizontal stress orientation is observed from azimuthal shear wave anisotropy from cross multipole array acoustic (XMAC) log for a well A. It varies from N110° to N115° in these coal seams. Permeability of coal seams are computed from X-tended Range Microresistivity Imager (XRMI) tool from a well C. Permeability of coal is varying from 0.5 md in Saunda seam to 17.29 md in Banasgarah seam. The estimated permeability matches well with the pre-fracture permeability of these seams. It is observed that increase in cleat density enhances coal seam fracture permeability in coal seam.

A study of sequence stratigraphy of the Early Cretaceous coal-bearing series in the southeastern Songliao Basin, NE China

The Early Cretaceous is an important coal accumulation period in China. Abundant coal resources were formed in the southeastern margin of Songliao Basin. Sequence stratigraphy and coal accumulation of the Early Cretaceous in the southeastern margin of Songliao Basin have been studied on the basis of extensive outcrop and borehole data. Based on regional unconformity, basal erosional surfaces of incised valley fills, and abrupt depositional facies-reversal surface, six sequence boundaries have been identified, which subdivide the Early Cretaceous coal-bearing series into 5 third-order sequences. Sequence I corresponds to Huoshiling Formation, sequences II and III correspond to member I and member II of Shahezi Formation. Sequences IV and V correspond to member I and member II of Yingcheng Formation. Sequence I developed at the initial subsiding stage, sequence II and III developed during the stable subsiding stage, while sequence IV and V developed during the basin shrinkage stage. The major coal seams were developed in the sequence II and III, which ensured the relative balance between the increase rate of the accommodation space and the rate of peat accumulation for a longer period, thus forming a thick coal seam.

Enrichment origin of critical elements (Li and rare earth elements) and a Mo-U-Se-Re assemblage in Pennsylvanian anthracite from the Jincheng Coalfield, southeastern Qinshui Basin, northern China

The Qinshui Basin is the largest reservoir of commercial coalbed methane in China. The No. 15 seam, one of the major coal seams for coalbed methane exploration in the Jincheng Coalfield, SE Qinshui Basin, has recently been found to be enriched in the critical element Li. This study further investigates the inorganic geochemistry of the No. 15 coal and associated rocks and reveals the enrichment origin of critical elements in these horizons. The Jincheng No. 15 coal is rich in Li, Mo, U, Se, Re, and rare earth elements and Y (REY). Concentrations of Mo, U, Se, and Re are higher in the two topmost coal benches, probably due to marine transgression in the early diagenetic stage after the peat had been established. The enrichment of Li and REY in a few lowermost coal benches is suggested to be derived from hydrothermal fluids that were related to magmatic activity (110–140 Ma) during the Yanshanian Orogeny (Late Jurassic-Early Cretaceous), or a Late Triassic-Early Jurassic abnormal thermal event occurring at 190–215 Ma. Light REY (La, Ce, Pr, and Nd) in the Jincheng No. 15 coal are predominantly associated with phosphate minerals. Heavier REY (Sm to Lu) show a mixed phosphate and organic affinity in the studied coal samples. Non-coal samples are characterized by light REY- and HREY-enrichment, which is probably inherited from the source material in the Trans North China Orogen.Trace elements in the coal can be highly enriched in the ash if the coal is combusted due to the low to medium ash yield of the coal. Critical elements, including Li, Ga, and REY, in the Jincheng No. 15 coal are considered as promising material for industrial recovery and have been previously under-estimated. On the other hand, environmentally sensitive elements including As, Hg, and Pb, while having concentrations within the normal range compared with average worldwide coals, can be highly enriched in the coal combustion residues if the coal is combusted, and thus careful consideration needs to be given to the utilisation of such coals.

Sequence stratigraphy and coal accumulation of Lower Cretaceous coal-bearing series in Erlian Basin, northeastern China

The detailed depositional systems and basin evolution of Lower Cretaceous coal-bearing strata in the Erlian Basin of northeastern China were analyzed based on extensive borehole and outcrop data. A total of 7 facies associations are interpreted and consist of 14 distinct lithofacies, with lithologies including conglomerates, sandstones, siltstones, mudstones, shales, and coals. Five third-order sequences were recognized, and their internal lowstand, transgressive, and highstand systems tracts were defined based on six key sequence stratigraphic boundaries. These boundaries were represented by regional unconformities, basal erosional surfaces of incised valley fills, interfluvial paleosols, and abrupt depositional facies-reversal surfaces. Sequences I–V correspond to the rift-initiation stage, the early-rift climax stage, the late-rift climax stage, the immediate postrift stage, and the late postrift stage of the basin, respectively. The preferred sites for coal accumulation were braided fluvial delta plain, meandering fluvial delta plain, and littoral–shallow lake environments. The major coal seams formed during the early and late transgressive systems tract of sequences III, IV, and V, which were well developed in the eastern, northeastern, and northeastern parts of the Erlian Basin, respectively. Three coal depositional models were summarized in the sequence stratigraphic framework, including types 1, 2, and 3, corresponding to the Newark type, Newark–Richmond type, and Richmond type, respectively. These coal depositional models were closely related to the basin evolution. These results could provide preferred depositional environments and favorable areas of coal and coalbed methane (CBM) for the exploration and development of coal and CBM in the Erlian Basin, with the Jiergalangtu, Huolinhe, Baiyinhua, and A’nan sags recommended as the key sags.

The characteristic and evolution of coal-forming swamp in Hanshuiquan district, Santanghu Coalfield, Xinjiang, NW China, during the Middle Jurassic: evidence from coal petrography, coal facies and sporopollen

Santanghu Coalfield is the largest integrated coalfield exploration area in China. The major coal seams developing in Xishanyao Formation (Middle Jurassic) are the high-quality steam coals characterized by large thickness, favorable horizontal continuity and high coal quality. In this paper, twenty-two samples were collected from the three typical boreholes in Hanshuiquan district, representing the 11 coal seam sequences (7#, 8#, 9#, 13#, 14#, 15#, 17#, 18#, 19#, 20#, 22#), respectively. The petrographic characteristics of the coal-bearing sequence in Xishanyao Formation were firstly summarized systematicly, and then the coal-forming swamp characteristics and succession mechanism of the coal seam in Xishanyao Formation were defined by analyzing the samples. The maceral composition, structure, geochemical and geophysical characteristics of coal are included in original genetic criteria of coal-forming swamp analysis. And the composition of coal petrography, maceral and microlithotype are the most frequently used parameters. Coal is composed of microscopic constituents and inorganic substances. The Xishanyao Formation maceral mainly consists of vitrinite (65.74%–97.01%), inertinite (1.93%–34%), and the exinite shows the mode of regular change. The coal-forming swamp in Xishanyao Formation possesses the characteristics of mainly marsh, wet forest swamp facies, and shallow water covered forest swamp facies, and a few of coal seams distribute in the deep water covered forest swamp facies. In addition, the sporopollens in Xishanyao Formation are mainly Pinaceae evergreen broad leaf and needle-leaved plants, Osmundaceae, Cyatheaceae and Lygodiaceae, indicating that the warm and humid tropic-subtropical climate conductive to the persistent growth of coal-forming plants in the Middle Jurassic. The coal-forming swamp shows the characteristics of vertically upward fluctuation through the periodic transition. It indicates a shallow-deep-shallow change process of the water covered depth in the swamp. This is the principal factor for the formation of the high-quality and continuous coal seam in Hanshuiquan district, Santanghu Coalfield.

Sequence paleogeography and coal accumulation of the Early–Middle Jurassic in central Qilian Mountain belt (Muli Basin), Qinghai Province, northwestern China

The Muli Basin in the Qinghai Province, located at the northeastern margin of the Tibetan Plateau, is a Jurassic coal-bearing basin, and is an important area for coal production in China. Recent explorations have revealed the presence of unconventional types of gases such as coalbed methane and gas hydrates. We have investigated the sedimentology, sequence stratigraphy, and lithofacies paleogeography of this basin based on data from outcrop and borehole sections. The coal-bearing strata include the Lower Jurassic Reshui and the Middle Jurassic Muli and Jiangcang Formations. Lithofacies including conglomerates, sandstones, mudstones, and coal were identified and have been interpreted to be formed in environments ranging from braided fluvial, braided fluvial delta, to lacustrine. The preferred sites of coal accumulation are the interdistributary bays of lower delta plain and upper delta plain environments. Three types of sequence boundaries are recognized, including regional unconformities between the Lower Jurassic and underlying Triassic, the basal surface of incised valley fills of thick-bedded sandstones in the Muli and Jiangcang Formations, and the surfaces that mark abrupt depositional facies shifts. Four third-order sequences were subdivided, namely S1, S2, S3, and S4 in ascending order, which correspond to the Reshui Formation, the Muli Formation, the lower member of the Jiangcang Formation, and the upper member of the Jiangcang Formation, respectively. Each sequence consists of a lowstand systems tract, a transgressive systems tract (TST), and a highstand systems tract. A series of sequence-specific basin-wide paleogeographic maps have been constructed based on contour maps of several lithological parameters including stratal thickness, sandstone-to-mudstone ratio, and mudstone thickness. From S1 to S4, the Muli Basin experienced an evolution from a braided fluvial system to braided fluvial delta, then to a lacustrine system, showing a gradual deepening process. Thick coal seams with thickness greater than 3.5 m (11.5 ft) were primarily developed in the delta plain environment where the rate of peat accumulation can be easily balanced by the rate of accommodation generation. A five-stage coal-accumulation model has been summarized, and the major coal seams mainly developed in the early and late TST of sequences S1 and S2.

Geological Factors and Reservoir Properties Affecting the Gas Content of Coal Seams in the Gujiao Area, Northwest Qinshui Basin, China

Coalbed methane (CBM) well drilling and logging data together with geological data were adopted to provide insights into controlling mechanism of gas content in major coal seams and establish gas accumulation models in the Gujiao area, Northwest Qinshui Basin, China. Gas content of targeted coals is various in the Gujiao area with their burial depth ranging from 295 to 859 m. Highly variable gas content of coals should be derived from the differences among tectonism, magmatism, hydrodynamism, and sedimentation. Gas content preserved in the Gujiao area is divided into two parts by the geological structure. Gas tends to accumulate in the groundwater stagnant zone with a total dissolved solids (TDS) value of 1300–1700 ppm due to water pressure in the Gujiao area. Reservoir properties including moisture content, minerals, and pore structure also significantly result in gas content variability. Subsequently, the gray correlation statistic method was adopted to determine the most important factors controlling gas content. Coal metamorphism and geological structure had marked control on gas content for the targeted coals. Finally, the favorable CBM exploitation areas were comprehensively evaluated in the Gujiao area. The results showed that the most favorable CBM exploitation areas were in the mid-south part of the Gujiao area (Block I).

Conceptual models for short‐eccentricity‐scale climate control on peat formation in a lower Palaeocene fluvial system, north‐eastern Montana (USA)

AbstractFluvial systems in which peat formation occurs are typified by autogenic processes such as river meandering, crevasse splaying and channel avulsion. Nevertheless, autogenic processes cannot satisfactorily explain the repetitive nature and lateral continuity of many coal seams (compacted peats). The fluvial lower Palaeocene Tullock Member of the Fort Union Formation (Western Interior Williston Basin; Montana, USA) contains lignite rank coal seams that are traceable over distances of several kilometres. This sequence is used to test the hypothesis that peat formation in the fluvial system was controlled by orbitally forced climate change interacting with autogenic processes. Major successions are documented with an average thickness of 6·8 m consisting of ca 6 m thick intervals of channel and overbank deposits overlain by ca 1 m thick coal seam units. These major coal seams locally split and merge. Time‐stratigraphic correlation, using a Cretaceous–Palaeogene boundary event horizon, several distinctive volcanic ash‐fall layers, and the C29r/C29n magnetic polarity reversal, shows consistent lateral recurrence of seven successive major successions along a 10 km wide fence panel perpendicular to east/south‐east palaeo‐flow. The stratigraphic pattern, complemented by stratigraphic age control and cyclostratigraphic tests, suggests that the major peat‐forming phases, resulting in major coal seams, were driven by 100 kyr eccentricity‐related climate cycles. Two distinct conceptual models were developed, both based on the hypothesis that the major peat‐forming phases ended when enhanced seasonal contrast, at times of minimum precession during increasing eccentricity, intensified mire degradation and flooding. In model 1, orbitally forced climate change controls the timing of peat compaction, leading to enhancement of autogenic channel avulsions. In model 2, orbitally forced climate change controls upstream sediment supply and clastic influx determining the persistence of peat‐forming conditions. At the scale of the major successions, model 2 is supported because interfingering channel sandstones do not interrupt lateral continuity of major coal seams.

Cleat Orientation from Ground Mapping and Image Log Studies for In Situ Stress Analysis: Coal Bed Methane Exploration in South Karanpura Coalfield, India

Conventional well logs from three wells in South Karanpura coalfield are analyzed to correlate 10 major coal seams belonging to the Barakar formation for coalbed methane (CBM) exploration. Face cleat orientations are studied for the Simana and Argada coal seams from the Sirka and Argada mines. It varies from 130 to 140°N for a total 349 face cleats observed from Simana and Argada coal seams. Cleat identification and its orientation have also been analyzed from simultaneous acoustic and resistivity (STAR) log from two CBM wells located 20–22 km away from the Sirka and Argada mines. Total number of fractures is found to be 1118 from two wells. Face cleats are not distinguishable from STAR image. Fracture density in coal is varying from 2.48 fractures per meter to 23.8 fractures per meter with a maximum density in the Banasgarah seam. Fracture orientations observed in Saunda, Sayal, Balkudra, Kurse, Hathidari, Banasgarah, and Argada vary from 10°N to 115°N. The in situ maximum horizontal stress (SH) is compu...

Prediction of Coal Proximate Parameters and Useful Heat Value of Coal from Well Logs of the Bishrampur Coalfield, India, Using Regression and Artificial Neural Network Modeling

The energy of coal is expressed by its useful heat value (UHV), and it is the major key player in coal pricing. The objectives of this paper are to obtain (a) the regression relationship between coal proximate parameters and UHVs, and (b) multilayered feed forward neural network (MLFN) models between geophysical log responses and UHVs. Six wells are used for training the networks, and three wells are used for validating the obtained results in the Bishrampur coalfield. The mean square error (MSE) of MLFN models along with correlation (R2) values at their training, validation, and testing stages are the criteria for selecting the best model for estimation of coal proximate parameters and UHVs using geophysical log responses. The final model is selected based on low MSE (≤0.07) and high R2 values (≥0.80) at training, validation, and testing stages. The predicted UHV obtained from the best MLFN model has excellent correlation (R2 = 0.98) with the laboratory determined UHVs of three major coal seams. The pred...

Inferring the Shape of Fractures and Hydraulic Properties of the Coal Seam Using Inverse Modeling on Pumping Test Results – Broke, NSW, Australia

Coal seam gas or coal bed methane production is becoming a significant industry in Australia. The area around the Broke township (located in the north-west of the Sydney Basin) has had coal seam gas exploration activities over the last decade. One methodology of well stimulation, hydraulic fracturing, has the potential to cause some environmental problems. The Broke region includes 4 aquifers (3 confined and semi-confined), more than 3 major coal seams (3 gas bearing) and has been covered by variety of different sedimentary rocks of Permian age. The groundwater system, with the gas bearing deposits is the function of conductivity and storativity (K and S) of the coal seam and geometry of properties of the fractures. The required data to investigate the hydraulic properties in the fractured zone includes; corehole data to assessment the geology and underground system, micro-seismic data to infer the fracture properties, pumping tests results, and monitoring wells data to evaluate the hydraulic properties of the coal seams. This paper investigates the shape of drawdown curves, resulting from the hydraulic pumping tests at Broke performed to determine the hydraulic and fracture properties, such as length, width, conductivity of fractures, and the proportion of the water and gas contained in the targeted coal seam. In order to reduce data uncertainty and increase the reliability of the hydraulic property estimation the Generalized Likelihood Uncertainty Estimation (GLUE) will be applied. Finally, with investigation of the shape (length and width) and conductivity of the fractures, the best monitoring method to ensure public safety of provide assurances that if problems occur the monitoring system will provide early warning for this study area will be determined.

Sequence stratigraphy and paleogeography of the Middle Jurassic coal measures in the Yuqia coalfield, northern Qaidam Basin, northwestern China

Detailed stratigraphic and paleogeographic analyses of data from 72 boreholes for the Middle Jurassic intermontane fluvial-lacustrine coal-bearing sequences were conducted in the Yuqia coalfield of the northern Qaidam Basin, northwestern China. Three third-order sequences lasting in total ca. 10.6 m.y., and an internal lowstand systems tract (LST), transgressive systems tract (TST), highstand systems tract (HST), and falling-stage systems tract (FSST) have been identified. A series of sequence-specific paleogeographic maps have been constructed based on the contours of lithological parameters. The paleogeographic units include alluvial fan-braided (meandering) fluvial plain, upper delta plain, lower delta plain, subaqueous delta, shore-shallow lake, and deep lake. The preferred sites of coal accumulation are interdelta bays, upper delta plains, lower delta plains, and fluvial back swamps. The sequence stratigraphic and sedimentological analysis of the Middle Jurassic coal-bearing measures of the Yuqia coalfield provides a basis for a comprehensive coal accumulation model that involves a six-period evolution from the LST, early TST, late TST, early HST, late HST to FSST. The major coal seams were accumulated in the early and late TST of the sequences S1 and S2. These results are of practical significance for coal resources exploration and enhance geological effects of prospecting engineering in the northern Qaidam Basin.

Classification of coal seams for coal bed methane exploitation in central part of Jharia coalfield, India – A statistical approach

Laboratory analyses data of coal core samples and coal seam characteristics, derived from well logs, have been used for quantitative analysis of proximate and petrophysical parameters of coals to assess the potential of coal bed methane (CBM) reservoir as clean energy source in central part of Jharia coalfield, India. Coal core samples and well log data of 27 exploratory wells have been used for this analysis. Coal seam permeability data for 14 major coal seams, obtained from shallow resistivity log, varies from 0.60md to 1.25md. Gas content values, calculated from available empirical equation varies from 11.11cc/g to 11.91cc/g. Hierarchical Cluster Analysis (HCA) has been applied to group the 14 coal seams of the study area based on these above mentioned parameters for quantitative assessment of CBM potentiality of coal seams. Based on this HCA, the total 14 numbers of coal seams/objects occurring within the depth intervals of 214.58–1345.05m have been classified into three categories in order of potentiality as CBM reservoir depending upon average coal seam permeability and average gas content. The data set, generated from the experimental work and assessment of CBM potentiality, may further be used in the investigations for enhanced CBM (ECBM) recovery with CO2 sequestration into coal beds in the Jharia coalfield.

CO2 sequestration into the Wyodak coal seam of Powder River Basin—Preliminary reservoir characterization and simulation

Injection of carbon dioxide captured from flue gas into coal beds is regarded as one of the value-added options of CO2 sequestration as the cost of injection can be partially or fully offset by the revenue generated through release of additional methane. The Powder River Basin is one of the major coalbed methane producing areas in the world. The paper presents findings of a preliminary reservoir simulation study on the feasibility of CO2 sequestration over a nine-section area (4.8km×4.8km) of the Powder River Basin into the thick Wyodak coal seam, one of the two major coal seams in the highly productive Fort Union formation.The reservoir model was built on the basis of information available in the public domain. Gamma ray logs from 60 wells were utilized for developing a 3-D geological model of the coal seam and overlying rocks in the area by employing geostatistical techniques. Considerable variability in gas and water production was observed in the 65 wells. This variability was utilized for capturing the reservoir heterogeneity by Gaussian geostatistical simulation, which produced realizations of fracture porosity and permeability distribution throughout the reservoir.Results of fluid flow simulation indicated that it would not be feasible to place more than one injector per 1.6km×1.6km (1mile×1mile) section of the area due to geomechanical constraint. As a preliminary estimate, it may be feasible to inject 0.658 million tons of CO2 through such injector over a period of 20 years. 12% more CO2 can be injected over the same period by using a horizontal well but the loss of injectivity may be substantial due to reduction of permeability by coal matrix swelling. The loss of permeability can partially be overcome by intermittent injection for 6 months followed by a similar soak period. Placing one vertical injector each into all the nine sections would result in a scaled-up volume of 5.5 million tons of CO2 injection. However, the nature of overlying rock could play a vital role in retention of injected CO2 and up to 20% of the gas may migrate up by buoyancy.

Mapping of cleats and fractures as an indicator of in-situ stress orientation, Jharia coalfield, India

Abstract Cleats and fractures in coal of Barakar Formation in Jharia coalfield, India have been mapped from the coal exposures around 21 opencast and 2 underground coal mines. Macro-cleat distribution, observed from this mapping is similar to that of well-developed coalbed methane (CBM) basins. The opencast coal mines are distributed in SE–NW direction along the boundary of the sickle shaped Jharia coal basin. Permeability of CBM through coal seams is the most critical property deciding the viability of any CBM field. It is largely controlled by the degree of cleat development. This paper discusses cleat orientation and other structural features, observed in the outcrops of 14 major coal seams in Jharia coalfield and its directional relationship with the in-situ stress (SH) orientation pattern. Cleat orientation is found to vary laterally within same seam at the different locations, distributed from the south-east part to the north-western part of Jharia coalfield. Face cleat orientation of the 21 opencast coal mines varies from N45°E to N45°W. Change of orientation of cleat, observed around the mining areas is related the orientation of fault systems and orientation of igneous intrusions occurring within the coal bearing packet. Maximum in-situ horizontal compressive stress (SH) direction is found to be parallel to the face cleat orientation in normal faulted basin like Jharia coalfield. An overall, NNE–SSW and NW–SE orientation of the SH direction is predicted in the coal mines from cleat orientation mapping. SH orientation is locally modified at places, close to the tectonic features and igneous intrusives. Finite element stress modeling is carried out near Moonidih area. Cleat orientation predicted stress direction matches well with the finite element stress results.

Determination of in-situ stress direction from cleat orientation mapping for coal bed methane exploration in south-eastern part of Jharia coalfield, India

Abstract Accurate prediction of in-situ stress directions plays a key role in any Coal Bed Methane (CBM) exploration and exploitation project in order to estimate the production potential of the CBM reservoirs. Permeability is one of the most important factors for determination of CBM productivity. The coal seams in Jharia coalfield generally show low permeability in the range of 0.5 md to 3 md. To estimate the in-situ stress direction in the study area, an attempt has been made to undertake the cleat orientation mapping of four regional coal seams of two underground coal mines located at south-eastern part of Jharia coalfield, India. Cleat orientation mapping is critical to determine the maximum principal compressive horizontal stress (S H ) direction for CBM exploration and exploitation, which in turn controls the direction of maximum gas or water flow though coal beds. From the field study it is found that the average face and butt cleat azimuths are towards N15°W and N75°E respectively. Average permeability of the four above-mentioned major coal seams has been calculated from well logs of nine CBM wells distributing over an area of 7.5 km 2 , adjacent to the underground mines. The cleat orientations are congruous with the regional lineament pattern and fits well with the average permeability contour map of the study area to infer the orientation of in-situ maximum horizontal stress. Goodness of fit for the exponential regressions between vertical stress and permeability for individual coal seams varies between 0.6 and 0.84. The cleat orientation is further validated from the previous fracture analysis using FMI well log in Parbatpur area located southern part of the Jharia coalfield. The major coal seams under the study area exhibit directional permeability, with the maximum permeability, oriented parallel to the direction of face cleat orientation.

Gas parameter characteristic and region prediction in Erdaoling coal mine area

Abstract In accordance with the large amount of test data, a systematic study of the coal body structure and gas parameter characteristic of Erdaoling coal mine area is carried out. With single index method, gas content method and comprehensive index method, region predictions of coal and gas outbursts are conducted in major coal seams of the mine, which offers reference and guidance in improving the efficiency and pertinence of preventing gas outbursts.

Fluvial Sequence Stratigraphy: The Wapiti Formation, West-Central Alberta, Canada

Abstract Outcrop exposures and high-resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the Campanian–Maastrichtian Wapiti Formation (Western Interior foreland basin, Alberta, Canada). This framework defines four unconformity-bounded depositional sequences (A–D), based on sequence stratigraphic methodology, well-log patterns, and facies analysis. In ascending order, sequence A records the transition from the underlying marine facies of the Puskwaskau Formation into the Wapiti fluvial facies, and consists of strongly progradational and aggradational stacking patterns. Sequences B and C show a similar pattern of basal amalgamated channel-fill deposits that grade upwards into floodplain-dominated strata. Finally, sequence D is dominated by channelized sediments and extensive overbank facies. An aggradational stacking pattern suggests deposition under high-accommodation conditions. Maximum flooding surfaces are interpreted within fine-grained deposits in the upper portions of sequences C and D. They are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline. This study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream-controlled fluvial realm. Furthermore, the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine Wapiti Formation into depositional sequences and component systems tracts.

Dynamic development characteristics of amounts of gas and levels of pressure in the Pan-1 coal mine of Huainan

The Pan-1 coal mine located in Huainan municipality, Anhui province, is abundant in coal resources. In order to discover the natural conditions of gas in its coal seams, we inverted the burial history of these coal seams using the software of Easy%Ro method and simulated the development process of gas volumes and pressure of the major coal seams using CBM History Simulation Software. Our analysis shows that the devolution of gas volumes and levels of pressure can be divided into four stages: i.e., a biogas stage (P 1-P 3), a pyrolysis gas stage (T 1-T 2), an active gas enrichment stage (T 3-K 1) and a gas dissipating stage (K 2-present). Currently, the average amounts of gas and gas pressure in coal seams Nos. 13-1, 11-2 and 8 of the Pan-1 coal mine are 8.18 m 3/t and 2.20 MPa; 3.89 m 3/t and 2.47 MPa and 6.35 m 3/t and 2.89 MPa, respectively. This agrees very well with current mining data.