Coalbed Methane Content Research Articles

Coalbed methane reservoir formation history and its geological control at the Shuigonghe Syncline

Coalbed methane (CBM) commercial developments have made breakthroughs in a few areas in China, including Qinshui Basin and Ordos Basin. For years, Eastern Yunnan Province and Western Guizhou Province have been the new hot spots of CBM study in China. Predecessors have discussed CBM reservoir characteristics, CBM system, and geological process evolution. Basing on previous research, we studied the formation history of the CBM reservoir by numerical simulation at the Shuigonghe Syncline in Western Guizhou. Data were obtained from geological survey and laboratory testing. According to the simulation results, the CBM reservoir formation history can be divided into five stages. In addition, a plane distributive contour map of CBM reservoir formation-related data was constructed to recognize the change in CBM content and CBM dissipation quality at different stages in the region. Each stage has its feature on CBM generation, dissipation, and accumulation speed. Geological process controlling factors, including burial history, tectonic history, geothermal history, and maturation, were analyzed. All factors acted together and formed the CBM reservoir in the Shuigonghe Syncline. Among these factors, tectonic evolution history is the most important because it determines the whole generation–preservation–dissipation process of CBM. The other factors affect the process in various ways.

Seismic studies of coal bed methane content in the west coal mining area of Qinshui Basin

The coal bed methane content (CBMC) in the west mining area of Jincheng coalfield, southeastern Qinshui Basin, is studied based on seismic data and well-logs together with laboratory measurements. The results show that the Shuey approximation has better adaptability according to the Zoeppritz equation result; the designed fold number for an ordinary seismic data is sufficient for post-stack data but insufficient for pre-stack data regarding the signal to noise ratio (SNR). Therefore a larger grid analysis was created in order to improve the SNR. The velocity field created by logging is better than that created by stack velocity in both accuracy and effectiveness. A reasonable distribution of the amplitude versus offset (AVO) attributes can be facilitated by taking the AVO response from logging as a standard for calibrating the amplitude distribution. Some AVO attributes have a close relationship with CBMC. The worst attribute is polarization magnitude, for which the correlation coefficient is 0.308; and the best attribute is the polarization product from intercept, of which the correlation coefficient is −0.8136. CBMC predicted by AVO attributes is better overall than that predicted by direct interpolation of CBMC; the validation error of the former is 14.47%, which is lower than that of the latter 23.30%. CBMC of this area ranges from 2.5m3/t to 22m3/t. Most CBMC in the syncline is over 10m3/t, but it is below 10m3/t in the anticline; on the whole, CBMC in the syncline is higher than that in anticline.

Coal Bed Methane Reservoir in the Mengjin Coalfield, Henan Province, China

Coal is a continuous unconventional gas reservoir and coal bed methane has the potential to make an important contribution to the future energy demands. The second member coal seam of Shaxi Formation in the Mengjin coalfield is one of the most important methane bearing and exploration formations. Based on industrial analysis, elemental analysis and methane content test of thirty-five coal samples from the Mengjin coalfield, together with other geological data of the past five-year exploration, the factors that controlling the coal bed methane reservoir are identified in the Mengjin coalfield. The thick-bedded No. 2 coal seam, about 6 meters, of the Shaxi formation are continuous distributed in the Mengjin coalfield. The burial depth is from 400 to 800 meters, this is suitable for coal bed methane exploit. There is a trend which an increase in the degree of coalification is correlated with rise content of methane in No. 2 coal. Coal rank has a significant effect on the content of coal bed methane. The relationships between methane content and basin hydrodynamics are also described and discussed in this paper. The deep stagnant zone contains the largest coal bed methane accumulation. Future geological exploration for coal bed methane in Mengjin coalfield should be guided by the essential factors identified in this study. The application of them could benefit to solving the discrepancy between the amount of reserves and the question of their exploitability.

Analysis of Distribution of Coalbed Methane and Geological Controlling Factors in Huanghebei Mining Area

Distribution characteristics of coalbed methane in Huanghebei mining area were studied and influence of geological factors such as faults, lithology of coal seam roof and floor, magmatic activities, burial depth and upper bedrock thickness of coal seam and hydrogeological conditions on occurrence of coalbed methane were deeply discussed in this paper. Coalbed methane content of mining area increased gradually from southeast to northwest. Coalbed methane in deep well points of mining area is dominated by methane and that in shallow parts contained higher content of nitrogen.

A study on coalbed methane gas contents estimation of the coal mine in Mongolia

This study presents both theoretical and experimental calculations for the amount of desorbed gas, lost gas, and residual gas from the coal core and gas composition analysis in order to measure the coalbed methane content of the studied coal mine in Mongolia. Three wells (1, 2, and 3) were studied, and the results from well 3 were analyzed. The amount of desorbed gas was measured to be 6.740 scf/ton in sample 7. The amount of lost gas was calculated using the direct method and the maximum amount calculated from sample 1 was 0.986 scf/ton. After crushing the sample to < 60 mesh and measuring four samples, the average crushing rate was approximately 71% and no residual gas was detected. Gas composition analysis showed that although methane gas was detected in almost all samples, the amount was only 1.17% in average, whereas nitrogen was detected with an average of 85.29% and with a small amount of carbon dioxide.

Characteristics of Coalbed Methane Reservoirs in Faer Coalfield, Western Guizhou

Based on analysis of the geological background and gas content data in Faer coalfield, we discuss the occurrence characteristics of coalbed methane (CBM) and its distribution along the stratigraphic sequence and in coal seams. We analyze the methane adsorption isotherm experiments, reservoir deformations and mercury intrusion porosimetry (MIP), and further discuss the reservoir physical properties. The results show that gas content and gas content gradient of CBM fluctuate with stratigraphic sequence that is mainly caused by the difference in absorption capacity of each coal seam and distributions of CBM reservoir pressure systems. The relatively low gas content gradients of those coal seams buried below 500 m depth result from the dissipation of CBM into the surrounding rocks of thin and unstable Nos. 28 to 34 coal seams and the lateral migration of CBM along the strata in high-elevation area. The Yangmeishu syncline and topography are the main controlling factors that affect the current distribution pattern of CBM content, which is higher in the north than in the south and has a northeastern trend. The theoretical gas saturation is generally lower than 60%, combined with well-developed brittle fractures and macropores, formed by structural deformation. The exploration prospects for CBM in Faer coalfield is good.

Geochemical characteristics and identification of thermogenic CBM generated during the low and middle coalification stages

Six woody peat samples were heated to 150, 250, 300, 350, 370, and 400°C to determine their geochemical characteristics and identify whether the coal bed methane (CBM) was thermogenic or secondary biogenic. The experiments were conducted in a closed pyrolysis system, from which the generated pyrolysis gas was collected. The composition of the gas and its carbon and hydrogen isotope concentrations were also determined. The results indicate that methane and carbon dioxide were the main hydrocarbon and non-hydrocarbon gases generated from the samples. The carbon isotopic compositions of the generated methane, ethane, and propane became initially lighter and then heavier with increasing experimental temperature; conversely, the hydrogen isotopic composition of the generated methane and the carbon isotopic composition of the generated carbon dioxide became gradually heavier. Therefore, a strong positive correlation exists between the aforementioned parameters. In addition, relationships have been established between carbon and hydrogen isotopic contents and Ro values, and a model for the identification of the maturity and relative content of thermogenic CBM is proposed. Then, the model was applied in a case study to evaluate the gas source of CBM in the Luling CBM field in Anhui Province, China.

Estimation of correction coefficients for measured coal bed methane contents

Improving the accuracy and precision of coal bed methane (CBM) estimates requires correction of older data from older coal exploration surveys to newer standards. Three methods, the depth gradient method, the contour aerial weight method, and the well-point aerial weight method, were used to estimate the correction coefficient required to predict CBM gas content from coal exploration data. The data from the Nos. 3 and 15 coal seams provided the coal exploration data while the CBM exploration stages within the X1 well block located in the southern part of the Qinshui Basin provided the data obtained using newer standards. The results show the correction coefficients obtained from the two aerial weight methods are similar in value but lower than the one obtained from the depth gradient method. The three methods provide similar results for the Nos. 3 and 15 seams in that the correction factor is lower for the former seam. The results from the depth gradient method taken together with the coal seam burial depth and the coal rank suggest that variations in the correction factor increase linearly along with coal seam burial depth and coal rank. The correlation obtained can be applied to exploration and the evaluation of coal bed gas resources located in coalfields.

Coal bed methane drainage with long directional boreholes

It has been stated that high-output coal mine degassing must take into account the lower limit of coal bed methane content in order to determine the need of preliminary methane drainage through degassing boreholes and the duration of the methane emission rate reduction.

Application of seismic multi-attribute fusion method based on D-S evidence theory in prediction of CBM-enriched area

D-S evidence theory provides a good approach to fuse uncertain information. In this article, we introduce seismic multi-attribute fusion based on D-S evidence theory to predict the coalbed methane (CBM) concentrated areas. First, we choose seismic attributes that are most sensitive to CBM content changes with the guidance of CBM content measured at well sites. Then the selected seismic attributes are fused using D-S evidence theory and the fusion results are used to predict CBM-enriched area. The application shows that the predicted CBM content and the measured values are basically consistent. The results indicate that using D-S evidence theory in seismic multi-attribute fusion to predict CBM-enriched areas is feasible.

Vertical Diversity of Coalbed Methane Content and its Geological Controls in the Qingshan Syncline, Western Guizhou Province, China

The distribution of methane content in the coalbed is complex in the Qinshan Syncline of western Guizhou Province. Analyses of factors controlling on the distribution of gas content are made in this paper. Coal ranks and geo-structure in the region showed strong controls on the gas distribution. Coals with higher degree of metamorphism or located in syncline most likely have higher gas content. With the concept of coalbed methane content unite thickness (CBMCUT), those factors such as coal seam buried depth and coal structure present positive relations with gas content. Results indicated that the variation of CBMCUT is not fixed in different research areas or in different coal structures. Namely, the variation follows “v-shaped” correlation with the increasing coal buried depth in the region of Qinshan Syncline. However, the trend is smooth for the coals in the Panzhuang mining area. Usually, the critical value for primary-texture coal and mylonitized is different based on the analysis of the relationship between coal structure and CBMCUT in those two areas described above. The value is commonly higher in mylonitized coal and lower in those mainly primary-texture and fragmented coals.

Approximate relationship of coal bed methane and magnetic characteristics of rock via magnetic susceptibility logging

In coal bed methane (CBM) exploration, how to improve the accuracy for locating and evaluating the CBM deposits is still a problem due to the rarity of occurrence of CBM. Combined with the distribution of the CBM content in the Huainan coalfield, the approximate relationship between the occurrence of CBM and the magnetic properties of the coal bed and adjacent mudstone have been widely discussed by magnetic logging. Experimental results show that magnetic susceptibility of the coal bed and adjacent mudstone would clearly increase with the CBM content in a coal bed. According to the results of the experiment, the prediction of the CBM content has been accomplished for different coal beds, and the results are consistent with the distribution of the CBM content throughout the whole coalfield. Preliminary data analysis reveals that there is indeed a correlation between the changes of magnetic rock characteristics and the occurrence of the CBM, and this finding may shed some light on the evaluation of CBM.

Study on Characteristics of Favorable Reservoirs for High-Rank Coals, North China

The Late Paleozoic coalbed methane (CBM) reservoirs for high-rank coal in North China have the characteristic of high CBM content. But due to the differences between CBM reservoirs in several aspects such as physical property and gas accumulation condition, CBM was developed for commercialization only in the south of Qinshui Basin. Coal samples were systematically collected from Qinshui Basin, Jiaozuo Coalfield, Yongxia Coalfield and Xinggong Coalfield, and then tested on coal petrology, porosity-permeability characteristics and isothermal adsorption, etc. Based on the analyses of these test data, this paper discusses the forming conditions and mechanisms of the favorable CBM reservoirs for high-rank coals. These factors like the coal petrology characteristics, reservoir physical property and gas accumulation conditions were detailedly discussed. The difference characteristics of the favorable CBM reservoirs in North China were comprehensively evaluated as conclusions. The result shows that in comparison with other high-rank coal areas, coals in Qinshui Basin have undergone slight tectonic destruction, which induces the widespread development of primary- and cataclastic-structured coals, developing better microfractures. Moreover, the Qinshui coals have not only the well-developed exogenetic fractures, but also well sedimentary and tectonic conditions at the key accumulation period of CBM. These factors resulted in the formatting of better CBM reservoir in Qinshui Basin when comparing to other high coal rank areas in North China.

Geological controls on prediction of coalbed methane of No. 3 coal seam in Southern Qinshui Basin, North China

article i nfo In order to better understand the geological controls on coalbed methane (CBM) in Southern Qinshui basin (SQB), North China, geological surveys and laboratory experiments, including coal petrology analysis, proximate analysis and methane adsorption/desorption, were conducted. Results show that the coals from the SQB contain 0.59-3.54% moisture, 3.5-15.54% ash yield, 73.62-88.92% fixed carbon and 2.14-4.04% hydrogen, with C/H ratios in the range of 19.96-36.25. The vitrinite reflectance (Ro,m) ranges from 1.95 to 3.49%. The coals are composed of 18.5-97.4% vitrinite and 2.4-81.4% inertinite. The geologic structures, coal-bearing strata and coal depositional environment were studied by both field geological research and laboratory tests. A positive relationship is found between CBM content and basin hydrodynamics, in which CBM easily concentrates in the groundwater stagnant zone because of the water pressure. Furthermore, integrated geographical information system (GIS) and analytical hierarchy fuzzy prediction method (AHP) were used to evaluate the CBM resources in the SQB. The results show that the amount of CBM associated with the No. 3 coal seam in the SQB is 3.62×10 11 m 3 .T he CBM resource concentration (gas-in-place per square kilometer) in the SQB is in the range of (0.72- 2.88)×10 8 m 3 /km 2 , with an average of 1.21×10 8

Factors influencing the methane content of coal beds of the Czech part of the Upper Silesian Coal Basin, Czech Republic

The article is one of the results of long-term efforts of the team of authors to evaluate the reserves of raw materials for energy purposes in the Czech part of the Upper Silesian Coal Basin and to assess possibilities of their realistic utilisation. A relatively large program of exploratory drilling to determine the content of coal bed methane (CBM) in the Czech part of the Upper Silesian Coal Basin (upper Mississippian to lower Pennsylvanian) was undertaken in the 1990s. The possibility of extracting CBM from coal beds undisturbed by mining was also investigated. Numerous analyses of the gas contents of coal beds by the Borowski and USBM methods and other parameters that affect the sorption of CBM were made. The relationships between these factors are described and discussed in the present paper. Factors governing the occurrence and spatial distribution of CBM in the Czech part of the Upper Silesian Coal Basin are divided into those of primary nature (the degree of coalification, the chemical and physical properties of the coal, its maceral composition and pore structure) and those of secondary nature (gas migration, erosion, tectonic setting). The ten most important factors are defined. However, in the area of all the Czech part of the Upper Silesian Coal Basin, the degree of their importance, which varies in individual boreholes, cannot be unambiguously determined. Future geological exploration for CBM in coal basins should be guided by the essential factors identified in this study. The application of them could contribute to solving a long-term known discrepancy between the amount of reserves and the question of their exploitability.

Evolution of methane sorption capacity of coal seams as a function of burial history — a case study from the Campine Basin, NE Belgium

Based on extensive data sets of high-pressure sorption isotherms and canister desorption data from two Central European coal basins (Campine and Ruhr basins) a computational scheme has been developed to calculate the maximum coal bed methane (CBM) sorption capacity of coal seams as a function of pressure, temperature and coal rank. In addition, the effects of in situ moisture content and maceral composition have been tentatively implemented. Using this algorithm it is possible to explicitly take into account variations in sorption capacity of the coal seams in sedimentary basins over geologic time as a function of burial history and thermal evolution. The procedure has been applied to model the evolution and the present-day coal bed methane content of the Campine Basin, NE Belgium. It is demonstrated how the present-day gas content of the Campine Basin is controlled by the burial history of the coal layers throughout geologic time. The maximum gas sorption capacity typically occurs at a depth range between 500 and 1000 m. During periods of uplift and erosion (∼250 and 90 Ma before present) the uppermost coal layers have lost methane due to a reduction of gas storage capacity while their storage capacity has increased during periods of burial (∼300 and 180 Ma ago, and present). Additionally, the present-day gas content is controlled by the gas generation history. Coal layers, which have lost storage capacity during geologic time, will stay undersaturated if not replenished by late-stage (e.g. microbial) gas. The gas content profile of test well KB206 in the NE Campine Basin, established from canister desorption tests, can be reproduced by assuming that undersaturation of the coals is due to erosion and re-burial, and that no significant gas generation (e.g. microbial gas) has taken place after the time of maximal burial. Isotopic data (δD∼178‰, δ13C∼59‰) indicate the presence of a small portion of microbial gas. The absolute gas contents in this well are lower than the calculated maximum present-day sorption capacity. This may be due to an underestimation of the effect of water content on sorption capacity or result from degassing via nearby faults, enforced by fluid circulation.

The upper Paleozoic coalbed methane system in the Qinshui basin, China

The coalbed methane resource is very abundant in Qinshui basin (3.28 1012 m3; 114 tcf). The investigation on the upper Paleozoic coalbed methane system is a guide to the exploration and development of coalbed methane. The upper Paleozoic coalbed methane system in the Qinshui basin is sealed by a low-permeability roof and floor strata comprising mudstone, siltstone, and bauxite of the Carboniferous Benxi Formation and the Permian Shanxi and Xiashihezi formations. The overburden is the Lower Permian Xiashihezi Formation and the Upper Permian, Triassic, and Middle Jurassic clastic deposits. The source and reservoir rocks are the Carboniferous–Permian coal seams. The hydrocarbon generation of the source rocks reached its first peak in the Late Triassic. The highest maturity was about Ro = 1.2% under a normal paleogeothermal gradient (2–3C/100 m; 1.1–1.7F/100 ft). A tectonic thermal event during the Jurassic and Cretaceous Yanshanian orogeny enhanced the coal maturity and caused a second peak of hydrocarbon generation. Varying igneous intrusions caused the coal maturity to be higher in the southern, northern, and eastern parts of the Qinshui basin instead of the central and western parts. The highest maturity was greater than Ro = 4% in the Jincheng area. The migrated thermogenetic coalbed methane accumulated in the reservoirs in which abnormally high reservoir pressure exists locally under the hydrodynamic drive. Because of the different hydrodynamic background and sealing condition, the distribution of coalbed methane content is inhomogeneous. The reservoir is undersaturated with gas in most areas. Based on the coalbed methane system investigation, we assessed the coalbed methane producibility in different parts of the Qinshui basin, and the major producibility area is in the southern part of the basin.

Coal and gas outbursts in footwalls of reverse faults

Instantaneous outbursts in coal mines involve catastrophic and forceful expulsion of coal and large quantities of gas, creating a major mining hazard. Other researchers have studied relationships between coal outbursts and many geological factors, such as coal seam thickness, coal rank, coal seam age, current burial depth, and distance to plutons, with different conclusions for different coal fields and regions because of the complexity of the causative mechanisms. Coal outbursts nearly always have a close relationship to geologic structures; the present research was designed to determine the location and characteristics of specific danger zones associated with reverse faults. Four coal mines in the Pingdingshan coal field, Henan Province, China were investigated in detail. Coal and gas outbursts associated with reverse faults nearly always occurred in the footwalls. Additional data were also used from two mines in Sichuan Province and one in Henan Province. The first important observation of the geological structural phenomena was that coal seams in the footwalls of the reverse faults underwent greater tectonic deformation than those in the hanging walls. Coal lost its banded character and was physically transformed into microstructurally altered forms categorized as cataclastic coal, granular coal and mylonitic coal. Outbursts always occurred within a zone of this tectonically altered coal surrounding the fault. Second, the zone of tectonic alteration in the footwalls extended farther from the fault than that in the hanging walls. Third, where present in association with reverse faults, zones of higher coalbed methane content nearly always occurred in the footwalls. These three factors are the principal controls on coal and gas outbursts associated with reverse faults. Through their application, coal safety experts can narrow the predicted outburst danger zone to a smaller area.

Resources Conditions of Coalbed Methane Districts in China

Abstract The China National Administration of Coal Geology accomplished an assessment of coalbed methane resources of China in 1988. The total amount of coalbed methane resources in China is 14336.944 billion m3, occurring in recoverable coal seams and beneath weathering zones, with coalbed methane content equal to or higher than 4 m3 per ton and buried depths smaller than 2000 m, among which there are 967.51 billion m3 of predicted reserves and 13369.434 billion m3 of future reserves. The resources in coal reservoirs with methane content of more than 8 m3 per ton are 12444.087 billion m3, and those with methane content between 4 to 8 m3 per ton are 1892.856 billion m3. There are 35 districts in which the resources abundance is higher than 150 million m3/km2, 49 districts with the abundance between 50 million and 150 million m3/km2, and 31 districts with the abundance less than 50 million m3/km2. There is 9256.078 billion m3 of methane occurring in coal seams with buried depths less than 1500 m, and 5080.866 billion m3 in coal seams with buried depths between 1500 and 2000 m. There are 28 large‐scale districts in which coalbed methane resources are more than 100 billions m3, 28 medium‐scale districts with coalbed methane resources between 20 billion and 100 billion m3 and 59 small‐scale districts with resources amount less than 20 billion m3. The Jincheng area is one of the most favourable districts for coalbed methane resources in China.

Geology and Methane Content of the Book Cliffs Coal Field

The Book Cliffs coal field contains as many as 14 coal zones, all within the Upper Cretaceous Blackhawk Formation. The Blackhawk Formation consists of deltaic and nearshore sediments deposited in a fluctuating, but overall regressive, setting along the western margin of a shallow seaway. Laramide deformation tilted strata in the Book Cliffs gently to the north toward the axis of the Uinta basin. One hundred and twenty-three drill-hole coal samples were collected and analyzed from the ten thickest and most continuous coal zones in the Book Cliffs field. Residual, desorbed, and total gas content were determined using the Bureau of Mines direct method. The resulting coal-bed methane content maps show areas of economic potential where 90% of the gas could be recovered. The 90% methane recovery level corresponds to a total methane content of 154 ft[sup 3]/ton. These results show that (1) methane contents increase with increasing depth, (2) methane content locally can exceed 3.5 billion ft[sup 3]/mi[sup 2] for a 10-ft-thick coal bed, and (3) methane gas resource of 4.4-5.0 tcf are conservatively estimated for the Book Cliffs coal field to a depth of 9000 ft.