Gas desorption index of drill cuttings affected by magmatic sills for predicting outbursts in coal seams

Core samples or drill cuttings from boreholes drilled in coal seams are used in direct measurements of gas content in coal. In soft coal seams, core samples are difficult or sometimes impossible to obtain due to poor borehole stability such as large borehole deformation and borehole collapse, drill cuttings have to be taken and used. Due to their faster initial gas desorption rates, drill cuttings need to be taken rapidly and accurately at given positions during borehole drilling to ensure the accuracy of gas content measurements. To meet these sampling requirements of drill cuttings, a new sampling-while-drilling (SWD) system has been developed. The SWD system is based on a special design of double-tubing drill rods and a reversed circulation of pressurized air. A field test of the SWD system was carried out with satisfactory results. This paper presents the principle and results of the field test of the SWD system.

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Nitrogen Injection To Flush Coal Seam Gas Out Of Coal: An Experimental Study

Archives of Mining Sciences ◽

10.1515/amsc-2015-0067 ◽

2015 ◽

Vol 60 (4) ◽

pp. 1013-1028 ◽

Cited By ~ 7

Author(s):

Lei Zhang ◽

Naj Aziz ◽

Ting Ren ◽

Jan Nemcik ◽

Shihao Tu

Keyword(s):

Coal Seam ◽

Clean Energy ◽

Gas Content ◽

Coal Seams ◽

Coal Seam Gas ◽

Gas Recovery ◽

Nitrogen Injection ◽

Gas Desorption ◽

Effective Role ◽

Study Laboratory

Abstract Several mines operating in the Bulli seam of the Sydney Basin in NSW, Australia are experiencing difficulties in reducing gas content within the available drainage lead time in various sections of the coal deposit. Increased density of drainage boreholes has proven to be ineffective, particularly in sections of the coal seam rich in CO2. Plus with the increasing worldwide concern on green house gas reduction and clean energy utilisation, significant attention is paid to develop a more practical and economical method of enhancing the gas recovery from coal seams. A technology based on N2 injection was proposed to flush the Coal Seam Gas (CSG) out of coal and enhance the gas drainage process. In this study, laboratory tests on CO2 and CH4 gas recovery from coal by N2 injection are described and results show that N2 flushing has a significant impact on the CO2 and CH4 desorption and removal from coal. During the flushing stage, it was found that N2 flushing plays a more effective role in reducing adsorbed CH4 than CO2. Comparatively, during the desorption stage, the study shows gas desorption after N2 flushing plays a more effective role in reducing adsorbed CO2 than CH4.

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Pulverization characteristics of coal affected by magmatic intrusion and analysis of the abnormal gas desorption index on drill cuttings

Adsorption Science & Technology ◽

10.1177/0263617417724276 ◽

2017 ◽

Vol 36 (1-2) ◽

pp. 805-829 ◽

Cited By ~ 4

Author(s):

Er-Tao Chen ◽

Liang Wang ◽

Yuan-Ping Cheng ◽

Hai-Jun Guo ◽

Cong-Meng Hao ◽

...

Keyword(s):

Particle Size ◽

Coal Seam ◽

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Total Pore Volume ◽

Tectonic Stress ◽

Drill Cuttings ◽

Magmatic Intrusion ◽

Gas Desorption

The gas desorption index of drill cuttings is a basic index that measures the initial desorption capacities of coal seams and predicts coal seam gas outbursts. Following a long period of gas drainage in the No.7 coal seam of the No.86 mining area in the Haizi coal mine, the gas desorption index of drill cuttings was still found to be much higher than the threshold value for outburst risks. This abnormal phenomenon led to the present study of the rational selection of test methods and objects in this context. In this study, particle size distribution, pore structure and gas desorption characteristics of coal samples in anomalous areas were analyzed. We found that desorption characteristics are related to particle size and particle size varies in relation to tectonic stress and magmatic intrusions. It appears that the anomalous readings are related to particle size of the coal, resulting from tectonic/magmatic pulverization. Furthermore, measured particle size of drill cuttings is not actually reflective of coal particle size – larger particles may be comprised of multiple smaller particles. The results show that coal samples with particle size <1 mm accounts for 76.3% of total samples and coal samples with particle size >1 mm only accounts for 23.7% of total samples. The porosity and total pore volume increase as the particle size decreases. The specific surface area increases with decreasing pore diameter. Transitional pores and micropores increase the specific surface area of the coal sample considerably. The desorption capacity increases with decreasing particle size. The additional tectonic stress caused by magmatic intrusion has a crushing effect, and 1–3 mm particles used in test were composed of a large amount of smaller particles, eventually resulting in abnormal gas desorption index phenomena. Therefore, we proposed an improved method for measuring the gas desorption index of pulverized coal.

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Differentiation of Carbon Isotope Composition and Stratabound Mechanism of Gas Desorption in Shallow-Buried Low-Rank Multiple Coal Seams: Case Study of Well DE-A, Northeast Inner Mongolia

Natural Resources Research ◽

10.1007/s11053-020-09781-6 ◽

2020 ◽

Author(s):

Geng Li ◽

Yong Qin ◽

Zhongling Yao ◽

Wutao Hu

Keyword(s):

Carbon Isotope ◽

Inner Mongolia ◽

Isotope Composition ◽

Carbon Isotope Composition ◽

Low Rank ◽

Coal Seams ◽

Gas Desorption

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The Relationship between Mining-Induced Stress and Coal Gas under an Optimized Support Scheme: A Case Study in the Guanyinshan Coal Mine, China

Geofluids ◽

10.1155/2021/2421398 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Tianjun Zhang ◽

Jiaokun Wu ◽

Yong Chen ◽

Hong Ding ◽

Hongyu Ma ◽

...

Keyword(s):

Gas Pressure ◽

Gas Content ◽

Rock Support ◽

Drill Cuttings ◽

Coal Gas ◽

Gas Desorption ◽

Induced Stress ◽

Coal And Gas Outbursts ◽

Residual Gas ◽

The Relationship

Stress is one of the main factors influencing coal and gas outbursts. The apparent effects of the crustal stress, the structural stress, and the mining-induced stress increase as the depth of mining increases. At present, there have been few studies of the relationship between the comprehensive analyses of the crustal stress, mining-induced stress, and coal gas. The in situ measurement of the relationship between stress-related behaviors and coal gas under the influence of mining was conducted through experimental analysis of surrounding rock support and coal and gas outburst control and optimization of surrounding rock support materials and system construction. The results showed that the mining-induced stress first increased to a peak value, then gradually decreased, and tended to stabilize as the footage progresses. Stress appears at 96 m ahead due to mining; after 57 m of advancing, there is a large increase until it passes through this area. The stress in front of the working face increases linearly, and the increase range is obviously larger than that of the coal body in a certain range on both sides. The support anchoring force gradually decreased and tended to be stable after rapidly increasing to a maximum value. The deep displacement of the roof increased linearly and tended to be stable after reaching an accumulated displacement which can reach 16-28 mm. The residual gas pressure in front of mining operations decreased rapidly, and beyond 15 m on each side of the roadway, it decreased significantly. The residual gas pressure and gas content were consistent with the gas desorption index of drill cuttings due to the influences of gas predrainage and mining. The stress along the direction of the roadway and the residual gas content, the residual gas pressure, and the gas desorption index of drill cuttings conform to the logarithmic functional relationship. The research results provide a basis for the comprehensive prevention and control of coal and gas outbursts from multiple angles considering stress, coal, and gas.

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Low-index Catastrophe Model of Deep Gas-bearing Coal Seams

10.21203/rs.3.rs-38979/v1 ◽

2020 ◽

Author(s):

Tie Li ◽

Xiyu Pi

Keyword(s):

High Stress ◽

Site Investigation ◽

Gas Migration ◽

Coal Seams ◽

Gas Emission ◽

Gas Channel ◽

Gas Desorption ◽

Mining Face ◽

Ultimate Equilibrium ◽

Gas Bearing

Abstract Coal and gas outburst always occur as some parameters reach its threshold in the mining process of gas-bearing coal seams. However, low-index catastrophes may happen in the deep mining although the parameters do not exceed its threshold values. This phenomenon has become a challenge for our traditional cognitions. In this paper, the mechanism of low-index catastrophes of high-stress area in the deep gas-bearing seams was investigated by the following methods including literature reviewing, on-site investigation, case analysis, physical experiments and theoretical analysis. The results indicate that there were not only primary state fissures but also many secondary fissures are formed after taking outburst eliminating measures, which is beneficial for improving the desorption performance of methane. A “three-zone” theory of gas migration in Coal Seams is given, coal seam in the front of coal mining face can be divided into three zones: the gas emission zone, the gas channel compaction zone, and disturbance gas desorption zone before reaching ultimate equilibrium, corresponding to coal and gas ejection zone, gas migration zone and gas launching zone after surpassing the limits. Importantly, the stress dike is redefined, and a new concept is proposed that the low-index catastrophe of gas bearing seams is caused by avalanche instability of the stress dikes, meanwhile its three modes are given by over static-load stress dike avalanche caused by hanging arch overlength, stress dike avalanche under roof breakage impact, and stress dike avalanche under floor breakage impact. In deep stress area, stress dike avalanche caused by dynamic-static loading could lead to low-index catastrophes of gas bearing seams. The insufficient residual gas energy could cause unusual gas emission. On the other hand, the sufficient gas energy may lead to coal and gas outbursts.

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Coal characterization and coalbed methane potential of the Chico-Lomã Coalfield, Paraná Basin, Brazil – Results from exploration borehole CBM001-CL-RS

Energy Exploration & Exploitation ◽

10.1177/0144598720931167 ◽

2020 ◽

Vol 38 (5) ◽

pp. 1589-1630

Author(s):

W Kalkreuth ◽

J Levandowski ◽

P Weniger ◽

B Krooss ◽

R Prissang ◽

...

Keyword(s):

Coalbed Methane ◽

Proximate Analysis ◽

Methane Adsorption ◽

Coal Seams ◽

Gas Desorption ◽

Coal Characterization ◽

Thermal Origin ◽

Methane Potential ◽

Gas Volume ◽

Hydrocarbon Distribution

The aim of this study was to determine the coal characteristics in the Chico-Lomã coalfield, Brazil and to evaluate the potential of natural gas associated with the coal seams (CBM), by carrying out a test well (CBM001-CL-RS) for collecting coal samples, followed by gas desorption measurements, and petrographical and chemical analyses of the coals and their methane adsorption capacities. The gas collected was analyzed for gas composition, stable carbon and hydrogen isotopes. The results indicate a cumulative coal thickness of 11.46 m in well CBM001-CL-RS, associated with an igneous intrusion of 10 m thickness. In the contact zone with the intrusion, the organic matter is severely altered with partial transformation of the coal to natural coke at distances less than 2 m from the intrusion. The ash content, based on proximate analysis, shows a variation from 29.1 to 82.8 wt.%. The sulphur content ranges from 0.43 to 3.89 wt.% and shows higher values in samples from the top of the Rio Bonito Formation. The gas desorption measurements range from 0.05 to 0.74 cm3/g, with methane being the predominant gas (>90%). A thermal origin of the gas is suggested by C and H isotopes and the C1 (methane) to C3 (propane) hydrocarbon distribution. The methane adsorption capacity of the samples varies from 2.50 to 6.50 cm3/g. Changes in microporosity related to thermal alteration may have a significant impact on the gas-holding capacity of samples located near the contact to the intrusion. For the study area, a 3D geological model was generated to estimate the volume of coal in the coalfield, followed by assessment of the gas volume associated with the coal. Based on the 3D model, a preliminary appraisal indicates resources of 7.2 billion tons of coal for the Chico-Lomã coalfield, associated with 2.7 billion m3 of gas.

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A Mechanical Model of Gas Drainage Borehole Clogging under Confining Pressure and Its Application

Energies ◽

10.3390/en11102817 ◽

2018 ◽

Vol 11 (10) ◽

pp. 2817 ◽

Cited By ~ 1

Author(s):

Yonglong Wang ◽

Zaijiang Yu ◽

Zhenfeng Wang

Keyword(s):

Mechanical Model ◽

Significant Risk ◽

Confining Pressure ◽

Dominant Factor ◽

Coal Seams ◽

Drilling Depth ◽

Drill Cuttings ◽

Soft Coal ◽

High Confining Pressure ◽

Drainage Borehole

Drilling in a coal seam that has gas and coal outburst activities is closely related to the discharge of drill cuttings into a borehole. Due to the low effectiveness of slagging, there is a risk that the drilling equipment will be lost if the borehole contains too many drill cuttings, especially when drilling in soft coal seams that suffer from borehole deformation and instability problems. In order to investigate the mechanisms underlying clogged boreholes, a mechanical model is established that considers the confining pressure pi that surrounds a borehole. The characteristics of clogged boreholes, which are affected by parameters such as the clogging segment’s length L, the drilling angle θ and confining pressure pi, were analyzed. The results show that the dredging pressure has nearly exponential growth as the clogging segment’s length L increases and the gravity of the clogging segment reduces the demand for dredging pressure, especially in upward drilling. In downward drilling, the blowing-through pressure increases as the absolute value of the drilling angle increases and will reach a maximum value when the drilling angle θD is in the range of −π/2~0. At the same time, the borehole’s confining pressure pi is the dominant factor in borehole clogging. Meanwhile, boreholes with a high confining pressure pi, especially in soft coal seams and coal seams with a coal outburst, constitute a significant risk. Finally, an actual drilling field construction was evaluated and optimized by applying the clogging segment mechanical model. The results show that the drilling depth was improved by 18.5% on average, and the drilling efficiency was improved by 39.7%, in comparison to drilling activities without optimization.

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