A New Coal Sampling System for Measurement of Gas Content in Soft 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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Gas desorption index of drill cuttings affected by magmatic sills for predicting outbursts in coal seams

Arabian Journal of Geosciences ◽

10.1007/s12517-015-2133-8 ◽

2015 ◽

Vol 9 (1) ◽

Cited By ~ 8

Author(s):

Long-biao Cheng ◽

Liang Wang ◽

Yuan-ping Cheng ◽

Kan Jin ◽

Wei Zhao ◽

...

Keyword(s):

Coal Seams ◽

Drill Cuttings ◽

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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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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A new mathematical model of the relationship between gas desorption index of drill cuttings and gas content

Progress in Mine Safety Science and Engineering II ◽

10.1201/b16606-173 ◽

2014 ◽

pp. 907-910

Author(s):

K Shen ◽

H Zhou

Keyword(s):

Mathematical Model ◽

Gas Content ◽

Drill Cuttings ◽

Gas Desorption ◽

The Relationship

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A Study of the Differences in the Gas Diffusion and Migration Characteristics of Soft and Hard Coal in High Gas Coal Seams

Advances in Civil Engineering ◽

10.1155/2020/8825625 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Anying Yuan

Keyword(s):

Coal Particle ◽

Gas Diffusion ◽

Hard Coal ◽

Coal Seams ◽

Surface Areas ◽

Soft Coal ◽

Gas Desorption ◽

Major Significance ◽

Specific Surface Areas ◽

And Migration

At the present time, it is of major significance to examine the differences in the gas diffusion and migration characteristics of soft and hard coal in order to prevent and control safety hazards in high gas coal seams. In this study, the differences in the gas diffusion and migration characteristics between soft coal and hard coal were examined in detail using macrostructural, mesostructural, and microstructural research methods. The root causes of the differences in the gas diffusion and migration between soft coal and hard coal were revealed in the obtained research results. The study shows that, in terms of the macrostructures, the soft coal particle grains were flakey and with shapes resembling fingernails. Meanwhile, the hard coal particle grains were observed to be in the shapes of complete blocks. In addition, in terms of the mesostructures of the different coal types, it was found that the proportion of granular coal below the particle size limit of 6 mm in the soft coal was much higher than that of the hard coal. Also, from the aspect of the characteristics of the microstructures, the pores and fissures on the soft coal surfaces were observed to be better developed, and the BJH specific surface areas of the soft coal were more than twice those of the hard coal. That is to say, the gas diffusion and migration conditions of the soft coal were better than those of the hard coal. At the same time, the increments of the specific surface areas and volumes of the pores of soft coal were above 100 nm, which provided channels for gas diffusion and migration at rates of more than twice those of the hard coal. Therefore, the soft coal was more conducive to gas emissions. This study conducted gas desorption experiments on both soft and hard coal samples and found that the initial gas desorption speed of the soft coal was significantly higher than that of the hard coal. Since the instantaneous gas emissions of the soft coal were significantly higher than those of the hard coal, it was considered to be more likely that gas outbursts and transfinite accidents could potentially occur in the soft coal layers of a project site. This study’s results provided a foundation and basis for effective gas control measures in coal seams composed of soft coal layers, which will be of major significance to the safety of coal mining activities in the future.

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The Determination of the Methane Content of Coal Seams Based on Drill Cutting and Core Samples from Coal Mine Roadway

Energies ◽

10.3390/en15010178 ◽

2021 ◽

Vol 15 (1) ◽

pp. 178

Author(s):

Nikodem Szlązak ◽

Marek Korzec ◽

Kazimierz Piergies

Keyword(s):

Coal Mine ◽

Standard Procedure ◽

Methane Content ◽

Gas Content ◽

Hard Coal ◽

Coal Seams ◽

Drill Cuttings ◽

Mine Roadway ◽

Drill Cutting

The determination of methane content of coal seams is conducted in hard coal mines in order to assess the state of methane hazard but also to evaluate gas resources in the deposit. In the world’s mining industry, natural gas content in coal determination is usually based on direct methods. It remains the basic method in Poland as well. An important element in the determination procedure is the gas loss that occurs while collecting a sample for testing in underground conditions. In the method developed by the authors, which is a Polish standard, based on taking a sample in the form of drill cuttings, this loss was established at a level of 12%. Among researchers dealing with the methane content of coal, there are doubts related to the procedures adopted for coal sampling and the time which passes from taking a sample to enclosing it in a sealed container. Therefore, the studies were designed to evaluate the degree of degassing of the sample taken in the form of drill cuttings according to the standard procedure and in the form of the drill core from a coal mine roadway. The results show that the determinations made for the core coincide with the determinations made for the drill cutting samples, with the loss of gas taken into account.

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Characterisation of Surat Basin Walloon interburden and overlying Springbok Sandstone: a focus on methane adsorption isotherms, permeability and gas content

The APPEA Journal ◽

10.1071/aj19078 ◽

2020 ◽

Vol 60 (2) ◽

pp. 748

Author(s):

Syed Shabbar Raza ◽

Julie Pearce ◽

Pradeep Shukla ◽

Phil Hayes ◽

Victor Rudolph

Keyword(s):

Adsorption Isotherms ◽

Gas Adsorption ◽

Methane Adsorption ◽

Gas Content ◽

Coal Seams ◽

X Ray ◽

Gas Desorption ◽

Water Wells ◽

Temperature And Pressure ◽

Coal Measures

The Surat Basin in Queensland is one of the world’s premier producers of natural gas from coal seams. We investigate the potential for clay-rich Walloon Coal interburden and the overlying Springbok Sandstone to hold or produce gas. Seventeen core samples were analysed from two wells from intervals within the Walloon Upper Juandah Coal Measures interburden and the Springbok Sandstone. Samples were characterised using high-pressure methane adsorption isotherms, canister gas desorption tests, moisture contents, ash contents, carbon contents, scanning electron microscopy/energy dispersive X-ray spectrometry, X-ray quantitative clay analysis, permeability, helium pycnometry and mercury intrusion porosimetry. Methane adsorption was conducted at 30°C with up to 8 MPa pressure on dried crushed samples. The adsorption capacity of methane at 8 MPa varied from 3 cc/g (calcite-cemented) up to 25 cc/g (standard temperature and pressure equivalent) (coal). Clay-rich interburden samples adsorbed ~5–14 cc/g (dry). The measured isotherms and methane content from canister desorption tests show that appreciable volumes of gas are contained within some portions of interburden and in the overlying Springbok Sandstone. Gas within the interburden likely represents a large volumetric resource, albeit in low permeability rock that restricts direct productivity. The gas adsorption and gas content results for the Springbok Sandstone help to explain field observations of high gas content in some landholder water wells.

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