Hydrogeologic factors affecting gas content distribution in coal beds

The gas loss in sampling is the root of coalbed gas content measurement error. The pressure and particle size have a significant impact on the gas loss. Using the self-developed coal particle pneumatic pipeline transportation experimental system, this study investigated the pressure and particle size changes in the sampling pipeline. It is found that the sampling process can be divided into four stages: no flow field stage, sample outburst stage, stable conveying stage, and tail purging stage. The extreme pressure in the sampling pipeline appears at the sample outburst stage; and the pressure in the pipeline has levelled off after sharp decrease in the stable conveying stage. It is also found that the extreme pressure increases first and then decreases with the increase of particle size. The duration of outburst stage is negatively correlated with particle size, and that of stable conveying stage is positively correlated with particle size. In addition, the results show that the loss rate of 1–3 mm particles is the smallest after the test but that particles less than 1 mm increase by about two times and particles greater than 3 mm decrease by more than three times. The study also shows that the particle size distribution of coal samples is a single peak with left skew distribution, and the gas reverse circulation sampling test does not change the location of the peak but makes it higher and sharper. The single size coal sample is more likely to collide than the mixture. This study can help to advance the understanding of impact factors on gas loss during reverse circulation sampling.

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Experimental Analyses of the Major Parameters Affecting the Intensity of Outbursts of Coal and Gas

The Scientific World JOURNAL ◽

10.1155/2014/185608 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9

Author(s):

W. Nie ◽

S. J. Peng ◽

J. Xu ◽

L. R. Liu ◽

G. Wang ◽

...

Keyword(s):

Water Content ◽

Relative Intensity ◽

Gas Content ◽

Horizontal Load ◽

Vertical Load ◽

Range Analysis ◽

Factors Affecting ◽

Mining Depth ◽

Physical Experiments ◽

Relative Threshold

With an increase in mining depth and production, the intensity and frequency of outburst of coal and gas have a tendency to increase. Estimating the intensity of outbursts of coal and gas plays an important role because of its relation with the risk value. In this paper, we described the semiquantitative relations between major parameters and intensity of outburst based on physical experiments. The results showed increment of geostress simulated by horizontal load (from 1.4, 2.4, 3.2, to 3.4 MPa) or vertical load (from 2, 3, 3.6, to 4 MPa) improved the relative intensity rate (3.763–7.403% and 1.273–7.99%); the increment of porosity (from 1.57, 2.51, 3, to 3.6%) improved the relative intensity rate from 3.8 to 13.8%; the increment of gas pressure (from 0, 0.5, 0.65, 0.72, 1, to 1.5 Mpa) induced the relative intensity rate to decrease from 38.22 to 0%; the increment of water content (from 0, 2, 4, to 8%) caused the relative intensity rate to drop from 5.425 to 0.5%. Furthermore, sensitivity and range analysis evaluates coupled factors affecting the relative intensity. In addition, the distinction with initiation of outburst of coal and gas affected by these parameters is discussed by the relative threshold of gas content rate.

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Abstract: Factors Affecting Geochemical and Production Heterogeneity in Coal Beds

AAPG Bulletin ◽

10.1306/c9ebc775-1735-11d7-8645000102c1865d ◽

1999 ◽

Vol 83 (1999) ◽

Author(s):

SCOTT, ANDREW R., and H. S. NANCE

Keyword(s):

Factors Affecting ◽

Coal Beds

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Geochemical investigation of hydrocarbon generation potential of coal from Raniganj Basin, India

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-021-01281-4 ◽

2021 ◽

Vol 11 (10) ◽

pp. 3627-3636

Author(s):

D. S. Panwar ◽

Ram Chandra Chaurasia ◽

V. K. Saxena ◽

A. K. Singh ◽

Akanksha

Keyword(s):

Gas Content ◽

Coal Bed ◽

Hydrocarbon Generation ◽

Type Iii ◽

Coal Beds ◽

Petrographic Examination ◽

Raniganj Coalfield ◽

Geochemical Investigation ◽

A Minor ◽

Van Krevelen Diagram

AbstractMethane content in a coal seam is a necessary parameter for evaluating coal bed gas, and it poses an environmental risk to underground coal mining activities. Keeping in pace with comprehensive studies of coal bed gas, 12 coal samples were selected from the Sitarampur block of Raniganj Coalfield for analysis. The Petrographic examination illustrated that significant values of reactive macerals present in samples demonstrate that organic matter is dominated by the prominent source of aromatic hydrocarbons with a minor proportion of aliphatic hydrocarbon, which falls in the region of (Type III) kerogen, confirms the suitability for the potential of hydrocarbon generation. “A” factor (aliphatic/aromatic bands) and “C” factor (carbonyl/carboxyl bands) value concluded that the sample has the lowest aromaticity and the highest hydrocarbon-generating potential, which was also validated by the Van Krevelen diagram. The Van Krevelen diagram plots between the H/C and O/C ratio indicate that coal samples lie in the type III kerogen, and bituminous coal (gas prone zone) is present in the block, which is confirmed by the cross-plot between desorbed and total gas (cc/g). The in situ gas content values are high enough to produce methane from coal beds. The overall study concludes that the Sitarampur block from Raniganj Coalfield is suitable for hydrocarbon generation and extraction.

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Model of Prediction of Gas Emission based on Gas Content Uncertainty in Coal Mine using Geostatistical Simulation and Monte Carlo Method

10.21203/rs.3.rs-607234/v1 ◽

2021 ◽

Author(s):

Shokofe Rahimi ◽

Majid Ataee-pour ◽

Hasan Madani

Keyword(s):

Monte Carlo ◽

Coal Seam ◽

Ventilation System ◽

Prediction Method ◽

Simulation Method ◽

Worker Safety ◽

Gas Content ◽

Geostatistical Simulation ◽

Gas Emission ◽

Factors Affecting

Abstract It is very difficult to predict the emission of coal gas before the extraction, because it depends on various geological, geographical and operational factors. Gas content is a very important parameter for assessing gas emission in the coal seam during and after the extraction. Large amounts of gas released during the mining cause concern about adequate airflow for the ventilation and worker safety. Hence, the performance of the ventilation system is very important in an underground mine. In this paper, the gas content uncertainty in a coal seam is first investigated using the central data of 64 exploratory boreholes. After identifying the important coal seams in terms of gas emission, the variogram modeling for gas content was performed to define the distribution. Consecutive simulations were run for the random evaluation of gas content. Then, a method was proposed to predict gas emission based on the Monte Carlo random simulation method. In order to improve the reliability and precision of gas emission prediction, various factors affecting the gas emission were investigated and the main factors determining the gas emission were identified based on a sensitivity analysis on the mine data. This method produced relative and average errors of 2% and 0.57%, respectively. The results showed that the proposed model is accurate enough to determine the amount of emitted gas and ventilation. In addition, the predicted value was basically consistent with the actual value and the gas emission prediction method based on the uncertainty theory is reliable.

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Multi-factor controls on initial gas production pressure of coalbed methane wells in Changzhi-Anze block, Central-Southern of Qinshui Basin, China

Adsorption Science & Technology ◽

10.1177/0263617420904482 ◽

2020 ◽

Vol 38 (1-2) ◽

pp. 3-23 ◽

Cited By ~ 2

Author(s):

Yang Zhao ◽

Xiaodong Zhang ◽

Shuo Zhang ◽

Jiaosheng Yang ◽

Xianzhong Li ◽

...

Keyword(s):

Coalbed Methane ◽

Gas Production ◽

Gas Content ◽

Working Fluid ◽

Water Yield ◽

Burial Depth ◽

Reservoir Pressure ◽

Pressure Drops ◽

Factors Affecting ◽

Control Factors

Adsorption and desorption of coalbed methane are generally at a dynamic equilibrium state under the undisturbed coal reservoir. However, as the reservoir pressure drops to a certain value during the extraction of coalbed methane, the equilibrium state is destroyed and thus more coalbed methane desorbs and escapes from coal to wellbore. Here the corresponding bottom-hole fluid pressure is called initial gas production pressure (IGPP) in the development practice of coalbed methane wells. This paper, which has taken Changzhi-Anze block in the central-southern part of Qinshui basin as the study object, addresses the distribution characteristic and control factors of IGPP of coalbed methane wells and then explores the key factors affecting IGPP using grey correlation analysis theory. The results indicate that IGPP varies from 1.09 MPa to 6.57 MPa, showing a distribution law with high in the middle and low in the west and east of the study area, which presents a similar distribution characteristic with burial depth, thickness, coal rank, gas content, original reservoir pressure, and in-situ stress. Further, through grey correlation analysis, it concludes that the correlation degrees of control factors affecting IGPP of coalbed methane wells in the descending order are decline rate of working fluid level, water yield before gas production, reservoir pressure, coal thickness, coal rank, minimum horizontal principal stress, burial depth, and gas content. Among these factors, engineering factors, including decline rate of working fluid level and water yield before gas production, present a key controlling effect, because they can determine the smooth migration pathway directly during initial water production. And another key factor, original reservoir pressure also builds strong and positive correlation with IGPP under the interaction of other geology and reservoir factors, revealing the capability of gas desorption and the transmission of pressure drops.

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The gas content distribution of coal reservoir at the Changzhi block, south-central Qinshui Basin, North China: Influences of geologic structure and hydrogeology

Energy Exploration & Exploitation ◽

10.1177/0144598718784037 ◽

2018 ◽

Vol 37 (1) ◽

pp. 144-165 ◽

Cited By ~ 3

Author(s):

Zhigang Du ◽

Xiaodong Zhang ◽

Qiang Huang ◽

Shuo Zhang ◽

Chenlin Wang

Keyword(s):

Coalbed Methane ◽

Content Distribution ◽

Gas Content ◽

Exploration And Exploitation ◽

Geologic Structure ◽

Stagnation Region ◽

Qinshui Basin ◽

Himalayan Orogeny ◽

South Central ◽

Coal Reservoir

Coalbed methane is now large-scalely explorated and exploitated in the world. The Changzhi coalbed methane block, south-central Qinshui Basin, is a new resource target zone for coalbed methane exploration and exploitation in China. However, the gas content distribution of this block and its influential factors have not yet studied. Based on the recent coalbed methane exploration and exploitation activities, the gas content distribution of coal reservoir in this block was studied. The results show that the gas content hold by the coal reservoir is 7.0 − 21.7 m3/t, which was determined by a combining control effect from geologic structure and hydrogeology. The Changzhi coalbed methane block has experienced multiple-stages geologic structure evolution, especially a tectonic-thermal event during the middle Yanshanian Orogeny improved the coal to the current R o,max 1.9 − 2.7% and meanwhile the coalbed methane was greatly generated. Subsequently, the widespreadly developed normal fault structures during the Himalayan Orogeny accelerated the coalbed methane escape through the “gas escape windows”, particularly where the location within the distance of about 1300 m to the “gas escape window” the gas content decreases significantly. Moreover, due to the action of the later Himalayan Orogeny, the slope areas of most Yanshanian fold structures were structurally cross-cut by the Himalayan normal faults, and thus an “open” syncline folds were formed. The coal reservoir was depressurized surrounding this “open” syncline structure and consequently the hydrodynamic losing effect has resulted in a comparatively lower gas content therein. By the control of geologic structure and hydrogeology, this block can be generally, compartmentalized into three hydrodynamic systems including the western groundwater stagnation region, the middle runoff region, and the north-eastern recharge region, where the hydrodynamic sealing effect at the groundwater stagnation region has made a comparatively higher gas content for the coal reservoir, but the hydrodynamic losing effect at the recharge region and runoff region has made a comparatively lower gas content of the coal reservoir.

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