scholarly journals Analytical Model of Wellbore Stability of Fractured Coal Seam Considering the Effect of Cleat Filler and Analysis of Influencing Factors

2020 ◽  
Vol 10 (3) ◽  
pp. 1169 ◽  
Author(s):  
Xinbo Zhao ◽  
Jianjun Wang ◽  
Yue Mei
Keyword(s):  
Boundary Condition ◽  
Theoretical Model ◽  
Coal Seam ◽  
Limit Equilibrium ◽  
Wellbore Stability ◽  
Coal Bed ◽  
Affecting Factors ◽  
Stability Model ◽  
Fractured Coal ◽  
Triangular Block

Currently, coal borehole collapses frequently occur during drilling. Considering that the coal near to the wellbore is cut into blocks, and the cleat filler of the coal influences the stress distribution near the wellbore, a new theoretical solution of a near-wellbore Stress Field in coal bed wells is established. In addition, according to the limit equilibrium theory and the E.MG-C criterion, the limit sliding formula of the quadrilateral and triangular block is deduced, and the slipping direction of the blocks is further judged. Finally, the wellbore stability model of the coal seam is established. The accuracy of the theoretical model is verified through a numerical method by using the PFC software. Based upon this wellbore stability theoretical model of coal, many cleat affecting factors such as cleat spacing, cleat length, cleat angle and the cleat geometric position, are studied, and the results show that a quadrilateral block slides off more easily than a triangular block under the same boundary condition; the bigger the cleat spacing and cleat length are, the lower is the risk that blocks slide off, and increasing the cleat angle could cause blocks to slide off easily. Under the same boundary condition, whether blocks slide off or not is closely related to the well round angle.

Low Rank Coalbed Gas Preservation Conditions of Inversion Study

2013 ◽  
Vol 448-453 ◽  
pp. 3747-3750
Author(s):  
Feng Long Huo ◽  
Cheng Wu Xu
Keyword(s):  
Coal Seam ◽  
Coalbed Methane ◽  
Prediction Method ◽  
Low Rank ◽  
Coal Bed ◽  
Accumulation Factor ◽  
Affecting Factors ◽  
Coalbed Gas ◽  
Lithology Prediction ◽  
Preservation Conditions

The preservation conditions of coalbed gas reservoir are one of the most important affecting factors. Coal seam roof and floor of coalbed methane is the most direct emission barrier. That is the direct control of coal seam gas accumulation factor. A coal seam roof lithology prediction method at present more popular is the wave impedance inversion. But the results have multiple solutions. While the technology of stratmagic seismic can be a very good solution to the traditional seismic attributes application problems. It can provide precise results for coal seam roof lithology prediction, providing geological basis for evaluation and development of coal bed gas.

A Review of Technical Potential for Coal Production and Coal Degasification – A Conventional Source of Methane – In Nigeria

2003 ◽  
Vol 14 (1) ◽  
pp. 59-67
Author(s):  
Adepo Jepson Olumide ◽  
Ayodele Charles Oludare ◽  
Balogun Olufemi
Keyword(s):  
Coal Seam ◽  
Fossil Fuels ◽  
Underground Mining ◽  
Simple Calculation ◽  
Gas Content ◽  
Gelling Agent ◽  
Coal Bed ◽  
Natural State ◽  
Mining Operations ◽  
Inorganic Matter

Coal, a solid fuel in its natural state has been identified as one of the world's major fossil fuels. It is a compact, stratified mass of mummified plant debris interspersed with smaller amounts of inorganic matter buried in sedimentary rocks. The use of coal as an energy source can be dated back to the prehistoric times. Methane is associated with many if not all coal seams, and is the dreaded “fire damp” responsible for many pit explosions. Coal mines are designed to vent as much methane as possible. It is present in the pores of coal under pressure, released during mining operations and can be extracted through vertical well bores. This paper highlights the fact that pipeline- quality methane can be extracted economically from coal seems before and during underground mining operations. The stimulation method involves hydraulic fracturing of the coal seam by using water, sand and, a gelling agent in a staged and alternating sand/and no sand sequence. The purpose is to create new fractures in the coal seam(s). The cleating of the coal helps to determine the flow characteristics of the coal formation and is vital in the initial productivity of a coal-methane well. The simple calculation of gas-in-place is achieved by multiplying the gas content of the coal by net coal thickness, the density, and the aerial extent of the drainage. The method is claimed to be suitable for use in Nigeria and potential sites for coal bed methane extraction in Nigeria are identified.

scholarly journals Prediction Model for Spontaneous Combustion of Coal around Boreholes Using Bedding Gas Drainage

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Youxin Zhao ◽  
Qingjie Qi ◽  
Xinlei Jia
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Negative Pressure ◽  
Spontaneous Combustion ◽  
Orthogonal Test ◽  
Gas Drainage ◽  
Positive Linear Correlation ◽  
Drainage Hole ◽  
Spontaneous Combustion Of Coal ◽  
Fractured Coal

To accurately and reliably predict the time of spontaneous combustion of fractured coal around a borehole induced by gas drainage along the seam, this study performed an orthogonal test taking the No. 10 Coal Mine of Pingdingshan as the research object, in terms of the suction negative pressure and coal seam buried depth. COMSOL Multiphysics was used to model the orthogonal test results, and a multielement statistical analysis of four factors and their relationships with the spontaneous combustion of coal around the borehole and a single-factor analysis in line with the site conditions were performed on the modeling results through multiple regression. The results showed a nonlinear regression relationship between the sealing hole length, sealing hole depth, negative pressure, and coal seam depth and the spontaneous combustion of the coal around the gas drainage borehole; the prediction regression model is significant. Taking the field gas drainage in the No. 10 Coal Mine of Pingdingshan as an example, the relationship between the time of spontaneous combustion of gas drainage and the drainage pressure follows a power of two. When the drainage negative pressure is less than 45 kPa, the coal around the borehole is more likely to undergo spontaneous combustion with increasing pressure, and the sealing hole length has a positive linear correlation with the time of spontaneous combustion of the coal around the borehole. When the sealing hole length is 23 m, the time of spontaneous combustion of the coal around the gas drainage hole is >500 days, and the coal around the borehole does not easily undergo spontaneous combustion. When the sealing depth is 15 m, the time of spontaneous combustion of the coal around the gas drainage hole is 76 days, which is most likely to cause spontaneous combustion.

Focus Within or On Others: The Impact of Reviewers' Attentional Focus on Review Helpfulness

2021 ◽  
Author(s):  
Zhanfei Lei ◽  
Dezhi Yin ◽  
Han Zhang
Keyword(s):  
Boundary Condition ◽  
Theoretical Model ◽  
Positive Impact ◽  
Online Reviews ◽  
Attentional Focus ◽  
Controlled Experiments ◽  
Review Helpfulness ◽  
Context Specific ◽  
The Impact ◽  
Consistent Support

When reviewers write online reviews, they differ in the focus of their attention: some focus on their own experiences, whereas some direct their attention to others—prospective consumers who may read the reviews in the future. This paper explores how, why, and when reviewers’ attentional focus can influence the helpfulness evaluation of reviews beyond the impact of substantive review content. Drawing on the attentional focus and persuasion literatures, we develop a theoretical model proposing that reviewers’ attentional focus may influence consumers’ perception of review helpfulness through opposing processes, and that its overall effect is contingent on the review’s two-sidedness. Results of one archival analysis and five controlled experiments provide consistent support for our hypotheses. This work challenges the predominant view of the positive impact of other-focus (vs. self-focus), explores the interpersonal impact of a reviewer’s attentional focus on prospective consumers who are total strangers, and reveals an important, context-specific boundary condition.

Coal-bed methane geology of the No. 2 coal seam in Fengfeng Coalfield, North China

2019 ◽  
Vol 12 (16) ◽  
Author(s):  
Dawei Lv ◽  
Changyong Lu ◽  
Zhijie Wen ◽  
Hongzhu Song ◽  
Shuai Yin
Keyword(s):  
Coal Seam ◽  
North China ◽  
Coal Bed ◽  
Coal Bed Methane

STUDY ON EVOLUTION OF FRACTAL DIMENSION FOR FRACTURED COAL SEAM UNDER MULTI-FIELD COUPLING

Fractals ◽  
2020 ◽  
Vol 28 (04) ◽  
pp. 2050072 ◽  
Author(s):  
GUANNAN LIU ◽  
BOMING YU ◽  
DAYU YE ◽  
FENG GAO ◽  
JISHAN LIU
Keyword(s):  
Fractal Dimension ◽  
Coal Seam ◽  
Pore Structure ◽  
Fractal Theory ◽  
In Situ Stress ◽  
Volume Strain ◽  
Fracture Length ◽  
Field Coupling ◽  
Pore Evolution ◽  
Fractured Coal

In the process of gas extraction, fracture-pore structure significantly influences the macroscopic permeability of coal seam. However, under the multi-field coupling, the mechanism of coal seam fracture-pore evolution remains to be clarified. In this paper, considering the effect of adsorption expansion, the fractal theory for porous media coupled with the multi-field model for coal seam is considered, and a multi-field coupling mechanical model is constructed by considering the influence of fracture-pore structure. Furthermore, the evolution mechanism of fractal dimension with physical and mechanical parameters of coal seam is studied. It is found that the fractal dimension for coal seam is inversely proportional to mining time and in situ stress, proportional to elastic modulus, Langmuir volume constant and Langmuir volume strain constant, and inversely proportional to Langmuir pressure constant. Compared with other factors, Langmuir pressure constant and Langmuir volume strain constant have the significance influence on the fractal dimension for the fracture length.

Study on Well Logging Technology with Methods of Evaluating Gas Content of Coal-Bed Methane Reservoir

2014 ◽  
Vol 1003 ◽  
pp. 183-187
Author(s):  
Huai Jie Yang ◽  
He Ping Pan
Keyword(s):  
Statistical Analysis ◽  
Coal Seam ◽  
Well Logging ◽  
Langmuir Equation ◽  
Gas Content ◽  
Coal Bed ◽  
High Yield ◽  
Coal Bed Methane ◽  
Analysis Method ◽  
Statistical Analysis Method

In this study, the well logging response of CBM reservoir have been analyzed, and discussing the factors that affect the gas content of coal seam. The well logging technology has been employed in connection with log data and gas content. Take one oilfield’s well logging data for example, statistical analysis method and Langmuir equation method are selected to calculate the gas content of one coal seam, the two calculated results are basically the same, the highest value are about 26 cm3/g, is a high-yield coal seam.

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