Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics
Water jet drilling (WJD) technology is a highly efficient method to extract coalbed methane from reservoirs with low permeability. It is crucial to efficiently remove the coal fragments while drilling. In this study, to disclose coal fragmentation features and size distributions under water jet impa...
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doaj-935060410e924300b98f85275710b1ae2020-11-25T00:29:48ZengMDPI AGApplied Sciences2076-34172018-10-01810198810.3390/app8101988app8101988Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal CharacteristicsSongqiang Xiao0Zhaolong Ge1Yiyu Lu2Zhe Zhou3Qian Li4Lei Wang5State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaState Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaState Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaState Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaState Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaState Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaWater jet drilling (WJD) technology is a highly efficient method to extract coalbed methane from reservoirs with low permeability. It is crucial to efficiently remove the coal fragments while drilling. In this study, to disclose coal fragmentation features and size distributions under water jet impact in drilling, the image processing method was utilized to obtain the geometric dimensions of coal fragments. The size distributions, morphologies and fractal characteristics of coal fragmentation were studied based on generalized extreme value distribution and fractal theory. The effects of the jet impact velocity and coal strength on the fragmentation features were analyzed. The results show that fine particles dominate the coal fragments in WJD for coal seams with various strengths. In experiments conducted at the Fengchun coal mine, owing to the higher coal strength of the M7 coal seam, the fragmentation degree of coal subjected to water jets during WJD is lower in the M7 coal steam than in the M8 coal seam, which results in a large dominant fragment size and small fractal dimension under the same impact energy. It was found that the higher the jet impact velocity is, the higher the quantity of fragments generated from WJD and the smaller the particle size. The NUM-based cumulative probability distribution curves of coal fragments are more intensive in the range of relatively small particle sizes and then become sparser with the increase in particle size. When the impact velocity increases, (i) the size distribution curves move toward smaller particle sizes, and the dominant fragment size decreases; (ii) the shape (major axis/minor axis) of coal fragments move toward the upper left, and the curve shape for a high impact velocity attains unity more quickly; and (iii) the fractal dimension value increases linearly. In addition, the fractal dimensions are obviously affected by the dominant fragment size; they increase with the decrease in the dominant fragment size. This study can provide a basis for further research on coal fragment transportation in WJD and parameter selection for discharging coal fragments during drilling for CBM development.http://www.mdpi.com/2076-3417/8/10/1988coalbed methane (CBM)water jetcoalsize distributionfractal theory |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Songqiang Xiao Zhaolong Ge Yiyu Lu Zhe Zhou Qian Li Lei Wang |
spellingShingle |
Songqiang Xiao Zhaolong Ge Yiyu Lu Zhe Zhou Qian Li Lei Wang Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics Applied Sciences coalbed methane (CBM) water jet coal size distribution fractal theory |
author_facet |
Songqiang Xiao Zhaolong Ge Yiyu Lu Zhe Zhou Qian Li Lei Wang |
author_sort |
Songqiang Xiao |
title |
Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics |
title_short |
Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics |
title_full |
Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics |
title_fullStr |
Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics |
title_full_unstemmed |
Investigation on Coal Fragmentation by High-Velocity Water Jet in Drilling: Size Distributions and Fractal Characteristics |
title_sort |
investigation on coal fragmentation by high-velocity water jet in drilling: size distributions and fractal characteristics |
publisher |
MDPI AG |
series |
Applied Sciences |
issn |
2076-3417 |
publishDate |
2018-10-01 |
description |
Water jet drilling (WJD) technology is a highly efficient method to extract coalbed methane from reservoirs with low permeability. It is crucial to efficiently remove the coal fragments while drilling. In this study, to disclose coal fragmentation features and size distributions under water jet impact in drilling, the image processing method was utilized to obtain the geometric dimensions of coal fragments. The size distributions, morphologies and fractal characteristics of coal fragmentation were studied based on generalized extreme value distribution and fractal theory. The effects of the jet impact velocity and coal strength on the fragmentation features were analyzed. The results show that fine particles dominate the coal fragments in WJD for coal seams with various strengths. In experiments conducted at the Fengchun coal mine, owing to the higher coal strength of the M7 coal seam, the fragmentation degree of coal subjected to water jets during WJD is lower in the M7 coal steam than in the M8 coal seam, which results in a large dominant fragment size and small fractal dimension under the same impact energy. It was found that the higher the jet impact velocity is, the higher the quantity of fragments generated from WJD and the smaller the particle size. The NUM-based cumulative probability distribution curves of coal fragments are more intensive in the range of relatively small particle sizes and then become sparser with the increase in particle size. When the impact velocity increases, (i) the size distribution curves move toward smaller particle sizes, and the dominant fragment size decreases; (ii) the shape (major axis/minor axis) of coal fragments move toward the upper left, and the curve shape for a high impact velocity attains unity more quickly; and (iii) the fractal dimension value increases linearly. In addition, the fractal dimensions are obviously affected by the dominant fragment size; they increase with the decrease in the dominant fragment size. This study can provide a basis for further research on coal fragment transportation in WJD and parameter selection for discharging coal fragments during drilling for CBM development. |
topic |
coalbed methane (CBM) water jet coal size distribution fractal theory |
url |
http://www.mdpi.com/2076-3417/8/10/1988 |
work_keys_str_mv |
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