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Applied Sciences
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Advances in Unconventional Natural Gas: Exploration and Development
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Advances in Unconventional Natural Gas: Exploration and Development

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: 30 August 2024 | Viewed by 2747

Special Issue Editors

Dr. Run Chen

E-Mail Website
Guest Editor
1. Jiangsu Key Laboratory of Coal-Based Greenhouse Gas Control and Utilization, Xuzhou 221008, China
2. Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China
Interests: unconventional natural gas; CCUS; carbon neutrality; underground coal gasification, CO2 mineralization
Special Issues, Collections and Topics in MDPI journals
Dr. Zheng Zhang

E-Mail Website
Guest Editor
1. Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221008, China
2. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
Interests: hydrogeochemistry; mine water environment; coal geology; hydrology; coal geochemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Unconventional natural gas mainly involves shale gas, coalbed methane, tight gas, natural gas hydrate, etc. Globally, unconventional natural gas resources are abundant. Unconventional natural gas is the most realistic replacement resource for conventional natural gas and plays an important role in the world energy pattern. Currently, the development and utilization technologies are becoming increasingly advanced, and countries around the world attach great importance to the development and utilization of unconventional natural gas resources.

This Special Issue on “Advances in Unconventional Natural Gas: Exploration and Development” aims to cover the recent advances in the exploration and development of unconventional natural gas. Topics include, but are not limited to, the methods and/or applications in the following areas:

  • Key technologies for the exploration and development of unconventional natural gas;
  • Deep unconventional natural gas resources;
  • Numerical simulation techniques for unconventional natural gas reservoirs;
  • Recovery-enhancing techniques for unconventional natural gas;
  • Favorable area selection for unconventional natural gas.

Dr. Run Chen
Dr. Zheng Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • unconventional natural gas
  • recovery-enhancing techniques
  • deep unconventional natural gas
  • numerical simulation
  • favorable area selection
  • reservoir evaluation

Published Papers (5 papers)

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Research

11 pages, 5279 KiB  
Article
Physical Simulation Experiment for Visualizing Pulverized Coal Transport in Propped Fractures
by Yufang Liu, Longbin Yang, Jinxing Song, Junke Shi and Qian Wang
Appl. Sci. 2024, 14(14), 6114; https://doi.org/10.3390/app14146114 - 13 Jul 2024
Viewed by 463
Abstract
The issue of pulverized coal in coalbed methane wells during the discharge and mining process spans all stages, and it is a key factor constraining the continuous and stable discharge and production capacity of coalbed methane. Among these stages, the single-phase water flow [...] Read more.
The issue of pulverized coal in coalbed methane wells during the discharge and mining process spans all stages, and it is a key factor constraining the continuous and stable discharge and production capacity of coalbed methane. Among these stages, the single-phase water flow stage features a high incidence of pulverized coal. Consequently, this paper presents a physical simulation experiment within the propped fractures during the single-phase water flow stage. The results of this study reveal the following: (1) Within the propped fracture channel, when pulverized coal is deposited along the flow line without causing blockage, the front end of the deposition exhibits a strip-like dispersion, evolving into “block deposition”, “flame-like accumulation”, “linear accumulation”, and “dispersed point-like accumulation”. (2) Agglomerated fracturing fluid can effectively mitigate the permeability damage caused by pulverized coal to the propped fractures. Both the driving speed and particle size of pulverized coal significantly influence pulverized coal transportation. The injury rate of propped fracture conductivity increases with increasing driving speeds, while the output of pulverized coal first increases and then decreases with increasing driving speed. Moreover, larger pulverized coal particle sizes result in notably greater damage to propped fracture conductivity than smaller particle sizes. Correspondingly, larger particles exhibit significantly lower output of pulverized coal compared to smaller particles, and transportation and output time are prolonged for larger particles. These findings underscore the importance of particle size and driving speed in the transportation dynamics of pulverized coal. The research results provide a theoretical basis for developing strategies for the prevention and control of pulverized coal during the single-phase water flow stage, thereby offering substantial scientific and practical value for the economic and efficient development of coalbed methane. Full article
(This article belongs to the Special Issue Advances in Unconventional Natural Gas: Exploration and Development)
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19 pages, 4462 KiB  
Article
Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity
by Jinliang Song, Yuan Liu, Yujie Luo, Fujian Yang and Dawei Hu
Appl. Sci. 2024, 14(13), 5825; https://doi.org/10.3390/app14135825 - 3 Jul 2024
Viewed by 385
Abstract
The field stress of the shale affects the proppant embedment, fracture conductivity, well production rate, and ultimately the recovery of hydrocarbons from reservoir formations. This paper presents, for the first time, an experimental study investigating the mechanical characteristics of a shale under confining [...] Read more.
The field stress of the shale affects the proppant embedment, fracture conductivity, well production rate, and ultimately the recovery of hydrocarbons from reservoir formations. This paper presents, for the first time, an experimental study investigating the mechanical characteristics of a shale under confining pressures that simulate the in situ stress state in deep reservoirs. Bidirectional but equal confining pressures were applied to the shale sample to replicate its field stress state. Microindentation tests were conducted to assess the alterations of mechanical properties resulting from the application of confining pressures. The results demonstrate a significant increase in Young’s modulus, hardness, and fracture toughness for the samples subjected to confining pressure. Considering the effect of confining pressure, the decrease in proppant embedment is proportional to Young’s modulus of the shale. For larger-sized proppants (e.g., D = 2.50 mm), the influence of confining pressure on fracture conductivity is relatively minor. However, when smaller-sized proppants (e.g., D = 1.00 mm) are used, particularly in scenarios involving shale debris swelling due to prolonged interaction with fracturing fluid, there is a noticeable improvement in fracture conductivity. Importantly, previous computational models have tended to overestimate proppant embedment depth while underestimating fracture conductivity. The findings from this study contribute to advancing the understanding of shale’s mechanical characteristics under in situ reservoir conditions and support the optimization of proppant embedment and fracture conductivity calculation models for the efficient extraction of shale gas. Full article
(This article belongs to the Special Issue Advances in Unconventional Natural Gas: Exploration and Development)
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18 pages, 4562 KiB  
Article
Analysis and Characterization of Micro–Nano Pores in Coal Reservoirs of Different Coal Ranks
by Jinxing Song, Yulu Yue and Yufang Liu
Appl. Sci. 2024, 14(12), 5198; https://doi.org/10.3390/app14125198 - 14 Jun 2024
Viewed by 362
Abstract
Coalbed methane represents a promising source of clean and efficient unconventional energy. The intricate network of micro–nano pores within coal serves as the primary adsorption space for gas, contributing to the complexity of gas migration channels. In this study, based on the box-counting [...] Read more.
Coalbed methane represents a promising source of clean and efficient unconventional energy. The intricate network of micro–nano pores within coal serves as the primary adsorption space for gas, contributing to the complexity of gas migration channels. In this study, based on the box-counting method, three coal samples representing low, medium, and high ranks were subjected to high-precision micro-CT scanning and nano-CT scanning to generate three-dimensional (3D) pore network models using Avizo visualization software. This facilitated the accurate and quantitative characterization of the micro–nano pore structures within coal reservoirs. The results indicated that the face rate distribution range of each sample was large, indicating relatively strong heterogeneity in each sample. The volume fractal dimension of each sample, determined through micro–nano-CT scanning, was around 2.5, while the surface fractal dimension exhibited oscillatory characteristics with moderate uniformity. The pore equivalent radius and throat equivalent radius distributions were unimodal across all the samples, with the micro-CT scanning revealing a concentration primarily within the range of 100–400 μm for the pore equivalent radius and within 200 μm for the throat equivalent radius. Conversely, the nano-CT scanning exhibited concentrations primarily within the range of 500–2500 nm for the pore equivalent radius and within 2000 nm for the throat equivalent radius. The analysis of the 3D reconstruction structures indicated that the middle-rank coal exhibited more developed large–medium pores compared with the low-rank and high-rank coal, while the low-rank and high-rank coal exhibited relatively more micro–small pores. Furthermore, the low-rank coal exhibited the fewest number of pores but the largest average pore equivalent radius and throat radius. Additionally, the middle–high-rank coal exhibited a relatively larger number of pores. Despite the complex topological structures observed in each sample, a significant proportion indicated a coordination number of 0–20, indicating excellent connectivity within the coal samples. This study is conducive to the optimization of coalbed methane surface development blocks and the formulation of reasonable development plans. Full article
(This article belongs to the Special Issue Advances in Unconventional Natural Gas: Exploration and Development)
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18 pages, 10152 KiB  
Article
Characteristics and Sources of CBM Well-Produced Water in the Shouyang Block, China
by Bing Zhang, Gang Wang, Wei Li and Xinglong Jiao
Appl. Sci. 2024, 14(10), 4218; https://doi.org/10.3390/app14104218 - 16 May 2024
Viewed by 427
Abstract
The Shouyang Block was selected as the research subject. Comprehensive analysis was conducted using coalbed methane (CBM) well production data, geochemical test data on water produced from the coalbed methane well, and fundamental geological information. The findings reveal the water dynamics in the [...] Read more.
The Shouyang Block was selected as the research subject. Comprehensive analysis was conducted using coalbed methane (CBM) well production data, geochemical test data on water produced from the coalbed methane well, and fundamental geological information. The findings reveal the water dynamics in the Shouyang Block are characterized by weak groundwater runoff or retention in most areas. The groundwater head height exhibits a gradual decrease from the north to south, which is closely associated with the monoclinic structure of the Shouyang Block. Overall, water production is relatively high. As the average water production increases, the average gas production gradually decreases. A concentration of high water production wells is observed in the northern part of the Shouyang Block, which gradually increases towards the southeast direction. A comprehensive analysis was conducted on the factors influencing water production, including total water content of coal seams, coal seam porosity, groundwater stability index, groundwater sealing coefficient, D value of the fracture fractal dimension, fault fractal dimension, and sand–mud ratio. The correlation degree was calculated and ranked in order of magnitude through grey correlation analysis. The order of factors that influence water production, from strongest to weakest, is as follows: sand–mud ratio > porosity > fractal dimension of fault > fracture fractal dimension D value > groundwater sealing coefficient > groundwater stability index > total water content of coal seams. The dissolution amounts of carbonate and sulfate are both small, and the water source may mainly come from the sandstone aquifer. Attention should be paid to the distribution and lithological combination of sandstone aquifers in coal-bearing strata in the future exploration and development process of the Shouyang Block. This will help to avoid the potential influence of fault structures and enable the identification of favorable areas for low water and high gas production. Full article
(This article belongs to the Special Issue Advances in Unconventional Natural Gas: Exploration and Development)
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11 pages, 2864 KiB  
Article
Study of the Methane Adsorption Characteristics in a Deep Coal Reservoir Using Adsorption Potential Theory
by Zhengjiang Long, Xushuang Zhu, Junqiao Liao, Dingnan Ye and Run Chen
Appl. Sci. 2024, 14(8), 3478; https://doi.org/10.3390/app14083478 - 20 Apr 2024
Viewed by 473
Abstract
The gas adsorption characteristics in deep coal reservoirs are the focus of deep coalbed methane geology research. In order to reveal the adsorption characteristics in deep coal reservoirs and quantitatively characterize the amount of adsorbed methane in the deep coal seams, four coals [...] Read more.
The gas adsorption characteristics in deep coal reservoirs are the focus of deep coalbed methane geology research. In order to reveal the adsorption characteristics in deep coal reservoirs and quantitatively characterize the amount of adsorbed methane in the deep coal seams, four coals were collected from the Permian Longtan Formation in southern Sichuan Province. Methane isothermal adsorption tests were carried out on the collected coal samples at 30 °C. The adsorption characteristic curve was established based on the data of the isothermal adsorption. The adsorption potential theory was used to predict the isothermal adsorption curves under different temperatures and the evolutionary relationship between the methane adsorption capacity and the coal seam burial depth in the C17 and C25 coal seams of the Permian in southern Sichuan Province, China. The results showed that the methane isothermal adsorption curve at 30 °C belonged to the Type I isotherm adsorption curve. The methane isothermal adsorption curves for various samples at 45 °C, 60 °C, and 75 °C were predicted based on the uniqueness of the methane adsorption characteristic curve. The amount of adsorbed gas in deep coal reservoirs was comprehensively controlled by pressure and temperature. The pressure showed a positive effect on the amount of methane adsorbed, while the temperature showed a negative effect on the adsorption of methane. The negative effect of temperature became more significant with the increase in pressure. The results of the study are beneficial for further promoting the exploration and development of deep coalbed methane in the southern Sichuan Province of China. Full article
(This article belongs to the Special Issue Advances in Unconventional Natural Gas: Exploration and Development)
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