Numerical Simulation Research on Well Pattern Optimization in High–Dip Angle Coal Seams: A Case of Baiyanghe Block

The Baiyanghe block in Fukang, Xinjiang, China, is rich in coalbed methane (CBM) resources, and several pilot experimental wells have yielded high production. Due to the high dip angle (35–55°) of the coal seam in this area, the lack of understanding of the geological characteristics, the physical properties of coal, and gas–water migration law lead to immature development techniques and poor overall development benefits. We first conducted desorption and adsorption tests on low-rank coal of this area and found residual gas in the coal. We established a coalbed methane desorption model suitable for this area by modifying the isotherm adsorption model. Next, by analyzing the influence of the gas–water gravity differentiation in the high–dip angle coal seam and the shallow fired coalbed methane characteristics in this area, we discovered the leakage of CBM from the shallow exposed area of the coal seam. Given the particular physical property of coal and gas–water migration characteristics in this area, we optimized the well pattern: (i) the U-shaped along-dip horizontal well group in coal seams is the main production well for gas production with a spacing distance of 312 m; (ii) a multistage fracturing well drilled in the floor of coal is for water production; and (iii) vertical wells with a spacing distance of 156 m in the shallow area is to capture CBM leakage. Using numerical simulation and net present value (NPV) economics models, we optimized the well pattern details. Applying our CBM desorption model, the numerical simulator can improve the accuracy of the low-rank coalbed methane productivity forecast. The optimization results demonstrated the following: 1) the cumulative gas production of single U-shaped well increased by 89% with the optimal well spacing, 2) the cumulative gas production of the well group increased by 87.54% after adding the floor staged horizontal well, and 3) the amount of CBM leakage decrease by 67.59%.

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Investigation on the CBM Extraction Techniques in the Broken-Soft and Low-Permeability Coal Seams in Zhaozhuang Coalmine

Geofluids ◽

10.1155/2021/1163413 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Zhaoying Chen ◽

Xuehai Fu ◽

Guofu Li ◽

Jian Shen ◽

Qingling Tian ◽

...

Keyword(s):

Coal Seam ◽

Hydraulic Fracturing ◽

Coalbed Methane ◽

Research Result ◽

Horizontal Stress ◽

Gas Production ◽

Vertical Stress ◽

Low Permeability ◽

Coal Seams

To enhance the coalbed methane (CBM) extraction in broken-soft coal seams, a method of drilling a horizontal well along the roof to hydraulically fracture the coal seam is studied (i.e., HWR-HFC method). We first tested the physical and mechanical properties of the broken-soft and low-permeability (BSLP) coal resourced from Zhaozhuang coalmine. Afterward, the in situ hydraulic fracturing test was conducted in the No. 3 coal seam of Zhaozhuang coalmine. The results show that (1) the top part of the coal seam is fractured coal, and the bottom is fragmented-mylonitic coal with a firmness coefficient value of less than 1.0. (2) In the hydraulic fracturing test of the layered rock-coal specimens in laboratory, the through-type vertical fractures are usually formed if the applied vertical stress is the maximum principal stress and is greater than 4 MPa compared with the maximum horizontal stress. However, horizontal fractures always developed when horizontal stress is the maximum or it is less than 4 MPa compared with vertical stress. (3) The in situ HWR-HFC hydraulic fracturing tests show that the detected maximum daily gas production is 11,000 m3, and the average gas production is about 7000 m3 per day. This implies that the CBM extraction using this method is increased by 50%~100% compared with traditional hydraulic fracturing in BSLP coal seams. The research result could give an indication of CBM developing in the broken-soft and low-permeability coal seams.

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Quantify Coal Macrolithotypes of a Whole Coal Seam: A Method Combing Multiple Geophysical Logging and Principal Component Analysis

Energies ◽

10.3390/en14010213 ◽

2021 ◽

Vol 14 (1) ◽

pp. 213

Author(s):

Chao Cui ◽

Suoliang Chang ◽

Yanbin Yao ◽

Lutong Cao

Keyword(s):

Principal Component Analysis ◽

Coal Seam ◽

Coalbed Methane ◽

Principal Component ◽

Component Analysis ◽

Gas Production ◽

Index Model ◽

Geophysical Logging ◽

The Relationship ◽

Observation Results

Coal macrolithotypes control the reservoir heterogeneity, which plays a significant role in the exploration and development of coalbed methane. Traditional methods for coal macrolithotype evaluation often rely on core observation, but these techniques are non-economical and insufficient. The geophysical logging data are easily available for coalbed methane exploration; thus, it is necessary to find a relationship between core observation results and wireline logging data, and then to provide a new method to quantify coal macrolithotypes of a whole coal seam. In this study, we propose a L-Index model by combing the multiple geophysical logging data with principal component analysis, and we use the L-Index model to quantitatively evaluate the vertical and regional distributions of the macrolithotypes of No. 3 coal seam in Zhengzhuang field, southern Qinshui basin. Moreover, we also proposed a S-Index model to quantitatively evaluate the general brightness of a whole coal seam: the increase of the S-Index from 1 to 3.7, indicates decreasing brightness, i.e., from bright coal to dull coal. Finally, we discussed the relationship between S-Index and the hydro-fracturing effect. It was found that the coal seam with low S-Index values can easily form long extending fractures during hydraulic fracturing. Therefore, the lower S-Index values indicate much more favorable gas production potential in the Zhengzhuang field. This study provides a new methodology to evaluate coal macrolithotypes by using geophysical logging data.

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Research on Nano-Emulsion Relieving Coal Seam Water Block Damage

10.1115/omae2021-62814 ◽

2021 ◽

Author(s):

Wei Sun ◽

LongHao Zhao ◽

Qian Wang ◽

Yanchi Liu ◽

Weiping Zhu ◽

...

Keyword(s):

Coal Seam ◽

Coalbed Methane ◽

Mixed Micelles ◽

Polymer Adsorption ◽

Coal Seams ◽

Fracturing Fluid ◽

Flow Experiment ◽

Nano Emulsion ◽

Water Block ◽

Lock In

Abstract Hydraulic fracturing is the most effective reservoirstimulation techniques in the coalbed methane. However, the polymer in the fracturing fluid has a strong effect on the surface of the coal, causing the water lock damage as high as 70% to 90%. It is important to develop an efficient method for releasing coal seam water lock. In this paper, adsorption experiment, SEM, particle size experiment, core flow experiment, wettability and surface tension experiment are used to study the cause of coal seam water lock damage during fracturing and the effect of nano-emulsion on releasing water lock damage in coal seams. Experimental results show that after coal fracturing, the adsorption amount of polymer on the surface of coal is 14.81 mg/g. The large amount of hydrophilic polymer adsorption causes the pore radius of the coal to narrow. And the surface wettability changes from weak hydrophilic to strong hydrophilic, which increase the water lock damage. Compared with conventional slick water, fracturing fluid, the composite of nano-emulsion and fracturing fluid forms mixed micelles, which reduces the polymer adsorption capacity from 14.81 mg/g to 7.42 mg/g. After scanning by electron microscope, it is observed that the surface roughness of the rock sample is restored; The size of the nano-emulsion is about 10nm, and the very small volume can act deep in the pores of the coal seam; After using nano-emulsion, the gas/water interfacial tension is reduced by 45.1mN/m, and the wettability of coal is improved from hydrophilic to neutral, which reduces the capillary pressure in the pores of the coal and reduces the breakthrough pressure of coalbed methane by 11.1KPa; The water lock release rate is as high as 53.09%. The Nano-emulsion is an ideal choice to remove water lock damage.

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The Role of Coal Mechanical Characteristics on Reservoir Permeability Evolution and Its Effects on CO2 Sequestration and Enhanced Coalbed Methane Recovery

Geofluids ◽

10.1155/2020/8842309 ◽

2020 ◽

Vol 2020 ◽

pp. 1-28

Author(s):

Hao Han ◽

Shun Liang ◽

Yaowu Liang ◽

Xuehai Fu ◽

Junqiang Kang ◽

...

Keyword(s):

Elastic Modulus ◽

Coal Seam ◽

Coalbed Methane ◽

Co2 Sequestration ◽

Mechanical Characteristics ◽

Co2 Adsorption ◽

Co2 Injection ◽

Permeability Change ◽

Coal Seams ◽

Enhanced Coalbed Methane

Elastic modulus is an important parameter affecting the permeability change in the process of coalbed methane (CBM)/enhanced coalbed methane (ECBM) production, which will change with the variable gas content. Much research focuses on the constant value of elastic modulus; however, variable stiffness of coal during CO2 injection has been considered in this work. The coupled thermo-hydro-mechanical (THM) model is established and then validated by primary production data, as well as being applied in the prediction of CO2/N2-ECBM recovery. The results show that the harder coal seam is beneficial to primary production, while the softer coal seam results in greater CO2/N2-ECBM recovery and CO2 sequestration. N2 and CO2 mixture injection could be applied to balance early N2 breakthrough and pronounced matrix swelling induced by CO2 adsorption, and to prolong the process of effective CH4 recovery. Besides, reduction in stiffness of coal seam during CO2 injection would moderate the significant permeability loss induced by matrix swelling. With the increase of the weakening degree of coal seam stiffness, CO2 cumulative storage also shows an increasing trend. Neglecting the weakening effect of CO2 adsorption on coal seam stiffness could underestimate the injection capacity of CO2. Injection of hot CO2 could improve the permeability around injection well and then enhance CO2 cumulative storage and CBM recovery. Furthermore, compared with ECBM production, injection temperature is more favorable for CO2 storage, especially within hard coal seams. Care should be considered that significant permeability change is induced by mechanical characteristics alterations in deep burial coal seams in further study, especially for CO2-ECBM projects.

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COAL SEAM GAS—PETROLEUM OR MINERAL

The APPEA Journal ◽

10.1071/aj96038 ◽

1997 ◽

Vol 37 (1) ◽

pp. 589

Author(s):

D.J. Gately

Keyword(s):

Private Sector ◽

Coal Seam ◽

Coalbed Methane ◽

Resource Development ◽

Coal Seams ◽

Coal Seam Gas ◽

Commercial Use ◽

Private Sector Investment ◽

History Of ◽

Policy Shift

1996 was a watershed year for gas exploration in Queensland: the increasing private sector investment in the search for and commercial use of methane gas from coal seams received legislative endorsement. Coal seam gas (CSG), also known as coalbed methane or CBM, was officially designated as petroleum, with exploration for and production of CSG to be administered under the Petroleum Act.The paper traces the history of exploration for CSG in Queensland since 1976, culminating in a policy shift in 1996. In Queensland there is now potential for overlapping titles and competitive resource development.

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Investigation of Hydraulic Fracturing Crack Propagation Behavior in Multi-Layered Coal Seams

Applied Sciences ◽

10.3390/app10031153 ◽

2020 ◽

Vol 10 (3) ◽

pp. 1153 ◽

Cited By ~ 1

Author(s):

Shirong Cao ◽

Xiyuan Li ◽

Zhe Zhou ◽

Yingwei Wang ◽

Hong Ding

Keyword(s):

Coal Seam ◽

Hydraulic Fracturing ◽

Crack Propagation ◽

Principal Stress ◽

Fracture Propagation ◽

Clean Energy ◽

Burial Depth ◽

Coal Seams ◽

Initiation Pressure ◽

Dip Angle

Coalbed methane is not only a clean energy source, but also a major problem affecting the efficient production of coal mines. Hydraulic fracturing is an effective technology for enhancing the coal seam permeability to achieve the efficient extraction of methane. This study investigated the effect of a coal seam reservoir’s geological factors on the initiation pressure and fracture propagation. Through theoretical analysis, a multi-layered coal seam initiation pressure calculation model was established based on the broken failure criterion of maximum tensile stress theory. Laboratory experiments were carried out to investigate the effects of the coal seam stress and coal seam dip angle on the crack initiation pressure and fracture propagation. The results reveal that the multi-layered coal seam hydraulic fracturing initiation pressure did not change with the coal seam inclination when the burial depth was the same. When the dip angle was the same, the initiation pressure linearly increased with the reservoir depth. A three-dimensional model was established to simulate the actual hydraulic fracturing crack propagation in multi-layered coal seams. The results reveal that the hydraulic crack propagated along the direction of the maximum principal stress and opened in the direction of the minimum principal stress. As the burial depth of the reservoir increased, the width of the hydraulic crack also increased. This study can provide the theoretical foundation for the effective implementation of hydraulic fracturing in multi-layered coal seams.

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Study on Drilling and Completion Techniques of Horizontal well for Coalbed Methane

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.513-517.2586 ◽

2014 ◽

Vol 513-517 ◽

pp. 2586-2589 ◽

Cited By ~ 1

Author(s):

Xin Feng Du ◽

Yong Zhe Zhao

Keyword(s):

Coal Seam ◽

Coalbed Methane ◽

Horizontal Well ◽

Horizontal Wells ◽

Mining Area ◽

Variable Density ◽

Technical Problems ◽

Development Direction ◽

Drilling Technology ◽

The Many

Due to the unique reservoir characteristics of the coalbed methane (CBM) in China, many technical problems have to be studied and solved in the development of horizontal wells for CBM. In this paper, based on the V-type wells, we have summarized the many techniques involved in Drilling and completion of horizontal well for CBM in Binchang mining area, such as leakage protection and sealing, geosteering while drilling, remote connection, variable density cementing, Coal seam cavitation, fiberglass casing running into the well, and etc. It is pointed out that the air foam under-balance drilling will be the development direction for coalbed methane drilling technology.

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Nuclear Magnetic Resonance Study on Microstructure and Permeability of Coals of Different Ranks

Advances in Civil Engineering ◽

10.1155/2020/7918510 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Jiajia Liu ◽

Jianmin Hu ◽

Gaini Jia ◽

Jianliang Gao ◽

Dan Wang

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Coal Seam ◽

Liquid Nitrogen ◽

Gas Permeability ◽

Low Rank ◽

Coal Seams ◽

Pore Characteristics ◽

Gas Drainage ◽

Nuclear Magnetic

The microscopic pore development of most coal seams in China leads to different permeability of coal seams and different gas drainage efficiency. Representative three coal rank coal samples were selected for saturation-centrifugation observation. The microscopic pore characteristics of coal samples were measured by nuclear magnetic resonance and liquid nitrogen adsorption methods. The experimental results showed that the coal samples were subjected to saturation-centrifugation and nuclear magnetic resonance (NMR) tests. It was found that the pores of the low-rank coal (XJ-1, XJ-2) were developed at various stages, and the connectivity between the pores was good and the permeability was also good. The adsorption pores of the intermediate coal (HB-1, HB-2) and high-rank coal (ZM-1, ZM-2) were relatively developed, and the connectivity between the pores was slightly poor. The parallel coal seam samples of coals of different ranks were better than the vertical bedding. The adsorption of liquid nitrogen showed that the low-order coal had more open pores and good gas permeability; the high-order coal had more openings at one end, more ink bottles, and narrow holes, and the gas permeability was not good. Studying the micropore structure and permeability of coals of different ranks has guiding significance for mastering the law of coal seam gas storage and transportation, extracting drilling arrangements, and increasing gas drainage and reducing greenhouse effect.

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WATER AND THE COAL SEAM GAS INDUSTRY

The APPEA Journal ◽

10.1071/aj06027 ◽

2007 ◽

Vol 47 (1) ◽

pp. 369

Author(s):

G. Scott ◽

C. Ammundsen

Keyword(s):

Coal Seam ◽

Environmental Protection Agency ◽

Poor Quality ◽

Gas Production ◽

End User ◽

Protection Agency ◽

Coal Seams ◽

Coal Seam Gas ◽

Gas Industry ◽

Access To Water

Access to water is a significant issue in Queensland as much of the State continues to be affected by a prolonged drought. Coal seam gas production involves extracting water from coal seams to reduce the groundwater pressure that keeps the methane trapped in the coal. This process produces large volumes of water. Local councils, primary producers and industrial developers are potential end users of this water; however, if the water is of poor quality, it may be unsuitable for release in the environment and for other direct beneficial uses.This paper examines the complex legislative and regulatory hurdles that need to be overcome before any mutually beneficial agreement between the coal seam gas producer and end user may be completed. It also examines an operational policy recently released by the Queensland Environmental Protection Agency that proposes a framework for the regulation and management of water extracted from coal seams.

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Low Rank Coalbed Gas Preservation Conditions of Inversion Study

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.448-453.3747 ◽

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.

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