Mechanisms and technological parameter optimization of near-wellbore laser thermal fracturing for deep coal seams

Authors

ZHAO Haifeng, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, ChinaFollow
YANG Ziyi, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China
LIANG Wei, China United Coalbed Methane National Engineering Research Center Co., Ltd., Beijing 100095, China
ZHONG Junbing, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China

Abstract

China boasts abundant deep coalbed methane (CBM) resources, which play a significant role in further CBM production. However, deep coal seams exhibit low porosities and ultra-low permeabilities due to intricate geological conditions. In the drilling process, drilling fluids enter the reservoirs, prone to cause near-wellbore contamination. Although conventional hydraulic fracturing technology tends to create fractures in the direction of the maximum horizontal principal stress, it is challenging for this technology to achieve blockage removing throughout the whole borehole. Laser thermal fracturing technology can break rocks in a short time. Furthermore, it allows for the laser irradiation angle to change freely by regulating mechanical equipment, thus forming radial fractures and reducing near-wellbore contamination. Using the ABAQUS finite element software, this study, establishing a model of laser thermal fracturing of coal seams, explored the fracturing mechanisms and the influence of laser technological parameters. Through analyses of the variation patterns of fracture length and number, this study determined the optimal laser parameters targeting near-wellbore contamination areas. Key findings include: (1) Laser thermal fracturing can cause thermal stress on the surfaces of coal seams through temperature differences, ultimately fracturing coal seams. (2) There was a positive correlation between the fracture number and the laser power and irradiation time. Specifically, the number increased from 10 to 37 as laser power expanded from 400 to 1 000 W. At a laser power of 600 W, the number increases from 24 to 36 as the irradiation time prolonged from 1 to 15 s. In contrast, the fracture number negatively correlated with the laser frequency. With an increase in the laser irradiation distance, the fracture number increased initially and then decreased, peaking at an irradiation distance of 10 cm. (3) The fracture length positively correlated the laser power, irradiation time, and laser frequency but negatively correlated the laser irradiation distance. Among these factors, the laser irradiation time produced the most significant influence on the fracture length, which soared from 1.52 to 57.6 mm as the irradiation time increased from 1 to 5 s. For instance, for samples collected from Hancheng, Shaanxi Province through deep coring, the optimal laser power and irradiation time of laser thermal fracturing for the near-wellbore contamination area of deep coal seams extending within 2 m were 20 kW and 2 280 s, respectively. Compared to hydraulic fracturing, laser thermal fracturing can form more complex but shorter fractures. In practical application, the approach combining hydraulic fracturing with laser thermal fracturing is recommended for blockage removing and permeability enhancement.

Keywords

deep coal seam, laser thermal fracturing, near-wellbore blockage-removing mechanism, fracture, ABAQUS

DOI

10.12363/issn.1001-1986.23.09.0572

Recommended Citation

ZHAO Haifeng, YANG Ziyi, LIANG Wei, et al. (2024) "Mechanisms and technological parameter optimization of near-wellbore laser thermal fracturing for deep coal seams," Coal Geology & Exploration: Vol. 52: Iss. 2, Article 17.
DOI: 10.12363/issn.1001-1986.23.09.0572
Available at: https://cge.researchcommons.org/journal/vol52/iss2/17

Reference

[1] 徐凤银，闫霞，林振盘，等. 我国煤层气高效开发关键技术研究进展与发展方向[J]. 煤田地质与勘探，2022，50(3)：1−14.

XU Fengyin，YAN Xia，LIN Zhenpan，et al. Research progress and development direction of key technologies for efficient coalbed methane development in China[J]. Coal Geology & Exploration，2022，50(3)：1−14.

[2]

RANJITH P G，ZHAO Jian，JU Minghe，et al. Opportunities and challenges in deep mining：A brief review[J]. Engineering，2017，3(4)：546–551.

[3] 蒋曙鸿，师素珍，赵康，等. 深部煤及煤层气勘探前景及发展方向[J]. 科技导报，2023，41(7)：106−113.

JIANG Shuhong，SHI Suzhen，ZHAO Kang，et al. Prospect and development direction of deep coal and coalbed methane exploration[J]. Science and Technology Review，2023，41(7)：106−113.

[4] 李松，汤达祯，许浩，等. 深部煤层气储层地质研究进展[J]. 地学前缘，2016，23(3)：10−16.

LI Song，TANG Dazhen，XU Hao，et al. Progress in geological researches on the deep coalbed methane reservoirs[J]. Earth Science Frontiers，2016，23(3)：10−16.

[5] 姚红生，肖翠，陈贞龙，等. 延川南深部煤层气高效开发调整对策研究[J]. 油气藏评价与开发，2022，12(4)：545−555.

YAO Hongsheng，XIAO Cui，CHEN Zhenlong，et al. Adjustment countermeasures for efficient development of deep coalbed methane in southern Yanchuan CBM Field[J]. Petroleum Reservoir Evaluation and Development，2022，12(4)：545−555.

[6] 袁玥辉，屈沅治，高世峰，等. 抗温抗盐水基钻井液降滤失剂研究进展[J]. 新疆石油天然气，2023，19(2)：62−68.

YUAN Yuehui，QU Yuanzhi，GAO Shifeng，et al. Advances in study on temperature–resistant and salt–tolerant fluid loss reducers for water–based drilling fluids[J]. Xinjiang Oil & Gas，2023，19(2)：62−68.

[7] 周静. 高产能气井试井中的表皮系数评价[J]. 天然气勘探与开发，2002，25(2)：54−62.

ZHOU Jing. Evaluation of skin factor in well testing of high productivity gas wells[J]. Natural Gas Exploration and Development，2002，25(2)：54−62.

[8] 陈华兴. 大功率超声波油层解堵技术及应用[J]. 重庆科技学院学报(自然科学版)，2019，21(6)：41−45.

CHEN Huaxing. High power ultrasonic reservoir plugging removal technology and its application[J]. Journal of Chongqing University of Science and Technology (Natural Science Edition)，2019，21(6)：41−45.

[9] XU Zhihong，REED C B，PARKER R A，et al. Laser rock drilling by a super–pulsed CO₂ laser beam：Proceedings of the International Congress on Application of Lasers and Electro–Optics[C]. Scottsdale，2002.

[10] 官兵，李士斌，张立刚，等. 激光破岩技术的研究现状及进展[J]. 中国光学，2020，13(2)：229−248.

GUAN Bing，LI Shibin，ZHANG Ligang，et al. Research progress on rock removal by laser technology[J]. Chinese Optics，2020，13(2)：229−248.

[11] 杨赟，谭平，韦孝忠，等. 激光钻井技术现状与关键技术[J]. 钻采工艺，2015，38(1)：35−39.

YANG Yun，TAN Ping，WEI Xiaozhong，et al. Development status and key technologies of laser drilling[J]. Drilling & Production Technology，2015，38(1)：35−39.

[12] BAKHTBIDAR M，HAFIZI R，BAKHTBIDAR M，et al. Effectiveness assessment of a new advanced laser perforation technique for improving well productivity[J]. Optics & Laser Technology，2020，129(2)：106301.

[13] BHARATISH A，KISHORE KUMAR B，RAJATH R，et al. Investigation of effect of CO₂ laser parameters on drilling characteristics of rocks encountered during mining[J]. Journal of King Saud University(Engineering Sciences)，2019，31(4)：395−401.

[14] JAMALI S，WITTIG V，BORNER J，et al. Application of high powered Laser Technology to alter hard rock properties towards lower strength materials for more efficient drilling，mining，and Geothermal Energy production[J]. Geomechanics for Energy & the Environment，2019，20：100112.

[15] 刘浩，易万福，朱双亚. 激光破岩耦合场仿真分析[J]. 激光与光电子学进展，2015，52(1)：011405.

LIU Hao，YI Wanfu，ZHU Shuangya. Coupled–fields numerical simulation of laser to rock[J]. Laser & Optoelectronics Progress，2015，52(1)：011405.

[16] 柯珂. 激光破岩温度应力数学模型的建立与实验研究[J]. 科学技术与工程，2012，12(29)：7532−7537.

KE Ke. The thermal–stress mathematical model and experimental study of rock–breaking by laser[J]. Science Technology and Engineering，2012，12(29)：7532−7537.

[17] NDEDA R A，SEBUSANG S E，MARUMO R，et al. Numerical model of laser spallation drilling of inhomogeneous rock[J]. IFAC–PapersOnLine，2017，50(2)：43−46.

[18] XIA Ming. Thermo–mechanical coupled particle model for rock[J]. Transactions of Nonferrous Metals Society of China，2015，25(7)：2367−2379.

[19] LI Qin，ZHAI Yuli，HUANG Zhiqiang，et al. Research on crack cracking mechanism and damage evaluation method of granite under laser action[J]. Optics Communications，2021，506：127556.

[20] 杨明军，王玉丹，文国军，等. 激光辐照煤岩的热效应数值模拟分析[J]. 煤田地质与勘探，2018，46(6)：217−222.

YANG Mingjun，WANG Yudan，WEN Guojun，et al. Numerical simulation of thermal effects of laser irradiation on coal and rock[J]. Coal Geology & Exploration，2018，46(6)：217−222.

[21] 魏晨慧. 热流固耦合条件下煤岩体损伤模型及其应用[D]. 沈阳：东北大学，2012.

WEI Chenhui. Damage model for coal and rock under coupled thermal–hydraulic–mechanical conditions and its application[D]. Shenyang：Northeastern University，2012.

[22] 朱万成，魏晨慧，田军，等. 岩石损伤过程中的热–流–力耦合模型及其应用初探[J]. 岩土力学，2009，30(12)：3851−3857.

ZHU Wancheng，WEI Chenhui，TIAN Jun，et al. Coupled thermal–hydraulic–mechanical model during rock damage and its preliminary application[J]. Rock and Soil Mechanics，2009，30(12)：3851−3857.

[23] 史雅丽. 激光照射岩石温度及热裂特性变化研究[D]. 徐州：中国矿业大学，2019.

SHI Yali. Study on the variation of temperature field and thermal cracking characteristics for rock irradiated by fiber laser[D]. Xuzhou：China University of Mining and Technology，2019.

[24] 王春萍，廖益林，刘建锋，等. 应力及含水状态对裂隙花岗岩蠕变特性的影响研究[J]. 岩石力学与工程学报，2024，43(10)：1−11.

WANG Chunping，LIAO Yilin，LIU Jianfeng，et al. Study on the influence of stress and water content on creep characteristics of fractured granite[J]. Chinese Journal of Rock Mechanics and Engineering，2024，43(10)：1−11.

[25] 谭现锋，张强，战启帅，等. 干热岩储层高温条件下岩石力学特性研究[J]. 钻探工程，2023，50(4)：110−117.

TAN Xianfeng，ZHANG Qiang，ZHAN Qishuai，et al. Study on rock mechanical properties of hot–dry rock reservoir under high temperature[J]. Drilling Engineering，2023，50(4)：110−117.

[26] 阴伟涛，冯子军. 高温高压下不同结构形式裂缝充填花岗岩热力学特性[J/OL]. 煤炭学报，2023：1–17

4-02-19]. https：//doi. org/10.13225/j. cnki. jccs. 2023.0696. YIN Weitao，FENG Zijun. Study on thermal and mechanical properties of fracture–filled granite with different structural forms under high temperature and high pressure[J/OL]. Journal of China Coal Society，2023：1–17 [2024-02-19].https：//doi. org/10. 13225/j. cnki. jccs. 2023. 0696.

[27] PAN Haizeng，HU Yi，KANG Yong，et al. Effect of the number of irradiation holes on rock breaking under constant laser energy[J]. Petroleum Science，2022，19(6)：2969−2980.

[28] GUO Chenguang，SUN Yu，LI Qiang，et al. Experimental research on laser thermal rock breaking and optimization of the process parameters[J]. International Journal of Rock Mechanics and Mining Sciences，2022，160：105251.

[29] 范超军，李胜，罗明坤，等. 基于流–固–热耦合的深部煤层气抽采数值模拟[J]. 煤炭学报，2016，41(12)：3076−3085.

FAN Chaojun，LI Sheng，LUO Mingkun，et al. Deep CBM extraction numerical simulation based on hydraulic–mechanical–thermal coupled model[J]. Journal of China Coal Society，2016，41(12)：3076−3085.

[30] 任帅京，张嬿妮，邓军，等. 烟煤升温过程中热物理特性[J]. 西安科技大学学报，2023，43(4)：697−704.

REN Shuaijing，ZHANG Yanni，DENG Jun，et al. Thermophysical properties of bituminous coal in heating[J]. Journal of Xi’an University of Science and Technology，2023，43(4)：697−704.

[31] 王霞，冯子军. 热力耦合作用下长焰煤的热变形规律试验研究[J]. 煤炭工程，2021，53(6)：135−139.

WANG Xia，FENG Zijun. Thermal deformation of long flame coal under thermo–mechanical coupling[J]. Coal Engineering，2021，53(6)：135−139.