Experimental study on fracture initiation and growth in coal using hydraulic fracturing with supercritical CO2 and normal water
WANG Lei1，2，LIANG Weiguo1，2
(1. Institute of Mining Technology，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China；2. Key Laboratory of In-situ Property-improving Mining of Ministry of Education，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China)
Abstract：In order to investigate the fracturing characteristics of coal in hydraulic fracturing with supercritical CO2 and water，the TCHFSM–I large-size true triaxial fracturing seepage device was used to simulate the process of fracturing coal seam by applying triaxial stress to 100 mm×100 mm×100 mm coal samples. Based on the theoretical basis of fracturing and experimental data，the pressure-time curves，surface fractures morphology and fractures width were compared and analyzed. The results showed that，compared to water fracturing，under the same three kinds of triaxial stress conditions，supercritical CO2 initiated the fractures more easily. The initiation pressure decreased by 28.3%，28.0% and 27.4%，respectively，and the reduction gradually decreased with confining pressure increasing. Supercritical CO2 fracturing could generate obvious bedding plane fractures and bifurcation fractures，and the more those fractures were generated，the smaller the growth range of main fractures was. The supercritical CO2 penetrated easily into the original bedding plane fissures and micro-fissures or pores in coal during the fracturing process，which caused the pressure to change gradually. Moreover，the fractured coal with supercritical CO2 could not easily maintain the pressure，so that the fractures width was narrow. The fractures width of water fracturing was mainly distributed in the interval of 0.450–0.650 mm and ＞1.250 mm，while the fractures width of supercritical CO2 was concentrated in the interval of 0.050–0.250 mm. The gap between the two kinds of fractures width was approximately 3–6 times，and for some local bifurcation and bedding plane fractures，even reaching about 2 orders of magnitude.
王 磊1，2，梁卫国1，2. 超临界CO2/清水压裂煤体起裂和裂缝扩展试验研究
[J]. 岩石力学与工程学报, 2019, 38(S1): 2680-2689.
WANG Lei1，2，LIANG Weiguo1，2. Experimental study on fracture initiation and growth in coal using hydraulic fracturing with supercritical CO2 and normal water. , 2019, 38(S1): 2680-2689.
MOORE T A. Coalbed methane：a review[J]. International Journal of Coal Geology，2012，101：36–81.
[5]
YAN F Z，LIN B Q，ZHU C J，et al. A novel ECBM extraction technology based on the integration of hydraulic slotting and hydraulic fracturing[J]. Journal of Natural Gas Science and Engineering，2015，22：571–579.
[7]
MIDDLETON R S，CAREY J W，CURRIER R P，et al. Shale gas and non-aqueous fracturing fluids：opportunities and challenges for supercritical CO2[J]. Applied Energy，2015，147：500–509.
[10]
TSUYOSHI I， KAZUHEI A，TOMOYA N，et al. Acoustic emission monitoring of hydraulic fracturing laboratory experiment with supercritical and liquid CO2[J]. Geophysics Research Letters，2012，39(3)：1–6.
[13]
鲜学福，殷 宏，周军平，等. 页岩气藏超临界CO2致裂增渗实验装置研制[J]. 西南石油大学学报：自然科学版，2015，37(3)：1–8.(XIAN Xuefu，YIN Hong，ZHOU Junping，et al. A new experimental apparatus for fracturing shale gas reservoir to enhance permeability with supercritical carbon dioxide[J]. Journal of Southwest Petroleum University：Science and Technology Edition，2015，37(3)：1–8.(in Chinese))
[1]
邵龙义，侯海海，唐 跃，等. 中国煤层气勘探开发战略接替区优选[J]. 天然气工业，2015，35(3)：1–11.(SHAO Longyi，HOU Haihai，TANG Yue，et al. Selection of strategic relay areas of CBM exploration and development in China[J]. Natural Gas Industry，2015，35(3)： 1–11.(in Chinese))
[2]
李辛子，王运海，姜昭琛，等. 深部煤层气勘探开发进展与研究[J]. 煤炭学报，2016，41(1)：24–31.(LI Xinzi，WANG Yunhai，JIANG Zhaochen，et al. Progress and study on exploration and production for deep coalbed methane[J]. Journal of China Coal Society，2016，41(1)：24–31.(in Chinese)))
[4]
VEDACHALAM N， SESHACHALAM S，RAJENDRAN G，et al. Review of unconventional hydrocarbon resources in major energy consuming countries and efforts in realizing natural gas hydrates as a future source of energy[J]. Journal of Natural Gas Science and Engineering，2015，26：163–175.
[6]
王耀锋，何学秋，王恩元，等. 水力化煤层增透技术研究进展及发展趋势[J]. 煤炭学报，2014，39(10)：1 945–1 955.(WANG Yaofeng，HE Xueqiu，WANG Enyuan，et al. Research progress and development tendency of the hydraulic technology for increasing the permeability of coal seams[J]. Journal of China Coal Society，2014，39(10)：1 945–1 955.(in Chinese)))
[8]
彭英利，马承愚. 超临界CO2流体技术应用手册[M]. 北京：化学工业出版社，2005：1–40.(PENG Yingli，MA Chengyu. Supercritical CO2 fluid technology application manual[M]. Beijing：Chemical Industry Press，2005：1–40.(in Chinese)))
[9]
SAMPATH K H S M.，PERERA M S A，RANJITH P G，et al. CH4-CO2 gas exchange and supercritical CO2 based hydraulic fracturing as CBM production-accelerating techniques：a review[J]. Journal of CO2 Utilization，2017，22：212–230.
[12]
王海柱，沈忠厚，李根生. 超临界CO2开发页岩气技术[J]. 石油钻探技术，2011，39(3)：30–35.(WANG Haizhu，SHEN Zhonghou，LI Gensheng. Feasibility analysis on shale gas exploitation with supercritical CO2[J]. Petroleum Drilling Techniques，2011，39(3)：30–35.(in Chinese))
[14]
赵志恒，李 晓，张 搏，等. 超临界二氧化碳无水压裂新技术实验研究展望[J]. 天然气勘探与开发，2016，39(2)：58–64.(ZHAO Zhiheng，LI Xiao，ZHANG Bo，et al. Experimental study on supercritical CO2 fracturing[J]. Natural Gas Exploration and Development，2016，39(2)：58–64.(in Chinese))
[16]
ZHOU J P，HU N，JIANG Y D，et at. Supercritical carbon dioxide fracturing in shale and the coupled effects on the permeability of fractured shale： An experimental study[J]. Journal of Natural Gas Science and Engineering，2016，36(A)：369–377.
[18]
ZOU Y S，LI N，MA X F，et al. Experimental study on the growth behavior of supercritical CO2 induced fractures in a layered tight sandstone formation[J]. Journal of Natural Gas Science and Engineering，2018，49：145–156.
[19]
文 虎，李珍宝，王振平，等. 煤层注液态CO2压裂增透过程及裂隙扩展特征试验[J]. 煤炭学报，2016，41(11)：2 793–2 799.(WEN Hu，LI Zhenbao，WANG Zhenping，et al. Experiment on the liquid CO2 fracturing process for increasing permeability and the characteristics of crack propagation in coal seam[J]. Journal of China Coal Society，2016，41(11)：2 793–2 799.(in Chinese))
[11]
CHEN Y Q， YUYA N， TSUYOSHI I. Observations of fractures induced by hydraulic fracturing in anisotropic granite[J]. Rock Mechanics and Rock Engineering，2015，48(4)：1 455–1 461.
[15]
刘国军，鲜学福，周军平，等. 超临界CO2致裂页岩实验研究[J]. 煤炭学报，2017，42(3)：694–701.(LIU Guojun，XIAN Xuefu，ZHOU Junping，et al. Experimental study on the supercritical CO2 fracturing of shale[J]. Journal of China Coal Society，2017，42(3)：694–701.(in Chinese))
[17]
ZHANG X W，LU Y Y，TANG J R，et al. Experimental study on fracture initiation and propagation in shale using supercritical carbon dioxide fracturing[J]. Fuel，2017，190：370–378.
2019, Vol. 38 
