超临界CO_2压裂下煤岩体裂缝扩展规律试验研究
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摘要
为了掌握超临界CO_2(简称SC-CO_2)压裂煤岩体的起裂及裂缝扩展规律,采用TCHSFM-I型大尺寸真三轴压裂渗流模拟装置进行试验,同时采集压裂孔内压力和表面裂缝数据并结合理论分析。结果表明:超临界CO_2压裂煤岩的压力时间曲线可分为4个阶段:空腔充填阶段、孔隙增压阶段、相变增压阶段和破坏失稳阶段;其中煤和砂质泥岩起裂压力分别为12.32、19.63 MPa;煤Biot系数0.91、脆性系数16.95%、弹性模量3.48 GPa,产生平行层理的水平裂缝;砂质泥岩Biot系数0.69、脆性系数47.53%、弹性模量10.52 GPa,产生垂直层理的贯通性复杂裂缝。可见SC-CO_2压裂下煤岩裂缝起裂扩展集中于破坏失稳阶段,起裂压力较小且为水力压裂的65%～70%,煤相比于砂质泥岩,由于其层理等弱面发育、Biot系数大、弹性模量低、脆性系数小,未产生贯通性的复杂裂缝。
In order to grasp the law of the initiation and the crack propagation in fracturing coal-rock mass with supercritical CO_2( SCCO_2),the experimental study was carried out by using TCHSFM-I large-scale true-triaxial simulation device for fracturing and seepage and by collecting pressure and surface cracks data,combined with theoretical analysis. The results showed that the pressure-time curves of fracturing coal-rock with supercritical CO_2 could be divided into four stages: cavity-filling stage,pore pressurization stage,phase-transiting pressurization stage and destabilization failure stage.The initiation pressure values of coal and sandy mudstone initiation were 12.32 MPa and 19.63 MPa respectively.The coal,with its Biot coefficient of 0.91,brittleness coefficient of 16.95% and elastic modulus of 3.48 GPa,produced horizontal cracks parallel to the bedding; while the sandy mudstone,with its Biot coefficient of 0.69,brittleness coefficient was47.53% and elastic modulus of 10.52 GPa,produced connective and complex cracks perpendicular to the bedding. It could be seen that the initiation of fracturing with SC-CO_2 fracturing was mainly concentrated in the destabilization failure stage. The initiation pressure of was65% ～ 70% of that of hydraulic fracturing. Compared with sandy mudstone,coal did not produce complex-through cracks for its development of stratification and joint weakness,large Biot coefficient,low elastic modulus and small brittleness coefficient.
In order to grasp the law of the initiation and the crack propagation in fracturing coal-rock mass with supercritical CO_2( SCCO_2),the experimental study was carried out by using TCHSFM-I large-scale true-triaxial simulation device for fracturing and seepage and by collecting pressure and surface cracks data,combined with theoretical analysis. The results showed that the pressure-time curves of fracturing coal-rock with supercritical CO_2 could be divided into four stages: cavity-filling stage,pore pressurization stage,phase-transiting pressurization stage and destabilization failure stage.The initiation pressure values of coal and sandy mudstone initiation were 12.32 MPa and 19.63 MPa respectively.The coal,with its Biot coefficient of 0.91,brittleness coefficient of 16.95% and elastic modulus of 3.48 GPa,produced horizontal cracks parallel to the bedding; while the sandy mudstone,with its Biot coefficient of 0.69,brittleness coefficient was47.53% and elastic modulus of 10.52 GPa,produced connective and complex cracks perpendicular to the bedding. It could be seen that the initiation of fracturing with SC-CO_2 fracturing was mainly concentrated in the destabilization failure stage. The initiation pressure of was65% ～ 70% of that of hydraulic fracturing. Compared with sandy mudstone,coal did not produce complex-through cracks for its development of stratification and joint weakness,large Biot coefficient,low elastic modulus and small brittleness coefficient.
引文
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[22]孙可明,辛利伟,吴迪,等.初应力条件下超临界CO2气爆致裂规律研究[J].固体力学学报,2017,38(5):473-483.SUN Keming,XIN Liwei,WU Di,et al. Mechanism of fracture caused by supercritical CO2explosion under the impact of initial stress[J].Chinese Journal of Solid Mechanics,2017,38(5):473-483.
[23]孙可明,辛利伟,张树翠,等.超临界CO2气爆致裂规律实验研究[J].中国安全生产科学技术,2016,12(7):27-31.SUN Keming,XIN Liwei,ZHANG Shucui,et al. Experimental study on laws of crack caused by gas burst of supercritical carbon dioxide[J]. Journal of Safety Science and Technology,2017,38(5):473-483.
[24]肖孙芸,张冲,张杰,等.基于阵列声波资料评价致裂砂岩可压裂性[J].中州煤炭,2016(4):125-128.XIAO Sunyun,ZHANG Chong,ZHANG Jie,et al.Fracability evaluation of tight sandstone reservoirs based on array acoustic date[J]. Zhongzhou Coal,2016(4):125-128.
[25]赵丹,王婷婷,赵万春,等.煤岩体压裂损伤突变演化模型的研究[J].中州煤炭,2016(4):118-121.ZHAO Dan,WANG Tingting,ZHAO Wanchun,et al,Study on damage mutation evolution model of coal and rock mass fracturing damage[J]. Zhongzhou Coal,2016(4):118-121.
[26] HAIMSON B,FAIRHURST C.Initiation and extension of hydraulic fracturing in rocks[J].Society of Petroleum Engineers Journal,1967,7(6):310-318.
[27]赵宇,张玉贵,岳高伟,等.煤层渗透性各向异性规律的实验研究[J].中国煤层气,2017,14(1):32-36.ZHAO Yu,ZHANG Yugui,YUE Gaowei et al. Experimental study on anisotropic permeability of coal seam[J]. China Coalbed Methane,2017,14(1):32-36.
[2] IAN Palmer. Coalbed methane completions:a world view[J]. International Journal of Coal Geology,2010,82(3/4):184-195.
[3] PAN Zhejun,WOOD David A. Coalbed methane(CBM)exploration,reservoir characterization,production,and modeling:a collection of published research(2009—2015)[J]. Journal of Natural Gas Science and Engineering,2016,26:1472-1484.
[4]张春华,张勇志,李江涛,等.深部煤层单段/多段水力压裂增透效果对比[J].煤炭科学技术,2017,45(6):50-54,175.ZHANG Chunhua,ZHANG Yongzhi,LI Jiangtao,et al.Comparison analysis on permeability improved effect of single and multi section hydraulic fracturing in deep depth seam[J]. Coal Science and Technology,2017,45(6):50-54,175.
[5]张金才,尹尚先.页岩油气与煤层气开发的岩石力学与压裂关键技术[J].煤炭学报,2014,39(8):1691-1699.ZHANG Jincai,YIN Shangxian. Some technologies of rock mechanics applications and hydraulic fracturing in shale oil,shale gas and coalbed methane[J]. Journal of China Coal Society,2014,39(8):1691-1699.
[6]路艳军,杨兆中,SHELEPOV V V,等.煤层气储层压裂现状及展望[J].煤炭科学技术,2017,45(6):73-84.LU Yanjun,YANG Zhaozhong,SHELEPOV V V,et al. Status and prospects of coalbed methane reservoir fracturing[J]. Coal Science and Technology,2017,45(6):73-84.
[7]王永辉,卢拥军,李永平,等.非常规储层压裂改造技术进展及应用[J].石油学报,2012,33(S1):149-158.WANG Yonghui,LU Yongjun,LI Yongping,et al. Progress and application of hydraulic fracturing technology in unconventional reservoir[J]. Acta Petrolei Sinica,2012,33(S1):149-158.
[8] ITO Takatoshi. Effect of pore pressure gradient on fractureinitiation in fluid saturated porous media:Rock[J]. Engineering Fracture Mechanics,2008,75(7):1753-1762.
[9] SCHIMITT D R,ZOBACK M D. Infiltration effects in thetensile rupture of thin walled cylinders of glass andgranite:implications for the hydraulic fracturingbreakdown equation[J]. International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts,1993,30(3):289-303.
[10] MIDDLETON Richard,CAREY Bill,CURRIER Robert P,et al.Shalegas and non-aqueous fracturing fluids:opportunities and challenges forsupercritical CO2[J].Applied Energy,2015,147:500-509.
[11]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 onshale gas exploitation with supercritical CO2[J]. Petroleum Drilling Techniques,2011,39(3):30-35.
[12] ISHIDA Tsuyoshi,AOYAGI Kazuhei,NIWA Tomoya,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] CHEN Youqing,NAGAYA Yuya,ISHIDA Tsuyoshi. Observations of fractures induced by hydraulic fracturing in anisotropic granite[J].Rock Mechanics and Rock Engineering,2015,48(4):1455-1461.
[14]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&Technology Edition,2015,37(3):1-8.
[15]陈立强,田守嶒,李根生,等.超临界CO2压裂起裂压力模型与参数敏感性研究[J].岩土力学,2015,36(S2):125-131.CHEN Liqiang,TIAN Shouceng,LI Gensheng,et al. Initiation pressure models for supercritical CO2fracturing and sensitivity analysis[J]. Rock and Soil Mechanics,2015,36(S2):125-131.
[16]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):2793-2799.WEN Hu,LI Zhenbao,WANG Zhenping,et al. Experiment on the liquid CO2fracturing process for increasing permeability and the characteristics of crack propagation in coal seam[J]. Journal of China Coal Society,2016,41(11):2793-2799.
[17]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 CO2fracturing[J]. Natural Gas Exploration and Development,2016,39(2):58-64.
[18]刘真光,邱正松,钟汉毅,等.页岩储层超临界CO2压裂液滤失规律实验研究[J].钻井液与完井液,2016,33(1):113-117.LIU Zhenguang,QIU Zhengsong,ZHONG Hanyi,et al. Study on filtration property of hypercritical fracturing fluid for shale reservoir[J].Drilling Fluid&Completion Fluid,2016,33(1):113-117.
[19] ZHOU Junping,HU Nan,JIANG Yongdong,et al.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(1):369-377.
[20]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 CO2fracturing of shale[J]. Journal of China Coal Society,2017,42(3):694-701.
[21] ZHANG Xinwei,LU Yiyu,TANG Jiren,et al. Experimental study on fracture initiation and propagation in shale using super critical carbon dioxide fracturing[J]. Fuel,2017,190:370-378.
[22]孙可明,辛利伟,吴迪,等.初应力条件下超临界CO2气爆致裂规律研究[J].固体力学学报,2017,38(5):473-483.SUN Keming,XIN Liwei,WU Di,et al. Mechanism of fracture caused by supercritical CO2explosion under the impact of initial stress[J].Chinese Journal of Solid Mechanics,2017,38(5):473-483.
[23]孙可明,辛利伟,张树翠,等.超临界CO2气爆致裂规律实验研究[J].中国安全生产科学技术,2016,12(7):27-31.SUN Keming,XIN Liwei,ZHANG Shucui,et al. Experimental study on laws of crack caused by gas burst of supercritical carbon dioxide[J]. Journal of Safety Science and Technology,2017,38(5):473-483.
[24]肖孙芸,张冲,张杰,等.基于阵列声波资料评价致裂砂岩可压裂性[J].中州煤炭,2016(4):125-128.XIAO Sunyun,ZHANG Chong,ZHANG Jie,et al.Fracability evaluation of tight sandstone reservoirs based on array acoustic date[J]. Zhongzhou Coal,2016(4):125-128.
[25]赵丹,王婷婷,赵万春,等.煤岩体压裂损伤突变演化模型的研究[J].中州煤炭,2016(4):118-121.ZHAO Dan,WANG Tingting,ZHAO Wanchun,et al,Study on damage mutation evolution model of coal and rock mass fracturing damage[J]. Zhongzhou Coal,2016(4):118-121.
[26] HAIMSON B,FAIRHURST C.Initiation and extension of hydraulic fracturing in rocks[J].Society of Petroleum Engineers Journal,1967,7(6):310-318.
[27]赵宇,张玉贵,岳高伟,等.煤层渗透性各向异性规律的实验研究[J].中国煤层气,2017,14(1):32-36.ZHAO Yu,ZHANG Yugui,YUE Gaowei et al. Experimental study on anisotropic permeability of coal seam[J]. China Coalbed Methane,2017,14(1):32-36.