煤层水力压裂过程中的微震活动规律及其时频特征
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摘要
为了研究煤层水力压裂过程中的微震活动规律及特征,以山东某深部矿井煤层水力压裂试验数据为基础,提出基于奇异值分解SVD法的微震信号去噪方法,并结合煤层应力监测、管内压力监测等手段,利用短时傅里叶变换STFT法研究了典型水力压裂微震信号的时频特征,最后初步尝试了基于微震指标的水力压裂效果表征。结果表明,伴随水力压裂"注水-起裂-扩展-结束"过程的开展,微震信号特征呈现出规律性变化:信号的振幅值先增后减(由6.64 m V迅速跃升至97.51 m V,后回落至30.61 m V);信号频率普遍分布在30~250 Hz,呈现出缓增趋势(由64.0 Hz升高至109.5 Hz,并短暂维持在105.3 Hz)。最后利用微震事件的空间分布和能量分布,初步表征了水力压裂影响范围及煤层应力迁移规律。上述研究成果为后期利用微震数据解译、评价水力压裂效果提供了参考。
In order to study the microseismic activity and time frequency characteristics of coal seam hydraulic fracturing,we developed a series of research about staged fracturing technology including theoretical research and field test in Shandong Province. The main works were carried out as follows: in the filed tests,the small shear failures were triggered by high response microseismic monitoring system.And we proposed a denoising method Singular Value Decomposition( SVD) for those microseismic signals. Short-Time Fourier Transform( STFT) was proposed in this paper to extract feature from microseismic signals in different stages.Microseismic event frequency and energy contours were plotted to characterize the fracture development and propagation process.The interpretation method was initially and successfully applied in the coal seam hydraulic fracturing tests.The test of on-site application shows that the method described above serve as a description method for hydraulic fracturing very well,signal amplitude increases firstly and then decreases( increase from 6.64 m V to 97.51 m V,and decrease to 30.61 m V),signal frequency shows a slow rise tendency( increase from 64 Hz to 109.5 Hz,and keep at 105.3 Hz)and in the range of 30 ~ 250 Hz.Based on the events number and energy distribution,the initial extent of hydraulic fracturing and regular of stress migration is evaluated.The conclusions above can provide some useful idea to quantitative evaluation of hydraulic fracturing in coal mines.
In order to study the microseismic activity and time frequency characteristics of coal seam hydraulic fracturing,we developed a series of research about staged fracturing technology including theoretical research and field test in Shandong Province. The main works were carried out as follows: in the filed tests,the small shear failures were triggered by high response microseismic monitoring system.And we proposed a denoising method Singular Value Decomposition( SVD) for those microseismic signals. Short-Time Fourier Transform( STFT) was proposed in this paper to extract feature from microseismic signals in different stages.Microseismic event frequency and energy contours were plotted to characterize the fracture development and propagation process.The interpretation method was initially and successfully applied in the coal seam hydraulic fracturing tests.The test of on-site application shows that the method described above serve as a description method for hydraulic fracturing very well,signal amplitude increases firstly and then decreases( increase from 6.64 m V to 97.51 m V,and decrease to 30.61 m V),signal frequency shows a slow rise tendency( increase from 64 Hz to 109.5 Hz,and keep at 105.3 Hz)and in the range of 30 ~ 250 Hz.Based on the events number and energy distribution,the initial extent of hydraulic fracturing and regular of stress migration is evaluated.The conclusions above can provide some useful idea to quantitative evaluation of hydraulic fracturing in coal mines.
引文
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[15]唐巨鹏,路江伟,许鹏,等.煤系页岩水力压裂声发射时频特征试验研究[J].中国安全科学学报,2017(10):87-92.TANG Jupeng,LU Jiangwei,XU Peng,et al.Experimental study on time-frequency characteristics of hydraulic fracturing acoustic emission in coal shale[J].China Safety Science Journal,2017(10):87-92.
[16]姜福兴,王博,翟明华,等.煤层超高压定点水力压裂防冲试验研究[J].岩土工程学报,2015,37(3):526-531.JIANG Fuxing,WANG Bo,ZHAI Minghua,et al.Field tests on fixed-point hydraulic fracture with extra-high pressure in coal seam for rock burst prevention[J].Chinese Journal of Gentechnical Engineering,2015,37(3):526-531.
[17]冯宇,姜福兴,翟明华,等.煤层定点水力压裂防冲的机制研究[J].岩土力学,2015,36(4):1174-1181.FENG Yu,JIANG Fuxing,ZHAI Minghua,et al.Mechanism of the fixed-point hydraulic fracturing method for preventing rockburst in coal seam[J].Rock and Soil Mechanics,2015,36(4):1174-1181.
[18]沈鸿雁,李庆春.线性域SVD地震波场分离与去噪方法[J].煤炭学报,2012,37(4):627-633.SHEN Hongyan,LI Qingchun.Seismic wave field separation and denoising in linear domain via singular value decomposition(SVD)[J].Journal of China Coal Society,2012,37(4):627-633.
[19]王金贵,张苏.煤岩静爆致裂微震活动规律及频谱演变特征[J].煤炭学报,2017,42(7):1706-1713.WANG Jingui,ZHANG Su.Characteristics of microseismic signals and its frequency-spectrum evolvement rule during the static cracking of coal[J].Journal of China Coal Society,2017,42(7):1706-1713.
[20]宋维琪,陈泽东,毛中华.水力压裂裂缝微地震监测技术[M].北京:中国石油大学出版社,2008.
[2]BANERJEEG,RAYAK,SINGH GSP,et al.Hard roof management:a key for high productivity in longwall coal mines[J].Journal of Mines,Metals&Fuels,2003,51(7/8):238-244.
[3]KLEE G,RUMMEL F,WILLIAMS A.Hydraulic fracturing stress measurement in Hong Kong[J].International Journal of Rock Mechanics and Mining Science,1999,36:731-741.
[4]郭启文,韩炜,张文勇,等.煤矿井下水力压裂增透抽采机理及应用研究[J].煤炭科学技术,2011,39(12):60-64.GUO Qiwen,HAN Wei,ZHANG Wenyong,et al.Study on mechanism and application of hydraulic fracturing and permeability improvement gas drainage in underground mine[J].Coal Science and Technology,2011,39(12):60-64.
[5]HUANG B X,HUANG C M,CHENG Q Y,et al.Hydraulic fracturing technology for improving permeability in gas-bearing coal seams in underground coal mines[J].Journal of the South African Institute of Mining and Metallurgy,2012,112(6):485-495.
[6]ZHU Q,FENG Y,CAI M,et al.Interpretation of the extent of hydraulic fracturing for rockburst prevention using microseismic monitoring data[J].Journal of Natural Gas Science&Engineering,2017,38:107-119.
[7]康红普,冯彦军.煤矿井下水力压裂技术及在围岩控制中的应用[J].煤炭科学技术,2017,45(1):1-9.KANG Hongpu,FENG Yanjun.Hydraulic fracturing technology and its application in strata control in underground coal mine[J].Coal Science and Technology,2017,45(1):1-9.
[8]张超超,成云海,田厚强,等.深井特厚煤层水力压裂防冲参数与监测分析[J].煤矿安全,2016,47(2):166-169.ZHANG Chao,CHENG Yunhai,TIAN Houqiang,et al.Parameters and monitoring analysis of hydraulic fracturing to prevent rock burst in deep and extra-thick coal seam[J].Safety in Coal Mines,2016,47(2):166-169.
[9]欧阳振华,齐庆新,张寅,等.水压致裂预防冲击地压的机理与试验[J].煤炭学报,2011,36(S2):321-325.OUYANG Zhenhua,QI Qingxin,ZHANG Yin,et al.Mechanism and experiment of hydraulic fracturing in rock burst prevention[J].Journal of China Coal Society,2011,36(S2):321-325.
[10]杨天鸿,唐春安,刘红元,等.水压致裂过程分析的数值试验方法[J].力学与实践,2001,23(5):51-54.YANG Tianhong,TANG Chun’an,LIU Hongyuan,et al.Numerical tests of progressive failure in hydraulic fracturing[J].Mechanics in Engineering,2001,23(5):51-54.
[11]陈江湛,曹函,孙平贺,等.三轴加载下煤岩脉冲水力压裂扩缝机制研究[J].岩土力学,2017,38(4):1023-1031.CHEN Jiangzhan,CAO Han,SUN Pinghe,et al.Mechanisms of fracture extending in coal rock by pulse hydraulic fracturing under triaxial loading[J].Rock and Soil Mechanics,2017,38(4):1023-1031.
[12]徐幼平,林柏泉,翟成,等.定向水力压裂裂隙扩展动态特征分析及其应用[J].中国安全科学学报,2011,21(7):104-110.XU Youping,LIN Baiquan,ZHAI Cheng,et al.Analysis of dynamic characteristics of cracks extension in directional hydraulic fracturing and its application[J].China Safety Science Journal,2011,21(7):104-110.
[13]郭印同,杨春和,贾长贵,等.页岩水力压裂物理模拟与裂缝表征方法研究[J].岩石力学与工程学报,2014,33(1):52-59.GUO Yintong,YANG Chunhe,JIA Changgui,et al.Research on hydraulic fracturing physical simulation of shale and fracture characterization methods[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(1):52-59.
[14]李保林,王恩元,李楠,等.煤层水力压裂声发射监测信号特征分析[J].工矿自动化,2015,41(8):38-42.LI Baolin,WANG Enyuan,LI Nan,et al.Characteristic analysis of acoustic emission monitoring signal in coal and hydraulic fracturing[J].Industry and Mine Automation,2015,41(8):38-42.
[15]唐巨鹏,路江伟,许鹏,等.煤系页岩水力压裂声发射时频特征试验研究[J].中国安全科学学报,2017(10):87-92.TANG Jupeng,LU Jiangwei,XU Peng,et al.Experimental study on time-frequency characteristics of hydraulic fracturing acoustic emission in coal shale[J].China Safety Science Journal,2017(10):87-92.
[16]姜福兴,王博,翟明华,等.煤层超高压定点水力压裂防冲试验研究[J].岩土工程学报,2015,37(3):526-531.JIANG Fuxing,WANG Bo,ZHAI Minghua,et al.Field tests on fixed-point hydraulic fracture with extra-high pressure in coal seam for rock burst prevention[J].Chinese Journal of Gentechnical Engineering,2015,37(3):526-531.
[17]冯宇,姜福兴,翟明华,等.煤层定点水力压裂防冲的机制研究[J].岩土力学,2015,36(4):1174-1181.FENG Yu,JIANG Fuxing,ZHAI Minghua,et al.Mechanism of the fixed-point hydraulic fracturing method for preventing rockburst in coal seam[J].Rock and Soil Mechanics,2015,36(4):1174-1181.
[18]沈鸿雁,李庆春.线性域SVD地震波场分离与去噪方法[J].煤炭学报,2012,37(4):627-633.SHEN Hongyan,LI Qingchun.Seismic wave field separation and denoising in linear domain via singular value decomposition(SVD)[J].Journal of China Coal Society,2012,37(4):627-633.
[19]王金贵,张苏.煤岩静爆致裂微震活动规律及频谱演变特征[J].煤炭学报,2017,42(7):1706-1713.WANG Jingui,ZHANG Su.Characteristics of microseismic signals and its frequency-spectrum evolvement rule during the static cracking of coal[J].Journal of China Coal Society,2017,42(7):1706-1713.
[20]宋维琪,陈泽东,毛中华.水力压裂裂缝微地震监测技术[M].北京:中国石油大学出版社,2008.