• Title, Summary, Keyword: Microseismic

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Temporal and spatial characteristics of coal-mine microseism based on single-link cluster

  • Zhang, Zhibo;Wang, Enyuan;Li, Nan
    • Geosciences Journal
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    • v.21 no.2
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    • pp.223-233
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    • 2017
  • Single-link cluster is introduced into mine microseism monitoring from a seismology point of view. The changes in spatial correlation length of mine microseismic events at different spatial scales are analyzed, and the underlying mechanisms are explained. The results show that large-energy microseismic events often occur after the spatial correlation length drops to a low value when the spatial scale is large. The larger the energy of microseismic events is, the more obvious the law is. Large-energy microseismic events occur after the spatial correlation length exhibits the power-law growth phenomenon, when the spatial scale becomes small. The smaller the spatial scale is, the more obvious the law is. The reason for this property is that microseismic events exhibit the space aggregation phenomenon before a large-energy microseismic event occurs, resulting in decreases in spatial correlation length when the spatial scale is large. By contrast, when the spatial scale is small, the spatial correlation degree of regional microseismic sources is high. Small-energy microseismic events occur gradually with concentration in low-intensity regions, and a large number of small cracks are produced before a large microseismic event occurs. The microseismic source is dispersed again once the regional stress is released. The entire system achieves a critical state. There is small cracks coalescence at a particular moment, which triggers a large-energy microseismic event. Therefore, it exhibits the phenomenon of power-law growth of the correlation length before the occurrence of the large-energy microseismic event. Moreover, statistical analysis of the bond length and frequency of SLC is performed. The result is that three non-scale ranges are identified. The turning points of the first two non-scale ranges are 180 m and 240 m, respectively, while the turning points of the second and third non-scale ranges are both approximately 450 m. The difference between the first turning points is due to the artificial disturbance, while the second turning point is affected by the geological environment.

Characteristics in hypocenters of microseismic events due to hydraulic fracturing and natural faults: a case study in the Horn River Basin, Canada

  • Woo, Jeong-Ung;Kim, Juhwan;Rhie, Junkee;Kang, Tae-Seob
    • Geosciences Journal
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    • v.21 no.5
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    • pp.683-694
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    • 2017
  • For two to three decades, microseismic monitoring has been popular in the development of unconventional resources, because the fracture network generated by hydraulic fracturing mainly controls the productivity, and microseismic monitoring enables direct measurements for imaging the fracture network. Nevertheless, some refinements are required to make this method more practical. One challenge is to quantify the effects of pre-existing natural fractures for generating microseismic events. We determine the hypocenters of microseismic events occurring in a shale gas play in the Horn River Basin, Canada, and report several interesting spatial and temporal features of the hypocenter distributions. Automatic phase-picking is applied to waveform data recorded at 98 shallow buried three-component geophones, and phases thought to be from the same event are associated. The initial hypocenters of events are determined by iterative linear inversion algorithm then relocated using a double-difference algorithm, where relative travel time measurements are obtained with the waveform cross-correlation. We group events into many clusters based on fracking stages and their hypocenters, and then define the best-fitting plane of hypocenters for each cluster. Most strikes of the best-fitting planes are consistent with the direction of local horizontal stress maximum, indicating that hydraulic fracturing induces most microseismic events. However, the best-fitting planes of several clusters have strikes similar to those of pre-existing faults or fractures, indicating that pre-existing natural faults or fractures can affect the generation of microseismic events. In addition, some observations suggest that natural fractures can affect the temporal evolution of the spatial occurrence pattern of microseismic events. We observed specific migration patterns of microseismic events around known faults in the study area. Although further work is required for complete understanding of this phenomenon, our observations help elucidate the nature of microseismic generation.

Microseismic Data Analysis Program for Monitoring Ground Subsidence in Mining Area (광산지역 지반침하 모니터링을 위한 미소진동 분석프로그램 개발 현황)

  • Park, Juhyun;Park, Jayhyun;Yang, Injae;Kim, Jungyul;Kim, Yoosung;Kwon, Sungil;Kwon, Hyongil
    • Geophysics and Geophysical Exploration
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    • v.21 no.4
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    • pp.262-272
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    • 2018
  • A system for microseismic monitoring due to underground displacements is being operated in several mining areas in order to analyze ground subsidence. Microseismic monitoring system mainly consist of three components; 3-component geophone, data logger and analysis program. The previous analysis program had found the location of microseismic source by analysing only first arrivals of P-waves, but the upgraded analysis program has improved accuracy of the location by analysing both P- and S-waves. This analysis program also has upgraded the function to calculate the microseismic magnitude by using regional specific coefficient and microseismic amplitude. Also the program has upgraded the function to confirm visual location of microseismic source by superimposing field aerial photographs and the results.

Case study of microseismic techniques for stability analysis of pillars in a limestone mine (석회석 광산 내 광주의 안정성 분석을 위한 미소진동 계측기술의 현장적용)

  • Kim, Chang Oh;Um, Woo-Yong;Chung, So-Keul;Cheon, Dae-Sung
    • Tunnel and Underground Space
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    • v.26 no.1
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    • pp.1-11
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    • 2016
  • This study deals with the case that was the field application of the microseismic monitoring techniques for the stability monitoring in a domestic mine. The usefulness and limitations of the microseismic techniques were examined through analyzing the microseismic monitored data. The target limestone mine adopted a hybrid room-and-pillar mining method to improve the extraction ratio. The accelerometers were installed in each vertical pillar within the test bed which has the horizontal cross-section $50m{\times}50m$. The measured signals were divided into 4 types; blasting induced signal, drilling induced signal, damage induced signal, and electric noise. The stability analysis was performed based on the measured damage induced signals. After the blasting in the mining section close to the test bed, the damage of the pillar was increased and rockfall near the test bed could be estimated from monitored microseismic data. It was possible to assess the pillar stability from the changes of daily monitored data and the proposed safety criteria from the accumulated monitored data. However, there was a difficulty to determine the 3D microseismic source positions due to the 2D local sensor arrays. Also, it was needed to use real-time monitoring methods in domestic mines. By complementing the problems encountered in the mine application and comparing microseismic monitored data with mining operations, the microseismic monitoring technique can be used as a better safety method.

Development of a Signal Conditioner to Improve the Measurement Reliability of a Microseismic Monitoring System (미소진동 모니터링 시스템의 측정 신뢰도 향상을 위한 시그널 컨디셔너 개발)

  • Cheon, Dae-Sung;Han, Cheol-Min;Lee, Jang Baek
    • Tunnel and Underground Space
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    • v.30 no.1
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    • pp.1-14
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    • 2020
  • Microseismic monitoring is utilized for the performance verification and safety management of the structure by detecting fine levels of damage. In order to construct a highly reliable microseismic monitoring system, the role of signal conditioner is critical. The signal conditioner helps with accurate data collection and precision control of the device, and performs additional functions such as signal conversion, linearization, and amplification. In this technical report, noise reduction signal conditioner suitable for mining sites was developed and reviewed for the purpose of implementing more precise monitoring by supplementing the previously developed microseismic monitoring system.

Stability evaluation and microseismic monitoring around Large Underground Oil Storage Cavern in Over-stressed Rock Mass (과지압 암반 내 대규모 지하 유류비축기지 안정성 평가 및 Microseismic 계측)

  • Lee Hee-Suk;Lee Dae-Hyuck;Kim Ho-Yeong;Hong Jee-Soo;Choi Young-Tae;Kim Seok-Jin;Park Yeon-Jun
    • 한국터널공학회:학술대회논문집
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    • pp.189-201
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    • 2005
  • Brittle failure has been detected in over-stressed rock mass during the construction of oil storage cavern. The main characteristics of stress induced brittle failure of the site are introduced. Various evaluation and measures are sought to stabilize the over-stressed rock mass. The major results from numerical analysis of the cavern are presented, and from current microseismic monitoring to detect hazard from brittle failure are presented.

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Case Study of Microseismic Management Systems for Basel EGS Project (Basel EGS Project의 미소진동관리 사례연구)

  • Lee, Sangdon
    • Tunnel and Underground Space
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    • v.23 no.6
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    • pp.572-580
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    • 2013
  • In this case study, I examined the microseismic safety management system of Deep Heat Mining Basel (DHMB) as EGS Geothermal Project which was conducted in Basel, Switzerland. EGS Geothermal Power projects which require induced seismic event by stimulation for creation of EGS geothermal reservoir have to be controlled pressure and flow rate of stimulation by establishment of microseismic safety management system. Traffic light system and Communication response procedure of DHMB project to respond step by step corresponding microseismic event intensity through continuous monitoring during stimulation period have been managed and established in advance of stimulation. However, the project was discontinued because of an earthquake to occur larger than expected one due to post-injection seismicity occurring in the geothermal reservoir after completion of injection for stimulation. The result of post analysis, Real-time traffic light system was verified to need a establishment of new microseismic safe management system to be considered post-injection seismicity phenomenon.

Study on Microseismic Data Acquisition and Survey Design through Field Experiments of Hydraulic Fracturing and Artificial Blasting (수압파쇄 및 인공발파 현장실험을 통한 미소지진 계측 및 설계에 대한 연구)

  • Kim, Jungyul;Kim, Yoosung;Yun, Jeum-Dong;Kwon, Sungil;Kwon, Hyongil;Shim, Yonsik;Park, Juhyun
    • Geophysics and Geophysical Exploration
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    • v.18 no.4
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    • pp.197-206
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    • 2015
  • The purpose of this study is to ensure microseismic data acquisition technique for hydraulic fracturing imaging at the site of shale gas development. For this, microseismic data acquisition was performed during hydraulic fracturing and artificial blasting at a site bearing shale layers. Measured microseismic event data during the hydraulic fracturing have the very small amplitude of 0.001 mm/sec ~ 0.003 mm/sec and the frequency contents of 5 Hz ~ 20 Hz range. Meanwhile microseismic event data acquired during artificial blasting have the bigger amplitude (0.011 mm/sec ~ 0.302 mm/sec) than hydraulic fracturing event data and their frequency contents have the range of 5 Hz ~ 2 kHz. For microseismic data acquisition design, the selection of appropriate instrumentation including sensors and the recording system, the determination of sensor array and the deployment range were investigated based on the theoretical data and field application experiences.

Development of Efficient Monitoring Algorithm at EGS Site by Using Microseismic Data (미소진동 자료를 이용한 EGS 사이트에서의 효율적인 모니터링 알고리듬 개발)

  • Lee, Sangmin;Byun, Joongmoo
    • Geophysics and Geophysical Exploration
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    • v.19 no.3
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    • pp.111-120
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    • 2016
  • In order to enhance the connectivity of fracture network as fluid path in enhanced/engineered geothermal system (EGS), the exact locating of hydraulic fractured zone is very important. Hydraulic fractures can be tracked by locating of microseismic events which are occurred during hydraulic fracture stimulation at each stage. However, since the subsurface velocity is changed due to hydraulic fracturing at each stage, in order to find out the exact location of microseismic events, we have to consider the velocity change due to hydraulic fracturing at previous stage when we perform the mapping of microseimic events at the next stage. In this study, we have modified 3D locating algorithm of microseismic data which was developed by Kim et al. (2015) and have developed 3D velocity update algorithm using occurred microseismic data. Eikonal equation which can efficiently calculate traveltime for complex velocity model at anywhere without shadow zone is used as forward engine in our inversion. Computational cost is dramatically reduced by using Fresnel volume approach to construct Jacobian matrix in velocity inversion. Through the numerical test which simulates the geothermal survey geometry, we demonstrated that the initial velocity model was updated by using microseismic data. In addition, we confirmed that relocation results of microseismic events by using updated velocity model became closer to true locations.