• Title/Summary/Keyword: Microseismic

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Monitoring of Fracture Occurrence During Carbon Dioxide Injection at the Meruap Oil Reservoir, Indonesia (인도네시아 머루압 유전에 이산화탄소 주입 시 균열대 생성 여부 모니터링)

  • Kim, Dowan;Byun, Joongmoo;Kim, Kiseog;Ahn, Taewoong
    • Geophysics and Geophysical Exploration
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    • v.19 no.1
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    • pp.37-44
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    • 2016
  • $CO_2$-EOR (Carbon Dioxide-Enhanced Oil Recovery), one of the enhanced oil recovery methods, helps to not only enhance the production of oil, but also store carbon dioxide in underground. However, if micro fractures occur when during the injection of $CO_2$, it is difficult to make permanent storage of $CO_2$ in reservoir and can cause contamination of groundwater and soil. Therefore, in this study, we performed microseismic monitoring to investigate the occurrence of fractures during the $CO_2$ injection at the Meruap oil reservoir, Indonesia. To pick the first arrivals of microseismic events, Improved MER (Modified Energy Ratio) method was used. After picking the first arrivals, hodogram analysis was carried out by using the data recorded at three component geophones to calculate the back azimuth of events. Finally, locations of microseismic events were decided by using the results of first arrival picking and hodogram analysis. Estimated locations showed that all microseismic events were occurred at surface and any fracture did not occur around the reservoir. Moreover, by analyzing noise characteristic, we confirmed that almost of picked first arrivals were due to the repetitive mechanical noise.

Locating Microseismic Events using a Single Vertical Well Data (단일 수직 관측정 자료를 이용한 미소진동 위치결정)

  • Kim, Dowan;Kim, Myungsun;Byun, Joongmoo;Seol, Soon Jee
    • Geophysics and Geophysical Exploration
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    • v.18 no.2
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    • pp.64-73
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    • 2015
  • Recently, hydraulic fracturing is used in various fields and microseismic monitoring is one of the best methods for judging where hydraulic fractures exist and how they are developing. When locating microseismic events using single vertical well data, distances from the vertical array and depths from the surface are generally decided using time differences between compressional (P) wave and shear (S) wave arrivals and azimuths are calculated using P wave hodogram analysis. However, in field data, it is sometimes hard to acquire P wave data which has smaller amplitude than S wave because microseismic data often have very low signal to noise (S/N) ratio. To overcome this problem, in this study, we developed a grid search algorithm which can find event location using all combinations of arrival times recorded at receivers. In addition, we introduced and analyzed the method which calculates azimuths using S wave. The tests of synthetic data show the inversion method using all combinations of arrival times and receivers can locate events without considering the origin time even using only single phase. In addition, the method can locate events with higher accuracy and has lower sensitivity on first arrival picking errors than conventional method. The method which calculates azimuths using S wave can provide reliable results when the dip between event and receiver is relatively small. However, this method shows the limitation when dip is greater than about $20^{\circ}$ in our model test.

Experimental Study on Microseismic Source Location by Dimensional Conditions and Arrival Picking Methods (차원 및 초동발췌방법에 따른 미소진동 음원위치결정 실험연구)

  • Cheon, Dae-Sung;Yu, Jeongmin;Lee, Jang-baek
    • Tunnel and Underground Space
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    • v.29 no.4
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    • pp.243-261
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    • 2019
  • Microseismic monitoring technologies have been recognized for its superiority over traditional methods and are used in domestic and overseas underground mines. However, the complex gangway layout of underground mines in Korea and the mixed structure of excavated space and rock masses make it difficult to estimate the microseismic propagation and to determine the arrival time of microseismic wave. In this paper, experimental studies were carried out to determine the source location according to various arrival picking methods and dimensional conditions. The arrival picking methods used were FTC (First Threshold Cross), Picking window, AIC (Akaike Information Criterion), and 2-D and 3-D source generation experiments were performed, respectively, under the 2-D sensor array. In each experiment, source location algorithm used iterative method and genetic algorithm. The iterative method was effective when the sensor array and source generation were the same dimension, but it was not suitable to apply when the source generation was higher dimension. On the other hand, in case of source location using RCGA, the higher dimensional source location could be determined, but it took longer time to calculate. The accuracy of the arrival picking methods differed according to the source location algorithms, but picking window method showed high accuracy in overall.

Monitoring Technique using Acoustic Emission and Microseismic Event (AE와 MS 이벤트를 이용한 계측기술)

  • Cheon, Dae-Sung;Jung, Yong-Bok;Park, Chul-Whan;Synn, Joong-Ho;Park, Eui-Seob
    • Tunnel and Underground Space
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    • v.18 no.1
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    • pp.1-9
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    • 2008
  • Acoustic emission (AE) and Microseimsic (MS) activities are law-energy seismic events associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. The main difference between AE and MS signals is that the seismic motion frequencies of AE signals are higher than those of MS signals. As the failure of geotechnical structures usually happens as a high velocity and small displacement, it is nat easy ta determine the precursor and initiation stress level of failure in displacement detection method. To overcame this problem, AE/MS techniques far detection of structure failure and damage have recently adapt in civil engineering. This study deal with the basic theory of AE/MS and state of arts in monitoring technique using AE/MS.

Guideline for the Diagnose of Geotechnical Structure (Underground Oil Storage Cavern) using a Microseismic Monitoring System (음향미소진동기반 모니터링 시스템을 이용한 지반구조물(유류 지하저장시설) 진단평가 가이드라인)

  • Cheon, Dae-Sung;Jung, Yong-Bok
    • Tunnel and Underground Space
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    • v.28 no.4
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    • pp.293-303
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    • 2018
  • Monitoring is the act of collecting and analyzing accurate engineering information using various methods and instruments. The purposes of the monitoring are design verification, construction management, quality control, safety management, and diagnose of structure etc.. The diagnose evaluation of the geotechnical structures corresponds to the confirmation of the structural performance. It is aimed to judge the soundness of geotechnical structures considering the degree of damage due to the environmental change and elapsed time. Recently, microseismicity, which is widely known in Korea, can be used for safety management and diagnoses of structure as it detects the micro-damage without disturbance of the structure. This report provides guideline on the procedure for assessing an underground oil storage cavern using microseismic monitoring techniques. Guidelines cover the selection of monitoring systems, sensor array, sensor installation and operation of systems, and interpretation.

Blast vibration of a large-span high-speed railway tunnel based on microseismic monitoring

  • Li, Ao;Fang, Qian;Zhang, Dingli;Luo, Jiwei;Hong, Xuefei
    • Smart Structures and Systems
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    • v.21 no.5
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    • pp.561-569
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    • 2018
  • Ground vibration is one of the most undesirable effects induced by blast operation in mountain tunnels, which could cause negative impacts on the residents living nearby and adjacent structures. The ground vibration effects can be well represented by peak particle velocity (PPV) and corner frequency ($f_c$) on the ground. In this research, the PPV and the corner frequency of the mountain surface above the large-span tunnel of the new Badaling tunnel are observed by using the microseismic monitoring technique. A total of 53 sets of monitoring results caused by the blast inside tunnel are recorded. It is found that the measured values of PPV are lower than the allowable value. The measured values of corner frequency are greater than the natural frequencies of the Great Wall, which will not produce resonant vibration of the Great Wall. The vibration effects of associated parameters on the PPV and corner frequency which include blast charge, rock mass condition, and distance from the blast point to mountain surface, are studied by regression analysis. Empirical formulas are proposed to predict the PPV and the corner frequency of the Great Wall and surface structures due to blast, which can be used to determine the suitable blast charge inside the tunnel.

Microseismic monitoring and its precursory parameter of hard roof collapse in longwall faces: A case study

  • Wang, Jun;Ning, Jianguo;Qiu, Pengqi;Yang, Shang;Shang, Hefu
    • Geomechanics and Engineering
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    • v.17 no.4
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    • pp.375-383
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    • 2019
  • In underground retreating longwall coal mining, hard roof collapse is one of the most challenging safety problems for mined-out areas. Identifying precursors for hard roof collapse is of great importance for the development of warning systems related to collapse geohazards and ground control. In this case study, the Xinhe mine was chosen because it is a standard mine and the minable coal seam usually lies beneath hard strata. Real-time monitoring of hard roof collapse was performed in longwall face 5301 of the Xinhe mine using support resistance and microseismic (MS) monitoring; five hard roof collapse cases were identified. To reveal the characteristics of MS activity during hard roof collapse development and to identify its precursors, the change in MS parameters, such as MS event rate, energy release, bursting strain energy, b value and the relationships with hard roof collapse, were studied. This research indicates that some MS parameters showed irregularity before hard roof collapse. For the Xinhe coalmine, a substantial decrease in b value and a rapid increase in MS event rate were reliable hard roof collapse precursors. It is suggested that the b value has the highest predictive sensitivity, and the MS event rate has the second highest.

A Study on the Improvement of Microseismic Monitoring Accuracy by Borehole 3-Component Measurement Field Experiments (시추공 3성분 계측 현장실험을 통한 미소지진 모니터링 정확도 향상 연구)

  • Kim, Jungyul;Kim, Yoosung;Yun, Jeumdong;Kwon, Sungil;Kwon, Hyongil;Park, Seongbin;Park, Juhyun
    • Geophysics and Geophysical Exploration
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    • v.20 no.1
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    • pp.1-11
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    • 2017
  • In order to improve the accuracy of microseismic epicenter location through the inversion techniques using P and S wave first arrivals, field experiments of microseismic monitoring were performed using borehole 3-component geophones. The direction of epicenter was estimated from the hodograms of P-wave first arrivals through the weight drop experiments in which the $\times$ component of 3-component geophone was aligned to the magnetic north. The picking of S wave first arrival was possible in the polarization filtered data even if S waves are difficult to be identified in raw data. The inversion technique using only P wave first arrival times can often converge to the local minimum when the initial values for epicenter are largely apart from the true epicenter, so that the correct solution can not be found. To solve this problem, the epicenter determination method using differences between P and S wave arrival times was used to estimate proper initial values of epicenter. The inversion result using only P-wave first arrival times which started from the estimated initial values showed the improved accuracy of the epicenter location.

Optimisation of multiplet identifier processing on a $PLAYSTATION^{(R)}$ 3 (플레이스테이션 3 상에서 수행되는 멀티플렛 식별자의 최적화)

  • Hattori, Masami;Mizuno, Takashi
    • Geophysics and Geophysical Exploration
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    • v.13 no.1
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    • pp.109-117
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    • 2010
  • To enable high-performance computing (HPC) for applications with large datasets using a $Sony^{(R)}$ $PLAYSTATION^{(R)}$ 3 ($PS3^{TM}$) video game console, we configured a hybrid system consisting of a $Windows^{(R)}$ PC and a $PS3^{TM}$. To validate this system, we implemented the real-time multiplet identifier (RTMI) application, which identifies multiplets of microearthquakes in terms of the similarity of their waveforms. The cross-correlation computation, which is a core algorithm of the RTMI application, was optimised for the $PS3^{TM}$ platform, while the rest of the computation, including data input and output remained on the PC. With this configuration, the core part of the algorithm ran 69 times faster than the original program, accelerating total computation speed more than five times. As a result, the system processed up to 2100 total microseismic events, whereas the original implementation had a limit of 400 events. These results indicate that this system enables high-performance computing for large datasets using the $PS3^{TM}$, as long as data transfer time is negligible compared with computation time.