Relative location of microseismic events with multiple masters

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. KS149-KS158 ◽  
Author(s):  
Vladimir Grechka ◽  
Zhao Li ◽  
Bo Howell
Keyword(s):  
Anisotropic Media ◽  
Gradual Decrease ◽  
Relative Location ◽  
Location Method ◽  
Location Errors ◽  
Satisfactory Performance ◽  
Microseismic Data ◽  
Event Location ◽  
Microseismic Events ◽  
Paraxial Ray

A recently proposed paraxial ray-based technique for relative location of microseismicity is extended to accommodate several master events with respect to which other events, termed the slaves, are located. The multi-master extension addresses two issues inherent for the existing single-master algorithm: a gradual decrease of its accuracy with the distance from the master and less than satisfactory performance in the presence of strong velocity heterogeneity. Those deficiencies are handled by applying an improved paraxial traveltime formula, exact in homogeneous elliptically anisotropic media, and by distributing masters in the subsurface to sample its heterogeneity. The contributions of different master events to the hypocenter of a given slave are automatically weighted to enhance the influence of adjacent masters, ensuring the precise slave location, and to suppress distant ones, tending to increase the slave-location errors. Tests of the multi-master relative event-location method on synthetic and field microseismic data demonstrate its precision and flexibility as well as applicability to both surface and downhole microseismic geometries.

Rapid Earthquake Association and Location

2019 ◽  
Vol 90 (6) ◽  
pp. 2276-2284 ◽  
Author(s):  
Miao Zhang ◽  
William L. Ellsworth ◽  
Gregory C. Beroza
Keyword(s):  
Travel Time ◽  
Time Windows ◽  
Grid Point ◽  
Seismic Events ◽  
Relative Location ◽  
Central Apennines ◽  
Location Method ◽  
Event Location ◽  
Seismic Characterization ◽  
Location Methods

ABSTRACT Rapid association of seismic phases and event location are crucial for real‐time seismic monitoring. We propose a new method, named rapid earthquake association and location (REAL), for associating seismic phases and locating seismic events rapidly, simultaneously, and automatically. REAL combines the advantages of both pick‐based and waveform‐based detection and location methods. It associates arrivals of different seismic phases and locates seismic events primarily through counting the number of P and S picks and secondarily from travel‐time residuals. A group of picks are associated with a particular earthquake if there are enough picks within the theoretical travel‐time windows. The location is determined to be at the grid point with the most picks, and if multiple locations have the same maximum number of picks, the grid point among them with smallest travel‐time residuals. We refine seismic locations using a least‐squares location method (VELEST) and a high‐precision relative location method (hypoDD). REAL can be used for rapid seismic characterization due to its computational efficiency. As an example application, we apply REAL to earthquakes in the 2016 central Apennines, Italy, earthquake sequence occurring during a five‐day period in October 2016, midway in time between the two largest earthquakes. We associate and locate more than three times as many events (3341) as are in Italy's National Institute of Geophysics and Volcanology routine catalog (862). The spatial distribution of these relocated earthquakes shows a similar but more concentrated pattern relative to the cataloged events. Our study demonstrates that it is possible to characterize seismicity automatically and quickly using REAL and seismic picks.

An effective polarity correction method for microseismic migration-based location

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. KS115-KS125
Author(s):  
Jincheng Xu ◽  
Wei Zhang ◽  
Xiaofei Chen ◽  
Quanshi Guo
Keyword(s):  
Signal To Noise Ratio ◽  
Computational Cost ◽  
Real Data ◽  
Correction Method ◽  
Fitting Procedure ◽  
Microseismic Data ◽  
The Status ◽  
Event Location ◽  
Microseismic Events ◽  
Polarity Correction

Microseismic methods are important tools for monitoring the status and consequences of hydraulic fracturing. Because microseismic data recorded at the surface have a low signal-to-noise ratio, migration-based algorithms are widely used to determine the locations of microseismic events. However, there may be polarity changes in waveforms at different receivers due to the source mechanisms, which will cause the stacking images to not reach a maximum at the event location. One way for polarity correction is to perform the source mechanism and the source location inversions simultaneously, which, however, is computationally expensive and not good for real-time monitoring. We have developed an effective polarity correction method in the data domain for migration-based location methods called the polarity correction migration-based (PCM) method. This method uses an amplitude trend least-squares fitting procedure to determine the polarities along the receiver line with low additional computational cost. Then, the fitted waveform polarities are used to convert the signs of the amplitude values to stack them consistently. Due to curve fitting, this method is more suitable for microseismic data acquired with regular arrays than with scattered arrays. Numerical experiments of synthetic and real data sets demonstrate that the proposed PCM method can improve accuracy in the detection and location of microseismic events.

Correlation and Interpretation of Microseismic Responses using Pressure Measurements in Offset Observation Wells

2015 ◽  
Author(s):  
Robert Downie ◽  
Joel Le Calvez ◽  
Barry Dean ◽  
Jeff Rutledge
Keyword(s):  
Surface Pressure ◽  
Source Parameters ◽  
Reservoir Pressure ◽  
Pressure Measurements ◽  
Observation Well ◽  
Fracture Pressure ◽  
Microseismic Data ◽  
Pressure Depletion ◽  
Microseismic Events ◽  
Observation Wells

Abstract Interpretation of the microseismic data acquired during hydraulic fracture treatments is based on a variety of techniques that make use of the locations, times, and source parameters of the detected events, in conjunction with the stimulation treatment data. It is sometimes possible to observe trends or changes in the microseismic data that correspond to the surface pressure measurements; however this aspect of interpretation becomes problematic due the variability of fluid friction, slurry density, perforation restrictions, and other near-wellbore pressures when computing bottom hole fracturing pressure. An interpretation technique is proposed that uses pressure measurements in observation wells that are offset to the treatment well during microseismic interpretations. The observation well can be any well with open perforations in close proximity to the treatment well. The observation well pressures are not affected by the many complicating factors that are encountered when estimating pressure in the fracture from the surface pressure measured in the treatment well. Example data from field observations are used to demonstrate that the detection of microseismic events near an observation well and corresponding detection of fluid pressure from the fracture in the observation well validates the calculated event locations. The relationship between fracture pressure, the state of stress, and microseismic responses is discussed using Mohr-Coulomb failure criteria. Observation-well pressures and microseismic events are also used to identify instances where reservoir pressure depletion near the observation well affects surface operations at the treatment well. The results of the study show that reliable measurements of fracture pressure for use in microseismic interpretations can be obtained from offset observation wells, and where reservoir pressure depletion causes deviations from expected fracture behavior. The results also show that microseismic responses are directly related to fracture pressure, and not simply the presence of fracturing fluid itself, leading to an improved understanding of the conditions under which microseismic events occur.

Relative location of microseismic events using P- and S-waves with surface array

2013 ◽  
Author(s):  
Robert Cieplicki ◽  
Leo Eisner ◽  
Mike Mueller ◽  
Julia Kurpan
Keyword(s):  
Relative Location ◽  
S Waves ◽  
Microseismic Events

scholarly journals Microseismic hydraulic fracture imaging in the Marcellus Shale using head waves

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. KS1-KS10 ◽  
Author(s):  
Zhishuai Zhang ◽  
James W. Rector ◽  
Michael J. Nava
Keyword(s):  
Marcellus Shale ◽  
P Wave ◽  
Head Wave ◽  
Wave Polarization ◽  
Horizontal Section ◽  
Location Accuracy ◽  
Arrival Times ◽  
Microseismic Data ◽  
Head Waves ◽  
Event Location

We have studied microseismic data acquired from a geophone array deployed in the horizontal section of a well drilled in the Marcellus Shale near Susquehanna County, Pennsylvania. Head waves were used to improve event location accuracy as a substitution for the traditional P-wave polarization method. We identified that resonances due to poor geophone-to-borehole coupling hinder arrival-time picking and contaminate the microseismic data spectrum. The traditional method had substantially greater uncertainty in our data due to the large uncertainty in P-wave polarization direction estimation. We also identified the existence of prominent head waves in some of the data. These head waves are refractions from the interface between the Marcellus Shale and the underlying Onondaga Formation. The source location accuracy of the microseismic events can be significantly improved by using the P-, S-wave direct arrival times and the head wave arrival times. Based on the improvement, we have developed a new acquisition geometry and strategy that uses head waves to improve event location accuracy and reduce acquisition cost in situations such as the one encountered in our study.

Results of the downhole microseismic monitoring at a pilot hydraulic fracturing site in Poland — Part 1: Event location and stimulation performance

2018 ◽  
Vol 6 (3) ◽  
pp. SH39-SH48 ◽  
Author(s):  
Wojciech Gajek ◽  
Jacek Trojanowski ◽  
Michał Malinowski ◽  
Marek Jarosiński ◽  
Marko Riedel
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Anisotropy ◽  
Transverse Isotropy ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Baltic Basin ◽  
Hydraulic Stimulation ◽  
Lower Paleozoic ◽  
Event Location ◽  
Microseismic Events

A precise velocity model is necessary to obtain reliable locations of microseismic events, which provide information about the effectiveness of the hydraulic stimulation. Seismic anisotropy plays an important role in microseismic event location by imposing the dependency between wave velocities and its propagation direction. Building an anisotropic velocity model that accounts for that effect allows for more accurate location of microseismic events. We have used downhole microseismic records from a pilot hydraulic fracturing experiment in Lower-Paleozoic shale gas play in the Baltic Basin, Northern Poland, to obtain accurate microseismic events locations. We have developed a workflow for a vertical transverse isotropy velocity model construction when facing a challenging absence of horizontally polarized S-waves in perforation shot data, which carry information about Thomsen’s [Formula: see text] parameter and provide valuable constraints for locating microseismic events. We extract effective [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] for each layer from the P- and SV-wave arrivals of perforation shots, whereas the unresolved [Formula: see text] is retrieved afterward from the SH-SV-wave delay time of selected microseismic events. An inverted velocity model provides more reliable location of microseismic events, which then becomes an essential input for evaluating the hydraulic stimulation job effectiveness in the geomechanical context. We evaluate the influence of the preexisting fracture sets and obliquity between the borehole trajectory and principal horizontal stress direction on the hydraulic treatment performance. The fracturing fluid migrates to previously fractured zones, while the growth of the microseismic volume in consecutive stages is caused by increased penetration of the above-lying lithologic formations.

Arrival-time picking of microseismic events based on MSNet

Geophysics ◽  
2021 ◽  
pp. 1-66
Author(s):  
Guanqun Sheng ◽  
Shuangyu Yang ◽  
Xiaolong Guo ◽  
Xingong Tang
Keyword(s):  
Arrival Time ◽  
Spatial Information ◽  
Synthetic Data ◽  
Microseismic Monitoring ◽  
Monitoring Data ◽  
Convolutional Network ◽  
Low Snr ◽  
Microseismic Data ◽  
Microseismic Events ◽  
Arrival Time Picking

Arrival-time picking of microseismic events is a critical procedure in microseismic data processing. However, as field monitoring data contain many microseismic events with low signal-to-noise ratios (SNRs), traditional arrival-time picking methods based on the instantaneous characteristics of seismic signals cannot meet the picking accuracy and efficiency requirements of microseismic monitoring owing to the large volume of monitoring data. Conversely, methods based on deep neural networks can significantly improve arrival-time picking accuracy and efficiency in low-SNR environments. Therefore, we propose a deep convolutional network that combines the U-net and DenseNet approaches to pick arrival times automatically. This novel network, called MSNet not only retains the spatial information of any input signal or profile based on the U-net, but also extracts and integrates more essential features of events and non-events through dense blocks, thereby further improving the picking accuracy and efficiency. An effective workflow is developed to verify the superiority of the proposed method. First, we describe the structure of MSNet and the workflow of the proposed picking method. Then, datasets are constructed using variable microseismic traces from field microseismic monitoring records and from the finite-difference forward modeling of microseismic data to train the network. Subsequently, hyperparameter tuning is conducted to optimize the MSNet. Finally, we test the MSNet using modeled signals with different SNRs and field microseismic data from different monitoring areas. By comparing the picking results of the proposed method with the results of U-net and short-term average and long-term average (STA/LTA) methods, the effectiveness of the proposed method is verified. The arrival picking results of synthetic data and microseismic field data show that the proposed network has increased adaptability and can achieve high accuracy for picking the arrival-time of microseismic events.

scholarly journals Automatic Classification of Microseismic Signals Based on MFCC and GMM-HMM in Underground Mines

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Pingan Peng ◽  
Zhengxiang He ◽  
Liguan Wang
Keyword(s):  
Rock Mass ◽  
Gaussian Mixture ◽  
Automatic Classification ◽  
Microseismic Monitoring ◽  
Underground Mines ◽  
Basic Step ◽  
Microseismic Data ◽  
Safety Risks ◽  
Microseismic Events

In order to mitigate economic and safety risks during mine life, a microseismic monitoring system is installed in a number of underground mines. The basic step for successfully analyzing those microseismic data is the correct detection of various event types, especially the rock mass rupture events. The visual scanning process is a time-consuming task and requires experience. Therefore, here we present a new method for automatic classification of microseismic signals based on the Gaussian Mixture Model-Hidden Markov Model (GMM-HMM) by using only Mel-frequency cepstral coefficient (MFCC) features extracted from the waveform. The detailed implementation of our proposed method is described. The performance of this method is tested by its application to microseismic events selected from the Dongguashan Copper Mine (China). A dataset that contains a representative set of different microseismic events including rock mass rupture, blasting vibration, mechanical drilling, and electromagnetic noise is collected for training and testing. The results show that our proposed method obtains an accuracy of 92.46%, which demonstrates the effectiveness of the method for automatic classification of microseismic data in underground mines.

Automated microseismic event location by amplitude stacking and semblance

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. KS191-KS210 ◽  
Author(s):  
Chengwei Zhang ◽  
Wenxiao Qiao ◽  
Xiaohua Che ◽  
Junqiang Lu ◽  
Baiyong Men
Keyword(s):  
Body Waves ◽  
S Waves ◽  
Advantages And Disadvantages ◽  
Location Uncertainty ◽  
Event Location ◽  
Time Average ◽  
Microseismic Events ◽  
Location Methods ◽  
Microseismic Event Location ◽  
Microseismic Event

Without the need to pick the arrival times of P- and S-waves, migration-based location methods, such as semblance-based and amplitude-stacking-based location methods, are best applied to microseismic events. By comparing and analyzing the advantages and disadvantages of these two methods, we have developed a new location method using amplitude information and semblance. First, we use the two-point ray-tracing method to calculate the traveltime of body waves from the trial point to each receiver, which determines the time-window positions of the P- and S-waves on all traces. Then, we calculate the semblance of the waveforms and the amplitude stacking of the ratio between the short-time average and the long-time average is computed upon the original waveform over the windows. Finally, the semblance weighted by amplitude stacking is used to image the spatial location of the microseismic events. Using experimental and synthetic data considering different factors that may affect the location result (e.g., the signal-to-noise ratio of the waveforms, the scale of the observation array, and the horizontal and vertical distances from the source to fracture zones), we perform microseismic event location with all three methods. According to the source imaging results from experimental and synthetic tests, the semblance method has great location uncertainty in the radial direction but it has good constraints in the circumferential direction; the amplitude-stacking method exhibits the opposite result; and the weighted-semblance method has good constraints in the circumferential and radial directions because it inherits the advantages of semblance-based and amplitude-stacking-based methods. Therefore, compared with existing migration-based location methods, our weighted-semblance method indicates stronger stability and lower location uncertainty, even when downhole monitoring is conducted with a limited aperture of the receiver array.

Relative location of microseismic events with multiple masters

2016 ◽  
Author(s):  
Vladimir Grechka ◽  
Zhao Li ◽  
Robinson Howell
Keyword(s):  
Relative Location ◽  
Microseismic Events ◽  
Multiple Masters
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