scholarly journals Targeted location of microseismic events based on a 3D heterogeneous velocity model in underground mining

PLoS ONE ◽  
2019 ◽  
Vol 14 (2) ◽  
pp. e0212881 ◽  
Author(s):  
Pingan Peng ◽  
Liguan Wang
Keyword(s):  
Underground Mining ◽  
Velocity Model ◽  
Microseismic Events

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.

scholarly journals Tomographic Experiments for Defining the 3D Velocity Model of an Unstable Rock Slope to Support Microseismic Event Interpretation

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 327
Author(s):  
Zhiyong Zhang ◽  
Diego Arosio ◽  
Azadeh Hojat ◽  
Luigi Zanzi
Keyword(s):  
Rock Mass ◽  
Velocity Distribution ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Time Inversion ◽  
Basic Step ◽  
Rock Face ◽  
3D Velocity Model ◽  
Microseismic Events ◽  
The Stability

To monitor the stability of a mountain slope in northern Italy, microseismic monitoring technique has been used since 2013. Locating microseismic events is a basic step of this technique. We performed a seismic tomographic survey on the mountain surface above the rock face to obtain a reliable velocity distribution in the rock mass for the localization procedure. Seismic travel-time inversion showed high heterogeneity of the rock mass with strong contrast in velocity distribution. Low velocities were found at shallow depth on the top of the rock cliff and intermediate velocities were observed in the most critical area of the rock face corresponding to a partially detached pillar. Using the 3D velocity model obtained from inversion, localization tests were performed based on the Equal Differential Time (EDT) localization method. The results showed hypocenter misfits to be around 15 m for the five geophones of the microseismic network and the error was significantly decreased compared to the results produced by a constant velocity model. Although the localization errors are relatively large, the accuracy is sufficient to distinguish microseismic events occurring in the most critical zone of the monitored rock mass from microseismic events generated far away. Thus, the 3D velocity model will be used in future studies to improve the classification of the recorded events.

A Case Study of Vertical Hydraulic Fracture Growth, Stress Variations with Depth and Shear Stimulation in the Niobrara Shale and Codell Sand, DJ Basin, Colorado

2021 ◽  
pp. 1-34
Author(s):  
Kevin L. McCormack ◽  
Mark D. Zoback ◽  
Wenhuan Kuang
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Oil And Gas ◽  
Velocity Model ◽  
Growth Stress ◽  
Hydraulic Fractures ◽  
Stress Profile ◽  
Microseismic Events ◽  
Stress Variations ◽  
Fracture Growth

We carried out a geomechanical study of three wells, one each in the Niobrara A, Niobrara C and Codell sandstone to investigate how the state of stress and stress variations with depth affect vertical hydraulic fracture growth and shear stimulation of pre-existing fractures. We demonstrate that the higher magnitudes of measured least principal stress values in the Niobrara A and C shales are the result of viscoplastic stress relaxation. Using a density log and a VTI velocity model developed to accurately locate the microseismic events, we theoretically calculated a continuous profile of the magnitude of the least principal stress with depth. This stress profile explains the apparent vertical hydraulic fracture growth as inferred from the well-constrained depths of associated microseismic events. Finally, we demonstrate that because of the upward propagation of hydraulic fractures from the Niobrara C to the Niobrara A, the latter formation experienced considerably more shear stimulation, which may contribute to the greater production of oil and gas from that formation.

scholarly journals Imaging crustal structures through a passive seismic imaging approach in a mining area in Saxony, Germany

Solid Earth ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 2703-2715
Author(s):  
Hossein Hassani ◽  
Felix Hloušek ◽  
Stefan Buske ◽  
Olaf Wallner
Keyword(s):  
Velocity Model ◽  
Mining Area ◽  
P Wave ◽  
Seismic Survey ◽  
3D Seismic ◽  
Origin Time ◽  
Seismic Image ◽  
Passive Seismic ◽  
Microseismic Events ◽  
Image Cube

Abstract. We have used several flooding-induced microseismic events that occurred in an abandoned mining area to image geological structures close to the hypocentres in the vicinity of the mine. The events have been located using a migration-based localization approach. We used the recorded full waveforms of these localized microseismic events and have processed these passive source data as if they resulted from active sources at the known hypocentre location and origin time defined by the applied location approach. The imaging was then performed using a focusing 3D prestack depth migration approach for the secondary P-wave arrivals. The needed 3D migration velocity model was taken from a recent 3D active (controlled-source) seismic survey in that area. We observed several clear and pronounced reflectors in our obtained 3D seismic image cube, some of them related to a major fault zone in that area and some correlating well with information from the nearby mining activities. We compared our results to the 3D seismic image cube obtained directly from the 3D active seismic survey and have found new structures with our approach that were not known yet, probably because of their steep dips which the 3D active seismic survey had not illuminated. The location of the hypocentres at depth with respect to the illumination angles of those structures proved to be favourable in that case, and our 3D passive image complements the 3D active seismic image in an elegant way, thereby revealing new structures that cannot be imaged otherwise with surface seismic configurations alone.

Microseismic Monitoring of Hydraulic Fracturing – Data Interpretation Methodology with an Example from Pomerania

2017 ◽  
Author(s):  
Michał Antoszkiewicz ◽  
Mateusz Kmieć ◽  
Paweł Szewczuk ◽  
Marek Szkodo ◽  
Robert Jankowski
Keyword(s):  
Hydraulic Fracturing ◽  
Signal To Noise Ratio ◽  
Velocity Model ◽  
Data Interpretation ◽  
Microseismic Monitoring ◽  
Grid Search ◽  
Moment Tensors ◽  
Spatial Image ◽  
Microseismic Events ◽  
Breakage Mechanism

Microseismic monitoring is a method for localizing fractures induced by hydraulic fracturing in search for shale gas. The aim of this paper is to conduct the data interpretation of the microseismic monitoring based on the results from Pom-erania region of Poland. The data has been collected from an array of geophones deployed on the surface. Ground vibrations have been recorded and analyzed for fracture location, magnitude and breakage mechanism. A velocity model of underlying formations has been used for successful microseismic monitoring. The model has been further tuned with signal from perfora-tion shots of known location. Imaging of events has been done using software MicSeis, which utilizes diffraction stacking of waveforms from multiple stations to image microseismic events with low signal-to-noise ratio. The imaging of microseismic events in MicSeis uses a grid search over all possible origin times and locations in the selected rock volume. The seismic moment tensors are automatically determined from the amplitudes from the grid search procedure and are used to model po-larities of events which then enhance constructive interference. Function characterizing a maximum stack per time sample have been calculated over whole volume and analyzed using the STA/LTA algorithm. Once the event has been detected in time, location has been determined through analysis of the 3D spatial image function. The procedure has been used to detect five events during hydraulic fracturing in Pomerania.

Microseismic velocity model inversion and source location: The use of neighborhood algorithm and master station method

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. KS49-KS63 ◽  
Author(s):  
Yuyang Tan ◽  
Chuan He ◽  
Zhonghua Mao
Keyword(s):  
Velocity Model ◽  
Source Location ◽  
Model Inversion ◽  
Tuning Parameters ◽  
Velocity Models ◽  
Systematic Methodology ◽  
Microseismic Source Location ◽  
Microseismic Events ◽  
Master Station ◽  
Half Length

The accuracy of the velocity model strongly affects the accuracy of microseismic source location and hence the reliability of fracture imaging. We have developed a systematic methodology for microseismic velocity model inversion and source location. A new misfit function is used for both problems, which yields more reliable result than the conventional ones. Using the same measure of misfit, the location errors resulting from the use of different misfit functions are eliminated. The neighborhood algorithm and master station method (MSM) are adopted for calculating the velocity model and source location, respectively. The reason for using the neighborhood algorithm is that it has fewer tuning parameters and is easy to be tuned, whereas the advantage of the MSM is that it can automatically remove the mispicks. The performance of the proposed methods is illustrated using the ball-hit events with known locations, and the validity of the inversion results is verified by the relocations of these events. We also used the inverted velocity models to locate the microseismic events detected from the monitoring data. The location result indicates that the fractures have an average half-length of 280 m and height of 55 m and the fracture azimuth is approximately N77°W.

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