Browsing by Author "Chen, Haichao"

Now showing 1 - 6 of 6
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    Hydraulic Injection‐Induced Velocity Changes Revealed by Surface Wave Coda and Polarization Data at a Shale Play Site in Southwest China
    (Wiley, 2020) Zhang, Yan; Niu, Fenglin; Tao, Kai; Ning, Jieyuan; Chen, Haichao; Tang, Youcai
    We investigated temporal variations of seismic wave velocity associated with hydraulic fracturing using Green's functions computed from ambient noise data. In October and November of 2014, we set up a broadband array at a shale play site inside the Sichuan basin where a pilot horizontal drilling and hydraulic injections were conducted. We first computed cross‐correlation functions using continuous data recorded by 21 three‐component broadband sensors deployed around the treatment well. We then employed a running window correlation‐based coda wave interferometry technique to measure apparent velocity changes from the daily Green's functions of all the station pairs in the frequency range of 1 to 3 Hz. We found significant velocity changes right after the hydraulic fracturing, which exhibited a clear direction‐dependent pattern. S wave velocity along raypaths parallel to the well trajectory showed a clear increase while those perpendicular exhibited a small decrease. The anisotropic changes in seismic velocity observed here were also confirmed from surface wave horizontal particle motion data. By comparing our observations with normal stress changes calculated with a half‐space elastic model, we speculate that stress changes induced by the hydraulic fracturing were likely to be responsible for the observed anisotropic changes in seismic velocity. Our results suggest that time‐lapse seismic imaging with ambient noise data provides a promising probe for monitoring geomechanical changes related to exploitation of unconventional oil and gas resources.
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    Measurement of Rayleigh wave ellipticity and its application to the joint inversion of high-resolutionﾠSwave velocity structure beneath northeast China
    (Wiley, 2016) Li, Guoliang; Chen, Haichao; Niu, Fenglin; Guo, Zhen; Yang, Yingjie; Xie, Jun
    We present a new 3-D S wave velocity model of the northeast (NE) China from the joint inversion of the Rayleigh wave ellipticity and phase velocity at 8–40 s periods. Rayleigh wave ellipticity, or Rayleigh wave Z/H (vertical to horizontal) amplitude ratio, is extracted from both earthquake (10–40 s) and ambient noise data (8–25 s) recorded by the NorthEast China Extended SeiSmic Array with 127 stations. The estimated Z/H ratios from earthquake and ambient noise data show good consistency within the overlapped periods. The observed Z/H ratio shows a good spatial correlation with surface geology and is systematically low within the basins. We jointly invert the measured Z/H ratio and phase velocity dispersion data to obtain a refined 3-D S wave velocity model beneath the NE China. At shallow depth, the 3-D model is featured by strong low-velocity anomalies that are spatially well correlated with the Songliao, Sanjiang, and Erlian basins. The low-velocity anomaly beneath the Songliao basin extends to ~ 2–3 km deep in the south and ~5–6 km in the north. At lower crustal depths, we find a significant low-velocity anomaly beneath the Great Xing'an range that extends to the upper mantle in the south. Overall, the deep structures of the 3-D model are consistent with previous models, but the shallow structures show a much better spatial correlation with tectonic terranes. The difference in sedimentary structure between the southern and northern Songliao basin is likely caused by a mantle upwelling associated with the Pacific subduction.
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    Microseismic Monitoring of Stimulating Shale Gas Reservoir in SW China: 2. Spatial Clustering Controlled by the Preexisting Faults and Fractures
    (Wiley, 2018) Chen, Haichao; Meng, Xiaobo; Niu, Fenglin; Tang, Youcai; Yin, Chen; Wu, Furong
    Microseismic monitoring is crucial to improving stimulation efficiency of hydraulic fracturing treatment, as well as to mitigating potential induced seismic hazard. We applied an improved matching and locating technique to the downhole microseismic data set during one treatment stage along a horizontal well within the Weiyuan shale gas play inside Sichuan Basin in SW China, resulting in 3,052 well‐located microseismic events. We employed this expanded catalog to investigate the spatiotemporal evolution of the microseismicity in order to constrain migration of the injected fluids and the associated dynamic processes. The microseismicity is generally characterized by two distinctly different clusters, both of which are highly correlated with the injection activity spatially and temporarily. The distant and well‐confined cluster (cluster A) is featured by relatively large‐magnitude events, with ~40 events of M −1 or greater, whereas the cluster in the immediate vicinity of the wellbore (cluster B) includes two apparent lineations of seismicity with a NE‐SW trending, consistent with the predominant orientation of natural fractures. We calculated the b‐value and D‐value, an index of fracture complexity, and found significant differences between the two seismicity clusters. Particularly, the distant cluster showed an extremely low b‐value (~0.47) and D‐value (~1.35). We speculate that the distant cluster is triggered by reactivation of a preexisting critically stressed fault, whereas the two lineations are induced by shear failures of optimally oriented natural fractures associated with fluid diffusion. In both cases, the spatially clustered microseismicity related to hydraulic stimulation is strongly controlled by the preexisting faults and fractures.
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    Observations and Modeling of Long‐Period Ground‐Motion Amplification Across Northeast China
    (Wiley, 2018) Chen, Haichao; Tsai, Victor C.; Niu, Fenglin
    Basin resonances can significantly amplify and prolong ground shaking, and accurate site‐amplification estimates are crucial for mitigating potential seismic hazards within metropolitan basins. In this work, we estimate the site amplification of long‐period (2–10 s) ground motions across northeast China for both surface waves and vertically incident shear waves. The spatial distribution of relatively large site amplifications correlates strongly with known sedimentary basins for both wave types. However, the site response of surface waves is typically twice as high as that of shear waves at most basin sites. We further show that these site‐amplification features can be well explained by predictions based on the local one‐dimensional structure at each site. Our results highlight the importance of accounting for surface‐wave contributions and demonstrate the usefulness of semi‐analytical theory for surface‐wave amplification, which may be broadly applicable in future seismic hazard analysis.
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    Sharp Changes of Crustal Seismic Anisotropy Across the Central Tanlu Fault Zone in East China
    (Wiley, 2023) Miao, Wenpei; Niu, Fenglin; Chen, Haichao
    Both seismic and geodetic data suggested that the ∼120-km long Weifang segment of the Tanlu fault zone, a large-scale active strike-slip system at east China, is a seismic gap with no obvious along-strike shear motion at surface. Measuring crustal deformation around the segment is crucial to constrain stress/strain buildup and potential seismic risk at the fault. We measured crustal and upper mantle seismic anisotropy using P-to-S converted waves at the Moho (Pms) and core-mantle boundary (SKS) recorded by broadband arrays across the Weifang fault segment. The measured crustal anisotropy inside the fault zone shows a fast direction of ∼NNE, parallel to the fault orientation. Right east to the fault zone, the fast axis rotates by almost 90° to ESE. The crustal anisotropy within the fault zone could be caused by aligned microcracks and foliated minerals due to long-lasting shear motion inside the fault zone.
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    Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China
    (Wiley, 2018) Zuo, Qiankun; Tang, Youcai; Niu, Fenglin; Li, Guoliang; Chen, Haichao; Tao, Kai; Chen, Benchi
    Knowledge of the geometric properties of fractures and cracks in a petroleum reservoir is important to reservoir exploitation. When aligned and partially connected, fractures and cracks can act as conduits for fluid flow and thus can significantly increase the permeability of the reservoir. The aligned fractures and cracks, on the other hand, are an effective means to generate seismic anisotropy. In this study, we utilize the seismic data recorded by a vertical array installed in a shallow borehole at a shale play site in southwest China. By applying seismic interferometry to the ambient noise data recorded by 12 three‐component geophones, we extract P and S waves propagating vertically along the borehole. The S waves show up to 20% velocity variations with respect to their polarization directions. Such large S wave anisotropy can be explained by the horizontal transverse isotropic model and is likely caused by natural fractures that are widely present in the area and align approximately in the NE‐SW direction. During the 13‐day period of hydraulic fracking treatment, we also observe large and systematic temporal variations in S wave velocity, degree of S wave polarization anisotropy, and fast polarization direction. By comparing our observations with normal strain changes calculated with a half‐space elastic model, we speculate that strain changes induced by hydraulic injection and fracturing are likely to be responsible for the observed temporal variations in seismic anisotropy. As such, seismic interferometry with shallow borehole acquisition might provide an alternative means to monitor hydraulic fracturing and wastewater injection in the future.