Microseismic Monitoring of Stimulating Shale Gas Reservoir in SW China: 1. An Improved Matching and Locating Technique for Downhole Monitoring

Meng, Xingbang; Chen, Haichao; Niu, Fenglin; Tang, Youcai; Yin, Chuancun; Wu, Furong

doi:10.1002/2017jb014488

Cited by 35 publications

(27 citation statements)

References 38 publications

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“…In this study, the fast polarization directions inferred from the vertically propagating S waves are in the range of N40°-70°E, which are generally parallel to the strike directions of the natural fractures observed by microseismic monitoring studies Meng et al, 2018). Such an orientation is also confirmed by well log data based on high electric conductivity (Figure 1b, Chen, Meng et al, 2018).…”

Section: Journal Of Geophysical Research: Solid Earthsupporting

confidence: 82%

Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China

et al. 2018

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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.

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Section: Journal Of Geophysical Research: Solid Earthsupporting

confidence: 82%

Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China

et al. 2018

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“…To improve the completeness of the catalog, we search for undetected events with an improved match and locate technique, which is specifically tailored for downhole array configuration. We briefly outline the technique here; the readers are referred to the companion paper and several other related studies for more details (Caffagni et al, ; Eaton & Caffagni, ; Meng et al, ; Zhang & Wen, ). We first employ an optimal set of well‐located high SNR events to act as waveform templates and detect smaller events that strongly resemble templates through stacking cross‐correlograms between the template waveforms and potential event signals in the continuous records over multiple stations and components.…”

Section: Methodsmentioning

confidence: 99%

Microseismic Monitoring of Stimulating Shale Gas Reservoir in SW China: 2. Spatial Clustering Controlled by the Preexisting Faults and Fractures

et al. 2018

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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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“…The preslip displacement was between 0 and 0.221 mm, the magnitude of microseismic monitoring was less than −1, and the corresponding shear displacement was less than 0.4 mm (Meng et al, 2018).…”

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 89%

“…When the normal stress increases to a certain value, the preslip displacement does not increase with the increase of clay and TOC. The preslip displacement was between 0 and 0.221 mm, the magnitude of microseismic monitoring was less than −1, and the corresponding shear displacement was less than 0.4 mm (Meng et al, ).…”

Section: Discussionmentioning

confidence: 99%

Effect of Clay and Organic Matter Content on the Shear Slip Properties of Shale

Wang

et al. 2019

JGR Solid Earth

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Shale gas reservoirs contain a large number of natural fractures. When shear slip occurs during hydraulic fracturing, it will increase reservoir permeability and improve the reservoir stimulation performance. Because shale contains a large amount of clay and organic matter, its shear slip behavior differs from that of other rocks. In this study, the shear behavior of different shale blocks is experimentally studied, and the proportion of clay and organic matter in the shale dominates the shear slip behavior. Specifically, the friction coefficient and shear strength decrease with the increasing content of clay and organic matter. A microscopic support model was developed to describe the different shear slip behaviors for different contents of clay and organic matter. When the clay and organic matter content is lower than a critical threshold (~35%), shale is microscopically grain supported and brittle shear occurs and the material is prone to shear dilation. When this content is greater than a critical content (~43%), the microscopic structure is a matrix‐supported fabric and plastic shear occurs, which is prone to shear contraction. Shale with contents between these two critical thresholds has a mixed‐support fabric, which is a transition type between brittle and plastic shear. If the proportion of clay and organic matter is less than ~35%, the natural fracture tends to dilate and retain a certain degree of opening after shearing, improving stimulation performance. When the proportion is more than ~43%, shear contraction occurs on the natural fracture surface, which is not conductive and cannot increase reservoir permeability.

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Microseismic Monitoring of Stimulating Shale Gas Reservoir in SW China: 1. An Improved Matching and Locating Technique for Downhole Monitoring

Cited by 35 publications

References 38 publications

Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China

Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China

Microseismic Monitoring of Stimulating Shale Gas Reservoir in SW China: 2. Spatial Clustering Controlled by the Preexisting Faults and Fractures

Effect of Clay and Organic Matter Content on the Shear Slip Properties of Shale

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