The effect of natural fractures on hydraulic fracturing propagation in coal seams

Wang, Tao; Hu, Wensheng; Elsworth, Derek; Zhou, Wei; Zhou, Wenyi; Zhao, Xianyu; Zhao, Long

doi:10.1016/j.petrol.2016.12.009

Cited by 140 publications

(67 citation statements)

References 27 publications

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“…Figure 8 also indicates that in anisotropic media the smaller differential stress becomes, the more directions of hydraulically induced fractures are influenced by anisotropy. Wang et al (2017) 12) showed that even when the fracture intersects with the bedding plane at right angle, it could propagate in the direction of bedding plane and blanch from the intersection point. The result of P5 is in good agreement with this example as shown in Figures 9 and 10.…”

Section: Discussionmentioning

confidence: 99%

DEM-SJM combined 2D-hydraulic fracturing simulation for consideration of the influence of differential stress

Ohtani

Mikada

Takekawa

2018

Recent Advances in Exploration Geophysics

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For improving the production of conventional oil and shale gas, the practice of hydraulic fracturing has been increasing in recent years. In addition, hydraulic fracturing is used for the development of geothermal energy known as hot dry rock (HDR) geothermal power, and enhanced geothermal system (EGS), and for measuring the rock failure strength and the orientation of principal stress direction, etc. On the other hand, hydraulic fracturing has some environmental impact, such as pollution caused by chemical substances in injected proppant or fluid, induced seismicity, etc. Since it is necessary to minimize the environmental impact, techniques to predict propagating directions and distances of fractures to be generated hydraulically, which are known still very difficult, have been waited for. In this paper, we demonstrate the influence of differential stress and the anisotropy using numerical experiments based on distinct element method (DEM) combined with smooth joint model (SJM). Hydraulic fractures in general propagate in the direction of maximum principal stress on large differential stress conditions. As the differential stress decreased, the propagating directions hydraulic fractures curves to the direction of bedding plane, i.e., anisotropic direction of weak rock strength, and sometimes fractures branch to plural directions. These results suggest that the behavior and propagating direction of hydraulic fractures are strongly influenced by both the differential stress and the rock strength anisotropy in the underground shallow layer.

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Section: Discussionmentioning

confidence: 99%

DEM-SJM combined 2D-hydraulic fracturing simulation for consideration of the influence of differential stress

Ohtani

Mikada

Takekawa

2018

Recent Advances in Exploration Geophysics

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“…Large-scale GWS changes exert loading and unloading of the Earth's surface, inducing vertically downward and upward displacements of the Earth's crust and uppermost mantle [7][8][9]. It should be noted that the ground surface subsidence induced by mining excavation is not discussed by this paper [10,11].…”

Section: Introductionmentioning

confidence: 91%

Vertical Displacements Driven by Groundwater Storage Changes in the North China Plain Detected by GPS Observations

Liu

Zou

et al. 2018

Remote Sensing

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Abstract:The North China Plain (NCP) has been experiencing the most severe groundwater depletion in China, leading to a broad region of vertical motions of the Earth's surface. This paper explores the seasonal and linear trend variations of surface vertical displacements caused by the groundwater changes in NCP from 2009 to 2013 using Global Positioning System (GPS) and Gravity Recovery and Climate Experiment (GRACE) techniques. Results show that the peak-to-peak amplitude of GPS-derived annual variation is about 3.7~6.0 mm and is highly correlated (R > 0.6 for most selected GPS stations) with results from GRACE, which would confirm that the vertical displacements of continuous GPS (CGPS) stations are mainly caused by groundwater storage (GWS) changes in NCP, since GWS is the dominant component of total water storage (TWS) anomalies in this area. The linear trends of selected bedrock-located IGS CGPS stations reveal the distinct GWS changes in period of 2009-2010 (decrease) and 2011-2013 (rebound), which are consistent with results from GRACE-derived GWS anomalies and in situ GWS observations. This result implies that the rate of groundwater depletion in NCP has slowed in recent years. The impacts of geological condition (bedrock or sediment) of CGPS stations to their results are also investigated in this study. Contrasted with the slight linear rates (−0.69~1.5 mm/a) of bedrock-located CGPS stations, the linear rates of sediment-located CGPS stations are between −44 mm/a and −17 mm/a. It is due to the opposite vertical displacements induced by the Earth surface's porous and elastic response to groundwater depletion. Besides, the distinct renewal characteristics of shallow and deep groundwater in NCP are discussed. The GPS-based vertical displacement time series, to some extent, can reflect the quicker recovery of shallow unconfined groundwater than the deep confined groundwater in NCP; through one month earlier to attain the maximum height for CGPS stations nearby shallow groundwater depression cones than those nearby deep groundwater depression cones.

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“…1 Hydraulic fracturing (HF) plays a very good role in stimulating the coal seam by increasing the permeability to enhance CBM recovery and prevent gas disasters. 5 However, it is tedious and complicated to acquire these parameters, and the accuracy is less reliable. There are two main factors influencing the formation of fracture network: the geological condition (regional tectonic, hydrological conditions, in situ stress field, and roof-floor properties) and the physical characteristics of coal and rock (strength, elastic modulus, Poisson's ratio, and pore and cleat, etc.).…”

Section: Introductionmentioning

confidence: 99%

“…There are two main factors influencing the formation of fracture network: the geological condition (regional tectonic, hydrological conditions, in situ stress field, and roof-floor properties) and the physical characteristics of coal and rock (strength, elastic modulus, Poisson's ratio, and pore and cleat, etc.). 5 However, it is tedious and complicated to acquire these parameters, and the accuracy is less reliable. As a consequence, it is necessary to find a brief and effective method to monitor fracture network growth of HF treatment in the coal seam.…”

Section: Introductionmentioning

confidence: 99%

Underground microseismic monitoring of a hydraulic fracturing operation for CBM reservoirs in a coal mine

Jiang

et al. 2019

Energy Science & Engineering

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Hydraulic fracturing can evidently improve the coalbed methane production in underground coal mines, but it is difficult to delimit the stimulated area accurately. In order to evaluate the stimulated area, microseismic (MS) monitoring technique is proposed to investigate the seismic responses of the induced fractures of hydraulic fracturing. Three coal seams were targeted to be treated in a coal mine. An array of geophones was set along the underground roadway to detect the MS signals caused by HF. In order to verify the result of MS monitoring, water content of each coal seam has been measured before and after HF treatment. The results showed that a series of MS events were detected during the entire HF process, and a sharp MS event usually occurred during the first hour of HF process. The energy of the sharp MS event had higher magnitude than others. The MS distribution exhibited complex morphological features. The directionless MS response was distributed over a radius of less than 40 m but tended to be significantly conjugated with a radius of more than 40 m. HF could stimulate both the coal seam and the rock layers nearby. The achievable stimulated area in the coal seam was determined to be 50 m × 50 m according to the MS density and water content. The stimulated area in terms of MS density was easily found to be broader than the area of water direct intrusion. The present study indicated that MS monitoring technique could potentially be used for evaluation of HF in underground coal mine.

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The effect of natural fractures on hydraulic fracturing propagation in coal seams

Cited by 140 publications

References 27 publications

DEM-SJM combined 2D-hydraulic fracturing simulation for consideration of the influence of differential stress

DEM-SJM combined 2D-hydraulic fracturing simulation for consideration of the influence of differential stress

Vertical Displacements Driven by Groundwater Storage Changes in the North China Plain Detected by GPS Observations

Underground microseismic monitoring of a hydraulic fracturing operation for CBM reservoirs in a coal mine

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