Imaging fractures and sedimentary fabrics using shear wave splitting measurements made on passive seismic data

Verdon, James P.; Kendall, J.‐M.; Wüstefeld, Andreas

doi:10.1111/j.1365-246x.2009.04347.x

Cited by 56 publications

(81 citation statements)

References 27 publications

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“…The results are inverted for fracture parameters using the methodology of Verdon et al (2009). This method finds the rock physics model that best fits the data by inverting for fracture parameters (strike and density) and Thomsen's anisotropy parameters " and # (Thomsen, 1986).…”

Section: Resultsmentioning

confidence: 99%

“…However, the challenge lies in separating fracture effects from other anisotropy effects. In Verdon et al (2009) we outline an inversion approach that uses rock physics modelling to select the best-!t fracture geometries and sedimentary fabrics to match shear-wave splitting observations. The approach has been demonstrated using a passive seismic dataset collected during hydraulic fracture stimulation (Verdon et al, 2010a).…”

Section: Fracture Inversionmentioning

confidence: 99%

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Microseismic Monitoring of Fracture Networks During Hydraulic Stimulation: Beyond Event Locations

et al. 2012

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The successful exploitation of tight-gas reservoirs requires fracture networks, sometimes naturally occurring, often hydraulically stimulated. Borehole microseismic data acquired in such environments hold great promise for characterising such fractures or sweet spots. The loci of seismic events delineate active faults and reveal fracture development in response to stimulation. However, a great deal more can be extracted from these microseismic data. For example, inversions of shear-wave splitting data provide a robust means of mapping fracture densities and preferred orientations, useful information for drilling programs. They can also be used to track temporal variations in fracture compliances, which are indicative of fluid flow and enhanced permeability in response to stimulation. Furthermore, the frequency-dependent nature of shear-wave splitting is very sensitive to size of fractures and their fluidfill composition. Here we demonstrate the feasibility of using such analysis of shear-wave splitting measurements on data acquired during hydraulic stimulation of a tight-gas sandstone in the Cotton Valley field in Carthage, West Texas.

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Section: Resultsmentioning

confidence: 99%

Section: Fracture Inversionmentioning

confidence: 99%

Microseismic Monitoring of Fracture Networks During Hydraulic Stimulation: Beyond Event Locations

et al. 2012

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“…Shear wave splitting is typically used as a tool for detecting anisotropy, in particular at reservoir scale (Verdon et al, 2009;Wuestefeld et al, 2011). When a polarized shear wave enters an anisotropic homogeneous medium, it splits into two orthogonally polarized shear waves with distinct velocities.…”

Section: Shear-wave Splitting Methodologymentioning

confidence: 99%

Crack Features and Shear-Wave Splitting Associated with Fracture Extension during Hydraulic Stimulation of the Geothermal Reservoir in Soultz-sous-Forêts

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Dorbath

Calò

et al. 2015

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-The recent tomography results obtained within the scope of the Enhanced Geothermal System (EGS) European Soultz project led us to revisit the meso-fracturing properties of Soultz test site. In this paper, we develop a novel approach coupling effective medium modeling and shear-wave splitting to characterize the evolution of crack properties throughout the hydraulic stimulation process. The stimulation experiment performed in 2000 consisted of 3 successive injection steps spanning over 6 days. An accurate 4-D tomographic image was first carried out based upon the travel-times measured for the induced seismicity [Calò M., Dorbath C., Cornet F.H., Cuenot N. (2011) Large-scale aseismic motion identified through 4-D P-wave tomography, Geophys. J. Int. 186, 1295Int. 186, -1314. The current study shows how to take advantage of the resulting compressional wave (Calò et al., 2011) and shear-wave velocity models. These are given as input data to an anisotropic effective medium model and converted into crack properties. In short, the effective medium model aims to estimate the impact of cracks on velocities. It refers to a crack-free matrix and 2 families of penny-shaped cracks with orientations in agreement with the main observed geological features: North-South strike and dip of 65°East and 65°West [Genter A., Traineau H. (1996) Analysis of macroscopic fractures in granite in the HDR geothermal well EPS-1, Soultz-sousForêts, France, J. Vol. Geoth. Res. 72, 121-141], respectively. The resulting output data are the spatial distributions of crack features (lengths and apertures) within the 3-D geological formation. We point out that a flow rate increase results in a crack shortening in the area imaged by both compressional and shear waves, especially in the upper part of the reservoir. Conversely, the crack length, estimated during continuous injection rate phases, is higher than during the increasing injection rate phases. A possible explanation for this is that cracks remain large because the system has time to relax. We also calculate the extension and opening rates during all hydraulic stimulation sets. While the opening rate is unchanged, the extension rate varies depending on the stimulation phase. It is also shown to be higher around and above the open-hole section than below. This can indicate a potential upward path that makes fluid percolation easier within the granite formation, this path being induced by the temperature gradient. We also compare the evolution of crack extension during injection with shear-wave splitting. Split shear waves were recorded at 2 stations during hydraulic stimulation and processed in terms of splitting parameters. The fast shear-wave polarization remains constant and parallel to the maximum horizontal stress orientation while the amplitude of splitting varies with time. We observe a good agreement between travel-time differences and crack extension rates during the first 4 days of the stimulation experiment. Afterwards, these two parameters depart from each other. This stud...

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“…Anisotropy along the raypath can be characterized by measuring the polarization ( ψ ) of the fast wave and the delay time ( δ t ) between the wave arrivals (typically δ t is normalized by path length to be expressed as a percentage S wave velocity difference, δ V S ). S wave splitting is particularly useful when applied to microseismic data recorded using downhole arrays, as microseismic events typically produce strong S waves and both the source and receiver are in the rock of interest (Baird et al, ; Verdon et al, ).…”

Section: Introductionmentioning

confidence: 99%

The Role of Texture, Cracks, and Fractures in Highly Anisotropic Shales

et al. 2017

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Organic shales generally have low permeability unless fractures are present. However, how gas, oil, and water flows into these fractures remains enigmatic. The alignment of clay minerals and the alignment of fractures and cracks are effective means to produce seismic anisotropy. Thus, the detection and characterization of this anisotropy can be used to infer details about lithology, rock fabric, and fracture and crack properties within the subsurface. We present a study characterizing anisotropy using S wave splitting from microseismic sources in a highly anisotropic shale. We observe very strong anisotropy (up to 30%) with predominantly VTI (vertical transverse isotropy) symmetry, but with evidence of an HTI (horizontal transverse isotropy) overprint due to a NE striking vertical fracture set parallel to the maximum horizontal compressive stress. We observe clear evidence of a shear wave triplication due to anisotropy, which to our knowledge is one of only a very few observations of such triplications in field‐scale data. We use modal proportions of minerals derived from X‐ray fluorescence data combined with realistic textures to estimate the contribution of intrinsic anisotropy as well as possible contributions of horizontally aligned cracks. We find that aligned clays can explain much of the observed anisotropy and that any cracks contributing to the vertical transverse isotropy (VTI) must have a low ratio of normal to tangential compliance (ZN/ZT), typical of isolated cracks with low hydraulic connectivity. Subhorizontal cracks have also been observed in the reservoir, and we propose that their reactivation during hydraulic fracturing may be an important mechanism to facilitate gas flow.

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Imaging fractures and sedimentary fabrics using shear wave splitting measurements made on passive seismic data

Cited by 56 publications

References 27 publications

Microseismic Monitoring of Fracture Networks During Hydraulic Stimulation: Beyond Event Locations

Microseismic Monitoring of Fracture Networks During Hydraulic Stimulation: Beyond Event Locations

Crack Features and Shear-Wave Splitting Associated with Fracture Extension during Hydraulic Stimulation of the Geothermal Reservoir in Soultz-sous-Forêts

The Role of Texture, Cracks, and Fractures in Highly Anisotropic Shales

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