Integrated Anisotropic Velocity Modeling Using Perforation Shots, Passive Seismic and VSP Data

Maxwell, Shawn; Shemeta, Julie

doi:10.3997/2214-4609.201402235

Cited by 6 publications

(8 citation statements)

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“…The perforation velocities (Figure 23a) are more than 10% faster than the VSP velocities ( Figure 25). This is consistent with observations for the Jonah Field by Maxwell et al (2006). …”

Section: Velocity Functions For Migration Traveltime Table Genesupporting

confidence: 82%

Natural and Induced Fracture Diagnostics from 4-D VSP Low Permeability Gas Reservoirs

Willis¹,

Burns²,

Toksöz³

2008

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Tight gas sand reservoirs generally contain thick gas-charged intervals that often have low porosity and very low permeability. Natural and induced fractures provide the only means of production. The objective of this work is to locate and characterize natural and induced fractures from analysis of scattered waves recorded on 4-D (time lapse) VSP data in order to optimize well placement and well spacing in these gas reservoirs. Using model data simulating the scattering of seismic energy from hydraulic fractures, we first show that it is possible to characterize the quality of fracturing based upon the amount of scattering. In addition, the picked arrival times of recorded microseismic events provide the velocity moveout for isolating the scattered energy on the 4-D VSP data.This concept is applied to a field dataset from the Jonah Field in Wyoming to characterize the quality of the induced hydraulic fractures. The time lapse (4D) VSP data from this field are imaged using a migration algorithm that utilizes shot travel time tables derived from the first breaks of the 3D VSPs and receiver travel time tables based on the microseismic arrival times and a regional velocity model. Four azimuthally varying shot tables are derived from picks of the first breaks of over 200 VSP records. We create images of the fracture planes through two of the hydraulically fractured wells in the field. The scattered energy shows correlation with the locations of the microseismic events. In addition, the azimuthal scattering is different from the azimuthal reflectivity of the reservoir, giving us more confidence that we have separated the scattered signal from simple formation reflectivity. Variation of the scattered energy along the image planes suggests variability in the quality of the fractures in three distinct zones.

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“…The perforation velocities (Figure 23a) are more than 10% faster than the VSP velocities ( Figure 25). This is consistent with observations for the Jonah Field by Maxwell et al (2006). …”

Section: Velocity Functions For Migration Traveltime Table Genesupporting

confidence: 82%

Natural and Induced Fracture Diagnostics from 4-D VSP Low Permeability Gas Reservoirs

Willis¹,

Burns²,

Toksöz³

2008

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“…We conclude our paper by observing that anisotropic velocitymodel building for microseismic data processing is in its infancy. While hundreds of authors discuss anisotropy in the context of seismic reflection data, we are aware of only a few publications (Teanby et al, 2004;Maxwell et al, 2006;Michaud et al, 2009) that describe estimation of anisotropy for microseismic monitoring. This makes us believe that a significant body of work needs to be done to develop practical approaches for measuring seismic anisotropy in microseismic geometries and using it to improve our knowledge of the properties of hydraulically treated formations.…”

Section: Discussionmentioning

confidence: 98%

Narrow-angle representations of the phase and group velocities and their applications in anisotropic velocity-model building for microseismic monitoring

Grechka

Duchkov

2011

GEOPHYSICS

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It is usually believed that angular aperture of seismic data should be at least 20°to allow estimation of the subsurface anisotropy. Although this is certainly true for reflection data, for which anisotropy parameters are inverted from the stacking velocities or the nonhyperbolic moveout, traveltimes of direct P-and S-waves recorded in typical downhole microseismic geometries make it possible to infer seismic anisotropy in angular apertures as narrow as about 10°. To ensure the uniqueness of such an inversion, it has to be performed in a local coordinate frame tailored to a particular data set. Because any narrow fan of vectors is naturally characterized by its average direction, we choose the axes of the local frame to coincide with the polarization vectors of three plane waves corresponding to such a direction. This choice results in a significant simplification of the conventional equations for the phase and group velocities in anisotropic media and makes it possible to predict which elements of the elastic stiffness tensor are constrained by the available data. We illustrate our approach on traveltime synthetics and then apply it to perforation-shot data recorded in a shale-gas field. Our case study indicates that isotropic velocity models are inadequate and accounting for seismic anisotropy is a prerequisite for building a physically sound model that explains the recorded traveltimes.

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“…Maxwell et al . () observed a traveltime variation with incidence angle for perforation shot records and proposed seismic anisotropy as a possible explanation for the difference between vertical velocities and horizontal perforation shot velocities. We stress that this velocity variability cannot explain the traveltime differences analyzed in this study.…”

Section: Observations and Analysismentioning

confidence: 96%

Tube wave to shear wave conversion at borehole plugs

Seher

Rondenay

Djikpesse

2014

Geophysical Prospecting

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In hydraulic fracturing experiments, perforation shots excite body and tube waves that sample, and thus can be used to characterize, the surrounding medium. While these waves are routinely employed in borehole operations, their resolving power is limited by the experiment geometry, the signal‐to‐noise ratio, and their frequency content. It is therefore useful to look for additional, complementary signals that could increase this resolving power. Tube‐to‐body‐wave conversions (scattering of tube to compressional or shear waves at borehole discontinuities) are one such signal. These waves are not frequently considered in hydraulic fracture settings, yet they possess geometrical and spectral attributes that greatly complement the resolution afforded by body and tube waves alone. Here, we analyze data from the Jonah gas field (Wyoming, USA) to demonstrate that tube‐to‐shear‐wave conversions can be clearly observed in the context of hydraulic fracturing experiments. These waves are identified primarily on the vertical and radial components of geophones installed in monitoring wells surrounding a treatment well. They exhibit a significantly lower frequency content (10–100 Hz) than the primary compressional waves (100–1000 Hz). Tapping into such lower frequencies could help to better constrain velocity in the formation, thus allowing better estimates of fracture density, porosity and permeability. Moreover, the signals of tube‐to‐shear‐wave conversion observed in this particular study provide independent estimates of the shear wave velocity in the formation and of the tube wave velocity in the treatment well.

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Integrated Anisotropic Velocity Modeling Using Perforation Shots, Passive Seismic and VSP Data

Cited by 6 publications

References 0 publications

Natural and Induced Fracture Diagnostics from 4-D VSP Low Permeability Gas Reservoirs

Natural and Induced Fracture Diagnostics from 4-D VSP Low Permeability Gas Reservoirs

Narrow-angle representations of the phase and group velocities and their applications in anisotropic velocity-model building for microseismic monitoring

Tube wave to shear wave conversion at borehole plugs

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