Phenomenological Study of Seismic Anisotropy in Shales

Pervukhina, Marina; Golodoniuc, Pavel; Dewhurst, D.

doi:10.3997/2214-4609.20131049

Cited by 2 publications

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“…; Sayers ; Pervukhina et al . ). Here, we use the Voigt approximation of shale elastic stiffness values obtained by Sayers () by expanding the clay platelet ODF as a series of generalised Legendre functions.…”

Section: Effect Of Burial/compaction On Shale Propertiesmentioning

confidence: 97%

“…After absorbing the dataset reported in Pervukhina et al . (), to the best of our knowledge, it is the most comprehensive state‐of‐the‐art collection of published and even unpublished data on shales. It is composed of more than 800 samples of “shaly” formations in a broad sense, including fine‐grained sedimentary rocks.…”

Section: Database On Elastic Properties In Shaly Formationsmentioning

confidence: 99%

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Compaction trend versus seismic anisotropy in shaly formations

Pervukhina

Rasolofosaon

2017

Geophysical Prospecting

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Shales comprise more than 60% of sedimentary rocks and form natural seals above hydrocarbon reservoirs. Their sealing capacity is also used for storage of nuclear wastes. The world's most important conventional oil and gas reservoirs have their corresponding source rocks in shale. Furthermore, shale oil and shale gas are the most rapidly expanding trends in unconventional oil and gas. Shales are notorious for their strong elastic anisotropy, i.e., so‐called vertical transverse isotropy. This vertical transverse isotropy, characterised by a vertical axis of invariance, is of practical importance as it is required for correct surface seismic data interpretation, seismic to well tie, and amplitude versus offset analysis. A rather classical paradigm makes a clear link between compaction in shales and the alignment of the clay platelets (main constituent of shales). This would imply increasing anisotropy strength with increasing compaction. Our main purpose is to check this prediction on two large databases in shaly formations (more than 800 samples from depths of 0–6 km) by extracting the major trends in the relation between seismic anisotropy and compaction. The statistical analysis of the database shows that the simultaneous increase in density and velocity, a classical compaction signature, is quite weakly correlated with the anisotropy strength. As a consequence, compaction can be excluded as a major cause of seismic anisotropy, at least in shaly formations. Also, the alignment of the clay platelets can explain most of the anisotropy measurements of both databases. Finally, a method for estimating the orientation distribution function of the clay platelets from the measurement of the anisotropy parameters is suggested.

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Section: Effect Of Burial/compaction On Shale Propertiesmentioning

confidence: 97%

Section: Database On Elastic Properties In Shaly Formationsmentioning

confidence: 99%

Compaction trend versus seismic anisotropy in shaly formations

Pervukhina

Rasolofosaon

2017

Geophysical Prospecting

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Prediction of sonic velocities in shale from porosity and clay fraction obtained from logs — A North Sea well case study

et al. 2015

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Prediction of sonic velocities in shales from well logs is important for seismic to log ties if the sonic log is absent for a shaly section, for pore pressure anomaly detection, and for data quality control. An anisotropic differential effective medium (DEM) was used to simulate elastic properties of shales from elastic properties and volume fractions of silt and wet clay (a hypothetical composite material that includes all clay minerals and water). Anisotropic elastic coefficients of the wet clay were assumed as a first-order approximation to be linearly dependent on wet clay porosity (WCP). Here, by WCP we mean a ratio of a pore volume occupied by water to a total volume of the wet clay. Effects of silt inclusions on elastic coefficients of shales were taken into account by using the anisotropic differential effective medium model. Silt inclusions were modeled as spherical quartz particles. Simulated elastic coefficients of shales were used to calculate compressional and shear velocities, and these were in a good agreement with the sonic velocities observed on a test data set from an offshore Mid-Norway well penetrating a 500-m vertical section of shale. To further study the elastic properties of wet clays, elastic coefficients calculated from compressional and sonic velocities measured in shales were inverted for vertical profiles of wet clay elastic coefficients. Analysis of these coefficients found that in the well considered, the increase in elastic coefficients of shales was controlled by the increase of silt fraction with depth. Elastic coefficients of wet clay found no increase with depth. The inverted elastic moduli of wet clay found much stronger correlation with WCP than do the moduli of shale. This confirmed the hypothesis that silt fraction is one of the key parameters for the modeling of elastic properties of shale.

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Phenomenological Study of Seismic Anisotropy in Shales

Cited by 2 publications

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Compaction trend versus seismic anisotropy in shaly formations

Compaction trend versus seismic anisotropy in shaly formations

Prediction of sonic velocities in shale from porosity and clay fraction obtained from logs — A North Sea well case study

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