A Viscoelastic Constitutive Model for Determining In-Situ Stress Magnitudes From Anelastic Strain Recovery of Core

Abstract

A three-dimensional viscoelastic model is developed to describe the anelastic-strain-recovery (ASR) process. Measured ASR data are curve-fit to the model by a least-squares algorithm, and viscoelastic material properties are calculated. The stress state at depth can then be determined given some additional information. Examples and comparisons with measured stresses are given.

Stress Field of the Earth’s Crust

“…To calculate S H and S h , the model requires S V from overburden, the pore pressure, Poisson ratio, and a poroelastic constant. Various rock types were investigated using ASR data interpreted in terms of Blanton's 2D creep model: volcanic tuff (Teufel 1982), sandstone, siltstone and mudstone (Teufel 1983), granite (Engelder 1984), sandstone, siltstone and shale (Warpinski and Teufel 1986), chalk (El Rabaa 1989), gneiss and metabasite , oceanic basalt (Brereton et al 1990). In all studies, vertical stress is assumed to be one of the principal stresses.…”

“…In their refined, first-order creep model, Warpinski and Teufel (1986) used two independent creep compliances, one for dilatation and one for distortion. A linear three-parameter model was adopted for both compliances by using the viscoelastic correspondence principle.…”

“…However, few practical applications of the 3D model are reported (Matsuki and Takeuchi 1993;Ito et al 1997;Lin et al 2006b, c). The Matsuki model states that the ASR depends on the in-situ stress tensor components, pore pressure, temperature change, thermal expansion and the two creep compliances introduced by Warpinski and Teufel (1986). Matsuki's 3D creep model overcomes the shortcoming of previous 2D models that the vertical stress is the principal stress and is calculated from density logs.…”

Poroviscoelasticity of transversely isotropic cylinders under laboratory loading conditions

“…Poroviscoelastic phenomena have been observed in the laboratory and in the field for a range of rock types (El Rabaa and Meadows, 1986;El Rabaa, 1989;Warpinski and Teufel, 1989;Nakken et al, 1989) as well as on a variety of biological materials (Mak, 1986;Cheng and Bilston, 2007;Noailly et al, 2008). Similarly, mechanical anisotropy has long been observed on various classes of rocks, probably most notably transverse isotropy on sedimentary rocks.…”

Explanatory Notes

“…At present, the theoretical analysis of anelastic strain recovery measurements (Blanton, 1983;Warpinski and Teufel, 1986) does not adequately account for the effect of pore-pressure dissipation during strain relief. Numerical modeling and closedform solutions will be used to improve the interpretation of results obtained during Leg 123, especially the phenomenon of observed core contraction (Teufel, 1986).…”