Stress‐dependent elastic wave velocity of microfractured sandstone

Abstract

SUMMARY A model for the stress‐dependent elastic wave velocity response of fractured rock mass is proposed based on experimental evidence of stress‐dependent fracture normal and shear stiffness. Previously proposed models and previous experimental studies on stress‐dependent fracture stiffness have been reviewed to provide a basis for the new model. Most of the existing stress‐dependent elastic wave velocity models are empirical, with model parameters that do not have clear physical meanings. To propose the new model, the rock mass is assumed to have randomly oriented microscopic fractures. In addition, the characteristic length of microfractures is assumed to be sufficiently short compared to the rock mass dimensions. The macroscopic stress‐dependent elastic wave velocity response is assumed to be attributed to the stress dependency of fracture stiffness. The stress‐dependent fracture normal stiffness is defined as a generalized power law function of effective normal stress, which is a modification of the Goodman's model. On the other hand, the stress dependency of fracture shear stiffness is modeled as a linear function of normal stress based on experimental data. Ultrasonic wave velocity responses of a dry core sample of Berea sandstone were tested at effective stresses ranging from 2 to 55 MPa. Visual observation of thin sections obtained from the Berea sandstone confirms that the assumptions made for microstructure of rock mass model are appropriate. It is shown that the model can describe the stress‐dependent ultrasonic wave velocity responses of dry Berea sandstone with a set of reasonable material parameter values. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Assessment of the structural representativeness of sample data sets for the mechanical characterization of deep formations

“…Other models relate stress dependency to crack closure, providing different expressions from equation 1 (e.g., Katsuki et al, 2014), also foreseeing increase of velocity (stiffness) with loading (see Appendix A for application of the Katsuki et al [2014] model to one of the case studies of this paper).…”

Hydromechanical Modeling of Unsaturated Flow in Double Porosity Media

“…It is also common in engineered geotechnical structures such as compacted soils and landfills (Feda 1998;Li and Zhang 2009;Najser et al 2010Najser et al , 2012Romero et al 2011;Della Vecchia and Romero 2013;Musso et al 2013;Burton et al 2014). It is well recognized that all natural reservoir rocks possess fissures to some extent (Barenblatt et al 1960;Warren and Root 1963;Kazemi et al 1976;Moench 1984;Lewandowska and Auriault 2013;Katsuki et al 2014;Vu et al 2014;Bennett et al 2015), and additional fissures may be induced by engineering activities (Abousleiman et al 2014;Carneiro 2009;Weng et al 2011;Foster and Mohammad Nejad 2013;Lamb et al 2013;Li et al 2013;Rahman and Rahman 2013a, b;Mohammadnejad and Khoei 2013;Zhang et al 2015;Yin 2013;White et al 2014;Tjioe and Borja 2015). Fissures have been observed in a variety of natural soils as well (Hu et al 2013;Vitone et al 2013a, b).…”

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