ABSTRACT

INTRODUCTION

Rocks can generally exhibit viscoelastic properties, depending on the loading conditions, the environment and the time scale of interest. For fluid saturated rocks, the coupling effects between pore pressure diffusion and the rock matrix deformation give rise to similar but different time dependent phenomena [1-3]. Within the limit of infinitesimal strain theory, rocks have been modeled as linear viscoelastic or poroelastic material, but rarely as poroviscoelastic [4]. With the simultaneous existence of poroand visco-elasticity, the response of fluid saturated rocks exhibits two time scales. The characteristic time of a viscoelastic response is an apparent material property; that for poroelasticity is dependent not only on the material itself, but also on a global geometry length scale. Although the coexistence of poroand visco-elastic phenomena has been observed in the laboratory and in the field for a range of rock types [5,6], no attempt was made to isolate and to quantify them by the simultaneous modeling of both of these mechanisms. This paper presents an interpretation of Biot's poroviscoelasticity theory [7] based on micromechanics. To demonstrate the impact of the combined poro and visco-elastic effects, problems of a borehole under plane strain deformation are examined.

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