ABSTRACT:

Aiming at constructing the relation between rock permeability and non-hydrostatic compressive stresses within pre yield range, the authors have experimentally investigated the change in permeability perpendicular to the bedding planes kp and that parallel to the bedding planes k, in Kimachi sandstone during the application of hydrostatic and non-hydrostatic compressive stresses. It was found that, for this rock under non-hydrostatic stresses, both kp and k, can be approximately related to effective average stress ('A), without appreciable errors.However, kp - бA

I.
INTRODUCTION

Fluids have significant effects on all crustal processes by transferring heat and masses, enhancing chemical reactions and exerting pore pressure on the crustal rocks. (e.g., Moore, 1989; Rice, 1992), with important consequences in seismotectonics, economic geology, petroleum geology, aqueous geochemistry, and geotechnical engineering. To model fluid percolation processes in the crustal rocks, permeability is a necessary quantity that physically depends on stresses. Numerous laboratory experiments have revealed that application of hydrostatic pressure results in a permeability reduction (e.g. Brace et al., 1968; Zhang et al., 1993; Takahashi et al., 1991). Motivated by laboratory measurements and observations, a few models have been proposed (Tiller. 1951; Gangi; 1978; Walsh, 1981), which relate the permeability to hydrostatic pressure. Rice (1992) and David (1994) coupled Tiller's correlation into their analyses where the hydrostatic pressure in the models was replaced simply by average stress and the permeability was treated as an isotropic quantity. However, in-situ nonhydrostatic (Howard and Fast, 1970). Recent permeability measurements (Takahashi et al., 1993; Bruno, 1994; Skoczylas and Henry, 1995; King et al., 1993; King et al., 1997; Li et al., 2000) and simulations (Bruno, 1994; Banks et al.. 1996) have illustrated the importance of stress anisotropy on both the porous sandstones and crystalline granites. In order to assess the feasibility of the replacement and treatment by Rice (1991) and David (1994), the authors have experimentally investigated the change in permeability perpendicular and parallel to the bedding planes of Kimachi sandstone during loading of hydrostatic and non-hydrostatic stresses within pre-yield range.

2.
TEST TECHNIQUES

The tests were conducted using a system that was constructed by combining a Mogi-type true triaxial compressive apparatus with permeability measurement device (transient pulse technique). This true triaxial compressive apparatus enabled three principal compressive stresses to be applied independently in load or dispIacement control mode. One of the characteristics of this loading apparatus was that it exerted two principal stresses by rigid pistons and the other stress directly by oil pressure. Fig.1 schematically shows the experimental arrangement of a rectangular prismatic specimen (70x35x35mm). We define the stress in the vertical direction as б one of the lateral stresses exerted by the pistons as б and the stress, directly by oil pressure, as б; As shown in Fig.1, the specimen (I) was jacketed with silicone rubber-copper foil composite (5), 0.05mm thick Teflon sheet and copper foil were placed between the specimen (I).

This content is only available via PDF.
You can access this article if you purchase or spend a download.