Fluid pressure response to undrained compression in saturated sedimentary rock

Abstract

The pore pressure response of saturated porous rock subjected to undrained compression at low effective stresses are investigated theoretically and experimentally. This behavior is quantified by the undrained pore pressure buildup coefficient, [Formula: see text] where [Formula: see text] is fluid pressure, [Formula: see text] is confining pressure, and [Formula: see text] is the mass of fluid per unit bulk volume. The measured values for B for three sandstones and a dolomite arc near 1.0 at zero effective stress and decrease with increasing effective stress. In one sandstone, B is 0.62 at 13 MPa effective stress. These results agree with the theories of Gassmann (1951) and Bishop (1966), which assume a locally homogeneous solid framework. The decrease of B with increasing effective stress is probably related to crack closure and to high‐compressibility materials within the rock framework. The more general theories of Biot (1955) and Brown and Korringa (1975) introduce an additional parameter, the unjacketed pore compressibility, which can be determined from induced pore pressure results. Values of B close to 1 imply that under appropriate conditions within the crust, zones of low effective pressure characterized by low seismic wave velocity and high wave attenuation could exist. Also, in confined aquifer‐reservoir systems at very low effective stress states, the calculated specific storage coefficient is an order of magnitude larger than if less overpressured conditions prevailed.

Hydraulic diffusivity of fault gouge zones and implications for thermal pressurization during seismic slip

“…It must be stressed that the use of Eq. (2) assumes that all constituent minerals have the same compressibility (β s ), which may not strictly be true for rocks containing both quartz and phyllosilicates (Green and Wang, 1986). Published nitrogen compressibility (β f ) data (at room temperature and Pp = 20 MPa, β f = 4.32 × 10 −8 Pa −1 ), a value of 1.2 × 10 −11 Pa −1 for compressibility of mica (β s ) independent of pressure (Birch, 1966) and the bulk framework compressibility data (β b ) (Fig.…”

Mechanical Properties, Slip and Nucleation of the 1999 Chia-Yi Earthquake: the Question of Static Stress Influence from the 1999 Chi-Chi Earthquake

“…3. In fact, since it has often been reported that most rocks have similar mechanical properties, i.e., 0.6 ≤ µ ≤ 0.85 (Byerlee 1978) and 0.7 ≤ β ≤ 1.0 (Green and Wang 1986;Berge et al 1993), which correspond to the small rectangular area in Fig. 3, we can narrow down the feasible mechanical conditions for static stress to have been a trigger to the area where the small rectangular and the white areas intersect.…”

“…Changes in the Coulomb failure stress ( ) ∆CFS transferred from the ChiChi earthquake onto the hypocenter of the Chia-Yi earthquake with various friction ( µ ) and Skempton's coefficients ( β ). The white area indicates the region with positive ∆CFS values, while the rectangular area confined by the dashed lines defines µ and β for most rocks (Byerlee 1978;Green and Wang, 1986;Berge et al 1993). The optimal µ and β values at the site of the Chia-Yi event, therefore, fall in the region where the rectangular and the white areas intersect with an average ∆CFS value of about 0.1 bar.…”

Pore-fluid effects on seismic waves in vertically fractured earth with orthotropic symmetry

“…The text by Wang (2000) contains tables of values taken from many sources, some of which are quoted here in Table 4. One series of related contributions on the same subject includes papers by Green and Wang (1986), Berge et al (1993), Hart andWang (1995, 2001). A very useful Ph.…”