EFFECTS OF PORE AND DIFFERENTIAL PRESSURE ON COMPRESSIONAL WAVE VELOCITY AND QUALITY FACTOR IN BEREA AND MICHIGAN SANDSTONES

Compressional-wave velocity (V-P) and quality factor (Q(P)) have been measured in Berea and Michigan sandstones as a function of confining p ressure (P-c) to 55 MPa and pore pressure (P-p) to 35 MPa. V-P values are lower in the poorly cemented, finer grained, and microcracked Bere a sandstone. Q(P) values are affected to a lesser extent by the micros tructural differences, A directional dependence of Q(P) is observed in both sandstones and can be related to pore alignment with pressure, V -P anisotropy is observed only in Berea sandstone, V-P and ep increase with both increasing differential pressure (P-d = P-c - P-p) and incr easing P-p. The effect of P-p on ep is greater at higher P-d. The resu lts suggest that the effective stress coefficient, a measure of pore s pace deformation, for both V-P and Q(P) is less than 1 and decreases w ith increasing P-d.