ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
For clastic silicate rocks sampled from a Rotliegendes well core the velocities vP and vs were obtained at 10 pressures up to 300 MPa using a pulse-transmission technique. The porosities of all rocks (57 sandstones, 26 siltstones, five claystones) ranged from 0.01 and 0.15 by volume fraction, and the clay content varied from less than 0.01 to 0.88 by volume fraction. Both velocities increase with pressure. In the low-pressure range the rate of increase is large, non-linear and is greater for vP than for vs. Above 120 MPa both velocities increase linearly. Velocities, porosity, and clay content were fitted by least-squares regression for pressures of 8, 24, 60, 120, 200, and 300 MPa. The fractional effect of porosity and clay on the velocities for dry clastic silicate rocks can be described (above 120 MPa) by v=A - Bø-CClay, where v is the velocity of the P-wave or S-wave, φ is the volume fraction of pores, and Clay is the volume fraction of clay. From this it is possible to obtain pressure-dependent velocity functions v=a+pb - c exp (-dp), where a is the crack-free velocity, linear in porosity and clay, b is the velocity slope under high pressure, a-c is the zero-pressure velocity, and d is related to closure of cracks.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1992.tb00843.x
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