scholarly journals The influence of clay-sized particles on seismic velocity for Canadian Arctic permafrost

1984 ◽  
Vol 21 (1) ◽  
pp. 19-24 ◽  
Author(s):  
M. S. King
Keyword(s):  
Wave Velocity ◽  
Seismic Velocity ◽  
Pore Space ◽  
Canadian Arctic ◽  
Clay Content ◽  
Compressional Wave ◽  
Specimen Preparation ◽  
Compressional Wave Velocity ◽  
Confining Stress ◽  
Ice Content

Seismic-wave velocities have been measured on 37 unconsolidated permafrost samples as a function of temperature in the range -16 to +5 °C. The samples, taken from a number of locations in the Canadian Arctic islands, the Beaufort Sea, and the Mackenzie River valley, were tighty sealed immediately upon recovery in several layers of polyethylene film and maintained in their frozen state during storage, specimen preparation, and until they were tested under controlled environmental conditions. During testing, the specimens were subjected to a constant hydrostatic confining stress of 0.35 MPa (50 psi) under drained conditions. At no stage was a deviatoric stress applied to the permafrost specimens. The fraction of clay-sized particles in the test specimens varied from almost zero to approximately 65%. At temperatures below -2 °C the compressional-wave velocity was observed to be a strong function of the fraction of clay-sized particles, but only a weak function of porosity. At temperatures above 0 °C the compressional-wave velocity was observed to be a function only of porosity, with virtually no dependence upon the fraction of clay-sized particles. Calculation of the fractional ice content of the permafrost pore space from the Kuster and Toksöz theory showed that for a given fraction of clay-sized particles the ice content increases with an increase in porosity. It is concluded that the compressional-wave velocity for unconsolidated permafrost from the Canadian Arctic is a function of the water-filled porosity, irrespective of the original porosity, clay content, or temperature.

EFFECT OF POROSITY, GRAIN CONTACTS, AND CEMENT ON COMPRESSIONAL WAVE VELOCITY THROUGH SYNTHETIC SANDSTONES

Geophysics ◽  
1961 ◽  
Vol 26 (1) ◽  
pp. 77-84 ◽  
Author(s):  
Andris Viksne ◽  
Joseph W. Berg ◽  
Kenneth L. Cook
Keyword(s):  
Wave Velocity ◽  
Atmospheric Pressure ◽  
Cement Content ◽  
Pore Space ◽  
Compressional Wave ◽  
Velocity Measurements ◽  
Compressional Wave Velocity ◽  
Ottawa Sand ◽  
Wave Velocities ◽  
The Relationship

Compressional wave velocities through 36 synthetic sandstone cores were measured and related to several of their physical properties, namely, porosity, manufacturing pressure, grain contacts, and amount of cement. The cores were composed of Ottawa sand grains averaging 0.12 mm in diameter and commercial Grefco cement; the manufacturing pressure was varied from 4,000 to 10,000 psi; the cement content by volume was varied from 10 to 100 percent; the effective porosities ranged between 2.1 and 30.4 percent; and the compressional wave velocities ranged between 9,170 and 17,420 ft.sec. All velocity measurements were taken at room temperature and atmospheric pressure using cores that contained only air in the pore space. The results are presented in graphic form, showing the relationship between the compressional wave velocity and manufacturing pressure, porosity, and cement content. For Grefco cement contents between 10.0 and 17.5 percent, the compressional wave velocity is controlled by the manufacturing pressure and the porosity. A change in manufacturing pressure of 1,000 psi changed the compressional wave velocity by one percent for cores having porosities of about 23 percent and by about 3 percent for cores having porosities of about 28 percent. A decrease in porosity of one percent increased the velocity by an average of 1.4 percent for effective porosities between 23 and 26 percent. The velocity is also dependent, to a great extent, on the number of grain contacts which is intimately associated with the manufacturing pressure, and the cement content which is intimately associated with the porosity. For cement contents greater than 17.5 percent by volume, the sand grains float in the cement, and the analogy between the synthetic sandstone cores and natural sandstones is questionable.

Effects of pore and differential pressure on compressional wave velocity and quality factor in Berea and Michigan sandstones

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1163-1176 ◽  
Author(s):  
Manika Prasad ◽  
Murli H. Manghnani
Keyword(s):  
Quality Factor ◽  
Wave Velocity ◽  
Pore Space ◽  
Confining Pressure ◽  
Compressional Wave ◽  
Differential Pressure ◽  
Berea Sandstone ◽  
Compressional Wave Velocity ◽  
Stress Coefficient ◽  
Space Deformation

Compressional‐wave velocity [Formula: see text] and quality factor [Formula: see text] have been measured in Berea and Michigan sandstones as a function of confining pressure [Formula: see text] to 55 MPa and pore pressure [Formula: see text] to 35 MPa. [Formula: see text] values are lower in the poorly cemented, finer grained, and microcracked Berea sandstone. [Formula: see text] values are affected to a lesser extent by the microstructural differences. A directional dependence of [Formula: see text] is observed in both sandstones and can be related to pore alignment with pressure. [Formula: see text] anisotropy is observed only in Berea sandstone. [Formula: see text] and [Formula: see text] increase with both increasing differential pressure [Formula: see text] and increasing [Formula: see text]. The effect of [Formula: see text] on [Formula: see text] is greater at higher [Formula: see text]. The results suggest that the effective stress coefficient, a measure of pore space deformation, for both [Formula: see text] and [Formula: see text] is less than 1 and decreases with increasing [Formula: see text].

EFFECT OF BRINE‐GAS MIXTURE ON VELOCITY IN AN UNCONSOLIDATED SAND RESERVOIR

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 882-894 ◽  
Author(s):  
S. N. Domenico
Keyword(s):  
Uniform Distribution ◽  
Wave Velocity ◽  
Pore Space ◽  
Compressional Wave ◽  
Fluid Injection ◽  
Injection Technique ◽  
Compressional Wave Velocity ◽  
Modified Technique ◽  
Uniform Size ◽  
Unconsolidated Sand

Gas in an unconsolidated sand reservoir encased in shale often results in a dramatic increase in amplitude of the seismic reflection from the shale/gas‐sand interface. Unfortunately, reflection amplitude appears not to vary linearly with water (brine) saturation, and thus cannot be used to estimate gas quantity. Previously presented theoretical velocity computations, for a Tertiary sedimentary section, which demonstrate that compressional‐wave velocity in an unconsolidated gas sand varies nonlinearly with brine saturation, qualitatively agree with laboratory velocity measurements on a sand specimen composed of pure quartz grains. However, significant departure of measured and theoretical velocities at high brine saturation indicates that the technique for partially saturating the sand specimen by flowing a gas‐brine mixture through the specimen does not provide a sufficiently uniform distribution. The gas preferentially seeks larger pores. In a subsequent experiment on a specimen composed of spherical glass beads of nearly uniform size, the previous, as well as a modified, fluid injection technique was used. For the latter, brine only was injected into the pore space previously filled with a mixture of gas and brine in nearly equal proportions. This resulted in a more uniform distribution of the gas‐brine mixture. For approximately equal brine saturations, this modified technique resulted in a measured compressional‐wave velocity approximately one‐half of the velocity measured for the previously used fluid injection technique. This result implies that if the gas‐brine mixture is uniformly distributed in a reservoir, the fluid compressibility is the weighted‐by‐volume average of the constituent compressibilities.

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