The Variation of the Elastic Constants of Rocks With Frequency*

Intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability, fluid properties, and saturation. However, in order to use attenuation as an attribute to extract information on rock/fluid properties from seismic data, experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies. An appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method, but technical challenges kept this technique from being widely used. There is a need for the standardization of devices employing this method, and a comparison of existing setups is a step towards it. Here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency‐dependent attenuation in fluid‐saturated and/or dry reservoir rocks under small strains (10−8–10−5). We list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one. We also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far.

Section: Techniques Of Attenuation Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks

Subramaniyan

Quintal

Tisato

et al. 2014

“…Ricker deduced that the absorbtion constant for a travelling wave was proportional to the square of the frequency (i.e. Generally speaking, the errors associated with laboratory measurements put a poorer limit on any dispersion present, although Bruckshaw and Mahanta (1954) did find an increase of 2 y. in the Young's Modulus of a rock over the range 40-120 c/s. a constant 'Q').…”

Section: Experimentsonabsorbtionmentioning

confidence: 99%

A Discussion on the Nature and Magnitude of Elastic Absorbtion in Seismic Prospecting*

O'Brien

1961

Laboratory measurements indicate that seismic absorbtion in sedimentary rocks lies in the range 0.1 to 1.0 decibel per wavelength. Field measurements on the amplitude attenuation of direct, reflected and refracted pulses give values consistent with this. If the absorption is linear, dispersion must occur. If it occurs field measurements show that it must be less than 1% over the frequency range 20 c/s to 20 kc/s. Seismic pulses broaden so slowly with distance that, if the absorbtion is linear it must be less than that measured in the laboratory by a factor of at least ten. This is inconsistent with the amplitude measurements and would mean that emplaced rocks are more perfectly elastic than steel. Seismic absorbtion must therefore be non‐linear. It is assumed that, for large values of Q, the non‐linear equation of motion may be linearised (Knopoff and MacDonald, 1958) and Fourier synthesis used. If this is valid, then the attenuation per unit distance must be practically independent of frequency and dispersion must be negligible. Whatever mechanism is acting it must produce an attenuation of roughly one decibel per 1000 feet and a pulse broadening of about 1–2% in the same distance. It is extremely desirable to make more field and laboratory experiments to determine the physical mechanism by which absorbtion takes place.

“…There is a corollary of these results which is of considerable practical importance. Birch and Bancroft (1938) observed no variation in Young's modulus over the frequency range from 120-4500 c.p.s., Bruckshaw and Mahanta (1954) observed an increase of about 2% between 40 and 120 c.p.s., Peselnick and Outerbridge (1961) found that Young's modulus was constant within 2% over the frequency range from 4 c.p.s. to IO Mc.p.s.…”

Section: Effect Of Water Saturation On the Velocitymentioning

confidence: 89%

A Laboratory Investigation Into the Elastic Properties of Limestones*

Koefoed

Oosterveld

Alons

1963

Measurementshave been made by the resonance method of the longitudinal bar velocities and the transverse velocities of 29 chemically pure limestones of varying porosity. The elastic anisotropy factors of the limestones were found to vary over a wide range. For the isotropic limestones, both the longitudinal and the transverse velocity decrease in general with increasing porosity, but this decrease is somewhat irregular. The irregularities in the velocity were found to correlate with the irregularities in the electrical resistivity of the samples when saturated with a standard salt solution, and with those in their tensile strength. This correlation indicates an influence on the velocity of the geometry of the pore space of the rock and of its counterpart: the geometry of the matrix. Indications have been obtained that a condition akin to weathering may be partly responsible for the irregularities in the velocities. Saturating the samples with water was found to result in a decrease of their velocities. An investigation of the available literature, combined with measurements made in our laboratory with a low frequency pulse method, indicate that water saturation results in a decrease of the velocity at low frequencies and in an increase of the velocity at high frequencies.Since other investigators have shown that the velocities of dry rock are hardly effected by the frequency, one must conclude that the velocities of water saturated rock do change appreciably with frequency. The values of Poisson's ratio were found to decrease with increasing porosity, but more so for the dry samples than for the water saturated samples. A possible explanation is that the cross-contraction and cross-dilatation is partly consumed in changing the diameters of the pores, thus reducing the effect on the outer diameter of the sample; this mechanism would be partly resisted by water filling the pores.In an earlier paper from this laboratory (Kuiper, van Rijen and Koefoed, 1959) laboratory determinations of the elastic properties of 13 different limestones were reported on. These measurements have now been extended in the following respects.