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ABSTRACT: We measured the extensional‐mode attenuation and Young's modulus in a porous sample made of sintered borosilicate glass at microseismic to seismic frequencies (0.05–50 Hz) using the forced oscillation method. Partial saturation was achieved by water imbibition, varying the water saturation from an initial dry state up to ∼99%, and by gas exsolution from an initially fully water‐saturated state down to ∼99%. During forced oscillations of the sample effective stresses up to 10 MPa were applied. We observe frequency‐dependent attenuation, with a peak at 1–5 Hz, for ∼99% water saturation achieved both by imbibition and by gas exsolution. The magnitude of this attenuation peak is consistently reduced with increasing fluid pressure and is largely insensitive to changes in effective stress. Similar observations have recently been attributed to wave‐induced gas exsolution–dissolution. At full water saturation, the left‐hand side of an attenuation curve, with a peak beyond the highest measured frequency, is observed at 3 MPa effective stress, while at 10 MPa effective stress the measured attenuation is negligible. This observation is consistent with wave‐induced fluid flow associated with mesoscopic compressibility contrasts in the sample's frame. These variations in compressibility could be due to fractures and/or compaction bands that formed between separate sets of forced‐oscillation experiments in response to the applied stresses. The agreement of the measured frequency‐dependent attenuation and Young's modulus with the Kramers–Kronig relations and additional data analyses indicate the good quality of the measurements. Our observations point to the complex interplay between structural and fluid heterogeneities on the measured seismic attenuation and they illustrate how these heterogeneities can facilitate the dominance of one attenuation mechanism over another. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the past few decades, great attention has been focused on uncovering the physics of seismic wave attenuation in fluid-saturated rocks. However, the relationship among many variables affecting attenuation is still not completely clear. For instance, although the role of strain in enhancing friction dissipation is relatively well known for dry rocks, it remains unclear how and how much it affects attenuation in fluid-saturated rocks. We experimentally measured attenuation in the extensional mode in Berea sandstone at strains between 7.8×10-7 and 1.9×10-5, and at frequencies in the seismic bandwidth (1-100 Hz). These strains were similar to those typically observed in seismic exploration (~10-6). We also measured the transient fluid pressure caused when a stepwise stress was applied resulting in such strains. For the studied strain range, our results indicated that: (1) the overall attenuation in dry Berea sandstone increased linearly with strain, (2) the frequency-dependent component of attenuation, which was associated with fluid saturation, was approximately insensitive to strain, and (3) the overall attenuation can be considered as a sum of a frequency-independent and a frequency-dependent components. [ABSTRACT FROM AUTHOR]

ABSTRACT A Seismic Wave Attenuation Module is developed to experimentally measure the attenuation in extensional-mode QE−1 and the Young's modulus of copper jacketed, 60 mm long and 25.4 mm in diameter samples in a gas medium (Paterson) rig. The new module is suitable for natural rock samples and was tested under confining pressure up to 50 MPa and room temperature. The module is designed to operate at a strain < 10−6, for which rocks behave linearly. To calculate attenuation, both the applied force and the bulk shortening of the sample are measured employing linear variable differential transformers. This technique allows measuring samples with a high degree of heterogeneity. Attenuation at low-seismic frequencies (10−2-102 Hz) is obtained for rocks at dry and various saturation conditions. We present a series of measurements on Berea sandstone in a room-dry condition and saturated with different fluids: water and glycerine solutions with viscosities of 10 cP and 22 cP, respectively, at a confining pressure of 10 MPa and with a pore pressure of 1 MPa. The accuracy of the attenuation data expressed as a phase shift is 0.0019 rad. [ABSTRACT FROM AUTHOR]