scholarly journals AMPLITUDE-DEPENDENT SPECTRA OF THE DAMPING OF A LONGITUDINAL WAVE IN DRY AND WATER-SATURATED SANDSTONE AT HYDROSTATIC PRESSURE

2018 ◽  
pp. 25-38
Author(s):  
E. I. Mashinskii
Keyword(s):  
Strain Amplitude ◽  
Wave Attenuation ◽  
Confining Pressure ◽  
Dominant Frequency ◽  
P Wave ◽  
Amplitude Dependence ◽  
P Wave Velocity ◽  
Waveform Distortion ◽  
Saturated Sample ◽  
Water Saturated

Data of experimental study of amplitude dependence of P-wave attenuation in the dry and watersaturatedsandstone under confining pressure of 10 MPa are presented. Measurements were conducted on samples  using the reflection method at a dominant frequency of the initial impulse of 1 MHz in the amplitude range   ~ (0,3 – 2,0)  10-6. P-wave attenuation spectra, 1( , ) P Q f  in the frequency range of 0,52 – 1,42  MHz in a dry and saturated sample have an appearance in the form of relaxation peak which depends on  the strain amplitude. In the saturated sandstone, attenuation is greater and the attenuation peak is shifted  to higher frequencies compared to the dry sandstone. With increasing amplitude, wave attenuation  decreases in dry sandstone by 4,5% and in saturated – by 9%. P-wave velocity practically doesn't depend  on the strain amplitude. The possible mechanism of discrete (intermittent) inelasticity which determines the waveform distortion and exerts influence on wave attenuation spectra is discussed. The received results  have fundamental and applied importance for seismics, acoustics and in Earth sciences.

Seismic attenuation: Effects of pore fluids and frictional‐sliding

Geophysics ◽  
1982 ◽  
Vol 47 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Kenneth W. Winkler ◽  
Amos Nur
Keyword(s):  
Fluid Flow ◽  
Strain Amplitude ◽  
Seismic Wave ◽  
Wave Attenuation ◽  
Velocity Ratio ◽  
Seismic Attenuation ◽  
P Wave ◽  
Amplitude Dependence ◽  
S Wave ◽  
Frictional Sliding

Seismic wave attenuation in rocks was studied experimentally, with particular attention focused on frictional sliding and fluid flow mechanisms. Sandstone bars were resonated at frequencies from 500 to 9000 Hz, and the effects of confining pressure, pore pressure, degree of saturation, strain amplitude, and frequency were studied. Observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts. Since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth, we infer that frictional sliding is not a significant source of seismic attenuation in situ. Partial water saturation significantly increases the attenuation of both compressional (P) and shear (S) waves relative to that in dry rock, resulting in greater P‐wave than S‐wave attenuation. Complete saturation maximizes S‐wave attenuation but causes a reduction in P‐wave attenuation. These effects can be interpreted in terms of wave induced pore fluid flow. The ratio of compressional to shear attenuation is found to be a more sensitive and reliable indicator of partial gas saturation than is the corresponding velocity ratio. Potential applications may exist in exploration for natural gas and geothermal steam reservoirs.

scholarly journals Metode Seismik dalam Pemodelan Fisis Letusan Gunung Lumpur Bledug Kuwu

2019 ◽  
Vol 2 (2) ◽  
pp. 61-66
Author(s):  
Ahmad Fauzi Pohan ◽  
Rusnoviandi Rusnoviandi
Keyword(s):  
Wave Velocity ◽  
Physical Modeling ◽  
Vertical Component ◽  
Dominant Frequency ◽  
P Wave ◽  
Physical Parameters ◽  
S Wave ◽  
Interesting Phenomenon ◽  
Central Java ◽  
P Wave Velocity

Aktivitas gunung lumpur Bledug Kuwu di Jawa  Tengah merupakan fenomena yang menarik dikaji menggunakan pemodelan fisis. Tujuan penelitian ini adalah mengetahui parameter dari medium gunung lumpur Bledug Kuwu. Adapun pemodelan fisis yang dilakukan dengan menggunakan media fisis akuarium berukuran 59 × 59 × 37,3 cm yang diisi material dari lumpur Bledug Kuwu. Sumber letusan dihasilkan dari tekanan kompresor yang dapat diatur kedalaman (10.5, 13, dan 15.5 cm) dan sudut (30o, 45o dan 60o) sumbernya. Sensor yang digunakan geophone komponen vertikal sebanyak 3 buah dengan durasi perekaman selama 5 dan 2,5 detik. Data diambil dengan frekuensi sampel 2 dan 4 kHz untuk masing-masing durasi perekaman. Konfigurasi sumber dan geophone dibuat sesuai dengan pemodelan fisisnya. Pengukuran desnsitas lumpur menunjukkan angka sebesar 1200 kg/m3. Berdasarkan hasil analisis seismogram model fisis diperoleh kecepatan perambatan gelombang-P pada medium lumpur Bledug Kuwu adalah sebesar 48,74 m/s,dan gelombang-S sebesar 28,14 m/s dengan frekuensi dominan antara 20 sampai 25 Hz.   Bledug Kuwu mud volcano activity in Central Java is an interesting phenomenon to be studied using both physical  modeling. The objective of this study was to determine the physical parameters of the medium of Bledug Kuwu. The Physical model was an aquarium with a dimension of 59 × 59 × 37.3 cm filled with Bledug Kuwu’s mud. The eruption source is generated by a compressor pressure that can be controled both the depth(10.5, 13, and 15.5 cm) and the angel of the source (30o, 45o and 60o). The resulting seismic signals were recorded by using 3 vertical component geophones for 10 and 5 seconds durations at a frequency of 2 and 4 kHz respectivel, mud density 1200 kg/m3 . The physical modeling shows that the P-wave velocity of the Bledug Kuwu’s medium is 48.7 m/s, S-wave velocity of Bledug Kuwu’s is 28,14 m/s  with a dominant frequency of 20 to 25 Hz.

scholarly journals A Modified Model for Predicting the Strength of Drying-Wetting Cycled Sandstone Based on the P-Wave Velocity

2020 ◽  
Vol 12 (14) ◽  
pp. 5655 ◽  
Author(s):  
Zhi-Hua Xu ◽  
Guang-Liang Feng ◽  
Qian-Cheng Sun ◽  
Guo-Dong Zhang ◽  
Yu-Ming He
Keyword(s):  
Wave Velocity ◽  
Confining Pressure ◽  
P Wave ◽  
Strength Prediction ◽  
Three Gorges ◽  
Cycle Number ◽  
Modified Model ◽  
The Three Gorges ◽  
P Wave Velocity ◽  
Confining Pressures

The drying-wetting cycles caused by operation of the Three Gorges Reservoir have considerable effect on the deterioration of reservoir bank rock mass, and the degradation of reservoir rock mass by the drying-wetting cycle is becoming obvious and serious along with the periodic operation. At present, the strength of the rock prediction research mainly focuses on the uniaxial strength, and few studies consider the drying-wetting effect and confining pressure. Therefore, in this paper, typical sandstone from a reservoir bank in the Three Gorges Reservoir area is taken as the research object, while the drying-wetting cycle test, wave velocity test and strength test are carried out for the research on the strength prediction of sandstone under the action of the drying-wetting cycle. The results show that the ultrasonic wave velocity Vp of the sandstone has an exponential function relation with the drying-wetting cycle number n, and the initial stage of drying-wetting cycles has the most significant influence on the wave velocity. Under different confining pressures, the compressive strength of sandstone decreases linearly with the increase of the drying-wetting cycle numbers, and the plastic deformation increases gradually. The damage variable of the sandstone has a power function relation with the increase of drying-wetting cycle numbers. A traditional strength prediction model based on P-wave velocity was established combined with the damage theory and Lemaitre strain equivalence hypothesis; in view of the defects of the traditional strength prediction model, a modified model considering both the drying-wetting cycle number and confining pressures was proposed, where the calculated results of the modified model are closer to the test strength value, and the prediction error is obviously decreased. This indicated that the modified model considering the drying-wetting cycle number and confining pressure is reasonable and feasible.

scholarly journals Experimental Measurement of the Transport Flow Path Aperture in Thermally Cracked Granite and the Relationship between Pore Structure and Permeability

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Kazumasa Sueyoshi ◽  
Tadashi Yokoyama ◽  
Ikuo Katayama
Keyword(s):  
Crustal Deformation ◽  
Confining Pressure ◽  
Flow Path ◽  
Pore Characteristics ◽  
Geological Processes ◽  
Saturated Sample ◽  
Transport Flow ◽  
Water Saturated ◽  
The Relationship ◽  
Direct Quantification

Fluid flow in rocks has a key role in many geological processes, such as in geothermal reservoirs and crustal deformation. Permeability is known to be dependent on porosity and flow path aperture, but direct quantification of pore structures is more difficult than direct estimation of permeability. The gas breakthrough method can be used to determine the radius of transport pores by using the gas pressure at which gas breaks through a water-saturated sample ( Δ P break ). In this study, we applied the gas breakthrough method under confining pressure to damaged granite, in order to evaluate the relationship between permeability and pore characteristics (i.e., porosity and transport flow path aperture) at pressures up to 30 MPa. The transport flow path aperture, permeability, and porosity of thermally cracked granite decrease with increasing confining pressure. We quantified the relationship between permeability and pore characteristics, which provides a better estimation of permeability by taking into account the fraction of hydraulically connected cracks.

Observations of wave velocity and attenuation in two‐phase media

Geophysics ◽  
1986 ◽  
Vol 51 (12) ◽  
pp. 2193-2199 ◽  
Author(s):  
G. W. Purnell
Keyword(s):  
Physical Model ◽  
Wave Velocity ◽  
Wave Attenuation ◽  
P Wave ◽  
Rubber Matrix ◽  
Two Phase ◽  
P Wave Velocity ◽  
Porosity And Permeability ◽  
Dispersion And Attenuation ◽  
Scattering Losses

The velocity and attenuation of a wave transmitted through a two‐phase material are functions of the material’s composition. In physical model experiments, I used suspensions of grains in a silicone rubber matrix to reduce or avoid uncertainties about framework elastic constants, porosity, and permeability that result from using fluid‐saturated grain frameworks. I varied the composition to produce materials that are useful in physical seismic modeling. In the tested suspensions, ultrasonic P-wave velocity, velocity dispersion, and attenuation all increase with grain concentration and frequency. I compared seven published mathematical models for wave propagation in two‐phase media. One given by Mehta most closely agrees with the P-wave velocities I observed. The agreement is sufficiently close to merit use of Mehta’s model in the design of physical model materials. The observed P-wave attenuation generally increases approximately linearly with frequency. This approximate linearity leads to reliable constant-Q estimates, ranging from 187 to 16 for grain concentrations from 0 to 0.49. I conclude that relative motion between the grains and the rubber matrix contributes most of the observed attenuation at lower concentrations, whereas scattering losses become much more important at higher concentrations and frequencies.

P‐wave velocity and permeability distribution of sandstones from a fractured tight gas reservoir

Geophysics ◽  
2002 ◽  
Vol 67 (1) ◽  
pp. 241-253 ◽  
Author(s):  
Helmut Dürrast ◽  
P. N. J. Rasolofosaon ◽  
Siegfried Siegesmund
Keyword(s):  
Velocity Distribution ◽  
Wave Velocity ◽  
Confining Pressure ◽  
P Wave ◽  
Tight Gas ◽  
Rock Fabric ◽  
The Core ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Tight Gas Reservoir

Fractures are an important fabric element in many tight gas reservoirs because they provide the necessary channels for fluid flow in rocks which usually have low matrix permeabilities. Several sandstone samples of such a reservoir type were chosen for a combined study of rock fabric elements and petrophysical properties. Geological investigations of the distribution and orientation of the fractures and sedimentary layering were performed. In addition, laboratory measurements were carried out to determine the directional dependence of the permeability and P‐wave velocities. Higher permeability values are generally in the plane of the nearly horizontal sedimentary layering with regard to the core axis. With the occurrence of subvertical fractures, however, the highest permeabilities were determined to be parallel to the core axis. Compressional wave velocities were measured on spherical samples in more than 100 directions to get the VP symmetry without prior assumptions. Below 50 MPa confining pressure, all samples show a monoclinic symmetry of the P wave velocity distribution, caused by sedimentary layering, fractures, and crossbedding. At higher confining pressure, sedimentary layering is approximately the only effective fabric element, resulting in a more transverse isotropic VP symmetry. Using the geological‐petrophysical model introduced here, the complex symmetry of the VP distributions can only be explained by the rock fabric elements. Furthermore, water saturation increases the velocities and decreases the anisotropy but does not change VP symmetry. This indicates that at this state, all fabric elements, including the fractures, have an influence on P‐wave velocity distribution.

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