scholarly journals Estimating rock porosity and fluid saturation using only seismic velocities

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 391-404 ◽  
Author(s):  
James G. Berryman ◽  
Patricia A. Berge ◽  
Brian P. Bonner
Keyword(s):  
Seismic Reflection ◽  
Seismic Velocity ◽  
Compressional Wave ◽  
Elastic Parameter ◽  
Seismic Velocities ◽  
Transmission Tomography ◽  
Wave Velocities ◽  
Fluid Saturation ◽  
Wide Range ◽  
Geophysical Imaging

Evaluation of the fluid content in deep earth reservoirs or fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting. Interpretation of seismic velocities and amplitudes is based on theories of fluid‐saturated and partially saturated rocks that have been available since the 1950s. Here we present a new synthesis of the same physical concepts that uses compressional‐wave velocities together with shear‐wave velocities in a scheme that is much simpler to understand and apply yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution. The key idea revolves around the fact that the density and the Lamé elastic parameter λ are the only two parameters determining seismic velocities that also contain information about fluid saturation. At low enough frequencies, Gassmann's well‐known equations show that the shear modulus is independent of the fluid saturation level. We use these facts to construct saturation‐proxy and data‐sorting plots from seismic velocity data. The new method does not require reflectivity data, although it can use such information if available. The method can therefore be applied to a wide range of source–receiver configurations, including seismic reflection profiling (surface to surface), vertical seismic profiling (well to surface), and cross‐well seismic transmission tomography (well to well), since availability of reflection data is not a requirement.

A Discussion on natural strain and geological structure - Strain and anisotropy in rocks

1976 ◽  
Vol 283 (1312) ◽  
pp. 27-42 ◽  
Keyword(s):  
Magnetic Susceptibility ◽  
Shear Wave ◽  
Finite Strain ◽  
Preferred Orientation ◽  
Seismic Velocities ◽  
Magnetic Susceptibility Anisotropy ◽  
Wave Velocities ◽  
Natural Strain ◽  
Shear Wave Velocities ◽  
Wide Range

The evaluation of finite strain in naturally deformed rocks is restricted by the limited occurrence of good natural strain indicators which are also homogeneous with respect to the matrix. This problem is overcome by establishing the relation between measured finite strain and those physical behaviour characteristics of rocks that are dependent upon the anisotropy resulting from deformation. Accordingly, the strain measured from natural indicators is calibrated against ( degree of preferred orientation, (b) magnetic susceptibility anisotropy, and (r) seismic anisotropy. This _ will permit three approaches to be used independently for the evaluation of strain, provided that a minimal number of actual strains are available. The relation between measured strain and the degree of preferred orientation of layer silicates as revealed by X-ray transmission goniometry is established for a group of fine grained tectonites of dominantly planar fabric which have an average deformation ellipsoid of form 1.6:1 :,0.26. The strains measured from the degree of preferred orientation are in remarkable agreement with those measured from natural strain indicators. The measured deformation ellipsoids for a wide range of strains are also compared to the correlative ellipsoids of magnetic susceptibility anisotropy. The axes of both sets of ellipsoids are coincidental and the shape relationship between deformation and magnetic susceptibility ellipsoids is established by linear regression. Finally, the anisotropy of seismic velocities is determined by measuring the pseudocompressional velocity and two orthogonally polarized pseudo shear wave velocities for each of a minimum of nine non-coplanar directions. The velocity surfaces thus obtained define an elastic or seismic velocity anisotropy ellipsoid, the axes of which are also precisely coincidental with those of the finite deformation ellipsoid. The influence of rock fabric upon seismic velocities is such that for a rock which has undergone a principal finite extension of 135 % and a finite shortening of 65 %, the difference of compressional and shear wave velocities between these two directions is in the ratio 1.26:1 for P waves and 1.33:1 for S waves.

FLUID SATURATION EFFECTS ON DYNAMIC ELASTIC PROPERTIES OF SEDIMENTARY ROCKS

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 895-921 ◽  
Author(s):  
A. R. Gregory
Keyword(s):  
Shear Wave ◽  
Elastic Moduli ◽  
Sedimentary Rocks ◽  
Compressional Wave ◽  
Reflection Coefficients ◽  
High Porosity ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Fluid Saturation ◽  
Saturation Effects

The influence of saturation by water, oil, gas, and mixtures of these fluids on the densities, velocities, reflection coefficients, and elastic moduli of consolidated sedimentary rocks was determined in the laboratory by ultrasonic wave propagation methods. Twenty rock samples varying in age from Pliocene to early Devonian and in porosity from 4 to 41 percent were tested under uniform pressures equivalent to subsurface depths of 0 to 18,690 ft. Fluid saturation effects on compressional‐wave velocity are much larger in low‐porosity than in high‐porosity rocks; this correlation is strengthened by elevated pressures but is absent at atmospheric pressure. At a frequency of 1 MHz, the shear‐wave velocities do not always decrease when liquid pore saturants are added to rocks as theorized by Biot; agreement with theory is dependent upon pressure, porosity, fluid‐mineral chemical interactions, and the presence of microcracks in the cementing material. Experimental results support the belief that lower compressional‐wave velocities and higher reflection coefficients are obtained in sedimentary rocks that contain gas. Replacing pore liquids with gas markedly reduces the elastic moduli of rocks, and the effect is enhanced by decreasing pressure. As a rule, the moduli decrease as the porosity increases; Poisson’s ratio is an exception to the rule. Liquid and gas saturation in consolidated rocks can also be distinguished by the ratio of compressional and shear wave velocities [Formula: see text]. The potential diagnostic value of elastic moduli in seismic exploration may stimulate interest in the use of shear‐wave reflection methods in the field.

Seismic velocities of unconsolidated sands: Part 1 — Pressure trends from 0.1 to 20 MPa

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. E1-E13 ◽  
Author(s):  
Michael A. Zimmer ◽  
Manika Prasad ◽  
Gary Mavko ◽  
Amos Nur
Keyword(s):  
Shear Wave ◽  
Pressure Dependence ◽  
Glass Bead ◽  
Theoretical Models ◽  
Compressional Wave ◽  
P Wave ◽  
Seismic Velocities ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
Shear Wave Velocities

Knowledge of the pressure dependences of seismic velocities in unconsolidated sands is necessary for the remote prediction of effective pressures and for the projection of velocities to unsampled locations within shallow sand layers. We have measured the compressional- and shear-wave velocities and bulk, shear, and P-wave moduli at pressures from [Formula: see text] in a series of unconsolidated granular samples including dry and water-saturated natural sands and dry synthetic sand and glass-bead samples. The shear-wave velocities in these samples demonstrate an average pressure dependence approximately proportional to the fourth root of the effective pressure [Formula: see text], as commonly observed at lower pressures. For the compressional-wave velocities, theexponent in the pressure dependence of individual dry samples is consistently less than the exponent for the shear-wave velocity of the same sample, averaging 0.23 for the dry sands and 0.20 for the glass-bead samples. These pressure dependences are generally consistent over the entire pressure range measured. A comparison of the empirical results to theoretical predictions based on Hertz-Mindlin effective-medium models demonstrates that the theoretical models vastly overpredict the shear moduli of the dry granular frame unless the contacts are assumed to have no tangential stiffness. The models also predict a lower pressure exponent for the moduli and velocities [Formula: see text] than is generally observed in the data. We attribute this discrepancy in part to the inability of the models to account for decreases in the amount of slip or grain rotation occurring at grain-to-grain contacts with increasing pressure.

scholarly journals Predicting Missing Seismic Velocity Values Using Self-Organizing Maps to Aid the Interpretation of Seismic Reflection Data from the Kevitsa Ni-Cu-PGE Deposit in Northern Finland

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 529 ◽  
Author(s):  
Niina Junno ◽  
Emilia Koivisto ◽  
Ilmo Kukkonen ◽  
Alireza Malehmir ◽  
Markku Montonen
Keyword(s):  
Seismic Reflection ◽  
Seismic Velocity ◽  
Seismic Velocities ◽  
Self Organizing Map ◽  
Borehole Data ◽  
Self Organizing Maps ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Olivine Pyroxenite ◽  
Self Organizing

We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. The site has been the target of extensive seismic reflection surveys, which have revealed a series of reflections beneath the Kevitsa resource area. The interpretation of these reflections has been complicated by disparate borehole data, particularly because of the scarce amount of available sonic borehole logs and the varying practices in logging of borehole lithologies. SOM is an unsupervised data mining method based on vector quantization. In this study, SOM is used to predict missing seismic velocities from other geophysical, geochemical, geological, and geotechnical data. For test boreholes, for which measured seismic velocity logs are also available, the correlation between actual measured and predicted velocities is strong to moderate, depending on the parameters included in the SOM analysis. Predicted reflectivity logs, based on measured densities and predicted velocities, show that some contacts between olivine pyroxenite/olivine websterite-dominant host rocks of the Kevitsa disseminated sulfide mineralization—and metaperidotite—earlier extensively used “lithology” label that essentially describes various degrees of alteration of different olivine pyroxenite variants—are reflective, and thus, alteration can potentially cause reflectivity within the Kevitsa intrusion.

Laboratory measurements of seismic velocities in ocean sediments

1954 ◽  
Vol 222 (1150) ◽  
pp. 336-341 ◽  
Keyword(s):  
Deep Sea ◽  
Compaction Pressure ◽  
Vertical Gradient ◽  
Compressional Wave ◽  
Seismic Velocities ◽  
Laboratory Measurements ◽  
Ultrasonic Methods ◽  
Wave Velocities ◽  
Deep Sea Sediments ◽  
Sedimentary Layer

Laboratory measurements have been made of the compressional wave velocities in samples of deep-sea sediments using ultrasonic methods. The variation of velocity with compaction pressure has been determined. From the results it has been concluded that a vertical gradient of velocity exists in the sedimentary layer of the ocean.

PHYSICAL ANALYSIS OF DEEP SEA SEDIMENTS

Geophysics ◽  
1957 ◽  
Vol 22 (4) ◽  
pp. 779-812 ◽  
Author(s):  
George H. Sutton ◽  
Hans Berckhemer ◽  
John E. Nafe
Keyword(s):  
Grain Size ◽  
Wave Velocity ◽  
Deep Sea ◽  
Compressional Wave ◽  
Coarse Grained ◽  
Unconsolidated Sediments ◽  
Physical Analysis ◽  
Seismic Velocities ◽  
Compressional Wave Velocity ◽  
Wide Range

A sonic pulse system, similar to that used at Lamont Geological Observatory for seismic model experiments, was used aboard the Research Vessel VEMA during the summer of 1954 to determine high frequency seismic velocities in fresh deep sea sediment cores. Velocity profiles were obtained from 26 cores covering a wide range of lithologies and ages (Recent to Miocene). Density, porosity, median grain size, sorting, carbonate content, and salt content were also measured. The compressional wave velocity in the ocean‐bottom unconsolidated sediments studied is well represented by the equation: [Formula: see text] where v′=compressional wave velocity in km/sec ϕ=median grain size in phi units γ=percentage of HCl soluble material η=porosity. Many measurements gave velocities less than the velocity of sound in sea water. Most of the low carbonate samples followed a velocity‐porosity relation given by the Wood (1941) equation. The regression coefficient, −.44η, agrees well with the average slope of the Wood equation over the observed porosity range. High carbonate and large median grain size samples gave velocities above that predicted by the Wood equation. These higher velocities are explained as the combined result of shear strength and low effective porosity in the samples. The highest velocities were found in slowly deposited sediments. The degrees of sorting of the sediments had no observable effect on the seismic velocities except that unexplained variations were greater for more poorly sorted materials. No correlation between velocity and age was evident in the sediments studied. The effect of temperature, between 40 and 80°F. on compressional velocity in sediments may be explained by changes in elastic properties of the water fraction alone. The effect of compaction in the upper 15 or 20 feet of homogeneous sediments produced a change in seismic velocity not greater than 1 or 2 percent. Attenuation was greater in the coarse‐grained high‐velocity sediments than in sediments of smaller grain size.

scholarly journals One dimensional seismic velocity structure beneath Western Nepal

2002 ◽  
Vol 27 ◽  
Author(s):  
S. Rajaure
Keyword(s):  
Arrival Time ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Compressional Wave ◽  
S Wave ◽  
Time Data ◽  
Seismic Velocity Structure ◽  
One Dimensional ◽  
Wave Velocities

An attempt has been made to study the velocity structure of western Nepal. Arrival time data of local earthquakes occurring in that region were used to derive the model. A three layered velocity model both for the P- as well as S-wave velocity has been estimated. The compressional wave velocities in the first, second and the third layers have been estimated to be 5.53 km/sec. 6.29 km/sec and 8.13 km/sec respectively. Similarly the corresponding S-wave velocities are 3.18, 3.62, 4.66 km/sec respectively. The model for the Western Nepal and that for the Centre-East Nepal are almost same. The crust and the mantle beneath west and center-east are homogeneous.

Interpreting laboratory velocity measurements in partially gas‐saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (7) ◽  
pp. 1100-1109 ◽  
Author(s):  
Grant A. Gist
Keyword(s):  
High Frequency ◽  
Seismic Velocity ◽  
Pore Space ◽  
Rock Physics ◽  
Velocity Versus ◽  
Biot Theory ◽  
Seismic Velocities ◽  
Rock Types ◽  
Aspect Ratios ◽  
Wide Range

It is an old problem in rock physics that the saturation dependence of high‐frequency laboratory velocities does not match the Biot‐Gassmann theory commonly used to predict the effects of gas on seismic velocities. A new interpretation of laboratory velocity data shows that the saturation dependence is controlled by two previously published high‐frequency acoustic mechanisms: (1) a gas pocket model that describes pressure equilibration between liquid and gas‐saturated regions of the pore space, and (2) local fluid flow, induced by pressure equilibration in pores with different aspect ratios. When these two mechanisms are added to Biot theory, the result describes published velocity versus gas saturation data for a wide range of rock types. These two mechanisms are negligible at the lower frequencies of seismic data, so the saturation dependence of laboratory velocities cannot be used to predict the saturation dependence at seismic frequencies. The one laboratory measurement that is relevant for predicting the seismic velocity is the ultrasonic velocity of the dry rock. The dry‐rock velocities should be used in the Biot‐Gassmann theory to predict the full saturation dependence of the seismic velocities.

scholarly journals Measuring and Modeling of P- and S-Wave Velocities on Crustal Rocks: A Key for the Interpretation of Seismic Reflection and Refraction Data

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Hartmut Kern
Keyword(s):  
Seismic Reflection ◽  
Theoretical Calculations ◽  
Seismic Refraction ◽  
Central China ◽  
Seismic Velocities ◽  
S Wave ◽  
Velocity Anisotropy ◽  
Crustal Rocks ◽  
Wave Velocities

Lithologic interpretations of the earth crust from seismic wave velocities are non-unique so that inferences about composition can not be drawn. In order to evaluate how elastic properties of rock materials are controlled by lithology at in situ pressures and temperatures, compressional (Vp), shear wave velocities (Vs) and velocity anisotropy of crustal rocks were measured at conditions of greater depth. The first part deals with the interdependence of elastic wave propagation and the physical and lithological parameters. In the second part data from laboratory seismic measurements and theoretical calculations are used to interpret (1) a shallow seismic reflection line (SE Finland) and (2) a refraction profile of a deep crust (Central China). The comparison of the calculated velocities with the experimentally-derived in situ velocities of the Finnish crustal rocks give hints that microcracks have an important bearing on the in situ seismic velocities, velocity anisotropy and the reflectivity observed at relative shallow depth. The coupling of the experimentally-derived in situ velocities of P- and S-wave and corresponding Poisson's ratios of relevant exhumed high-grade metamorphic crustal rocks from Central China with respective data from seismic refraction profiling provided a key for the lithologic interpretation of a deep seismic crustal structure.

Seismic velocities of unconsolidated sands: Part 2 — Influence of sorting- and compaction-induced porosity variation

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. E15-E25 ◽  
Author(s):  
Michael A. Zimmer ◽  
Manika Prasad ◽  
Gary Mavko ◽  
Amos Nur
Keyword(s):  
Compressional Wave ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
Seismic Velocities ◽  
Porosity Variation ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
Grain Size Distributions ◽  
Gassmann Fluid Substitution ◽  
Water Saturated

Unaccounted-for porosity variation in unconsolidated sediments can cloud the interpretation of the sediment’s seismic velocities for factors such as fluid content and pressure. However, an understanding of the effects of porosity variation on the velocities can permit the remote characterization of porosity with seismic methods. We present the results of a series of measurements designed to isolate the effects of sorting- and compaction-induced porosity variation on the seismic velocities and their pressure dependences in clean, unconsolidated sands. We prepared a set of texturally similar sand and glass-bead samples with controlled grain-size distributions to cover an initial porosity range from 0.26 to 0.44. We measured the compressional- and shear-wave velocities and porosity of dry samples over a series of hydrostatic pressure cycles from [Formula: see text]. Over this rangeof porosities, the velocities of the dry samples at a given pressure vary by [Formula: see text]. However, the water-saturated compressional-wave velocities, modeled with Gassmann fluid substitution, demonstrate a consistent increase with decreasing porosity. In both the dry and water-saturated cases, the porosity trend at a given pressure is approximately described by the isostress (harmonic) average between the moduli of the highest-porosity sample at that pressure and the moduli of quartz, the predominant mineral component of the samples. Empirical power-law fit coefficients describing the pressure dependences of the dry bulk, shear, and constrained (P-wave) moduli from each sample also demonstrate no significant, systematic relationship with the porosity. The porosity dependence of the water-saturated bulk and constrained moduli is primarily contained in the empirical coefficient representing the modulus at zero pressure.

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