Preface 1. Basic tools 2. Elasticity and Hooke's law 3. Seismic wave propagation 4. Effective media 5. Granular media 6. Fluid effects on wave propagation 7. Empirical relations 8. Flow and diffusion 9. Electrical properties Appendices.

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The Rock Physics Handbook: Tools for Seismic Analysis of Porous Media

We consider the response of a Newtonian fluid, saturating the pore space of a rigid isotropic porous medium, subjected to an infinitesimal oscillatory pressure gradient across the sample. We derive the analytic properties of the linear response function as well as the high- and low-frequency limits. In so doing we present a new and well-defined parameter Λ, which enters the high-frequency limit, characteristic of dynamically connected pore sizes. Using these results we construct a simple model for the response in terms of the exact high- and low-frequency parameters; the model is very successful when compared with direct numerical simulations on large lattices with randomly varying tube radii. We demonstrate the relevance of these results to the acoustic properties of non-rigid porous media, and we show how the dynamic permeability/tortuosity can be measured using superfluid 4He as the pore fluid. We derive the expected response in the case that the internal walls of the pore space are fractal in character.

Theory of dynamic permeability and tortuosity in fluid-saturated porous media

Responding to the latest developments in rock physics research, this popular reference book has been thoroughly updated while retaining its comprehensive coverage of the fundamental theory, concepts, and laboratory results. It brings together the vast literature from the field to address the relationships between geophysical observations and the underlying physical properties of Earth materials - including water, hydrocarbons, gases, minerals, rocks, ice, magma and methane hydrates. This third edition includes expanded coverage of topics such as effective medium models, viscoelasticity, attenuation, anisotropy, electrical-elastic cross relations, and highlights applications in unconventional reservoirs. Appendices have been enhanced with new materials and properties, while worked examples (supplemented by online datasets and MATLAB® codes) enable readers to implement the workflows and models in practice. This significantly revised edition will continue to be the go-to reference for students and researchers interested in rock physics, near-surface geophysics, seismology, and professionals in the oil and gas industries.

The Rock Physics Handbook

Methane has been detected in several cores of rapidly deposited (> 50 m/my) deep sea sediments. Other gases, such as carbon dioxide and ethane, are commonly present but only in minor and trace amounts, respectively. The methane originates predominantly from bacterial reduction of CO2, as indicated by complimentary changes with depth in the amount and isotopic composition of redox-linked pore water constituents: sulfate-bicarbonate and bicarbonate-methane.

The Origin and Distribution of Methane in Marine Sediments

[1] Mud volcanism and diapirism have puzzled geoscientists for ∼2 centuries. They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios. This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described. Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases. Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input). The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important. In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction-driven pore fluid expulsion of the accretionary wedge. Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000RG000093

Significance of mud volcanism

This paper considers a mathematical model to describe the propagation of low‐amplitude waves in saturated sediments. Losses due to inelasticity of the skeletal frame and to motion of the pore fluid relative to the frame are both accounted for, and each is found to be significant in a different frequency range. The theory shows favorable agreement with experimental results where available for both sands and finer‐grained sediments over a wide range of frequencies.

Wave Attenuation in Saturated Sediments

Reflection and refraction of plane acoustic waves are studied for the case where the sediment is modeled as a porous viscoelastic medium. The model is based on the classical work of Biot which predicts that three different kinds of attenuating body waves may propagate in the sediment. As a consequence when homogeneous plane waves in water are incident to a water‐sediment interface, three nonhomogeneous waves are generated in the sediment. In these waves the direction of phase propagation and the direction of maximum attenuation are not the same and particle motion follows an elliptic path. Moreover, the velocity and attenuation of the refracted waves become dependent on the angle of incidence and no “critical” angle occurs. Numerical examples show that the reflectivity of a porous viscoelastic model differs significantly from the case where the sediment is modeled as a viscoelastic solid with constant complex modulus. Finally, because of the frequency dependence of reflectivity in the porous model, it is ...

Reflection of acoustic waves at a water–sediment interface

An acoustic model for unconsolidated sediments is used to study velocity, attenuation, and reflection in ocean sediments. The model predicts attenuation and wave velocity on the basis of physical parameters such as porosity, grain size, permeability, and effective stress. Two mechanisms for energy loss are included in the model; one accounts for intergranular losses in the skeletal frame and the other for viscous losses in the porewater as it moves relative to the frame. As a result, in certain sediments such as sands and silts, attenuation is found to vary in a manner quite different from the usual dependency on the first power of frequency that is almost universally assumed. Furthermore, the amplitudes of reflected and refracted waves at boundaries between water and sediment or between sediment layers become frequency dependent. In the immediate vicinity of such boundaries, a significant amount of energy may be lost owing to the generation of a second kind of dilatational wave with extremely high attenuation.The model is able to handle variations in a variety of different physical parameters such as overburden stress, fluid compressibility, and stiffness of the sediment frame owing to lithification. For this reason it is well suited for use in predicting changes in velocity and attenuation with depth in real sediments where nonhomogeneous changing conditions are the rule and simple extrapolation of experimental data is not possible.

Acoustic Waves in Ocean Sediments

In order to better understand the occurrence and distribution of gas hydrates and their effects on acoustic and thermal measurements in ocean sediments, the authors have conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate. The most significant result of these studies is that the formation of hydrate tends to cause a decrease in the thermal conductivity of a sediment. This is contrary to what might be expected on the basis of an analogy with the behavior of frozen sediment and implies that some thermal gradients assumed in earlier studies of in situ deposits of hydrate may be too small. Other results of the research based on measurements of acoustic wave velocity confirm that both pure water and water-bearing sediment are converted to a stiff elastic mass by the formation of a sufficient quantity of hydrate. This clearly establishes the potential for a sharp acoustic impedance contrast at the boundary of a region of sediment containing a significant quantity of hydrate.

Physical properties of sediments containing gas hydrates

Natural gas and water combine to form an ice-like substance called a gas hydrate under certain conditions of temperature and pressure These conditions appear to exist over large areas of the ocean bottom An experiment is described in which artificially formed gas hydrate in shown to cause marked increase in acoustic wave velocity suggesting that anomalously high velocities observed in situ in gassy sediments may indicate the presence of such hydrates

Robert D. Stoll

Papers

Wave Attenuation in Saturated Sediments

Reflection of acoustic waves at a water–sediment interface

Acoustic Waves in Ocean Sediments

Physical properties of sediments containing gas hydrates

Anomalous wave velocities in sediments containing gas hydrates