ABSTRACT Fractured rock is often modelled under the assumption of perfect fluid pressure equalization between fractures and equant porosity. This consistent with laboratory estimates characteristic squirt‐flow frequency. However, these measurements are carried out on samples which do not contain large fractures. We consider coupled motion two scales: grain scale controls behaviour in experiments fracture scale. Our approach reproduces generally accepted results low‐ high‐frequency limits....

Analysis of seismic data suggests that hydrocarbon deposits are often associated with higher than usual values attenuation, but this is generally ignored during amplitude versus offset (AVO) analysis. The effect can be modelled equivalent medium theory based on the squirt flow concept, excess attenuation strong velocity dispersion. Consequently, when we study reflections from interface between such an and elastic overburden find reflection coefficient varies frequency. impact variation...

The standard description of wave propagation in fluid-saturated porous media is given by the Biot–Gassmann theory poroelasticity. enjoys strong experimental support, except for specific and systematic failings. These failings may be addressed introduction concept squirt flow. A wide range flow models exist, but predictions these contradict each other those We argue that a valid model should consistent with evidence favour poroelasticity rigorous results effective medium theory. then proceed...

ABSTRACT Measurements of seismic anisotropy in fractured rock are used at present to deduce information about the fracture orientation and spatial distribution intensity. Analysis data is based upon equivalent‐medium theories that describe elastic response a containing cracks or fractures long‐wavelength limit. Conventional models assume frequency independence cannot distinguish between microcracks macrofractures. The latter, however, control fluid flow many subsurface reservoirs. Therefore,...

This study models the seismic response of porous rock containing two fracture sets with different orientations, sizes, and connectivities. Modeling demonstrates frequency-dependent anisotropy controlled by characteristic frequencies that are defined fluid mobility length scales fractures. Fracture-related dispersion attenuation typically occur over a wider frequency band than is seen in case single set. When one set fractures modeled as being sealed, azimuthal variation velocity can be...

ABSTRACT We present laboratory ultrasonic measurements of shear‐wave splitting from two synthetic silica cemented sandstones. The manufacturing process, which enabled cementation quartz sand grains, was found to produce realistic sandstones average porosity 29.7 ± 0.5% and permeability 29.4 11.3 mD. One sample made with a regular distribution aligned, penny‐shaped voids simulate meso‐scale fractures in reservoir rocks, while the other left blank. Ultrasonic shear waves were measured...

Approximations for frequency-dependent and complex-valued effective stiffness tensors of cracked porous media (saturated with a single fluid) are developed on the basis an inclusion-based model (the T-matrix approach to rock physics) unified treatment global-flow squirt-flow mechanisms. Essentially, this study corrects inconsistency or error related fluid-mass conservation in existing expression t-matrix (wave-induced deformation) communicating cavity, cavity that is isolated respect stress...

Abstract Elastic wave attenuation anisotropy in porous rocks with aligned fractures is of interest to seismic remote sensing the Earth's structure and hydrocarbon reservoir characterization particular. We investigated effect partial water saturation on fractured laboratory by conducting ultrasonic pulse-echo measurements synthetic, silica-cemented, sandstones penny-shaped voids (fracture density 0.0298 ± 0.0077), chosen simulate natural Earth according theoretical models. Our results show,...

For many years geophysicists have attempted to exploit attenuation measurements in exploration seismology, because is perhaps the seismic property most closely related saturating fluid. The routine application of such ideas has proven elusive, however, largely difficulty experienced when we attempt measure reflection data. Recent developments spectral decomposition methods data opened possibility making further progress this direction.

ABSTRACT Anisotropic variations in attenuation are of interest since they can give information on the fracture system and may be more amenable to measurement than absolute values. We examine methods for detecting changes relative with azimuth from VSP data, validate techniques synthetic data. Analysis a multi‐azimuth walkaway data set fractured hydrocarbon reservoir indicates that such azimuthal P‐wave observable. The effects localized reservoir, analysis allows prediction strike direction,...

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2009Frequency‐dependent AVO inversionAuthors: Adam WilsonMark ChapmanXiang‐Yang LiAdam WilsonEdinburgh Anisotropy Project, British Geological Survey.Search for more papers by this author, Mark ChapmanEdinburgh and Xiang‐Yang LiEdinburgh authorhttps://doi.org/10.1190/1.3255572 SectionsSupplemental MaterialAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail...

ABSTRACT Seismic amplitudes contain important information that can be related to fluid saturation. The amplitude‐versus‐offset analysis of seismic data based on Gassmann's theory and the approximation Zoeppritz equations has played a central role in reservoir characterization. However, this standard technique faces long‐standing problem: its inability distinguish between partial gas “fizz‐water” with little In paper, we studied dispersion attenuation partially saturated poroelastic media by...

The effectiveness of fracture stimulation techniques depends on the microstructural features which control rock strength. We analyze brittleness index, fractures, and microstructure Barnett Shale for a better understanding correlation between mechanical properties, mineralogy, pore geometry. complexity multiple minerals, geometries, inclusions are modeled using self-consistent approximation (SCA) model, with consideration statistical distributions pores cracks in shales. method is applied to...

Fluids hosted in fractures, or low aspect ratio inclusions, exist many different settings within the Earth. In near surface, understanding systems of fluid-filled fractures is important to various industrial applications such as geothermal energy production, monitoring CO2 storage sites and exploring for metalliferous sub-volcanic brines (e.g., Blundy et al., 2021). mantle, melting an geodynamic process, exerting control over its composition dynamic processes. Upper mantle weakens...

Rock brittleness plays a significant role in effective hydraulic fracturing for shale gas production, and is often related to mineralogy, mechanical properties, microstructure features shales. We construct rock physics workflow link elastic properties of shales complex constituents specific attributes. Multiple compositions various pore geometries are considered using self-consistent approximation (SCA) method. The laminated textures due the preferred orientations clay particles possible...

ABSTRACT Ultrasonic (500 kHz) P‐ and S‐wave velocity attenuation anisotropy were measured in the laboratory on synthetic, octagonal‐shaped, silica‐cemented sandstone samples with aligned penny‐shaped voids as a function of pore fluid viscosity. One control (blank) sample was manufactured without fractures, another known fracture density (measured from X‐ray CT images). Velocity four directions relative to bedding fabric (introduced during packing successive layers sand grains construction)...

ABSTRACT P‐wave‐to‐S‐wave ratios are important seismic characterization attributes. Velocity sensitive to the petrophysical properties of rocks and presence gas. Attenuation have also been shown be partial liquid/gas saturation. The relationship between saturation P‐wave S‐wave has used distinguish gas‐saturated from liquid‐saturated rocks. Aligned fractures common in Earth's crust cause anisotropy shear wave splitting. However, most existing relationships gas/liquid for non‐fractured We...

Recent observations from several walkaround, walkaway, and 3D VSPs various parts of the world have shown that anisotropy symmetry directions (or fracture orientations) estimated traveltime or velocity do not necessarily agree with amplitude attenuation analysis. We also consistently found in reservoir intervals is generally stronger than overburdens. argue this article that, instead reconciling differences between attributes, we should try to understand mechanisms use difference which may...

P- and S-wave velocity attenuation coefficients (accurate to ±0.3% ±0.2 dB/cm, respectively) were measured in synthetic porous rocks with aligned, penny-shaped fractures using the laboratory ultrasonic pulse-echo method. Shear-wave splitting was observed by rotating transducer noting maximum minimum velocities relative fracture direction. A block of rock density 0.0201 ± 0.0068 size 3.6 0.38 mm (measured from image analysis X-ray CT scans) sub-sampled into three 20–30 long, 50 diameter core...

ABSTRACT We used a laboratory scale model to study the effects aligned fractures might have on seismic wave propagation at larger in real Earth imaging. Our main objective was investigate effect of P‐wave amplitude through estimation induced attenuation. The physical constructed from mixture epoxy resin and silicon rubber, with inclusions designed simulate two sets inclined an angle 29.2° each other. Two‐dimensional reflection data were acquired using pulse transmission method three...

Fractured rocks are known to exhibit seismic anisotropy and shear wave splitting (SWS). SWS is commonly used for fractured rock characterization has been shown be sensitive fluid type. The presence of partial liquid/gas saturation also affect the elastic properties rocks. combined effect both fractures still unknown. Using synthetic, silica-cemented sandstones with aligned penny-shaped voids, we conducted laboratory ultrasonic experiments investigate at an oblique angle propagation would...

The seismic properties of rocks are known to be sensitive partial liquid or gas saturation, and aligned fractures.P-wave anisotropy is widely used for fracture characterization the saturating fluid.However, studies combining effect multiphase saturation fractures limited even though such conditions common in subsurface.An understanding effects on P-wave could help improve fractured, bearing reservoirs.Using octagonal-shaped synthetic sandstone samples, one containing penny-shaped other...

Accurate modelling of the dependence seismic wave speed from frequency and fluid content is crucial to quantitative interpretation data. Dispersive effects such as squirt flow become important at a critical that proportional mobility. When porous medium partially saturated it not clear how respective mobilities are be averaged. Building on previous work, we use nonzero, static capillary pressure parameter relative permeability model simulate in realistic sand by water CO2 where can either...

Sleipner (North Sea) is the world's first commercial-scale carbon capture and storage (CCS) project, active since 1996, with ∼17 million tonnes of CO2 stored. The main reservoir, Utsira Sand, constitutes an ideal host formation exceptionally high porosity-permeability large lateral extent. However, extensive seismic time-lapse, gravity electromagnetic monitoring surveys deployed at have not been well-supported by laboratory measurements. Here, we investigate geophysical geomechanical...