Elastic properties of two VTI shale samples as a function of uniaxial stress: Experimental results and application of the porosity-deformation approach

Geophysics ◽  
2017 ◽  
Vol 82 (6) ◽  
pp. C201-C210 ◽  
Author(s):  
Viacheslav A. Sviridov ◽  
Sibylle I. Mayr ◽  
Serge A. Shapiro
Keyword(s):  
Elastic Properties ◽  
Pore Space ◽  
Uniaxial Stress ◽  
Data Sets ◽  
Seismic Velocities ◽  
Transverse Isotropic ◽  
Compliant Parts ◽  
Stress Dependent ◽  
Deformation Approach ◽  
Stress Dependency

Shale is a complex medium composed of clay, other mineral phases, and a pore space. The combined elastic properties of these components control the effective (anisotropic) properties of the composite solid. The factor that is the most dependent on the stress field is the structure of the pore space, which greatly influences the elastic properties of the medium. We have further developed and experimentally validated the porosity deformation approach (PDA) for understanding and modeling stress-dependent changes of the elastic properties of sedimentary rocks. PDA separates the pore space into stiff and compliant parts. The load dependencies of the elastic properties have linear contributions due to the former and exponential contributions due to the latter. We evaluate data sets of elastic properties of two vertical transverse isotropic shale samples measured under uniaxial stress. Then we apply the PDA and our optimization algorithm to the measured data sets to model the stress dependency of the seismic velocities and validate the modeling with experimentally obtained results. We have developed for the first time the constant anellipticity approach (CAN), which estimates the off-axis velocity (in an inclined direction relative to the symmetry axis direction) as a function of stress. Measurements of off-axis velocities are often missing information, and CAN permits us to fill this gap. This provides further background for the reconstruction of the stress dependency of the compliance tensor from acoustic log data.

Stress-dependent anisotropy in transversely isotropic rocks: Comparison between theory and laboratory experiment on shale

Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. D7-D12 ◽  
Author(s):  
Radim Ciz ◽  
Serge A. Shapiro
Keyword(s):  
Effective Stress ◽  
Elastic Moduli ◽  
Pore Space ◽  
Transversely Isotropic ◽  
Stress Sensitivity ◽  
Seismic Velocities ◽  
The North ◽  
Compliance Tensor ◽  
Stress Dependent ◽  
Deformation Approach

Understanding the effect of stress and pore pressure on seismic velocities is important for overpressure prediction and for 4D reflection seismic interpretation. A porosity-deformation approach (originally called the piezosensitivity theory) and its anisotropic extension describe elastic moduli of rocks as nonlinear functions of the effective stress. This theory assumes a presence of stiff and compliant parts of the pore space. The stress-dependent geometry of the compliant pore space predominantly controls stress-induced changes in elastic moduli. We show how to apply this theory to a shale that is transversely isotropic (TI) under unloaded conditions. The porosity-deformation approach shows that components of the compliance tensor depend on exponential functions of the principal components of the effective stress tensor. In the case of a hydrostatic loading of a TI rock, only the diagonal elements of this tensor, expressed in contracted notation, are significantly stress dependent. Two equal shear components of the compliance will depend on a combination of two stress exponentials. Exponents of the stress exponentials are controlled by components of the stress-sensitivity tensor. This tensor is an important physical characteristic directly related to the elastic nonlinearity of the porous rock. We simplify the porosity-deformation theory for TI rocks and provide corresponding explicit equations. We apply this theory to ultrasonic measurements on saturated shale samples from the North Sea. We show that the theory explains the compliance tensor, anellipticity, and three anisotropic parameters under a broad range of loads.

scholarly journals Diagenetic Trends of Synthetic Reservoir Sandstone Properties Assessed by Digital Rock Physics

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 151
Author(s):  
Maria Wetzel ◽  
Thomas Kempka ◽  
Michael Kühn
Keyword(s):  
Elastic Properties ◽  
Pore Space ◽  
Rock Physics ◽  
Mineral Dissolution ◽  
Ct Scans ◽  
Micro Ct ◽  
Digital Rock Physics ◽  
Gravity Driven ◽  
Stress Dependent ◽  
The Impact

Quantifying interactions and dependencies among geometric, hydraulic and mechanical properties of reservoir sandstones is of particular importance for the exploration and utilisation of the geological subsurface and can be assessed by synthetic sandstones comprising the microstructural complexity of natural rocks. In the present study, three highly resolved samples of the Fontainebleau, Berea and Bentheim sandstones are generated by means of a process-based approach, which combines the gravity-driven deposition of irregularly shaped grains and their diagenetic cementation by three different schemes. The resulting evolution in porosity, permeability and rock stiffness is examined and compared to the respective micro-computer tomographic (micro-CT) scans. The grain contact-preferential scheme implies a progressive clogging of small throats and consequently produces considerably less connected and stiffer samples than the two other schemes. By contrast, uniform quartz overgrowth continuously alters the pore space and leads to the lowest elastic properties. The proposed stress-dependent cementation scheme combines both approaches of contact-cement and quartz overgrowth, resulting in granulometric, hydraulic and elastic properties equivalent to those of the respective micro-CT scans, where bulk moduli slightly deviate by 0.8%, 4.9% and 2.5% for the Fontainebleau, Berea and Bentheim sandstone, respectively. The synthetic samples can be further altered to examine the impact of mineral dissolution or precipitation as well as fracturing on various petrophysical correlations, which is of particular relevance for numerous aspects of a sustainable subsurface utilisation.

Porosity and elastic anisotropy of rocks under tectonic stress and pore-pressure changes

Geophysics ◽  
2005 ◽  
Vol 70 (5) ◽  
pp. N27-N38 ◽  
Author(s):  
Serge A. Shapiro ◽  
Axel Kaselow
Keyword(s):  
Pore Pressure ◽  
Elastic Moduli ◽  
Elastic Anisotropy ◽  
Pore Space ◽  
Tectonic Stress ◽  
Stress Sensitivity ◽  
Seismic Velocities ◽  
Confining Stress ◽  
The Difference ◽  
Stress Dependent

Elastic properties of rocks depend on tectonic stress. Using the theory of poroelasticity as a constraint, we analyze features of these dependencies related to changes in rock pore-space geometry. We develop a formalism describing elastic moduli and anisotropy of rocks as nonlinear functions of confining stress and pore pressure. This formalism appears to agree with laboratory observations. To a first approximation, elastic moduli and seismic velocities as well as porosity depend only on the difference between the confining tectonic stress and pore pressure. However, in general, both the confining stress tensor and the pore pressure must be taken into account as independent variables. The stress-dependent geometry of the pore space fully controls the stress-induced changes in elastic moduli and seismic velocities. Specifically, the compliant porosity plays the most important role, despite the fact that in many rocks the compliant porosity is a very small part of total porosity. Changes in compliant porosity with pressure and stress explain the often observed behavior of elastic moduli: in the low compressive stress regime — say, below 50 to 100 MPa — moduli increase rapidly and then taper exponentially into a flat and linear increase with increasing load. Taking into account the strain of the compliant pore space, we introduce a tensor quantity defining the sensitivity of elastic moduli of rocks to the difference between confining stress and pore pressure. We call it the stress sensitivity tensor. This tensor is an important physical characteristic directly related to elastic nonlinearity of rocks. The stress sensitivity tensor governs the changes in elastic anisotropy of a drained poroelastic system as it depends upon the applied load.

scholarly journals Stress dependency of elastic properties of shales: The effect of uniaxial stress

2011 ◽  
Author(s):  
Marina Pervukhina ◽  
Boris Gurevich ◽  
Pavel Golodoniuc ◽  
David N. Dewhurst
Keyword(s):  
Elastic Properties ◽  
Uniaxial Stress ◽  
Stress Dependency

The effect of microstructure and nonlinear stress on anisotropic seismic velocities

Geophysics ◽  
2008 ◽  
Vol 73 (4) ◽  
pp. D41-D51 ◽  
Author(s):  
James P. Verdon ◽  
Doug A. Angus ◽  
J. Michael Kendall ◽  
Stephen A. Hall
Keyword(s):  
Time Lapse ◽  
Data Sets ◽  
Seismic Velocities ◽  
S Wave ◽  
Hydrocarbon Reservoir ◽  
Fluid Saturation ◽  
Nonlinear Stress ◽  
Intrinsic Shape ◽  
Saturation Effects ◽  
Stress Dependent

Recent work in hydrocarbon reservoir monitoring has focused on developing coupled geomechanical/fluid-flow simulations to allow production-related geomechanical effects, such as compaction and subsidence, to be included in reservoir models. To predict realistic time-lapse seismic signatures, generation of appropriate elastic models from geomechanical output is required. These elastic models should include not only the fluid saturation effects of intrinsic, shape-induced, and stress-induced anisotropy, but also should incorporate nonlinear stress-dependent elasticity. To model nonlinear elasticity, we use a microstructural effective-medium approach in which elasticity is considered as a function of mineral stiffness and additional compliance is caused by the presence of low-aspect ratio displacement discontinuities. By jointly inverting observed ultrasonic P- and S-wave velocities to determine the distribution of such discontinuities, we assessed the appropriateness of modeling them as simple, planar, penny-shaped features. By using this approximation, we developed a simple analytical approach to predict how seismic velocities will vary with stress. We tested our approach by analyzing the elasticity of various sandstone samples; from a United Kingdom continental shelf (UKCS) reservoir, some of which display significant anisotropy, as well as two data sets taken from the literature.

scholarly journals Stress-dependent elastic properties of shales: Measurement and modeling

2008 ◽  
Vol 27 (6) ◽  
pp. 772-779 ◽  
Author(s):  
Marina Pervukhina ◽  
Dave Dewhurst ◽  
Boris Gurevich ◽  
Utpalendu Kuila ◽  
Tony Siggins ◽  
...  
Keyword(s):  
Elastic Properties ◽  
Stress Dependent

Stress-Dependent Elastic Properties of Porous Microcracked Ceramics

2009 ◽  
pp. NA-NA ◽  
Author(s):  
Irina Pozdnyakova ◽  
Giovanni Bruno ◽  
Alexander M. Efremov ◽  
Bjørn Clausen ◽  
Darren Hughes
Keyword(s):  
Elastic Properties ◽  
Stress Dependent

scholarly journals Parameterization of elastic stress sensitivity in shales

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. WA147-WA155 ◽  
Author(s):  
Marina Pervukhina ◽  
Boris Gurevich ◽  
Pavel Golodoniuc ◽  
David N. Dewhurst
Keyword(s):  
Elastic Properties ◽  
Anisotropy Parameter ◽  
Transversely Isotropic ◽  
Bedding Plane ◽  
Stress Sensitivity ◽  
Crack Orientation ◽  
Fluid Identification ◽  
Orientation Anisotropy ◽  
Characteristic Pressure ◽  
Stress Dependency

Stress dependency and anisotropy of dynamic elastic properties of shales is important for a number of geophysical applications, including seismic interpretation, fluid identification, and 4D seismic monitoring. Using Sayers-Kachanov formalism, we developed a new model for transversely isotropic (TI) media that describes stress sensitivity behavior of all five elastic coefficients using four physically meaningful parameters. The model is used to parameterize elastic properties of about 20 shales obtained from laboratory measurements and the literature. The four fitting parameters, namely, specific tangential compliance of a single crack, ratio of normal to tangential compliances, characteristic pressure, and crack orientation anisotropy parameter, show moderate to good correlations with the depth from which the shale was extracted. With increasing depth, the tangential compliance exponentially decreases. The crack orientation anisotropy parameter broadly increases with depth for most of the shales, indicating that cracks are getting more aligned in the bedding plane. The ratio of normal to shear compliance and characteristic pressure decreases with depth to 2500 m and then increases below this to 3600 m. The suggested model allows us to evaluate the stress dependency of all five elastic compliances of a TI medium, even if only some of them are known. This may allow the reconstruction of the stress dependency of all five elastic compliances of a shale from log data, for example.

scholarly journals Squirt flow due to interfacial water films in hydrate bearing sediments

2017 ◽  
Author(s):  
Kathleen Sell ◽  
Beatriz Quintal ◽  
Michael Kersten ◽  
Erik H. Saenger
Keyword(s):  
Flow Model ◽  
Pore Space ◽  
Seismic Attenuation ◽  
Interfacial Water ◽  
Seismic Velocities ◽  
High Attenuation ◽  
Water Films ◽  
Direct Model ◽  
In Situ Experiments ◽  
Hydrate Bearing Sediments

Abstract. Sediments containing gas hydrate dispersed in the pore space are known to show a characteristic seismic anomaly which is a high attenuation along with increasing seismic velocities. Currently, this observation cannot be fully explained albeit squirt-flow type mechanisms at the microscale have been speculated to be the cause. Recent major findings from in-situ experiments coupled with high-resolution synchrotron-based X-ray micro-tomography revealed a systematic presence of thin water films between the quartz grains and the encrusting hydrate. In this study, the data was obtained from the experiments and underwent an image processing procedure to quantify the thicknesses and geometries of the aforementioned interfacial water films. Overall, the water films vary from sub-μm to a few μm in thickness where some of them are interconnected by water bridges. This geometrical analysis is then used to propose a new conceptual squirt flow model for hydrate bearing sediments. Subsequently the established model acts as a direct model input to obtain seismic attenuation. Our results support previous speculations that squirt flow can explain high attenuation at seismic frequencies in hydrate bearing sediments, but based on a conceptual squirt flow model which is different than those previously considered.

Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – II. Sardinia’s margin

2015 ◽  
Vol 186 (4-5) ◽  
pp. 331-351 ◽  
Author(s):  
Alexandra Afilhado ◽  
Maryline Moulin ◽  
Daniel Aslanian ◽  
Philippe Schnürle ◽  
Frauke Klingelhoefer ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Passive Margin ◽  
Data Sets ◽  
Wide Angle ◽  
Seismic Velocities ◽  
The West ◽  
Reflection Seismic ◽  
Gulf Of Lion ◽  
Deep Crustal Structure ◽  
Domain Iii

Abstract Geophysical data acquired on the conjugate margins system of the Gulf of Lion and West Sardinia (GLWS) is unique in its ability to address fundamental questions about rifting (i.e. crustal thinning, the nature of the continent-ocean transition zone, the style of rifting and subsequent evolution, and the connection between deep and surface processes). While the Gulf of Lion (GoL) was the site of several deep seismic experiments, which occurred before the SARDINIA Experiment (ESP and ECORS Experiments in 1981 and 1988 respectively), the crustal structure of the West Sardinia margin remains unknown. This paper describes the first modeling of wide-angle and near-vertical reflection multi-channel seismic (MCS) profiles crossing the West Sardinia margin, in the Mediterranean Sea. The profiles were acquired, together with the exact conjugate of the profiles crossing the GoL, during the SARDINIA experiment in December 2006 with the French R/V L’Atalante. Forward wide-angle modeling of both data sets (wide-angle and multi-channel seismic) confirms that the margin is characterized by three distinct domains following the onshore unthinned, 26 km-thick continental crust : Domain V, where the crust thins from ~26 to 6 km in a width of about 75 km; Domain IV where the basement is characterized by high velocity gradients and lower crustal seismic velocities from 6.8 to 7.25 km/s, which are atypical for either crustal or upper mantle material, and Domain III composed of “atypical” oceanic crust. The structure observed on the West Sardinian margin presents a distribution of seismic velocities that is symmetrical with those observed on the Gulf of Lion’s side, except for the dimension of each domain and with respect to the initiation of seafloor spreading. This result does not support the hypothesis of simple shear mechanism operating along a lithospheric detachment during the formation of the Liguro-Provencal basin.

Sign in / Sign up

Export Citation Format

Share Document