Linking reservoir geomechanics and time-lapse seismics: Predicting anisotropic velocity changes and seismic attributes

Geophysics ◽  
2009 ◽  
Vol 74 (4) ◽  
pp. W13-W33 ◽  
Author(s):  
Jorg V. Herwanger ◽  
Steve A. Horne
Keyword(s):  
Stress State ◽  
Vertical Velocity ◽  
Rock Physics ◽  
Stress Path ◽  
Time Lapse ◽  
Triaxial Stress ◽  
P Wave ◽  
Triaxial Stress State ◽  
Wave Velocities ◽  
P Wave Velocity

Seismic technology has been used successfully to detect geomechanically induced signals in repeated seismic experiments from more than a dozen fields. To explain geomechanically induced time-lapse (4D) seismic signals, we use results from coupled reservoir and geomechanical modeling. The coupled simulation yields the 3D distribution, over time, of subsurface deformation and triaxial stress state in the reservoir and the surrounding rock. Predicted changes in triaxial stress state are then used to compute changes in anisotropic P- and S-wave velocities employing a stress sensitive rock-physics transform. We predict increasing vertical P-wave velocities inside the reservoir, accompanied by a negative change in P-wave anisotropy [Formula: see text]. Conversely, in the overburden and underburden, we have predicted a slowdown in vertical P-wave velocity and an increase in horizontal velocities. This corresponds to positive change in P-wave anisotropy [Formula: see text]. A stress sensitive rock-physics transform that predicts anisotropic velocity change from triaxial stress change offers an explanation for the apparent difference in stress sensitivity of P-wave velocity between the overburden and the reservoir. In a modeled example, the vertical velocity speedup per unit increase in vertical stress [Formula: see text] is more than twice as large in the overburden as in the reservoir. The difference is caused by the influence of the stress path [Formula: see text] (i.e., the ratio [Formula: see text] between change in minimum horizontal effective stress [Formula: see text] and change in vertical effective stress [Formula: see text]) on vertical velocity. The modeling suggests that time-lapse seismic technology has the potential to become a monitoring tool for stress path, a critical parameter in failure geomechanics.

Stress path dependent effective medium model for granular media - Comparison with experimental data

Geophysics ◽  
2020 ◽  
pp. 1-56
Author(s):  
Sondre Torset ◽  
Rune M. Holt
Keyword(s):  
Stress State ◽  
Path Dependence ◽  
Effective Medium Theory ◽  
Laboratory Data ◽  
Rock Physics ◽  
Stress Path ◽  
Effective Medium ◽  
P Wave ◽  
Burial History ◽  
Stress Changes

Modeling velocity changes in response to stress changes plays an important part in understanding seismic responses from the sub- surface. One branch of such modeling consists of treating an assemblage of grains as an effective medium and using established grain contact theories to determine the elastic moduli. Such models are commonly limited to hydrostatic or uniaxial strain scenarios, not capable of capturing the anisotropy induced by a general triaxial stress state. A new set of expressions is developed by extending an existing effective medium theory to a general stress state where the radial (horizontal) stress is different from the axial (vertical) stress. The theory is valid at the limits of slip and no-slip. Novel functions to combine the no-slip and slip limits are implemented to match the model to observed laboratory data on glass beads and sand grain assemblages loaded along different stress paths. The new expressions provide a good agreement between modeled and measured stress and stress path dependence of P- and S-wave velocities and associated P-wave anisotropy. This stress dependence is of particular importance in rock physics workflows evaluating time-lapse feasibility for shallow or unconsolidated sand reservoirs or for characterizing burial history.

Time-average equation revisited

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 460-464 ◽  
Author(s):  
Jack Dvorkin ◽  
Amos Nur
Keyword(s):  
Solid Phase ◽  
Rock Physics ◽  
Pore Fluid ◽  
P Wave ◽  
Well Logs ◽  
Fluid Type ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Solid Phase Material

Expressions that relate velocity to porosity and to pore-fluid compressibility are among the most important deliverables of rock physics. Such relations are used often as additional controls for inferring porosity from well logs, as well as in-situ indicators of pore fluid type. The oldest and most popular is the Wyllie et al. (1956) equation: [Formula: see text]where [Formula: see text] is the measured traveltime of a P-wave, [Formula: see text] is the traveltime expected in the solid-phase material, and [Formula: see text] is the traveltime expected in the pore fluid. It follows from equation (1) that [Formula: see text]where ϕ is porosity, [Formula: see text] is the measured P-wave velocity, and [Formula: see text] and [Formula: see text] are the P-wave velocities in the solid and in the pore-fluid phases, respectively.

scholarly journals Determination of a stress-dependent rock-physics model using anisotropic time-lapse tomographic inversion

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. C141-C152
Author(s):  
Nicolas Mastio ◽  
Pierre Thore ◽  
Marianne Conin ◽  
Guillaume Caumon
Keyword(s):  
Rock Physics ◽  
Real Data ◽  
Time Lapse ◽  
P Wave ◽  
Velocity Change ◽  
Data Set ◽  
Tomographic Inversion ◽  
P Wave Velocity ◽  
Cap Rock ◽  
Velocity Changes

In the petroleum industry, time-lapse (4D) studies are commonly used for reservoir monitoring, but they are also useful to perform risk assessment for potential overburden deformations (e.g., well shearing, cap-rock integrity). Although complex anisotropic velocity changes are predicted in the overburden by geomechanical studies, conventional time-lapse inversion workflows only deal with vertical velocity changes. To retrieve the geomechanically induced anisotropy, we have adopted a reflection traveltime tomography method coupled with a time-shift estimation algorithm of prestack data of the baseline and monitor simultaneously. For the 2D approach, we parameterize the anisotropy using five coefficients, enough to cover any type of anisotropy. Before applying the workflow to a real data set, we first study a synthetic data set based on the real data set and include velocity variations between baseline and monitor found in the literature (vertical P-wave velocity decrease in the cap rock and isotropic P-wave velocity change in the reservoir). On the synthetics, we measure the angular ray coverage necessary to retrieve the target anisotropy and observe that the retrieved anisotropies depend on the offset range. Based on a synthetic experiment, we believe that the acquisition of the real case study is suitable for performing tomographic inversion. The anisotropic velocity changes obtained on three inlines separated by 375 m are consistent and show a strong positive anomaly in the cap rock along the 45° direction (the [Formula: see text] parameter in Thomsen notation), whereas the vertical velocity change is surprisingly almost negligible. We adopt a rock-physics explanation compatible with these observations and geologic considerations: a reactivation of water-filled subvertical cracks.

scholarly journals Estimation of rock physics properties from seismic attributes — Part 2: Applications

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. M55-M69 ◽  
Author(s):  
Bastien Dupuy ◽  
Stéphane Garambois ◽  
Amir Asnaashari ◽  
Hadi M. Balhareth ◽  
Martin Landrø ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Rock Physics ◽  
Time Lapse ◽  
Seismic Attributes ◽  
Data Availability ◽  
P Wave ◽  
Accurate Estimation ◽  
Baseline Model ◽  
Gas Saturation ◽  
P Wave Velocity

The estimation of quantitative rock physics properties is of great importance for reservoir characterization and monitoring in [Formula: see text] storage or enhanced oil recovery as an example. We have combined the high-resolution results of full-waveform inversion (FWI) methods with rock physics inversion. Because we consider a generic and dynamic rock physics model, our method is applicable to most kinds of rocks for a wide range of frequencies. The first step allows determination of viscoelastic effective properties, i.e., quantitative seismic attributes, whereas the rock physics inversion estimates rock physics properties (porosity, solid frame moduli, fluid phase properties, or saturation). This two-step workflow is applied to time-lapse synthetic and field cases. The sensitivity tests that we had previously carried out showed that it can be crucial to use multiparameter inputs to accurately recover fluid saturations and fluid properties. However, due to the limited data availability and difficulties in getting reliable multiparameter FWI results, we are limited to acoustic FWI results. The synthetic tests are conclusive even if they are favorable cases. For the first time-lapse fluid substitution synthetic case, we first characterize the rock frame parameters on the baseline model using P-wave velocity estimations obtained by acoustic FWI. Then, we obtain an accurate estimation of fluid bulk modulus from the time-lapse P-wave velocity. In the Marmousi synthetic case, the rock frame properties are accurately recovered for the baseline model, whereas the gas saturation change in the monitor model is not estimated correctly. On the field data example (time-lapse monitoring of an underground blowout in the North Sea), the estimation of rock frame properties gives results on a relatively narrow range, and we use this estimation as a starting model for the gas saturation inversion. We have found that the estimation of the gas saturation is not accurate enough, and the use of attenuation data is then required. However, the uncertainty on the estimation of baseline rock frame properties is not critical to monitor gas saturation changes.

scholarly journals Upscaling of elastic properties in carbonates: A modeling approach based on a multiscale geophysical data set

2020 ◽  
Author(s):  
Jerome Fortin ◽  
Cedric Bailly ◽  
Mathilde Adelinet ◽  
Youri Hamon
Keyword(s):  
Elastic Properties ◽  
Wave Velocity ◽  
Representative Elementary Volume ◽  
P Wave ◽  
Elementary Volume ◽  
Data Set ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Ultrasonic Measurements ◽  
Seismic Scale

<p>Linking ultrasonic measurements made on samples, with sonic logs and seismic subsurface data, is a key challenge for the understanding of carbonate reservoirs. To deal with this problem, we investigate the elastic properties of dry lacustrine carbonates. At one study site, we perform a seismic refraction survey (100 Hz), as well as sonic (54 kHz) and ultrasonic (250 kHz) measurements directly on outcrop and ultrasonic measurements on samples (500 kHz). By comparing the median of each data set, we show that the P wave velocity decreases from laboratory to seismic scale. Nevertheless, the median of the sonic measurements acquired on outcrop surfaces seems to fit with the seismic data, meaning that sonic acquisition may be representative of seismic scale. To explain the variations due to upscaling, we relate the concept of representative elementary volume with the wavelength of each scale of study. Indeed, with upscaling, the wavelength varies from millimetric to pluri-metric. This change of scale allows us to conclude that the behavior of P wave velocity is due to different geological features (matrix porosity, cracks, and fractures) related to the different wavelengths used. Based on effective medium theory, we quantify the pore aspect ratio at sample scale and the crack/fracture density at outcrop and seismic scales using a multiscale representative elementary volume concept. Results show that the matrix porosity that controls the ultrasonic P wave velocities is progressively lost with upscaling, implying that crack and fracture porosity impacts sonic and seismic P wave velocities, a result of paramount importance for seismic interpretation based on deterministic approaches.</p><p>Bailly, C., Fortin, J., Adelinet, M., & Hamon, Y. (2019). Upscaling of elastic properties in carbonates: A modeling approach based on a multiscale geophysical data set. Journal of Geophysical Research: Solid Earth, 124. https://doi.org/10.1029/2019JB018391</p>

scholarly journals Void growth in 6061-aluminum alloy under triaxial stress state

2003 ◽  
Vol 341 (1-2) ◽  
pp. 35-42 ◽  
Author(s):  
H Agarwal ◽  
A.M Gokhale ◽  
S Graham ◽  
M.F Horstemeyer
Keyword(s):  
Aluminum Alloy ◽  
Stress State ◽  
Void Growth ◽  
Triaxial Stress ◽  
Triaxial Stress State ◽  
6061 Aluminum Alloy
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