Effects of vertically aligned subsurface fractures on seismic reflections: A physical model study

We investigate the effects of subsurface fractures on moveout velocity and on reflection amplitudes by constructing a fractured model with three layers. The physical model was constructed by embedding a Phenolitic disc within the intermediate layer, which acts as a zone of vertical fractures. Survey lines were run along seven azimuthal directions between the strike direction and the transverse direction to the fractures at an angle increment of 15°. For our set of experimental conditions, we observe that the horizontal moveout velocity decreases from the strike direction toward the transverse direction to the fractures, and that the rate of decrease in amplitude variation with offset (AVO) increases from the strike direction toward the transverse direction to the fracture.

Download Full-text

Improving lateral and vertical resolution of seismic images by correcting for wavelet stretch in common-angle migration

Geophysics ◽

10.1190/1.2781619 ◽

2007 ◽

Vol 72 (6) ◽

pp. C95-C104 ◽

Cited By ~ 22

Author(s):

Gabriel Perez ◽

Kurt J. Marfurt

Keyword(s):

Signal To Noise Ratio ◽

Incident Angle ◽

Large Angle ◽

Acoustic Medium ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Velocity Anisotropy ◽

Time Migration ◽

Reflection Angle ◽

Seismic Reflections

Long-offset or high-incident-angle seismic reflections provide us with improved velocity resolution, better leverage against multiples, less contamination by ground roll, and information that is often critical when estimating lithology and fluid product. Unfortunately, high-incident-angle seismic reflections suffer not only from nonhyperbolic moveout but also from wavelet stretch during imaging, resulting in lower-resolution images that mix the response from adjacent lithologies. For an arbitrary acoustic medium, wavelet stretch from prestack migration depends only on the cosine of the reflection angle, such that the amount of wavelet stretch will be the same for all samples of a common-reflection-angle migrated trace. Thus, we are able to implement a wavelet stretch correction by applying a simple stationary spectral shaping operation to common-angle migrated traces. We obtain such traces directly by a prestack Kirchhoff migration algorithm. Correcting for stretch effectively increases the fold of imaged data, far beyond that achieved in conventional migration, resulting in improved signal-to-noise ratio of the final stacked section. Increasing the fidelity of large incident angles results in images with improved vertical and lateral resolution and with increased angular illumination, valuable for amplitude variation with angle (AVA) and amplitude variation with offset (AVO) analysis. Finally, such large-angle images are more sensitive to and therefore provide increased leverage over errors in velocity and velocity anisotropy. These ideas were applied to prestack time migration on seismic data from the Fort Worth basin, in Texas.

Download Full-text

Azimuthal variation of converted-wave amplitude in a reservoir with vertically aligned fractures − a physical model study

Geophysical Prospecting ◽

10.1111/1365-2478.12357 ◽

2016 ◽

Vol 65 (1) ◽

pp. 221-228 ◽

Cited By ~ 3

Author(s):

Chih-Hsiung Chang ◽

Young-Fo Chang ◽

Po-Yen Tseng

Keyword(s):

Physical Model ◽

Wave Amplitude ◽

Converted Wave ◽

Azimuthal Variation ◽

Model Study ◽

Vertically Aligned

Download Full-text

AVO as a fluid indicator: A physical modeling study

Geophysics ◽

10.1190/1.2392817 ◽

2007 ◽

Vol 72 (1) ◽

pp. C9-C17 ◽

Cited By ~ 14

Author(s):

Aaron Wandler ◽

Brian Evans ◽

Curtis Link

Keyword(s):

Physical Model ◽

Physical Modeling ◽

Model Experiment ◽

Close Agreement ◽

Time Lapse ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Zoeppritz Equations ◽

Seismic Amplitude ◽

Gradient Domain

Information on time-lapse changes in seismic amplitude variation with offset (AVO) from a reservoir can be used to optimize production. We designed a scaled physical model experiment to study the AVO response of mixtures of brine, oil, and carbon dioxide at pressures of 0, 1.03, and [Formula: see text]. The small changes in density and velocity for each fluid because of increasing pressure were not detectable and were assumed to lie within the error of the experiment. However, AVO analysis was able to detect changes in the elastic properties between fluids that contained oil and those that did not. When the AVO response was plotted in the AVO intercept-gradient domain, fluids containing oil were clearly separated from fluids not containing oil. This was observed in the AVO response from both the top and base of the fluids in the physical model. We then compared the measured AVO response with the theoretical AVO response given by the Zoeppritz equations. The measured and theoretical AVO intercept responses for the top fluid reflection agree well, although the AVO gradients disagree slightly. For the fluid base reflection, the measured and theoretical responses are in close agreement.

Download Full-text

Time-lapse amplitude variation with offset inversion using Bayesian theory in two-phase media

Geophysics ◽

10.1190/geo2018-0359.1 ◽

2019 ◽

Vol 84 (3) ◽

pp. N55-N79

Author(s):

Longxiao Zhi ◽

Hanming Gu

Keyword(s):

Objective Function ◽

Physical Model ◽

Time Lapse ◽

Bayesian Theory ◽

Amplitude Variation ◽

Two Phase ◽

Amplitude Variation With Offset ◽

Zoeppritz Equations ◽

Avo Inversion ◽

Rock Physical Model

In time-lapse seismic analysis, the Zoeppritz equations are usually used in the time-lapse amplitude variation with offset (AVO) inversion and then combined with a rock-physical model to estimate the reservoir-parameter changes. The real-life reservoir is a two-phase medium that consists of solid and fluid components. The Zoeppritz equations are a simplification, assuming a single-phase solid medium, in which the properties of this medium are estimated by effective parameters from the combined components. This means that the Zoeppritz equations cannot describe the characteristics of the seismic reflection amplitudes in the reservoir in an accurate way. Therefore, we develop a method for time-lapse AVO inversion in two-phase media using the Bayesian theory to estimate the reservoir parameters and their changes quantitatively. We use a reflection-coefficient equation in two-phase media, a rock-physical model, and the convolutional model to build a relationship between the seismic records and reservoir parameters, which include porosity, clay content, saturation, and pressure. Assuming that the seismic-data errors follow a zero-mean Gaussian distribution and that the reservoir parameters follow a four-variable Cauchy prior distribution, we use the Bayesian theory to construct the objective function for the AVO inversion, and we also add a model-constraint term to compensate the low-frequency information and improve the stability of the inversion. Using the objective function of the AVO inversion and the Gauss-Newton method, we derived the equation for time-lapse AVO inversion. This result can be used to estimate the reservoir parameters and their changes accurately and in a stable way. The test results from the feasibility study on synthetic and field data proved that the method is effective and reliable.

Download Full-text

Physical Model Study of Flowerpot Discharge Outlet, Western Closure Complex, New Orleans, Louisiana

10.21236/ada583046 ◽

2013 ◽

Author(s):

Stephen T. Maynord

Keyword(s):

New Orleans ◽

Physical Model ◽

Model Study

Download Full-text

Two-Dimensional Numerical Modeling of Flow in Physical Models of Rock Vane and Bendway Weir Configurations

Water ◽

10.3390/w13040458 ◽

2021 ◽

Vol 13 (4) ◽

pp. 458

Author(s):

Drew C. Baird ◽

Benjamin Abban ◽

S. Michael Scurlock ◽

Steven B. Abt ◽

Christopher I. Thornton

Keyword(s):

Numerical Modeling ◽

Physical Model ◽

Numerical Models ◽

Hydraulic Performance ◽

Physical Models ◽

Protection Measures ◽

Design Engineers ◽

Model Study ◽

Study Results ◽

Wide Range

While there are a wide range of design recommendations for using rock vanes and bendway weirs as streambank protection measures, no comprehensive, standard approach is currently available for design engineers to evaluate their hydraulic performance before construction. This study investigates using 2D numerical modeling as an option for predicting the hydraulic performance of rock vane and bendway weir structure designs for streambank protection. We used the Sedimentation and River Hydraulics (SRH)-2D depth-averaged numerical model to simulate flows around rock vane and bendway weir installations that were previously examined as part of a physical model study and that had water surface elevation and velocity observations. Overall, SRH-2D predicted the same general flow patterns as the physical model, but over- and underpredicted the flow velocity in some areas. These over- and underpredictions could be primarily attributed to the assumption of negligible vertical velocities. Nonetheless, the point differences between the predicted and observed velocities generally ranged from 15 to 25%, with some exceptions. The results showed that 2D numerical models could provide adequate insight into the hydraulic performance of rock vanes and bendway weirs. Accordingly, design guidance and implications of the study results are presented for design engineers.

Download Full-text

Fracture mapping using seismic amplitude variation with offset and azimuth analysis at the Weyburn CO2 storage site

Geophysics ◽

10.1190/geo2011-0075.1 ◽

2012 ◽

Vol 77 (6) ◽

pp. B295-B306 ◽

Cited By ~ 17

Author(s):

Alexander Duxbury ◽

Don White ◽

Claire Samson ◽

Stephen A. Hall ◽

James Wookey ◽

...

Keyword(s):

Cross Sections ◽

Co2 Storage ◽

Horizontal Stress ◽

Storage Site ◽

Fracture Zones ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Seal Integrity ◽

Cap Rock ◽

Weyburn Field

Cap rock integrity is an essential characteristic of any reservoir to be used for long-term [Formula: see text] storage. Seismic AVOA (amplitude variation with offset and azimuth) techniques have been applied to map HTI anisotropy near the cap rock of the Weyburn field in southeast Saskatchewan, Canada, with the purpose of identifying potential fracture zones that may compromise seal integrity. This analysis, supported by modeling, observes the top of the regional seal (Watrous Formation) to have low levels of HTI anisotropy, whereas the reservoir cap rock (composite Midale Evaporite and Ratcliffe Beds) contains isolated areas of high intensity anisotropy, which may be fracture-related. Properties of the fracture fill and hydraulic conductivity within the inferred fracture zones are not constrained using this technique. The predominant orientations of the observed anisotropy are parallel and normal to the direction of maximum horizontal stress (northeast–southwest) and agree closely with previous fracture studies on core samples from the reservoir. Anisotropy anomalies are observed to correlate spatially with salt dissolution structures in the cap rock and overlying horizons as interpreted from 3D seismic cross sections.

Download Full-text

The impact of reservoir scale on amplitude variation with offset

Geophysical Prospecting ◽

10.1111/1365-2478.12431 ◽

2016 ◽

Vol 65 (3) ◽

pp. 736-746 ◽

Cited By ~ 1

Author(s):

Chao Xu ◽

Jianxin Wei ◽

Bangrang Di

Keyword(s):

Amplitude Variation ◽

Amplitude Variation With Offset ◽

The Impact

Download Full-text

Canal Wave Oscillations from Expansion of I-84 Bridge in Boise, Idaho

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2309-19 ◽

2012 ◽

Vol 2309 (1) ◽

pp. 200-205

Author(s):

William Rahmeyer ◽

J. M. Clegg ◽

S. L. Barfuss

Keyword(s):

New York ◽

Physical Model ◽

Unique Solution ◽

Wave Phenomenon ◽

Bridge Columns ◽

Bridge Abutments ◽

Wave Problem ◽

Model Study ◽

Bridge Crossing

Recent improvements and the widening of the I-84 Bridge crossing of the New York Canal in Boise, Idaho, have increased the number of bridge columns from 28 to 60. The resulting structure has two parallel rows of columns that extend across the width of the bridge longitudinally within the canal. After the widening of the bridge and addition of the bridge columns, the canal began experiencing an oscillating wave phenomenon that originated from the bridge columns and caused erosion of upstream and downstream canal banks and bridge abutments. A physical model study was conducted to investigate the wave phenomenon and determine what modifications to the columns or canal would be necessary to prevent the wave oscillations. The physical model was successful in simulating the wave phenomenon, and four different modifications for resolving the wave problem were tested in the model. A unique solution was found that used precast nose cones attached to selected columns. The nose cones have been installed in the prototype bridge crossing, and no wave oscillations have occurred since installation. This paper discusses the study to simulate the wave phenomenon and the four modifications that were evaluated to reduce or prevent wave oscillations.

Download Full-text