A cracked porous medium elastic wave theory and its application to interpreting acoustic data from tight formations

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. D245-D252 ◽  
Author(s):  
Xiao-Ming Tang ◽  
Xue-lian Chen ◽  
Xiao-kai Xu
Keyword(s):  
Elastic Wave ◽  
Crack Density ◽  
Measurement Data ◽  
Acoustic Property ◽  
Wave Theory ◽  
Velocity Variation ◽  
Porous Rocks ◽  
Tight Sandstone ◽  
Acoustic Data ◽  
Tight Formations

Rocks in the earth’s crust usually contain pores and cracks. Typical examples include tight sandstone and shale rocks that have low porosity but contain abundant microcracks. By extending the classic Biot’s poroelastic wave theory to include the effects of cracks, we obtain an elastic wave theory for porous rocks containing cracks, adding crack density and aspect ratio as two important parameters to the original theory. Because the flat- or narrow-shaped cracks can easily deform under acoustic wave excitation, the acoustic property of a cracked porous rock is quite different for different saturation conditions. The predicted fluid sensitivity is used to interpret acoustic velocity log data from tight sand and shale gas formations. In both scenarios, the new theory correctly predicts the trend of velocity variation with gas saturation. The results confirm that the presence of cracks in tight rocks can give rise to significant hydrocarbon signature in the acoustic measurement data, allowing for identifying hydrocarbons from the data.

Simulation of multipole acoustic logging in cracked porous formations

Geophysics ◽  
2014 ◽  
Vol 79 (1) ◽  
pp. D1-D10 ◽  
Author(s):  
Xue-Lian Chen ◽  
Xiao-Ming Tang ◽  
Yu-Ping Qian
Keyword(s):  
Porous Medium ◽  
Crack Density ◽  
Wave Theory ◽  
Flexural Wave ◽  
Low Permeability ◽  
Acoustic Wave Propagation ◽  
Stoneley Waves ◽  
Hydrocarbon Detection ◽  
Porous Formation ◽  
Tight Formations

Rocks in the earth’s crust usually contain pores and cracks. We developed a cracked porous medium elastic wave theory by modifying Biot’s poroelastic wave theory to include the effects of cracks, adding the crack density and aspect ratio as two important parameters to the original theory. The new theory was applied to model multipole acoustic wave propagation along a borehole surrounded by a cracked porous formation. The modeling results showed that the multipole acoustic waveforms were significantly affected by the presence of cracks even when the formation had low permeability and porosity. Particularly, cracks can cause the monopole P- and Stoneley waves and the dipole flexural wave to have significant sensitivity to hydrocarbon saturation, suggesting use of the waveform characteristics for hydrocarbon detection in tight formations.

The Button Head Bullet Effects on the Incident Pulse of Split Hopkinson Press Bar

2015 ◽  
Vol 782 ◽  
pp. 311-315
Author(s):  
Jia Qu ◽  
Geng Chen ◽  
Guang Ping Zou
Keyword(s):  
Elastic Wave ◽  
Wave Length ◽  
Constant Strain Rate ◽  
Peak Stress ◽  
Wave Theory ◽  
Pulse Shaper ◽  
Lagrange Method ◽  
Stress Increase ◽  
Split Hopkinson ◽  
Peak Value

In order to make the specimen deformed under a constant strain rate and the stress in the specimen kept homogeneous, the wave shaper technology was adopted to modify the incidence waves of the normal Split Hopkinson Press Bar. A method of changing the shape of the bullet was suggested to be applied on the SHPB. Bullets with different length and different curvature have been researched in this paper. And the effection of the button head bullet about incidence pulse was simulated with Lagrange method by ANSYS/LS-DYNA. It is shown in the results that changing the curvature of the bullet impact the rising edge of incidence waves, and the peak stress increase with the speed of the bullet increase, the peak stress and length of incidence waves increased with the length of the button head bullet, when the peak stress reached a certain strength, increasing the bullet length could make the stress peak value lasted longer. Due to the reason that the button head bullet was based on the elastic wave theory, the wave length and the max stress of the shaped wave would be controlled conveniently and avoid the shortcoming that the analogue specimens could not be recycled in the normal pulse shaper technology.

Real-Time Simulation of Dynamic Traffic Flow with Traffic Data Assimilation Approach

2016 ◽  
Vol 11 (2) ◽  
pp. 246-254 ◽  
Author(s):  
Yosuke Kawasaki ◽  
◽  
Yusuke Hara ◽  
Takuma Mitani ◽  
Masao Kuwahara
Keyword(s):  
Real Time ◽  
State Space Model ◽  
Measurement Data ◽  
Wave Theory ◽  
Variational Theory ◽  
Dynamic Traffic ◽  
Fundamental Diagram ◽  
Real Time Traffic ◽  
Probe Vehicle ◽  
Traffic Detector

The real-time traffic state estimation we propose uses a state-space model considering the variability of the fundamental diagram (FD) and sensing data. Serious congestion was caused by vehicle evacuation in many Sanriku coast cities following the great East Japan earthquake on March 11, 2011. Many of the vehicles in these congested queues were caught in the enormous tsunami after the earthquake [1]. Safe, efficient evacuation and rescue and restoration require that dynamic traffic states be monitored in real time especially in natural disasters. Variational theory (VT) based on kinematic wave theory is used for the system model, with probe vehicle and traffic detector data used to for measurement data. Our proposal agrees better with simulated benchmark traffic states than deterministic VT results do.

Elastic-wave evaluation of downhole hydraulic fracturing: Modeling and field applications

Geophysics ◽  
2018 ◽  
Vol 83 (1) ◽  
pp. D1-D8 ◽  
Author(s):  
Yuan-Da Su ◽  
Zhen Li ◽  
Song Xu ◽  
Chun-Xi Zhuang ◽  
Xiao-Ming Tang
Keyword(s):  
Wave Propagation ◽  
Hydraulic Fracturing ◽  
Elastic Wave ◽  
Fracture Network ◽  
Velocity Variation ◽  
Fracture Aperture ◽  
Filling Material ◽  
S Wave ◽  
Velocity Change ◽  
Main Fracture

We numerically simulate elastic-wave propagation along a fluid-filled borehole with a hydraulically fractured formation. The numerical model is based on the results of hydraulic fracturing on laboratory specimens. Two typical models are simulated: a main fracture crossing the borehole and a fracture network extending from the borehole. In addition, both models contain small, secondary fractures surrounding the borehole. Our result indicates that wave propagation in the main-fracture model is characterized by significant S-wave anisotropy for polarization along and normal to the fracture orientation, with the magnitude of anisotropy depending on the fracture aperture and filling material. In contrast, no significant anisotropy is observed for the fracture network model. In both models, wave propagation is significantly affected by small-fracture-induced near-borehole velocity variation. Our modeling results provide a theoretical foundation for evaluating hydraulic fracturing using the borehole acoustic logging. The hydraulic fracture-induced S-wave anisotropy can be evaluated with the cross-dipole S-wave logging, and the fracturing-induced velocity change can be detected by acoustic traveltime tomography. We used field data examples to demonstrate the effectiveness and practicality of using the borehole acoustic techniques for hydraulic fracturing evaluation.

Incorporating mechanisms of fluid pressure relaxation into inclusion‐based models of elastic wave velocities

Geophysics ◽  
2003 ◽  
Vol 68 (4) ◽  
pp. 1173-1181 ◽  
Author(s):  
S. Richard Taylor ◽  
Rosemary J. Knight
Keyword(s):  
Elastic Wave ◽  
Water Saturation ◽  
Laboratory Data ◽  
Fluid Pressure ◽  
P Wave ◽  
Porous Rocks ◽  
Low Frequencies ◽  
Wave Velocities ◽  
Exact Agreement ◽  
Flow Through

Our new method incorporates fluid pressure communication into inclusion‐based models of elastic wave velocities in porous rocks by defining effective elastic moduli for fluid‐filled inclusions. We illustrate this approach with two models: (1) flow between nearest‐neighbor pairs of inclusions and (2) flow through a network of inclusions that communicates fluid pressure throughout a rock sample. In both models, we assume that pore pressure gradients induce laminar flow through narrow ducts, and we give expressions for the effective bulk moduli of inclusions. We compute P‐wave velocities and attenuation in a model sandstone and illustrate that the dependence on frequency and water‐saturation agrees qualitatively with laboratory data. We consider levels of water saturation from 0 to 100% and all wavelengths much larger than the scale of material heterogeneity, obtaining near‐exact agreement with Gassmann theory at low frequencies and exact agreement with inclusion‐based models at high frequencies.

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