Browsing by Subject "Seismic anisotropy"

Now showing 1 - 2 of 2

Seismic anisotropy analysis with Muir-Dellinger parameters
(2017-05-03) Sripanich, Yanadet; Fomel, Sergey B; Fowler, Paul; Sen, Mrinal; Spikes, Kyle; Torres-Verdin, Carlos
Seismic anisotropy, defined as the dependency of seismic-wave velocities on propagation direction, is an important factor in seismic data analysis. Neglecting anisotropy can lead to significant errors in the subsurface images. Even after decades of considerable research efforts, the topic of anisotropy remains at the center of attention of the research community. In this dissertation, I address the fundamental problem of choosing parameterization to characterize the effects of seismic anisotropy and propose an alternative approach based on the Muir-Dellinger (MD) parameters. I first give their definitions and discuss their properties with respect to the classic qP-wave phase velocity in transversely isotropic (TI) media in the second chapter. I show that, when expressed in terms of MD parameters, the exact expression of phase velocity in this case is controlled by the elliptical background and two anelliptic parameters (q1 and q3) defined as the curvature of the qP-wave phase velocity measured along the symmetry axis and its orthogonal. The wide range of possible values for the vertical shear-wave velocity (vS0) expressed under the conventional Thomsen parameterization translates to a considerably narrower range of the slope in the nearly linear dependence between q1 and q3. This discovery suggests a possibility of using such a relationship to characterize the complete stiffness tensor, infer more information about the subsurface directly from qP kinematics, and provide a physical basis for reducing the number of parameters in qP-wave analysis. Based on various experimental measurements of stiffness coefficients reported in the literature, I relate such properties in shales, sandstones, and carbonates with corresponding values of slope. I further investigate this empirical linear relationship in the third chapter and show that it can also gives additional rock physics implications about the type of pore fluids. I provide some supportive evidence of its reality from self-consistent rock physics modeling and Backus averaging for shale samples. In addition, I find that both the 2D MD parameterization and its 3D extension, suitable for studies of qP waves in orthorhombic media, also provide a convenient foundation for the parameter estimation process. I carry out a detailed study on the sensitivity of MD parameters to qP-wave kinematics in comparison with other known anisotropic parameterization schemes in the fourth chapter. In the last chapter, using the MD parameters, I propose novel analytical approximations for qP-wave phase and group velocities in 2D TI and 3D orthorhombic media. The novel approximations are highly accurate and possess an advantage of having similar functional form with reciprocal coefficients, which adds practical convenience to considering both phase (wave) and group (ray) velocities. Finally, I discuss known limitations of the MD parameterization and suggest possible future research topics.
Using direct S-wave seismic modes for reservoir characterization in Wellington Field, Kansas
(2017-05) Gupta, Menal; Hardage, Bob Adrian, 1939-; Spikes, Kyle T; Tatham, Robert H; Grand, Stephen P; Wagner, Don E
S-waves exhibit birefringence, provide independent measurements of subsurface elastic properties and play a vital role in reservoir characterization. Despite obvious advantages, direct S-wave data (S-S and SV-P) remain under-utilized for characterization of fractured reservoirs, partly due to limited understanding of seismic attributes quantitatively estimate fracture properties, and because of the high-cost associated with direct S-wave data acquisition. This dissertation offers solutions to these challenges by creating S-S AVO attributes that can estimate fracture properties, and demonstrating use of low-cost, mode-converted P-wave data (SV-P) generated by conventional P-wave sources, for reservoir characterization. Multicomponent seismic data and well data from Wellington Field, Kansas are analyzed to understand reservoir facies and fractures characteristics in the Arbuckle Group, which is being considered for CO₂ injection. Results from multicomponent seismic interpretation suggest a mechanically stratified Arbuckle interval with varying lithofacies, and presence of seismic anisotropy caused by fractures. Rock physics modeling and S-wave AVO analysis demonstrate that the Intercept Anisotropy (IA) attribute and Gradient Anisotropy (GA) attribute proposed in this dissertation can be used to estimate fracture-density and fluid-fill in fractures, respectively. Results show that amplitude-based anisotropy analysis, in conjunction with travel-time-based analysis for seismic anisotropy, helps reduce ambiguity and provides high-resolution fracture characterization. Finally, a series of comparisons between the inversion results of P-P, P-SV and SV-P seismic data show that vertical-vibrator SV-P data from vertical geophones work as good as P-SV seismic data from horizontal geophones to estimate reservoir properties, and provide better subsurface resolution than do SV-P data generated by a horizontal vibrator. These results validate that direct S-wave data generated by conventional P-wave sources are a low-cost, yet highly-effective, alternative to data generated by more expensive S-wave sources. Overall, this dissertation advances our understanding of S-wave AVO attributes, and offers novel workflows to characterize naturally fractured reservoirs using direct S-wave data that do not require expensive seismic data acquisition. Multicomponent seismic data and well data from Wellington Field, Kansas are analyzed to understand reservoir facies and fractures characteristics in the Arbuckle Group, which is being considered for CO2 injection. Results from multicomponent seismic interpretation suggest a mechanically stratified Arbuckle interval with varying lithofacies, and presence of seismic anisotropy caused by fractures. Rock physics modeling and S-wave AVO analysis demonstrate that the Intercept Anisotropy (IA) attribute and Gradient Anisotropy (GA) attribute proposed in this dissertation can be used to estimate fracture-density and fluid-fill in fractures, respectively. Results show that amplitude-based anisotropy analysis, in conjunction with travel-time-based analysis for seismic anisotropy, helps reduce ambiguity and provides high-resolution fracture characterization. Finally, a series of comparisons between the inversion results of P-P, P-SV and SV-P seismic data show that vertical-vibrator SV-P data from vertical geophones work as good as P-SV seismic data from horizontal geophones to estimate reservoir properties, and provide better subsurface resolution than do SV-P data generated by a horizontal vibrator. These results validate that direct S-wave data generated by conventional P-wave sources are a low-cost, yet highly-effective, alternative to data generated by more expensive S-wave sources. Overall, this dissertation advances our understanding of S-wave AVO attributes, and offers novel workflows to characterize naturally fractured reservoirs using direct S-wave data that do not require expensive seismic data acquisition.