Avo

Derived Rock Attributes Analysis for Enhanced Reservoir Fluid and Lithology Discrimination

“…There are several different approaches but the common goal of all the methods is to extract information about lithology, reservoir quality, and pore fluids from the prestack seismic amplitudes for reservoir characterization (Chopra and Castagna, 2014). The onshore Niger Delta has gradually assumed the status of a matured oil and gas producing province.…”

Approximations to seismic AVA responses: Validity and potential in glaciological applications

“…This is usually neglected in practice, and θ A can be substituted with θ i provided that velocity contrasts are weak and incident angles are small. For typical contrast magnitudes, the Aki-Richards approximation is valid for θ i ≤ 35° (Aki and Richards, 1980;Chopra and Castagna, 2014), although stronger contrasts can invalidate it at smaller angles. Because most other AVA approximations derive from equation 1, they inherit (and in some cases, add to) these underlying assumptions.…”

“…The complicated K-Z equations do not support an intuitive interpretation of the physical properties that underlie the AVA response (Chopra and Castagna, 2014). Consequently, the K-Z equations are usually simplified according to linear or quadratic approximations (Aki and Richards, 1980;Shuey, 1985;Smith and Gidlow, 1987;Rüger, 1997;Fatti et al, 1994;Wang, 1999).…”

“…Fatti et al (1994) rearrange equation 2 in terms of acoustic impedance and shear impedance, Y (the product of V S and ρ) to define the reflectivity as (Wang, 1999;Chopra and Castagna, 2014). Here, θ i represents the largest angle for which the approximations are considered valid, for the typical seismic contrasts for which they are applied.…”

“…Here, although well logs are usually available to calibrate reflectivity (Armstrong et al, 1995), the standard practice is to characterize and report AVA responses according to a simplified classification strategy (e.g., Rutherford and Williams, 1989;Castagna and Swan, 1997). Although the reflectivity of an interface is described exactly by the Knott-Zoeppritz (K-Z) equations (Aki and Richards, 1980), these are not intuitively interpreted (Chopra and Castagna, 2014), and reflectivity is more routinely described using parameters derived from AVA approximations to the K-Z equations. Such approximations make several assumptions about the reflectivity of an interface and typically require that the seismic contrast across it is small.…”