Extended elastic impedance for fluid and lithology prediction

Abstract

Constant angle projections of seismic sections can be designed to provide maximum discrimination between fluids or lithologies. The optimum projection for a noise‐free, isotropic environment can be obtained using an extension to the elastic impedance concept, which itself is an extension of acoustic impedance (AI) to nonzero angles of incidence. To achieve this, we modify the definition of elastic impedance (EI) beyond the range of physically meaningful angles by substituting tanχ for sin2 θ in the two‐term reflectivity equation. The primary variable now becomes χ rather than θ. We allow it to vary between −90° and +90°, which gives an extension of EI for any combination of intercept and gradient. We refer to this form of elastic impedance as extended elastic impedance (EEI). In this paper we demonstrate that EEI can be tuned using different χ values to be approximately proportional to a number of elastic parameters, and we give EEI expressions for shear impedance (SI), bulk modulus, shear modulus, Lamé's parameter, and Vp/Vs. This leads to the identification of different areas of EEI space that tend to be optimum for fluid and lithology imaging. Having identified an appropriate χ value, the equivalent seismic section can be obtained from combinations of intercept and gradient stacks from routine AVO processing.

The application of high-resolution 3D seismic data to model the distribution of mechanical and hydrogeological properties of a potential host rock for the deep storage of radioactive waste in France

“…Such a processing refers to elastic inversion (Whitcombe et al, 2002). A model-based elastic inversion (a priori impedance model obtained from well data), applied to the angle migrated stacks, provides 3D impedance blocks (Ip and Is blocks).…”

Prestack inversion and multiattribute analysis for porosity, shale volume, and sand probability in the Havert Formation of the Goliat field, southwest Barents Sea

“…EI is the equivalence of AI for nonzero incidence angles. Some limitations of this concept were later addressed by Whitcombe et al (2002), and a normalized version of the EI called the EEI was then derived. A standard EEI inversion was done to obtain V sh and PHIE-tuned impedances.…”

Tertiary deep-marine reservoirs of the North Sea region: an introduction

“…In the pre-stack domain, Connolly (1999) introduced elastic impedance (EI) as a generalization of AI to non-zero angles of incidence and this allows the construction of a pseudo impedance curve calibrated with well logs at any angle of incidence. The development of extended elastic impedance (EEI) inversions in the late 1990s (Whitcombe et al 2002) has revolutionized lithology and fluid prediction in the North Sea Tertiary. EEI lithology inversion techniques are the basis of much of the reservoir architecture work described by Rose & Pyle (2014) in the Forties Field.…”