Pore structure effects on elastic wave propagation in rocks: AVO modelling

Abstract

Pore structure in rocks at reservoir pressures can affect strongly elastic wave velocities. For a reservoir where the fluid type and lithology are known, elastic wave velocity V can be described by a two-parameter model in terms of porosity and a pore structure parameter referred to as the frame flexibility factor (γ). Using this two-parameter elastic model V(, γ), the concept of pore structure type (PST) is introduced to quantify the pore structure effects on elastic properties of sedimentary rocks. To illustrate the concept, three PSTs are defined and they have their distinct characteristics on elastic wave propagation. Through solving exact Zoeppritz equations and elastic finite-element modelling, this study indicates that it may be feasible to detect pore structure variations in reservoir rocks from seismic data via amplitude variation with offset (AVO) analysis. AVO interpretation aimed at fluid detection can be complicated where the presence of large pore structure variations is expected because the effects of pore structure on wave propagation can be much stronger than the fluid factor, especially in carbonate rocks.