Guided seismic waves in layered poroviscoelastic media for continuity logging applications: model studies1

Abstract

AbstractThe gas industry is continuing to concentrate its research and development efforts on new and advanced technology to improve reservoir descriptions through the producing life and development history of heterogeneous gas reservoirs. A very important aspect of this need is the ability to reduce the uncertainty of estimating probable reserves and to lower the operating costs to recover incremental reserves in producing and depleted gasfields. Established methods for reducing uncertainty in heterogeneous reservoir compartments, such as VSP and cross‐well techniques may enhance resolution, but they are currently not economically justifiable in on‐shore gasfields. Continuity logging using guided waves is an alternative approach to analysing inter‐well seismic data to confirm the continuity of heterogeneous gas reservoir compartments; in particular, the continuity of sand and shale stratigraphy in gas reservoirs.The solution of a coupled system of differential equations based on Biot and homogenization theories is adapted to calculate guided seismic waves trapped in low‐velocity layers. The general solution is for a 3D source in a horizontally layered poroviscoelastic medium having isotropic and laterally homogeneous material properties. A unified representation of the medium that includes fluid‐solid interactions and viscoelastic losses is incorporated into the solution. The guided‐wave part of the vector wave field and fluid‐pressure of the complete wave motion in layered dissipative media is verified and used to simulate dispersion and attenuation of guided seismic waves for continuity logging applications. The results of this work suggest that the multimode wave solution is appropriate to simulate guided seismic wave signatures to indicate continuity of layered earth structures in poroviscoelastic reservoirs. In particular, the normal mode information can be used for planning continuity logging surveys and for interpreting the corresponding seismic data. Further, fluid‐pressure waveforms show that maximum amplitude normal modes can be detected at layer interfaces in fluid‐filled porous media, and the corresponding Airy phase wave groups may carry information on the formation permeability.