Simulation of Seismic Wave Propagation in Porous Rocks Considering the Exploration and the Monitoring of Geological Reservoirs
2021Konferenzbeitrag
Englisch
Boxberg, Marc S.; Friederich, Wolfgang, 2021: Simulation of Seismic Wave Propagation in Porous Rocks Considering the Exploration and the Monitoring of Geological Reservoirs. DOI: 10.23689/fidgeo-3967.
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Modelling the propagation of seismic waves in porous media gets more and more popular in the
seismological community since it is an important but challenging task in the field of computational
seismology. The fluid content of, for example, reservoir rocks or soils, and the interaction between the fluid
and the rock or between different immiscible fluids has to be taken into account to accurately describe
seismic wave propagation through such porous media. Often, numerical models are based on the elastic
wave equation and some might include artificially introduced attenuation. This simplifies the problem but only
approximates the true physics involved. Hence, the results are also simplified and could lack accuracy or
miss phenomena in some applications.
The aim of the conducted work was the consistent derivation of a theory for seismic wave propagation in
porous media saturated by two immiscible fluids and the accompanying numerical solution for the derived
wave equation. The theory is based on Biot's theory of poroelasticity. Starting from the basic conservation
equations (energy, momentum, etc.) and generally accepted laws, the theory was derived using a
macroscopic approach which demands that the wavelength is significantly larger than the size of the
heterogeneities in the medium due to the size of the grains and pores or due to effects on the mesoscopic
scale. This condition is usually fulfilled for seismic waves since the typical wavelength of seismic waves is in
the order of 10 m to 10 km. Fluid flow is described by a Darcy type flow law and interactions between the
fluids by means of capillary pressure curve models. In addition, consistent boundary conditions on interfaces
between poroelastic media and elastic or acoustic media are derived from this poroelastic theory itself.
The nodal discontinuous Galerkin method is used for the numerical modelling. The poroelastic solver is
integrated into the 1D and 2D codes of the larger software package NEXD that uses the nodal discontinuous
Galerkin method to solve wave equations. The implementation has been verified using symmetry tests and
the method of exact solutions.
This work has potential for applications in various scientific fields like, for example, exploration and
monitoring of hydrocarbon or geothermal reservoirs as well as CO2 storage sites.