ADNR

Numerical simulation of low frequency seismic waves of fluid bearing layers in geological structures

(A joint R&D project in collaboration with the ADNR Exploration GmbH, project duration: 2008-2010, PI:
J. Zschau, Participants: R. Wang, Y. Ma, H. Woith, S. Parolai)

To analyse the local amplification effect on seismic signals depending on site conditions, several tools have been developed and published by the GFZ Potsdam. Using the H/V spectrum as well as the dispersion curve of ambient noise data, for example, we can estimate the shallow soft sediment structure. Many such tools require synthetic seismograms which are computed so far almost for layered elastic or viscoelastic media and the site amplification is solely interpreted as the resonance effect of local soft sediment cover with a very low shear wave velocity. The role of pore fluid, i.e., the poroelastic effect, which may be significant at sites with shallow fluid-saturated reservoirs, is still unknown. Hydrocarbon reservoirs seem to be characterized by a unique spectral signature with this frequency window. The technology has been applied by the ADNR Exploration GmbH successfully in numerous oil and gas producing areas worldwide. The theoretical base of the observed phenomena is, however, not yet fully understood and is the objective of the proposed research collaboration. In the first step of the project we will concentrate on the theoretical development that includes (1) derivation of the fundamental wave solutions for homogeneous poroelastic media based on Biot’s linear poroelasticity theory, (2) extension of the synthetic seismogram code QSEIS (Rongjiang Wang) and other related tools for analysing seismic noise data, and (3) some numerical tests to investigate the feature of seismic wave propagation within shallow reservoirs saturated by different fluids (water, oil, gas). In the second step, the obtained theoretical results will be used to interpret the available field data (provided by ADNR) and to develop new seismic methods for localizing subsurface reservoirs with low measurement efforts.