PGK AGM & Monthly meeting
Met gast spreker Peter Mesdag.
18.00-18.30 Algemene Leden Vergadering
18.30-19.00 Presentatie Peter Mesdag: “A new approach to quantitative azimuthal inversion for stress and fracture detection. Working with effective elastic parameters in anisotropic media.”
va. 19.00 Buffet receptie in Hathor
Exploration and development of unconventional reservoirs, where fractures and in-situ stress play a key role, calls for improved characterization workflows. The effects of anisotropy on the estimated reservoir parameters can no longer be ignored. In this work, we present a method for quantitative estimation of anisotropic parameters related to stress and fracture detection that makes use of standard isotropic modelling and inversion techniques in anisotropic media. Based on reflectivity equations for TI media, we build a set of transforms that map the elastic parameters used in prestack inversion into effective anisotropic elastic parameters. When used in isotropic forward modelling and inversion, these effective parameters accurately mimic the anisotropic reflectivity behaviour of the seismic data, thus closing the loop between well log data and seismic inversion results in the anisotropic case.
Here we show that using these effective elastic parameters in isotropic modelling we produce exactly the same synthetics as when using more complex anisotropic modelling.
When estimates of the Thomsen parameters are known at well control, isotropic well measurements can be transformed into effective elastic parameters. This allows for more accurate well tying and wavelet estimation, and also for quantitative post-inversion analysis.
Results from azimuthally sectored inversions are analysed through Fourier techniques to produce measures of anisotropy magnitude and orientation. Assuming an underlying model these quantitative measures can be transformed into measures of fracture density, rock weakness or stress.
After a brief introduction the power of this proposed method will be illustrated by means of a feasibility study. Here the importance of an Azimuthal Low Frequency Model (ALFM) will become evident.