Seismik s.r.o. - Passive Seismic Services

StressInversion is a proprietary effective, autonomous tool that specifies the stress state that accounts the best for a set of microearthquake focal mechanisms.

The orientations of the principal stress axes σ₁, σ₂ and σ₃ (σ₁ > σ₂ > σ₃) are determined from passive seismic datasets, adding a new value to the existing microseismic data. Using the orientation of the stresses, one can optimally place wellbores optimizing the recovery from a reservoir.

StressInversion recovers four parameters of the stress tensor: three angles defining the directions of the three principal stresses, σ₁, σ₂ and σ₃, and the ratio between their differences, Φ = (σ₂ - σ₃) / (σ₁ - σ₃). StressInversion calculates the effective stress corresponding to a homogeneous tectonic stress in the source region. The uncertainties of the retrieved stress directions are calculated by the jack-knife method.

Left picture: Variability of the input source mechanisms of events recorded during the Soultz injection experiment in 2003. Stacked principal axes: T-axes - triangle apex up, P-axes - triangle apex right. Right picture: The results of StressInversion. Stress is inverted using the 45 focal mechanisms from input. The optimum position of the directions of the principal stresses σ₁, σ₂ and σ₃ are marked by darker colour symbols. Clusters of same coloured symbols denote the confidence zones of maximum σ₁ (red), medium σ₂ (grey) and minimum σ₃ (blue) stress axes derived from the jack-knife uncertainty test.

REFERENCES

• Staněk F., Jechumtálová Z., Eisner L. (2015), Reservoir stress from microseismic source mechanisms, The Leading Edge, 34(8), 890–893, 895