In-situ Stresses:
Whether stresses are being locally perturbed as a result of interaction with faults or lithological boundaries with depth?
Are we really considering the ‘variations’ in the azimuth of ‘maximum horizontal stress’ between wells within a single basin (rather than going for a regional average); and do we really take into account the “vertical rotations” in ‘maximum horizontal stress’s orientation (resulting from the differences in mechanical properties between fault zones and/or at the boundaries between lithological units), while obtaining the ‘orientation of the principal stress’ using the traditional techniques (such as ‘earthquake focal mechanism’, ‘borehole breakout - BOs analysis’ and/or ‘drilling induced tensile fractures - DITFs’)?
Having means for precise determination of (a) overburden stress at a particular depth (from the density measurement of the sedimentary sequence); and (b) the overburden-related confining stress (induced by the elastic effect of the reservoir rock); will it be feasible to estimate the in-situ ‘tectonic stresses’ precisely, as it generally shows ‘significant variations’ depending on the ‘measurement location’ relative to the ‘regional tectonic movement’?
This could be helpful, Suresh:
https://www.nature.com/articles/s41598-021-89019-4
There is anecdotal evidence that faulting changes the in-situ stress field locally, at least in the near surface (~0-4 km). This comes from azimuthal inversion of commercial seismic data, which is typically used to determine the orientation of minimum and maximum horizontal stress and infer the presence of fractures. The signal-to-noise ratio of this type of analysis is low, however, and requires verification from (e.g.) oriented cores from wells.
Hello,
the answer is both, first, faults can perturb the in situ stresses. a simple example is a slip-on potentially active fault (critically stressed) that will eventually rotate the stress and thus cause stress perturbation (this will have an effect on hydraulic fracture propagation for example)
Secondly, lithological variation will disturb Horizontal stresses "Shmin and SHmax", due to lithological dependence (read Zhang and Zhang, 2017 for more). One thing to consider is that different lithofacies have different mechanical properties, sandstones are usually stiffer than shales, hence sandstones have higher Young's modulus and smaller Poisson's ratio, whereas shales are characterized by higher Poisson's ratio and thus have higher horizontal stress magnitude, therefore shales are used as a stress barrier to hydraulic fracturing in the adjacent sandstones (lower horizontal stresses). Another way to think about lithological boundaries is that when an unconformity is present it can act as a stress refractor, thus causes a refraction of the stresses, hence the stresses will eventually rotate when encountering a huge lithological variation.
hope I have answered your question.
Generally, two mentioned factors can influence of it indirectly, you can find the impact of faults in this article:
"Zhang et al. 2021, In Situ Stress Prediction in Subsurface Rocks: An Overview and a New Method, https://doi.org/10.1155/2021/6639793"
And analysis of different rocks effect on stress in models in this study:
"Delavar et al. 2021, An investigation into the effect of geomechanical properties of reservoir rock on drilling parameters—a case study, DOI: 10.1007/s12517-021-08168-y"
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