Present-day stress profile in the Baltic Basin sedimentary succession constrained by drilling-induced structures: interpretation uncertainties

Abstract

A far-field stress model based on theory of elasticity and utilizing the Mohr-Coulomb criterion is commonly used in the petroleum industry as a reliable method for present-day stress profiling. We have analysed the present-day stress profile in the Lower Paleozoic shale succession of the Baltic Basin (northern Poland), based on data from a single borehole. Our analyses take into account the vertical transverse isotropy (VTI) of the mechanical properties. Initial modelling of the stress profile showed – despite general agreement concerning the length and location of the modelled and observed breakouts – systematic differences when the profile of these structures is analysed in detail. Analyses carried out for selected segments of the borehole have shown that the mere presence of breakouts affects the interpretation of the mechanical properties, and thus also the stress profile. We have analysed the size of the necessary correction for tectonic strain, to avoid this effect, as well as uncertainty resulting from the failure criteria adopted. The final model, corrected for stress disturbances by breakouts, reveals the stratification of stress regime, with the dominance of a normal faulting regime, and low values of differential stresses in the shale formations