ABSTRACT
The in-situ stresses in the Potiguar Basin, Northeast of Brazil, have been estimated through the Anelastic Strain Recovery Test – ASR-3D, in order to help defining the orientation for horizontal wells, regarding well stability concerns. The in-situ stress orientation was directly computed by assuming the same orientation of the principal strains, which were determined by the usual ASR test procedures. The stress magnitudes, however, could not be calculated by the existing formulations, since the rock samples presented shrinkage, instead of the expected expansion. A recently developed poroviscoelastic model was then applied for estimating the stress magnitudes. In this model, the rock contractions are assumed to be caused by porepressure diffusion, shrinking the pore volume as the porefluid is allowed to flow out of the rock. The original stresses were obtained by back-analyzing the field data: the anelastic strains calculated by the physical model were fitted to the experimental strains with the numerical SIMPLEX algorithm. The results have shown good agreement with available seismic events and microfracs, as well as contributed to successful well drilling.
