This paper presents a semi-analytical large strain elastoplastic analysis of an internally pressurized wellbore embedded in a Mohr-Coulomb medium. The constitutive equations for a non-associated deformation theory with strain hardening material were fitted on true stress-strain data from triaxial tests on Jurassic shale. The model is used to investigate the effect of plastic yielding on the initiation of a tensile fracture and to interpret the experimental results obtained from hydraulic fracturing tests on hollow cylinders.