Utilising calibrated MEM to constrain geomechanical uncertainty in the Pelican CCS Project, Gippsland Basin

The Pelican site in the offshore Gippsland Basin contains multiple saline aquifer seal and reservoir pairs that provide potential targets for long-term geological storage of carbon dioxide. To evaluate geomechanical risks associated with injection and containment, a comprehensive 1D Mechanical Earth Model (MEM) was constructed for the Gular-1 greenhouse gas appraisal well using an unusually rich dataset acquired specifically for carbon capture and storage (CCS) site assessment. The workflow integrated full-diameter core and mechanical sidewall cores tested under tri-axial conditions, unconfined compressive strength and Brazilian tensile strength measurements, extended leak-off tests, Modular Formation Dynamics Tester mini-fracture tests, advanced Sonic Scanner full-waveform data, and borehole image logs. Dynamic elastic properties from sonic and density logs were converted to static moduli using empirically derived correlations and calibrated against laboratory measurements, while stress magnitudes were constrained by field tests and Sonic Scanner stress inversion in stress-sensitive sandstone zones. A key outcome of the study was the recognition that the primary reservoir sandstones at Pelican are in a normal-faulting stress regime (vertical stress maximum horizontal stress minimum horizontal stress), contrary to earlier expectations of a strike-slip setting. Sonic Scanner stress inversion, supported by borehole image log interpretation and laboratory data, was critical in resolving this uncertainty. The calibrated MEM indicates stress contrasts of approximately 700 psi across the T2 seal and around 900 psi across the T4 seal, providing strong evidence for robust vertical containment. The model was validated using wellbore stability analysis that reproduced observed drilling-induced failures. This paper demonstrates how a multi-measurement, fully calibrated MEM can significantly reduce uncertainty in CCS site evaluation and highlights the value of acquiring advanced geomechanics data early in the project lifecycle.