Geomechanical modeling of salt diapirs: A field scale analysis for a 3D salt structure from the North Sea

Underground salt deposits deform with time, leading to a structure known geologically as a salt diapir. Salt diapirs play an important part in hydrocarbon developments and are significant for petroleum exploration. Presence of geological inhomogeneities such as salt domes causes significant perturbation of in-situ stresses, which has serious implications for the stability of boreholes drilled in the vicinity of the diapirs. This work presents a modelling methodology to study stress distribution throughout a rock mass surrounding a diapir. Salt diapirs of simplified axisymmetric geometry were modeled, and the effects of grid zone size, stress regime, rock mechanical properties and creep constitutive behaviour were analysed. The results showed good agreement with the published data. Also actual salt dome geometry from the North Sea was modeled. The results of the computations agreed well with those found in literature showing raised deviatoric stress in certain areas in the vicinity of the diapir, which results in greater potential for borehole instability. The model can be useful in borehole failure risk assessment with the potential to improve drilling efficiency, reduce downtime, by planning the boreholes so that their trajectories avoid areas of high risk where practicable.