NUMERICAL MODELING OF THE FORMATION OF POCKMARKS ON THE SEABED AS A RESULT OF DECOMPOSITION OF GAS HYDRATES

Abstract

A geomechanical model of pockmark formation on the seabed resulting from gas hydrate decomposition has been developed. The process of destruction and formation of pockmarks occurs in a medium whose behavior is described by a nonlinear creep model combined with a yield  criterion dependent on internal friction. Constitutive relations for an elastic-viscous-plastic medium with a temperature-dependent power law of creep are used. The law of non-associated plastic flow with the Drucker–Prager limit condition and softening is used to describe the destruction of the medium. Softening leads to the development of instability of viscoplastic flow and localization of shear deformation in narrow zones, along which destruction occurs. Analysis of the development of deformations and stresses showed that shear deformation is localized on the inner contour of the dome-shaped cap, forming a narrow conical zone. After it reaches the surface, cohesion drops to zero and the pressure pushes the material to the surface, completing the formation of a crater. The time it takes for the conical surface to form depends on the pore pressure in the inclusion. If the pressure does not exceed the critical value, the stresses in the cap do not reach the strength limit, the fracture surface does not form, and the pockmark does not form.