Three-dimensional mechanical behaviors of casing during gas production from marine hydrate reservoirs using depressurization

Abstract

During marine hydrate production, some potentially undesirable consequences of casing failure and deformation are prone to occur. However, conventional planar model used in oil-gas production casing analysis is unable to handle failure and deformation of the casing, as the temporal-spatial evolution of formation caused by hydrate decomposition could not be calculated. This paper aimed at proposing a methodology to research 3D stress distribution and deformation of casing. In the proposed approach, a multi-field coupled algorithm of seepage-mechanics-decomposition was developed, and a 3D interaction model of casing-formation was established, in which dynamic characteristics of formation deformation could be considered. The effect of slanting formation on casing behaviors was investigated by improving the established 3D model. A case study illustrated the application of the proposed methodology. Results indicated that casing strength yielding was dominated by axial stress, which increased first and then gradually stabilized as production advanced. When formation inclination changed from 0° to 5°, axial stress would increase by 15%, the recommended differential pressure of production should be decreased from 10 MPa to 8 MPa, and the casing deformation pattern changed from diameter reduction to bending. The proposed approach could be used to provide theoretical reference for casing design of marine hydrate production.