OS5C-3：NUMERICAL INVESTIGATION OF CASING INTEGRITY IN OFFSHORE INDONESIA MARINE GAS HYDRATE-BEARING SEDIMENTS

Xiaoyan LONG¹, Tjok Ko-MIN¹, Chris WRIGHT², Okewunmi SHOLA²
1. Fugro GeoConsulting Inc., USA; 2. Chevron Indonesia Company., Indonesia.

　　Casing integrity during well production could be compromised due to gas hydrate dissociation and destabilization of marine gas hydrate-bearing sediments (HBS) induced by a hot wellbore.  Assessment of wellbore stability in HBS is complex with many key factors involved such as character, distribution and saturation of gas hydrate habitat, thermal and geomechanical properties of sediments overlying, within and vertical adjacent to hydrate bearing zones, and design and installation details of production wells including well product temperature and thermal characteristics of well components.

　　This paper presents numerical investigation of casing integrity in the face of in-situ gas hydrate dissociation due to well heating in the Rapak PSC development areas, Offshore East Kalimantan, Indonesia.  Hydrate accumulation (nature, saturation and distribution) for study areas are interpreted using seismic inversion method and rock physics transform along with available geophysics seismic data and offset well log data.  The simulation entails thermodynamic stability analyses of the gas hydrates including hydrate dissociation, gas dissolution and pore pressure evolution, fracture development assessment and soil movement prediction followed by soil-well interaction modeling to determine potential stresses in the well components.  Fracture models of crack dimensions are premised on two scenarios:  (1) development of a pattern of laterally expanding horizontal fractures evenly spaced vertically throughout the hydrate-bearing zone and centered on the wells, or (2) development of vertical fractures which will intersect the seafloor to allow gasses from hydrate dissociation to vent into water column.

　　With high computational efficiency, the described numerical investigation supplies bounding estimates of gas hydrate dissociation effects around producing wells and the possible risk of well instability.  The model provides very useful insight in understanding gas hydrate melting behavior and the effect of dissociation on casing integrity.