Wellbore shrinkage during drilling in methane hydrate reservoirs

Abstract

Abstract Methane hydrates as a clean and abundant energy source, have attracted the attention of the world. However, the instability of hydrate reservoirs makes it difficult to drill production wells. After drilling, the creep properties of hydrate reservoir would cause wellbore shrinkage, which will affect the drilling safety. This study is to analysis law of wellbore shrinkage after a hydrate well drilled. The results demonstrate that wellbore shrinkage mainly results from plastic deformation and creep deformation. The largest and smallest values are separately found in the directions of the maximum and minimum horizontal in‐situ stress. With the increase of initial in‐situ stress ratio, wellbore shrinkage linearly rise. Under the condition of low horizontal in‐situ stress ratio, wellbore shrinkage is mainly determined by creep deformation. Under the condition of high horizontal in‐situ stress ratio, wellbore shrinkage commonly depends on plastic deformation and creep deformation. With deepening methane hydrate reservoirs, wellbore shrinkage shows a nonlinear increase. For formations with higher hydrate saturation, larger wellbore shrinkage would occur. The research results can provide a theoretical basis for the selection of drilling method while drilling in hydrate formations.

Keywords

• creep
• drilling
• energy
• methane hydrate
• wellbore shrinkage