Effect of using transient polyaxial failure criterion in wellbore instability analysis

ABSTRACT

Wellbore instability is one of the major challenges facing the drilling industry and it shows itself in the form of wellbore collapse and/or fracture. The major reason for this challenge is the inability of the mud density to balance the weight of the excavated materials. While most drilling operations are carried out through shale formations, the complexities of drilling such wells are increased because of the tendency for shale to react with water-based mud. Moreover, the very low permeability of shale means that time-dependent effects may set in. The convention used to incorporate time-dependent effect is to couple the constitutive stress model and chemical diffusion, but in this study, we considered the effect of incorporating time variable into the rock failure criterion. The choice criterion used is the Mogi-Coulomb rock failure criterion, which was modified to incorporate the time effect. The results indicate that in an open-hole the mud density to prevent wellbore collapse increases with time while that to prevent wellbore fracture decreases, thus making the mud window reduce with time.

KEYWORDS:

• Wellbore instability
• drilling window
• time-dependent effect
• wellbore collapse
• wellbore fracture

Disclosure statement

No potential conflict of interest was reported by the authors.