Abstract

Oil reservoirs underneath salt rocks are very common due to the sealing capabilities of these rocks. Drilling across salt layers requires a careful consideration of the rock behavior. Due to is inability to sustain deviatoric stresses, the time-dependent deformations close the wellbore and may jeopardize the drilling plan. Many creep laws try to describe the creep deformations of the salt, but applicability in the wellbore drilling usually neglect the transient creep. Therefore, this work focuses on quantifying the differences in the short-term creep when primary creep is added to the steady state creep response. Based on a Multimechanism Deformation creep law, two salts from U.S. Gulf Coast were considered: i) Big Hill, and ii) Bryan Mound. Results indicate that in the short term, the addition of primary creep results in wellbore displacements 3-6 times faster for mud weights lower than 80% of the overburden stress. However, stress relaxation is also faster, and the differences reduce to 1.5 to 2 times after 10 days.

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