Modeling Reveals Hidden Conditions That Can Impair Wellbore Stability and Integrity

Abstract

Abstract This paper describes thermal modeling and its combination with drilling fluid analysis to reveal concealed changes in well conditions during various drilling and completion operations. These hidden conditions represent significant changes in the well's drilling and completion fluid temperature, pressure, and density (FTPD) that may help explain wellbore stability and integrity issues. For example, the model results may allow operators to look for FTPD-related wellbore stability issues where the hole is not circulated and is static for many hours. Deeper wells and those with greater differences between induced and natural temperature and pressure conditions may have dangerous conversions of pressure over-balances into under-balances that can cause pore fluid influx, cross-flow, collapse, and other severe wellbore failures. Long, deep holes that are being circulated may also be modeled to look for FTPD-related issues not revealed by other means. Conditions such as over-balanced pressure and stable rock conditions may actually change to under-balanced pressure and unstable rock conditions with consequences including kicks, solids beds from formation breakouts, flow after cementing, stuck pipe by hole collapse, salt creep acceleration, etc. A case history is discussed where the prototype model correctly predicted that no formation gas influx would occur during a long static period. A nearby well with similar open-hole conditions experienced a blowout during the same static time period. A comparison of the well's annular pressure measurements to the model's predictions indicated that the pressure changes were thermally induced and were not from a formation pore-pressure source. When the annular pressures subsided as predicted, no gas was found in the annulus. Studies will continue to test the FTPD model in different types of wells, well conditions, and applications for drilling and completion operations, and the prototype model may be modified accordingly.