Thixotropic behavior of phpa mud system for managed pressure drilling

Abstract

Managed Pressure Drilling (MPD) is an adaptive drilling process to precisely control the annular pressure profile throughout the wellbore. MPD has many advantages such as reduction on the number of casings, avoiding lost circulation, mitigating pipe stuck from differential sticking, increasing in rate of penetration and reducing formation damage compared to conventional drillings. The rheology of most drilling fluids shows thixotropic behavior. In other word, if they are exposed to a constant shear rate after some time at rest, their viscosities will start at an initial higher value and finally drop over time to lower value. This higher viscosity can cause the high bottomhole pressure during the restarting circulation, which can induce fracture in formation. In this study, PHPA mud system is subjected to constant shear rate after leaving at rest. Gelling time is varied to be 10 seconds, 3 minutes and 10 minutes. Shear rate is varied to be 30, 100, 200 and 300 rounds per minutes. The study showed that PHPA mud system exhibits thixotropic behavior which trend in annular frictional pressure loss difference is logarithmic decline. Gelling time does not affect thixotropic behavior except when drilled solid exists in the mud that increasing gelling time results in higher thixotropic behavior. Increasing in shear rate does not always result in higher thixotropic behavior. In conclusion, PHPA mud system has potential to be suitable for MPD based on small thixotropic behavior.