Saving a Hole Section by Using Real-Time Wellbore Stability Analysis

Abstract

A real-time wellbore stability analysis capability was developed to help an operator reduce high costs of nonproductive time (NPT) in an area prone to stuck pipe, lost borehole assemblies (BHAs), and lost hole sections. A multidisciplinary team created integrated processes for predrill, dynamic real-time, and post-drill modeling to help identify wellbore instability and pore pressure events that cause kicks, tight holes, and stuck pipe incidents.

A Predrill wellbore stability model for the proposed well was built based on offset well data. The model enabled the identification of depth intervals and formations where there are potential wellbore stability issues. A multidisciplinary team consisting of geomechanics engineers, pore pressure specialists and drilling optimization engineers provided 24-hour monitoring of drilling parameter trends and analyzed quad-combo logging-while-drilling (LWD) data in real time to determine the health of the wellbore. This enabled calibration of the predrill model in real time, which consequently served as an ahead-of-bit prediction of undrilled sections of the well.

Four wells were drilled in this project. The first two wells had lost hole sections resulting from wellbore stability challenges that caused high NPT costs. The new process was instituted on the third well which resulted in no lost time due to troubled hole sections and subsequently resulting in 30% lower well cost due to reduction in expected NPT. The same results were achieved on the fourth well, which demonstrated repeatability of the new process. The predrill model indicated that a pore pressure ramp was expected and that the operator's planned mudweight and casing program posed potential risks of formation fluid influx and hole breakout with resultant cavings falling into the wellbore. During drilling operations the expected pressure ramp was confirmed by an observed increase in connection gas and cavings across the depth intervals identified in the predrill model. This was communicated to the operator and informed their timely decision to increase the mud weight range for the hole interval and to set the casing shallower than planned to avoid potential hole problems.

This multidisciplinary approach to address well challenges by integrating technology, tailored expert response, and collaboratively managed delivery helps to reduce uncertainty, improve safety, and increase efficiency of planned wells and depth intervals. The new process comprising predrill, dynamic real-time, and post-drill phases identifies drilling hazards for correct mitigation. Lessons learned during the drilling operations are documented and applied to subsequent wells for continued improvement of operational parameters and best practices.