For a number of years, conventional underreamers have been used in shallow-water exploratory wells in Mexico; however, today's operating conditions require the latest technology to reduce trips, decrease operating time, and eliminate nonproductive time (NPT). Local operator and Schlumberger jointly evaluated the newest generation underreamers available, and implemented them to obtain efficient solutions for well designs. As a result, a campaign was initiated by introducing on-demand underreamers with multiple activation capabilities.
Most underreamers in the market have a lock-out mechanism that prevents them from opening while drilling the shoe track (Torvestad et al. 2012); however most of these technologies require a ball or device to be dropped from the surface to activate the tool. Nevertheless, the main limitation these technologies have is that the tool cannot open and close multiple times, leading to extra trips, increasing operating time, and NPT due to tool reliability.
New underreamer developments have targeted the limitations of not being able to perform multiple activations and deactivations by manipulating the underreamer through a sequence of flow rate changes to allow infinite cycles. These new developments have increased the potential to save rig time due to their activation technology, and they have proved to be a key factor in reducing trips and decreasing NPT.
The latest underreamer developments have individual benefits; however, it is important to evaluate each application to select the proper underreamer for the well. Introduction of the newest borehole enlargement (BHE) technologies resulted in tools adaptable to changing scenarios and the following accomplishments: Full-cycle expandable underreamer—the preferred tool when enlarging well sections after a cased hole wellbore departure or conventional drilling operation, eliminating 30 days of NPT due to previous underreamer operations in which the underreamer did not close while pulling out of hole (six total applications in four different exploratory wells).On-demand activation underreamer—the preferred tool for complicated sections requiring multiple underreamer activations and deactivations. In conjunction with a newly designed bit containing ridge-shaped cutters, 2 days of NPT were saved by eliminating an extra trip to remove the underreamer from the bottomhole assembly (BHA). Because the underreamer used to enlarge the hole to 14 ½ in. could be closed, drilling the 12 ¼-in. section and running 9 7/8-in. casing continued after determining that the contingency 11-7/8-in. liner was no longer needed.Additional on-demand activation application—using the same technology, these underreamers have been used whenever wellbore instability, caving, and possible stuck pipe are expected. As an example, these underreamers (in closed mode position) allowed full circulation and helped to free the BHA in a stuck pipe scenario, preventing 2.5 days of fishing operations.
Three case studies will be presented to demonstrate successful deployment of the new underreamers in offshore Mexico. For each case study, the details of the operators' benefits will be provided. This paper will demonstrate how the methodology and technology used for BHE operations in exploratory wells can be accomplished in a cost-effective and safe manner.
