This paper demonstrates how Forward Synchronous Whirl (FSW), when induced in an underreaming while drilling BHA through the application of an Asymmetric Vibration Damping Tool (AVDT), substantially reduces both stick-slip and lateral vibrations and significantly improves drilling performance. The physics of operation, pre-job planning and modeling, followed by a thorough examination of run data and comparisons to offset wells will be documented and quantified.
The performance of underreaming while drilling assemblies in long salt sections, as well as in pre-salt environments around the world has improved considerably in recent years. However, down-hole vibration still limits rates of penetration and overall drilling efficiency. Often, these long salt sections comprise the most challenging intervals of a deepwater well.
A major development project in the Green Canyon section of the Gulf of Mexico contains wells with hole sections exceeding 9,000 ft in length through salt, and into the pre-salt. In order to evaluate the potential benefits of FSW, an AVDT has recently been added to the drilling assembly while keeping all other variables constant (rig, bit type, BHA, etc).
The results showed that overall penetration rates increased by more than 50% and Stick-Slip (SS) vibration reduced by more than 75%. While there was a substantial across-the-board reduction in vibration and an increase in ROP, the benefits of the AVDT were recognized most in the portion of the hole section where elevated vibration levels typically cause a reduction in ROP as energy is lost to vibration (near the base of salt).
With the addition of the AVDT there was little to no increase in SS, and no decrease in ROP. In fact, on one of the wells that used the AVDT, the final 2,500 ft of the 9,000 ft section was drilled 83% faster than the closest offset (178 fph vs. 97 fph), with 90% less SS vibration. Of the five wells analyzed, three were without the AVDT and two were with. All of the runs in question were with a 14 1/2"-16 1/2" underreaming while drilling, rotary steerable drilling assembly.
This novel approach has wide-spread application in global deepwater basins, particularly in vibration-prone wells. This paper demonstrates how the technology is being applied effectively, and provides a platform for further application.
Reducing drilling induced down-hole vibrations has been instrumental in improving drilling performance. Various techniques and models exist in designing dynamically stable BHA's and drill bits. There are also ways to predict the behavior of cutting structures and drilling assemblies when rotated at various speeds through different formations and trajectories. All of these methods help to reduce the chances of damaging vibration events occurring, but do little to actively damp these vibrations when they do occur.
In addition to designing more stable drilling assemblies, there has been quite a bit of research into recognizing whirl and other potentially damaging vibrational events in real time. These detection methods give the operator the ability to take action to reduce vibration levels before damage occurs. The available courses of action are limited and usually involve the altering of drilling parameters or stopping all rotation, pulling off-bottom and allowing the drill string to stabilize.
Unfortunately, all of the time not spent drilling, and dealing with vibrations, increases overall cost while reducing drilling efficiency. If vibrational events can be actively damped while drilling, significant gains in drilling performance and reliability can be obtained. In other words, a lower overall well cost.
