Soft Torque Impact on Drilling Performance in Qatar
Authors: Attar F. , Grauwmans R. , Ikhajiagbe O. 
Published: May 2016

The drilling industry has identified torsional stick-slip vibrations as one of the obstacles to the progress and efficiency of drilling operations, and a common cause for tool failures. Therefore, significant research into different technologies and methods has been conducted to mitigate this issue. The Soft Torque Rotary System (STRS) is one of these technologies which aim to actively dampen these vibrations from surface. This system was originally developed by Shell in the early '90's. In recent years, the implementation of the original Soft Torque technology has been improved and this improved implementation is now rapidly being deployed on the Shell global rig fleet. In 2009, Qatar Shell was one of the first to use this new Soft Torque implementation for the Pearl GTL development wells. Gulf Drilling International, GDI, has also taken up this technology and installed it on their Al-Khor jack-up rig, currently on contract with Qatar Shell. This paper highlights the experience Qatar Shell had by comparing the drilling performance on Pearl GTL between wells with STRS installed and those that did not have STRS. This paper also details the experience and improvements seen as a result of the STRS installed on Al-Khor rig and the tests conducted with having the STRS system switched on and off in the same formations to compare its efficiency. Finally, this paper will also cover Shell's global experience with these systems.

Motivation

In 2009, the IADC/SPE conducted industry surveys regarding prevalent drilling issues and the technologies needed and they concluded a high demand for stick-slip mitigation (Springett 2010). As a result of this survey, in 2010 the IADC Future Technology held a workshop in Houston dedicated to stick-slip mitigation. To highlight the severity of stick-slip, an example of the worst stick-slip case seen was a "24 second bit stall and a 1.4 second backward drill rotation", which is as bad as someone driving his car forward and then suddenly shifting into reverse (Womer 2011).

Gulf Drilling International (GDI) was established in Qatar in 2004 as a joint venture between Qatar Petroleum and Japan Drilling Co. who come with more than 40 years of offshore experience. GDI started working with Qatar Shell in 2011 on an appraisal well campaign and is still providing its services via the "Al-Khor" jack-up rig. Vibrations in all their forms: axial, lateral and torsional have been experienced by GDI. In terms of the impact that these vibrations have, some of which are due to stick-slip, the failures recorded and attributed to them are plenty. Top drive failures due to vibrations are very common in the industry. As an example, a major drilling contractor who had significant experience using top drives on their rig fleet conducted an analysis to find out where most of their rig downtime occurred. They found that 40% of all rig equipment failures were related to top drive failures (Fraser 2009).

GDI have experienced and are currently experiencing TDS failures mainly as a result of vibration (axial/lateral/Torsional). Following a survey from January 2008 to November 2012, as illustrated in table 1, GDI identified that of the entire top drive related NPTs, 13% were due to heavy vibration drilling.

Across the GDI drilling fleet, top drive failures have been continuously observed. The recorded failures are described below:TDS Gooseneck parted connection and this led to a leakageTDS Rotating Link Adaptor (RLA) failureTDS Saver Sub had cracked and sheared off (Fig. 1):While coring 6" hole on Al-Khor sister rigdrillstring parted from 3 1/2" IF saver sub connection and hung on elevator but did not drop on the rig floor thus nobody was hurt but the floor men were wet with mudFollowing a root cause analysis, failure was due to vibration experienced by the top drive during coring operations