(Surface installed) soft torque systems
27 October 2011
(This post submitted on behalf of a member who has poor internet access).
"We have been experiencing severe downhole vibrations that have been damaging bits and (potentially) tools.
Our primary course of action has been to adjust drilling parameters (RPM, WOB). That was moderately successful.
Our secondary course of action is to investigate a range of downhole tools and bits that either minimise the onset of drilling dysfunctions or mitigate their effect. Please do not submit any responses about this potential solution.
Now we are looking to invest in a soft-torque system. The two systems that we know about are Martin-Decker and Siemens. We are leaning towards the MD system.
Please may members share their experiences with soft-torque systems (especially those mentioned above). How to bring out the best in them, things to watch for etc.,
We are also interested in opening a dialogue on the relative merits of such systems. e.g. do they really work ?"
Thanks and kind regards
Soft torque systems were used extensively on deep land rigs in the middle east and though beneficial to the equipment did not demonstrate any reduction in downhole vibrations. Running a very stiff assembly (upto 6 reamers & stabilisers in total, based upon expected drilling parameters) proved very successful in minimising vibrations Ã¢ï¿½ï¿½ these were vertical wells.
Bit designs can incorporate features for countering specific types of vibrations.
A vibration sub can be run in current BHA to create a baseline, if not already done so. This will provide specific information regarding the type of vibration that is damaging the tools, and the solution can then be tailored to the cause.
IADC conducted a Stick-slip Mitigation Workshop in July/2010, and several of the papers presented are available online. The Shell and Geoservices presentations are very informative and a list of parameters could be generated from them to compare the various systems on the market.
Although I have no recent experience with these systems, the Bentec system is easy to install and control of the top drive motor is unobtrusive. Downhole instrumentation technology is constantly improving and can be integrated with the TD motor control.
A paper presented by Svein Ove Aanesland of NOV discusses the differences in TD motor characteristics and the implications for stick-slip.
BEWARE: I am a mechanical engineer, not a drilling engineer, so my first consideration is the equipment!
Be very careful of prescription without full diagnosis is such cases.
Taking the time to seek primary 'root cause and effects analysis' is what is required first. Here I am sure SPREAD members can/would assist with more specifics provided.
If a soft torque system is then justified, then indeed source the system deemed most suited.
In my active time, Deutag STRS Mark III was the leader, with very good performance.
Training of rig electricians, the challenge.
I was also aware of Tech Power Controls but unaware of field experience.
From memory, Maurer Engineering was also on the ball.
Typically these systems operate in two ways and are defined as soft torque and soft speed. Initial soft torque systems simply added power to the TDS to maintain constant SRPM however in some cases this has made torsional oscillations worse here is why.
If the string is oscillating at a resonant natural frequency it is quite possible to add energy from a classic soft torque system at a resonant harmonic this is also true if the string is forced into damaging oscillations . This can push the assemblies into damaging chaotic / Backward whirl with other mode coupled vibrations.
The most current soft speed systems use elements found in noise cancellation, this where the rate at which the TQ is applied at surface is inversely proportional to that of what the string harmonic is thus the string manages to maintain a smoother RPM downhole where on surface this might not seem the case.
Another key point for consideration prior to using soft torque systems is the TDS type, it has been established that AC TDS are more prone to developing torsional string oscillations when compared to that of DC TDS, weather can also play a big part if you´re on a drillship or semi.
I would always recommend adjusting the BHA/Bit matched to parameters & practices prior to purchasing costly systems such as these, many service providers today can model for an array of vibration scenarios and offer a well review which in most cases can help identify the correct fiscal approach.