RSS combined with conventional mud motor
02 June 2010
I would like to ask best practice for above topic. How common is it?How should I position the motor? Any constraints for running LWD with source? Any comments would be very much appreciated. Integral/special motor within RSS from several huge players sounds too fancy for our application.
We are using point bit RSS and it suffers from lacking off surface rotation due to TDS limitation.
It's all good for ROP (weight, water & ROTARY) as I was always told.
If you're wells are directional, make sure that you have the string rpm to clean the hole i.e. 120 rpm min (preferably more) for OH > 8.5in, 100 rpm for OH 8.5in or less. As angle increases over 40 deg and section length increase beyond 500m, so too does the importance of doing this, drilling on connections and during clean-up.
All the best
Merlin ERD Ltd
Gents, thanks very much for the responses.
So I guess the best shot for me for now is to arrange as Bit-RSS-PDM-LWD. Negatives are loss of communication with precious closer-to-bit sensor of RSS, longer distance for LWD/MWD from the bit and the ability to fish RA sources if stuck happens.
I'll also look through RSS with integrated motor.
Another question if I may ask is, how aggressive is your PDC bit in RSS environment? What's the minimum blade quantity you ever run with RSS? We drill 8-1/2" hole with RSS in vertical portion and build to 90 deg landing point. Thanks.
Various companies have been using PDMs above the MWD and LWD tools for that very reason and often will sort out uneven torque / cyclical torque in particular formations. Even walled motors have been favoured historically due to the better torque output and less chunking.
One word of caution would be is that if you are putting full gauge LWD tools, stabilised tools such as the density neutron, which has a full gauge stabiliser experience of LWD failure from various companies is common. The slicker LWD tools like sonic/acoustic, resistivity etc are okay but be careful of trying to do too much in one run.
Mike, I cannot comment on the RSS/ Motor combination aspects of your question but wanted to comment on the LWD source inclusion in your BHA. Recent events have me rethinking the consequence side of the risk equation (consequence and likelihood). I have never had the experience of losing a radioactive source in a well but have seen it happen to another Operator on a neighboring campaign where my company had a participating interest. While the likelihood of losing the source was low when it did happen the consequences were far reaching. After several weeks of fishing attempts "we" were forced after a long protracted discussion with the nuclear regulation agency as well as the local oil and gas regulator to leave the tools behind. Our country has long lasting rules about the impact of this incident that has left us with a long term liability. When the gas being produced from the well is all produced (20 years) the well will continue to reside on our company's books as a liability for many years. Something to think about when you are making short term decisions about the best way to get information from a well and you are being rewarded on the capital cost of the project...
Well Construction Champion
During my time with SLB/Anadrill PDM motors were frequently run with a push-the-bit RSS. Negatives (at that time) were loss of realtime communication with the RSS tool. This wasn't really that big an issue, however. At least not from my perspective as a DD. Gulf of Mexico drilling was expenxive and the additional ROP from the motor in the BHA was economical.
Note: if casing wear an issue drillstring rpm may require you to run a motor with your RSS.
Regarding LWD tools: SLB tools allow you to run LWD on top followed by motor & RSS/bit. I would suggest running it this way if you have a choice. Assuming you can rotate the drillstring of course. SLB azimuthal data needs a minimum rpm, 40 rpm worked rather well in my applications. Your area/needs may be different.
RSS & Conventional PSM was offerred by two service providers in the past here in Egypt to Petrobel and GUPCO as a cheap powered RSS compared to an RSS with integrated motor. Both Petrobel and GUPCO decided to remain with the integrated motor. They considered to run the RSS/Conventional PDM combination far too risky - one two many weak points in the BHA (i.e. the RSS Drive Sub and Motor Drive Sub). At a time when DDS/LWD day rates have been hammered by discounting and intense competition you should be able to get a decent deal on RSS with integrated motor.
With regards your LWD source question - without understanding your application this will depend on several factors - how close you need the measurement in relation to the bit, whether GR/RES is more critical (there would be the option to swap them around, and what options you have to run a sourceless porosity tool such as LWD NMR -this would give you porosity, a permeability measurement and moveable hydrocarbons and reduce the amount of RA sources you have in hole - tools exist for 6" to 8 1/2" nominal hole sizes.
With the issue of the RSS/Conventional PDM BHA, you would have to place the motor above all the LWD jewellry. I'll leave you to decide whether this would be a risk you want to take.
Deepwater Business Development Mgr