How difficult is it to operate the NSD Sub?
What are the special features of the NSD Connection Valve?
What seals are used and how often do they need to be redressed?
What type of connection do the NSD subs come with?
What are the strength limitations of the NSD sub?
What is the flow capacity through the NSD sub?
Can the NSD sub withstand typical drilling jarring and vibrational forces?
What are the depth and hole condition limitations of the NSD sub?
Is it possible to run wireline tools thru the NSD sub?
What is the added connection time for each NSD sub?
What type of NSD Ball Valve is used?
Is there any concern with having a pressurised hose close to where rig personnel are making up a connection?
What is the consequence if an NSD sub leaks on the drill floor while switching over circulation from the standpipe to the side entry port of the NSD?
What is the potential for NSD sub accessories to be dropped in the hole?
What about LWD and MWD tool operation?
What other advantages does continuous circulation provide?
I have drilled my section. How do I get out of hole? How do I run my completion?
What other versions of NSD are available?
How expensive is the NSD system?
Can the NSD system be used with down hole mud motors?
Can directional surveys be taken with Positive or Negative Pulse MWD tools?


How difficult is it to operate the NSD Sub?
NSD System is designed as an ultra fast and safe operating system that uses a quick connector system with no hammering to make up hoses. The unique patented bayonet locking system allows very quick operation.

What are the special features of the NSD Connection Valve?
  • Bayonet Locking System – a patented quick connect hose system
  • Spiralock thread – the NSD connection valve design utilizes an aerospace spiralock thread and locking pin technology to prevent the cap from vibrating loose
  • Seal technology – leak paths are protected by seals with dual directional sealing capability
  • Magnetic retainer – Powerful retainer magnet in cap removal tool to prevent dropped objects
What seals are used and how often do they need to be redressed?
The NSD subs utilize a number of features that minimize the redress time, and interval between redresses.
  • 100 connections – NSD subs are cycle tested to 100 connections and typically redressed after each well.
  • Seals – NSD subs utilize seals certified to Norsok M710 spec (Norwegian standard) which ensures:
    • They have excellent resistance to high pressure, temperature, wear, abrasion and explosive decompression
    • Long life capability and fluid compatibility with most drilling fluids
    • -10degC to +121degC (14degF to +250degF) rating
What type of connection do the NSD subs come with?
NSD subs are custom manufactured by MPO to match the Customer’s drillpipe tool joint connection, so no extra crossover subs are required. Typical sizes include 4-1/2" IF and 5-1/2" FH.

What are the strength limitations of the NSD sub?
The NSD subs are manufactured to greater tensile yield strength and torsional yield strength than the drill pipe they are used with. Subs are a single solid piece construction with no breaks.

What is the flow capacity through the NSD sub?
  • Down the drill string through the sub the rating is the same as drill pipe
  • Through side port the current rating is 600 gpm, with an increase in standpipe pressure of about 300 psi
  • Higher rates can be achieved with a corresponding increase in standpipe pressure
Can the NSD sub withstand typical drilling jarring and vibrational forces?
Yes. The NSD subs are manufactured exceeding API 7-1 Class 2 and have a higher specification of strength/vibration characteristics than the drill pipe they are used with.

What are the depth and hole condition limitations of the NSD sub?
  • They are designed and tested to standards exceeding the API 7-1 Class2 specification for lower Kelly valves, which means they are suited to running below the BOP stack.
  • The 10k NSD sub has an internal pressure rating of 10,000 psi and external to internal differential rating of 10000 psi.
  • Nitrogen tested to 5000 psi differential as well as low pressure leak testing.
Is it possible to run wireline tools thru the NSD sub?
  • Yes, the internal I.D of the NSD Subs are full bore: 3.0” in 5-1/2” FH and 2.813” in 4-1/2” IF sizes. The top part of the Kelly Valve ball utilizes a funnel guide to help prevent tool hang up.
  • Can the NSD subs be re-tooled in case of damaged threads?
  • Yes, allowance made for pin and box recuts.
What is the added connection time for each NSD sub?
  • Extra time will be required to make up an NSD sub to the top of each stand prior to running in hole.
  • Running in hole or drilling there is extra time required when switching over from normal flow through the top drive, to flow through the side entry port, plus time to bleed off the side entry port pressure before disconnecting the hose assembly. This will be about 5 additional minutes.
  • Pulling out of hole some additional time is required to drain the wet stand with the MPO mud bucket. This takes about 7 total additional minutes.
  • These times are easily saved by the elimination of time taken in establishing steady state circulation after a conventional connection, especially on air/foam drilled and UBD wells.
What type of NSD Ball Valve is used?
MPO has taken care to qualify a proven Kelly valve design with the following additional features:
  • Check Seal – one seat sealing which substantially reduces ball stress and differential pressure open/close friction
  • Double Seal – double stem seals, an additional safety feature for the NSD system
  • Lite-Torc technology – a design feature of the ball valve assembly which dramatically reduces the amount of torque required to open or close the valve under high pressure conditions
  • Sure-Stop mechanism – gives a positive indication of fully open or closed ball valve
  • Canister Guard – the unique one piece canister design of the ball valve assembly allows easy removal from the NSD sub for maintenance
Is there any concern with having a pressurised hose close to where rig personnel are making up a connection?
  • Crash Plate installed above Quick Connect for protection.
  • Whip checks are in place to secure hose ends.
  • Safety Overpressure Relief Valve on NSD Manifold.
  • A proper Risk Assessment should be undertaken for any application of a Continuous Circulation System.
  • Proper care needs to be taken to minimize contact with the NSD sub assembly during make-up or break-out of drillpipe above the NSD sub. A protective dropped object frame is provided.
  • MPO utilizes a unique quick-connect hose system that has robust, positive locking mechanisms to prevent accidental dislodging during pressurized flow conditions.
  • Hoses themselves are high grade materials chosen for either oil-base mud or air/N2 pumping operations with excellent wear/abrasion characteristics.
  • MAWP = 5000 psi, test pressure = 10,000 psi, burst pressure = 15,000 psi minimum.
What is the consequence if an NSD sub leaks on the drill floor while switching over circulation from the standpipe to the side entry port of the NSD?
  • This event is very unlikely based on the extremely high specification and quality checks of the components used.
  • Should a leak occur while drilling, the complete stand will be racked by and replaced with a new stand and NSD Sub. This is detailed in the procedures.
  • The pre-job Risk Assessment done by MPO personnel will identify the Risks, Consequences and Action of each different risk scenario.
What is the potential for NSD sub accessories to be dropped in the hole?
  • NSD hand tools and accessories are large with positive locking mechanisms to prevent parts from breaking free from tools.
  • Connection Valve Cap Removal Tool has powerful magnetic retainer.
  • Fabric hole cover placed over hole while NSD Sub is being used.
What about LWD and MWD tool operation?
  • Continuous logging and uninterrupted transmission of down hole pressure data is possible.
  • Operations that normally require the pumps to be shut off like a directional survey need to be re-evaluated in terms of necessity, or for some tools it is possible to receive this at programmed intervals.
What other advantages does continuous circulation provide?
  • Eliminates wellbore ballooning effects.
  • More effective solids control – no slugs of cuttings.
  • Minimise cuttings bed build up on high angle/ERD wells.
  • Fewer stuck pipe incidents.
  • Reduce drilling duration & program disruption.
  • Reduce risk of kicks during connections.
  • Eliminate downtime circulating out ‘connection gas’ especially on HPHT wells.
  • Place drill-in liners with tight clearance.
  • Eliminate surface float valves – No more problems running free-point indicator or survey tools.
  • Reduce stabilisation time on multiphase drilling (air, foam, underbalanced).
  • Provides several fully rated kelly valves as safety devices in the drill string.
  • Can be used instead of surface float valves for UBD and Air Drilling operations.
I have drilled my section. How do I get out of hole? How do I run my completion?
Once the section has been drilled, proceed as follows:
  • Plan and prepare ahead of time a balanced mud pill system consisting of:

    o Viscous pill spacer

    o Higher mud weight pill

  • Continuously pump out of hole, until the bit is above the shoe.
  • Air Operated NSD Mud Bucket Supplied for Wet Tripping.
  • Stage in the balanced mud pill, dropping the pump rate in steps
  • The goal is to finish at a slow circulating rate of about 2bbls/min with the pill fully displaced
  • If done correctly the BHP can be maintained in the desired bottom hole pressure window.
What other versions of NSD are available?
A 10,000 psi sour service version is available. The following versions are under development:
  • 15,000 psi valve coupled with a 7500 psi connector. This is a system for 15k BOP stack operations.
  • High flowrate version going up to 1200 gpm. This will have a lower pressure rating around 6000 psi and is targeted for drilling top-hole sections, especially for deep water drilling.
How expensive is the NSD system?
The cost is about 25-30% of an automated choke system.

Can the NSD system be used with down hole mud motors?
Maintaining circulation during a connection means a positive displacement or turbine driven down hole directional mud motor run in the BHA is continuously rotating the bit, with the bit off bottom. However, the drilling fluid (mud or multiphase fluid) is also still cooling and lubricating the mud motor. No evidence of any detrimental effects of continuous circulation on mud motors have been seen on NSD projects so far, i.e mud motor stator rubbers did not show any sign of burning out.

Can directional surveys be taken with Positive or Negative Pulse MWD tools?
To get full directional surveys without stopping circulation, the MWD would need to be pre-programmed to pump up surveys at regular time intervals (on the fly), for example every 10 mins. Ideally the rig pumps would not be stopped to cycle the pumps and initiate a directional survey sequence. In MPD/UBD the BHP data from the PDW will be pumped up as frequently as possible, then the MWD would be programmed to continuously pump up LWD data and surveys on the fly at set regular time intervals.

The drill string has to be static with no rotation or up/down movement while the directional survey is taken, to get accurate survey data. So to get a full directional survey the drill string would have to stay static in the same position over the time interval when the survey is taken, or the survey could be taken during a connection. Unless the well is directionally very complicated, or the rig is performing a complex sidetrack kick off or build, then surveys taken every stand on a connection will be sufficient. Most MWD companies tools have QC software built into their negative and positive pulse telemetry decoding software that will only accept stable survey data with no pipe movement / rotation, thus ensuring the directional surveys are good.

Programming MWD tools to take surveys on the fly at regular time intervals is commonly done when using PDMs, to get frequent inclination data when sliding. So, the BHA needs to be kept static while a full directional survey is taken, including azimuth data, and circulation can continue uninterrupted.