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On what parameters the suitability of UBD over MPD to drill a well can be decided.
15 February 2020
If a reservoir is sub hydrostatic. can it be drilled with MPD? Further can it be drilled with UBD also. if yes then what are the parameters which can decide the superiority of UBD over MPD or vice a versa in a particular case.
5 answer(s)
MPD Engineer
Total Posts: 1
Join Date: 28/06/17
I would agree with all of the above and also mention it may depend on regulations where you are going to drill.
Using MPD with a hydroststically underbalanced fluid but maintaining a margin of overbalance with surface pressure at all times is often done here in Norway drilling in underbalance is not.
The decision is driven by the aims and objectives of the project. 
GM chem
Oil and Natural Gas Corporation Limited
Total Posts: 3
Join Date: 21/01/19
The choice of UBD/MPD is a decision taken by the Project Team and vetted by the Management on the basis of the Structured planning of the project. There are challenges in mobilisation, rig up , location challenges and availability of downstream connections. The cost factor needs to be an important factor. The reservoir potential along with flow rates.
Well Engineering Consultant and Instructor
Olango Consulting
Total Posts: 36
Join Date: 23/03/16
Any well can in theory be drilled using MPD or even UBD.
The well objectives and the benefits of implementing MPD or UBD will have to be looked at. 

If a well can be drilled conventionally without issues then why use MPD or UBD you do not want to add complexity. But if a well is likely to encounter drilling challenges, related to pressure events, such as losses, kicks, hole stability, ballooning, hole stability MPD can be considered. 

UBD is really a reservoir focused technology. it should be used to improve production and reduce reservoir damage. But in order to use UBD need to make sure that the damage mechanisms of the reservoir are understood. A poor reservoir drilled with UBD remains a poor reservoir.

Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 445
Join Date: 10/01/05
To select the right solution for any well particularly in more complex situations, conditions you need to work through a very detailed and rigorous concept to base case design solution. 

Well safety, well control assurance, well integrity, pressure and stability management are principal areas to focus on. 

Where MPD or UBD candidate selection has to tick all the right boxes to select the many methods on offer. 

I think I have some slides on UBD and MPD candidate selection from training course material  that may assist.

 I will resource these and attach in a following post. 

One will conclude this is a very tenuous process to plan assure check verify, do and control to select the right pressure management method for all the right treasons. 
Drilling Consultant
Total Posts: 2
Join Date: 15/02/19
Yes, reservoir can be drilled MPD with subhydrostatic pressure.  You will need a fluid system and additional surface pressure (WHP) to balance your reservoir pressure. With MPD, your aim will be to keep the BHP just above the reservoir pressure during the drilling, connection, tripping. Completion operations.

With UBD, you will create the BHP below to the reservoir pressure, thus enabling the well to flow during the drilling operations. 

The benefits of MPD are recognised as it minimizes drilling problems. UBD benefits are mainly recognised as it minimizes or mitigates reservoir problems. 

For MPD, your surface equipment setup can be quite small and much easier to rig up. For UBD, you will need a surface separation system to take the reservoir fluids, separate  it and handle it on surface. 

This is just the basic overview of the two. If you are after solving specific challenges in drilling your reservoir, you can possibly list them and the group maybe able to help you choose the appropriate technology to solve your challenge.
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