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Conductor Pipe Study
20 August 2017

Hi all,

Can anyone provide me an educated guess about Conductor Pipe size, In the environment of 10m to 26m which Pipe size would be appropriate to use.

 1) 24" external Dia - 1" wall thickness??  Or

2) 26" Ext Dia0 2" wall thickness??

We are in the process of performing the Geotechnical study of the soil  

Casing design has 

24"x185/8"x135/8x103/4x75/8- Well TD @ 16000ft.

Of if possible can anyone share the procedure to evaluate the designing forces to be applied for this Conductor Pipe Design.


As in what kind of Data is required to be analyzed to decide the size and wall thick ness of the Conductor pipe.

Appreciate your help

Thanks

Hari     

8 answer(s)
Elaine_2H
Senior Engineer
2H Offshore Inc.
Total Posts: 1
Join Date: 03/06/15

Hi Hari,

 

I’m from 2H Offshore, a company which specialises in the design and structural analysis of riser and conductor systems.


A typical analysis scope for a shallow water conductor system would include the following:


·        Stability Analysis – to ensure the conductor won’t buckle under the vertical loads acting on the well (surface equipment and casings);

·        Strength Analysis – to ensure the conductor (and casings) are not over-stressed and that the bending moment and tensile capacities of connections are not exceeded under the extreme loading conditions expected in that location;

·        Wave Induced Fatigue Analysis – to ensure that the conductor is sufficiently sized to provide fatigue life for the duration of the operations.

 

I saw that VIV fatigue analysis has already been mentioned. In this particular case, due to the shallow water depth I wouldn’t expect VIV to be a concern but a short screening exercise can be carried out to confirm this. VIV is a concern in deeper waters (>120m) or where the string in the water column is particularly slender i.e drill string. For a water depth of 10-26m, the waves will be the main concern to the fatigue life.


Fatigue from installation has also been mentioned. If the conductor is to be driven, the fatigue life accrued during installation can be determined and considered alongside the wave induced fatigue damage. If the conductor is drilled and cemented, this analysis is not required.


The response of the system is based on the particular seastates expected to occur in that area, the currents and importantly the soil conditions. Data on the wave, current and soil conditions along with the sizes, weights and arrangement of the conductor system and surface equipment is also required to conduct analysis.


If you have any questions regarding the above, please just let me know.


Regards,

Elaine

Phil.Ward
Director
2H Offshore Inc.
Total Posts: 1
Join Date: 19/02/15
Hi Hari,

A good conductor design process will consider all the things alluded to by yourself and others, holistically. Namely, it should assess:
  • the role of the conductor as structural support for the well (supporting the axial well casing loads and dissipating these adequately into the surrounding soil) 
  • its capacity to withstand the environmental loads imparted into it by wave, current and vessel motions when connected to a riser string during drilling/workover etc.
  • its suitability for the planned installation method. 

Well established techniques for conducting these checks, using specialist software tools, exist. Please let me know if you would like to discuss what a scope of work for your particular case should include as I'd be happy to share our extensive experience.

Thanks,
Phil 
Hari
engineer
Transocean
Total Posts: 15
Join Date: 03/07/12

Hi Scott,

It is Offshore well - Jack up rig - water depth 10m-26m -

Casing design has 

Shallow well - 24"x185/8"x135/8x103/4x75/8- Well TD @ 16000ft.

Deep wells - 36"x24"x185/8"x135/8x103/4x75/8x5" Well TD-20000ft


the environmental conditions are not that severe!! no severe storms, tidal and current profile

Wellhead & BOP Stack will be surface , we will be using MLS and first casing-"structural" casing will be drilled and cemented.

Do we need to consider the loading and bending moments at the mudline water depth being very less i.e 10m - 26m

which companies supply Conductor pipe & Connectors analysis to determine the weight & grade of pipe and type of connector needed we are using GE Vetco and vallourec.


If any one can provide any excel sheet , for the design calculations, wil help a lot , or any SPE papers for reference.  

Thanks and really appreciate your help,
Best Regards

Hari

Augusto
Consultant [retired Shell staff]
SPREADAssociates
Total Posts: 231
Join Date: 02/09/05
I refer you to ABS (American Bureau of Shipping) and to "Sig" Harris book (an introduction to Deepwater floating drilling).

Essentially, you have to know the forces of the wind, waves and above all currents. There are formalae to deal with it.

In my experience VIV - vortex induced vibrations - are the killer.

Conductor top tension - at the expense of deckload - can be effective; so is the smaller pipe or cable helically disposed around the conductor (experience drilling in the English Channel).

The rest avoid socket weld connections - full penetration weld is a must - and pre-welded connectors designed to sustain fatigue.

Lower grade steel and thickwall are recipes that work well.
learning.lifewayne@g
D&C Project Coordinator / Decommissioning
Society of Petroleum Engineers
Total Posts: 8
Join Date: 25/01/16
Lot of issues being missed here on how things are described.  Conductor pipe is used to cover shallow sands and hole integrity issues prior to drilling surface hole and setting surface casing where a well head / BOP connection is installed.   Pipe which is driven and used to support conductor casing is called Structural Casing.  The two issues involved regarding its sizing relates to:
  •  the size of the conductor casing to be run in it and
  • the loads that are to be carried through the landing of the conductor casing on it.  Load may be carried at the structural pipe shoe so wall thickness must be adequate.  Very important to have less then 2 degree inclination when setting the structural pipe. 
Scott_McNeil
Consultant
SPREADAssociates
Total Posts: 101
Join Date: 05/03/08
Hi Hari,

To give the best response, we'd really need to know if it's Onshore or Offshore.

Onshore you need to know the soil loading, which can be obtained from the test bore(s) you will need to give the Drilling Contractor anyway. Normally I either get to location constructor to install it, or use an Auger to install it before the main rig arrives.

If it's Offshore, what water depth and are you going to use a JU or Semi/DS?

For Offshore, you will need to know the environmental conditions (e.g. 100 yr storm criteria, tidal and current profile) to help work out the loading on the Conductor.

For a JU, you will need to identify things such as the expected top loading (Wellhead & BOP Stack) and if it's going to be driven or drilled and cemented.

For a Semi or DS, you'll need to know the loading and bending moments at the mudline.

Most Companies who supply Conductor pie & Connectors will do an analysis for you to determine the weight & grade of pipe and type of connector needed.

They will charge a fee for this, but normally will give full credit if you buy the pipe from them.

Best Regards

Scott
OPNZ
Director
Offshore Piling
Total Posts: 8
Join Date: 26/01/15

Hi Hari

Conductor design is driven by following:

Onshore or Offshore ?

Driven or drilled & cemented?

Welded or Threaded connectors

Well is expendable or potentially a Keeper? (with MLS capability) or production batch drill ?

Anticipated life of well vs fatigue analysis  (above refers)

Water depth, quality of formation below mud line. are there expected to be losses in highly permeable formations that may be present below mud line ? or communication concerns between conductors in the instance of batch drill campaign ?

Typically Conductors with WT< 0.750" are drilled and cemented. if operator is considering driving conductor to setting depth then WT > 0.750" should be used  in order to facilitate driving particularly of the shoe depth is > 45 m below mud line  and prolonged hard driving is expected.

If there is a spud can penetration report for an offshore vocation this will typically contain Geotech info to perhaps 35 meters below mud line, from this one can gain an insight in the  seafloor conditions immediately below the mud line. and using offset data for the local area if available,  a fairly coherent impression of the conductor installation requirements can be determined.

Rgds

Ahamid1977
Senior drilling and completion Engineer
SPREADAssociates
Total Posts: 3
Join Date: 04/08/17
Dear HarI The Only issue related to conductor pipe is the number if blows required to drive the pipe in place. There's an equation relates the pipe diameter and thickness to the number of blows. This will allow reaching conductor depth without any deformation. There are no other issues for conductor related to we'll design but selecting suitable size, install and weld diverted flange,, etc. Regards
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