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Changing DP size from 5″ to 5½
24 November 2009
My colleagues ..

I woud like to get your thoughts on the following :if we drill 10,000 ftTVD (12,000 ft MD) using 2000 HP rig
usually mud pump (3 X 1600 HP) with maximum surface pressure 4500 - 5000 psi. So, for hydraulics, we have a limitation of flow rate because of the surface pressure on limits on the mud pumps.

If we want to change DP size from 5" to 5½, are there any dis-advantages the change the DP size.?
what about HWDP --> do we must to change to 5½ ?
what kind of equipment that we must change to, if we change the DP size to 5½?
10 answer(s)
Drilling engineer
Total Posts: 16
Join Date: 14/07/09
I support Scott McNeil advice of moving the KOP up higher to reduce your final inclination angle, so as to enhance hole cleaning and also minimize vibration, that,s good, but it has to be supported by the pick up load,doing this would also shift your TVD, and sail angle(which could lead to axial tension and well bore friction with in the build section) you have to be very careful, so you wont miss your target, during well placement, because TVD are suppose to be placed on tight margin so as to hit your target precisely.
If at all the change of your drill pipe was supported by the best offset, that is just a starting point, you need to find out what went right and what went wrong.
Once again, the selection of the size of the outer diameter of drill pipe must be supported by :- 1)limitation of your pump. 2)torque capacity of your drill pipe.3) ECD. and 4) hole cleaning.
Solution to your problems:-
1) you need to select your drill pipe size based on the above 4 factors.
2)use oil based mud to reduce contact force.
3)increased pipe size would minimize turbulent flow, down hole vibration problems, also minimize annular friction pressure loss but for a short time( by this, ECD issue is slightly taking care off).
4) the increased pipe size would lead to reduce annular velocity for hole cleaning.
If the risk involved for not using the 51/2" drill pipe out weighs the cost, it is up to you.
You have just one thing to do, to solve the problem of annular friction pressure loss that must come up again and hole cleaning problem, that is look at your mud weight and hydraulic modeling.
I rest my discussion here.
Good luck.
Training consultant, Kuala lumpur.
Total Posts: 101
Join Date: 05/03/08

There have been several good replies dealing with the Rig and downhole aspects of your question.

From my own experience, I have drilled many wells similar to yours with 5" DP and 2 x 1,600 Hp pumps, so I would say your requirement for 5 1/2" DP is not absolutely necessary.

Having said that, it could well be economically justifiable.

But have you thought about the 'big picture' though?

Are you talking a one well program, or a multi well program?

For a single well, it may not be economic to rent / purchase all the necessary equipment and make the required changes to the Rig.

Is the equipment readily available in your area, or does it have to come from a significant distance away, with the mob/demob costs & time that will be incurred if it is?

Are other Operators in the vicinity using 5 1/2" DP? This is from a 'commonality of spares' viewpoint and also if they found it to be cost beneficial.

One other point, the well design has a final inclination of 50 Deg. This is lousy from a hole cleaning point of view - could the KOP be moved up higher and the final inclination reduced to, say 40 Deg? This would certainly help your hole cleaning issues.

Best Regards

Scott McNeil
Chief Drilling Sp, Deepwater
Total Posts: 4
Join Date: 28/11/05
In addition to the hydraulics advantages with the 5 1/2" D/P, some suggestions when you make the switch from 5 to 5 1/2" size-
Please review the ram configuration on the BOP stack.
The tool joint OD selection is also important specially for the 8 1/2" hole.
Please also review the well testing slick joint dia in case it is being planned.

Ashutosh Rai
Reliance (RIL), Navi Mumbai
Drilling engineer
Total Posts: 16
Join Date: 14/07/09
The change of drill pipe from, 5" to 5 1/2" is very good because, it would minimise flow rate to prevent turbulent flow that would lead to increase in ECD, that might fracture your formation in a very tight safe drilling margin, it would also reduce annular friction pressure loss,lets assume you are using an oil based mud to reduce hydraulic friction, the problem is still there.
What I meant is the change has to be supported by your hydraulic analysis at that restricted surface pump pressure, becuse pump pressure is directly popotional to your length of reach.
Moreso drill string design is characterise by Pump limitation, ECD, toque capacity of the drill pipe and hole cleaning.
Your can get this problem solved easily by hydraulic modeling. How is your safe drilling window? is it tight? are you in which of the stress rigme? you should also consider bore hole quality/well bore stability analysis.
Non rotating drill pipe protectors would minimise torque level with in your build and laterial section, but remember the annular fricture pressure loss due to their non rotating effect.
Directional Driller
Total Posts: 125
Join Date: 27/02/08

Maybe I am over-simplifying but;
If the issue is purely to get flow and you have high pressure drop directional tools - consider a diverter sub run above the BHA.
Drilling engineer
Total Posts: 16
Join Date: 14/07/09
Dear Dans,
The fact that the TVD (ie 10000ft) of your well path is deep, Hook load should be a limiting factor.
I perfectly agree with you that changing Drill pipe size(ie outer diameter) would minimize or reduce annular friction pressure loss with in the sail section of your well path, but changing the drill pipe from 5" to 51/2" would lead to an increase in pipe weight.
Was the selection and change of your drill pipe supported by hydraulic modeling, if yes, I would advice that you opt for a drill pipe of a composite material.
Then model the build and lateral section of your well path, using the above composite drill pipe, after modeling find out whether your rig could handle the cumulative torque.
Do you know that increasing the out diameter of the drill pipe would lead to a reduction in flow rate,then how would you clean your well(especially the build and lateral section of your well), with out increasing the pressure of your mud pump? So I would advice you to review your hydraulic modeling for hole cleaning properly
Drilling Engineer
Medco Energi
Total Posts: 12
Join Date: 22/10/09
OK gents .. Thanks for your experience sharing with me.
Our well candidate is (10,000 ft TVD, and 12,000 ft MD, directional with KOP at 6000 ft using 3 DLS and the inclination will be around 50 deg. KOP at 17-1/2" hole, set 13-3/8" casing at 7200 ft and 9-5/8" at 10,000 ft and finally liner at TD.

From our experience we have limitations in flow rate in 17-1/2", 12-1/4" and 8-1/2" because there are directional tools, which have a higher pressure loss.
Because we usually use a 2000 HP rig (land rig) which has 3 X 1600 which have surface pressure limit of 4500 - 5000 psi, so we can't apply more flow rate to accomodate better hole cleaning.

So our idea is to decrease pressure loss in the string, mainly in DP, by changing to a larger DP (from 5 to 5-1/2), which I think is good way to improve hydraulics.
Lead Drilling Engineer
British Gas
Total Posts: 10
Join Date: 27/08/09

In addition to Mark's comments and questions here are some additional considerations;
Setback loading constraints due to heaver DP weight,
Reduction in setback capacity due to larger tool joint OD,
IR capability if you have one,
addtional accessories: SJ pick up elevators, lift caps, pump through & side entry subs etc, hand slips, inserts for power slips, x-overs, DP drifts
BHA: stringly recommend at leaset 5.1/2" HWDP, perhaps even 6.5/8" HWDP, also look a spiral option for the HW.
Tapered string: you may not need a full 5.1/2" string but this needs to seriously weighed against operational completxity that a tapered string brings eg BOPs & ram configuration, well control, racking plans, pipe service rotation & others

Connection selection; DSTJ has a good reputation, Woodside have a 5.7/8" string for their ERD platform drilling and I understand ,they have been happy with the selection, BUT don't rule out an API connection if your well design will allow, cheaper and easier to maintain. Look to maximise the TJ ID if hydraulics are a concern BUT check the torsional capacity, Ref T.H.Hill
TJ length: go for maximum lengths to allow for repairs
DP length: Have you considered Range 3 pipe? Vam Drilling can manufacture 5.1/2" 47.5' joints, be careful about problems transporting R3 pipe with over length loads. In this case the mouse hole would need to be deeper and I would recommend a 90' effective length to make up stands off line if possible.

Downside: potentially slower tripping due to heavier string loads (minor)

Bruce Richardson
Geodynamics, Brisbane
Drilling engineer
Total Posts: 16
Join Date: 14/07/09
Dear Dans,
It is very possible for you to drill with the 5" pipe to 12000ft, but from the information you povided about your ERW,if you are changing from 5" to 5 1/2" pipe, below are the limiting factors:
1)Hydraulic system.
2)Hook load.

In order to over come the above limitation you need the following equipment/corrective measure:
1)you need a mud pump with higher pressure. Also, make sure that your mud weight for your lateral section or sail section takes care of the ECD due to the annular friction pressure loss. It should be an oil based mud.
2)you need to increase the hoisting capacity of your rig or you get a rig with a higher hoisting capacity.
Best regards.

Divine Somiari
Training consultant, Kuala Lumpur
Senior Drilling Engineer
Total Posts: 19
Join Date: 04/05/06
What kind of well are you drilling? You should be able to get down to 12000ft with 5" pipe? There are many things you can do to optimise your hydraulics- rotary assembly, reduced flowrates etc.

Is the limitation in the 17 1/2" section- is this section very deep? We use 5 1/2" DSTJ for hydraulics due to long 17 1/2" sections or in ERD wells in the 12 1/4" section at high inclinations. The main disadvantages are: BOP rams need to be changed, Saver subs need to be changed and in some cases the fingerboard to accommodate the different pipe size.

Mark Knorz
TOTAL, Aberdeen
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