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torque reduction with centralised casing string
11 October 2017
Is there a way to quantify surface torque reduction when running a well centralised casing string (80% stand off). How to evaluate the rotational friction factor reduction when adding rigid centraliser to a casing string
6 answer(s)
StuartForrester
Regional Sales Mgr
Centek Limited
Total Posts: 1
Join Date: 21/10/16
Good morning Tony,

Centek type centraliers is a very misleading brush stroke,that only does damage to the brand name. While i concede there are now several single piece bow spring centralisers on the market, there is only one that bears the Centek name. the others are copycat products.
All of our standard products are to gauge, and never undersized, this is one of the reasons we say we are an aid to pipe rotation, we keep the casing/liner as far away as possible from the annulus, suspending the casing and acting as a bearing, an undergauge product certainly would not act in the same way. The only variation we have on this is products that you would call overgauge. Our TUR/UROS range are designed for washouts/ under ream sections and will open up wider than the diameter of the previous set casing. None of our bow spring centralisers are under gauge, at all. Our data sheets for standard products do show zero start and zero running force, this is because they are gauge products anf therefore will not add any forces to RIH, that might be where the confusion has materialised. 
The software we use for simulations uses real measurements we obtain from our extensive testing, also casing tolerances and manufacturing tolerances as well. This means the stand off figures we produce from our simulations are closer to what you would experience RIH, not test facility figures. We have numerous case studies on our website where we have achieved excellent results in rotational operations. 
PaulHowlett
CEO
Sudelac
Total Posts: 81
Join Date: 10/04/08
It is possible to achieve 80% stand-off with solid bodied slip on centralisers you just need to specify the right OD for the hole size. Most solid centralisers are 1/4" under the hole size and hence only 1/8" clearance radially, but when laying on the low side there is no gap on the bottom between the centraliser OD and the hole ID and the full 1/4" gap on the high side. Solid centralisers can be supplied in a variety of materials with composites being the lowest friction factor materials. The inside surface of a solid centraliser is a bigger bearing face of lower friction material than a steel slip on which has just end rings and of course its metal to metal contact. Someone mentioned Centek style spring bow centralisers but be aware these designs are not bows oversized to the hole size like conventional bows, Centek bows are either at or usually less than the hole size too, so the stand-off numbers need to be looked at carefully too. There is a lot of confusion around the Centek design and its features compared to conventional oversized spring-bows and solid bodied centralisers. Based on my 30+ years working in the cementing equipment arena I would describe the Centek type designs as flexible solid centralisers, they are not bigger than the hole size but are not solid either but they are often run wiht a bow OD less than the hole size and they have very stiff bows but are somewhat flexible. The API 10D centraliser test for drag does not work for a solid centraliser not a Centek type design because neither are oversized to the hole size so beware of people marketing zero starting force for Centek type designs its just a miss-quote from applying the API 10D test. It is highly likely you can achieve a high percentage of stand-off for cementing and achieve lower rotating torques by using low friction material solid bodied centralisers of the right OD, but also without stiffening the string too much. Good luck with your operation regardless of what you decide to do.
Regis STUDER
General Manager
DrillScan
Total Posts: 4
Join Date: 27/02/16
Hi Tony,

Generally, Steel to Steel FF is lower that Steel to Formation.

Typical values are respectively 0.1-0.15 and 0.2-0.25 in OBM. Higher in WBM.

Bear in mind that in drilling applications FF encompass more than just friction. Sometimes we call them Fudge Factor. The state of hole cleaning within open hole and cased hole will affect them, as well as many other things, such as casing wall rugosity, bore hole micro tortuosity, mud solids content, etc…

Régis STUDER
DrilScan Europe


TonyMikeChembou
Drilling Engineer
Perenco - Oil and Gas
Total Posts: 2
Join Date: 07/09/17

Hi Handewitt,

thank you for your response. It's clear that this stand-off value cannor be achieve with solid centralisers. We are mainly interested in knowing if the pipe were well centralised can we assume that it can be turning as if it was supported on different points and therefore experience torque reduction (with less friction factor)


Régis,

you're right. Can we imagine that the steel to steel friction factor will be less than steel to formation and therefore we can see less torque when rotating.

jsshandewitt
Business Development Manager
Baker Hughes
Total Posts: 1
Join Date: 04/08/17

With a solid centralizer you will not achieve 80% Stand-off.

Proper placement of centralizers can reduce torque and drag,

suggest you contact Centek and let them run a simulation on

your well, their model is one of the few accurate ones on the

 market, and their product can achieve 80% stand-off.

I work for BHGE, so have no affiliation with Centek, this advice is based on my 40 + years experience in primary cementing products and applications.

Regis STUDER
General Manager
DrillScan
Total Posts: 4
Join Date: 27/02/16
Hello Tony,

Your case shall be modelled using a Stiff string TnDnB model so that stiffness of the centralized string and borehole clearance are taken into account. Furthermore local doglegs / wellbore tortuosity is another key factor to consider in teh model, we are talking here about dog-legs generated locally following slide & rotate sequence with a steerable motor assembly or steered / non-steered intervals with a RSS BHA. Based on a well documented DD steering sheet one can map accurately such doglegs.
Stiffening the casing string in a tortuous well bore may not result in surface torque reduction, it is a case by case answer. I guess the rigid centralizers you are talking about may be free to rotate. In such case FF betwwen casing and centralizer is steel to steel, while tubular body & connections in contact with bore hole will be steel to formation. This is well managed using Stiff TnDnB modelleing. We can assist should need be in your case analysis.
Régis STUDER
DrillScan Europe
Posted by

Tony Mike Chembou

Drilling Engineer

Perenco - Oil and Gas

Total Posts: 2
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