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Drilling shoetrack with 1.15 deg bend in motor (and PDC bit)
04 August 2012
Hi folks

At a recent DWOP, the draft programme being reviewed had a BHA with a 1.15 degree bend in the motor. A PDC bit is planned.


We discussed the possibility of severe damage to the bit whilst drilling the shoetrack, and also challenged the need for such an aggressive bend in what amounts to a vertical well; bend was proposed to give some capability to correct inclination.

As usual, there were as many opinions as there were people sitting at the table.

We're interested to hear of members' experiences in this regard.

With kind regards.

Dave Taylor
24 answer(s)
Fernando
Drilling Superintendent
SPREADAssociates
Total Posts: 3
Join Date: 09/09/13
Most of the time drill out shoe track with PDC is not an issue regarding bit damage, however, 13⅝", 88.2 ppf casing drift is 12.25"; for the combination of 1.15º bend, damage can produced in the gauge rows and may be in the shoulder cutters depending on the bit design. For tight drifts combined with some bend, the damage of the PDC bit can actually be inflicted while running in the hole, due to the gap between pins if the casing connection is BTC or similar. 
I experienced severe bit damage running 8½ bit in special drift 9⅝" 53.5 ppf casing, slightly deviated well with 1.15" motor bend. (Drift 8.500")
rajatkhanna
Drilling Manager
GeoEnpro Petroleum Ltd
Total Posts: 3
Join Date: 26/01/13
We have drilled about 20 deviated wells in past about 4 yrs & after every casing cementation (both surface & intermediate) have always run PDC bits on motors with 1.5 degree bend setting for drilling the shoe track followed by hole deviation. Have never had any serious issue with PDC bit damage but for slight chipping on gauge area on few occasions. Most of these PDC bits have been re-run too & have given good ROP.
Rajat Khanna
Drilling Manager   
mikegy
Directional Drilling Supervisor
SPREADAssociates
Total Posts: 29
Join Date: 06/06/11
Very much depends where you are, what hole size and formation. Some places (such as Kurdistan) you need at least a 1.5 ABH just for minor corrections.

I always use PDC's and never have a problem drilling out, with water based muds, in fact I barely see anything, but am convinced it induces PDC bit shoulder damage.

Guess it's the economical way to go if you don't have to spend time reaming with the next bit.

If it's only shoulder damage, and not gauge wear, then that's not a problem.

But again, depends where you are.

You will soon learn!    

Pcoates
Senior Drilling Engineer
British Gas
Total Posts: 5
Join Date: 02/12/07
Not really an issue but depends on csg ID, stabilisation, motor size, bit to bend distance etc. Have done so many times with different configurations and bends up to 1.5 deg. Damage most likely to occur if good practice is not followed when drilling out. Have also observed chipped cutters on rotary BHAs pulled after drilling the shoe track - so damage may not be solely linked to bent motor BHAs.
Augusto
Consultant [retired Shell staff]
SPREADAssociates
Total Posts: 244
Join Date: 02/09/05
My major worry is unscrewing the shoetrack.

Obviously, if you had selected a Left-Handed Threaded shoe track that problem is solved.

Thread-locking compound can be mildly effective if you torque the threads correcting for the friction factors.

Tack-welding is the least desirable solution... There is an interesting paper by Maraven on that subject.

Ensure that the float equipment plugs system is selected based on its anti-rotation characteristics and drillability 
JDDrouin
Project Quality
SPREADAssociates
Total Posts: 96
Join Date: 06/05/09

Jeff,

IMOP only but:

a). The motor v hole size means the motor's under way more stress than is necessary.

b). The directional capability results desired can be achieved by a 'better' combination than a ~25' stab-bend-stab.

c). If you plan on rotating the string much, and it's not a brand-new bent housing, make sure you have plenty of fishing gear available.

James Drouin

Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 361
Join Date: 10/01/05
On offshore wells with high day rates we would not give this a second thought.

There may be and could be a minor or more severe bit damage problem if best practices are not followed but in my experience this is  a far lower risk than drilling out and making an extra costly trip or drilling ahead far slowly with a tri cone vs a Pdc bit that even damaged will generally outlive and outperform a tri cone at a high day rate spread.  

When drilling cement optimise pump rate weight and moderate rotation. Keep pipe moving at all times and avoid stationary rotation. 

The critical phase is drilling plugs, floats and shoes. Here again observe torque where if there is none you are not making progress. Rather than sitting on bottom going nowhere, the driller needs to vary parameters to obtain torque needed to make progress required. It is here's that PDC bits will most likely become damaged whatever bend is present, where if best practices are not followed. E.g If more weight is required, then slow down rotary, etc. keep pipe moving, pick up off bottom frequently etc will reduce and mitigate likeliness of bit damage. 

Bit, bit gauge Bha's considerations can all also assist in reducing damage that remember simply does not happen but is caused. Understanding the causes therefore and preventing these can deliver the desired results through best practice management and control. 

In conclusion we have run an drilled out with motors, big bends etc without any resulting issues far more often than not. 
jeff
Drilling Engineer
spd
Total Posts: 2
Join Date: 05/09/10
What is everyone's views if the motor is a 9⅝" motor with a 1.5° Bent housing setting with a 17½ PDC, 17¼" Motor Sleeve, 17â…›" Motor top stabilizer?

Casing is 20", 133ppf that we need to drill out with the above assembly.  ID / drift are 18.73"/18.5", so there is ~1" of clearance. 

I am thinking as long as we use good practices, we should be fine. 

Cheers
Jeff
adoubleuk
Consultant DSV
SPREADAssociates
Total Posts: 26
Join Date: 04/03/11
I'd agree with a number of the correspondents here. The most important observation being that 1.15 degrees is not a 'severe bend' ....

People can get ridiculously paranoid about PDC cutter damage in casing, and in most instances this is an unfounded fear, dating back a long while.

One thing which hasn't been mentioned, though. Downhole costs of your motor and MWD. Presumably you're going to do a LOT / FIT after drilling out? Which also involves circulating clean, adding maybe an hour or two to your motor circulating hours, and reducing your useful MWD battery life. Do some sums: sometimes it can be financially advantageous to run a simple rockbit Bha for drilling out on this basis alone.

AK
sadiqdd
Directional Drilling Supervisor
Baker Hughes Inteq
Total Posts: 15
Join Date: 24/07/10
Dave,

I actually do not see much concerns here. I had drilled out casing shoes and almost all the time with more than 1 deg bend on mud motor, often 1.2 deg, in Angola and Nigeria. This is not so unusual as much as the fears expressed by the team. It is basically justified for possible directional course correction.If there was any offset information, it might be useful in predicting the deviation tendency of the assembly as you mentioned it was planned to be vertical section.
Sometimes also, we make a pendulum assembly to maintain verticality.
considerations are usually given to interval length, the directional objectives of the next section, proximity of/to other wells, the target tolerances, etc
jl2002
Special Ops Mgr
Murex Petroleum
Total Posts: 3
Join Date: 29/07/10
I can't speak for the sizes you have, but certainly with 8-3/4" and 6" bit sizes we do this all the time. Yes,we have occasionally seen some PDC damage, but it is very rare (< 5%).

We are drilling out with 8-3/4" in vertical and with 6" in horizontal, both cases are with bent motors, PDC bits drilling Weatherford PDC drillable float equipment. We just run light weight.

Typically we are using a 1.15° bend motors.
Salis
DW Well Operation Superintendent
ENI
Total Posts: 4
Join Date: 27/06/10
If you can avoid to use motor and bent housing 1.5deg . Pumping keep your bit rotating all the time and is not good pratice to use to drillout cmt.
If you can plan touse EDL Geopilot for high dog leg.Withthis it is easy drillout cmt and drilling ahead.
cheers
Augusto
Consultant [retired Shell staff]
SPREADAssociates
Total Posts: 244
Join Date: 02/09/05
Because I did colate events that I became aware of since I did join the Oilwell drilling business back in 1965, I would be reluctant to do this.

Two main reasons:

1. Afraid of losing/damaging/unscrewing/leaking the shoe track (check for metal shavings...)

2. The PDC bit can "O-ring", lose cutters, etc suggesting that the round trip to drill the shoe track with mill-tooth bit is perhaps wise.
As the "auld drillers" concluded "shoetracks are not PDC drillable.

If the casing is a Production casing, you may have a leak - unscrewing/cutting/holing one joint. Even if a production liner overlaps the shoetrack you can not ensure that the top cement or liner top packer will work to your satisfaction for the duration of the production life of the well.

So shoe tracks do back off, they do part, sometimes they go further down on their own rendering re-entry very tricky.

In my view, the risks are too many to be neglected. In fact we did introduce LEFT-HAND threaded shoe tracks to minimise the risks of having a faulty one.
mikegy
Directional Drilling Supervisor
SPREADAssociates
Total Posts: 29
Join Date: 06/06/11
Good comments.
It's pretty routine and wouldn't expect any problems in the case quoted.
Hopefully non-rotating plugs are being used, simply because they reduce the rotating time inside casing. Drilling the float collar is what usually takes a bit of time, but often no more than 10 minutes or so.
Good practice, easy parameters and no problems with future bit life.

Highly deviated wells sometimes need circulating, and rotating well up inside casing for hole cleaning, and nobody seems to worry about that regarding PDC damage, etc.
admin
Managing Director (rp-squared.com)
Relentless Pursuit Of Perfection Ltd.
Total Posts: 409
Join Date: 10/01/05
Hi folks

Thanks for the input. The well will be vertical, its' a 12-1/4" bit in 13-5/8" 88.2 lb/ft casing.

Kind regards

Dave
hendo
Directional Driller
SPREADAssociates
Total Posts: 127
Join Date: 27/02/08
Dave,

The main concern that many a Company Man will express is bit cutter damage.
Here there (in my opinion) many factors to consider;

Bit side loading is primarily caused by the "trepaning" effect of the bit and is related to the bend setting and the distance from the bit face to the bend (which describes the radius of the base of the cone thus formed).
The jam angle relates to the gauge length and the angle at which the bit would wedge itself in the casing.
Hence the data required is;
Bit gauge length (and also amount and type of gauge protection).
Bit to bend angle.
Casing weight (which affects effective hole diameter).

In relation to the motor and BHA the following are relevant;
Motor size (ie in 12 1/4" hole a 9 5/8" motor will give greatly different side loading to an 8" motor).
Size and position of Motor Lower Bearing Stabiliser. (Possible supportive effect and potential pivot point in BHA).
Size and position of Stabiliser (if any) on top of motor. (Affects the side loading by affecting the position of the motor relative to the axis of the hole).

Your stated 1.15 degree bend may or may not be classed as excessive - depends on the hole size. You mention that the well is essentially vertical and so the motor bend is correctly back to the vertical (if required). Remember that without inclination (and hence a low side) that the effect of the BHA. particularly toward low-side will be minimal and bend size could be a great help further down the section.
If you really wanted to get scientific you could research into bit cutter size and number of blades, then do a vibration and bit dynamics model to see if the effects of harmonics and chatter would be worse that side loading on the life of the bit.

And last, but not least, would be drilling parameters.
I assume PDC drillable jewellery on the end of the casing.
Again here BHA geometry will define the limberness of the BHA and so dictate safe working parameters (ie if patience runs out while drilling the shoe and excessive WOB is applied this could cause the BHA to bend and increase bit side loading).

Conclusion.
I personally see nothing wrong in running in hole with a bent motor as described, drilling the shoe then drilling ahead - providing the operation is correctly planned and care is taken.
This involves - bit side loading calculations and drill-string dynamics models.

As a footnote I remember many a time getting the sharp end of a co Man's tongue because I asked the rig crew to put a PDC bit down directly onto steel grating (and not a rubber mat).
The same guy would then urge the crew to trip the bit into the hole as fast as possible - I would be interested to hear from any bit engineers why the bit on surface could not take being laid on a steel deck, but down hole its no problem to risk high speed impact with ledges in the hole.

Hope this helps..................Hendo.
gregcrum
DSupt
CNR International
Total Posts: 23
Join Date: 17/05/08
Some other things to consider which will affect the side force hence damage to the bit are casing size, motor size and BHA configuration. Further, flow rate use and motor specification (rev/gal) will also have an effect on bit wear/damage.

There is no doubt that the lower the bend the better, but stabiliser placement has a major effect on side force, the more rigidly stabilised the motor is the greater the side force.

The degree of bend needed will be dictated by firmness of formation to be drilled, expected directional tendencies of the formation. Harder formations will likely need a higher degree of bend to get any decent directional change.

One other thing to look at is cuter size, smaller cutters (say 13mm vs 16mm) generally will suffer less damage.
Scott_McNeil
Consultant
SPREADAssociates
Total Posts: 110
Join Date: 05/03/08
Hi Dave,

I'd only be wary if you have a tight bit / casing clearence.

For example, with a 1.15 Deg setting, I'd be a little concerned about being able to rotate sucessfully with a 12 1/4" bit inside 13 3/8" 72 lb/ft casing, or 8 1/2" inside 9 5/8" 53.5 lb/ft.

All the best

Scott
JDDrouin
Project Quality
SPREADAssociates
Total Posts: 96
Join Date: 06/05/09
Dave,

Without trying to be critical, there is no 'good' justification for rotating (using) a bent motor inside of casing for all the reasons detailed above.

Undoubtably, the bend recommendation came from the DD contractor who has entirely different objectives than the opreator or bit supplier.

If the hole trajectory (i.e. a kick-off) requires a bent motor, make the trip.

If the hole trajectory requires a very accurate vertical bore, then use weight or a vertitrac.

James Drouin
Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 361
Join Date: 10/01/05
Vertical hole?
0-30deg?
30-60deg?
Horizontal drill out?

In general there are always compromises when drilling out with a bend and PDC bit. However this rarely gets a second thought and is not high enough on a risk register in assessment to worry about.

Perhaps slightly more risk in a vertical hole (e.g. easier to induce side loadings atetc)
less in a directional hole that already has some angle.

As long as best practices are applied and where a PDC is fully justified to drill far more efficiently and effectively in the open hole. Note: in some direcitonal applications and notably softer sedimentary sequences PDC's are not always the most preferred when using bent subs and motors etc.

e.g. When drilling out,
- Rotate slowly,
- keep pipe moving.
- dont stay stationary for long periods.
- use good pump to assure bit cutters are always bein
- don't apply too much weight (excepting) float and shoe will require more.g effectively cleaned.
- dont waste time reaming backreaming etc inside steel pipe.
Drilling out section once is usually enough.

Hence for decades now we rarely do seperate clean out runs and opt to run the drilling ahead assembly. Unlesswe had junk in hole or some other anticipated wellbore, downhole or equipment related problem to face or contend with.
sadiqdd
Directional Drilling Supervisor
Baker Hughes Inteq
Total Posts: 15
Join Date: 24/07/10
Dave,

I actually do not see much concerns here. I had drilled out casing shoes and almost all the time with more than 1 deg bend on mud motor, often 1.2 deg, in Angola and Nigeria. This is not so unusual as much as the fears expressed by the team. It is basically justified for possible directional course correction.If there was any offset information, it might be useful in predicting the deviation tendency of the assembly as you mentioned it was planned to be vertical section.
Sometimes also, we make a pendulum assembly to maintain verticality.
considerations are usually given to interval length, the directional objectives of the next section, proximity of/to other wells, the target tolerances, etc
timclay
Energy-in-Focus
Total Posts: 3
Join Date: 08/11/07
Dave,

In case you had not already covered these points the DWOP:

1. Is it possible to use a 0.78 degree setting on the mud motor and still be able to make a correction run as required? Your DD contractor should be able to confirm this.
2. The float equipment should be pdc-drillable
3. Consult with the bit supplier concerning recommended parameters for drilling the shoetrack.

Trust this helps

Tim
cnduncan
Drilling Consultant
SPREADAssociates
Total Posts: 25
Join Date: 10/04/11
Dave,
I agree with Cordialdevil in that any bend is likely to cause some damage. I have used a 0.78 degree bend many times with relatively low damage to the gauge cutters and a .78 bend is sufficient to do some useful directional work in the formations I was drilling.I would be weighing this request in relation to the formation to be drilled and how hard the bit will need to work to get thejob done. Where I was drilling the formations were soft and the bit could handle a little damage without greatly affecting ROP or the ability to reach section TD.
cordialdevil
Drilling Supervisor
SPREADAssociates
Total Posts: 9
Join Date: 17/08/09
Although 1.15 degrees is not considered a "severe bend", my experience with using PDC bits to drill out casing shoes is that any bend causes cutter damage to some extent, depending upon the bend setting. This has been verified several times by myself when, for whatever reason, the BHA was pulled before drilling ahead from the shoe. Bends of 1.5 degree and above, from my observations, can cause significant damage and reduction of useful drilling life to a PDC bit.
A roller cone bit suffers much less damage drilling out casing shoes, but will not stay in the hole for as long and may not achieve the same penetration rates as a PDC bit, depending upon the formation, so the decision to use PDC bits is an economic trade-off, damage for longevity in the hole.
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