Tag Archives: drilling operation

What You Need To Know About Drilling Bit Balling Up and How To Troubleshooting It

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Bit balling is one of the drilling operational issues which can happen anytime while drilling. This issue can cause several problems such as reduction in rate of penetration and surface torque, increase in stand pipe pressure. Personnel may eventually need to pull out of hole the BHA in order to clear the balling issue at the bit. This article will teach you about the bit balling and how to prevent it in the planning phase and how to effective detect and clear the balled up bit before it becomes a worse problem.

bit-balled-up

How You Recognize the Bit Balled Up While Drilling

Drilling Torque – Drilling torque will be lower than normal drilling torque since most of the cutters are covered up by cuttings.

Rate of Penetration – The ROP will decrease more than projection. If you drill 100 fph and later on the ROP drops to 50 fph without any drilling parameters changed, this might be this problem.

Standpipe Pressure – Standpipe pressure increases with no changes in flow rates or drilling parameters. Balling up around the bit reduce annular flowing area resulting in increasing pressure.

Factors Affecting Drill Bit Balling Up

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Mechanical Blind Back Off Drill String and Tubular

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Mechanical blind back off is the procedure to intentionally break out stuck drill string by applying left hand torque and transmitting down hole. This is the last method to recover drill string because back-off position cannot exactly determine. One situation that I used to do the blind back of is when the perforating gun cannot be run into tubing string.

 mechanical-Blind-Back-Off-Drill-String-and-Tubular-1

Procedure to Perform Blind Back Off Operation

1. Determine drilling parameters prior to get stuck if possible.

Pick up weight __ lb

Slack off weight __ lb

Rotating weight __ lb

2. Pick up drill string at 10% over the rotating weight. Apply 50% of make-up torque with left hand turn and lock TDS. Record how many turns. Slowly work string down for 5-10 minutes to transmit surface torque to the bottom. Weight while working should be between pick-up and slack off weight.

3. Repeat step#2 with 70%, 90%, 100%, 110% make up torque

4. The string should be back off while working down.

 mechanical-Blind-Back-Off-Drill-String-and-Tubular-2

Note: The concept is to have overpull tension applied at each connection while left hand torque is transmitted into the drillstring. Once the drill string is worked, the torque will be transferred to the bottom connection of the well.

 

Fishing Drill Pipe Procedure – Screw in Drill Pipe

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Sometimes drillpipe is accidentally dropped into the well and you need to fish it out of the well. One easy option that may be feasible to perform is to use a drill string to screw into the drill pipe in the well.

 Fishing-Drill-Pipe-Procedure-screw-in

Before going into a detailed procedure, you may need to check the following conditions.

• Tight clearance between hole and tool joint

• Tool joint at the top of fish is in a good condition

Data that you need to know before going to fish the drill string

• Fish length

• Top of fish

• Weight of fish in the mud

• Actual turn to fully engage when screw in

Detailed procedure for fishing drill pipe by screwing into the fish

Fish length = xxx ft

Expected TOF = xxx ft

Weight of the fish (BHA + DP) = xx Klb

 

1. Trip in hole 1 stand

2. Count the actual turn of drill pipe

3. Run in hole to xxx MD (200 ft above the Top Of Fish)

4. Make up top drive

5. Break circulate with 160 GPM using current drilling fluid in the well

• Record pressure

6. Record pick up and slack off weight without rotation

7. Record pick up and slack off weight with 20 RPM

8. Record torque with 20 RPM

– In the steps 5-8, you will get the base line values when the drill string does not engage with another part.

9. Slowly run in hole without rotation

10. Tag top of fish while pumping with 160 GPM

11. Pick up 5 ft

12. Slowly run in hole with 20 RPM

13. Attempt to screw into the top of fish (tool joint)

14. Indicators if the fish is engaged.

– Increase in pumping pressure, torque, weight on bit and pick up weight.

– When picking up drill string, increment of pick up weight should close to buoyed weight of the fish (dropped drill string).

15. Flow check

16. Pull out of hole to surface.

 Note: This is the generic guideline. You may need to adapt some parameters/steps to match with your rig operation.

 

Deal With Soft Clay Formation in Sea Water

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The well was drilled with sea water and the formation is soft clay formation. Then, the bit was totally plugged. We did not have any chance to displace well with water based mud prior to coming out of the hole. We flow checked and came out of hole to change the bit.

Because the formation is clay which will react with seawater resulting formation swelling, we need to develop specific rig procedure to deal with when tripping in hole.

What are the foreseeing issues?

• Clay formation swell

• Pack off due to formation instability

• Soft formation tends to get side tracked easily with mud motor

What is the objective?

• Attempt to condition the well before running back in hole with motor assembly to minimize chance of side track.

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How to Determine Mud Motor Failure

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Mud motor failure downhole may be happened from time to time. The questions that are usually raised are things like “How do I know if the mud motor fails down hole?” and “What indications will I see that this has happened?” etc. We would like to share our experience regarding mud motor failure and its symptoms.

The following signs indicate that you may be faced with downhole mud motor breakdown.

Frequent Mud Motor Stall – Motor stall happens when the rotor of the mud motor has stopped moving. Typically, the motor stalls only with a high differential of pressure. However, if the motor doesn’t perform as normal, it will get stalled with by a small amount of differential pressure. For instance, a mud motor normally drills at 400 psi differential pressure, but if the motor is stalled out with only 100 psi you can suspect the problem is with the motor.

Pressure fluctuation while rotating –  Rotating with a good mud motor won’t create pressure fluctuations, whereas a bad mud motor will show fluctuation in stand pipe pressure and you may not be able to maintain constant pressure.

Abnormally high surface pressure – A stator is made of rubber. When the stator rubber is worn out and breaking into pieces, small parts of rubber can jam into the flow path in the motor. This situation also results in high stand pipe pressure.

Reduction in Rate of Penetration – If there are no changes in formation and drilling parameters, the decreasing in ROP (Rate of Penetration) may be caused by failure of the down hole tool. Moreover, if the took is severely damaged, you will be able to drill any footage.

What should you do if the problem is clearly identified?

If any failure sign is seen, it is recommended to pull out of the hole and change a new tool. It is almost impossible to drill with a damaged mud motor unless you only have a few feet to the well target depth.

With the mentioned indicators of mud motor failure above, you should be able to identify your suspected problem and begin troubleshooting as soon as possible to minimize non-productive time on a drilling rig.

References

Inglis, T.A. (2010) Directional drilling. Dordrecht: Springer-Verlag New York.

Mitchell, R.F., Miska, S.Z. and Aadnoy, B.S. (2012) Fundamentals of drilling engineering. Richardson, TX: Society of Petroleum Engineers.

Short, J.J.A. (1993) Introduction to directional and horizontal drilling. Tulsa, OK: PennWell Books.