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.
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
Formation – Clay stone and shale has tendency to ball up the bit even though you use highly inhibitive water based mud or oil based mud.
Weight On Bit – High weight on bit will have more chance to create this issue.
Hydrostatic Pressure in Wellbore – High hydrostatic pressure (pressure above 5,000 psi) can induce bit balling issue in water based mud.
Bit Design – Poor bit cutting structure and poor junk slot area in PCD bits contribute to this issue.
Hydraulic – Low flow rate will not be able to clean the cutting around the bit.
Planning To Mitigate The Problem
Bit Selection – For the rock bits, steel tooth bits are better than insert bits because the steel tooth ones have greater teeth intermesh. For the PCD bits, the larger junk slot area is preferred.
Bit Nozzle Selection – The bits with high flow tube or extended nozzles are not recommended. If the bigger bit size is utilized, don’t block off the center jet. The center jet will flush all cutting more effectively.
Good Hydraulic – Hydraulic horse power per cross sectional area of the bit is the figure which can be utilized for measuring good hydraulic for bit balling mitigation. Hydraulic horse power per square inch (HSI) less than 1.0 will not be able to clean the bits. It is good practice to have more than 2.5 of HSI for good bit cleaning.
Weight On Bit – Don’t try to run a lot of WOB. If you increase WOB but you get lower ROP, you may have bit balling up issue. You should lower the weight and attempt to clean the bit as soon as possible.
Drilling Fluid– Mud chemical additives as PHPA which can prevent clay swelling issue must be added into the water based mud system. If feasible, drilling with oil based fluid will have less chance of balling up bit/BHA.
What Should We Do if The Bit Balling Is Occurred?
Stop drilling and pick up off bottom – if the drilling operation keeps continue, it will make the situation even worse. It is a good practice to stop and pick up off bottom to fix the issue quickly.
Increase RPM and Flow Rate – Increasing RPM will spin the cutting around the bit more. Additionally, increase flow rate to the maximum allowable rate will help clean the bit.
Monitor pressure – if you see decreasing in stand pipe pressure to where it was before, it indicates that some of cuttings are removed from the bit.
Lower WOB – Drill with lower weight on bit.
Pump high vis pill – Pumping high viscosity pill may help carry out cutting from a wellbore.