Bit balling occurs in soft gumbo / swelling shales while drilling, the shale adsorbs water from the mud it then becomes plastic with a ball of compacted shale building up and covering the whole bit, stabilizers and drill collars, thus preventing further drilling progress.
TO CONFIRM THAT A BIT HAS BEEN BALLED UP
To be certain it’s a bit balling issue we are dealing with the mud engineer should observe some of the following or collect the following information from the following rig personnel, with the first 3 information from the driller being very important:
FROM THE DRILLER:
Did the Rate of Penetration (ROP) decrease when no drilling parameters were changed?
REASON: The bit cutting face is completely covered with a cake.
Was a lower than normal drilling torque observed?
REASON: A change in torque response such as torque signal remaining flat when WOB is increased signifies bit balling.
Was there an increase in the standpipe pressure using the same flow rates?
REASON: this is due to reduced annular diameter
Confirm what the weight on bit was (WOB).
REASON: If high, then there is a possibility for bit balling to occur, because the bit would be forced ahead of where it can remove cuttings.
Was a low mud flow rate used while drilling the section?
REASON: if the flow rate is low cuttings around the bit can’t be cleaned
Are you having surge and swab pressures while tripping?
REASON: “The built up mass at the bit causes it to behave similar to a piston in a cylinder, leading to surge and swab pressures while tripping”.1
Any Overpull on tripping out?
REASON: On tripping out materials accumulated on the BHA might be observed in surface parameters as overpull.2
FROM THE MUD LOGGER/GEOLOGIST
The nature of the formation being drilled
REASON: If the formation being drilled is clay stone / shale they have a tendency to ball up the bit.
FROM THE DRILLING ENGINEER / DIRECTIONAL DRILLER
The type of bit used for the section: bit profile and bit hydraulics design, affect bit balling the most.
REASON: “PDC bits are especially susceptible to bit balling because of their shear cutting action and the mechanism of chip generation”.1
“Shallow cone profile bits have a greater tendency to ball”.1
FROM THE MUD ENGINEER
Type of mud used for drilling
REASON: If the mud system doesn’t inhibit clay then it will definitely swell and result in bit balling.
Are the shaker screens plugged
REASON: Blocked shaker screens with soft clays.3
Selecting a bits profile and hydraulic design determines the type of influence it would have on bit balling tendencies. Example:
There is an absence of bit balling in parabolic profile bits because cuttings are generated in these bits at different planes, with no interference between the cuttings at the different planes, which makes it easy for them to be flushed away promptly.1
Selecting a bit with a center jet “C”. Center jets are designed to help prevent bit balling by cleaning the cutters in larger diameter bits drilling soft formations.4
Increasing RPM and Maintaining good bit/hole cleaning with hydraulic horse power per square inch (HSI) not less than 2.5 helps prevent bit balling.5
Drill gumbo shales with less weight to avoid bit balling.1 With this the bit works best by making smaller cuttings.
While drilling gumbo, to keep the bit clear increase mud flow.
Pull out and clean BHA, but before doing so attempt the following :
To achieve little weight on bottom -pick up
Increase your pump rate and spin the rotary as fast as you can.
Stroke the pipe up and down, bumping bottom each time in an attempt to surge the mud and free the cones.
Try to wash the ball off by dropping the pipe fast i.e. if the formation is solid, this increases flow and pressure at the bit.
Thin the mud.6
MUD ENGINEERS SOLUTION
To prevent bit balling from occurring it is advisable to adopt procedures that worked in your geographical area in overcoming bit balling by always reviewing previous drilling mud report (DMR).
Use mud system that can inhibit clay swelling example: Formulating KCl mud with PHPA (to avoid using higher concentrations of KCl) in which KCl prevents clay swelling while PHPA (partially hydrolyzed polyacrylamide ) coats the shales surfaces (encapsulates) thereby inhibiting their dispersion and incorporation into the mud.7
“When drilling gumbo, the pH should be maintained at 9.0-10.0. If bit balling occurs, increase the mud alkalinity (PM) to 5 or more with lime”.8
Drill with Oil based mud (with sufficient salinity), if possible.
Lubricant addition helps to prevent bit balling. Apply a 3% to 5% concentration by volume of DRIL-N-SLIDE™ lubricant to help stabilize the clay and improve ROP
Use drilling detergent, they are a specific type of dispersant that helps prevent formation of shales and clay from sticking to the drilling assembly and prevents agglomeration and plugging of the annulus by gumbo shale. They reduce occurrences of bit balling9, help in reducing the drag and torque of the drill string when it is rotated and moved up and down.
A concentration of 0.6 – 0.8 l/m3 is suitable.
It can also be pumped as a pill when bit balling occurs -as a concentrated surfactant (15-20%drilling detergent in 4-5 m3). 10
Drilling detergent can also be added into the drill pipe box on each connection.
Pump and spot Caustic Soda Pill. Note that it could create hole enlargement.
“If all else fails, before you trip out of the hole, you might pump a walnut-hull sweep. It will tend to sandblast the bit and remove the ball, and won’t hurt the mud. Don’t try this if you are running small jets in the bit, as plugging can be an issue.”11
There are several other ways of fixing bit balling problems and we would love to hear from you on what worked for you.
List of References
- Amoco Production Company, Amoco drilling Fluids manual, [Online] Available at: https://www.slideshare.net/VyanPersad/amoco-drilling-fluid-manual (Accessed 10 June 2018)
- C.H Darley and George R. Gray (1988) Composition and properties of drilling and completion fluids, 5th Edition [Online] Available at: http://nigc.ir/portal/Images/Images_Traning/files/files/chemist%20book/Composition_and_Properties_of_Drilling_and_Completion_Fluids_5E.pdf (Accessed 17 June 2018)
- Drilling Formulas.com (2014) What you need to know about Drilling Bit Balling up and how to troubleshooting it Available at: http://www.drillingformulas.com/what-you-need-to-know-about-drilling-bit-balling-up-and-how-to-troubleshooting-it/ (Accessed 16 June 2018)
- Hariharan and J.J. Azar . (1996) Oil and gas journal, Available at: https://www.ogj.com/articles/print/volume-94/issue-50/in-this-issue/drilling/pdc-bit-hydraulics-design-profile-are-key-to-reducing-balling.html (Accessed 10 June 2018)
- Mahmood Jassim AL-Khafaji (2014) The Brief In Oil Well Drilling, University Of Misan College Of Engineering Petroleum Eng. Dep.
- National Driller (2017) For Drilling Jobs, Bit Selection and Mud Flow Can Head Off Balling Available at https://www.nationaldriller.com/articles/90874-for-drilling-jobs-bit-selection-and-mud-flow-can-head-off-balling? (Accessed 16 June 2018)
- National Purity, LLC. (2018) Industrial degreasers, chemical blending, bulk cleaning solutions Available at: http://www.nationalpurity.com/drilling-detergent-can-save-company-money/ (Accessed 16 June 2018)
- Pal Skalle (2015) Drilling Fluids Engineering 6th Edition [Online] Available at: https://bookboon.com/en/drilling-fluid-engineering-ebook (Accessed 17 June 2018)
- Petroskills (2014) Drilling Practices [Lecture notes], Rotary Drilling Bits, Petroskills Houston, Well Construction / Drilling Training Courses, 11th February 2013.
- Q’Max Technical Bulletin #9. Mud Rings and Bit Balling, [Online] Available at: http://www.qmax.com/upload/media_element/30/01/q-maxtechbulletin9.pdf (Accessed 16 June 2018)
- Wayne Nash (2010) The World According to Wayne: Bit Balling Available at: https://www.nationaldriller.com/articles/87798-the-world-according-to-wayne-bit-balling (Accessed 10 June 2018)