Suggested Rotary Drilling Techniques for ACT Cement Retainers and Bridge Plugs
When drilling a cast iron cement retainer or bridge plug the same considerations should be used as when drilling a medium hard formation. Drilling with a medium tooth medium hard formation rock bit is usually the best combination. Spudding the work string and variations in rotary speed and set down weight should be used to aid in breaking up large metal parts and preventing bit tracking. One or more junk baskets should be used above the bit when normal circulation is employed.
Bit – Medium tooth medium hard formation rock bit. Rotary Speed – 75 to 120 RPM is suggested.
Weight on bit – Apply 5,000-7,000 lbs. until top end of bridge plug or cement retainer body is drilled away, 4-1/2 thru 7 (3-5 inches) 7-5/8 and larger (5-9 inches). An additional 3,000 lbs. of weight can now be applied per inch of bit diameter to drill the remainder of the cast iron product. Example: 4-1/2 bit will use 9,000-13,500 lbs. of weight.
Drill Collars – Should be used for weight on bit and bit stabilization. Example: 4-1/2 thru 5-1/2 (8-min.) 7 and larger (12 min.).
Junk Baskets – One or more junk baskets should be used above the bit. Annular Velocity – 120 feet per minute is suggested.