Simplified Roller Bit Classification System

A new roller bit classification system has been approved by the American Petroleum Institute as a "recommended practice" and It will be included in the forthcoming edition of RP7G.

(Recommended practice for drill stem design and operating limits).

The system is meant to standardise the nomenclature for roller bits according to the application recommended by the manufacturer and their special features and not to standardise the bit design itself.

A 3-digit code is used. The first digit (series) indicates the type of formation for which the bit is designed and whether the bit is a milled tooth (series 1 -3) or an insert type bit (series 4-8). The second digit (types) stands for the hardness of the formation, 1 for the softest to 4 for the hardest formation of the type indicated by the first digit, The last digit (features) indicates special features of the bit such as bearing type, heel tooth model, incorporation of gage inserts, combinations of the foregoing or special features.

The rock bit comparison chart shows bits manufactured by Smith, Hughes, Reed and Security according to the system and under their own codes.

The formation to be drilled is Medium to Medium Hard with a High Compressive Strenght and is non abrasive.

High progress was booked in similar formations in the past using a "Hughes R4 bit", but bearing wear was recorded at B-6 and tooth wear at T-2.

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