ROCK ROLLER BIT FOR WATER WELL DRILLING
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RECOMMENDED WEIGHT ON ROCK ROLLER BIT FOR WATER WELL DRILLING

S.S. Chauhan

Member ( ED & MM )

C.G.W.B., Faridabad

The weight required on any rock roller bit for effective and Maximum Efficient Rate of Penetration" (MERP) varies directly as the compressive strength of material being cut.  This is a broad statement which is basically true but within which there are many variations and exceptions.  The heavy weights necessary to drill hard formations are required to give effective crushing force to the bit tooth and probably to keep the tool more or less flat running at bottom.

It is experienced that even with the heavy weights, there is enough eccentricity in rotation drill string.  Variation of weight at high speed over the bearing area of the bit might cause tooth breakage, uneven wear on bearings, excessive fatigue and premature failure of drill pipe and tool joints.

Broadly it is stated that the most efficient rotating speed varies inversely proportional to the hardness and compressive strength of the formation in many formations a higher rotating speed will result in a much higher rate of penetration than with a slower speed but, the wear and tear on the bit and other tools will be excessive in the overall efficiency of the operation.

The drill string is the most delicate portion of the equipment used in drilling a water well. It provides and limits the amount of weight that may be carried on the bit.  It is essential during the process of drilling that the drill pipe above the drill collars be held in tension, otherwise its rotation in unbalanced compression will cause undue fatigue and eventually fatigue failure.

In determining the proper weight on the bit the following four major factors are to be consider by the driller while drilling a hole.

The weight which is carried within the drill string is governed by the size and weight of the drill pipe, drill collar, type of bit and type of formation being cut.  If the load capacity of string exceeds the limit, it will cause undue strain and fatigue resulting premature failures.  From the technical efficiency point of view correct size of drill pipes should be used, but, still it does not meet the full requirement of economic drilling operations.

amount of weight that may be carried on the bit.  It is essential during the process of drilling that the drill pipe above the drill collars be held in tension, otherwise its rotation in unbalanced compression will cause undue fatigue and eventually fatigue failure.