Roller rock bit

Classification of Drilling Bits 769. Roller Rock Bit 771. Bearing Design 774. Tooth Design 776. 

Roller rock bits (milled tooth bits)... 

The elements of the roller rock bit are shown in Figure 4-137 [45]. Roller rock bits have three major components the cone cutter, the bearings and the bit body. The cutting elements are circumferential rows of teeth extending from... 

Figure 4-137. Roller (rock) bit elements [45]. (Courtesy Canadian Association of Oilwell Drilling Contractors.)...

A roller rock bit is pulled out of the hole after 12 hr of rotation at the bottom. The driller estimates that the worst cone could rotate 4 hr more before being completely worn out thus total bearing life estimated is 16 hr. 

Roller rock bit nozzle sizes are given in Table 4-98. The total pressure drop across a roller rock bit, Pj (psi), is [47]... 

Figure 4-143 gives convenient graphs for nozzle selection for roller rock bits [47]. 

Diamond bits are being employed to a greater extent because of the advancements in mud motors. High rpm can destroy roller rock bit very quickly. On the other hand, diamond bits rotating at high rpm usually have longer life since there are no moving parts. 

A tricone roller rock bit is furnished with three nozzles with the diameters of 32 od -il in. Calculate the bit pressure drop if the mud weight is 10 Ib/gal and flowrate is 300 gpm. 

The downhole turbine motors that are hydraulically operated have some fundamental limitations. One of these is high rotary speed of the motor and drill bit. The high rotary speeds limit the use of downhole turbine motors when drilling with roller rock bits. The high speed of these direct drive motors shortens the life of the roller rock bit. 

Motor speeds and, therefore, bit speeds are high, which limits the use of roller rock bits. 

For straight hole drilling the turbine motor with the highest possible torque and the lowest possible speed is of most use. Thus the turbine motor is selected such that the motor produces the maximum amount of power for the lowest possible circulation flowrate (i.e., lowest speed). The high power increases rate of penetration and the lower speed increases bit life particularly if roller rock bits are used. 

Soft, medium and hard rock formations can be drilled with a positive displacement motor using nearly any type of rock bit. The positive displacement motor is especially adaptable to drilling with roller rock bits. 

The positive displacement motor whose performance characteristics are given in Table 4-115 is a 5 6 lobe profile motor. This lobe profile design is usually used for straight hole drilling with roller rock bits, or for deviation control operations where high torque polycrystalline diamond compact bit or diamond bits are used for deviation control operations. 

Bit Nozzle Sizes. The pressure loss through the bit must be 500 psi with a circulation flowrate of 348 gal/min with 11.6-lb/gal mud weight. The pressure loss through a roller rock bit with three nozzles is (see the section titled Drilling Bits and Downholes Tools )... 

The rotary drill bits are generally made from quench and tempered steel alloys such as AISI 3115 to 3120, 4620, 4815 to 4820 and 8620 to 8720. The only corrosion related problem that can arise may result from a hydrogen sulfide environment. The bearing in the roller rock bits can be damaged by H S contamination of drilling fluid. However, a well conditioned drilling fluid at... 

The most frequently used bit types are the roller cone or rock bit (F g. 3.8) and the polycrystalline diamond cutter or PDC bit. 

Bit Wear and Rock Type. Using downhole weight-on-bit and torque the roller cone bit wear can be estimated while drilling. The well site computer can be used to compute in real-time a dimensionless torque (T ) and a dimensionless rate of penetration (R ) using the following equation ... 

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