What is the principle of selection of roller cone bits?
date:
2022-07-07
For soft formations, roller cone bits with three structures of shift axis, overtop and compound cone should be selected, and the teeth should be milled teeth or inserts with high, wide, thin, and large tooth tip angles. With the increase of rock hardness, the above three structural values of the selected drill bit should be reduced accordingly, the teeth should also be short, narrow and dense, and the tooth tip angle should also be reduced accordingly.
(1) For soft formations, roller cone bits with three structures of shift axis, over-top and compound cone should be selected, and the teeth should be milled teeth or inserts with high, wide, thin, and large tooth tip angles. With the increase of rock hardness, the above three structural values of the selected drill bit should be reduced accordingly, the teeth should also be short, narrow and dense, and the tooth tip angle should also be reduced accordingly.
(2) When drilling abrasive formations, an insert bit with a gauge tooth should be used. When it is found that the outer teeth of the previous drill are rounded and the middle teeth are less worn, the next drill should use an insert drill with gauge teeth.
(3) When drilling in easily inclined formations, a drill bit with no shaft shift or a small amount of shaft shift, no gauge teeth, and many and short teeth should be selected; The formation should be slightly softer than the formation being drilled, so that the ROP can be increased at a lower WOB.
(4) When choosing a drill bit with cemented carbide teeth, pay attention: when the shale is mostly drilled, use a wedge-shaped tooth bit; when using a diamond-limestone formation, use a parabolic or double-conical tooth bit; when drilling with high-density drilling fluids When the shale composition in the selected formation increases or the density of drilling fluid increases, use a bit with a large offset value; in diamond limestone or sandstone formations, use a bit with a small offset value; drill hard grinding When cutting limestone, flint, and quartz, use a ball-tooth drill without shaft shift.
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