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Rational use and selection of diamond bits

2017/08/07 16:38
Rationaluseandselectionofdiamondbits Becauseofitsbrittleness,poorimpactresistanceandhighthermalsensitivity,diamondbitshavemuchstricteroperatingconditionsthanotherbits.1.requirementsforcleaningholebott
Rational use and selection of diamond bits
Because of its brittleness, poor impact resistance and high thermal sensitivity, diamond bits have much stricter operating conditions than other bits.
1. requirements for cleaning hole bottom
Before entering a diamond bit, a cemented carbide bit with a powder tube similar to a diamond bit must be used for workover. The O Iwa and the broken metal and other objects on the bottom of the hole are washed up by hydraulic power and sink into the powder collecting pipe.
2. new drill bit initial grinding
The diameter of the new diamond bit must be smaller than that of the non diamond bit and run in. The initial rotational speed should be 40-50r/min, the initial drilling pressure is 1/8 of the normal drilling pressure, about 0.15-0.2m after drilling into the normal drilling.
3. selection of normal drilling parameters
(1) to determine drilling pressure, we should consider the formation lithology and hydraulic flushing induced lift force. Usually, the maximum specific pressure of the bit lip is 6.9MPa in the soft formation. In hard stratum, because diamond has small cutting depth, small contact area with rock, and diamond is easy to be fractured by overload in hard stratum, it is recommended to use smaller specific pressure, generally 5.1 MPa. The drilling pressure of diamond bit with different caliber applied to different strata can be selected according to figure 5-14. In normal drilling, the lower limit of the curve should be selected first, and the drilling pressure should be increased gradually with the bluntness of diamond, but it should not exceed the upper limit of the curve. The actual value of drilling pressure is obtained by estimating or checking the curve, and the influence of buoyancy and lift-off force in the hole should be added.
(2) The ideal rotational speed should be as high as possible after running-in of the bit, so as to give full play to the benefits of diamond drilling. It is generally believed that the safe rotational speed is 150 r/min. It is better to increase the rotational speed to 300 r/min when the formation conditions, drill pipe quality and equipment capacity permit. Diamond bit has been successfully applied to 600~1 100r/min with turbine drill and achieved good results.
(3) The pump capacity should first meet the requirements of minimum reflux velocity in annular space, and at the same time ensure the needs of cleaning hole bottom and cooling bit. Fig. 5-15 shows the recommended pumping range for drills of different diameters. The lower limit is used for high density mud and the upper limit is used for low density mud.
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