Monday, 27 May 2013

Waterway Configurations for Surface-Set Core Bits

With the exception of some thin-kerf surface-set core bits, most sizes are offered in three different waterway configurations. These various waterway configurations have distinct ranges of application and have the function of controlling the bit hydraulics.

Regular Configuration

Unless otherwise specified, this is the standard waterway configuration used on all mineral exploration of surface-set core bits manufactured by IDP. This design uses canal type waterways that are approximately 0.12 inch (3 mm) wide. These waterway canals pass the circulating fluid from inside diameter of the bit crown, across the face and eject the fluid and cuttings at the outside diameter of the bit crown.
The Style ‘W’ waterway configuration is available for all sizes of surface-set diamond core bits produced by IDP.

The IDP code for this waterway configuration style is ‘W’. (Example: A IDP core bit with the descriptor ‘6W’ in its designation would indicate that the bit is supplied with 6 internal discharge canal type waterways).

Other customer specified waterway canal widths are available on request. In addition to the rectangular shaped waterway canals, thick-kerf, large diameter surface-set diamond core bits are often supplied with either trapezoidal or spiral shaped waterway canals to aid in the ejection of cuttings from the bit face. They also commonly include the use of junk slots in their waterway configurations.

Face-Discharge Configuration

This waterway configuration is recommended for use when drilling in relatively soft, unconsolidated formations and/or when using triple-tube wireline core barrel systems. Unlike core bits that are manufactured with conventional canal type waterways that eject the circulating fluid through ports on the inside diameter of the bit crown, the Face-Discharge configuration ejects the fluid through ports molded into the face of the bit. The re-direction of the circulating fluid results in minimum core wash and reduces the potential for subsequent core erosion.
Each waterway element typically has a canal width and flushing port diameter of 0.25 inch (6.3 mm).

The Style ‘FD’ waterway configuration is available on all Wireline core bits as well as on core bits with kerf widths greater than 0.39 inch (10 mm) that are used with conventional (non-Wireline) core barrel systems. The IDP code for this waterway configuration style is ‘FD’. (Example: A IDP core bit with the descriptor ‘6FD’ in its designation would indicate that the bit is supplied with 6 face-discharge type waterways).

Junk Slots

These are large output fluid passages that are molded into the outside diameter of a surface-set diamond bit crown to permit the ejection of large cuttings from the face of the bit. Typically, the addition of junk slots to a surface-set bit crown is restricted to large diameter coring and non-coring bits used in geotechnical and petroleum drilling applications where the formations are relatively soft and abrasive, the bit is set with either large particle size diamonds or PCD elements and the resulting cuttings tend to be long and sheared.

The number of junk slots that may be placed on a bit crown is a function of both its diameter and waterway configuration and must be divisible by the number of input waterways in order to establish a uniform pattern. The preferred number of junk slots is three (equally spaced) in order to preserve the dynamic balance of the bit during operation. Consideration should also be given to the effect of reducing the amount of outside gauge diameter setting resulting from the incorporation of junk slots into the bit crown design

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