Patent Application
20160017665
Not Applicable.
Not applicable.
This disclosure is related to the field of fixed cutter drill bits used to drill wellbores through subsurface rock formations. More specifically, the disclosure relates to structures and compositions of cutters used on such drill bits.
Fixed cutter drill bits known in the art include a plurality of cutters affixed to a bit body. The bit body has features to enable coupling to a drill string or other drilling tool that rotates the bit and applies axial force so that the bit drills through rock formations to create a wellbore.
The cutters are typically formed from a substrate in the form of a right cylinder. A diamond “table” made of polycrystalline diamond, or a layer of other “super hard” material, e.g., cubic boron nitride, is affixed to one end of the substrate to for the cutting surface of the cutter.
Cutters of the foregoing type known in the art have about 12 to 15 percent cobalt content in the substrate. An overall length of the cutter is typically about 13 millimeters, including both the substrate and the diamond table or super hard material layer. Shorter cutters are known in the art, however, they generally are only used either in the very center of the bit, called the “cone” (where torsional loading and work rates are a lot lower) or in either backup positions or gage positions. What are known as “primary” cutter positions are positions where the cutters are subjected to the most loading (the positions where the cutters are at the front of the blade and are between the center of the bit and the gage of the bit). Primary cutters may be considered any cutter located radially inwardly of the gage and outwardly of the cone. It is not known in the art to use short cutters (i.e., cutters shorter than about 13 mm overall length) in the above-defined primary cutter locations as it is generally believed that there will not be enough surface area for brazing and that will lead to cutters falling out while drilling.
The cobalt content of cutter substrates known in the art is believed to be necessary to provide the cutters with sufficient resistance to brittle fracture during drilling. The overall length is believed to be necessary to provide sufficient surface area to attach the cutter, typically by brazing the substrate to the bit body, so that the cutters will be attached to the bit body strongly enough to avoid being removed from the bit body during drilling.
An example fixed cutter drill bit is shown at 10 in
In the present example, the substrate 16 may be made from tungsten carbide and have a cobalt content of at most ten percent by weight. In the present example, the substrate 16 may have a cobalt content of at least six percent by weight.
An overall length of the cutter 14 may be about 10 millimeters, including both the substrate 16 and the cutting material surface 18. The thickness of the cutting material surface may be about 2 millimeters in the present example. The substrate is thus about six millimeters in length. In other examples, the overall length of the cutter may be about 8 millimeters, wherein the substrate is about 6 millimeters in length.
An oblique view of the cutter 14 is shown in
It has been found through testing that having a cobalt content in the substrate between six and ten percent by weight increases the resistance of the substrate 16 to wear during drilling, but has not resulted in increased incidence of brittle failure. Correspondingly, the overall length of the cutter 14 of about 8 millimeters has been found to provide sufficient bonding surface area to affix the cutter to the bit body (12 in
A fixed cutter drill bit made according to the various aspects of the present disclosure may have reduced costs of manufacture, and may have longer usable life span than fixed cutter bits known in the art prior to the bit and cutters of the present disclosure.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
