Diamond drill bit – Drilling Equipment – Readyzone

Diamond drill bit


Diamond drill bit

Diamond drill bit, similar to drag bits, have no independently moving parts. They drill by direct abrasion or scraping against the bottom of the hole. Diamonds are much harder than the common rock minerals and are the only material which has been used economically for such severe service. When diamonds are mined, the stones of gem quality are separated from the commercial diamonds, which are colored or imperfect in crystalline form. The better grades of these stones are used in cutting tools for lathes and milling machines.

In manufacturing a diamond drill bit, a steel bit blank is machined with threads suitable to attaching it to a core barrel or the drill collars. Diamonds are placed in a bit mold and covered with powdered metal. With the bit blank held in position, the assembly is heated until the powdered metal fuses, and then it is slowly cooled. In this manner, the diamonds are held in a matrix which is attached to the steel bit blank. The matrix is composed partly of hard particles such as tungsten carbide, together with a softer alloy which acts as the binder material. The binder material must melt at a sufficiently low temperature that the diamonds will not be injured in the process. The hard particles in the matrix are necessary in order that the matrix will not erode or wear away, thus causing loss of the diamonds and failure of the bit. In the early 1940’s, several attempts were made to develop solid diamond bits which would drill out the entire hole without requiring a periodic round trip to empty the core barrel. These bits failed in the center, for in that area the diamonds have little or no peripheral speed and consequently tend to drill more slowly and take more drilling weight than the diamonds at the outer edges of the bit. About 1950, diamond bit manufacturers began using a much harder matrix material, and subsequently solid diamond bits have been developed which give satisfactory service.

Diamond drill bits are much less sensitive to the nature of the drilling fluid than are the rolling cutter bits. It is generally believed that thinner drilling fluids are advantageous in diamond bit performance and economy; however, they will continue to drill with thick mud. They differ in another important respect, for small-diameter diamond bits perform as well and better than larger-diameter bits and are, of course, much less expensive. A disadvantage of the diamond drill bit is its fragility. If drill cuttings or broken chips from rolling cutter bit teeth remain on the bottom of the hole and roll under the bit as it is rotated, they may rapidly cause bit failure. Thus it is necessary to wash the bottom of the hole thoroughly with mud circulation each and every time the diamond drill bit is set back on bottom. In this operation care must be taken that the throbbing action of the mud pump and consequent longitudinal vibration of the drill string does not cause the bit to pound on bottom. While slightly higher rotary speeds might often be advantageous for faster drilling, the bits are customarily rotated in the same range of speed as rolling cutter bits at about 40 to 100 rpm, in order to avoid any irregular action of the drill string which would damage the bit.

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Keywords – Diamond drill bit, diamond drill bits, diamond bit, diamond bits, diamond drilling bit, diamond core drill bit, diamond drilling bits, diamond drill bit

Reference : Mc Cray & Cole, Oil Well drilling Technology, New India Publication.

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