Boring or penetrating the earth – Bit or bit element – Magnetized or with magnet
Patent
1984-05-10
1986-03-25
Novosad, Stephen J.
Boring or penetrating the earth
Bit or bit element
Magnetized or with magnet
175393, 175410, E21B 1000, E21B 1060, E21B 1046
Patent
active
045777063
DESCRIPTION:
BRIEF SUMMARY
The invention relates to rotary drill bits and in particular to bits which are used to drill holes in rock or subsurface formations for example to extract oil, gas or water or in mining or in the removal of cores.
A drill bit comprises a bit body with means for connection to a drill string, a leading bit face and a trailing gauge region. The face of the bit carries cutting elements such as polycrystalline diamond compacts which may be arranged in rows at the leading edges of wall portions known as "blades". The face of the bit may also carry so-called fences to control fluid flow and preferably has so-called kickers to centralise the bit in the hole. Fluid such as drill mud is passed down a central bore in the drill string and body and exits via passageways and openings into fluid channels between the blades and/or fences and kickers to flow past the cutting elements and up to junk slots between the kickers in the gauge region, carrying away cuttings and chippings and serving to cool the formation being drilled.
In known drill bits of this type, the passageways usually lead to openings located in the central region of the bit face, and there are usually many fluid channels which extend away from the centre of the bit. Sufficient fluid channels or waterways are required ot ensure that cuttings and heat are removed from the vicinities of all the cutting elements.
Typical designs have the cutting elements arranged in rows in the leading edges of blades, and have a fluid channel in front of each blade. Depending on the design, there may be 3 to 30 blades and the same number of fluid channels.
In certain rock formations, there is a tendency for the channels to become blocked by cuttings of rock formation, and blockage of one channel means that its associated cutting elements are not cooled and cleaned and the entire flow of fluid passes through the remaining channels. Although this will cause some increase in pressure at all the openings, this increase in pressure will not always be sufficient to unblock the blocked channel, so that the cutters associated with that channel will become overheated and/or clogged and so substantially ineffective. The clogging presents a barrier between the bottom of the hole and the cutting elements, preventing penetration or slowing the rate of penetration of the drill bit. This problem is particularly acute when the drill bit is used to drill certain types of claystone and shale using a water-based drilling fluid.
One solution to this problem is to isolate the fluid channels from each other and to feed each through one or more openings or nozzles of restricted area. The area of the nozzles is chosen so that the pressure difference between the common bore and the fluid channels is large enough to clear an accumulation of cuttings in the channel and prevent a blockage. Examples of bits having these features are illustrated in U.S. Pat. Nos. 2,371,489, 2,371,490, and 3,112,803 and in French Patent Specification No. 1,265,943. To provide enough cutting elements in a compact design, many blades may be required. Even if all the required cutting elements can be accommodated on three or four blades, the fluid channels diverge rapidly which means that fluid velocity falls off towards the edge. This can be corrected by the use of fences, but dead sectors are formed and they are uncooled in use of the bit. For these reasons, more than three or four blades are preferred. In the simple designs, there is one fluid channel in front of each blade and so the number of nozzles cannot be less than the number of blades. The presence of many openings or nozzles with adequate pressure drop requires each opening or nozzle to be small and there is a risk of some of the openings themselves becoming blocked.
It is one object of this invention to provide a drill bit body in which the number of openings is kept to the minimum without an undesirable decrease in the number of blades or fences, consistent with ensuring that there is a suitable fluid flow distribution for the purposes of cleaning and cooling.
REFERENCES:
patent: 3112803 (1963-12-01), Rowley
patent: 3215215 (1965-11-01), Kellner
patent: 3308896 (1967-03-01), Henderson
patent: 4098363 (1978-07-01), Roh et al.
Bagnell David J.
NL Petroleum Products Limited
Novosad Stephen J.
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