Boring or penetrating the earth – With below-ground tool drive prime mover – Below-ground storage of motivating energy
Reexamination Certificate
2002-05-31
2004-03-09
Schoeppel, Roger (Department: 3672)
Boring or penetrating the earth
With below-ground tool drive prime mover
Below-ground storage of motivating energy
C175S296000, C175S100000, C175S415000, C175S402000, C175S417000, C175S171000, C175S189000, C173S017000, C173S135000
Reexamination Certificate
active
06702045
ABSTRACT:
This invention has particular application to a reverse circulation down hole face sampling hammer, and for illustrative purposes reference will be made to this application. However, it is envisaged that this invention may find application in other forms of drilling apparatus such as blasthole hammers, tricone RC drills and crossover sub RC hammers.
In the operation of sampling hammers it is understood that sampling integrity is improved if the hammer exhaust air used to flush cuttings is directed towards the cutting face of the bit. By this means chips are entrained at the point of their production. In Australian Patent Numbers 638571 and 656724, there are disclosed face sampling reverse circulation downhole hammers including a shroud or sleeve that extends beyond the lower end of the chuck or drive sub to surround the head of the bit, which is relieved to accommodate the sleeve or shroud.
The shroud or sleeve cooperates with air passages down the side of the bit head to direct air toward the cutting face of the bit. Air exhausted from the hammer free-piston motor passes down the splines that engage the bit for rotation and reciprocation in the chuck or drive sub. Air exits the lower end of the shroud or sleeve throught the air passages in the side of the bit head, to pass substantially to and across the cutting face of the bit.
Chippings are entrained in the air stream and conducted to the surface through sample apertures in the bit cutting face communicating with a sample recovery conduit comprising an axial passage defined through the hammer to the inner tube of a dual wall drill string.
The shroud or sleeve is selected to be of substantially the same diameter as the gauge row of carbides of the bit head, and of greater diameter than the hammer casing, in order to provide a partial seal between the borehole and the hammer to constrain air to the cutting face of the bit and to thus substantially reduce both blowby of exhaust air and contamination of the sample from above.
The prior art hammers described above rely on the bit head itself to provide one wall of the conduits or passages conveying air towards the cutting face of the bit. The bit must necessarily run at a clearance from the sleeve, and the bit head necessarily oscillates relative to the sleeve. As a result of this, combined with the fact that the shroud or sleeve must stop well short of the cutting face to allow sufficient bit head metal to remain to support the gauge row, the air exiting the passages is not fully directed downward towards the cutting face through the grooves in the bit head exclusively. The exiting air also describes an outwardly expanding path from the passages, to be constrained by the borehole and turned across the cutting face of the bit. In tests it has been determined that the divergence from the vertical direction of the air flow is between 30 to 40° included angle.
The present applicant is the developer of an alternative RC hammer. In this embodiment, an extended lower bearing surface on the bit shank cooperates with a bore in the lower end of the drive sub. The bore is relieved with four lenticular section cut-outs to provide for egress of exhaust air, the cut-outs being indexed to respective grooves down the side of the bit head. The bit head is shortened to bring the egress point closer to the face of the bit. This embodiment may be termed a sleeved sub/short bit head type. Again, the bearing surface oscillates relative to the bore and the cut-outs well short of the cutting face to allow sufficient bit head metal to remain to support the gauge row. Accordingly, the air exiting the passages is not fully directed downward towards the cutting face through the grooves in the bit head exclusively. The exiting air also describes an outwardly expanding path from the passages, to be constrained by the borehole and turned across the cutting face of the bit. Yet further, the cut-out positions are necessarily closer to the axis than the shrouded bit head passages described in Australian Patent Numbers 638571 and 656724. Accordingly, the bit head passages in the present applicant's prior art hammer must direct the air outward of the axis to a degree, thus exacerbating the outward component of direction of the expanding exhaust air. In fact, in tests it has been determined that the divergence of a component of the air flow is close to 180° included angle in this embodiment, or at right angles to the drilling direction. This observation is borne out in practice, where this apparatus performs less effectively in soft or broken ground than the commercial embodiment of Australian Patent Number 638571 in that the walls of the borehole are eroded by the divergent component.
At least part of this tendency arises since the air is directed between the shank of the drill bit and the minor bore of the drive sub. Thus there is a major change in diameter requiring an outward component of direction of air flow. Typically, the section changes from about 88 mm at the shank to 140 mm at the bit head.
In soft ground, the turbulence and expansion of air exhausted from prior art hammers tends to scour the borehole such that the hole is significantly larger than the gauge sleeve. This in turn causes loss of seal resulting in loss of sample up the borehole. As air velocity up the sample recovery conduit is lost through blowing by the seal, there is an increased tendency of the conduit to block, particularly at the sample return holes in the drill bit.
In one aspect the present invention relates to drilling apparatus including:
a chuck;
a drill bit supported in said chuck and having a bit head extending below said chuck, said bit head having at least one substantially longitudinal air channel defined down the outside of the bit and extending through the cutting face thereof;
a gauge sleeve secured in relation to said chuck; and
at least one air passage defined between said gauge sleeve and said chuck having a terminal portion extending substantially parallel to the axis of the drill bit and substantially in register with said air channel.
The drilling apparatus may be selected from any suitable apparatus commonly used for reverse circulation drilling. For example the drilling apparatus may comprise a tricone reverse circualtion arrangement or a down-the-hole (DTH) hammer. It is envisaged that this invention will find its best application in respect of face sampling DTH hammers and for illustrative purposes the invention will be further described with reference to this application. Further the invention will be described with reference to those hammers of the type having a pair of sample recovery ports through the cutting face of the bit communicating with respective ones of a pair of siamesed sample ducts, whereby chips and exhaust air are conveyed to a sample recovery path extending up through the hammer to the inner tube of the drill string and thence to the surface.
The chuck may be of any suitable form. For example, the chuck may comprise the type associated in the DTH hammer art as a drive sub, or alternatively may comprise the variant known as a SAMPLEX chuck. The chuck may be secured to the hammer casing by any suitable means. Typically the chuck or drive sub is threadably engaged with the hammer casing.
The chuck or drive sub may mount the drill bit in any known manner in the art. Typically the drill bit comprises a splined shank portion which is adapted to mounted in sliding relation to a correspondingly splined portion of the chuck or drive sub. Alternatively, the drill bit and drive sub may be engaged with drive pins and cooperating slots or any other suitable means.
The gauge sleeve may be secured in relation to the chuck by any suitable means. For example, the gauge sleeve may be secured to the chuck or hammer casing by threads. However it is preferred that the gauge sleeve be retained by means of an annular flange whereby the chuck in engaging the hammer casing thereby secured the gauge sleeve in position. If desired the gauge sleeve may be further located against rotation by the provision of keys or
Azuko Party Ltd
Fulbright & Jaworski L.L.P.
Schoeppel Roger
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