Boring or penetrating the earth – With above-ground means for handling drilling fluid or cutting – With tool shaft having plural passages for drilling fluid
Patent
1996-07-31
1998-07-14
Schoeppel, Roger J.
Boring or penetrating the earth
With above-ground means for handling drilling fluid or cutting
With tool shaft having plural passages for drilling fluid
175296, 175306, E21B 414
Patent
active
057789932
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved sample tube for a downhole hammer, and in particular to a means for mounting a sample tube in a reverse circulation downhole hammer.
Reverse circulation downhole hammers normally comprise a downhole hammer housing which has a drill bit attached at one end. It has a drill string connection point via a top sub at the other. A compressed air powered piston reciprocates back and forth within a housing and impacts against the drill bit. A central sample tube extends through the hammer housing from a sample delivery aperture that extends through the drill bit, and is connected at its upper end to the inner tube of a reverse circulation drill pipe. The sample delivery tube extends through a central bore within the piston.
The sample tube is fixed with respect to the downhole hammer housing, and therefore both the piston and the drill bit move with respect to this stationary tube. The lower end of the sample delivery tube is located within a central bore in the upper end of the drill bit. A bore or channel extends through the drill bit to allow drill chips from the cutting face to enter the sample tube. There is a sliding fit between the end of the sample tube and the drill bit to prevent blow-back from the lower piston chamber and to ensure that drilling debris does not enter the lower piston chamber.
The bore through the center of the piston is sufficiently large to provide a clearance with respect to the sample tube. Although there is no contact by the piston, the impact forces transmitted from the drill bit result in significant longitudinal and torsional loads being applied to the sample tube.
The sample tube is provided with a radial flange or projection intermediate its upper and lower ends. This flange or projection locates within recesses in an assembly which is fixed with respect to the downhole hammer housing. In most cases, the assembly comprises a compressed air distributor and a check valve guide. The two components abut against one another, and are held with respect to the downhole hammer housing by the top sub which screws into the end of the hammer body.
The compressed air distributor is provided with a recess or counterbore portion within which the radial flange locates. The upper surface of the flange is flush with the upper level of the compressed air distributor and when the valve guide body locates against this surface, the sample tube is held in place.
The radial flange and respective recess within the compressed air distributor are designed to secure the sample tube with respect to the downhole hammer housing. However, because of the forces transmitted along the sample tube as a result of the drill bit, wear can occur which allows the sample tube to rotate within its mounting assembly. The rotation itself causes further rapid wear, and as a result, compressed air can leak from the center of the compressed air distributed along the outside surface of the sample tube into the upper piston chamber. This will prevent the hammer from operating at full power, or at worst prevent its operation altogether.
Although the downhole hammer is a complex piece of equipment, its design nonetheless needs to be as simple as possible to ensure easy maintenance and assembly, while at the same time providing a robust design that can withstand the severe operating conditions.
Therefore, it is an aim of this invention to provide a means of preventing excessive wear of various components normally caused by rotation of the sample tube, and to provide a design which is simple yet effective.
In its broadest form, the invention is a sample tube for a reverse circulation downhole hammer comprising said percussive hammer comprises a hammer body having an upper and lower end, a percussive drill bit connected to said hammer body at said lower end, a piston that reciprocates within said hammer body and strikes said drill bit at one end thereof and a sample tube extending from said drill bit, through said piston towards the upper end of said hammer body, said sample tube comprising: ena
REFERENCES:
patent: 1636084 (1927-07-01), Thompson
patent: 2140417 (1938-12-01), Conklin
patent: 3207239 (1965-09-01), Hugel
patent: 3207240 (1965-09-01), Hugel
patent: 3420322 (1969-01-01), Mark
patent: 4296822 (1981-10-01), Ormsby
patent: 4739844 (1988-04-01), Farris et al.
patent: 4921052 (1990-05-01), Rear
Meller Michael N.
Schoeppel Roger J.
SDS Pacific PTE, Ltd.
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