Note: Descriptions are shown in the official language in which they were submitted.
INTRO~U~TION
This invention relates to an improved casing shoe for use
on well casing or drill string.
BACKGROUND OF T~E INVENTION
Well casing is used to keep the drill hole free from debris
and, additionally, to prevent contamination of ground water
which may be present in an area which is passed through by the
drill bit and is not of interest. Well casing follows the
drill bit downwardly and it may be installed by impact or
torsional twisting. When casing is used which has no hardened
tip, it tends to collapse inwardly or "orange peel" as it
passes through the formation. To change the drill bit, the
drill must be withdrawn through the casing. If the casing has
collapsed, it is not possible to withdraw the bit without also
withdrawing the casing. This is costly and time consuming.
A further problem is presented with untreated well casing
in hard rock formations. Casing may not penetrate hard rock
formations without "under reaming. n That is, the drill must
drill a hole larger than the casîng diameter to allow easier
casing penetration. This is obviously ine~ficient if it can be
avoided.
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Some improvement in the longevity of well casing was
achieved by installing casing utilizing a hard facing. This
took various forms but one technique was to utilize a
pulverized carbide mix and bonding the mix to the bottom of the
casing by using a brass bonding agent. This improved the
ability of the casing to penetrate the formation being drilled
but the carbide layer could wear out quickly because it tended
to peel off in a layer and, of course, only a single layer
could be bonded on the bottom of the casing. Once the layer
was removed, the problems previously described reappeared as
with untreated casing~
RIEF SVMMARY OF THE INVENTION
According to one aspect of the invention, there is
disclosed a cylindrical casing shoe adapted for connection to
well casing or drill string, said shoe having a first surface
adapted to connect to said well casing or drill string, a
second surface opposed to said first surface, an inside
diameter, an outside diameter and a plurality of metallic
protuberances having cylindrical bases extending outwardly from
said second surface, said bases being mounted in complementary
recesses extending inwardly from said second surface between
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said inside and o~tside diameters.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
An embodiment of the invention will now be described, by
way of example on?y, with reference to the following drawings
in which:
Figure 1 is an exploded view of the casing and the casing
shoe of the present invention
Figure 2 is a view of the casing shoe in cutaway showin~
the shoe installed to the casing; and
Figure 3 is a view taken along the section III-III of
Figure 2.
DETAILED DESCRIPTION
Referring now to Figure 1, well casing 10 is cylindrical in
form and extends downwardly to the casing shoe shown generally
at 11.
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Casing shoe 11 is cylindrical with an outside diameter ~.D.
and an inside diameter I.D. It is manuactured by using steel
tubing or steel plate which is cut into proper size, Following
cutting, the steel is milled and is made in various sizes to
fit the well casing with which it is to be used. Depending on
the drilling conditions, the steel may or may not be
additionally hardened.
The casing shoe 11 is counter sunk at 12 to allow the
casing shoe 11 to be mounted on the well casing 10 by welding
at weld 13.
The lower surface of the casing shoe 11 is divided into two
areas 14,15. The first portion 14 of the lower surface is
substantially normal to the centre line 16 of the casing 10 and
shoe 11. The second portion 15 is bevelled and it extends from
the junction of the first portion 14, upwardly and outwardly to
the outside diameter 0.~. of the casing shoe 11.
Carbide buttons 17 are manufactured and have rounded tips
and cylindrical bases. Complementary cylindrical recesses 18
are drilled in the casing shoe 11.
As seen in Figures 2 and 3, the carbide buttons 17 are
mounted both in the irst and second portions 14,15
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respec~ively, of the lower surface. The recesses 18 for the
second portion lS of the lower surface are drilled such that
they extend normal to the surface. This is also so in respect
of the recesses drilled in the first portion 14 of the lower
surface but, as seen in Figure 3, the recesses 18 whlch are
shown mainly being within the first surface portion 14 also
extend over to the second portion 15. This creates no undue
problems and facilitates manufacture.
The carbide buttons 17 mounted within the second portion 15
are pressed into recesses 18 such that their rounded tips
extend slightly beyond the outside diameter of the casing shoe
11. They may also be installed using an epoxy adhesive.
OPERATIO~
In operation, the correct size casing shoe 11 will be
selected for the particular casing with which it is decided to
use for the well being drilled. The shoe 11 is mounted on the
well casing 10 by fitting the shoe 11 over the end of the first
piece of well cas~ng and welding the shoe 11 to the casing 10
as at weld 13.
Thereafter, drilling and the insertion of subsequent pieces
of well casing continues until the operating depth of the well
is reached whereupon the shoe is simply left in place at the
bottom of the well on the casing.
Many modifications can be made to the specific embodiment
of the invention just described. ~he casing shoe could also be
attached to the well casing at other locations than on the
bottom. For example r a casing shoe could be attached on the
outside of the well casing with ~he carbide buttons facing
upwardly. This would be useful if it was desired to remove the
well casing when necessary such as if the well was a dry hole.
The shoe would be installed by simply welding the first surface
to the outside of the casing.
To like effect, the shoe could be used directly on drill
string for drilling in some formations. Thus, a first shoe
could be installed on the lowermost piece of drill string and,
if desiredr a second shoe could be installed upwardly therefrom
with the carbide buttons facing upwardly so as to aid when
removing the drill string from the hole.
Yet a further modification could be made in the placement
of the carbide buttons. A second bevelled edge could be formed
on the inside of the casing shoe. Thus, one set of carbide
buttons would face inwardly. This would be useful when the
shoe was used for drilling or when enlarging the hole diameter.
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The carbide buttons 17 may be ground or they may be utility
grade. Since the tolerances can be maintained more accurately
with ground buttons, they are preferable for heavy duty
application or in an application where it is desirable to
minimize replacing a casing shoe during drilling operations.
It is also possible to case harden the steel of the casing
shoe 11. This case hardening may be desirable for particularly
hard formations or where drilling conditions subsequently
dict~te the use of a harder casing shoe.
The carbide buttons 17 may be additionally reinforced when
being pressed into recesses 18. They can be inserted with an
epoxy solution which helps to keep the buttons within their
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comp~lementary recesses. One such~solution is known as LOC-TITE~.
The outside diameter O.D. of the casing shoe may also be
bevelled inwardly from the lower surface to the ~pper surface.
This taper allows the casing shoe to be withdrawn from the well
hole more easily.
Accordingly, there has been described a casing shoe for use
on drill string or well casing. Many modifications can be made
additional to those described above which will still fall
within the scope of the invention. The invention should,
therefore, be construed by the scope of the accompanying claims.
