Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This is a division of Canadian application 360,814
filed September 23, 1980.
The present invention relates to an apparatus for
drilling underground inverted arcuate paths and installing
production casings, conduits, or flow pipes therein.
Techniques have recently been developed for installing
production casings, conduit, or flow pipes beneath rivers and
other surface obstacles without dredging the riverbed, digging a
trench, or otherwise altering the obstacle. See, e.g. United
States Patent No. 3,878,903. Instead a pilot hole is first
drilled from a position at or near the surface on one side of
the obstacle to a position at or near ground level on the other
side. As the pilot hole is being drilled a washover pipe of
inside diameter larger than the outside diameter of the drill
string is advanced behind the leading end of the drill string and ~;
surrounding it. See United States Patent No. 4,003,440. Reaming
apparatus is then pushed or drawn through the pilot hole to en-
large the hole to a larger diameter. The production casing is
thrust into the hole immediately behind the reaming appara-tus and
follows it along the drilling path. See United States Patents
Nos. 3,894,402; 4,043,136 and 4,091,631.
Prior methods of drilling the pilot hole have utilized
sections of drill string which are of uniform external diameter.
When joined together such sections produce a drill string of
unifoxm external diameter having no external protrusions at the
joints between the sections or elsewhere along the string. Such
joints are relatively weak, and the entire drill string tends to
frequently stick during the drilling of the pilot hole.
Existing methods of advancing the w-ashover pipe around
the drill string, such as that disclosed in United States Patent
No. 4,003,440, provide the leading end of the washover pipe with
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a cutting edge which enlarges the pilot hole to a diameter equal
to that of the washover pipe. Since no provision is made for
supplying drilling mud to the leading end of the advancing
washover pipe to entrain the cuttings dislodged by the cutting
edge, the cuttings accumulate at the leading end of the washover
pipe and inhibit its advance.
Prior methods of reaming the pilot hole and installing
the production casing have used a single reamer and required that
powered means be provided to thrust the production casing into the
hole. Prior attempts to draw the reaming apparatus or production
casing through the hole with, or example, the drill string used
in drilling the pilot hole, have resulted in the drill string
knifing through the soil and the reaming apparatus or production
casing not following the original drilling path. In -these methods
it is also necessary to frequently interrupt the installation pro-
cess in order to join additional sec-tions of the production casing
to the trailing end of the casing.
The present invention provides for an apparatus for
drilling along an underground inverted path comprising: a
directional drill including an in-hole motor; a trailing drill
string of non-uniform external diameter attached to said direction-
al drill, the largest external diameter of said drill string
being lessthan the diameter of the hole produced by said direction-
al drill, said in-hole motor including a rotor and a stator, said
drill including a bit connected to said rotor, one end of said
drill string being connected to said stator, said drill string
including a plurality of integral extexnal concentric collars
disposed at intervals along said drill string, the diameter of
each of said collars being less than the diameter of the hole
produced by said directional drill, said collars comprising ex-
ternal upsets at the ends of the joints making up said trailingdrill string, a drill rig providing means at the other end of
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said drill string for crowding said drill string into said hole
and for azimuthally positioning said drill string in the hole,
washover pipe connected at one end to said drill rig and dis-
posed about said drill string and extending from said o~ne~end of
the drill string toward but separated from said one end of the
drill string, leaving an exposed portion of the drill string
without said washover pipe and forming with the covered portion
of the drill string therewithin an inner annulus, cutting means
connected to the other end of said washover pipe, said drill rig
providing means to rotate said washover pipe around said drill
string and advance the washover pipe along said path, said wash-
over pipe having an outer diameter larger than said drill bit but
smaller than said cutting means whereby to form an outer annulus
for drilling mud returns around the washover pipe as it is advanc-
ed along said path, said drill rig providing means to deliver
drilling mud to said drill string and said inner annulus, fresh
drilling mud from the drill rig flowing in said inner annulus
forwardly past said collars toward said cutting means providing
lubricant between said collars of said covered portion of the
drill string and said washover pipe splindled on the drill string
and rotating about said collars, detritus laden drilling
mud flowing backwards along the path back from the drill bit along
the exterior of the exposed portion of the drill string past said
collars which h.elp size the hole drilled by said bit along said
path by directing the detritus ou-twardly from the drill strinq,
said collars -tending to prevent the exposed por-tion of said drill
string from sticking when it is moved axially along said path
without continuous rotation in the ~bore) hole.
The present invention provides an apparatus and relates
to a method for installing production casings, conduits, flow
pipes and the like underneath and spanning an obstacle such as a
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river. As in existing methods, a directional drill attached to
a drill string is advanced in an inverted arcuate path to form
a pilot hole underneath the obstacle. A larger concentric
washover pipe follows the advance of the drill at some distance
behind the drill to form a concentric annulus about the drill
string and enlarge the pilot hole.
The preferred drill string of the present invention is
made up of sections having external upsets at each end, making
each drill string section of slightly larger external diameter
at each end than in the middle. When these sections are joined
together a drill string is produced with integral concentric
collars formed by the upsets at each joint between the sections.
This produces a stronger connection at each joint and during
the drilling of the pilot hole the collars help size the hole
and prevent the drill string from sticking in the hole as
frequently as in prior methods.
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The leading end of the washover pipe is provided with
cutting blades which enlarge the pilot hole to a diameter greater
than that of the washover pipe. This produces an annulus between .
the enlarged pilot hole and the washover pipe. During the advance
of the washover pipe drilling mud is supplied through the inner
annulus between the washover pipe and the drill string to entrain
the cuttings dislodged by the cutting blades and return them
through the outer annulus between the enlarged pilot hole and the
washover pipe. This prevents the cuttings from accumulating with- :
in the washover pipe at its leading end and inhibi-ting its advance.
When both the drill string and the washover pipe reach
the surface on the other side of the obstacle, a first reamer,
preferably a flycutter reamer, of larger diameter than the pro-
duction casing is attached to the end of the washover pipe where
it exits the drilling path; a second reamer, preferably a float-
ing reamer, having a relatively smaller leading end and a larger
-trailing end of smaller diameter than the first reamer and larger
diameter than the casing is attached to the other end of the fly-
cutter reamer by means, such as a section of washover pipe,
providing for some separation between the two reamers; and the
production casing is attached to the other end of the second :
reamer with a s~ivel. The end of the casing attached to the
swivel is closed to prevent the entry of mud and cuttings during
the reaming and installation operation. Preferably the casing
joints have been previously welded together into a casing
portion and the joints inspected and coated for corrosion
resistance, so that the casing is in only one, or no more than
a few, portions. This allows the casing to be installed in an
almost continuous movement. The portions of the product.~on
casing may be supported in line with the pilo-t hole some distance
above the ground on rollers placed beyond the exit point oE the
pilot hole.
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During the reaming of the pilot hole and installation of
the production casing the exit point of the pilot striny may be-
come the entry point of the reaming apparatus and production cas-
ing. The reaming apparatus is rotated, and drawn through the
pilot hole, typically by the washover pipe, followed by the non-
rotating production casing. As in existing methods, drilling mud
is provided to exit at the first reamer and entrain the cuttings.
Unlike existing methods, two reamers are used and drilling mud
may additionally exit at the second real~er.
The mud supply system of the present method is capable
of supplying much more mud at a higher pressure than the supply
systems of existing methods. This provides lubrication for the
passage of the production casing and permits the reamers and
production casing to be drawn through the hole without having the
washover pipe knife into the soil and cause the reamers and pro-
duction casing to leave the original drilling path.
As the reaming apparatus is drawn through the pilot
hole the first reamer enlarges the hole to a diameter greater
than that of a second reamer and the cuttings dislodged by the
first reamer are entrained in the drilling mud. The separation
provided between the first reamer and the second reamer which
follows it permits the cuttings to separate within the drilling
mud and produces a more accurate hole than other methods.
The smaller diameter second reamer forces the drilling .
mud and entrained cuttings into the annulus betw-een itself and
the sides of the enlarged hole to form a concentric ring of mud
and cuttings around the interior of the enlarged hole while
leaving a concentric opening within this ring for passage of the
production casing~ The ring of drilling mud and entrained cut-
tings acts as a bushing in the concentric annulus between the
production casing and the hole to lubricate the advance of the
even smaller diameter production casing. Since the leading end
of the casing is closed, the mud and cuttings do not enter the
casing.
As the non-rotating production casing is drawn along
the drilling path behind the rotating reaming apparatus, the
remaining length of the first portion of the production casing
outside of the hole is drawn along the rollers supporting it
towards thepoint where the casing enters the hole. That part of
the casing which is between rollers advances towards the hole
horizontally, and that part of the casing which is between the
rollers nearest the hole and the entry point of the hole bends
due to gravity towards the entry point, advancing at a downward
angle and entering the hole. The ~eight of this downward-angled
part of the casing helps crowd the casing into the hole and
reduces the force required to draw the reaming apparatus and
following casing through the hole.
Using the weight of part of the production casing to
crowd the casing into the hole eliminates the need for powered
means to thrust the casing into the hole behind the reamer as in
2Q existing methods. Furthermore, since the advancing casing is
permitted to bend from its horizontal path along the rollers to
its angle of entry into the hole over the entire distance from
the rollers nearest the entry point to the entry point itself,
the shear stress on the casing and the risk of casing failure are
much less than they are ~hen the casing is placed on the ground
immediately in front of the hole and must bend into the hole over
a relatively short distance.
This method also permits joints of the production cas-
ing to be joined together into longer portions prior to the begin-
ning of the reaming and casing installation process. Thiseliminates the need in existing methods to frequently interrupt
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the installation of the casing in order to join additional joints
to the trailing end of the casing extending out of the entry
point.
In an alternative aspect of the method, the reaming
operation may be performed without the production casing attached
to the reaming apparatus, followed by a second reaming operation
with the production casing attached in order to complete the
installation. In this embodiment, in the first reaming operation
washover pipe is attached to the trailing end of the second
reamer to provide a means for drawing the reaming apparatus and
production casing through the enlarged hole in the second reaming
operation. In the second reaming operation the production casing
is attached to the trailing end of the second reamer as before
and the reaming and installation process proceeds as described
above.
In drawings which illustrate embodiments of the
invention and the method to which it relates:
Figure 1 is a cross-sectional elevation view lllustrat-
ing the operation of the present method in drilling a pilot hole
along an underground inverted arcuate path under an obstacle; ~ ;
Figure lA is an enlarged elevation view of a portion of
the drill string illustrated in Figure l;
Figure 2 is an elevation view of the leading end of the
drilling apparatus illustrated in Figure l;
Figure 2A is a schematic view illustrating one method of
advancing the drill string into the hole during the drilling of
the pilot hole;
Figure 2B is a schematic view illustrating one method
of advancing the washover pipe into the hole during the drilling
of the pilot hole;
Figure 3 is a cross-sectional elevation view illustrat-
ing the operation of the present method in reaming the pilot hole
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and installing a:production casing along the reamed hole;
Figure 4 is an elevation view of the leading end of
the reaming apparatus and production casing illustrated in
Figure 3;
Figure 5 is a front view of the leading end of the
leading reamer illustrated in Figures 3 and 4; and
Figure 6 is a cross-sectional elevation view illustrat- - :.
ing an alternate aspect of the present method in which the reaming
operation proceeds without installing the production casing.
The first operation of the present method is illustrat-
ed generally in Figure 1. In the situation depicted in Figure 1,
it is desired to traverse a w-ater course 10, drilling from a
first position 12 on the surface of the ground at one side of the
water course to a second position 14 beyond a structure 16 at the
other side. The desired path is illustrated generally by dashed
line 18, and can comprise either a constant radius arc or a path
of complex curvature. A pilot hole is drilled along path 18 by a
directional drill 20 powered hy mud pumped through a trailing
drill string 22 which extends through the drilled hole and exits
at position 12. Directions drill 20 can be controlled according
to the principles set forth in United States Patent No. 3,878,903
for "Apparatus and Process for Drilling Underground Arcuate Paths." ;~
Other directional drilling techniques could be used as well.
Washover pipe 24 extends from a position substantially
behind directional drill 20 to the entrance 12 to the drilled
hole. Washover pipe 24 is of larger diameter than drill string
22 so that the washover pipe ~ill fit circumferentially around
the drill string ~ithin the hole. Washover pipe 24 is typically
made of ordinary 5" or larger diameter drill pipe. During the
drilling along arcuate path 18, a survey tool, oE a type well
known in the art, is periodically inserted within drill string
22 to a position
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immediately behind-directional drill 20 to determine the current
position of the directional drill. This survey tool utilizes
magnetic compasses to obtain such readings, and it is necessary
for washover pipe 24 to trail directional drill 20 at a sufficient
distance, typically at least 100 feet, so that it will not inter-
fexe with the operation of the survey tool, usually by drilling
the pilot hole for some distance before beginning to insert the washover
pape. Typically washover pipe 24 is not advanced until drill
string 22 begins to stick in the hole. Drill string 22 is advanced
a desired distance, or until it begins to stick, the advance of
drill string 22 is halted while washover pipe 24 is advanced
around drill string 22, the leading end of washover pipe 24
remaining some distance behind the leading end of drill string 22
at all times, then the advance of washovçr pipe 24 is halted
while drill string 22 is again advanced until it begins to stick.
At the entrance position 12 of the drilled hole into
the ground, an inclined drill rig 26 is positioned in a slanted
hole 28. The forward surface 30 of hole 28 is normal to the
initial direction of the path into the ground for ease in drill-
ing the hole.
A portion of drill string 22 is illustrated in more de-
tail in Fig. lA. Each section, such as that numbered 31, of
drill string 22 has an upset 37 at each end, making each drill
string section of slightly larger, e.g. about 3/~", external
diameter at each end than in the middle. When these sections are
joined together drill string 22 is produced with an integral con-
centric collar 35 at each joint 33 between the sections. This
produces a stronger connection at each joint 33 and d~ring the
drilling of the pilot hole collars 35 help size the hQle and pre
vent drill string 22 from stick~ng as freguently.
The leading end of the drilling apparatus illustrated
in Fig. 1 is shown in more detail in Fig. 2. Directional drill
20 has a leading drill bit 40 powered by drilling mud supplied
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through drill string 22. As drill bit 40 dislodges the earth
along the desired arcuate path, these cuttings are entrained in
the drilling mud which flows backwardly in the small annular
space 42 surrounding dril~ string 22 and into and through annulus
46 between drill string 22 and washover pipe 24.
The leading end of washover pipe 24 is/~ e~ h
c~tting blades 45 which enlarge the pilot hole to a di-ameter
greater than that of the washover pipe. For example, if washover
pipe 24 is of 5" diameter, cutting blades 45 may enlarge the
pilot hole to a 7 1/2" diameter. This produces outer annulus 49
between the enlarged pilot hole and washover pipe 24. During the
advance of washover pipe 24 drilling mud is supplied through
inner annulus 46 between drill string 22 and washover pipe 24 as
shown by arrows 48. The drilling mud entrains the cuttings
dislodged by cutting blades 45 and returns them through outer
annulus 49 as shown by arrow 50. This prevents the cuttings from
accumulating at the leading end of washover pipe 24 and inhibiting
its advance.
Fig. 2A illustrates in more detail one method of ad-
vancing drill string 22. The trailing end of drill string 22 is
attached to a chuck on drill rig 26. (One embodiment of a suit-
able drill rig 26 is described in U.S. Patents No. 4,051,911 and
4,078,617.) Drill rig 26 is advanced down ramp 52 as shown by
ar-row 55 to crowd drill string 22 into the hole. Drilling mud is
pumped through conduit 53, through drill rig 26, and down throu~h
drill string 22 as shown by arrow 54. When drill rig 26 reaches
lower end 56 of ramp 52, drill rig 26 is drawn back up ramp 52 to
the position shown in Fig. 2A. Drill rig 26 is now r~ady for the
attachment of another section of drill string to the ~railing end
of drill string 22 to again adv~nce the drill string or for the
attachment of another section of washover pipe to the trailing
end of washover pipe 24 to advance the washover pipe.
Fig. 2B illustrates in more detail one method of ad-
vancing washover pipe 24. The trailing end of washover pipe 24
is attached to a chuck on drill rig 26. Drill rig 26 is advanced
down ramp 52 as shown by arrow 55 to crowd washover pipe 24 into
the hole. Drilling mud is pumped through conduit 53, through
drill rig 26, and down through washover pipe 24 as shown by arrow
57. W~en drill rig 26 reaches lower end 56 of ramp 5~, drill rig
2~ is drawn back up ramp 52 to the position shown in Fig. 2B.
Drill rig 26 is now ready for the attachment of another section
of washover pipe to the trailing end of washover pipe ~4 to again
advance the washover pipe or for the attachment of another section
of drill string to the trailing end of drill string 22 to advance
the drill string.
Referring again to Fig. 1, when drill string 22 reaches
the surface on the other side of water course 10 at point 14,
washover pipe 24 is advanced to also exit at point 14. Drill
string 22 is withdrawn from the pilot hole, leaving the washover
pipe occupying the entire pilot hole from point 12 to point 14.
To prepare for the reaming and installation operation,
as is shown by Fig. 3, first reamer 60 is attached
to washover pipe 24 where the latter extends out the pilot hole
at point 14. Second reamer 66 is attached to the other end of
first reamer 60 by a section of washover pipe 64 to provide for
some separation between the reamers. Preferably the reamers
should be separated a distance of 5 to 15 times the diameter of
the reamed hole. For a 36 inch hole, a separation of 30 feet
proYides good results. Production casing (or conduit or flow
pipe) 70 is attached to the other end of second reame~ 66 by a
swivel 68 to prevent rotation of casing 70 during th~ reaming and
the installation operation. The leading end 69 of casing 70 is
closed to prevent the entry of mud and cuttings during the reaming
and installation operation. Since the hole sometimes contains
water or mud, casing 70 may be weighted to neutralize its buoyancy
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so that it floats into the hole, facilitating its installation
and minimizing any damage to the casing, as described in U. S.
Patent No. 3,894,402.
The remaining length of the first portion o~ production
casing 70 is supported in line with the pilot hole some distance
above the ground on rollers 80 and 81 located beyond pilot hole
e~it point 14. Two rollers are shown, but more may be provided.
The first portion of production casing 70 consists of a plurality
of casing joints, such as those numbered 83, joined end to end.
The first portion of production casing 70 may constitute the
entire length of casing to be installed but this may be unwieldy.
Hence, it may desirable to provide one or more additional portions
of production casing, such as casing portion 82. Casing poxtion
82 is joined to the trailing end of casing portion 70 after most
of casing portion 70 has been installed along reaming path 61.
If necessary, additional portions of production casing like
casing portion 82 may be fabricated.
The reaming apparatus is shown in more detail in Fi~ures
4 and 5. As should be evident from Fig. 4, first reamer 60 is of
a larger diameter than second reamer 66. As shown in Fig. 5,
first reamer 60 has a plurality of reaming teeth 62, as well as a
plurality of ports 72 through which drilling mud exits to entrain
the cuttings dislodged by the reamer. Typically first reamer 60
is a flycutter reamer of relatively small-l~ngth having longitudinal
openings/ a's shown in Fig. 5, through which the drilling mud and
entrained cuttings may pass into the enlarged hole. As shown in
Fig. 4I second reamer 66 has a ~ ll~r, typically, leading end pro-
vided with reaming teeth 78. Ports 89 are optional a~d, when
provided, provide further exits for drilling mud in ~ddition to
ports 72 in first reamer 60. Typically second reamer 66 is a
floating reamer of substantially neutral buoyancy in drilling mud
weighing approximately 10 pounds per gallon so as to float through
the enlarged holeO ~he trailiny end of second reamer 66 is typically
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cylindrical and of smaller diameter than first reamer 60 and of
larger diameter than production casing 70. For example, first
reamer 60 may be of 36" diameter, second reamer 66 of 30" diameter,
and production casing 70 of 24" diameter.
The reaming and production casing installation opera-
tion proceeds generally as is shown in Fig. 3. Washo~er pipe 24
is rotated and drawn through the pilot hole in the direction of
arrow 75 by drill rig 26. Reamers 60 and 66 are rotated and
drawn along reaming path 61 by the rotating washover pipe.
Swivel 68 draws production casing 70 along behind second reamer
66 and prevents casing 70 from rotating with the reamers so that
the casing is not subjected to the torsional stress which would
be caused by rotation. Drilling mud is provided to flow from
drill rig 26 through washover pipe 24 and exit a-t first reamer
60, and, optionally, at second reamer 66.
Sufficient drilling mud must be provided at the reamers
to lubricate the advance o production casing 70. If there is
too little lubrication, the force which must be exerted on washover
pipe 24 in order to draw the reaming apparatus and production
casing 70 along drilling path 61 will be so large that washov~r
pipe 24 will knife into the soil and cause the reaming apparatus
and production casing 70 to leave drilli~g path 61. For example,
it has been found that the use of a pump supplying 15 barrels of
drilling mud a minute to the reamers at a pressure o 900 - 1100
PSI provides sufficient lubrication to install a 24" production
casing.
Typically, the reaming apparatus and production casing
are attached to the end of the washover pipe at point 14, but it ~¦
should be understood that these may be attached to the end of the
washover pipe at point 12, in which case the reaming and instal-
lation operation would proceed in the direction opposite the one
illustrated in Figure 3. This would, o course, require that
drill ris 26, or one like i~, be provided a~ point 1~, rather
than at point 12, as illustrated in Figure 3.
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The reaming and production casing installation opera- ¦
tion is illustrated in more detail by Fig. 4. As the apparatus
is rotated and drawn along drilling path 61 in the direction of
arrow 75 by washover pipe 24, reaming teeth 62 of first reamer 60
enlarge pilot hole 77 to a diameter greater than that of production
casing 70. Drilling mud 74 pumped through washover pipe 24 in
the direction of arrow 76 exits through ports 72 in first reamer
6~ (shown in Fig, 5) to entrain the cuttings dislodged by reaming
teeth 6~. The separation provided between first reamer 60 and
second reamer 66 by the section of washover pipe 64 permits the
cuttings to separate within the drilling mud in space 65 and
produces a more accurate hole. Reaming teeth 78 on second reamer
66 further break up and separate the cuttings. Optionally an
open passage may be provided through hub.67 of first reamer 60
such that some of the drilling mud 74 continues through hub 67
and section of washover pipe 64 to exit at optional ports 89 in
second reamer 66. Second reamer 66, of a smaller diameter than
first reamer 60 and a larger diameter than production casing 70,
forces the drilling mud and entrained cuttings into annulus 71.
The mud and cuttings form a concentric ring 63 around the interior
of the enlarged hole while leaving a concentric opening 79 within
this ring for passage of the even smaller diameter production
casing. Production casing 70, of a smaller diameter than reamers
60 and 66, is drawn into the enlarged hole behind second reamer
66 by swivel 68. Swivel 68 prevents production casing 70 from
rotating. The ring 63 of mud and cuttings acts as a bushing in
the concentric annulus 73 between production casing 70 and the
sides of the enlarged hole to lubricate the advance of production
casing 70. Since leading end 69 of casing 70 is closed, the mud
and cuttings do not enter ~he casing.
Referring again to Figure 3, as non-rotating production
casing 70 is drawn along drilling path 61 behind second reamer
66, the length of ~he first portion of production casing 70 which
is outside the hole is drawn along rollers 80 and 81 towards
point 14 where the casing enters the hole. The distance between
rollers 80 and 81 depends on the strength and characteristics of
the production casing. The distance must be short enough that
the unsupported part of the production casing 86 which is between
rollers 80 and 81 is not subjected to such stress due-to its own
wèight that there is a risk of casing failure. That part of the
casing 86 which is between rollers 80 and 81 advances horizontally,
and that part of the casing 88 which is between rollers 81 and
point 14 bends towards point 14, advancing at a downward angle
and entering the hole at point 14. The weight of the downward-
angled part of the casing 88 which is between rollers 81 and
point 14 helps crowd casing 70 into the hole and reduces the
force required to draw the casing along reaming path 61. Ad-
vancement of casing 70 is further aided by the weight of that
part of the casing 90 which is within the hole along the down-
ward-angled portion of reaming path 61.
Using the weight of part of the casing to crowd the
casing into hole eliminates the need for powered means to thrust
casing 70 into the hole behind the reaming appratus as in existing
methods. Furthermore, since casing 70 bends from its horizontal
path along rollers 80 and 81 down to ~oint 14 along the entire
length of part 88 of the casing between rollers 81 and point 14,
the shear stress on the casing and risk of casing failure are
much less than when casing 70 is placed on the ground immediately
in ront of point 14 and must bend into the hole over a relatively
short distance.
When most of the first portion of production casing 70
has been drawn into the hole, the trailing end of casing portion
70 is lifted off of rollers 80 and 81 and onto the ground, casing
portion 82 is joined to the trailing end of casing portion 70,
the casing is lifted back onto the rollers, and the reaming and
installation process continues. Since casing portions 70 and 82
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consist of many casing sections, such as those numbered 83, it is
unnecessary to frequently interrupt the installation operation in
order to join additional casing sections to the trailing end of
the casing extending out of the hole. '
In an alternative aspect of the method the reaming op-
eration may be performed without production casing 70 attached to .
second reamer 66, followed by a second reaming operation with the
production casing attached in order to complete the installation.
In the first reaming operation, illustrated by Figure 6, a section
of washover pipe 93 is attached to the trailing end of secondreamer 66. As the reaming apparatus and trailing washover pipe
is drawn along reaming path 61 additional sections of washover
pipe, such as section 94 are joined to the trailing end of wash-
over pipe section 93 to form washover pipe string 92. Sections
of the leading washover pipe 24 are removed as they exit the hole
at point 12. When the reaming operation is completed and the
reaming apparatus reaches point 12, the reaming apparatus is
disconnected from washover pipe string 92, transported aboveground
to point 14, and attached to the end of washover pipe string 92
where it exits the enlarged hole at point 14. Swivel 68 and
production casing 70 are attached to second reamer 66 as described
above and shown in Figure 3. Washover pipe string 92 functions .-
as washover pipe 24 for purposes of the second rearning operation,
which. includes installation of the production casing and proceeds
as described above and illustrated in Figures 3 and 4.
It is also possible to use washover pipe string 92 to
draw the reaming apparatus back through the enlarged hole from
point 12 to point 14 after the-initial reaming operation is com-
pleted rather than transporting the reaming apparatus aboveground
to point 14. As the reaming apparatus is being drawn back through
the enlarged hole, the sections of w-ashover pipe 24 which were
removed at point 12 during the reaming operation are reattached
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to the now trailing end of washover pipe 24 at point 12, again
providing a washover pipe 24 extending from point 12 to poin-t 14
in enlarged hole 95. Sections of washover pipe string 92 are
removed as they exit at point 14 and, when the reaming apparatus
reaches point 14, washover pipe section 93 is removed. Swivel 68
and production casing 70 are attached to second reamer 66 and a
second reaming operation including installation of the production
casing proceeds as described above and illustrated in Figures 3
and 4.
Although the foregoing description assumes that drilling
mud used in these operations will flow back through the drilled
hole to the entrance of the hole, carrying cuttings with it, in
many types of formations little or no returns will be obtained.
In very porous or uncompacted formations the cuttings and a major
portion of the drilling mud may be forced into the surrounding
formation, building up a tubular bushing around the drill pipe,
washover pipe, reamer or casing, as the case may be. In the
method in which the hole is first reamed without the casing,
followed by a second reaming and pulling the casing through, such
a bushing may be formed by the first reaming operation, thereby
facilitating the passage of the reamer and casing on -the second
reaming operations. The lubricity of the drilling mud being
pumped through in the second reaming operation will greatly im-
prove the ability to pull the casing through this tubular bushing.
The presence of the bushing will help to seal the walls of the
hole so as to improve the returns of the drilling mud, thereby
providing lubrication of the casing throughout substantially its
entire length.
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