Note: Descriptions are shown in the official language in which they were submitted.
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EXTENDED REACH DRILLING METHOD
ack~round of the Invention
This invention is concerned with an extended reach
drilling technique for providing a highly deviated wellbore
that extends from a surface location, land or marine,
essentially vertically into the earth and thereafter extends
in a highly deviated attitude into the earth such that the
wellbore penetrates a mineral-bearing formation at a
subsurface location spaced a great lateral distance from
the surface location.
Wellbores and wells have been drilled to extend
into the earth in directions other than vertical for various
reasons and by various techniques. A need for such wells
was early recognized and still exists today for tapping
mineral reserves located beneath water bodies or located
beneath other poorly accessible surface locations. For
example,`before the turn of the century the Summerland ~ield
located underwater near Santa Barbara, California was drilled
by whipstocking holes out under the water from land locations.
More recent developments have enabled ultrahigh-
angle wellbores to be drilled and completed. Techni~ues ~or
drilling ultrahigh-angle wellbores are sometimes referred
to as "extended reach dril~ing", a term that has been coined
to describe rotary drilling procedures used to drill wellbores
greater than 50 degrees from the vertical and wherein complex
wellbore profiles may be used to extend the horizontal limits
of wellbores Such techniques may be used to provide a
wellbore that extends from a surface location to a
subsurface location spaced a great lateral distance
therefrom.
In an article entitled "Ultrahigh-Angle Wells Are
Technical and Economic Success", THE OIL AND GAS JOURNAL,
July 19, 1976, pp. 115-120, there is described a proiect
wherein a well was drilled and completed to a 12,300-foot
measured depth at an average angle of 82C. In a paper,
SPE 6818, "Improved Techniques For Logging High-Angle Wells"
by M. W. Bratovitch, W. T. Bell, and K. D. Kaaz, which was
presented at the 52nd Annual Fall Technical Conference and
Exhibition of the Society of Petroleum Engineers of AIME in
Denver, Colorado, October 9-12, 1977, it is said that high-
angle wells are becoming commonplace, particularly in off-
shore areas. The paper describes work which contributes to
increasing the deviation angles at which wells can be
conventionally logged and to deciding whether to try gravity
descent or pump-down tools as a first attempt at logging high-
angle welLs.
In U.S. Patent No. 4,063,592 to Arthur H. Youmans,
there is described a system for logging highly deviated earth
boreholes which system is comprised of a conventional logging
instrument that is adapted to traverse 2 slanted or deviated
earth borehole on the end of a conventional logging cable.
In U S Patent No. 3,285,350 to J K Henderson,
there is described a technique for drilling off-vertical holes
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through earth formations and more particularly a technique
and apparatus for controllably drilling holes through and
substantially parallel to mineral formations between separated
we~ls.
Summary of the Invention
This invention is directed to a method of drilling
a highly de~iated wellboré into the earth's crust by a
rotary drilling technique wherein a drill string comprised
of drill collars and drill pipe is used to advance a drill
bit attached to the drill pipe at the lower end of the drill
string into the earth and form the wellbore. A first portion
of the wellbore is formed to extend essentially verticalLy
into the earth's crust from a surface location thereof to a
kick-off point at the lower end of the first portion. A
second portion of the wellbore is initiated at the ~ick-off
point which second portion is deviated to a highly deviated
attitude from the vertical. The second portion of the wellbore
is formed and extended into the earth with the drill string
arranged to provide for the drill collars to be located within
the first vertical portion and the drill pipe and bit to be
located within the second deviated portion of the wellbore.
The second portion of the wellbore is extended until the
lower end of the lowermost drill collar in the first vertical
portion of the wellbore descends to a ~ocation of about the
2~ kick-off point, Thereafter the drill string is at least
partially pulled from the wellbore and additional drill pipe
is added thereto below the drill collars after which drilling
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is continued to extend the second portion of the wellbore
further into the earth's crust.
Brief Description of the Drawin~
J The drawing is a schematic view of a highly deviated
S wellbore illustrating the method and system of this in~ention.
Description of the Preferred Embodiments
This invention is directed to a rotary drilling
technique for drilling a highly deviated wellbore into the
earth and is applicable for drilling an extended reach
wellbore. Hereafter when reference is made to a highly
deviated wellbore it is to be understood that the term
includes an extended reach wellbore and other wellbores that
~ are sufficiently deviated that conventional rotary drilling
techniques are not satisfactory for supplying sufficient
weight on the bit for effective drilling Extended reach
drilling techniques are particularly useful for providing
multiple offshore wells from a single drilling platform,
though they may also be used in land drilling
In rotary drilling operations a drill string is
employed which is comprised of drill pipe, drill collars,
~nd a drilling bit. The drill pipe serves to transmit
rotary torque and drilling mud from a drilling rig to the
bit and to form a tensile member to pull the drill string
from the wellbore In normal operation the drill pipe is
always in tension during drilling operations Drill pipe
commonly varies from 3~" to 5" in outside diameter, Drill
collars are thick-walled pipe as compared to the drill pipe
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and thus are heavier per linear foot than the drill pipe
and may be referred to as "heavy weight pipe". The drill
collars act as stiff members in the drill string. The drill
collars are normally installed in the drill string im~ediately
above the bit and serve to supply weight to the bit. In
common rotary drilling techniques, only about the bottom three-
fourths of the drill collars are in axial compression to load
the bit during drilling while about the top one-fourth of the
drill collars is in tension as is the drill pipe. The drill
collars used in conducting rotary drilling techniques are of
larger diameter than the drill pipe in use and normally are
within the range of 4~" to lO" outside diameter.
In carrying out rotary drilling techniques, a
drilling rig is employed which utilizes a rotary table for
applying torque to the top of the drill string to rotate the
drill string and the bit. The rotary drill table also acts
as a base stand on which all tubulars, such as drill pipe,
drill collars and casing, are suspended in the hole from the
rig floor. A kelly is used as a top tubular member in the
drill string and the kelly passes through the rotary table and
is acted upon by the rotary table ~o apply the torque through
the drill string to the bit. Fluid or mud pumps are used for
circulating drilling fluid or mud intermediate the drilling
rig and the ~ottom of the wellbore. ~ormally, the drilling
fluid is pumped down the drill string and out through the drill
bit and returns to the surface through the annulus for~ed
outside of the drill string. The drilling fluid ser~es such
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purposes as cooling the bit, remo~ing earth cuttings made by
the drilling bit from the wellbore, and lubricating the drill
string to lessen the energy required in rotating the drill
pipe. In completing the well, casing is normally run
thereinto and is cemented to maintain the casing in place.
Rotary drilling equipment is utilized in carrying
out extended reach drilling but many problems are encountered
in providing the complex profiles and the greater-than-sixty-
degree wellbores that are formed in carrying out extended
reach drilling which are not encountered in carrying out
conventional rotary drilling techniques. One such pro~lem
involves applying weight on the drilling bit as required to
form the wellbore, As discussed above, in conventional
rotary drilling techniques drill collars are used in the
drill string immediately above the drill bit to supply this
weight, In conducting extended reach drilling in the highly
deviated portion of a wellbore, the use of drill collars
immediately above the drill bit results in the weight of the
drill collars being applied primarily to the lower side of
the highly deviated wellbore rather than to the bit, The
effect of the weight of the drill collars on the weight
applied to the bit becomes progressively less as the angle
from vertical of the highly deviated portion of the wellbore
is increased and the wellbore is extended into the earth until
the weight of the drill collars is applied essentially only to
the lower side of the extended portion of the wellbore.
Thereafter the drill collars become a detriment with regard to
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applying weight on the bit inasmuch as they must be forced
along the highly deviated portion of the ~7ellbore to apply
weight on the bit.
In accordance with this in~ention, there is provided
a method of drilling a highly de~iated wellbore into the
earth's crust by employing rotary drilling equipment including
a drill string that is comprised of drill collars, drill pipe,
and a drill bit, and wherein there is formed a first portion
of the wellbore that extends essentially vertically into the
earth's crust from a surface location thereof to a kick-off
point at the lower end of the first portion. A second portion
of the wellbore is initiated at the kick-off point and is
deviated to follow a track or direction that is highly deviated
with the ~ertical. Thereafter the drill string is pulled
from the wellbore and arranged to provide for the drill bit at
the lower end thereof and drill pipe connecting therewith to
be of a length greater than that length of the wellbore from
the kick-off point to the bottom thereof. Drill collars are
next attached to the drill pipe in a desired length to apply
compressive force through the drill pipe to the drill bit and
to be maintained in the first vertical portion of the wellbore.
The drill string is run into the wellbore and drilling is
commenced by rotating the drill string and circulating drilling
fluid intermediate the drilling rig and the bottom of the
wellbore. As drilling proceeds and the length of the borehole
is increased, additional drill collars are added to the drill
collar section as desired to supply ~7eight on the drill bit.
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After a sufficient length of drill collars is inserted into
the first vertical portion of the wellbore to supply
sufficient weight on the bit, drill pipe may again be added
to the drill string above the drill collars to connect with
the kelly which extends through thé rotary table. The
drilling operations are carried out until the lower end of
the column of drill collars reaches about the kick-off point
at the lower portion of the vertical section of the borehole,
Thereafter the drill string is pulled until at least all of
the drill collars are removed from the wellbore. Quite often
the entire drill string will be pulled from the wellbore such
that the drill bit may be inspected or replaced as desired.
The drill bit is then again reassembled to drill pipe of
sufficient length to provide a length thereof equi~alent to
at least the length of the highly deviated portion of the
wellbore from the kick-off point to the bottom thereof plus
an additional length equivalent to the length which the
wellbore will be extended during the neY.t cycle of operation.
Thereafter, drill collars are added to the drill string and
the drill string is rerun in the wellbore until the drill bit
reaches the bottom thereof and drilling is resumed and
continued until the lower portion of the column of the drill
collars again reaches about the kick-off point after which the
drill string is again pulled from the wellbore such that
additional drill pipe may be added above the drill bit for
another cycle of drilling.
There also may be employed along the drill pipe in
the vicinity of the drill bit a means for applying force
along the drill pipe to the drill bit. A hydraulic drill
- collar is such a means which is suitable for applying
additional weight on a bit.
This invention is hereafter described in more
detail by reference to the drawing. There sho~l is a highly
deviated wellbore 1 which extends from the surface 3 of the
earth to the lower portion 5 of the wellbore. The highly
deviated wellbore is comprised of a first portion 7,
illustrated in the drawing as being vertical but which may be
a low-angle portion that makes an angle with the vertical of
no more than about 40~, that extends from the surface of the
earth 3 to a kick-off point 9 at which point the deviation
of the wellbore is initiated and a highly deviated second
portion 11 which extends from the kick-off point 9 therefrom
to the wellbore bottom 5. A casing string 13 is normally
installed in the first vertical portion of the wellbore to
extend sufficiently beyond the kic~-off point 9 to facilitate
the initiation ~f the highly deviated second portion of the
wellbore. This casing string 13 will normally be held in
place by a cement sheath 15 The wellbore 1 may be also
provided with a shallow or surface string of casing 17 which
is held in place by cement sheath 19.
In providing the highly deviated wellbore 1 there
is formed a first portion of the wellbore which extends from
the surface 3 of the earth be this from a land surface or
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from the bottom of a marine body, to about the kic~-off point
9. This first portion of the wellbore may be provided by
drilling, using conventional rotary drilling techniques. The
second portion 11 of the wellbore is then initiated at about
the kick-off point 9 and the initial deviated portion of the
wellbore is shown at 21 At this stage of the drilling
operation, it is highly desirable as discussed above to set a
string of casing 13 in the first portion of the wellbore which
extends beyond the kick-off point along the portion 21 of the
wellbore --
Thereafter the drill string is arranged for drilling
the second portion 11 of the wellbore. This arrangement is
comprised of the drill bit 23 being attached to drill pipe 25
which is in turn attached to the drill collars 27 As
illustrated in the drawing, the second portion 11 of the
wellbore has been extended beyond the kick-off point 9 around
the portion 21 where the deviation of the wellbore is primarily
initiated and to the well bottom 5. A sufficient length of
the drill pipe 25 is provided to extend from the drill bit 23
along the entire length of the second portion 11 of the
wellbore and up into the first portion 7 of the wellbore to the
bottom 29 of the drill collar column 27. The dr;ll coLlar
column 27 is of sufficient length to provide a desired weight-
on-bit for effective drilling, but a length which allows it to
be maintained in the first portion of the wellbore. In this
illustration, the second portion 11 of the wellbore may be
extended for the distance from the bottom 29 of the drill
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collars 27 to about the kick-off point 9. If extended
significantly beyond the kick-off point 9, the drill collars
27 will begin contacting the deviated portion 21 of the
wellbore 11 and lie along the lower side of the second portion
11, thus lessening the weight applied to the bit. Thus, at
about the time that the bottom 29 of the drill collars 27
reaches the kick-off point,the drill string 31 is pulled
fr~m the wellbore or at least all of the drill collars 27
are pulled therefrom. Normally, the drill pipe 25 will also
be pulled from the wellbore such that the drill bit 23 may-be
inspected and replaced as desired. Thereafter the drill
string 31 is again run into the wellbore 1 and arranged such
that the drill bit 23 is connected to a sufficient length of
drill pipe 25 to extend from the bottom 5 of the wellbore up
into the first section 7 thereof for a distance equivalent to
that which the second portion 11 will be extended into the
earth's crust during the next cycle of the drilling operation.
As mentioned above, a suitable tool for applying
pressure on the rock bit in conjunction with the compressive
pressure applied by the drill pipe is a downhole tool known as
a hydraulic drill collar, The hydraulic drill collar is also
referred to as a hydraulic wall-anchored drill collar and a
hydraulic-actuated drill collar. The hydraulic drill collar
has two major sections, a push-down section 28 and an anchor
section 30 plus a retaining latch. The push-down section 28
has one or more single acting hydraulic cylinders staged in
series and the bit load or weight or weight-on-bit that is
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applied on the bit is a result of a differential pressure that
is applied on the pistons within the cylinders. For a more
complete description of the hydraulic drill collar,reference
is made to an article entitled "Hydraulic Wall-Anchored Drill
Collar Promises Lower Drilling Costs" by J. M. Kellner and
A. P. Roberts, published in THE OIL AND GAS JOURNAL, October 3,
1960, vol. 48, No. 40, pp.- 87-89 and to U.S. Patent No.
3,105,~61, "Hydraulic Actuated Drill Collar" to J. M. Kellner.
For a still better understanding of this invention a
more detailed description thereof is given describing a me-thod
of drilling a highly deviated or extended reach wellbore of a
designed profile wherein the first portion of the wellbore is
- designed to be about 2000 feet in length and wherein the second
highly deviated portion of the wellbore is designed to be about
10,000 feet in length. In the carrying out of this method to
provide this designed highly deviated wellbore, the first
~ertical portion of the wellbore is provided by conventional
rotary drilling methods. At the kick-off point 9, the hole is
deviated from the vertical by any of several deflection means,
such as jet deflection or a downhole mud motor and bent sub.
As an example, 1000 feet of drill collar in a 2000-foot section
of vertical hole will permit the hole ~o be extended 1000 feet
before the bottom 29 of the drill collar reaches the kick-off
point 9. At this point the drill string is removed from the
hole to at least the bottom of the drill collars, a 1000-foot
length of drill pipe placed in the string and then the drill
collars are again placed at the top of the drill pipe.
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Another advancement of 1000 feet is now possible with the
drill collars remaining in the vertical portion of the hole.
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