Note: Descriptions are shown in the official language in which they were submitted.
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The present inverltiorl relates, iII yeneral, to
directional drilling in earth formations and, more
specifically, to an adjustable bent ~ub for u~e in
directional drilling.
~AC~GROU~D OF TEE I~VENTION
"Directional drîlling" is a procedure employed in
the ~arth drilliny i~dustry when it is necessary to
change the direction of a borehole. In e~sence,
10 directional drilling is achieved by inserting, at the
downhole end of a drill striny, a small section of pipe,
called as ~ "sub", which has been "bent" such that the
longitudinal axis at one end its ends is at a slight
angle, ~eferred to herein as the "offset angle" to the
15 lonyitudinal axis at the other end. 5uch a tool is
called a "bent sub".
In practice, a vertical borehole is drilled to a
predetermined depth. The drill string is then withdrawn
and a bent sub having the desired offset angle is
20 inserted between the end of the drill string and the
downhole motor. The drill string is then inserted back
into the borehole. Since the longitudinal axis of th~
drill bit will now be a-t an angle to the original
borehole, the direction of the bore hole will be
2~ altered. The bent sub may be replaced any number of
times in order to provide a borehole of the desired
angular offset.
The positioning of the bent sub in the drill string
has an effect upon the operation of the downhole motor.
30 The more r~mote the bent sub is from the drill bit,
within practical limitations for directional drillin~,
the more interference there is between the borehole and
drill bit, and between the borehole and bent ~ub when
inserting the drill string into the bor~hole. When
35 drilling such int~rference causes a loss of power which
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would otherwise be available for drilling, a~ the mo-tor
must overcome the interference and the drill bi-t is not
desi~ned to drill sideways. It i5 desirable -to be able
to rotate the drill string in the borehole. An
excessive amount of in-terfererlce will prevent or render
difficult such rotation. It has been ascertained, that
if the ben-t sub is placed closer -to -the drill bit
interference between the borehole and bent sub is
reduced. If the bent sub is placed closer to the drill
10 bit, interference between the borehole and the drill bit
i5 similarly reduced and the angle of engagement between
the drill bit and the side of the borehole is improved.
The optimum positioning o the bent sub is
15 considered to be between the power unit and beariny
components of the downhole motor. This creates severe
limitations upon the use of conventional bent subs. The
angular offset of conventional bent subs is achieved by
physically bending the sub or by otherwise modifyiny the
20 longitudinal axis of the sub during the machininy stage
of its manufacture. In order to provide for selectivity,
it i5 necessary to provide a series of bent subs having
offset angles ranging from about 1/4 of one degree in
lJ4 increments to about 2 degrees. Once a downhole
2~ motor unit is assembled having a power unit, a bearing
assembly, and a bent sub in between, the rig crew will
not under ordinary circumstances take the motor unit
apart to interchange the bent sub component, such work
must be performed in a service shop which is usually at
30 a location remote from the drill site. It is therefore,
the practise to have a plurality of downhole motor units
on site having incorporated therein bent subs of varying
degrees of offset. This practise results in a needless
duplication of expense, If the available units do not
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hav~ the correc-t angular offset work must ~top until one
is obtained.
S~ARY OF T~ INV~NTION
The present inven-tion seek6 to prov:ide a bent sub
which overcomes the above described disadva~tages of the
prior art.
Accordingly -to the present inverltiorl, t~ler~ is
provided an adjustable bent sub for use in directional
10 drilling in earth formation~ which iY compIi~ed of a
first member havin~, a primary axis, and external,
cylindrical surface means defining a secondary axi5
disposed at a predetermined offset angle with respect to
the primary axis; a tubular second member secured to
15 the first member against axial displacement and having,
a primary axis; internal, cylindrical surface means
defining a secondary axis disposed at a predetermined
offset angle with respect to the second member primary
a~is, the internal sur~ace being adapted to
20 telescopically receive the first member external surface
in sliding fit relation for rotation about the secondary
axis, and first clutch means extending axially from one
end thereof; locking sleeve means telescopically
receiving and non-rotatably coupled to the external
25 surface means cf the first member and having second
clutch means extending axially of one end thereof toward
the second member, the sleeve means being axially
moveable on the first member between an engaged position
whereat the first and ~econd clutch means are
30 interengaged and non-rotatably couple the second member
and the first member in a predetermined angular position
and a disengaged position whereat the locking sleeve is
axially displaced from the second member and the first
and second clutch means are disengaged from one ~nother
35 so as to permit angular adjustment of the second member
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with respect t~ the first member; and means threaded
onto the external surface of the first mernber or
securing the sleeve in the engaged position thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the in~en-tion ~ill
become more apparen-t from the following de~criptioIl in
which reference i~ made to the apperlded drawin0s,
wherein:
FIGURE 1 i5 a partially broken view, o~ a drill
~tring in a borehole illustrating a oonventional bent
sub arrangement;
FIGURE 2 is a view similar to FIGURE 1 but
illustrating an adjustable bent sub assembly according
15 to the preferred embodiment of the present invention;
FIGURE 3a is a partial broken, elevational view of
a portion of a drill ~tring illustrating the adjustable
bent sub of the present invention at its maximum offset
angle;
FIG~RE 3b is a view similar to FIGURE 3a, but
illustrating the bent sub of the pre~ent invention at
its minimum offset angle;
FIGURE 4 is a view si.milar to FIGURE 3a but in
partial section illustrating the internal structure of
25 the adjustable bent sub of the present invention; and
FIGUR~ 5 i5 an enlarged view of indi~ia means
disposed on the adjustable bent sub of the present
invention for facilitating adjustment of the offset
angle.
D~TAIL~D D~SCRIPTIO~ OF _R~F~R~D ~MBODIMENT
Figure 1 illu~trates a conventional assembly
employed ~or directional drilling in earth formations.
The assembly includes a bent sub 12 threadedly e~gaged
at its uphole end to the downhole end of a drill ~tring
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14 and -threadedly engaged at its lower end to the uphole
end of a downhole motor assembly 16. The lower erld o~
the drilling motor assembly i~ secured to a drill bit
18. The bent sub is constructed so that the axis of its
5 dOWllhOle end i8 disposed at an offset angle ran~ g ~rom
a fract:ion of one degree to about two degrees to the
axis of its uphole end. This i~ typically ac~lieved by
machining the threads of the lower threaded cont~ectiort
at an offset angle to the a~is of the sub and upper
10 connection. It will be understood that with the axi~
of the drill bit being angularly off~et with resp~c-t to
the axis of the drill string, it is then possible to
alter the direction of the borehole. The magnitude of
the angular deviation from the axis of the drill string
15 may be altered by selecting a bent sub with the proper
ang~lar offset, within functional limitations where
interference with the borehole becomes too great. Thus,
it is conventional to maintain an inventory at the drill
site of bent subs 12 having differen-t offset angles so
20 that when a new drilling direction is required, the
drill string i5 withdrawn from the borehole and the bent
sub is replaced with a bent sub having the appropriate
offset angle.
The present invention, generally designated by
25 reference numeral 20, will be now be described with
reference to FIGUR~S 2 to 5 where the same reference
characters designate similar parts.
With particular reference to FIGURE 2, the bent sub
20 of the present invention is disposed between the
30 power unit and the bearing section of a downhole motor
16. This location permits larger off~et angles and/or
reduces interference whils running in the boreh~le. The
bent sub of the present invention is constructed in such
a manner that the offset angle can be easily adjusted
35 between predetermined limits without removal of the
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downhole motor from the drill ~trirlg and thus render~
unnecessary the maintenance of a large inventory of
downhole motors with bent subs having diff~rent offse-t
anyles.
With reference to FIGURES 3 and 4, bent ~ub 20 will
be seen to be compri~ed of five componerlt~, namely, a
mandrel 22, a bent sub housing 24, a sleeve 26 and a
first nut 2a and a ~econd nut 30.
Mandrel 22 is in the ~orm of a pipe section having
10 an externally threaded end 32 adapted to a threadedly
engage the bearing assembly 34 of a downhole motor 16.
The mand~el includes a first exterior surface portion 36
whose diameter is the same as that of the beari~g
assembly 34 and a second exterior ~urface portion 38
15 having two portions 40 and 42 of reduced di~meter.
Reduced diameter portions 40 and 42 are separated by a
conical shoulder 44. The end 46 of mandrel 22 is
externally threaded for threaded engagement with nut 30
while end of reduced diameter portion 40 is externally
20 threaded to receive nut 28.
The common axis of the threaded ~nd 32 and the
first exterior portion 36 of the mandrel defines a first
primary axis 50 which is coaxial with the axis of the
bearing assembly 34 of the downhole motor, while the
25 axes of the outer cylindrical surfaces of reduced
diameter portions 40 and 42, respectively, are machined
such that their longitudinal axis is anyularly off~et
from primary axis 50, so as to define a first secondary
axis 56. The significance of this will become clear a~
30 the description proceeds. The mandrel defines a central
fluid passageway 58 for conveying drill.ing fluid to the
drill bit.
Bent sub housing 24 i5 a generally tubular member
having an outer ~urface 60, who~e diameter is the same
as that of the bearing assembly 34 of -the downhole motor
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and portion 36 of -the mandrel, and a -threaded end 62
threadedly engageable with the internally threaded power
unit section 64 of the downhole motor. Housiny 24 i~
formed with a pair of concentric internal surface 66 and
68 separated by conical shoulder 70 which i5 engageable
with conical ~houlder 44 of the mandrel which coop~rate
to limit tele~copic movement irl olle axial directiorl v~
th~ bent sub housi~g with respect to th~ mandrel when
nut 28 is loosened. Internal surfaces 66 and 6~ of
10 housing 24 are machined to receive the outer surf~ce~ of
reduced diameter portion 40 and 42 of the mandrel in
sliding fit relation.
The axi~ of concentric cylindrical surfaces 66 and
68 define a ~econd primary axis 72 while the axis of the
15 threaded housing end 62 defines a second secondary axis
~4, which is angular offset from the second primary
axis. When housing 24 is assembled upon mandrel 22, the
first secondary axis 56 is coaxial with the second
primary axis ~2 50 as to define a co~mon axis about
20 which the housing is rotat~ble, when permitted to do so
as explais~ed later. The angular offset between the
fir~t primary and secondary axe~ is nominally one degree
but may range from a fraction of one degree to two
degrees if desired. The magnitude of the offs~t angle
25 is not important to the essence of the pre~ent
invention. It will be seen, then, that the angular
disposition of housin~ 24 with respect to mandrel 22
will determine the angular offset between the drill
string and the drill bit. Maximum offset i5 obtained
30 when the oEfset of the mandrel is in the same radial
plane and extends in the same direction as that of the
housing. This configuration i9 illustrated in ~IG~RE
3a. Thus, if the angular offset is one degree, then the
overall angular offset, i.e. between the axis of the
35 drill string and the axis of the drill bit will be -two
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degrees. This position is referred to as -the "ba~e"
position. Minimum offset is obtained when the offset of
the mandrel is in the same radial plane and ex-tends in
the opposite direction to that of the hou~in~. This
configuration i5 illustrated in FIGURE 3b. This occur~
when the housing i5 angularly displaced from the ba~e
position by 180 degrees whereat the off~et anglc ~ the
housing cancels the offset angle of the mandrel ~o that
the net overall angular offse-t between the axiB of the
10 drill string and the axis of the drill but will be zero
degrees. In this position, there will be a slight radial
offset of the axis of the drill striny a~d that of the
drill bit; however, the two axes will be parallel to
one another. This is reflected in FIGUR~ 3b, where
15 fir~t primary axis 50 i5 shown as being parallel to
second secondary axis ~4. It will be understood that
angular displacements of mandrel 22 with resp~ct to
housing 24 will provide overall angular offsets ranging
from a maximum of two degrees (~I6~R~ 3a) to a minimum
20 of zero degrees (FIG~R~ 3a).
As already mentioned, nut 30 threadedly engages
threaded end 46 of the mandrel and is formed with a
first annular shoulder B0 which bears against the end 82
of the mandrel as well as a second annular ~houlder 84
25 which bears against end 86 of the housing. In this
manner, nut 30 prevents axial displacement of the
housing with respect to the mandrel, while permitting
rotational movement of the housing about the mandrel.
Sleeve 26 provides the means by which rotary forces
30 can be transmitted between the mandrel and the housing
end, with nut 28, provide the means by which the housing
can be angularly adjustea with respect to th~ mandrel as
explained hereinbelow. Shoulders 44 and ~0 p~event
displacement of the housing with re~pect to the mandrel,
3~ when nut 28 is loosened.
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The end 100 of housing 24 a~d the snd 102 of sleeve
26 are formed with mating teeth 106 forming dog clutch
elemen-ts of a dog clutch generally designa-ted by
reference numeral 108. When the teeth, and, thus, the
clutch are engaged, rotary ~orces can be -transmit-ted
between the sleeve and the hou~in~. Conver~ely, when the
~leeve is displacecl axially away from the houslng ~wch
that the teeth are no lonyer engaged, the hou~iny will
be free to rotate with respect to the mandrel. In this
10 manner, the housing can be set to the desired po~ition.
Nut 28 is formed with a shoulder 110 which is
abuttingly engageable with the end 113 of the sleeve 26
80 that when nut 28 is threaded against the sleeve, the
15 dog clutch is maintained in an engaged or locked
position. Conversely, whe~ the nut i~ threaded away
from the sleeve a sufficient distance, the ~leeve can be
slid axially away from the mandrel to allow
disengayement of the clutch and angular adjustment of
20 the housing with respeot to the mandrel.
In order to transmit rotary forces between the
mandrel and housing, internal surface 120 of the ~leeve
is formed with splines 122 arranged to receive keys 124
located in keyways 126 of the mandrel. The splines
2~ extend to both ends of the sleeve to allow the sleeve to
clear keys 124 in order to facilitate assembly and
adjustment of the assembly.
Advantageously, as best shown in ~I~URE 5, the
sleeve and housing are each~ formed with alignable
30 indicia 130 to facilitate po~itioning the housing iIl the
proper and desired anyular position with respect to the
mandrel. As shown, the indicia may be in increments of
0.25 degrees and extend 180
deyrees about the sleeve housing. Further, the
35 circumferential width of teeth 106 of the doy clutch may
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2 10
be arranged ~uch that it correspands w.ith any desired
angular increment, such as 0.25 degrees, for example, to
facilita-t~ positioning of the housing with re~pect to
the mandrel.
The preferred location of bellt ~ub in the drlll
string is between the power unit sectio~ arld bearitlg
assembly ~ection o the dowrlhole motor. Prior to
loweriny the motor a~sembly into the borehole, the bent
sub 20 is adjusted to provide the desired an~ular offse-t
10 between the axis of the drill bit and the axi~ of the
drill string. This is accomplished by loo~ening lock nut
28 and sliding sleeve 26 along keys 124 until mating dog
clutch elements 106 are di~enga~ed. Once the do~ clutch
is diaengaged, housing 24 may be an~ularly adjusted with
15 respect to mandrel 22 as previously explained.
Once the housing ha~ been placed in the desired
positivn, the dog clutch is re-engaged and nut 28 is
threaded against sleeve 26 thereby securing sleeve 26
and mandrel 22 in the selected position.
It will be appreciated that the above de~cribed
preferred embodiment of the present inventioI~ overcomes
the disadvanta~es, discus ed earlier, oE the prior art.
First, according to the present invention, it is
unneces~ary to maintain a large inventory of downhole
25 motors having a bent subs with differing angles oP
offset. 5econd, adjustment of the bent ~ub of the
present invention i~ extremely ~imple and does not
re~uire the di~a~sembly of the downhole motor.
It will also be apparent to one ~killed in the art
30 that adjustable bent sub can be run in an inverted
position with threaded connectior. 32 coupled to power
unit ~ection 64 of a downhole motor and threaded
connection 62 coupled to bearing assembly 34 of a
downhole motor.
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2 11
It will be apparent to those ~killed in the art
that various modifications and alterations may be made
to the above de~cribed embodimerlt without departin~ from
the spirit of -the invention as defined by the appended
claim~.
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