U.S. patent number 3,743,034 [Application Number 05/139,526] was granted by the patent office on 1973-07-03 for steerable drill string.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to William B. Bradley.
United States Patent |
3,743,034 |
Bradley |
July 3, 1973 |
STEERABLE DRILL STRING
Abstract
Method and apparatus for maintaining the orientation of a
laterally unsupported driven shaft constant with respect to a
non-rotating coordinate system as the driven shaft is rotated by a
non-coaxial rotating driving shaft. In a directional drilling
method, the apparatus is disposed in a well drill string along with
means for adjusting the orientation of the portion of the drill
string below the apparatus to provide a steerable drill string. The
apparatus for maintaining the orientation of the shafts comprises
an axial-piston machine mounted on one of the shafts and
operatively connected to a control flange affixed to the other of
the shafts. A universal coupling connects the shaft in
driving-driven relationship. The deflection of the shaft at the
universal joint is maintained constant with respect to a
non-rotating coordinate system by driving the pistons of the axial
piston machine in timed relationship with the rotation of the
shafts so that each piston completes one reciprocating cycle each
time the shafts complete one rotation.
Inventors: |
Bradley; William B. (Houston,
TX) |
Assignee: |
Shell Oil Company (New York,
NY)
|
Family
ID: |
22487088 |
Appl.
No.: |
05/139,526 |
Filed: |
May 3, 1971 |
Current U.S.
Class: |
175/61;
175/73 |
Current CPC
Class: |
E21B
7/06 (20130101) |
Current International
Class: |
E21B
7/04 (20060101); E21B 7/06 (20060101); E21b
007/08 () |
Field of
Search: |
;175/61,73,256,45,74 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leppink; James A.
Assistant Examiner: Favreau; Richard E.
Claims
I claim as my invention
1. A method for maintaining the orientation constant with respect
to a non-rotating coordinate system of a laterally unsupported
driven shaft, connected in end to end relationship with a
non-coaxial driving shaft as the driving shaft rotates to drive the
driven shaft comprising the steps of
interconnecting the shafts through a universal joint means;
applying controlled amounts of force to at least one element which
is anchored to one of the shafts and moveably coupled to the other
of the shafts;
and controlling the amount and direction of the applied force in
coordination with the rotation of the shafts to displace the
element with respect to the shaft to which it is moveably connected
in a direction and amount substantially equal to the direction and
amount of displacement the element would undergo if the shafts were
rotated with the driven shaft supported in the orientation desired
to be maintained constant.
2. A method for directionally drilling a well into a subsurface
earth formation comprising the steps of
affixing a drilling bit to one end of a lower pipe segment;
attaching to the opposite end of the lower pipe segment a means for
maintaining a selected angle of axial intersection and direction of
deflection of the lower pipe segment constant with respect to a
reference non-rotating coordinate system as the lower pipe segment
is rotated;
attaching an upper pipe segment to the means for maintaining a
selected angle of axial intersection and direction of deflection
constant;
extending the drilling bit, lower pipe segment, means for
maintaining a selected angle of axial intersection and direction of
deflection constant, and upper pipe segment into a well;
rotating the upper pipe segment with a rotary drive means at the
earth surface to rotate the bit and thereby advance the well into
the earth;
while rotating the upper pipe segment, applying controlled amounts
of force to at least one element of the means for maintaining a
selected angle of intersection and direction of deflection
constant, the element being anchored to one of the pipe segments
and slidably coupled to the other of the pipe segments; and
controlling the amount and direction of the force applied to the
element in coordination with the rotation of the upper pipe segment
to displace the element with respect to the pipe segment to which
it is moveably connected in a direction and amount substantially
equal to the direction and amount of displacement the element would
undergo if the pipe segment were rotated with the lower pipe
segment supported at the angle of inclination and direction of
deflection at which it is desired to advance the drilling bit into
the earth formation.
3. The method of claim 2 including the step of adjusting the for
maintaining a selected angle of inclination and direction of
deflection by sending a signal via a telemetering drill string from
the earth surface to a control means carried by the means for
maintaining a selected angle of axial intersection and direction of
deflection constant.
4. The method of claim 2 including the step of measuring the
orientation of the lower pipe segment while the lower pipe segment
is in the operative position to determine the direction in which
the well is advancing into the earth.
5. The method of claim 4 including the step of signaling the
measured orientation of the lower pipe segment to the earth surface
via a telemetering drill string.
6. Apparatus for maintaining the orientation constant with respect
to a non-rotating coordinate system of a laterally unsupported
driven shaft connected in end to end relationship with a
non-coaxial driving shaft as the driving shaft rotates to drive the
driven shaft comprising:
universal coupling means coupling the driving shaft to the driven
shaft;
a plurality of control elements each of which is anchored on a
first of the shafts and moveably connected to the second of the
shafts; and
means for applying controlled amounts of force to the control
elements in coordination with the rotation of the shafts to
displace the control elements with respect to the shaft to which
they are moveably connected in a direction and amount substantially
equal to the direction and amount of displacement the control
elements would undergo if the shafts were rotated with the driven
shaft supported in an orientation desired to be maintained
constant.
7. The apparatus of claim 6 including:
a housing mounted on a first of the shafts; and
a control flange affixed to the second shaft;
and wherein the plurality of control elements comprise
a plurality of pistons slideably mounted within the housing for
reciprocating movement in a direction coaxial with the first shaft;
and
a plurality of connecting rods, each connecting rod connected to
one of the pistons at one end of the rod and pivotably mounted on
the control flange at the other end of the rod for maintaining the
point of mounting of the rod on the control flange a fixed distance
from the piston as the piston moves reciprocally within the
housing.
8. The apparatus of claim 7 wherein the means for applying
controlled amounts of force to the control elements in coordination
with the rotation of the shafts comprises:
variable amplitude drive means for reciprocally driving the pistons
within the housing; and
timing means associated with the drive means for timing the motion
of each piston to complete one full reciprocating cycle each time
the driven shaft completes one revolution whereby the connecting
rods maintain the orientation of the control flange substantially
constant with respect to a non-rotating coordinate system as the
driving shaft is rotated to drive the driven shaft.
9. The apparatus of claim 8 wherein the variable amplitude drive
means comprises a pump.
10. The apparatus of claim 8 wherein the timing means comprises an
inertial reference means.
11. A directionally controllable well drill string for connecting
rotary drive means on the earth surface in driving relationship to
a drilling bit in a well borehole comprising:
an upper pipe segment adapted to be coupled to the rotary drive
means for transmitting rotation from the rotary drive means;
a lower pipe segment adapted to be coupled to the drilling bit for
transmitting rotation to the bit;
universal coupling means coupling the upper pipe segment in rotary
driving relationship to the lower pipe segment; and
means for maintaining a selected angle of axial intersection and
direction of deflection of the lower pipe segment with respect to
the upper pipe segment constant with respect to a non-rotating
coordinate system as the drill string is rotated by the rotary
drive means to drive the drilling bit, the means for maintaining a
selected angle of axial intersection and direction of deflection
constant comprising an axial piston machine carried by one of the
pipe segments and a control flange affixed to the other of the pipe
segments, the axial piston machine being operatively connected to
the control flange to maintain the control flange in a
substantially fixed plane with respect to a non-rotating coordinate
system.
12. The apparatus of claim 11 including:
means for adjusting the selected angle of axial intersection of the
upper pipe segment with the lower pipe segment from the earth
surface while the drill string is operatively positioned in the
well bore hole.
13. The apparatus of claim 12 including:
means mounted on the lower pipe segment for measuring the angle of
the axis of the lower pipe segment with respect to the
vertical;
means operatively connected to the angle measuring means for
signaling to the surface the angle measured by the angle measuring
means; and
means at the earth surface operatively connected to the signaling
means for displaying the angle measured by the angle measured
means.
14. The apparatus of claim 13 wherein the signaling means comprises
circuit means disposed in the upper pipe segment.
15. The apparatus of claim 11 wherein the axial-piston machine
comprises:
a housing;
a plurality of pistons slideably mounted within the housing for
reciprocating movement in a direction co-axial with the pipe
segment upon which the housing is carried;
variable amplitude drive means for reciprocally driving the pistons
within the housing;
a plurality of connecting rods, one connecting rod connected to
each of the pistons at one end of the rod and pivotably mounted on
the control flange at the other end of the rod for maintaining the
point of mounting of the rod on the control flange a fixed distance
from the piston as the piston moves reciprocally in the housing;
and
timing means associated with the drive means for timing the motion
of each piston to complete one full reciprocating cycle each time
the drilling bit completes one revolution whereby the connecting
rods maintain the control flange in a substantially fixed plane
with respect to a non-rotating coordinate system as the drill
string is rotated to drive the drilling bit, the angle of
intersection of the fixed plane with the axis of the pipe segment
upon which the axial-piston machine is carried being a function of
the amplitude of the reciprocal motion of the pistons in the
housing.
16. The apparatus of claim 15 wherein the variable amplitude drive
means comprises a pump.
17. The apparatus of claim 15 wherein the timing means comprises an
inertial reference means.
18. The apparatus of claim 15 including means for controlling the
amplitude of the variable amplitude drive means from the earth
surface and thereby controlling the angle of intersection of said
fixed plane with the axis of the pipe segment upon which the
axial-piston machine is carried.
19. The apparatus of claim 15 wherein the timing means includes
means for adjusting the phase of the reciprocating motion of the
pistons with respect to the rotation of the drilling bit thereby
rotating the plane of the control flange within the non-rotating
coordinate system to change the direction of deflection of the
lower pipe segment with respect to the upper pipe segment; and
wherein
the means for adjusting the phase of the reciprocating motion of
the pistons is coupled to a phase control means at the earth
surface for activating the means for adjusting the phase of the
reciprocating motion of the pistons to change the deflection of the
lower pipe segment with respect to the upper pipe segment.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of drilling wells. More
particularly, the invention relates to a method and apparatus for
directionally drilling a well into the surface of the earth and to
a method and apparatus for maintaining the orientation constant
with respect to a non-rotating coordinate system of a laterally
unsupported driven shaft connected in end to end relationship with
a non-coaxial driving shaft as the driving shaft rotates to drive
the driven shaft.
2. Description of the Prior Art
In the drilling of wells, such as oil and gas wells, it is often
necessary to adjust the direction in which the well drilling
equipment is progressing into the earth's surface. In some cases,
it may be desired to redirect the drill string toward the vertical.
In other cases, it may be desired to direct the string away from
vertical in order to reach a point which is displaced horizontally
as well as vertically from the surface drilling location. Such a
practice is quite common, for example, when drilling operations are
conducted from an off-shore platform or from a drilling island in a
city.
A number of techniques are currently in use for directing wells.
One of these is to whipstock the drilling stem. According to this
technique, a wedge-like device or shoe is located in the hole so
that upon drilling past the wedge the bit is deflected by the wedge
to change the angle at which the hole progresses. Each time a
change in direction is desired, the drill pipe must be withdrawn
from the hole and a new setting of the shoe must be made.
A second technique is to use a bent sub or a variably bendable sub
in conjunction with a down hole powered bit driven by an electrical
or hydraulic motor carried at the end of the drill string near the
bit. In such an apparatus, the drill string above the bent sub is
held stationary while the down hole motor turns the bit on the
other side of the bent sub. If a variably bendable sub is used, the
direction of drilling can be changed without withdrawing the drill
string from the hole by changing the angle of the bending sub.
However, prior art variably bendable subs have not been suited for
use in conventional drilling where the drill pipe is rotated from
the surface to turn the drill bit because they have not been
capable of maintaining the orientation of the portion of the drill
string below the sub constant as the portion of the drill string
above the sub is rotated. Therefore, it has not heretofore been
possible using whip stock or bent sub techniques to directionally
control a conventionally powered drill string without interrupting
drilling operations.
SUMMARY OF THE INVENTION
This invention is a broad aspect comprises a method and apparatus
for maintaining the orientation constant with respect to a
non-rotating coordinate system of a laterally unsupported driven
shaft (such as the portion of a drill string adjacent the bit)
connected in end to end relationship with a non-coaxial driving
shaft (such as a segment of drill pipe) as the driving shaft
rotates to drive the driven shaft. The method comprises
interconnecting the shafts through a universal joint means;
applying controlled amounts of force to a plurality of elements
which are fixedly positioned with respect to one of the shafts and
moveably connected to the other of the shafts; and controlling the
amount and direction of the applied force in coordination with the
rotation of the shafts to displace the elements with respect to the
shaft to which they are moveably connected in a direction and
amount substantially equal to the direction and amount of
displacement the elements would undergo if the shafts were rotated
with the driven shaft supported in the desired orientation with
respect to the driving shaft.
An apparatus for maintaining the orientation constant with respect
to a non-rotating coordinate system of a laterially unsupported
driven shaft connected in end to end relationship with a
non-coaxial driving shaft as the driving shaft rotates to drive the
driven shaft comprises a plurality of control elements each of
which is anchored on a first of the shafts and moveably connected
to the second of the shafts; and means for applying controlled
amounts of force to the elements in coordination with the rotation
of the shafts to displace the elements with respect to the shaft to
which they are moveably connected in a direction and amount
substantially equal to the direction and amount of displacement the
elements would undergo if the shafts were rotated with the driven
shaft supported in an orientation desired to be maintained
constant.
In another aspect this invention provides a method and apparatus by
which a drill string rotated from the earth surface may be
directionally controlled without withdrawing the drill string from
the borehole for directional drilling. The method comprises the
steps of affixing a drilling bit to one end of a lower pipe
segment, attaching to the opposite end of the lower pipe segment a
means for maintaining a selected angle of axial intersection and
direction of deflection of the lower pipe segment with respect to
an upper pipe segment constant with respect to a non-rotating
coordinate system as the upper pipe segment is rotated to drive the
lower pipe segment; attaching an upper pipe segment to the means
for maintaining a selected angle of axial intersection and
direction of defection constant; extending the drilling bit, lower
pipe segment, means for maintaining a selected angle of axial
intersection and direction of deflection constant, and upper pipe
segment into a well; and rotating the upper pipe segment with a
rotary drive means at the earth surface to rotate the bit and
thereby advance the well into the earth. The means for maintaining
a selected angle of axial intersection and direction of deflection
constant can be adjusted to control the direction in which the well
is advanced into the earth. Advantageously, the direction in which
the drill bit is advancing into the earth is measured while
drilling is progressing so that deviations of this direction from
that desired may be corrected by appropriately adjusting the means
for maintaining a selected angle of axial intersection and
direction of deflection constant.
A directionally controllable drill string which can be used in the
practice of this method of directional drilling comprises an upper
pipe segment adapted to be coupled to a conventional rotary drive
means for transmitting rotation from the drive means into the bore
hole. This upper pipe segment may be a conventional string of drill
pipe or, according to a preferred embodiment, may be telemetering
drill string in which segments of an insulated electrical conductor
are built into each joint of drill pipe to carry electrical signals
through the drill pipe to the surface. Such a telemetering drill
string is described in U.S. Pat. NO. 3,518,699, issued June 30,
1970, to J. E. Fontenot. The upper pipe segment is coupled in
rotary driving relation to a lower pipe segment by a directional
control sub which includes a universal coupling means, such as a
heavy duty universal joint. The lower pipe segment is coupled to
the drilling bit for transmitting rotation to the bit. Associated
with the universal coupling means is a means for maintaining the
angle of axial intersection of the two pipe carried by one of the
pipe segments constant with respect to a non-rotating coordinate
system as the drill string is rotated by the rotary drive means to
drive the drilling bit.
The angle maintaining means can comprise an axial-piston machine,
segments and operatively connected to a control flange which is
affixed to the other pipe segment. In conventional applications of
such a machine, the displacement of the pistons of the axial piston
machine is controlled by varying the displacement of the control
flange. In the apparatus of this invention, the angle of the plane
of the control flange is controlled by varying the displacement of
the pistons.
The axial-piston machine may comprise a plurality of pistons
slideably mounted within a housing for reciprocating movement in a
direction co-axial with the upper pipe segment. Each piston is
connected by a connecting rod to the control flange on the lower
pipe segment. The connecting rods maintain the point on the control
flange at which they are mounted a fixed distance from the piston
as the piston moves reciprocally in the housing. A variable
amplitude drive means is preferably associated with the piston for
reciprocally driving them within the housing. This drive means may
be, for example, a mud turbine or differential-slip mechanism
powered hydraulic motor, an electrically powered linear actuator,
or a mechanically powered push-pull rod system operatively
associated with a cranking mechanism. The variable amplitude drive
means is preferably coupled to an amplitude controller at the
surface via the telemetering drill string. If a conventional string
of drill pipe is used the variable amplitude drive means is coupled
to a programmed downhole controller which can be carried on the
control sub adjacent the drive means.
A timing means is associated with the drive means for synchronizing
the motion of the pistons. Preferably, the pistons complete one
full reciprocating cycle each time the drill bit completes one
revolution. In this way, the connecting rods maintain the control
flange in a fixed plane with respect to a non-rotating coordinate
system as the drill string is rotated to drive the drilling bit.
The angle of intersection of the plane of the control flange with
the axis of the upper pipe segment is a function of the amplitude
of the reciprocal motion of the piston in the housing. The
direction toward which the control flange is inclined is a function
of the phase relationship between the reciprocating motion of the
piston and the rotating of the drill string. The timing means
preferably comprises remotely controlled means for adjusting this
phase relationship coupled to a controller at the surface via the
telemetering drill string.
An angle measuring means such as an inertial platform may be
mounted on the lower pipe segment to measure the orientation of
this pipe segment with respect to the vertical and the direction in
which the pipe segment is deflected. The angle measuring means is
preferably associated with signaling means of a type capable of
signaling the measured angle to the surface. A preferred signaling
means is an electrical transducer means coupled to a display means
at the surface via a telemetering drill string.
The angle measuring means provides a signal from which the driller
may be able to determine the direction and inclination of the drill
pipe segment directly above the drill bit. The driller may adjust
this orientation while drilling operations are in progress by
adjusting the variable amplitude drive means to change the angle
between the upper drill pipe segment and the lower drill pipe
segment and by adjusting the phase relationship of the pistons to
change the direction of deflection. Thus, the apparatus of this
invention provides a drill string which is steerable from the
earth's surface.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view, partially in cross section, showing
the steerable drill string of this invention in the operative
position in a well bore.
FIG. 2 is a side view, partially in vertical cross-section, of an
embodiment of the directional control sub of this invention.
FIG. 3 is a side view of the directional control sub of FIG. 2 in a
deflected condition.
FIG 4 is a partially cut-away side view of the control sub of FIG.
3 looking in the direction of arrow 65 of FIG. 3.
FIG. 5 is a block diagram showing the elements of a timing means of
a type which may be used in the directional control sub of FIG.
2.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 1, we see a rotary drilling rig 10 of a
conventional type drilling a well bore hole 11 with an embodiment
of the drill string 12 of this invention. A drill bit 13 is affixed
to the lower end of the drill string 12. The drilling bit 13 is
driven by drill string 12 which transmits rotary power to the bit
13 from a rotary drive means, such as rotary table 14 on the
earth's surface.
The drill string 12 comprises an upper pipe segment 15, which
preferably is a string of telemetering drill pipe and drill collars
having an insulated electrical conductor provided with the pipe,
such as the telemetry drill pipe described in the aforementioned
patent to Fontenot. The upper pipe segment 15 is joined to a
preferably telemetering kelly 16 which is in turn driven by a kelly
bushing 17 which matingly engages the rotary table 14. The drill
string 12 can also comprise a lower pipe segment 20 adjacent the
drill bit which may comprise one or more joints of drill pipe
and/or one or more drill collars. The lower pipe segment 20 or the
bit 13 is coupled in driven relationship to the upper pipe segment
15 by directional control or bending sub 21.
The directional control sub 21 comprises a universal coupling
capable of transmitting rotation from the upper pipe segment 15 to
the lower pipe segment 20 when the pipe segments 15 and 20 are not
co-linear. It additionally comprises means for adjusting the angle
of axial intersection of the upper pipe segment 15 and the lower
pipe segment 20, and means for maintaining a selected angle of
intersection and direction of deflection constant with respect to a
non-rotating coordinate system.
FIG. 2 illustrates one preferred embodiment of the directional
control sub 21. The sub 21 of this embodiment comprises top portion
22 and bottom portion 23 provided with coupling means such as
threaded connections 24 and 25 for coupling the sub 21 to the upper
pipe segment 15 and the lower pipe segment 20. The top portion 22
of the sub 21 comprises an axial-piston at least four piston (see
FIG. 4), such as piston 27 and 28 (FIG. 2), slideably mounted in a
housing 29 for reciprocal motion in a direction parallel to the
central axis of the top portion 22 of the sub 21. The pistons 27
and 28 are connected by connecting rods 31 and 32, respectively, to
a control flange 30 which is affixed, as by welding, to the lower
portion 23 of the sub 21. The control flange 30 may have a central
opening or hole 30a through which drilling mud may pass. The
connecting rods 31 and 32 may be pivotably attached to pistons 27
and 28 and are preferably pivotably attached to the control flange
30 for pivotable movement in any direction. For example, the
connecting rod 31 and 32 may carry ball members 33 and 34 at the
ends of the rods opposite the piston 27 and 28. The ball members 33
and 34 may be pivotably mounted in socket members 35 and 36 which
are fixedly attached to the control flange 30. The axial-piston
machine 26 preferably is provided with a central throughbore 37
through which drilling mud may pass.
The lower portion 23 of the sub 21 is connected to the upper
portion 22 by means of a pivotable connection such as ball joint 38
which comprises a socket portion 39 carried by the upper portion 22
of the sub 21 and a hollow semi-spherical ball portion 39a affixed
to the lower portion 23 and pivotably held by the socket 39. The
diameter of the outer surface of ball 39a is preferably
sufficiently smaller than the diameter of the inner surface of the
socket 39 to allow some drilling mud to leak out of the sub 21
through the joint 38, thereby lubricating the joint 38.
The bottom portion 23 of the sub 21 preferably carries an angle
measuring means such as inertial reference means 72 capable of
sensing the orientation of the bottom portion 23 of the sub 21 with
respect to vertical and north. It may be advantageous to dispose
this inertial reference 72 in the lower pipe segment 20 near the
bit 13 if the sub 21 is positioned a significant distance above the
bit 13. The reference 72 may be coupled to a display means 61 (FIG.
1) at the surface by means of a circuit which comprises an
insulated electrical conductor 62 in the sub 21 coupled to the
electrical conductor of the telemetering upper pipe segment 15. The
display means 61 is preferably of a type adapted to display the
orientation of the bottom portion 23 of the sub 21 with respect to
both vertical and horizontal axes. For example, the display means
62 may project a beam 63 on a round screen 64 which beams 63 moves
radially away from the center of the screen 64 in the direction of
deflection as the bottom portion 23 of the sub 21 is deflected from
the vertical.
The pistons 27 and 28 are driven by a drive means such as a
positive displacement pump 40, shown in block form on FIG. 2. The
pump 40 discharges fluid at high pressure through a conduit 91 into
an annular high pressure chamber 42. The high pressure chamber 42
opens into the cylinders 43 and 44 which house the pistons 27 and
28. Fluid flow form the high pressure chamber 42 into the cylinders
43 and 44 is controlled by inflow valves 45 and 46. The inflow
valves 45 and 46, for example, can be poppet or reed valves or
piston type valves affixed to valve stems 47 and 48 which are
slideably mounted in the housing 29. The valves 45 and 46 are
operatively connected to valve drive means for opening and closing
the valves. For example, the valve drive means may include
hydraulic means, electrical means, or mechanical means such as cams
49 and 50 which are adapted to open and close the inflow valves 45
and 46 under the control of an appropriate electrical signal.
The intake of the pump 40 draws fluid through a conduit (not shown)
from an annular low pressure chamber 51 which is in fluid
communication with, and acts as the fluid discharge from, the
cylinders 43 and 44 of the axial-piston machine 26. Fluid flow from
the cylinders 43 and 44 into the low pressure chamber 51 is
controlled by exhaust valves 52 and 53 which can be, for example,
poppet or reed valves or piston type valves affixed to valve stems
54 and 55. The valve stems 54 and 55 are slideably mounted in the
housing 29 and are operatively connected to valve drive means for
opening and closing the exhaust valves 52 and 53. The valve drive
means may, for example, include hydraulic means, electrical means,
or mechanical means such as cams 56 and 57 which are adapted to
open and close the inflow valves 45 and 46.
The positive displacement pump 40 is preferably driven by a
downhole power source 58 of a conventional type. For example, the
power source 58 can be a fluid turbine of the type which may be
driven by drilling mud pumped down the drill string 12 and through
the sub 21 from the earth surface, or the power source 58 can be a
down hole electric motor of the type used in "electro-drilling".
The particular power source used is not critical to the present
invention.
The control sub 21 is advantageously provided with means for
maintaining the pressure in the high pressure chamber 42
substantially constant regardless of the rate at which the pump 40
is pumping fluid. For example, the high pressure chamber 42 can be
coupled to the low pressure chamber 51 by a conduit (not shown) in
which an adjustable constant-pressure inlet valve is disposed. The
adjustable inlet valve is preferably of a type which opens to fluid
flow when the inlet pressure, i.e., the pressure in high pressure
chamber 42, exceeds a preselected value.
The valve drive means, cams 49, 50, 56 and 57 in FIG. 2, preferably
are operatively associated with a timing means 71 mounted in the
sub 21 for synchronizing the motion of the pistons 27 and 28 both
with one another and with the rotation of the sub 21. Preferably,
the pistons complete one full reciprocating cycle each time the
bottom portion 23 of the sub 21 completes one revolution. In this
way the pistons maintain the control flange 30 in a fixed plane as
the drill string 12 is rotated to drive the bit 13, the plane being
fixed with respect to a non-rotating coordinate system such as the
system defined by the central axis of the upper portion 22 and a
pair of orthogonal lines intersecting this axis at right angles. If
the top portion 21 is vertical, the pair of orthogonal lines may be
north -- south and east -- west axes.
The manner in which the angle is maintained may be understood by
referring to FIGS. 3 and 4 which show the sub 21 operating with the
bottom portion 23 disposed at an angle .THETA. with respect to the
top portion 22. FIG. 4 is a cut-away view looking in the direction
of arrow 65 of FIG. 3 (i.e., north). We can see in FIG. 4 that the
sub comprises four pistons 27, 28, 66 and 67 disposed in housing 29
which is mounted in the top portion 22 of the sub 21. The pistons
are connected by connecting rods, such as rods 31, 32 and 68, to
the control flange 30.
In the embodiment of the sub 21 illustrated, as the top portion is
rotated, torque is transmitted to the control flange 30 via the
pistons and connecting rods. Therefore, the bottom portion 23
rotates with the top portion 22. Thus the axial-piston machine 26,
control flange 30, and ball joint 38 in combination act as a
universal coupling means for transmitting rotation from the top
portion 22 to the non co-axial bottom portion 23 of the sub 21.
Additionally, the orientation of control flange 30 with respect to
a reference non-rotating three dimensional coordinate system will
be maintained constant if each of the pistons 27, 66, 28 and 67 is
always in the same position relative to the cylinder 43, 69, 44,
70, respectively, in which it moves when that cylinder occupies a
given position within the reference coordinate system. For example,
if the reference coordinate system comprises vertical, north-south,
and east-west axes and if in FIG. 4 cylinders 69 and 70 intersect
the north-south axis and cylinders 43 and 44 intersect the
east-west axis with cylinder 70 to the north, then the orientation
of control flange 30 will remain constant with respect to the
reference coordinate system as the sub 21 rotates if the piston in
each cylinder attains the top of its reciprocating cycle (as has
piston 67) as the center of that cylinder crosses the north axis
and if the piston attains the other relative positions illustrated
as the center of the cylinder crosses the east, south, and west
axes, respectively. This means the pistons must complete one full
reciprocating cycle each time the sub 21 turns once.
Therefore, to maintain the northward deflection of the bottom
portion 23 of the sub 21 (as shown in FIGS. 3 and 4) as a cylinder,
such as cylinder 43 in FIG. 4, rotates from north to south, the
fluid inflow valve 45 of that cylinder should be open (and the
exhaust valve 52 closed) to admit high pressure fluid from high
pressure chamber 42 to drive cylinder 27 downward. Similarly as a
cylinder, such as cylinder 44 of FIG. 4, rotates from south to
north the exhaust the exhaust valve 53 of that cylinder should be
open (and the inflow valve 47 closed) to allow fluid to flow out of
the cylinder 44 in a control manner into the low pressure chamber
51 so that the piston 28 may move upwardly relative to the cylinder
44.
FIG. 5 shows in block form the elements of a timing means of a type
which may be used to synchronize the motion of the pistons 27, 28,
66 and 67. The timing means 71 comprises a position signal
generating means which is capable of generating a signal
proportional to the angular position of a point of interest on the
rotating sub 21 with respect to a reference such as the center of a
gimbled gyroscopic platform. For example, the inertial reference 72
in addition to functioning as an angle measuring means may generate
a signal which varies as the angular displacement of a reference
point, for example a cylinder such as cylinder 44 of the axial
piston machine 26, varies with respect to the center of the timing
means 71.
The inertial reference 72 is coupled to a value control signal
generator 73 which is in turn coupled to the various valve drive
means such as cams 49, 50, 56 and 57. The valve control signal
generator 73 is preferably a pre-programmed device for generating
appropriate signals to the respective valve drive means in response
to the angular position of reference cylinder 44 as indicated by
the inertial reference output. For example, in response to a signal
which indicates that cylinder 44 is rotating past a north-directed
axis, the valve control signal generator 73 may generate an
appropriate signal to couple the cams 49, 50, 56, and 57 (FIG. 2)
with a power source 74 in such a way that the cams move causing
inflow valve 45 and exhaust valve 53 to open and exhaust valve 52
and inflow valve 46 to close so that piston 27 is forced downwardly
and piston 28 moves upwards in a controlled manner in the housing
29. The power source 74, for example, may be a source of electrical
power 93 at the earth surface coupled to the valve control signal
generator 73 by means which include telemetering upper pipe segment
15 or may be a generator driven by down hole power source 58.
Similarly in response to a signal which indicates cylinder 44 is
rotating past a south-directed axis the valve control signal
generator 73 may generate an appropriate signal to couple the cams
49, 50, 56 and 57 with the power source 74 in such a way that the
cams move causing inflow valve 45 and exhaust valve 53 to close and
exhaust valve 52 and inflow valve 46 to open so that piston 28 is
forced downwardly and piston 27 moves upwardly in the housing 29.
Thus the timing means 71 controls the valves in such a way that the
pistons 27 and 28 complete one reciprocating cycle each time the
sub 21 completes one revolution. It should be understood that
pistons 66 and 67 are controlled in a similar manner by valve
control means 73 in cooperation with appropriate valve drive means
for these cylinders.
As can be seen in FIG. 4, and as described above, the deflection of
the bottom portions 23 of the sub 21 with respect to the top
portion 22 will be to the north if each of the pistons 27, 28, 66
and 67 reaches the peak of its reciprocating cycle as it rotates
past north. To change the direction of the deflection of the bottom
portion 23 with respect to the top portion it is necessary to
change the phase of the reciprocal movement of the pistons with
respect to the rotation of the sub 21 so that each piston reaches
the peak of its reciprocating cycle as it rotates past the desired
direction of deflection. Such a phase change may be achieved by
associating with the valve control signal generator 73 a phase
adjust means 75 capable of adjusting the phase of signals generated
by the valve control signal generator with respect to the angular
rotation of the sub 21. The phase adjust means 75 may be, for
example a delay circuit capable of delaying the signal from
inertial reference 72 for a time corresponding to the angular
rotational phase delay desired. Another example of a suitable phase
adjust means is an adjustable detector means or sensor capable of
detecting a signal from the inertial reference 72 indicating a
desired direction of deflection and generating an appropriate
signal to the respective valve drive means (via the valve control
signal generator 73) to orient the sub 21 in the desired
direction.
The phase adjust means 75 is advantageously coupled by appropriate
circuit means to phase controller 76 at the earth surface. The
circuit means may comprise the insulated conductor of telemetering
upper pipe segment 15.
The angle of deflection of the directional control sub 21 may be
adjusted by regulating the amplitude of the reciprocating motion of
the pistons. This can be achieved by adjusting the amount of the
fluid allowed to flow into and out of the cylinders 43, 44, 69 and
70. Such an adjustment may be made by adjusting the length of time
of opening and closing of the valves 45, 46, 52 and 53 to allow
greater or lesser amounts of fluid to enter or leave the cylinders.
An amplitude adjust means 59 can be associated with the valve
control signal generator for adjusting this length of time. The
amplitude adjust means 79 advantageously is coupled via electrical
conductor 62 and telemetering upper pipe segment 15 with a
deflection amplitude controller 92 at the earth surface. The
amplitude controller is preferably associated with a display means
coupled to the inertial reference 72 on the sub 21.
The power source 93, phase control 76 and deflection amplitude
control 92 may, if desired, all be coupled to the sub 21 by means
of a signal electrical circuit circuit in the telemetering upper
pipe segment 15 via a multiplex transmitting means of a well known
type.
To practice the method of this invention with the above-described
apparatus, the drill string 12 and bit 13 are lowered into the well
bore hole 11. The rotary table 14 is turned to rotate the drill
string 12 and bit 13 and thereby advance the bore hole 11 into the
earth. While drilling is progressing signals from the deviation
sensor in the bottom portion of the directional control sub 21 are
telemetered up the upper pipe segment 15 and displayed on display
means 61. When the displayed angle or direction of deflection of
the bending sub 21 indicates that the bore hole 11 is deviating
from the desired path or when a change in path is desired, the
deflection amplitude control 92 or phase control 76 can be
appropriately adjusted to change the angle or direction of
deflection of the bending sub 21 to direct the drill string 12 in
the desired direction.
* * * * *