U.S. patent application number 11/945383 was filed with the patent office on 2009-05-28 for method and apparatus for hydraulic steering of downhole rotary drilling systems.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to RADOVAN ROLOVIC.
Application Number | 20090133931 11/945383 |
Document ID | / |
Family ID | 40668759 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133931 |
Kind Code |
A1 |
ROLOVIC; RADOVAN |
May 28, 2009 |
METHOD AND APPARATUS FOR HYDRAULIC STEERING OF DOWNHOLE ROTARY
DRILLING SYSTEMS
Abstract
A method for hydraulically controlling the direction of a drill
bit or bottom hole assembly containing a drill contains lateral
orifices which can be selectively opened and closed to move a
portion of drilling fluid from the drill string out into a narrow
gap between the lateral orifices and a lateral bore hole face or
wall, which produces a lateral hydraulic force to thereby push the
drill bit or bottom hole assembly in an opposite direction of the
fluid flow through the lateral orifices. The apparatus for
accomplishing this hydraulic steering can provide for the movement
of the tip of the orifice into close proximity with the bore hole
face to thereby increase the lateral hydraulic force created. This
method can also be adapted to push-the-bit bore hole pads to
minimize their contact with the bore hole while increasing the
lateral force obtained by their engagement.
Inventors: |
ROLOVIC; RADOVAN;
(Cheltenham, GB) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
200 GILLINGHAM LANE, MD 200-9
SUGAR LAND
TX
77478
US
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
Sugar Land
TX
|
Family ID: |
40668759 |
Appl. No.: |
11/945383 |
Filed: |
November 27, 2007 |
Current U.S.
Class: |
175/26 |
Current CPC
Class: |
E21B 7/065 20130101 |
Class at
Publication: |
175/26 |
International
Class: |
E21B 44/00 20060101
E21B044/00 |
Claims
1. A method for hydraulic steering of a drill bit comprising:
setting an angular direction from a longitudinal axis of a bottom
hole assembly providing the drill bit; and, opening one or more
lateral orifices at a selected interval to divert drilling fluid
from the drill bit to provide motive hydraulic force in an angular
direction opposite the angular direction required for forward
progress of the drill bit toward the set direction.
2. The method of claim 1 further comprising determining a direction
for forward progress of a drill bit and directing the flow of
drilling fluid from the orifices toward a lateral face of a well
bore.
3. The method of claim 1 further comprising determining a direction
for forward progress of a drill bit and directing the flow of
drilling fluid from the orifices to a universal joint sleeve
connected to a drill bit to move the drill bit in set
direction.
4. The method of claim 1 further comprising adjusting a gap between
a distal tip of the orifices and a well bore face to increase a
force applicable to move the bottom hole assembly in an opposite
direction.
5. The method of claim 1 further comprising adjusting a gap between
a distal tip of the orifices and a universal joint sleeve to
increase a force applicable to move the bottom hole assembly in an
opposite direction.
6. The method of claim 1 further comprising diverting a portion of
drilling fluid through a lateral pad of a rotary steerable drill
bit system to direct additional force against a lateral bore hole
wall.
7. The method of claim 1 further comprising diverting a portion of
drilling fluid through one or more lateral orifices to direct the
drill bit and the entire drilling BHA straight ahead along the
longitudinal axis of the drilling BHA.
8. The method of claim 1 further comprising using a control
module/unit to measure and process drilling parameters, direction
and orientation of the BHA, and using that information to control
opening and closing of said lateral orifices to achieve the desired
drilling direction.
9. A directional drilling bottom hole assembly comprising: a bottom
hole assembly; one or more lateral orifices circumferentially
spaced around said bottom hole assembly; and, activation valves to
selectively open and close said lateral orifices to provide lateral
hydraulic force on said directional drilling bottom hole
assembly.
10. The directional drilling bottom hole assembly of claim 9
wherein the bottom hole assembly comprises a drill bit and a
control unit.
11. The directional drilling bottom hole assembly of claim 9
wherein the bottom hole assembly comprises a control unit located
adjacent a drilling motor.
12. The directional drilling bottom hole assembly of claim 9
wherein the lateral orifices are located in the drill bit body.
13. The directional drilling bottom hole assembly of claim 9
wherein the lateral orifices are located in the hole gauge section
of the drill bit assembly.
14. The directional drilling bottom hole assembly of claim 9
wherein the lateral orifices are located in a separate BHA section
between the drill bit and the control unit.
15. The directional drilling bottom hole assembly of claim 9
wherein the lateral orifices are located in a section that is
integral part of a control unit.
16. The directional drilling bottom hole assembly of claim 9
wherein the lateral orifices are located inside a universal joint
sleeve connected to a drill bit in a point-the-bit drilling
assembly.
17. The directional drilling bottom hole assembly of claim 9
wherein the bottom hole assembly comprises a push-the-bit drilling
assembly and wherein the lateral orifices are in a control pad.
18. The directional bottom hole assembly of claim 9 wherein the
bottom hole assembly comprises a mechanism for adjusting a gap
between a distal tip of the lateral orifices and a well bore face
or a universal joint sleeve to increase a force applicable to move
the bottom hole assembly in an opposite direction.
19. The directional bottom hole assembly of claim 9 wherein the
bottom hole assembly comprises a mechanism for diverting a portion
of drilling fluid through lateral orifices to direct the drill bit
and the entire drilling BHA straight ahead along the longitudinal
axis of the drilling BHA.
20. The directional bottom hole assembly of claim 9 wherein the
bottom hole assembly comprises a control module/unit to measure and
process drilling parameters, direction and orientation of the BHA,
and uses that information to control opening and closing of said
lateral orifices to achieve the desired drilling direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a directional rotary
drilling method and apparatus; specifically, to a method and
apparatus for moving a drill bit in a desired path by selectively
adjusting a portion of drilling fluid flow through orifices located
adjacent a drill bit body to apply a lateral hydraulic force and
minimize contact with a bore hole with mechanical guides.
[0003] 2. Related Art
[0004] All methods known to applicant use some manner of mechanical
contact with the well bore to achieve the desired steering of the
drilling tool, or as in the case of point-the-bit methods, the
steering is achieved by offsetting the angle of the drill bit axis
relative to the rest of the drill tool. Fluid pressure necessary to
cause fluid flow through changing flow geometries (orifices, bends,
narrow passages, conduits, etc.) commonly described as pressure
loss is typically considered a negative effect of changing flow
conditions because it often requires alternative design
requirements. That same changing fluid flow conditions is used in
the described method and apparatus to create a pressure
differential between the two sides of the drilling tool and thereby
achieve a desired lateral force on the drilling tool useable for
steering the tool in the given direction. There have been attempts
to use changing directional fluid flows that are different than
this invention and not intended to use the hydraulic pressure
difference around the drilling tool for steering the tool in the
preferred direction. See U.S. Pat. No. 4,836,301 as an example of
these types of fluid directing systems, which uses changing
direction of drilling fluid flow inside the drilling tool to
generate a hydrodynamic force to tilt the drill bit axis in a given
direction using a point-the-bit steering method and system.
SUMMARY OF THE INVENTION
[0005] A method for hydraulic steering of a drill bit is described
which provides the steps of setting an angular direction from a
longitudinal axis of a bottom hole assembly providing the drill
bit; and, opening one or more lateral orifices at a selected
interval to divert drilling fluid from the drill bit to provide
motive hydraulic force in an angular direction opposite the angular
direction required for forward progress of the drill bit toward the
set direction. The method can further comprise adjusting a gap
between a distal tip of the orifices and a universal joint sleeve
to increase a force applicable to move the bottom hole assembly in
an opposite direction.
[0006] This method can further provide for determining a direction
for forward progress of a drill bit and directing the flow of
drilling fluid from the orifices toward a lateral face of a well
bore in a manner currently practiced in directional drilling
programs.
[0007] Where the point-the-bit directional drilling apparatus is
used, this method can include determining a direction for forward
progress of a drill bit and directing the flow of drilling fluid
from the orifices to a universal joint sleeve connected to a drill
bit to move the drill bit in set direction. Since the lateral
hydraulic force exerted by the drilling fluid flow through the
lateral orifices is a function of the distance from the distal tip
of the orifice to the opposing well bore face, this method can also
provide the steps of adjusting a gap between a distal tip of the
orifices and a well bore face to increase a hydraulic force
applicable to move the bottom hole assembly in an opposite
direction, or diverting a portion of drilling fluid through a
lateral pad of a rotary steerable drill bit system to direct
additional force against a lateral bore hole wall.
[0008] A directional drilling bottom hole assembly used to practice
the method of this invention is a bottom hole assembly having one
or more lateral orifices circumferentially spaced around said
bottom hole assembly, and activation valves to selectively open and
close said lateral orifices to provide lateral hydraulic force on
said directional drilling bottom hole assembly. The directional
drilling bottom hole assembly can further provide in the bottom
hole assembly a drill bit and a control unit for sensing and
controlling drilling fluid flow through the lateral orifices which
control the movement of the assembly while drilling. This may be
controlled either from the surface by the collection and
transmission of data or using auto-steering techniques to control
the direction based upon sensor input.
[0009] The directional drilling bottom hole assembly can be
entirely located in a control unit located adjacent a drilling
motor. Alternatively, the directional drilling bottom hole assembly
can be adapted to a standard push-the-bit drilling assembly by
providing orifices in each control pad to selectively and lateral
forcefully move drilling fluid against the borehole thereby
minimizing wear on the pads to achieve directional control.
[0010] The method can additionally further comprise diverting a
portion of drilling fluid through a lateral pad of a rotary
steerable drill bit system to direct additional force against a
lateral bore hole wall or diverting a portion of drilling fluid
through one or more lateral orifices to direct the drill bit and
the entire drilling BHA straight ahead along the longitudinal axis
of the drilling BHA. This method can further be accomplished by
using a control module/unit to measure and process drilling
parameters, direction and orientation of the BHA, and using that
information to control opening and closing of said lateral orifices
to achieve the desired drilling direction.
[0011] The present invention also encompasses a directional
drilling bottom hole assembly comprising: a bottom hole assembly;
one or more lateral orifices circumferentially spaced around said
bottom hole assembly; and, activation valves to selectively open
and close said lateral orifices to provide lateral hydraulic force
on said directional drilling bottom hole assembly. This embodiment
can also be realized wherein the bottom hole assembly comprises a
drill bit and a control unit or wherein the bottom hole assembly
comprises a control unit located adjacent a drilling motor or
wherein the lateral orifices are located in the drill bit body.
[0012] The apparatus of this embodiment can also provide the
lateral orifices either located in the hole gauge section of the
drill bit assembly, or in a separate BHA section between the drill
bit an the control unit or in a section that is integral part of a
control unit. Additionally, this apparatus can provide the lateral
orifices inside a universal joint sleeve connected to a drill bit
in a point-the-bit drilling assembly thereby permitting the
hydraulic pressure to move the sleeve in the desired direction. The
directional drilling bottom hole assembly can be accomplished
wherein the bottom hole assembly comprises a push-the-bit drilling
assembly and wherein the lateral orifices are in a control pad or
wherein the bottom hole assembly comprises a mechanism for
adjusting a gap between a distal tip of the lateral orifices and a
well bore face or a universal joint sleeve to increase a force
applicable to move the bottom hole assembly in an opposite
direction.
[0013] The directional bottom hole assembly apparatus of this
invention can also provide the bottom hole assembly which provides
a mechanism for diverting a portion of drilling fluid through
lateral orifices to direct the drill bit and the entire drilling
BHA straight ahead along the longitudinal axis of the drilling BHA.
Finally, the bottom hole assembly of this invention can comprise a
control module/unit to measure and process drilling parameters,
direction and orientation of the BHA, and uses that information to
control opening and closing of said lateral orifices to achieve the
desired drilling direction.
[0014] Possible benefits/advantages of the proposed drilling tool
steering method and apparatus are: [0015] Simpler tool
design--elimination of many parts, subassemblies and manufacturing
processes, such as clamp plate subassemblies, kickers, pads,
pistons, toroidal bore, hardfacing, nuts and bolts and other parts
currently needed to achieve the push-the-bit force used for
steering drilling tools. [0016] Elimination or minimization of wear
of outer bias or steering unit parts due to fluid-only contact with
the abrasive borehole. [0017] Substantial reduction of shock loads
on the drilling bottom-hole assembly (BHA), because the fluid used
to produce the lateral hydraulic force would absorb much of shock
loading thereby increasing BHA reliability. [0018] Substantially
lower cost of new bias or steering units because of fewer parts and
manufacturing processes. [0019] An order of magnitude reduction in
service and maintenance cost because there would be no bias or
steering unit parts exposed to the borehole contact (no clamp plate
assemblies, kickers, pads, pistons, toroidal bores, nuts and bolts,
etc. that currently need to be replaced regularly) [0020] Smoother
borehole--no pads to scrape it. [0021] Faster rate of penetration
and reduced drilling time--more torque is available for drilling
because there is little or no mechanical contact of the bias or
steering unit with the borehole to consume torque while steering
the BHA. [0022] Improved reliability of drilling operations--fewer
parts, as well as no moving parts on the outside of the BHA, no
lost-in-hole parts, etc. [0023] Improved steering through softer
formations because the lateral force used for steering is
distributed as pressure only and over a much larger borehole area.
[0024] Improved opportunity to operate at higher temperature
because of the elimination of elastomer parts
[0025] The steering of the drilling tool is achieved by applying
hydraulic forces to one side of the tool, thus achieving the
steering of the tool in the opposite side direction. A portion of
drilling fluid (mud) is diverted through a number of lateral
orifices and through a narrow gap between the tool steering section
and the bore hole. Only orifices on one side of the tool are opened
at a time to provide a pressure differential in the tool-borehole
annulus between that and the opposite side of the tool, thus
creating a side hydraulic force on the tool, which steers the tool
in the opposite side direction. The pressure differential is
achieved mainly by the pressure needed to push a certain amount
(flow rate) of drilling fluid through the fight gap between the
tool and the borehole. The pressure needed to push the fluid
through the narrow tool-borehole gap is provided by the pressure
difference between the inside and the outside of the drilling tool.
The new approach requires a controlled flow of part of drilling mud
through the steering system and out into the tool-borehole annulus
through the narrow annular gap.
BRIEF DESCRIPTION OF THE FIGURES
[0026] FIG. 1 is a schematic diagram of the lateral orifice
arrangement located in a drill bit.
[0027] FIG. 2 is a schematic diagram of the lateral orifice
arrangement located in a bottom hole assembly.
[0028] FIG. 3 is a schematic diagram of an adjusting orifice body
which moves the distal tip of the orifice closer to a lateral well
bore face.
[0029] FIG. 4 is a schematic diagram of a point-the-bit rotary
steering system using the hydraulic force from the orifice to move
fluid against a pivot arm of the bit.
[0030] FIG. 5 is a schematic diagram of an orifice arrangement in
the body of a directional drilling control pad.
[0031] FIG. 6 is a graph describing the expected relation between
the annular gap and the lateral hydraulic force at various flow
rates.
[0032] FIG. 7 is a graph describing the expected relation between
the lateral flow rate and the lateral hydraulic force at various
gap distances.
DETAILED DESCRIPTION
[0033] As shown in FIG. 1, a method for hydraulic steering of a
down hole drilling tool without the mechanical contact of the tool
steering section with the bore hole 100 is presented herein.
Substantial lateral hydraulic force on a down hole tool can be
achieved by the diversion of a portion of a drilling fluid that is
forced to flow out on one side of the tool into the relatively
small annular gap h between the lateral edge of the tool 10 and the
bore hole 100. As more fully shown in the schematic drawing of FIG.
1, the pressure differential created this way around the tool/bit
50 in the tool-borehole annulus 110 can produce a large lateral
force, depending on the geometry of the flow (the gap width h and
length, size of the lateral fluid exit hole, etc.), pressure
differential between the inside of the tool and the outside of the
tool, fluid properties, and other factors. The lateral force on the
tool and/or the bit 50 created this way can be sufficient to
provide steering of down hole drilling systems. The hydraulic
lateral force can be achieved by using a design that is similar to
the current bias or steering unit design, but which has a plurality
of lateral orifices 40 (only one of which is shown in this
cross-sectional view), instead of the current pad-piston assembly.
The lateral orifice 40 exit area needs to be sufficiently close to
the borehole wall or face 100 to ensure a sufficiently small gap h
between the lateral edge of the tool body 10 where the side orifice
40 is located and the borehole 100 in order to provide enough
pressure differential around the tool in the tool-borehole annulus
110. The lateral force can also be achieved with lateral orifices
40 placed in the hole gauge 10 next to the drill bit 50 itself,
where a smaller gap h between the tool 50 and the borehole 110 is
easier to maintain during drilling (the smaller the gap, the bigger
the hydraulic side force).
[0034] As the entire drilling BHA is rotated during drilling,
including the lateral orifices, one or more lateral orifices are
open only when they are approximately opposite to the desired
change in drilling direction, while all other lateral orifices are
closed until they get approximately opposite to the desired change
in drilling direction as the entire BHA rotates around its
longitudinal axis. The corresponding opening and closing of the
lateral orifices, or opening and closing of the drilling fluid
paths to these orifices, can be achieved and controlled by using
existing methods for opening and closing fluid paths to the
steering pads of a traditional bias or steering unit and
controlling the process with a traditional control unit that
performs necessary measurements and provides control and steering
functions. For example, a counter-rotating valve that rotates at
the same rotational speed as the drilling BHA but in the opposite
direction can be used to open and close the drilling fluid path to
the lateral orifices, thus keeping the fluid flow through the
lateral orifices geo-stationary, i.e. in the same relative
direction/orientation to the earth, while the rest of the drilling
BHA rotates relative to the earth. The drilling fluid flow through
the lateral orifices is kept geo-stationary in the lateral
direction that is opposite to the desired change in drilling
direction.
[0035] The desired opening and closing of the lateral orifices or
the fluid paths to these orifices also can be achieved by other
means, such as a piston or valve mechanism controlled from the
control unit that measures the relative BHA position and
orientation in real time, or by other means.
[0036] The described methods and mechanisms can also be used to
direct the drilling BHA to drill straight ahead in a straight line
along its longitudinal axis. For example, the rotary valve
described above can be used to direct the drilling fluid flow to
one or more lateral orifices to achieve the desired lateral
hydraulic force and the corresponding drill bit movement in the
opposite direction. When the rotary valve is not kept
geo-stationary but instead it is rotated fully or partially with
the rest of the BHA, or partially counter rotated relative to the
BHA, the drilling fluid is effectively directed to the lateral
orifices while they are in various orientations to the earth, thus
applying the lateral hydraulic force in all directions around the
bore hole and thus directing the drilling BHA straight ahead along
its longitudinal axis. Another way of directing the BHA to drill
straight ahead is to open all the lateral orifices at the same
time, or to close all lateral orifices while drilling straight and
switch back to the steering mode when the BHA starts to deviate
from the straight path.
[0037] In another embodiment as shown in FIG. 4, the proposed
method can be used to achieve steering of a drilling tool 51 by
discharging a portion of the drilling fluid into the tool-borehole
annulus on one side of the drilling tool between two integral parts
of the down hole tool itself, for example, between the tool inner
body 52 and an outer sleeve 53 connected together with a universal
joint UJ, where the outer sleeve 53 is connected to the bit shaft
54, and where an angular offset of the sleeve 53 and the bit axis
relative to the tool inner body axis, which provides the desired
steering of the bit, is achieved by a similar hydraulic force. By
opening the lateral orifices only when they are opposite to the
desired change in the drilling direction as the BHA rotates, and by
using one of the methods described above for controlling the
opening and closing of the lateral orifices, the outer sleeve 53
and the drill bit axis are kept at an angular offset relative to
the rest of the BHA, which steers the tool in the direction of the
angular offset that is kept geo-stationary in the desired drilling
direction.
[0038] Current directional drilling systems use a down hole mud
motor with a bend sub or a rotary steerable system (RSS) with a
steering section to create a 2-D or a 3-D well bore trajectory. RSS
systems have many advantages over mud motor systems and are used
for most drilling applications today. The current RSS systems use
push-the-bit or point-the-bit approaches to achieve the desired
steering of the drilling tool.
[0039] Most of the today's drilling market is covered by systems
using the push the bit technology, which uses mechanical pads 200,
an example of which is partially shown in FIG. 5, that extend
radially from the drilling tool and push against the borehole 100
to achieve a side force on the tool that in turn forces the bit to
drill in the same direction of the side force acting on the tool.
The principal problem with these pad systems is high wear that
results from contacts with the borehole 100, which results in a
high manufacturing and repair cost and therefore an overall higher
cost of service delivery. The novel approach proposed herein
minimizes mechanical contacts with the bore hole for steering
purposes.
[0040] Pressure drop test data show that a large pressure
differential and thus a large lateral force could be achieved with
the currently used pressure difference between the inside and the
outside of the drilling tool and with a fraction of the current
overall flow rate of the drilling fluid. FIGS. 6 and 7 summarize
this relationship.
[0041] Steering of the drilling tool or drill bit can be achieved
by applying hydraulic forces to one side of the tool, thus
achieving the steering of the tool in the opposite direction. The
concept of the proposed invention can be explained by using FIG. 2.
A portion of drilling fluid (mud) is diverted through a lateral
orifice (Q.sub.s) and into a narrow gap (h) between the tool
steering section 11 and the borehole 100. Only orifices 40 on one
side of the tool are opened for the lateral fluid flow (Q.sub.s) at
a time to provide a pressure differential between that and the
opposite side of the tool (p.sub.1-p.sub.2), thus creating a
lateral hydraulic force on the tool and the bit (F.sub.s), which
steers the tool and the bit in the opposite direction of the side
flow Q.sub.s. The pressure differential is achieved principally by
the pressure required to push a certain amount of drilling fluid
(at fluid flow rate--Q.sub.s) through the tight gap between the
tool and the borehole (dimension h in FIG. 2). The pressure needed
to push the fluid through the narrow tool-borehole gap h is
provided by the pressure difference between the inside p.sub.o and
the outside of the drilling tool p.sub.2.
[0042] In another embodiment the lateral discharge of portion of
the drilling fluid Q.sub.s can be forced into an even tighter
annular gap h between the bit hole gauge section 10 and the bore
hole 100 on an adjacent lateral side of the drill bit 50 as shown
in FIG. 1. In this manner, a higher lateral hydraulic force F.sub.s
for steering the bit can be achieved with less fluid loss. Also,
this system may be less complex because it would eliminate the need
for an entirely separate steering section/module of the downhole
tool. For example, the flow control mechanism, e.g. a rotary valve,
can be part of the control unit, and the lateral orifices used for
steering can be part of the drill bit assembly. Traditionally,
there is a separate steering section/module, e.g. a bias unit,
between the drill bit and the control unit. If the annular gap (h)
between the tool 50 in FIG. 1 or 11 in FIG. 2 and the borehole 100
is too large or may change significantly during drilling, a
modified orifice body, an example of which is shown in FIG. 3, can
be used to provide a self-adjusting tight annular gap (h). The
fluid pressure on the inner end of the adjustable adapter p.sub.o
would push the adapter 300 radially outwards, reducing the annular
gap (h) in the process. When the annular gap h is small enough to
produce fluid pressure on the outer end of the adapter 300 (in the
gap h) which produces an inward force on the adaptor end that is
equal to the outward force on the adaptor from the inner fluid
pressure, the adaptor reaches an equilibrium state resulting in an
annular gap (h) that can be smaller than those described in the
previous examples. The size of the adjustable gap (h) mainly
depends on the geometry of the adaptor, geometry of the fluid flow,
and the pressure difference between the inside and the outside of
the drilling tool. Thus, a desired, self-adjusting annular gap h
can be achieved and maintained by carefully specifying and
controlling these parameters. When the adapter 300 is not used for
steering purposes, and to prevent it from protruding radially out
of the BHA too much, a spring, or an elastomer or other means can
be used to keep the adapter in its inner-most position inside the
BHA, example of which is shown in FIG. 3. In another embodiment,
the proposed method can be used to achieve steering of a drilling
tool by discharging a portion of the drilling fluid on one side of
the drilling tool between two integral parts of the down hole tool
itself, for example, between the tool inner body 52 and an outer
sleeve 53 connected together with a universal joint (UJ), as shown
in FIG. 4, where the outer sleeve 53 is connected to the bit shaft
54, and where an angular offset of the sleeve and the bit axis
relative to the tool inner body axis, which provides the desired
steering of the bit, is achieved by a similar hydraulic force. The
particular design concept in FIG. 4 can be optimized to further
restrict the exit of the fluid between the sleeve and the tool
inner body to increase the pressure (p.sub.1) between the two
parts, thus increasing the differential pressure (p.sub.1-p.sub.2)
and increasing the hydraulic lateral force F.sub.s that is used for
steering.
[0043] The proposed method also can be used with the existing
drilling tool designs to minimize the abrasion wear and tool shocks
and vibrations as shown in FIG. 5. A small amount of drilling fluid
can be discharged under pressure through the pad 200 at the
pad-bore hole interface 210 to produce a hydraulic force F.sub.s on
the pad and reduce or eliminate the mechanical contact between the
pad 200 and the bore hole 100. Because the gap between the active
pad and the bore hole is very small or basically non-existent while
the pad is pushing against the bore hole, only a small amount of
drilling fluid would need to be discharged to achieve a relatively
large hydraulic lateral force between the pad 200 and the borehole
100 and, therefore, minimize or eliminate the mechanical contact
between the pad 200 and the borehole 100.
[0044] Estimates of the lateral hydraulic forces associated with
the steering method described herein are shown in FIG. 6 and FIG.
7. The pressure in the annular gap h between the tool and the bore
hole used to calculate these lateral hydraulic forces was estimated
based on measured pressure drop data when water was pumped through
a down hole nozzle with an equivalent overall fluid discharge area
(total area of all nozzle orifices). The pressure distribution in
the annular gap was assumed to correspond to the measured pressure
drop through the down hole nozzle for the same total flow area,
i.e. the fluid flow in the annular gap h requires the same pressure
to achieve the same flow rate as the fluid flow through the nozzle
for the same flow area (total nozzle orifice area). Since the flow
area in the annular gap h progressively increases with distance
from the lateral orifice, the pressure in the gap was estimated at
various radial distances from the lateral orifice and the lateral
force was calculated as the sum of products of each discrete
pressure and the corresponding tool area. Although these
pressure-force estimates are based on test data from a different
flow system, they provide an approximation of the pressure
distribution in the annular gap h and the lateral hydraulic force
F.sub.s on the drilling system under consideration.
[0045] As can be seen from FIG. 6 and FIG. 7, lateral hydraulic
forces higher than the pad forces of a comparable commercial
drilling system, shown as Standard Pad system in FIG. 6 and FIG. 7,
can be achieved for many practical flow rates and annular gaps,
which depend on the hole size drilled, among other factors. For the
examples in FIG. 6 and FIG. 7, practical flow rates through the
lateral orifices (lateral flow rates) can be on the order of 100
gpm and the practical annular gap h can be on the order of 2 mm,
but other lateral flow rates and annular gaps can be practical as
well. For example, a tighter annular gap h can be made practical
with the method and mechanism shown in FIG. 3, thus increasing the
lateral hydraulic force even further, and reducing the required
lateral flow rate for effective steering of the drilling BHA.
[0046] Additionally, to achieve a higher pressure in the annular
gap h and, consequently, higher lateral force F.sub.s for hydraulic
steering of the drilling tool, the geometry of the annular flow can
be changed so that a higher pressure drop is achieved in the
annular gap both near and away from the lateral orifice, for the
same nominal annular gap h and the same lateral fluid flow rate
Q.sub.s. For example, the lateral flow can be discharged in the
localized annular gap at multiple points in different directions to
create a higher pressure drop and a higher pressure in a larger
annular gap area, producing a larger lateral force (e.g. multiple
lateral flows in the same annular gap would flow against each
other, thus possibly creating a higher pressure drop before the
fluid exits the annular gap area). Other ways, for example without
limitation include changing the flow and tool geometries, fluid
properties, and pressure differentials can be substituted for a
more optimized hydraulic lateral forces on the drilling tool
thereby providing adequate steering with a minimum disruption to
the fluid flow through the drill bit.
[0047] Numerous embodiments and alternatives thereof have been
disclosed. While the above disclosure includes the best mode belief
in carrying out the invention as contemplated by the named
inventors, not all possible alternatives have been disclosed. For
that reason, the scope and limitation of the present invention is
not to be restricted to the above disclosure, but is instead to be
defined and construed by the appended claims.
* * * * *