U.S. patent application number 10/018747 was filed with the patent office on 2002-10-31 for apparatus and method of oscillating a drill string.
Invention is credited to Tulloch, David William.
Application Number | 20020157871 10/018747 |
Document ID | / |
Family ID | 9890344 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157871 |
Kind Code |
A1 |
Tulloch, David William |
October 31, 2002 |
Apparatus and method of oscillating a drill string
Abstract
Apparatus and methodology for reducing frictional forces on
drilling apparatus when being progressed or retracted within a well
bore. This is achieved through mechanical or hydraulic action on
the drilling fluid to create a fluid pressure differential which is
transmitted on to the drill string via pumps, causing the drill
string to oscillate. The oscillation reduces the frictional
interface between the drill string and the well bore, thus enabling
increased depth or reach of the well bore.
Inventors: |
Tulloch, David William;
(Suffolk, GB) |
Correspondence
Address: |
Fleshner & Kim
P O Box 221200
Chantilly
VA
20153-1200
US
|
Family ID: |
9890344 |
Appl. No.: |
10/018747 |
Filed: |
December 21, 2001 |
PCT Filed: |
April 23, 2001 |
PCT NO: |
PCT/GB01/01791 |
Current U.S.
Class: |
175/56 ;
166/381 |
Current CPC
Class: |
E21B 47/16 20130101;
E21B 7/24 20130101; E21B 28/00 20130101; E21B 47/22 20200501 |
Class at
Publication: |
175/56 ;
166/381 |
International
Class: |
E21B 007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2000 |
GB |
0009848.3 |
Claims
1. Apparatus for oscillating a drill string within a well bore,
comprising one or more pumps for introducing fluid into a drill
string and a modifying means, wherein the modifying means induces a
fluid pressure differential which is transmitted to the drill
string via the pumps, and wherein the fluid pressure differential
causes said drill string to oscillate.
2. Apparatus as claimed in claim 1, wherein the modifying means is
mechanically operated.
3. Apparatus as claimed in claim 1, wherein the modifying means is
hydraulically operated.
4. Apparatus as claimed in any preceding claim, wherein the one or
more pumps communicate with at least one fluid containment
vessel.
5. Apparatus as claimed in claim 4, wherein said fluid containment
vessels are mud pits.
6. Apparatus as claimed in any preceding claim, wherein the one or
more pumps are connected to the drill string by flow lines.
7. Apparatus as claimed in any preceding claim, wherein the
modifying means provides an oscillating mechanism.
8. Apparatus as claimed in claim 7, wherein the oscillating
mechanism is provided by periodical expulsion of a predetermined
volume of fluid from the pump.
9. Apparatus as claimed in claim 8, wherein the volume of fluid is
expelled from the pump by a choking means.
10. Apparatus as claimed in claim 7, wherein the oscillating
mechanism is provided by a turbine.
11. Apparatus as claimed in claim 10, wherein the turbine is
accentrically positioned.
12. Apparatus as claimed in claim 7, wherein the oscillating
mechanism is provided by an acentric helix.
13. Apparatus as claimed in claim 7, wherein the oscillating
mechanism is provided by one or more motors.
14. Apparatus as claimed in claim 13, wherein the one or more
motors are connected to a piston.
15. Apparatus as claimed in claim 1, wherein the modifying means is
provided on the drill string, or on the pumps.
16. Apparatus as claimed in claim 6, wherein the modifying means is
provided on the flow lines.
17. A method for running a drill string into a well bore comprising
creating a fluid pressure differential by mechanical or hydraulic
means, and transmitting the fluid pressure differential to the
drill string, the fluid pressure differential thereby causing the
drill string to oscillate.
Description
[0001] This invention relates to drilling methods for drilling well
bores such as may be used for oil or gas production. The invention
finds a particular application in providing apparatus and
methodology for reducing frictional forces on drilling apparatus,
as it progresses and retracts a within the well bore.
[0002] There are various limitations upon the depth of well bores
using known drilling practices. For example, the geological
structure may limit the depth of a well, as where the formation is
unconsolidated or otherwise physically unstable, the well may not
be able to support the various forces and loads imposed upon it by
the drilling equipment. Additionally, location of the production
reservoir relative to the drilling rig influences the depth and
reach of any new well. Yet further, rheology, i.e., the relevant
fluid pressures and types of fluid in the vicinity of the well also
bear upon the ability and desirability of the well depth.
[0003] However, regardless of these external or environmental
conditions, there is nevertheless physical limitations to maximum
reach or depth of a well which are imposed simply because of the
equipment or apparatus used. Specifically, the load capacities of
known drilling operation components and equipment are inevitably
limited.
[0004] In one object of the present invention, it is desired to
provide apparatus and methodology for enabling increased depth or
reach of a well bore. This is achieved by providing apparatus and
methodology for reducing frictional interface between a drill
string and the surrounding geological formation.
[0005] Typically, a drill string assembly consists of a bottom hole
assembly and the drill string pipe. The bottom hole assembly
comprises a drill bit incorporating a cutting structure, a motor
for driving the drill bit and further telemetry equipment. The
drill string pipe is usually made up of individual lengths of pipe
(typically 30 ft in length), called "singles". For handling
purposes during the drilling operation, three singles are
conventionally joined together to form a "stand".
[0006] Co-ordinating with the drill string is a drilling assembly.
A drilling assembly is made up to the blocks or top drive which is
suspended from the drilling derrick on a drilling rig. The top
drive is controlled via the draw works by the driller and enable
the drill string assembly to be moved up and down, as well as
acting as the point where the drill string is made up to the flow
lines. Such flow lines come from mud pumps and return lines that
typically run to the mud containment vessels, i.e., mud pits.
[0007] During drilling operations, the well bore is drilled by a
combination of the rotation of the drill bit and a directional or
longitudinal force. This directional force results from the weight
on top of the drill bit imparted by the drill string. It will be
appreciated that the deeper the hole, the greater the weight that
is available of drill string suspended from the blocks. This weight
is utilised efficiently in situations where the well bore is
vertical, as the drill string is suspended free of the well bore
wall and bears directly upon the drill bit. However, in situations
where the well that is being drilled is deviated from the vertical,
the force imparted by the drill string is significantly reduced,
since the drill string is not suspended freely in the middle of the
well bore, but lays on the wall of the drilled well bore. This is
particularly so where a deviated well is horizontal or near
horizontal. The longer the horizontal or deviated well that is to
be drilled, the greater the surface area of drill string that is in
contact with the well bore wall. This in turn increases the
frictional drag imposed by the wall on the drill string. Depending
upon the type of formation through which the drill string is
roving, this frictional drag may be further exacerbated.
[0008] Turning now to the requirement of retrieving the drill
string from the well bore, such frictional drag continues to be a
consideration. Yet further, the frictional drag must be added to
the weight of the string being retrieved, and this is one of the
limiting factors in the maximum depth achievable, since the load
capacity of the draw works must be taken into consideration, as
well as the strength of the joints or connections upon each of the
singles of drill pipe. If any of the load capacities of these or
other areas are exceeded, then failure of such components will
occur with catastrophic consequences.
[0009] It is therefore desirable in the art to provide apparatus or
methods of reducing the frictional drag of drill pipe on the walls
of the well bore. In the past, such apparatus and methods have been
developed to some extent and these have been offered as both
chemical and mechanical solutions. Chemical mixes are employed to
stabilise well bore walls and reduce the frictional drag. These
chemical mixes are typically added to the drilling fluid, and in
some operations silica beads may further be added to enhance the
friction reducing properties of the chemicals used.
[0010] However, chemical mixes tend to provide only a limited use
solution, as they degrade over a period of time. The chemicals are
of course diluted by the other well fluids and absorbed by the well
formation. They also may be chemically degraded by their
inter-action or reaction with well fluids and the geology
downhill.
[0011] Mechanical friction reducing devices are most conventionally
provided as "centralisers", which are well known in the art. The
function of a centraliser is to physically keep the drill pipe away
from well bore wall. However, centralisers also are not entirely
satisfactory, as while they may help to mitigate frictional drag,
they can similarly induce other disadvantages. For example, with
the weight of the drill string bearing upon the centraliser, the
centraliser only provides a localised surface area, and in
consequence at times tend to dig into the well bore as the drill
string moves. Attempts have been made to mitigate this problem by
reducing more expensive and sophisticated centralisers, with a
friction reducing surface. While such additional friction reducing
coatings or surfaces (including those which incorporate rollers)
are effective to some extent in a well bore, which as walls that
are stable, this does not solve the herein before mentioned problem
where the bore wall is unstable or unconsolidated. In such
situations, the centralisers will tend to dig in to the well bore
and any advantage imparted by the friction reducing surface is
compromised.
[0012] Three rotating collars are also used to reduce rotational
resistance caused by the drilling string bearing against the bore
wall. However, while such collars may be effective in reducing
rotational resistance, they do not reduce vecta or directional
resistance, and therefore encounter the same problems or
disadvantages as that which are associated with centralisers.
Similarly, the aforesaid silica beads, while reducing surface
friction in all directions, nevertheless suffer the problem of
being able to be used only once, as a percentage are lost to the
well formation and at present no cost effective means of extracting
or separating the beads is available. Thus, the beads cannot be
efficiently returned to surface in the drill fluid, at least in a
manner which separates then from the cuttings. Typically therefore,
any retrieved silica beads are disposed of in conjunction with the
well cuttings.
[0013] It will be appreciated that the movement of the drill string
in the situation of non-vertical drilling, particularly through
unstable formations, can act to destabilise the well bore wall by
its physical contact with the wall. By this, the bore wall in
certain circumstances may collapse around the drill string. This
causes the drill string to become fixed in place or, as is commonly
known in the trade, "stuck in hole". Drilling can therefore not
progress, nor can the drill string be retrieved. In this
catastrophic situation, the string may either be physically pulled
out, circulated out by increasing the circulation of drilling
fluids, retrieved by a combination of physically pulling out and
increasing drilling fluid circulation or, alternatively, jarred
out. If none of these techniques succeed, it is necessary to
abandon the drill string in the well. In all cases, the costs are
extremely high in terns of rig time and in the case of abandonment,
equipment cost.
[0014] An object of the present invention therefore is to enable
drill pipe to move cleanly through geological formations by
reducing frictional drag.
[0015] A further object of the present invention is to allow for
drilling operations with significantly reduced occurrence of the
drilling string getting "stuck in hole", and increasing achievable
drill depths beyond current limits, in the region of 20,000 ft to
30,000 ft. Accordingly, by meeting these objects, there is provided
a reduction in the costs associated with drilling operations and a
increased ability to reach reservoirs are that are not able to be
reached due to current constraints, as described herein before.
[0016] According to a first aspect of the present invention, there
is provided apparatus for oscillating a drill string within a well
bore, comprising one or more pumps for introducing fluid into a
drill string and a modifying means, wherein the modifying means
induces a fluid pressure differential which is transmitted to the
drill string via the pumps, and wherein the fluid pressure
differential causes said drill string to oscillate.
[0017] Optionally the modifying means is mechanically operated.
[0018] Alternatively the modifying means to hydraulically
operated.
[0019] Preferably the one or more pumps communicate with at least
one fluid containment vessel.
[0020] Most preferably said fluid containment vessels are mud
pits.
[0021] Preferably the one or more pumps are connected to the drill
string by flow lines.
[0022] Typically the one or more pumps transfer fluid from the
fluid containment vessels to the drill string via the flow
lines.
[0023] Preferably the modifying means provides an oscillating
mechanism.
[0024] In one embodiment the oscillating mechanism is provided by
periodical expulsion of a predetermined volume of fluid from the
pump.
[0025] Preferably the volume of fluid is expelled from the pump by
a choking means.
[0026] In one embodiment the oscillating mechanism is provided by a
turbine.
[0027] Preferably the turbine is accentrically positioned.
[0028] In one embodiment the oscillating mechanism is provided by
an acentric helix.
[0029] Typically the helix rotates under the influence of fluid and
thereby provides a centrifugal force.
[0030] In one embodiment the oscillating mechanism is provided by
one or more motors.
[0031] Preferably the one or more motors are connected to a
piston.
[0032] The modifying means can be provided on the drill string,
flow line or on the pumps.
[0033] According to a second aspect of the present invention, there
is provided a method for running a drill string into a well bore
comprising creating a fluid pressure differential by mechanical or
hydraulic means, and transmitting the fluid pressure differential
to the drill string, the fluid pressure differential thereby
causing the drill string to oscillate.
[0034] In order to provide a better understanding of the invention,
various embodiments will now be described by way of example only,
and with reference to the accompanying drawings, in which:
[0035] FIG. 1 shows a schematic of a typical drilling package;
[0036] FIGS. 2A, 2B and 2C show schematically a description of the
drill pipe oscillation theory, in accordance with the present
invention;
[0037] FIG. 3 provides a schematic of a triplex pump as used on
drilling rigs;
[0038] FIGS. 4A and 4B show a modification to mud pumps that would
induce oscillation in accordance with a method of the present
invention;
[0039] FIGS. 5A and 5B demonstrate pictorially mechanical methods
of inducing oscillation in accordance with the present
invention;
[0040] FIGS. 6A and 6B illustrate a hydraulic mechanism fitted onto
a flow line between mud pipes and the drill string for inducing
oscillation.
[0041] A typical drilling package is represented in FIG. 1, from
which the relationship between the various components discussed in
this specification may be determined. Specifically, drilling fluid
may be mixed and stored in holding tanks, namely the mud pits (2).
The fluid is pumped by the mud pumps (3) from the mud pits (2) and
pumped along the flow Lines (8). These flow lines (8) join up with
the drilling string (5) via the top drive (10). The drilling fluid
or mud, as it is more commonly known, has a -multiple function of
lubricating and cooling the drill bit which is carried at the end
of the drill string (5), carrying away the cuttings and acting as a
power source for the motor that drives the drill bit through the
well bore (9). The drilling mud is a mixture of various chemicals,
which aid in its functions, as well as helping to stabilise the
formation that is being drilled through.
[0042] During drilling, the mud returns up the annular space
between the drilled bore a wall and drill string (5). The mud
containing the cuttings returns to the mud pits (2) via the surface
return lines; the drill cuttings being separated from the mud-on
the shakers(1). The cuttings are disposed of via the OB line (6)
and the mud is returned to the mud pits and treated by the return
lines (7). The process may then be repeated for as long as the
drilling phase of the operation continues.
[0043] Under normal conditions, the mud pumps inject the drilling
fluid through the flow lines and drill pipe in a smooth rhythmic
pattern as graphically depicted in FIG. 2a. However, in the present
invention, it is recognised that by acting on this fluid
flow/pressure, it is possible to induce a fluid pulse.
[0044] The mud pump (3) may operate as a reciprocating pump with
multiple cylinders. As the pump operates, pistons draw fluid into
the chamber on the up-stroke via intake valves. The drilling fluid
is then directed into the flow line (8) to the drill string (5) on
the downstroke through outlet valves. Each of the cylinders are
operated progressively out of phase with each other, providing a
smooth and continuing flow of drilling fluid.
[0045] Noting that the axis Y relates to pressure and the axis X
relates to time, the peaks in the graph shown in FIG. 2a illustrate
the action of the pump cylinders as they operate out of phase with
each other.
[0046] In FIG. 2B, it may be seen that by periodically reducing
this fluid flow/pressure, a fluid pulse may be induced. This slow
pressure cell of drilling fluid is transmitted through the drill
string by the action of the mud pumps. Again axis Y relates to
pressure and axis X relates to time.
[0047] In reducing the drilling fluid pressure, e.g., as the
pistons operate, a pressure differential is created and this is
illustrated in the graph by the drop in the peak value at 11. This
pressure differential causes the drill string to oscillate by
creating an uneven flow of fluid. The oscillation agitates the
formation particles that surround and adhere to the drill pipe
assembly, creating the friction boundary, causing lamina movement.
This movement reduces surface resistance between the drilling
assembly and formation.
[0048] The oscillating action of the drill string which reduces the
surface resistance between the drilling assembly and formation, is
analogous to one attempting to progress one's finger into a bucket
of fine sand, whereby the progress is improved by moving one's
finger. The oscillation of the drill string (5) renders it much
easier to overcome surface resistance and to allow more efficient
progress of the drill string (5) in the formation.
[0049] FIG. 2C shows, simply, how this oscillation affects the
drill pipe In the well bore. Under normal conditions while drilling
a deviated well, the drill string (12) will sit on the bottom (13)
of the well bore (9) being drilled, as shown at (i). As has been
described above, the oscillation of the drill string (5) will cause
the surrounding particles in the well bore (9) to vibrate. The
lamina movement of the particles will create a gap (14) of movement
around the drill string and reduce frictional resistance, as shown
at (ii).
[0050] FIG. 3 shows the basic functioning of a triplex mud pump, as
to commonly used in the art. The mud pump is a reciprocating pump
with multiple cylinders (15). As the pump operates, the pistons
(16) in the cylinder (15) draw fluid into the chamber (17) on the
upstroke, via the intake (13). Drilling fluid is then directed in
to the flow line to the drill string on the downstroke through the
discharge valve (18). Each of the cylinders (15) are operated
progressively out of phase with each other, providing a smooth and
continuous flow of drilling fluid.
[0051] In FIG. 4A, it is shown that a modifying mechanism (19) has
been located on the mud pump (20) that allows a controlled volume
of fluid to be evacuated from the mud pump chamber (17), via a
choke manifold (21) and expelled via a through bore during the mud
pump's (20) cycle. As described above, under normal conditions the
mud pump (20) operates as a reciprocating pump with multiple
cylinders (15). As the pump operates, the pistons (16) draw fluid
into the chamber (17) on the upstroke via the intake (13) and this
is controlled by valve (22). The drilling fluid is then
directed-into the flow line to the drill string on the downstroke
through the outlet (23), controlled by valve (24). Each of the
cylinders are operated progressively out of phase with each other,
providing a smooth continuous flow of drilling fluid. The modifying
device (19) acts as a periodic bleed, the volume of fluid being
controlled by a choking device (21). The expelled fluid is returned
to the mud containing vessels. The loss of the small volume of
fluid creates a pressure differential or a pulse of fluid. This
pulse oscillates the fluid line and drill string by creating an
uneven flow.
[0052] In FIG. 4B, the location of the pump modification (19) and
the return line (25) may be determined. The return line (25)
carries the excess volume back to the mud pits. The modification
may be located at one or all of the mud pumps.
[0053] Turning now to FIG. 5, in FIG. 5A there is illustrated a
mechanical oscillator. The oscillator consists of a body (26) that
is designed to be connected to and part of the drill strings by
means of connections (27) and (28). The body defines a through bore
between the inlet and outlet (29), (30), wherein the through bore
is of a diameter appropriate for corresponding with the through
bore of the drill pipe in the drill string. Located within the
through bore is provided an ascentric turbine, incorporating an
impeller (31). In use, the drilling fluid passes through the
ascentric turbine (32) via the through bore (29), (30), causing the
device and drill pipe and device attached to it to oscillate.
[0054] An alternative oscillator is shown in FIG. 5B. Specifically,
a mechanical oscillator consists of a body (31) that is designed to
be connected to and be part of the drill string by means of
connections (32), (33). As before, a through bore of appropriate
diameter to suit the through bore of the drill pipe in the drill
string is provided through the body of the mechanical oscillator.
However, in the embodiment illustrated in FIG. 5B, there is no
ascentric turbine, rather drilling fluid passes through an
ascentric helix (34) which, using the fluid's mass, causing the
device in the drill pipe attached to it to oscillate. A section of
the mechanical oscillator is shown as (35), from which the
ascentricity of the helix may be noted.
[0055] As the drilling fluid passes through the helix section (39),
it rotates causing a vortex. The speed of rotation creates a
centrifugal force that starts to separate the fluid components
according to their specific gravity. The lighter fluid will move
along a higher velocity and will pass through the restrictions (36)
and (37) with relative ease. The restriction (36) slows the heavy
fluid even more as it passes into the chamber (38).
[0056] As the chamber (38) fills up with this heavy fluid, a back
pressure forms at the inflow side. Due to the movement of the
lighter fluids, a lower pressure cells forms at the outflow side
(37). When the chamber (38) fills with the heavy weight fluid, the
pressure built up on the inflow side will force it through the
restriction (37), creating a slug of fluid capping the low pressure
cell, creating a pulse. This fluid pulse causes the device and the
drill string connected to it to oscillate, as may be seen in FIG.
5B (iii).
[0057] The through bore of the device at the outflow side (40) is
ascentric to the through of the drill string. This enhances the
oscillating movement already being induced at the inflow side (41)
of the device, by use of the fluid's mass as it passes through this
section and back into the drill string.
[0058] FIG. 6A shows an alternative hydraulic oscillating mechanism
that is made up to and/or included in the flow line that connects
the mud pus to the drill string. The hydraulic oscillating
mechanism may consist of a fixed or variable speed motor (42) or
motors. The or each motor (42) may be connected to a piston (43) by
a series of connecting rods (44) and (45) and/or drive wheels (46).
The piston cylinders may be attached by any means deemed necessary
to the flow line that runs between the mud pumps and the drill
string.
[0059] FIG. 6B shows the location of the mechanism (13) in relation
to the rest of the drilling package. As has already been described
above, the mechanism (130 is located on the flow line (8) which
runs between the mud pumps (3) and drill string (5).
[0060] During drilling operations the pistons operate by extraction
and injection of a volume of the drilling fluid that is passing
along the flow line (8). this causes pulses of high and low
pressure drilling fluid to be transmitted down the flow line (8)
and drill string (5). This fluid pulse causes the fLow line (8) and
drill string (5) to oscillate.
[0061] The advantage of the present invention lies in the fact that
drilling operations can be carried out to depths beyond those which
are possible with conventional drilling procedures. It is therefore
possible to reach reservoirs which previously could not be drilled
to. The degree of frictional drag on the drill string is reduced,
allowing deeper drilling to be carried out and facilitating
retrieval of the apparatus from a well.
[0062] Further modifications and improvements may be incorporated
without departing from the scope of the invention here intended,
and is to be joined simply and inexpensively.
* * * * *