Note: Descriptions are shown in the official language in which they were submitted.
a
CA 02247490 2004-12-22
PCT/GB97/00547
A DOWNHOLE DRIFT INDICATOR
This invention relates to a downhole tool, and in
particular but not exclusively to a drift indicator for use in
measuring the deviation from the vertical of a drilled hole.
The invention also relates to elements of such a downhole
tool, and to an arrangement for mounting a pivotable member,
and to a biasing arrangement.
Drift indicators are utilised to facilitate drilling
operations by providing surface recordings of hole deviation.
The tool is generally located in the drill string adjacent the
drill bit. One of the most widely used drift indicators
currently available is the Teledrift (Trade Mark) tool as
supplied by Dies Downhole Drilling Inc, of Oklahoma City,
Okla. The tool is provided with a pendulum that moves along a
series of graduated stop shoulders within a fluid reservoir,
and a signalling plunger that traverses a series of seven
annular restrictions to produce pressure pulses in the mud
stream. The plunger is biassed upwardly by a spring within the
fluid reservoir but during normal drilling operations is
pushed to a lower position by the flow of drilling mud over
the head of the plunger.
To measure the hole deviation, or drift, the bit is
pulled off bottom, rotation of the string is stopped and the
mud pump is stopped. The plunger, under the influence of the
spring, rises, passing one or more annular restrictions and
lifting the pendulum, until the pendulum engages one of the
CA 021247490 2004-12-22
2
stop shoulders; the smaller the degree of drift, the further
the pendulum will travel without engaging a shoulder. If the
mud pumps are started once more, the plunger is pushed
downwardly past the annular restrictions. As the plunger
passes each restriction there is an increase in mud pressure
above the plunger and this is detected at the surface, in the
form of a mud pressure pulse, the number of pulses indicating
the degree of drift; typically, each pulse represents a 0.5
degree deviation from the vertical. The pulses are produced at
10-30 second intervals, and the first pulse usually appears
within 10 to 15 seconds of starting the pump.
The mud pressure is measured at a surface chart recorder
which is linked to a surface mud line via a is diaphragm and
oil-filled hose. The drill operator determines the degree of
drift by examining the print-out from the chart recorder,
counting the number of pulses detected, and correlating the
pulse count with a set of tables supplied with the tool.
It is among the objectives of the embodiments of the
present invention to provide improved downhole tools, and also
an improved drift indicator.
According to the present invention there is provided a
combination of a downhole drift indicator and a mounting
arrangement for a pivotable member of the downhole drift
indicator, the combination comprising relatively moveable
first and second members of the downhole drift indicator
defining respective normally spaced apart first and second
CA 021247490 2004-12-22
3
surfaces, a pivot connection between the members including a
pivot member connecting the first and second members and
wherein the first and second surfaces are capable of engaging
one another on said pivot connection experiencing a
predetermined load to limit said load experienced by said
pivot connection, wherein the first member is a plunger and
the second member is a pendulum of the downhole drift
indicator.
In use, the arrangement permits provision of a sensitive
pivot connection which does not have to be constructed to
withstand high loads which the first and second members may
experience.
Preferably, the pivot connection permits pivoting of the
second member relative to the first member, the pivot member
defining a pivot surface for supporting the second member. The
pivot surface may be of relatively small area, for example a
point or line, as the surface will not be subject to high
loads and the corresponding force concentration that would
result.
Preferably also, the pivot member is linked to the first
member via a resilient deformable mounting which deforms under
said predetermined load to allow the second member to move
relative to the first member and the first and second surfaces
to engage. Most preferably, the pivot member is spring
mounted.
i
CA 02247490 2004-12-22
3A
According to another aspect of the present invention
there is provided a downhole drift indicator comprising:
a housing for location in a drill string and defining a
passage for drilling fluid;
a restriction body defining a series of flow restrictions
in the passage;
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
4
a restriction member for cooperating with the flow
restrictions to define a restricted flow area when located
adjacent a flow restriction, said restriction member being
r
moveable in one direction relative to the housing under the
influence of the flow of drilling fluid through the
passage, towards a first position;.
return means for biassing the restriction member in
the other direction, towards a second position; and
a drift responsive member being moveable relative to
ZO the housing and pivotally connected to the restriction
member, the pivot connection including a pivot member
connecting the restriction member and the drift responsive
member, the arrangement being such that on the pivot
connection being subject to a predetermined load surfaces
of the restriction member and drift responsive member
engage to limit the load experienced by the pivot member,
the degree of movement of said drift responsive member
in said other direction from a respective first position
being related to the inclination of the housing, the
arrangement being such that, in use, reducing the flow of
drilling fluid through the passage results in movement of
said restriction member in said other direction from said
first position until arrested by the drift responsive
member, and restarting the flow of fluid resulting in
movement of said restriction member from the arrested
position towards said first position, the reduction in flow
area resulting as the restriction member passes each flow
restriction producing a pressure pulse in the drilling
CA 02247490 1998-08-27
WO 97/3920 PCT/GB97/00547
fluid, which pulse is detectable at the surface, the number
of pulses indicating the degree of drift.
Preferably, the restriction member cooperates with the
4
flow restrictions to define a minimal flow area when
S located adjacent a flow restriction such that, in use, the
magnitude of the pulses is such. that the pulses may be
counted by the operator simply by monitoring an existing
drilling fluid pressure gauge at the surface. This
obviates the requirement to provide pressure sensors and
chart printers, considerably simplifying the monitoring of
drift of a hole being drilled.
Preferably also, the flow area defined between the
restriction member and an adjacent restriction is no more
than 60 0 of the flow area when the restriction member is
spaced from a restriction. Most preferably, the restricted
flow area is around 400 of the flow area between pulses.
Preferably also, the drift responsive member is
adapted to engage a selected one of a series of graduated
engagement members defined by the housing. The engagement
members may be in the form of annular or part-annular
teeth, and the pivotally mounted drift responsive member
may be a pendulum. The pendulum is preferably located
within a fluid reservoir, isolated from the drilling fluid.
To permit pressure equalisation, to accommodate movement of
the restriction member, the reservoir preferably includes
a moveable wall, most preferably in the form of a floating
piston.
To allow the pulses produced on movement of the
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
6
restriction member to be more easily detected, it is
preferable that damping means is provided for damping the
movement of the restriction member and the drift responsive
member. Preferably, the damping means only permits
movement of the restriction member once a predetermined
fluid pressure force is exerted on the restriction member.
The damping arrangement may include valve means for
limiting fluid flow between parts of the fluid reservoir
and such a damping arrangement preferably includes a coiled
tube and may also include a check valve.
Preferably also, the return means acts on the
restriction member via the fluid reservoir. Most
preferably, the retuxn means acts against the floating
piston. The return means preferably maintains the fluid
reservoir under pressure.
According to a further aspect of the present invention
there is provided a biassing arrangement, the arrangement
including a housing partially defining a volume for
containing a fluid reservoir, first and second members
defining respective wall portions of the volume and being
moveable relative to the housing, and biassing means for
acting on the second member to transfer force via the fluid
in the volume and move the first member relative to the
housing.
In use, the invention provides advantages over
biassing arrangements including such fluid reservoirs,
particularly in downhole tools, in which the biassing means
acts directly on a first member and is, for example,
located within the volume. In such arrangements the
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
7
movement of the first member under the influence of the
biassing means may result in a drop in pressure in the
volume, possibly to a negative pressure relative to the
n
surrounding f luid, such that surrounding f luid may be drawn
into the volume. Further, the pressure drop may result in
undesirable cavitation in a liquid medium in the volume.
In particular, the arrangement of the present
invention may be incorporated in a downhole drift
indicator, wherein the first member is a signalling plunger
and the second member is a floating piston.
Preferably, the biassing means maintains the fluid
under positive pressure. This positive pressure energises
any seals between the housing and the members defining the
volume, minimising the possibility of fluid leaks.
According to another aspect of the present invention
there is provided a downhole drift indicator comprising:
a housing for location in a drill string and defining
a passage for drilling fluid;
a restriction body defining a series of flow
restrictions in the passage;
a restriction member for cooperating with the flow
restrictions to define a restricted flow area when located
adjacent a flow restriction, said restriction member being
moveable in one direction relative to the housing under the
influence of the flow of drilling fluid through the
passage, towards a first position;
return means for biassing the restriction member in
the other direction, towards a second position, the return
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
8
means including a sleeve partially defining a volume
containing a fluid reservoir, the restriction member and a
second member defining respective wall portions of the
volume and being moveable relative to the housing, and
biassing means for acting on the second member to compress
the fluid in the volume and move the restriction member
relative to the housing; and
a drift responsive member being moveable relative to
the housing and connected to the restriction member,
the degree of movement of said drift responsive member
in said other direction from a respective first position
being related to the inclination of the housing, the
arrangement being such that, in use, reducing the flow of
drilling fluid through the passage results in movement of
said restriction member in said other direction from said
first position until arrested by the drift responsive
member, and restarting the flow of fluid resulting in
movement of said restriction member from the arrested
position to said first position, the reduction in flow area
2D resulting as the restriction member passes each flow
restriction producing a pressure pulse in the drilling
fluid, which pulse is detectable at the surface, the number
of pulses indicating the degree of drift.
Preferably, the biassing means is in the form of one
or more springs, and may be located within a further fluid
reservoir.
These and other aspects of the present invention will
now be described, by way of example, with reference to the
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
9
accompanying drawings, in which:
Figures 1, 2 and 3 are sectional views of a drift
indicator in accordance with a preferred embodiment of the
present invention, illustrating the indicator in three
difference configurations; and
Figures 4 and 5 are enlarged sectional views of the
pendulum of the drift indicator of Figure 1, illustrating
the pendulum in two different positions.
Reference is first made to Figures 1, 2 and 3 of the
drawings, which illustrate a downhole drift indicator 10 in
accordance with a preferred embodiment of the present
invention. In use, the drift indicator 10 is located
within an appropriate sub forming part of a drill string.
The drift indicator 10 and the sub in which the indicator
is positioned are configured to allow mud to flow through
and around the indicator 10, Figure 2 illustrating the sub
bore outline 12, and the mud flow path 14.
The upper end of the indicator 10 (towards the left
hand side of the Figures) is in the form of a tubular
restriction body 18 with a throughpassage 20 defining a
series of restrictions 22. Positioned within the passage
20 is a restriction member 24 which, as will be described,
co-operates with the flow restrictions 22 to define a
restricted flow area where located adjacent to a flow
restriction 22. The restriction member 24 forms the head
- of a plunger 26 which is slidable in a bore 28 defined by
a portion of the indicator body 30. The restriction body
18 is joined to the body portion 30 by a tapered sleeve 32
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
defining ports 34 to allow flow of fluid from the passage
into an annulus 36 between the exterior of the body
portion 30 and the sub bore wall 12.
The lower end of the plunger 26 extends into an oil
5 filled volume 38 defined by a sleeve 40 joined to the lower '
end of the body portion 30 and a floating piston 42. As
will be described below, the volume 38 is divided into two
parts 38a, 38b by a damping mechanism.
Reference is now also made to Figures 4 and 5 of the
10 drawings, which illustrate drift detection means comprising
a series of nine annular graduated teeth 44 defining a
taper and mounted on the sleeve 40, and a pendulum 46
pivotally mounted to the lower end of the plunger 26, and
provided with a single annular tooth 48 adapted to engage
15 with one of the teeth 44. As may be seen from Figures 4
and 5, the pendulum comprises a pendulum bob 50 defining
the tooth 48, the bob 50 being threaded and pinned to the
lower end of a pendulum shaft 52. The upper end of the
shaft 52 is pivotally connected to the lower end of the
20 plunger 26 via a pivot connection 54 including a pivot pin
56. The upper end of the shaft 52 defines a spherical ball
53 and with a bore 58 therethrough to accommodate the pin
56, the pin ends 60, 61 being mounted in a support bushing
62 located in a recess 64 in the lower end of the plunger
26. The bushing 62 engages a thread 66 defined within the
recess 64 and is further retained in place by a spring clip
68. The pin ends 60, 61 pass through apertures 70, 71 in
the upper end of the bushing 62 and normally rest upon a
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
1 ~.
washer 72 supported by a bushing-mounted spring 74, as
illustrated in Figure 4. However, when the tooth 48
engages with one of the teeth 44 on upward movement of the
plunger 26 and pendulum 46, the spring 74 is compressed
' 5 such that the spherical ball 53 engages a corresponding
seat 76 defined by the bushing 62, such that the maximum
load experience by the pin 56 equals the force applied by
the compressed spring 74, as shown in Figure 5. This
arrangement allows the pendulum 46 to be normally mounted
on a small area pivot surface defined by a larger diameter
central portion 78 of the pin 56.
As noted above, the sleeve 40 defines an enclosed
volume 38 which, in use, is filled with oil, and to
accommodate movement of the plunger 26 the floating piston
42 defines a movable lower wall. Further, this oil
reservoir 38 is internally sub-divided by a fixed wall 80
providing mounting for a crack valve 82 and a coil tube 84.
The valve 82 is configured to allow relatively unrestricted
flow from the lower part 38b to the upper part 38a of the
reservoir when the plunger 26 is moving upwardly. However,
the valve 82 only opens to permit flow in the opposite
direction when there is a substantial pressure differential
across the wall 80. Similarly, the length and diameter of
the coil tube 84 is selected such that a substantial
differential pressure is required to initiate flow through
the tube 84.
A pendulum seat 86 is provided above the wall 80 in
the upper volume 38a and is configured to accommodate the
CA 02247490 1998-08-27
WO 97/39220 PCT/GB97/00547
12
pendulum 46 when the plunger 26 is a.n its lowermost
position, as illustrated in Figure 2.
The floating piston 42 which defines the lower wall of
the volume 38 is biassed upwardly by a pair of return
springs 88, 89 located within a further oil-filled volume
90 defined by the lower end of the sleeve 40, the lower
face of the piston 42, and a bladder 92. The springs 88,
89 tend to push the piston 42 upwardly to compress the oil
within the volume 38 and thus push the plunger 26 upwardly
towards the position illustrated in Figure 1. This
arrangement has the advantage that the oil in the volume 38
is constantly pressurised, which ensures that the oil seals
96 are always energised by a positive pressure inside the
volume 38. This constant energisation of the seals in one
direction minimises oil leaks and the positive pressure
inside the volume 38 prevents any tendency for drilling
fluid to be drawn into the volume 38 during the upward
stroke of the plunger 26, as described below.
In use, the drift indicator 10 is located in a drill
string, just above the drilling bit. During normal
drilling operation the indicator 10 simply acts as part of
the drill string, with drilling mud passing through the
passage 20 and the annulus 36. The dimensions of the
plunger head 24 and the ratings of the springs 88, 89 are
selected such that the flow of mud will retain the plunger '
26 in a first position with the head 24 resting on the
upper end of the body portion 30, and the pendulum 46 in
the seat 86, as illustrated in Figure 2. If the operator
CA 021247490 2004-12-22
13 PCT/GB97/00547
wishes to measure the deviation of the hole from the vertical,
the bit is pulled off bottom, rotation of the string is
stopped, and then the mud circulation pumps are shut down. When
the flow of mud through the passage 20 stops, the springs 88,
89, acting via the piston 42 and the oil in the volume 38,
pushes the plunger 26 upwardly, and also lifts the pendulum 46.
As the pendulum 46 is pivotally mounted to the plunger 26 it
assumes a vertical position such that if the indicator 10 is
inclined to the vertical the pendulum 48 will lie at an angle
relative to the indicator body. Thus, as the pendulum 46 rises
it will engage one of the teeth 44, and arrest further movement
of the plunger 26, as illustrated in FIGS. 3 and S.
Alternatively, if the indicator 10 is lying vertically the
pendulum 46 will travel upwardly, past the teeth 44, until
encountering a stop provided by the lower end of the body
portion 30, as illustrated in FIG. 1. Thus, the upward movement
of the plunger 26 moves the plunger head 24 into the sleeve 16
to a position corresponding with the arrested position of the
pendulum 46.
Before the pendulum 46 engages one of the teeth 44, the
pendulum is free to pivot on the small area pivot surface 78
defined by the pivot pin 56. However, as described above, once
the pendulum 46 engages one of the teeth 44 the load
experienced by the pivot connection increases sharply, causing
the spring 74 to compress and transferring the load to the
surface of the ball 53 and the seat 76.
CA 02247490 1998-08-27
WO 97!39220 PCT/GB97100547
14
If the mud pumps are activated once more, and the mud
flow brought up to, for example, 400 gallons per minute,
there will be build-up of mud pressure above the plunger ,
head 24. However, the plunger 26 will not move downwardly
immediately as the crack valve 82 and coil tube 84 will not
permit flow of oil through the wall 80. Movement of the
plunger 26 only occurs when the pressure differential
across the indicator 10 reaches a predetermined level
(typically 200 psi?. Once the crack valve 82 has opened,
the plunger 26 may move downwardly into the sleeve 40 while
the valve 82 and tube 84 continue to provide resistance to
movement of the plunger, to ensure that the plunger 26
moves smoothly and steadily. As the plunger 26 moves
downwardly, the head 24 passes the flow restrictions 22
thus varying the cross-sectional flow area past the head
24; as described above, the dimensions of the flow
restrictions 22 and the head 24 are selected such that flow
area is substantially restricted when the head 24 is
adjacent a restriction 22. This results in a significant
pressure pulse in the drilling mud, which is readily
detected at the surface, simply by monitoring an existing
mud pressure gauge. By counting the number of pulses,
which occur every two to three seconds, the operator may
determine the drift or inclination of the tool, and thus
the drift of the drilled hole.
It will be clear to those of skill in the art that the
above-described embodiment is merely exemplary of the
present invention, and that various modifications and
CA 02247490 1998-08-27
WO 97/39220 PCT/G~97/00547
improvements may be made thereto, without departing from
the scope of the invention.
_r!!u~lra'~.~"1Y'#.i.l~v-;~(A~'J ,
