Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02462987 2004-04-O1
VIBRATION-DAMPENING DRILL iCOLLAR
FIELD OF THE INVENTIOIV
The present invention relates generally to apparatus for protecting down-hole
tools such as
sensors during drilling, and more particularly to apparatus for protecting
down-hole sensors
from the effects of vibration produced when drilling a well.
BACKGROUND OF THE INVENTION
In typical drilling systems utilized in the oil and gas industries, a rig is
established at a
desirable location, the rig comprising a rotatable drill string (consisting of
drill pipe sections
and heavier drill collars, the latter fitting around the lower drill pipe) and
a drill bit at the
down-hole end. During drilling, this rotatable component of the rig is rotated
from the
surface, causing the drill bit to cut into the downwardly adjacent rock
formations, with the
weight of the drill collar assisting in driving the drill bit downward into
contact with the
underlying rock. Drill collars also act as conduits for the drilling fluids
used to lubricate the
drill bit and carry cuttings back to the surface. Mud motors and turbines are
sometimes
employed down-hole to aid the drill bit rotation.
At various points during drilling, specialized measurement and telemetry tools
can be
employed to assess conditions in the rock formations adjacent the wellbore.
Methods well
known in the art include measurement-while-drilling {MWD) and logging-while-
drilling (LWD),
which methods employ a diverse and evolving range of sensors. These sensors
are usually
located in the drill string near the drill bit, with the derived data from
such sources as
resistivity, gravity, magnetic and nuclear magnetic resonance measurements
being stored in
down-hole memory or transmitted to the surface.
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While such sensors provide highly useful information about the down-hole
drilling
environment, vibration due to the drilling process can damage the sensors. An
axial load is
applied to the drill bit during drilling into underlying formations, and this
produces vibrations
in the overlying drill string, and vibration can occur due to drill string
rotation in deviated or
directional wellbores. Also, drilling fluid flow around the tool can initiate
harmonic vibrations
and side-to-side "slapping" of the tool ensues. While most of these sensors
are sufficiently
robust to address the vibrations of normal drilling conditions, a variety of
attempts have been
made to counter the potentially damaging vibrations.
United States Patent No. 4,522,271 to Bodine et al., for example, teaches a
sonic damper
unit which is placed directly above a drill collar string to damp out unwanted
complex wave
vibrations of the string both longitudinal and lateral in vibration mode, the
damper unit
comprising a tubular section filled with small pieces of material capable of
motion in a
random pattern and thereby responding to the frequency contenf to damp out
unwanted
vibrational energy. In another example, United States Patent No. 6,429,653 to
Kruspe et al.
discloses a method and apparatus for protecting a sensor frorn impact and
abrasion,
including a drill collar having a section of electrically non-conductive
material, the sensor
being located inside the drill collar within the section of electrically non-
conductive material.
Kruspe et al, alternatively disclose placing the sensor in a removable probe
fitted with
protective stabilizers. A variety of other shock absorbing devices are also
known in the art,
such as mechanical stabilizing projections mounted on the tool.
However, existing means to dampen drill string vibrations or provide shock
absorption suffer
from numerous disadvantages, including high manufacturing cost, failures of
inherently
unreliable "point-contact" mechanical shock absorbers (such as belly springs),
and the
requirement for a significant drilling fluid throughflow to support certain
stabilization devices
(which can result in formation damage from fluid invasion). Also, in rough or
underbalanced
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drilling environments, conditions are such that excessive vibration can defeat
currently
known tool protection means.
What is therefore required is a means for addressing the problem of down-hole
vibration
(from the drill bit as well as harmonic vibration) and resultant tool damage,
the means being
relatively inexpensive to manufacture, preferably more reliable than point-
contact
mechanical stabilizers and capable of effective use in rough or underbalanced
environments,
and not requiring reliance on significant fluid flow to support the
stabilization of the down-
hole tool.
SUMMARY O~ THE INVENTION
It is an object of the present invention, therefore, to provide a simple
apparatus effective in
dampening down-hole vibration in the tool-housing region of a drill string,
even in rough or
underbalanced drilling environments, while not requiring significant fluid
flow for its utility.
According to a first broad aspect of the present invention, there is provided
a drill collar for
use with a down-hole tool, the drill collar comprising: a hollow, cylindrical
sleeve having a
longitudinal axis and an inner surface facing towards the longitudinal axis;
and a plurality of
elongate ribs parallel the longitudinal axis and mounted on the inner surface
in spaced-apart
arrangement, defining thereby a central aperture within the sleeve for
receiving the down-
hole tool and inter-rib apertures for receiving drilling fluid.
According to a second broad aspect of the present invention, there is provided
a vibration-
dampening apparatus for use with a down-hole tool used in measurement-while-
drilling
and/or logging-while-drilling applications, the vibration-dampening apparatus
comprising: a
drill collar comprising a hollow, cylindrical sleeve having a longitudinal
axis and an inner
surface facing towards the longitudinal axis; and a plurality of elongate ribs
parallel the
longitudinal axis and mounted on the inner surface of the drill collar in
spaced-apart
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arrangement, defining thereby a central aperture within the drill collar for
receiving the down-
hole tool and inter-rib apertures for receiving drilling fluid.
According to a third broad aspect of the present invention, there is provided
a drill collar for
use with a measurement-while-drilling andlor logging-while-drilling sensor,
the drill collar
comprising: a hollow, cylindrical sleeve having a longitudinal axis, an inner
surface facing
towards the longitudinal axis, and a box end and a pin end at opposed ends of
the sleeve,
the sleeve composed of a non-magnetic nickel alloy; and four elongate ribs
parallel the
longitudinal axis and mounted on the inner surface in spaced-apart
arrangement, defining
thereby a central aperture within the sleeve for receiving the sensor and
inter-rib apertures
for receiving drilling fluid, the elongate ribs extending along substantially
the entire length of
the sleeve and composed of a nitral elastomer.
In exemplary embodiments of the present invention, the do~ron-hole tool is a
sensor used in
measurement-while-drilling andlor logging-while-drilling applications. The
sleeve is
preferably composed of a non-magnetic material, and most preferably a nickel
alloy, and the
sleeve preferably but not necessarily comprises a box end and a pin end at
opposed ends of
the sleeve, while double box end or double pin end connections may be used in
some
preferred embodiments. The elongate ribs are preferably composed of an
elastomeric
material, most preferably a nitral elastomer. The ribs are preferably three or
four in number,
depending primarily on sleeve dimensions, the ribs preferably equally spaced
around the
inner surface of the sleeve and preferably but not necessarily extending along
substantially
the entire length of the sleeve.
This novel drill collar is especially useful in rough or underbalanced
drilling applications,
supporting and centralizing the sensor and enhancing measurement accuracy by
dampening
flow-based harmonic vibrations, absorbing vibration from lateral tool
movement, and
stabilizinglcentralizing the sensor within the central aperture. Also, the
novel drill collar
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allows the operator to run lower fluid rates while drilling, minimizing
formation damage from
fluid invasion.
A detailed description of an exemplary embodiment of the present invention is
given in the
following. It is to be understood, however, that the invention is not to be
construed as limited
to this embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary embodiment of the
present
invention:
Figure 1 is a cut-away side elevation view of a drill collar according to the
present invention,
showing the positioning of the elongate ribs in relation to the longitudinal
axis of the drill
collar;
Figure 2A is a cross-sectional view of the drill collar of Figure 1 along line
2-2, illustrating the
use of four elongate ribs; and
Figure 2B is a cross-sectional view similar to Figure 2A but illustrating the
use of three
elongate ribs.
DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT
Referring now in detail to the accompanying drawings, there is illustrated an
exemplary
embodiment of a drill collar according to the present invention generally
referred to by the
reference numeral 2.
The exemplary drill collar 2 is for use with measurement-while-drilling andlor
logging-while-
drilling sensors (not shown) employing electro-magnetic transmission modes,
the drill collar
2 comprising a hollow, cylindrical sleeve 4 having a longitudinal axis 6. The
sleeve 4 has an
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inner surFace 8 facing towards the longitudinal axis 6, and a box end 16 and
pin end 18 at
opposed ends of the sleeve 4 for connecting the drill collar ? to adjacent
string sections (not
shown) (although double box end or double pin end connections may be used in
some
preferred embodiments). In this exemplary embodiment, the sleeve 4 is composed
of a non-
magnetic nickel alloy such as MoneIT"", although other non-magnetic materials
may be
suitable in various contexts. In exemplary embodiments, the drill collar 2 may
be from 2 to
12 metres in length, depending on tool requirements, witll an outside sleeve 4
diameter
accordingly ranging from 89 to 229 mm, and an internal sleeve 4 diameter
accordingly
ranging from 57 to 82.55 mm. Multiple collar sizes will be required to address
different hole
sizes, flow rates, and MWDILWD tool sizes. The following table provides
dimensions for a
variety of drill collars 2 according to the present invention, including
preferred rib 10
numbers:
Minimum Maximum Outside SleeveInternal SleeveNumber of
Sleeve LengthSleeve LengthDiameter Diameter Elongate
Ribs
2 metres 9.5 metres 89 mm 57 mm 3 or 4
2 metres 9.5 metres 95.25 rnm 57 mm 3 or 4
2 metres 9.5 metres 121 mm 57 mm 4
3 metres 12 metres 159 mm 71.44 mm 4
3 metres 12 metres 165 mm 71.44 mm 4
3 metres 12 metres 171 mm 71.44 mm 4
3 metres 12 metres 177.8 mm 76.2 mm 4 or 5
3 metres 12 metres 190.5 mm 76.2 mm 4 or 5
3 metres 12 metres 203 mm 76.2 mm 5
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3 metres 12~metres 229 mm 82.55 mm 5 or 6
Referring now to Figures 2A and 2B, the drill collar 2 is provided with a
plurality of elongate
ribs 10. In Figure 2A, there are four ribs 10, spaced evenly apart on the
inner surface 8 of
the sleeve 4. In Figure 2B, there are three ribs 10, again spaced evenly apart
on the inner
surface 8 of the sleeve 4. The required flow area (determined by collar size
and drilling flow
requirements) will determine the number and size of elongate ribs 10 required
in a given
application, with six ribs 10 for the largest collar 2 lengths (see the above
table). The
elongate ribs 10 are permanently attached to the inner surface 8 and are
parallel the
longitudinal axis 6, thereby defining a central aperture 12 (best seen in
Figures 2A and 2B)
within the sleeve 4 for receiving the down-hole tool; this central aperture 12
has a diameter
of 44.5 to 47.63 mm depending on tool clearance requirements. The positioning
of the
elongate ribs 10 also results in inter-rib apertures 14, best seen in Figures
2A and 2B, for
receiving drilling fluid (not shown).
In the exemplary embodiment, the elongate ribs 10 extend along substantially
the entire
length of the sleeve 4 and are composed of a nitral elastomer; this is the
same elastomer
that is used with some mud motor stators. Elastomeric material is known in the
art for its
ability to absorb energy from vibration and impact (for example, United States
Patent No.
6,102,142 to Besson et al.). The ribs 10 support the cylindrical tool along
its entire length,
not just at contact points as is the case with current mechanical stabilizers,
so the tool does
not start moving and causing harmonic vibrations. The present invention
accordingly does
not require the minimum fluid rates used in a multiphase flow in underbalanced
drilling
applications to stabilize and protect the tool, which therefore minimizes
formation damage
from fluid invasion. It has been found, in fact, that only minor lubrication
is required to work
this invention. Where a specific desired elastomer may swell due to the
presence of certain
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fluids, or experience possible down-hole temperature limitations where hot
hole conditions
are encountered, a special elastomer may be required.
In addition to being composed of a relatively inexpensive material, the
manufacturing
process is relatively simple and akin to known elastomer processes in mud
motor contexts;
the existing process for building a mold for injecting mud motor stators can
be employed to
inject the drill collars 2. A mold (not shown) will incorporate three or more
rib voids based on
the required flow data. The drill collar 2 is then prepared for the mold and a
bonding agent
(not shown) is prepared and installed on the inner surface 8 of the drill
collar 2. The mold is
then inserted into the drill collar 2 and an elastomeric material is injected
into the drill collar 2
with the mold seated therein. The elastomeric material then sets and adheres
to the inner
surface 8, and the mold is removed, creating a set of elastomeric ribs 10 that
run
substantially the entire length of the drill collar 2. When the elongate ribs
10 wear down from
prolonged use, the drill collar 2 can be provided with replacement ribs 10
using the same
process.
The present invention is especially useful in underbalanced applications, and
also with
coalbed methane drilling. The elastomeric fins 10 will both centralize the
tool and dampen
vibration during the drilling process in single phase or multiphase flow
regimes. The result is
a stable environment in which the sensor can conduct measurements, with a
significantly
reduced risk of tool damage due to vibration. Tool life and performance are
accordingly
enhanced by use of the present invention.
A prototype according to the present invention was tested for performance, and
test drillings
without a drill collar according to the present invention were conducted for
the sake of
comparison. The present invention was found to significantly enhance the tool
life. The test
drillings were conducted with an electromagnetic MWD tool in an underbalanced
drilling
medium, a hole size of 6 '/<" (159 mm), and a drilling medium comprising 5
gallons/min. (20
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litres/min.) fluid and 1300 cfm (36.8 cubic metres/min.) gas. Two test runs
were conducted
without a drill collar according to the present invention, g values were
measured up to 125 x
g (the force exerted by gravity), and catastrophic tool failure occurred
within a matter of
minutes on both test runs. In a test run conducted with a drill collar
according to the present
invention, g values were measured at 2 to 4 x g during drilling, and there was
no tool failure.
During the test run of the drill collar according to the present invention,
the drilling fluid was
reduced near the bottom of the well, and even when running "dry" the g values
did not
exceed 7 x g. These results accordingly indicate up to 18 to 31 times
potential reduction in
vibration when utilizing the present invention.
While a particular embodiment of the present invention has been described in
the foregoing,
it is to be understood that other embodiments are possible within the scope of
the invention
and are intended to be included herein. It will be clear to any person skilled
in the art that
modifications of and adjustments to this invention, not shown, are possible
without departing
from the spirit of the invention as demonstrated through the exemplary
embodiment. The
invention is therefore to be considered limited solely by the scope of the
appended claims.
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