Note: Descriptions are shown in the official language in which they were submitted.
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Borehole opener
The present invention relates to a borehole opener, particularly for enlarging
this hole underneath a casing in the field of oil prospecting, the hole opener
comprising a body of longitudinal axis, a duct for drilling fluid, formed
longitudinally in the body, and having a fluid passage cross section of inside
radius i, and at least two hole-opening arms which have an active part
equipped with cutting means, which are arranged in such a way that they
can slide between a position of rest in the body and an active position
partially out of the body, which are guided and supported for this purpose in
the body over a distance g and which, in the active position, project from the
body by a length o.
This kind of opening tool has, for example, a body diameter of, for example,
between 119 and 427 millimeters. That leaves only a small amount of space
in which to build a simple mechanism, provide the aforesaid elements, and
give these proportions which give them, and the opener as a whole, a
balanced relative solidity.
It is an object of the present invention to provide a solution to this problem
and the present invention proposes to observe a given proportional
relationship between, on the one hand, the respective values mentioned
above for the inside radius i, distance g, length o and, on the other hand,
the
sum s of these three values.
To this end, according to the invention, the values of i, g and o are chosen
to
simultaneously satisfy the following conditions:
i+9+o--s.
0.30 < i/s < 0.45, 0.40 < gls < 0.60, 0.07 < ols < 0.20.
Surprisingly, it has been found that these conditions can advantageously be
successfully applied to various sizes of hole opener, as explained
hereinbelow.
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According to one embodiment of the invention, for its sliding guidance in the
body, each arm may comprise a cylindrical portion of diameter d, the value
of which is at least equal to the value of g above.
According to a particular embodiment of the invention, in order to move it
from the position of rest into the active position, each hole-opening arm has
a face, internal to the body, designed to be subjected directly, in the same
way as an active face of a piston, to the pressure of the drilling fluid
flowing
through the body.
Other details and particular features of the invention will become apparent
from the appended claims and from the description of the schematic
drawings attached to this text and which illustrate, by means of non-limiting
example, one preferred embodiment of the hole opener of the invention.
Figure 1 shows, in axial section, a hole opener, an arm visible in the figure
being in the position of rest.
Figure 2 shows a partial axial section in which the visible arm is in the
active
position.
Figures 3 and 4 each show a cross section in which three hole-opening arms
are depicted in the position of rest, and in the active position,
respectively.
Figure 5 shows, to a larger scale and in longitudinal section, an assembly
comprising an arm and an intermediate support so that arms can be
mounted and exchanged quickly.
In the various figures, the same references denote similar or analogous
elements.
The hole opener 1, as depicted by way of example in Figures 1 to 4,
comprises a body 2 of longitudinal axis 3, a duct 4 for drilling fluid, formed
longitudinally in the body 2, and at least two hole-opening arms 5 which are
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distributed symmetrically in the body 2 about the longitudinal axis 3 to make
sure that the operation of the hole opener 1 is approximately balanced.
Figures 3 and 4 show that three arms 5 can easily be arranged in the body 2
with angles of 120° between two successive arms 5.
The arms 5 each have an active part 7 equipped with cutting means 8
(Figures 3 to 5) which are known and explained hereinbelow. The arms 5
are arranged in the body 2 so that they can be moved between a position of
rest 9 in this body 2 and an active position 10 partially out of this same
body
2.
Each arm 5 may comprise, for moving it from the position of rest 9 into the
active position 10, a face 12 internal to the body 2 and designed to be
subjected directly, in the same way as an active face of a piston, to the
pressure of the drilling fluid flowing through the body 2. Through this
arrangement, it is possible to avoid having intermediate mechanical parts
between the fluid which is to actuate the arm 5 and this arm, and the
problems known to those skilled in the art which may ensue.
The internal face 12 of the arm 5 should be understood as meaning any
facelsurface in contact, at any moment in the drilling andlor hole-opening
operation, with the pressurized fluid flowing through the duct 4. It is
obvious
that some of these faces/surfaces subjected to the same pressure will
compensate for each other but, overall, there remains enough positive area
that, for example with a positive pressure differential of the order of 2 MPa
(about 300 psi) between the pressure of the fluid in the duct 4 and that of
the
fluid outside the body 2 in the region of the arm or arms 5, a thrust force of
the order of 2000 kg can be obtained, in order to deploy the arm 5 from the
body 2.
The arm 5 is mounted in such a way that it can slide parallel to itself in the
body 2, so as to move from the position of rest 9 into the active position 10
and vice versa. The choice of a movement of this kind is one of the more
favorable types of movement, for operation in the manner of a piston.
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The movement of the arm 5 can be directed radially andlor in any other
favorable direction, whether this be upward or downward with respect to a
direction of work of the hole opener, andlor forward or backward with respect
to a direction of rotation of the hole opener, possibly in any combination of
these directions of movement.
A movement of pivoting about an axis (not depicted) perpendicular to the
longitudinal axis 3 and to the direction of the travel of the arm 5, and
arranged somewhat away from the arm 5 is, however, also possible, but
would require special machining of significantly higher cost than the
machining of the previous embodiment in order to implement it.
In order to provide the aforementioned piston function, sealing means 11 are
provided at places which are known to those skilled in the art.
To move it from the active position 10 into the position of rest 9 when the
pressure in the duct 4 decreases, the or each arm 5 advantageously
comprises elastic return means 13, for example compression coil springs 14
as depicted in the drawings. This arrangement allows the hole opener 1 to
be withdrawn from the borehole without difficulty.
The arm 5 may, in the active position 10 out of the body 2, have a posterior
face 16 (with reference to a direction F of advance for opening out the hole)
which is at an angle, designed, for example if the springs 14 should be
deficient, to help the arm 5 back into the body 2 when the hole opener 1 is
being withdrawn from the borehole.
The arm 5 can be mounted in the body 2 by means of an intermediate
support 15 which acts as a housing and a guide for the arm 5 in the body 2
and which is fixed to the latter, for example by screws 17. Sealing means 18
may then be provided between the body 2 and said intermediate support 15.
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The fluid duct 4 has (figures 2 and 4) a passage cross section of inside
radius i. The term radius is to be understood in a broad sense, for example
half the mean linear dimension of this passage cross section.
The arms 5 are guided, at least in the active position, in the body 2 or, as
appropriate, in their respective intermediate support 15 over a distance g.
These same arms 5, in the active position, project from the body 2 by a
length o.
As figures 2 and 4 show,
- the sum s of the three values i, g and o corresponds to the radius or
half the diameter of opening of the arms 5,
- the outside diameter of the body 2 is equal to (i + g) x 2 or to (s - o) x
2,
- thus, the projecting length o is equal to s - g - i
The invention proposes to keep the three values i, g and o related to their
sum s within respective determined values. This stems from various
experiments which surprisingly yielded fairly narrow ranges for the following
three proportions:
0.30 < ils < 0.45, 0.40 < gls < 0.60, 0.07 < ols < 0.20.
The value of o considered is the maximum possible value for the movement
of the arm 5 in the hole opener.
Table 1 appended hereto gives, for seven hole openers of different sizes,
ranging, in increasing size, from size 1 to size 7, characteristic dimensions
and the corresponding proportions. It is evident from this that preference
may be given to the following respective ranges for said proportions:
0.34<i/s<0.39, 0.45<gls<0.53, 0.10<o/s<0.16.
For any other identical construction condition, proportions outside these
ranges gave rise to hole openers which did not perform as well as those
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whose proportions fell within the above ranges, whether in terms of
operational reliability, life, quality of work, performance, etc.
For its sliding guidance in the body 2 or in the intermediate support 15, each
arm 5 may comprise a portion, preferably cylindrical, of diameter d, the value
of which is advantageously at least equal to the value of g above. In doing
this, attempts are made at making a weighty and robust arm 5.
This advantageously cylindrical portion of the arm 5, in the form of a piston,
may be made of a steel, for example surface-hardened on the guide surface
so as to reach a hardness of the order of at least 120 or even 140 or as
much as 240 kg/mm2. The guide cavity of the body 2 or of the intermediate
support 15, acting as cylinder for said piston, may be formed in a steel
treated, for example, by through-hardening of the guide surface to obtain a
hardness of at least 120 or preferably 140 kglmm2.
Of course, the most favorable technical and economical combination is
sought when choosing these hardnesses.
As a preference, prior to a hole-opening operation, each arm 5 is kept in the
position of rest 9 in the body 2 by at least one pin 19 designed to break
when the pressure of the drilling fluid flowing through the body 2 exceeds a
predetermined value higher than a maximum usual boring value.
For this purpose, the pin 19 may have a region 19A of calibrated weakness,
at the or each point of transition 20 where the pin 19 passes, as the case
may be, either from the body 2 or from the intermediate support 15 into the
arm 5. It is obvious that, unlike what has been depicted in Figures 3 and 4,
the pin 19 does not necessarily have to emerge from both sides of the arm
5.
This pin 19 may fix the arm 5 merely to the intermediate support 15
(Figures 3 and 4).
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Figure 4 shows the pin 19 broken into one part 19B in the arm and two parts
19C in the intermediate support 15.
The intermediate support 15, the arm 5, the aforementioned elastic means
14 and the pin 19 may therefore constitute an assembly 21 (Figure 5)
designed to be assembled beforehand outside the body 2 and then installed
therein. This then makes the hole opener 1 not only easier to assemble, but
also easier to maintain or repair in the event of damage, etc.
It must be understood that the present invention is not in any way restricted
to the embodiments described hereinabove and that many modifications
may be made thereto without departing from the scope of the claims given
hereinbelow.
On its outer face, between two successive arms 5, the body 2 may have a
longitudinal passage 22 for returning drilling fluid to the surface, and a
boss
23 arranged in this passage 22 so as to divert andlor deflect the drilling
fluid
which is rising back up toward the surface onto that part of the wall of the
hole on which the arms 5 are acting. The passage 22 and the boss 23 are
produced in such a way as not to form too great a restriction to the passage
of the returning fluid.
In the preferred embodiment of the hole opener 1, the travel of an arm 5
between the position of rest 9 and the active position 10 is limited in both
directions of travel by stops. In the position of rest 9, the arm 5 is usually
completely retracted into the body 2 and is held therein by reciprocal stop
surfaces 25 (Figure 3) or, as appropriate, by the pin 19. In the active
position
10, the arm 5, retained by reciprocal stop surfaces 26 (Figures 2 and 4),
sweeps through an area, the largest diameter of which is equal to between
1.05 and 1.3 times, preferably 1.2 times the nominal diameter of a drill bit
associated with the hole opener 1 for a combined drilling and hole-opening
operation.
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The cutting means 8 on the arms 5 are arranged by the person skilled in the
art in such a way as, for example, to obtain cutting efficiency similar to
that of
the cutting means of the associated drill bit.
The reciprocal stop surfaces 26 may be arranged on exchangeable or
adjustable elements so as to allow a user of the hole opener 1 to choose the
extent to which the arms 5 can deploy out of the body 2 during service.
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Key to the figures
1 hole opener
2 body
3 longitudinal axis
4 duct
5 hole-opening arms
7 active part
8 cutting means
9 position of rest
10 active position
11 sealing means
12 internal face
13 elastic return means
14 coil springs
15 intermediate support
16 posterior face
17 screws
18 sealing means
19 pin
19A weakened regions)
19B part of the pin
19C part of the pin
20 transition point
21 assembly
22 longitudinal passage
23 boss
25 reciprocal stop surfaces
26 reciprocal stop surfaces
S direction of advance of a hole-openinglboring
process
