Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPLICATION FOR PATENT
INDUCTION LOGGING SUNDAY
WITH METALLIC SUPPORT
The present invention relates to well logging apparatus for
investigating the properties of subsurface formations traversed
by a Barlow and more particularly to an induction logging
Sunday.
An induction logging apparatus basically comprises a
transmitting coil and a receiving coil mounted on a support and
axially spaced from each other in the direction of the
Barlow. The transmitting coil is energized by an
alternating current at a frequency which is typically 20 kHz
and generates a magnetic field which induces in the surrounding
formation eddy currents which flow coccal to the Barlow
and the intensity of which is proportional to the conductivity
of the formation. The field generated in turn by these
currents induces in the receiving coil an electromotive force.
By suitably processing the signal from the receiving Cole
measurement of the conductivity of the formation is obtained.
In the conventional induction logging Sundays, the support
- of the coils is in the form of a tubular mandrel of non-
of Jo tier
conductive material such as egos reinforced epoxy resin
(see for instance US Patents No. 3,179,879 to Tangy, 3~147,429
to Moran, and 3,706,025 to Roget). It has always been the
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belief that because of the very low level of the signal from
the receiving coil, it is critical to minimize any presence of
conductive material in the vicinity of the coils, in order to
avoid spurious currents flowing near the coils and creating a
spurious component ("Sunday error") see for instance the
publication SPY. 12 167 society of Petrolellm Engineers) "The
Electromagnetic Wave Resistivity MUD Tool" by P. F. Rodney
et at, presented at the Thea Annual Technical Conference and
Exhibition, San Francisco~ October 5-8, 1983, page 1, left
column, second paragraph. An obvious drawback of using
supports of synthetic resin is that they are very fragile in
use, and among the different types of logging apparatus, the
induction Sundays are considered to be most fragile. Moreover,
since measurement- while-drilling devices have to be built
around a collar of steel (or other high strength material)
inside of which the drilling mud can be circulated, it has been
considered that induction tools cannot be used in the
measurement-while- drilling context, as pointed out in the
above-mentioned SPY. publication
It should be pointed out that totally excluding metallic
parts near the coils is impossible because electrical leads are
necessary to energize the transmitting coil and convey the
signal from the receiving coil. In conventional induction
Sundays, the leads are in the form of rigid, pressure-resistant
multi layer coaxial cables. These cables have coaxial metal
"layers" insulated from each other, with the inner layers
I
acting as conductors conveying signals while the outer layers
provide the mechanical strength and a shielding for the
conductors. These cables and the discontinuities at the
connection with the coils give rise in the presence of the
transmitting field to eddy currents which produce an error in
the output signals. In the case of low conductivity
formations, this error can be of the same order as the useful
signal. Additionally, this error is highly subject to
temperature drift and its value at room temperature is
substantially different from its value in the Barlow
environment where the temperature may be above 150C. The
error may further vary with the age of the equipment, for
instance because of the aging of the synthetic resin and the
bending that may affect the support.
It was proposed in US Patent 3,249,858 (Gould) to use a
support of metal for the purpose of increasing the mechanical
strength. This patent teaches that in order to minimize the
generation of spurious currents in the metallic support, the
latter should comprise a diametrical through-slot extending
over substantially its entire length. The patent also
indicates that the coils should be made of circular turns
connected to each other by linear conductive segments the mid-
points of which are located in the diametrical plane of the
slot. It is to be noted, however, that the improvement of the
mechanical strength is limited my the slot traversing the
support and also that the problems that arise from the presence
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of the electrical leads are not addressed.
one object of the present invention is to provide an
induction logging Sunday having an excellent mechanical strength
and ruggedness.
Another object of the invention is to provide an induction
logging Sunday which presents a low, stable and predictable
Sunday error.
Another object of the invention is to provide an induction
logging Sunday in which the use of multi layer coaxial cables for
the connections to and prom the coils is avoided.
Another object ox the invention is to provide an induction
logging Sunday which can be inserted in a combination of logging
tools at any position within the combination.
Another object of the invention is to provide an induction
logging Sunday suitable or measurement-while-drilling applique-
lions.
There is provided in accordance with the invention an
induction logging Sunday comprising an elongate support of
electrically conductive metal, generally cylindrical in shape,
at least one transmitting solenoid coil and at least one
receiving solenoid coil in coaxial and spaced relationship to
the support. The transmitting coil operates at such a
frequency that it produces an electromagnetic field
substantially free of dielectric effects, a suitable frequency
range being between about 10 and 400 kHz, a preferred lower
limit of the frequency range being about 20 kHz and a preferred
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upper range being about 200 kHz. The support, at least in its
portions adjacent the coils, has a substantially continuous,
preferably axisymmetrical outer surface to favor the flow of
eddy currents circularly around said surface.
Preferably the support includes an outer sleeve made of a
metal having a high electrical conductivity, such as copper,
and an inner core of a material of smaller conductivity but of
higher strength, such as stainless steel.
The invention can be readily understood upon reading the
following description with reference to the accompanying
drawings.
- Figure 1 shows schematically an embodiment of an
induction logging Sunday in accordance with the invention
and the surface equipment connected to it,
- Figure 2 is an enlarged detail view of a coil unit of the
apparatus of Figure 1, in a first embodiment,
- Figure 3 illustrates a modified embodiment of the coil
unit,
- Figure 4 shows an induction logging Sunday according to
the invention adapted to measurement-while drilling
operation,
Figure 5 is a partly sectional longitudinal view of a
preferred embodiment of the induction logging Sunday, and
- Figure 6 is a section according to line TV of Figure 5.
inure 1 shows an induction logging Sunday 10 for invest-
grating the geological formations 11 traversed by a Barlow 12.
- 6 S
The Barlow is filled with drilling mud 13. The apparatus is
suspended from a multi conductor cable 14 which passes on a
sheave 15 and is wound on a winch 16 which is part of the
surface equipment associated with the Donnelly logging Sunday.
The surface equipment supplies the Donnelly apparatus 10 via
the cable 14 with electrical power and signals for controlling
its operation and receives from the Donnelly apparatus 10
measurement signals. The surface equipment includes means 17
for processing and recording these signals. A sensor aye for
detecting the motion of the cable it provided The signals
from the sensor aye are indicative of the instantaneous depth
of the Donnelly apparatus and are fed to the processing means
for depth matching the measurement signals.
The Donnelly apparatus 10 comprises an electronic cartridge
18 connected to the cable 14 through the cable head 19. The
cartridge 18 includes a telemetry cartridge 20 which converts
the signals from the surface equipment produced by the Donnelly
apparatus to a format suitable for transmission by the cable.
The Donnelly apparatus 10 also comprises an elongate
support 30 the upper end of which is secured to the cartridge
18. The support 30 mounts a coil system which comprises a
transmitting coil 31 and a receiving coil 32 coaxial to and
spaced from each other in the longitudinal direction of the
support 300 The transmitting coil 31 is energized to produce a
magnetic field which induces in the formation eddy currents
which flow coccal of the axis of the support. The receiving
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coil generates in response to the field created by these
currents an output signal representative of the conductivity of
the formation. The frequency of operation of the transmitting
coil is such that the field setup in the formations can be
classified as a "~uasi-static" electromagnetic field. In other
words, the operating frequency is such that the displacement
currents are negligible, conduction currents being predominant.
The frequency suitably lips between about 10 and about 400 kHz.
Above 400 kHz, displacement currents become significant and the
output signal would be responsive not only to the conductivity
of the formation but also to its dielectric constant, which
would be undesirable for the purposes of the present invention.
A preferred upper limit of the frequency range is about 200
kHz. A preferred lower limit of the frequency range is about
20 kHz.
In the schematic drawing of Figure 1, the Sunday is shown to
have only a transmitting coil and a receiving coil, but it will
be clear that each coil system can comprise more than two
coils, for instance one or more transmitters, several receiver
coils, and bucking coils respectively associated with the
receiver coils to cancel out the effect of direct coupling
between the transmitter coil and the receiver coils. The Sunday
could further comprise several coil systems distributed over
its length.
The support 30 has a generally tubular shape and is made of
a metal, preferably a non-magnetic metal having an excellent
I
electrical conductivity. Suitable materials include copper and
copper alloys, and stainless steel.
The support comprises cylindrical longitudinal portions 33
the outer wall 34 of which are in contact with the outside i.e.
with the drilling mud, and cylindrical longitudinal portions 35
having an outside diameter smaller than portions 33. The
portions 35 thus define recesses aye for receiving the coils 31
and 32 which era coaxial to, and electrically insulated from,
the respective portions 35. The embodiment shown in Figure
includes such a recess for each coil, but it will be understood
that one portion 35 can as well mount an entire coil system,
i.e. one recess aye can receive a plurality of axially spaced
coils. The intermediate portions 33 have preferably an inside
diameter larger than portions 35 and define inner spaces 36,
and in the embodiment shown in Figure 1, the portions 33 and 35
are connected by transverse portions 37. The walls of portions
33 have a sufficient thickness to withstand by themselves the
hydrostatic pressure of the Barlow fluid.
Respective conductors 38 routed inside the support connect
the coils 31 and 32 to the electronic cartridge 18.
Since the support in the portions adjacent the coils is
made of a highly conductive material and has a continuous
axisymmetric outer surface, it is almost e~livalent to a
perfect conductor. This favors the generation of eddy currents
in the presence of the electromagnetic field produced by the
transmitting coil, which currents flow around the surface of
Lo
the support. As a result, the tangential electric field is
forced to zero at the surface of the support and no
electromagnetic field is generated in the closed space defined
ho the interior of the support. The support constitutes
therefore a very efficient electromagnetic shield. For
instance, with an operating frequency of 20 kHz and a
conductivity of 5.8xlO S/m (copper), a thickness of 5
millimeters represents 10 skin depths. The spurious effect of
direct couplings between the conductors and the coils is thus
eliminated and it is possible to use simple conductor wires
rather than the conventionally used multi layer coaxial cables.
Moreover, since the tangential electric field is
substantially eaneelled at the surface of the support, the
Sunday error brought about by the eddy currents flowing around
the support is low. It has been found that the Sunday error,
with a perfectly axisymmetric metallic support, is a decreasing
function of the electrical conductivity of the material of the
support and of the frequency. The mathematical expression of
this variation is
= k. -1/2 f-3/2
where E stand for the Sunday error, for the conductivity, f
for the frequency, and k is a coefficient. Accordingly, the
Sunday error is minimized if a metal of high conductivity is
used. A typical value for the Sunday error of the support,
measured in the air, is 2 millisiemens~ which is of the same
order as the output signal as obtained in the case of most high
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resistivity formations. Additionally, a very significant
advantage of the invention is that this Sunday error shows a
very low temperature drift and is well predictable. It is thus
easy to correct the output signal for the influence of the
metal support, by subtracting the well defined Sunday error from
the output signal.
The fact that the coils are mounted around metallic
portions has the effect of reducing the cross-sectional area
available or the magnetic fluxes transmitted by coil 31 and
received by coil 32, the surface area being dependent of the
spacing between the coils and the outer surface of the portions
35. This causes a reduction in the sensitivity of the
measurement, but this reduction can easily be compensated for
by a proper design of the coils i.e. the number of turns of the
coils is increased with respect to the conventional arrangement
with a non-conductive support.
It should be noted, that the axial spacing e between the
ends of a coil and the adjacent walls of the transverse
portions 37 is suitable kept beyond a predetermined value. The
vertical response of the Sunday, when measured along the outer
surface of the Sunday, shows sharp peaks opposite the coils, the
average width of the peaks being equal to about one diameter of
the respective coil. In order to avoid any substantial
alteration of the Sunday response, the spacing between the ends
of the coils and the adjacent transverse portion is chosen
equal to at least about one diameter of the respective coil.
I: .
3~3~
If a plurality of coils are received within one recess aye,
then the spacing between each transverse portion and the end of
the coil located nearest this transverse portion should be at
least equal to about one diameter of the coil in question. In
other words, the cylindrical portion of the support which
mounts an individual coil or an entire coil system must have an
axial dimension which exceeds that of the coil (respectively of
the coil system) on each side of the coil (respectively of the
coil system) by at least about one diameter of the coil
(respectively one diameter of the end coils of the coil
system).
In view of the foregoing, a support with a perfectly
axisymmetric and continuous outer surface in the portions
adjacent the coils is the optimum, but designs which slightly
depart from this optimum are within the scope of the invention,
provided that the flow of eddy currents around the support is
not substantially affected. For instance, a cross-section
generally similar to, but different from a circular
cross-section, e.g. polygons, could be used. Also, small holes
provided through the support, e.g. for passing conductors to
the coils, will not substantially alter the flow of eddy
currents. On the other hand, longitudinal slots through the
support would oppose the flow of eddy currents and be
detrimental to the shielding effect of the support.
A further advantage of the metal support is that it
provides the Sunday with an improved mechanical strength and
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ruggedness, and the portions 33 of the support are pressure
resistant by themselves.
The spaces I defined inside the portions 33 can be taken
to advantage for accommodating some of the electrical circuits
of the Sunday. In this case, instead of grouping all the
circuitry in the cartridge 18 as shown in Figure 1, there would
be a transmission block connected to the transmitting coil 31
and disposed in a space 36 adjacent this coil, and a reception
block connected to the output of the receiving coil and
likewise mounted in a space 36 adjacent the receiving coil.
It should also be noted that owing to the mechanical
strength of the support 30 and the possibility of routing
conductor wires inside the support, the above described
induction Sunday can be combined with one (or more) logging
apparatus of different type sonic, nuclear) attached to the
lower end of the induction Sunday. Such an apparatus is shown
in dotted lines in Figure 1 with reference numeral 40. The
conductors connecting this apparatus to the telemetry cartridge
20 via the inside space of the support 30 are also shown in
dotted lines with reference numeral 41. Thus the induction
Sunday of the invention can be inserted at any location within a
combination of logging Sundays, while the conventional induction
Sundays with a non-metallic support can only be placed at the
bottom of the combination.
Figure 2 shows in more detail a suitable embodiment of the
coil 31 and 32. Each coil is in the form of a coil unit 50.
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The coil unit is insulated from the portion 35 of the support
by an insulating sleeve 51 for instance of ceramic. The sleeve
51 is secured to the portion 35 by a means such as a pin 52.
The sleeve 51 mounts several rings 53, and several rings 54,
screwed to the respective ends of the tubular part 51 on both
sides of the coil unit so as to hold the latter in position.
The coil unit comprises a coil form made of two
generally annular support parts 56, 57 of insulating material,
for instance ceramic, which together have a rectangular section
and define an annular internal space 58. The space 58 receives
the turns 60 of the coil, which turns are disposed coccal of
the axis of the support 30. A plurality of conductive wires
61 are wrapped around the support parts 56, 57 in towardly
arrangement. Each wire is cut to prevent it from forming a
closed loop and all the wires are connected to a ground ring
not shown, and thus at the same ground potential. The wires 61
form an electrostatic shield which prevents any electrostatic
coupling of the respective coil with the other coil or coils or
with the drilling fluid.
A fluid-tight sleeve 62 of non-conductive material e.g.
of fiberglass-reinforced epoxy is mounted around the coil unit to
protect the coil unit from contact with the mud, with pressure
I,......
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seals aye at both ends The rings 53, 54, support the sleeve
62 on its inner surface to allow it to withstand the pressure
of the mud. Holes such as 63 are provided in portion 37 of the
support for the passage of electrical conductors connected to
the coil.
In the above-mentioned case of several coils mounted on the
same portion 35, additional rings similar to rings 53 would be
provided in the spaces between the coils to hold the latter in
position and support the sleeve 62 closing the recess aye
between the coils.
Furthermore, Figure 2 shows the portions 35 and 33 as
distinct parts, with threads 64 at both ends of the portions 35
for attaching them to the transverse portions 37, and the
support is assembled after the coil units have been mounted on
the portions 35.
It should also be noted, regarding the material of the
support, that the portions 33 and 35 can be made of different
materials, for instance stainless steel for the portions 33 and
copper or copper alloy for the portions 35.
A modified embodiment is shown in Figure 3. The coil 70 is
enclosed in a coil form 71 similar to that constituted by parts
56,57 of Figure 2. The coil is electrostatically shielded by a
slotted cylindrical member 72 made of a conductive material,
with insulating material to fill the slots 73. Like in the
above-described embodiment, the coil form is held in position
by rings screwed to a tubular part, which rings also engage the
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inner wall of the slotted member to back it against the
pressure of the Barlow fluid.
A modification to the above embodiments would be to
pressurize the interior of the recesses accommodating the coil
units to the pressure of the Barlow fluid. Fluid lines would
be routed inside the support 30 to connect these recesses to a
conventional pressure compensation device. In that case,
fluid-tight electrical feedthroughs would be provided to make
the electrical connections through the wall of the recesses.
Figure 4 shows an induction Sunday in accordance with the
invention adapted for measurement-while-drilling operation.
The Sunday 80 is located above the drill bit unit 82. The
support for the coils is provided by a section of the drill
collar 83, a tubular member of steel which is conventionally
connected to the bottom end of the drill string so as to be
mounted above the bit unit. The drilling mud is circulated
during drilling operation through the central bore 84 of the
drill collar. The drill collar has a large thickness in order
to add a suitable weight on the bit for drilling purposes.
Figure 4 shows only two coils, a transmitter coil 85 and a
receiver coil 86, but it will be understood that a bucking
coil, not shown, is associated with the receiver coil for the
purpose explained above, and the Sunday can comprise several
coil arrays having different spacings from the transmitter
coil. All those coils will be arranged in the same fashion as
coils 85 and 86.
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The drill collar section 83 has portions of reduced outer
diameter, thus defining circular recesses I in which the coils
are received, each coil being embedded in a sleeve 88 of rubber
or similar material which fills the recess. The rubber filling
is such that the outer surface of the sleeve 88 is
substantially flush with the cylindrical outer surface of the
portions 89 of the drill collar section 83 exposed to the
Barlow fluids. Each recess 87 has a central cylindrical
portion 90 of outer diameter Do smaller than the outer
diameter Do of portions 89, the respective coil being mounted
around that central portion, and frusto-conical portions 91
joining the central portion 90 to the portions I owe the drill
collar. Suitably the axial dimension of the frusto-conical
portions is equal to about one diameter of the respective coil.
Signals applied to the transmitter coil and received from
the receiver coils are conveyed by conductors, not shown, which
are preferably routed in longitudinal grooves formed on the
outer surface of the drill collar and willed with a suitable
insulating and protecting material. Those conductors are
connected to an electronic cartridge, not shown, located inside
the drill collar at the top of the induction Sunday.
In a preferred embodiment, a layer 92 of copper or other
highly conductive material is formed at least on the central
portion 90 of each recess to provide a surface of high
conductivity in the vicinity of the coils, the drill collar
section 83 being otherwise of steel as noted above.
~.~23~
Figure 5 shows in partly sectional view a preferred
embodiment of the induction Sunday according to the invention.
In the embodiment of Figure 5, a transmitter coil unit is
shown at 100 and a plurality of arrays of solenoid coils are
provided, each coil array including a receiver coil and a
bucking coil designed and positioned so as to cancel out the
effect of the direct coupling of the transmitter coil to the
respective receiver coil. Receiver coils with different
spacings from the transmitter are shown at 101, 102, and the
bucking coils respectively associated with the receiver coils
are shown at 101', 102'. All the coils are mounted about a
central support 105 having an outer cylindrical surface of
circular cross-section as clear from the section of Figure 6.
End portions 106, 107 of enlarged diameter are secured to the
support 105 at both ends thereof. A tubular sleeve 108 of
fiberglass epoxy is mounted about the coils to prevent contact
with the Barlow fluids. The sleeve is held in position
between the end portions 106, 107, the sleeve having the same
outer diameter as the end portions 106, 107. The free spaces
in the annuls 110 defined between the central support 105 and
the sleeve 108 are filled with pressurized oil and to that
effect, they are in communication with a pressure compensation
device, shown at 111 adjacent the lower end portion 107. The
compensation device 111, a conventional element of well logging
Sundays, acts to pressurize the oil present in the annuls 110
to a pressure slightly greater than the pressure of the
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Barlow fluids, so that the differential pressure on the
sleeve 108 is small.
The section of Figure 6 shows a preferred embodiment of the
central support 105. The support comprises two parts, an outer
sleeve 115 preferably of a highly conductive metal such as
copper or a copper alloy, and an inner core 116 preferably of a
metal of higher strength such as stainless steel. The outer
sleeve is mounted over the inner core with a loose fit to take
into account the difference between copper and steel with
regard to thermal expansion. The inner core 116 has a
plurality of longitudinal grooves 117 formed in its outer
periphery for routing conductors. As shown in Figure 6, the
grooves receive conductors 118 threaded inside a tubular shield
119. Although each groove can receive a pair of conductors
inside a shield, only one shield with conductors inside has
been shown in Figure 6. The purpose of the shield 119 is to
minimize interferences between the conductors located in
adjacent grooves. The shield can suitably be made of
ferromagnetic material such as mu metal. In addition to the
grooves 117, the inner core has a central longitudinal bore 120
which is used to route a power line and possibly conductors
connected to other logging apparatus suspended from the
induction logging Sunday of the present invention. The grooves
117 and the central bore 120 are in fluid communication with
the annuls 110 through radial holes, not shown, and therefore
are filled with oil at the same pressure as in the annuls 110.
s
A suitable method for manufacturing the inner core is extrusion
through a die of appropriate design.
The coils can be in the form of the same coil units as
described with reference to Figure 2. The receiver coil and
the associated bucking coil can be mounted on the same
insulating sleeve of ceramic, as shown for coils 101 and 101',
the respective sleeve being shown at 122, or they can be
mounted on separate insulating sleeves as shown for coils 102,
102'. Radial holes are formed through the outer sleeve 115 of
the support for passing conductors 123 connected to the
receiver and the bucking coils, while another conductor 124
connects the coils of each pair to each other.
Filler elements 125 e.g. of epoxy are provided in the
annuls 110 between the coils, to reduce the amount of oil
which is to be pressurized by the compensation device 111 and
thereby the length of this device.
The electronic cartridge necessary for the operation of the
transmitter is schematically shown at 130 adjacent the lower
end of the swindle with a pressure bulkhead 131 disposed between
the compensation device 111 and the cartridge 130. The
electronic cartridge 132 connected to the receiver coils is
mounted adjacent the upper end of the Sunday, with likewise a
pressure bulkhead 133 between the cartridge 132 and the coil
section of the Sunday. Figure 5 also shows an embodiment of the
upper end and lower end portions of the coil section of the
Sunday. In the lower end portion, two half rings 135, 136 are
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clamped over the end of the inner core, which has a peripheral
groove 137 for engagement with an inner collar 138 of the
half-rings. The half rings abut the end of the copper sleeve
and are secured to each other by bolts not shown, so that they
form a sleeve rotatable about the end of the support core. A
sleeve 140 is threaded over the half-rings and restrained
against rotation with respect to the support core 116 by a key
141 engaging key slots formed in the support and the sleeve
140. The sleeve 140 has a portion 142 of reduced outer
diameter over which the outer sleeve 108 fits. The housing 145
of the compensation device is connected to the sleeve 140 by a
nut 148 positioned between the sleeve 140 and the end portion
of the housing 145 and in threaded connection with the latter,
the nut 148 being secured against axial displacement with
respect to the sleeve 140 by a retainer 149. By turning the
nut by means of a special wrench, the housing is displaced
axially relative to the sleeve 140, hence to the support of the
coils In addition, the grooves 117 are connected at their
ends to inclined passages 121 which open into the central bore
120.
The arrangement at the upper end of the coil section
includes a sleeve 160 having threads 161 engaging threads
formed on the core 116 of the support adjacent its end. The
sleeve has a portion 163 of reduced outer diameter over which
the outer sleeve 108 fits. The sleeve 160 is connected to the
housing 165 of the pressure bulkhead 133 by a nut 166 similar
. .
to nut 148, in threaded engagement with the sleeve 160 and
restrained against axial displacement with respect to the
housing 165~
- The pressure bulkhead itself, schematically shown at 170,
is a conventional piece of equipment in we'll logging Sundays and
has axially oriented passages, not shown, receiving
pressure-resistant feedthroughs to which conductors are
connected on both sides. An intermediate tubular member 171 is
provided between the bulkhead 170, on the one hand, and the
sleeve 160 and the end 172 of the coil support, on the other
hand. The end 172 of the support core 116 has a reduced outer
diameter and is engaged within an annular recess of the
intermediate tubular member 171. A helical compression spring
173 is mounted between the intermediate member 171 and the end
of the support 172, to apply a resilient force to the bulkhead.
Axially oriented passages 175, 176 are formed respectively in
the intermediate member 171 and the sleeve 160 for the
conductors connected to the coils. The passages 176
communicate with the respective grooves 117 of the support
through a part 178 secured to the support and having a
respective plurality of radial slots for passing conductors.
