FR2585851A1 - OPTICAL FIBER CABLE. - Google Patents

Abstract

THE INVENTION RELATES TO A MEASURING INSTALLATION HAVING A FIBER OPTIC CABLE. AN OPTICAL FIBER IS PLACED IN A TUBET THE FIBER AND THE TUBE HAVING THE SAME COEFFICIENT OF THERMAL EXPANSION, AND A FLUID0 IS PLACED BETWEEN THE TUBE AND THE FIBER, THIS FLUID BEING A SILICONE OIL THE DENSITY OF WHICH IS EQUAL TO THAT OF THE FIBREF. THE CABLE CAN THEREFORE SUPPORT HIGH TEMPERATURES AND THEN ALLOWS THE TRANSMISSION OF PASSIVE OPTICAL SIGNALS FROM REGIONS LOCATED AT HIGH TEMPERATURES. APPLICATION TO THE DIAGRAPHY OF OIL BORES.

Description

The present invention relates to an optical fiber cable, intended to be

used in the instruments of

  logging surveys, non-exclusively.

  When drilling a new oil well, the pressures and temperatures must be detected at depths that may be, for example, 5 km. At this depth, the temperatures can be of the order of 400 C and the pressures of the order of 600 bars. Current techniques for measuring these temperatures and pressures

  electronic circuits and semiconductors

  drivers who can not be exposed to such conditions

  only for very short periods. We can not

  therefore, to take a sample of pressure and temperature

  only erase, then remove the equipment. It is not normally possible to leave the equipment in these conditions for a relatively long time so that

  measurements can be made during a period.

  The present invention relates to a data transmission installation which allows remote measurements under conditions of high temperatures and pressures,

  as described above, for a period of

quente.

  More specifically, the invention relates to an installation

  which includes an optical fiber housed in

  a hermetically sealed tube constituting an organ of

  constraint box, and a flotation fluid, placed in the tube and intended to support the optical fiber so that, when the cable is supported vertically, the optical fiber is protected against excessive stresses,

  thanks to its floating in the fluid that surrounds it.

  The invention also relates to an optical fiber cable which comprises an optical fiber housed in a hermetically sealed tube intended to absorb the stresses, the fiber being coated with an adherent material having a density different from that of the fiber, and a flotation fluid placed in the tube and intended to support the coated optical fiber, the density of this fluid

  being such that, when the cable is supported vertically-

  lently, the coated optical fiber is protected against

  undesirable constraints, given its float-

sound in the fluid that surrounds it.

  A high pressure resistant seal preferably provides a seal around the fiber at least

  in the region that must form the lower part.

  The installation can advantageously have a cap-

  A pressure sensor modulates the light reflected back along the optical fiber or along a second return fiber in proportion to the detected pressure. The system

  may include, instead of or in addition to, a temperature sensor

  erase that modulates the light sent back along the fiber

  or along a separate return fiber, proportional-

at the detected temperature.

  Preferably, the sensor or each sensor comprises a reflector in which the light is focused by a focusing arrangement and the reflector is moved so that it passes through the focus, depending on the temperature

or the detected pressure.

  Other features and advantages of the invention

  tion will become more apparent from the following description,

  with reference to the accompanying drawing in which Figure 1 is a schematic elevation in partial section of a data transmission installation for logging soundings, according to one embodiment of the invention; and Figure 2 shows a sensor array

  of the apparatus of Figure 1, in more detail.

  We first refer to Figure 1; an optical fiber F (the apparatus can include several) is

  housed in a stainless steel tube T welded longitudinally

  This tube is connected with a housing H which contains a ferrule G and a lens L, to form a complete cable termination assembly. The tube T was laser welded (or otherwise hermetically sealed) and the tube was tightened with S-type metal-on-metal (or other) hermetic seals so that a high-pressure seal was formed between the housing H and the tube T, a connection formed between the housing H and the inside of the tube T for the transmission of the fluid. The whole system is filled with a liquid,

  for example a silicone oil O having a density of

  prescribed to correspond to that of the optical fiber and its main coating. In this mode of

  realization, the preferred main coating is a rubber

  silicone rubber, but a secondary coating may allow sealing and obtaining a low coefficient of friction, as described in the following

present memory.

  The tube T is formed of a material whose coefficient

  The thermal expansion is well adapted to that of the optical fiber. It has the effect of reducing the thermally induced stresses in the fiber when the assembly

  is placed in variable temperature conditions.

  An advantageous type of tube is a laser-welded stainless steel tube marketed by Amortech under the designation of tube K. Preferably, the tube T, the housing H and the shell G are formed of "Invar" which is a nickel alloy. However, there are other alloys

  which can be selected so that the coef-

  ficient thermal expansion of the fiber and the alloy correspond, such alloys being commonly used

  for the formation of glass-to-metal joints.

  An important feature of the installation

  is the filling fluid, formed of a silicone oil.

This fluid has several purposes.

  1. First, it gives the optical fiber a float

  neutral by proper selection of the oil and the thickness of the main coating carried by the fiber,

  when the cable is suspended vertically for example.

  The silicone oil is chosen with a density corresponding to

  to that of fiberglass augmented by its coating

  primary education. The fiber "floats" in the filling fluid and does not have to support its own weight

  when suspended vertically.

  2. It transmits the stresses regularly over the entire length of the fiber, when it exceeds

  stresses induced by hydrostatic pressure.

  3. The tube T can withstand a crushing pressure difference of the order of 600 bar, when selecting a diameter and a wall thickness which

  suitable. The liquid prevents the transmission of pressure

  differential pressure to the fiber which only suffers

  hydrostatic flow due to the height of the oil column

of silicone.

  4. During winding and handling of the cable,

  the compression stresses are cashed by

fluid.

  All of these characteristics contrast with the case in which the fiber is surrounded by a polymer. In this case, the stresses due to mechanical forces or thermal stresses applied to the outer tube T can

  be cashed only by "creep" of the polymer with respect to

  wearing to fiberglass. This can create excessive crushing stress on the fiber or stress

  shear, as a result of the axial displacement of the polymer.

  In the manufacture of the installation shown in FIG. 1, the tube T can be filled by using pressurized silicone oil introduced at one end of the assembly formed by the tube and the fiber, with a vent hole at the other extremity. It is possible to fill a stretch of cable of 10 km in length from a few hours. When the cable is suspended vertically, while the temperature and the external pressure are high, higher than the normal ambient values, for example in a log of a petroleum survey, the result of the encapsulation technique is the following: a) the Differential thermal expansion and the corresponding mechanical stresses are minimized by selecting the tube material so that its coefficient of thermal expansion corresponds to that of the glass fiber, b) the presence of a stress relieving device, when the cable is coiled while subjected to forces. The compression forces of the tube are transmitted to the fluid which can only transmit the

local hydrostatic pressure.

  Referring now to Figure 2 of the drawings.

  This represents an extension of the housing H of the

  Figure 1. In this extension H 'are arranged a diaphragm

  D and a mirror M fixed to this diaphragm D. The latter is fixed at its periphery between flanges J and K. The internal cavity of the extension H 'of the casing is filled with a gas at normal ambient pressure and, when there is a difference of pressure on both sides of the diaphragm D, this one flexes and moves the mirror M with respect to

  beam B from the L-lens.

  re returned to the lens is therefore increasingly reduced when the mirror is more and more defocused

  while the pressure increases outside the box.

  When calibration is suitable, the absolute pressure

can be measured.

  In addition to the pressure sensor, a temperature sensor

  structure has a temperature-sensitive N bar,

  which may have a linear coefficient of thermal expansion

  important and which carries at its end, a mirror M 'for receiving a light beam B' focused on the mirror M 'by a second lens L', itself coupled to a second optical fiber F 'encapsulated in a tube

  metal, in the same way as the previous fiber.

  Thus, the installation may comprise two or more fibers each individually encapsulated in a tube

hermetic.

  The individual encapsulated fibers are incorporated

  electro cables or cables capable of

to support constraints.

  In the embodiment described, the diameter

tube T is of the order 1 mm.

  Fibers having a primary coating have, for example, an outer diameter of 250 to 350 microns. A value of 250 microns is normal in the case of a fiber

multimode type 50/125 microns.

  The encapsulation scheme described creates

  induced stresses under the action of external pressure, external temperature variations (and especially high temperatures up to about 400 C), tensile forces applied when the optical fiber is suspended vertically, in lengths equal to or greater than 5 km, bending during winding of a cable section, and compression during winding

of the cable section.

  Flotation fluids can be various qualities of silicone oils. They have a decent beach

  of density so that a whole range of coated fibers

  can be performed with neutral flotation.

  Silicone oils also resist degradation

at a high temperature.

  The optical fiber (singlemode or multimode) carries the buffer coating which ensures the flotation of the fiber, the preferred buffer coating being a silicone rubber of the type previously described. A secondary coating may be placed on the silicone rubber to reduce friction between the fiber and the metal tube T. This secondary coating may be a thin metal layer obtained by sputtering or otherwise on a silicon nitride layer. The secondary coating also forms a hermetic seal preventing expansion of the silicone rubber and preventing contact between the rubber

and silicone oil.

  The hole of the metal tube T preferably has an internal diameter of between 1 and 2 mm and can contain one, three or even seven optical fibers. The water in which the cable is used has a density of 1.0, but this density varies in the dense drilling mud and approaches 2.0 and even exceeds this value.

reaching for example 2.2.

  As described above, the possibilities of using the cable fiber at high temperature can be exploited by means of passive optical sensors which do not use electronic circuits.

  and semiconductor materials for their operation.

Claims (11)

  1. Data transmission facility,   characterized in that it comprises an optical fiber (F) housed in a hermetically sealed tube (T) constituting a stress-receiving member, and a floating fluid (O) placed in the tube and intended to support   optical fiber so that when the cable is   vertically, the optical fiber is protected by   its floating in the surrounding fluid against the excessive strains.   2. Fiber optic cable, characterized in that it comprises an optical fiber (F) housed in a tube (T) hermetically closed and constituting a collection member   constraints, the fiber being coated with an adhered material   whose density is different from that of the fiber, and a flotation fluid (O) placed in the tube and intended to support the coated optical fiber, the density of the fluid being such that, when the cable is supported vertically, the coated optical fiber is   protected against undue stresses by its float- its in the surrounding fluid.   Cable according to Claim 2, characterized   in that the adherent material is a silicone rubber.   4. Cable according to claim 2, characterized in that the tube (T) is a longitudinally welded stainless steel tube. Cable according to claim 2, characterized   in that the fluid (O) is a silicone rubber.   Cable according to claim 2, characterized   in that the coated optical fiber (F) has a coating tightly sealed.   7. Cable according to claim 6, characterized in that the waterproof coating comprises a coating   secondary placed outside the coated fiber.   8. Cable according to claim 6, characterized in that the waterproof coating is selected from the group   which comprises a metal and a silicon nitride.   9. Data transmission installation, including   A cable according to claim 2, characterized in that it further comprises a housing (H '), a gasket   ensuring the sealed cooperation of the housing with one end   mity of the tube, and a sensor placed in the housing and intended to detect the physical parameters and optically coupled to the fiber so that the data corresponding to the parameters detected are transmitted.   10. Installation according to claim 9,   characterized in that the sensor comprises a device (L L ') for transmitting light in a larger quantity.   or smaller depending on the variation of the detected parameter.   11. Installation according to claim 10, characterized   characterized in that the housing (H ') is connected to the inside   of the tube (T) so that fluid can be transmitted.