Abstract:
The present invention is a strengthened fiber optic cable and the process for inserting the strengthened cable into a duct. The invention consists of pre-coating a fiber optic waveguide with an ultra violet (UV)/visible light curable resin such that the resin buffers the fiber optic waveguide. The pre-coated fiber optic waveguide is then cured in an UV/visible light oven at a temperature at ambient or above. An UV/visible light curable resin is pre-heated to a selected temperature and the buffered fiber optic waveguide and the at least one reinforcing fiber are transported through a binding resin bath, the fiber optic waveguide maintaining linear alignment throughout the bath as at least one reinforcing fiber is disposed about the fiber optic waveguide. The resin coated fiber optic waveguide and the least one reinforcing fiber are then cured in an UV/visible light curing station so as to form a fiber optic cable. The fiber optic cable is then transported to and insertion means which imparts sufficient translational force to the cable to impel the cable to a selected location in a duct.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to the field of fiber optic communications and more particularly to fiber optic cables, and more particularly to a process and apparatus for installing and retrieving a fiber optic cable in difficult locations, such as oil, gas and geothermal well bores, buildings, vessels, such as aircraft and ships, conduits, or in other extreme or difficult environments. Specifically, the present invention provides a process for treating a fiber optic microcable to provide a strengthened member and means of inserting and retrieving the cable in such structures. 
     2. Background of the Art 
     Fiber optics are used to carry transmission signals for cable television applications, data transmissions, as well as for use as sensors in the measurement of temperatures and pressures under various conditions. More recently, due to their higher capacity for transferring data, inherent abilities to withstand temperature variances, ability to perform distributed temperature sensing, and their reduced size, optical fiber cable has started to replace conventional electronic cables and gauges. Frequently, when the purpose of deployment is for testing, an electrical conductor is also installed to operate a testing device or apparatus. In many instances, the optical fiber cable is deployed in a conduit that has already been installed in the structure. A fiber optic microcable is basically comprised of a glass or plastic fiber core, one or more buffer layers, and a protective sheath. If there are no means of pulling the cable into the conduit, then the optical fiber must be of a light weight, such as a single optical fiber strand, coated with a thin layer, 125 microns, of a protective material. Such an optical fiber strand is both fragile and flexible, however the light weight is necessary so that the optical fiber may be inserted over the full length of the conduit by means of pressurized fluid injection. The protective sheath is typically composed of a heat polymerized organic resin impregnated with reinforcing fibers. Conventional resin materials are typically polymerized or cured at temperatures which may exceed 200° C. Such cables are not sufficiently robust for installation in well bores where the operating temperatures may reach 150° C. The protective sheath is typically composed of a heat polymerized organic resin impregnated with reinforcing fibers. In addition, the micro-cables frequently must be installed at lengths of up to 40,000 feet. State-of-the-part apparatus for installing such fiber optic microcable typically include means for pulling the cable from a cable reel, propelling the cable by means of tractor gears, or a capstan, and in some cases, impelling the cable through the duct by means of fluid drag. In some horizontal duct installations, a drogue is first fed through the duct, and the cable is then pulled through the duct by means of the drogue itself, or by a pulling line attached to the drogue at one end and the cable at the opposite end. All of the state-of-the-art methods for installing the cable place various stresses on the fiber optic core, causing degradation in the performance of the cable, and reducing the ability of the cable to resist conditions in which the cable may be installed. 
     U.S. Pat. No. 5,593,736 to Cowen discusses state-of-the-art processes for strengthening optical fiber cables, and details the reasons why the fiber optic properties are degraded by the strengthening processes. Cowen then describes and claims a process for fabricating a protective sheath about a fiber optic microcable, the process consisting of bathing the microcable in an ultraviolet light curable resin which may be impregnated with fibers to enhance the physical strength characteristics of the microcable. However, one of ordinary skill in the art would recognize that the cable of Cowen can not be installed in high-temperature environments due to the inherent properties of the resin. The fiber of Cowen has a glass transition temperature range of 60-105° and a strain elongation at failure of 1½%. Cowen teaches the use of a resin that is viscous at ambient temperatures. Such a resin would break down at high temperatures. As such, the Cowen process does not produce a microcable sufficiently rugged to be used in well bores and other high temperature environs. In addition, the process of Cowen itself can cause degradation of the optical properties of the fiber optic cable. It has been discovered that passing the fiber optic cable through too many rollers and/or tensioners, as with Cowen, can result in damage to the glass or plastic fiber core, cause micro-bends or broken fiber strands, and further degrade the cable. This is particularly true using standard telcom-grade multi-mode cable. Further, the process of Cowen cannot produce a cable that can be installed in high-temperature locations, the matrix coating of the cable of Cowen loses mechanical integrity and degrades rapidly at temperatures in excess of 150° C. 
     U.S. Pat. No. 4,479,984 to Levy et al. describes a process in which multi-filament bundles are impregnated with an ultraviolet curable resin to form a composite material suitable for use as a strength member in cables and other applications. 
     SUMMARY OF THE INVENTION 
     The present invention provides a process and apparatus for installing a fiber optic microcable in structures, where integrity of the cable is critical, and where such strengthened cable may be deployed, which process and apparatus overcome problems inherent in the prior art of cable installation. The resin selected is not limited to low viscosities at ambient temperatures as needed by Cowen and such resins need not be applied at ambient temperatures. The result is a process which can use high performance resins, with higher viscosities than the Cowen process permits, that are applied at an elevated temperature, and when cured, allow the resultant microcable to withstand high temperature environments. The process permits the construction of a cable with a strain elongation at failure greater that 2%, and which can match the strain elongation at failure of the reinforcing members. The process provides for fabricating a protective sheath, comprised of an ultra violet (UV)/visible light curable resin, about a standard fiber optic cable. The resultant fiber optic cable is relatively semi-rigid, permitting the pushing of the fiber optic cable into the duct. The fiber optic cable is then fed into a means for installation in said duct, and impelled in the duct to a selected location. For the purposes of this invention, a duct is defined to include any structure through which, or into which, it is desirable to insert fiber optic cable. The duct may be a channel, conduit, pipe, well bore, or tube, either in a closed or open system, all of which collectively will be referred to as a duct. The duct may be horizontal, vertical, slanted, or a combination of the foregoing, housed in aircraft, buildings, vessels, or in oil, gas or geothermal wells. 
     OBJECTS OF THE INVENTION 
     One object of the invention is to produce a fiber optic cable that may be installed in a duct without degrading the optical properties of the fiber optic. 
     A second object of the invention is to produce a cable that is resistant to temperatures in excess of 260° C. 
     It is a third object of the invention to produce means for installing the cable in the duct. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of the process for installing a cable in a duct. 
     FIG. 2 is a pictorial drawing of one embodiment of the apparatus for strengthening the cable 
     FIG. 3 is a pictorial drawing of a second embodiment of the apparatus for strengthening the cable 
     FIG. 4 is a plane drawing of a guide plate of the apparatus. 
     FIG. 5 is a plane view of apparatus for impelling the cable into a duct. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a fiber optic waveguide  100 , as typically received from a manufacturer, includes a buffer and core, is shown on optic feed reel  110 . Waveguide  100  is commercially available from various sources. Standard multimode fiber core is available from Corning. Alternatively, a hermetically sealed multimode fiber core, designed for high temperature, is available from Spectram. Reel system  140  contains a plurality of feed packages (not shown) containing reinforcing fibers  142 . The number of reinforcing fibers  142  can be varied, dependent on the amount of tensile strength to be imparted to the cable. Such reinforcing fibers  142  may be glass, Aramid, carbon, Spectran, ultra high molecular weight polyolefin, or equivalent reinforcing material, and in some cases, an electrical conductor. The combined waveguide  100  and reinforcing fibers  142  are drawn from their respective reels and through resin bath  150  and UV/visible curing station  170  by pulling means  175 . Pulling means  175  may be any conventional method for pulling cable, such as a capstan, winch, opposing tractors, or the like. 
     Waveguide  100  is fed directly to entry plate  151  of resin bath  150  without the need of being guided by feed rolls. Entry plate  151  (a plane view of which is depicted in FIG. 4) is adapted to sealingly receive both waveguide  100  and the plurality of reinforcing fibers  142  to allow fresh resins to continuously wet and lubricate the entrance opening of the waveguide  100  and the plurality of reinforcing fibers  142 . The geometry of waveguide  100  in relation to reinforcing fibers  142  is determined when initially feeding waveguide  100  and reinforcing fibers  142  into resin bath  150  through entry plate  151 , however, typically reinforcing fibers  142  are simultaneously pulled parallel to and radially about waveguide  100 . Resin bath  150  contains a UV/visible light curable resin, which is maintained at a constant temperature of between about 60° C. to about 100° C. by heating means  152 , such as a re-circulating heat exchanger. The resin is re-circulated through resin bath  150  by pump  154  so as to create a resin flow in the direction opposite to the direction of pull of waveguide  100  and cable  200  through resin bath  150 . The geometric relationship of waveguide  100  vis-{overscore (a)}-vis reinforcing fibers  142  is maintained as they are drawn through resin bath  150  by cable guides  158  and  160 , which have the same guide geometry as entry plate  156 , but which provide a progressively convergent path in order to guide waveguide  100  and reinforcing fibers  142  to a convergent point at focal plate  162 , which is sized to receive the resin coated waveguide  100  and reinforcing fibers  142  at a selected outside diameter. The resin of resin bath  150  is typically a formulation of heterocyclic high temperature (meth)acrylate with a cured glass transition of greater than 150° C. This formulation is optimal for reinforcing a cable which may encounter temperatures in excess of 260° C. In those situations where a lower temperature may be encountered, such as 200° C., a formulation using less (meth)acrylate may be used, as would be known by one of ordinary skill in the art. It is understood that the number of holes in entry plate  156  and cable guides  158  and  160  can be of any selected number, and that typically waveguide  100  will be fed through a center hole with strength members radially and uniformly disposed about waveguide  100 . 
     Upon exit from focal plate  162  the combined waveguide  100  and reinforcing fibers  142  now form a cable  200  which is pulled through the remaining portion of resin bath  150  and through exit plate  164 , which is also sized to a selected diameter to remove undesired amounts of resin. Resin coated cable  200  is then drawn through an ultra-violet/visible light curing station  170  at a constant speed of 20 feet per minute, curing station  170  having a power rating of 300 watts per inch, and being 10 inches in length. Such UV/visible light ovens are commercially available from Fusion and are well known in the art. The above rate, power rating and length are not limitations of the invention. The speed through curing station  170  is only dependent on the power of the curing station and the formulation of the UV/visible light curable resin. Curing stations may have a rating greater than 300 watts. The length is either increased or decreased dependent upon the power of the curing station and the curing characteristics of the resin, varying from about 1 inch to about 96 inches, as would be understood by one of ordinary skill in the art. 
     Upon curing, cable  200  is disposed on take-up reel  180 , or alternatively, fed directly into the means for inserting cable  200  in the duct, as described below. The silicone-sheathed cable and strength members are then collected on a storage means, such as a cable reel. Alternatively, the strengthened cable may be fed directly into the means for inserting the cable into a duct as described below. 
     FIG. 3 depicts a second embodiment of the invention wherein the waveguide  100  is additionally pre-treated with an UV/visible light curable soft cushioning buffer layer prior to being fed into the resin bath of FIG.  2 . The buffer layer provides an additional sheath about the periphery of the fiber of approximate thickness of 50 microns. This additional buffer layer can be a silicone resin. As in the first embodiment, waveguide  100  is drawn from reel  100 , and is then fed through a pre-treatment resin bath  120  containing an UV/visible light curable silicone resin, which resin is maintained at ambient temperature. If it is desired to increase the linear speed of the line, the temperature may be raised from ambient to about 60° C. The parameters of treating waveguide  100  at ambient temperature are taught in Cowen. Waveguide  100  coated with the UV/visible light silicone resin is then fed into UV/visible light curing station  130 , wherein the resin cures to provide a buffered fiber, which is then fed in to resin bath  150  in the same manner as in the first embodiment. As in the first embodiment, the optic strand is drawn from feed reel  110  into pre-treat resin bath  120 , through UV/visible light curing station  130 , into resin bath  150 , through UV/visible light curing station  170  and to take-up reel  180 , or directly to the injection means process described below, in a substantially linear path, and without being guided around any feed rolls in a manner that would tend to cause degradation of the optical properties of the fiber optic cable. Although the above embodiments have been discussed in terms of resin coating only one waveguide  100 , it is contemplated that a plurality of waveguides and a plurality of reinforcing fibers could be combined in one cable. 
     FIG. 5 describes a means  230  for inserting the strengthened cable  200  into a duct. It is irrespective whether or not there is any fluid pressure opposing the insertion of the cable. Upon exit from UV/visible light curing station  170  cable  200  is sufficiently rigid to permit it to be impelled into a duct, but cable  200  is also sufficiently flexible that it can be impelled around curves of approximately 12 inch radius. For the purposes of describing the invention, insertion means  230  will be sized for inserting cable  200  into capillary tubing. It should be appreciated, however, that cable  200  can be installed in any type duct. 
     Cable  200  is initially fed through a 0.25 inch outside diameter capillary tubing, inlet guide  206 , linearly aligned with a motive force  204 . Cable  200  is conducted through the feed wheel of  208  of motive force  204  and into a second capillary tube, outlet guide  210 , which communicates between the motive force and external guide  210 , which, in turn communicates with the duct (not shown). In the case in which the duct does not have any opposing fluid pressure, cable  100  may be directed straight into the duct. In some applications it will not be necessary to employ external guide  210 , and cable  100  can be directed into the duct. In those instances in which there is opposing fluid pressure in the duct, the strengthened cable is fed through a pressure chamber (not shown) and then into the duct. Pressure chambers are commonly used in operating oil, gas and geothermal well systems and arc known to one of ordinary skill in the art. Once cable  200  is in place, motive force  204  is actuated by applying power from power source  202 , and cable  200  then feeds from take-up reel  180 , or in some instances directly from UV/visible light curing station  170 , through inlet guide  206 , motive force  204 , outlet guide  210 , external guide  218 , and into the duct. The motive force  204  may be selected which can impart the requisite amount of force to overcome opposing fluid pressure in the duct. In the exemplary embodiment, motive force  204  was selected to be motor driven feed wheel  208  which includes an adjustable following roller  212 . Cable  200  was fed between feed wheel  208  and following roller  212 , with the linear speed of the cable determined by the amount of tension applied to the cable by following roller  212 . Tensioners  214  may be employed to adjust the bias of following roller  212  against the outside surface of cable  200  against feed wheel  208 , thereby either increasing or decreasing the linear speed of cable  200  and without damaging fiber waveguide  100 . The insertion means of the exemplary embodiment of FIG. 5 may also contain a counter pressure wheel  220  which monitors the number of linear feet of fiber optic cable deployed in the duct. Output from counter pressure wheel  220  can be visibly presented in counter  222 . The means of monitoring the linear feet of fiber optic cable deployed is not restricted to a pressure wheel. There are many monitors known in the art for measuring linear feet of cable deployed, such as photo-optic sensors, laser trackers, and the like. Further, the invention is not limited by the means of motive power employed to insert the cable. For example, caterpillar drive may be used, the only restriction being that the means of motive force may not crimp or overly bend the fiber core, thereby imparting degradation to the cable. 
     Since cable  200  is of semi-rigid construction, it may be deployed and used in a manner hereto not possible. It is well known that the protective surfaces of cables for instruments, including fiber optic cable, deteriorate sufficiently over time in oil, gas, and geothermal well bores, and other corrosive or remote locations, due the high temperature and corrosive natures of the fluids in such well bores or locations, to become unstable and unusable. Yet it may be desirable to be able to periodically monitor parameters in the well bore without having to run a new fiber optic installation each time. It would be advantageous to install the instruments in the well boreand attached to the standard tubing permanently installed in the well bore. With the cable of the invention, such instruments may be adapted with a sealed optical coupler to receive the semi-rigid cable  200 , then when it is desirable to monitor the well bore conditions, cable  200  is inserted in the well to the location of the selected instrument. into the optical coupler, permitting monitoring of the well bore. 
     Concomitantly, reinforcing fibers  142  could include an electrical conductor which could then be used to power the remote instrument, or a conductor could be attached to cable  200  upon insertion of cable  200  in the duct, permitting installation of the electrical cable with cable  200 . 
     While the present description contains much specificity, this should not be construed as limitations on the scope of the invention, but rather as exemplifications of one/some preferred embodiment/s thereof. The full scope of the invention is further illustrated by the claims appended hereto.