Patent Description:
Many industries and applications utilize apparatus sensors to measure parameters, such as pressure. In some cases, such sensors may utilize optical waveguides that are designed to penetrate a wall, bulkhead, or other feedthrough member wherein a relatively high fluid differential pressure exists across a feedthrough member. In addition, one or both sides of the feedthrough member may be subjected to relatively high temperatures and other harsh environmental conditions, such as corrosive or volatile gases, liquids, and other materials. For example, a bulkhead feedthrough may call for sealing an optical waveguide at high pressures of about <NUM>,<NUM> kilopascal (kPa) and above, and high temperatures of about <NUM> to <NUM> and above, with a service life of <NUM> to <NUM> or more years.

Several challenges exist with constructing a sensor utilizing such an optical fiber feedthrough. One of these problems involves the susceptibility of the glass fiber to damage and breakage due to its small size, flexibility, and brittle nature. Another challenge involves the potential for leaks when the optical fiber is sealed in a feedthrough bore using epoxy or other bonding materials, which may crack when exposed to an extreme range of temperatures and pressures.

<CIT> describes an optical waveguide feedthrough assembly that passes at least one optical waveguide through a bulk head, a sensor wall, or other feedthrough member. The optical waveguide feedthrough assembly comprises a cane-based optical waveguide that forms a glass plug sealingly disposed in a feedthrough housing. The optical waveguide includes a tapered surface biased against a seal seat formed in the housing. The feedthrough assembly can include an annular gold gasket member disposed between the tapered surface and the seal seat. The feedthrough assembly can further include a backup seal. The backup seal comprises an elastomeric annular member disposed between the glass plug and the housing. The backup seal may be energized by a fluid pressure in the housing. The feedthrough assembly is operable in high temperature and high pressure environments.

According to a first aspect, there is provided a feedthrough assembly according to the appended claims. According to a second aspect, there is provided an optical transducer according to the appended claims.

Embodiments of the invention generally relate to feedthroughs (e.g., feedthroughs for optical sensors, slickline, wireline, other electrically or optically conductive lines or pathways, and the like) suitable for use in high pressure, high temperature, and/or other harsh environments.

For some embodiments, an optical transducer is provided. A "measuring" portion of the transducer may be exposed to a high pressure, high temperature fluids when the optical transducer is deployed (e.g., in a wellbore or other industrial setting). The transducer may include an optical waveguide with a first portion that forms a first seal that isolates an "instrumentation" portion of the transducer from exposure to the high pressure and fluids to which the measuring portion may be exposed. The transducer may also include a second seal with a "stack" of material elements that contact a second portion of the optical waveguide to also isolate the instrumentation portion of the transducer from exposure to the high pressure and fluids to which the measuring portion may be exposed.

Together, the first and second seals may be considered to form primary and secondary seals, providing redundancy and some assurance of sealing (backup) even in the case where one seal is breached. Which is considered primary or secondary may be relatively arbitrary. Exact materials of various components of the transducer may be selected based on the desired pressure performance and the temperature criteria. For example, the second seal may include a stack of two or more (possibly alternating) materials selected to achieve a desired temperature performance while still maintaining the integrity of their shape for adequate sealing.

Also described is an optical transducer that generally includes at least one optical waveguide; at least one sensing element formed in a portion of the optical waveguide; and a feedthrough element designed to isolate a first portion of the transducer in communication with the sensing element from a second portion of the transducer containing the sensing element, wherein the feedthrough element comprises at least a first seal formed by a first portion of the optical waveguide in contact with a bore extending through a housing of the feedthrough element and a second seal formed by contact between an arrangement of sealing elements with a second portion of the optical waveguide and an inner surface of the feedthrough housing.

Also described is an optical transducer that generally includes at least one optical waveguide; at least one sensing element disposed in a portion of the optical transducer; and a feedthrough element designed to isolate a first portion of the transducer in communication with the sensing element from a second portion of the transducer containing the sensing element, wherein the feedthrough element comprises a seal formed by a first portion of the optical waveguide in contact with a bore extending through a housing of the feedthrough element and wherein a portion of a mating surface of the bore for forming the seal is undercut to reduce at least one of a magnitude or a gradient of a stress distribution in a region transitioning from high stress to no stress along the first portion of the optical waveguide.

Also described is a feedthrough assembly that generally includes at least one conductive line and a feedthrough element designed to isolate a first portion of the assembly from a second portion of the assembly, wherein the feedthrough element comprises a first seal formed by a first portion of the line in contact with a bore extending through a housing of the feedthrough element and wherein a portion of a mating surface of the bore for forming the first seal is undercut to reduce at least one of a magnitude or a gradient of a stress distribution in a region transitioning from high stress to no stress along the first portion of the line. The at least one conductive line may include at least one of an optical waveguide or a wireline. For some embodiments, a pre-loading force is applied to promote sealing of the first seal prior to deployment in an operating environment. For some embodiments, the feedthrough element also includes a second seal formed by contact between an arrangement of sealing elements with a second portion of the line and an inner surface of the feedthrough housing.

Also described is a feedthrough assembly that generally includes at least one conductive line and a feedthrough element designed to isolate a first portion of the assembly from a second portion of the assembly, wherein the feedthrough element comprises at least a first seal formed by a first portion of the line in contact with a bore extending through a housing of the feedthrough element and a second seal formed by contact between an arrangement of sealing elements with a second portion of the line and an inner surface of the feedthrough housing.

So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

Embodiments of the invention generally relate to feedthrough assemblies applicable for use in high temperature, high pressure environments. While transducers with optical waveguide feedthrough assemblies are described in detail below, embodiments of the invention also apply to other types of feedthroughs (e.g., wireline feedthrough assemblies, where wireline for electrical communication, logging, or running and retrieving downhole tools is isolated from harsh environments).

According to some embodiments, an optical transducer may incorporate a feedthrough assembly having a first seal formed by a frustoconical glass plug disposed in a recess (e.g., a counterbore) of a feedthrough housing. The glass plug may define a large-. diameter, cane-based, waveguide sealed within the recess in the housing and providing optical communication through the housing. All embodiments described herein provide for sealing with respect to the housing at or around the glass plug as the glass plug is brought into contact with a sealing surface of the recess.

As used herein, "optical fiber," "glass plug," and the more general term "optical waveguide" refer to any device for transmitting optical signals along a desired pathway. For example, each of these terms can refer to single mode, multi-mode, birefringent, polarization-maintaining, polarizing, multi-core or multi-cladding optical waveguides, or flat or planar waveguides. The optical waveguides may be made of any glass (e.g., silica, phosphate glass, or other glasses), glass and plastic, or solely plastic. Furthermore, any of the optical waveguides can be partially or completely coated with a gettering agent and/or a blocking agent (such as gold) to provide a hydrogen barrier that protects the waveguide.

<FIG> shows an example optical transducer <NUM> incorporating a feedthrough (F/T) element <NUM> that isolates a first (measuring) portion <NUM> of the transducer from a second (instrumentation) portion <NUM> of the transducer. The measuring portion <NUM> of the transducer may be used to sense a parameter (e.g., temperature or pressure) and convert the sensed parameter to a varying optical signal. The instrumentation portion <NUM> may provide an interface for sending the optical signals to electronic sensing equipment via a connector and an optical cable having one or more optical fibers.

As illustrated, according to certain aspects, the transducer <NUM> may be a pressure transducer, and the measuring portion <NUM> may include a pressure foot and bellows assembly <NUM>, which may move axially in response to external pressure, thereby transferring pressure changes to a filling fluid inside of the bellows assembly and to a sensing element. The sensing element may be formed from an optical waveguide having one or more Bragg gratings formed therein. The pressure changes in the filling fluid may cause a change in a grating wavelength. One or more second gratings may be isolated from changes in pressure or configured to respond with different sensitivities, providing for unique and separated values of the pressure and temperature changes via solutions to the resulting system of multiple equations.

The sensing element may be contained in a filling fluid (e.g., silicone oil) providing some protection and dampening, as well as transferring the pressure changes to the sensing element. As illustrated, this portion may be filled via an integrated fill port <NUM>, which may be sealed to ensure no communication between the environment (e.g., wellbore fluids) outside of the transducer and the housing containing the filling fluid. In some cases, this sealing may be accomplished by a sealing element and, for some embodiments, by a threaded element. The threaded element may provide reinforcement of the sealing element and may act as a backup seal to contain any leaks if the sealing element fails.

As shown in <FIG>, a sealing portion <NUM> of the optical waveguide <NUM> may be conical (or frustoconical) shaped and mate with a complementary shaped mating surface of a bore in a metal housing <NUM>, thereby forming a glass-to-metal seal <NUM>. Naturally occurring pressure during deployment and operation (e.g., within a wellbore) may force the sealing portion <NUM> towards the mating surface forming a seal. As will be described in greater detail below, a mechanism is also provided to "pre-load" the glass-to-metal seal <NUM> during fabrication of the transducer <NUM>, prior to transportation and deployment.

For some embodiments of the invention, an element, such as a thin washer <NUM> (illustrated in <FIG>), may be used between the sealing portion <NUM> and the mating surface of the housing <NUM> to promote sealing (e.g., by filling in any imperfections between the sealing surfaces, as well as alleviating the concentration of contact stresses). The washer <NUM> may comprise any suitable material for aiding the glass-to-metal seal <NUM>, such as a relatively soft metal (e.g., gold).

As described above, the optical waveguide <NUM> in the instrumentation portion <NUM> may be connected with an optical cable for sending the optical signals to electronic sensing equipment. Similarly, in a wireline feedthrough assembly, for example, the one or more wirelines may pass through the feedthrough element's housing and couple with a connector and an electrical cable having one or more wires for sending the electrical signals traversing the wirelines to electronic equipment.

Unlike conventional feedthrough optical transducers, the optical waveguide <NUM> is a monolithic structure providing both the sensing and the feedthrough aspects. In contrast, conventional transducers typically include two separate components to achieve these aspects: a sensing optical waveguide and a separate feedthrough glass plug, connected with the sensing waveguide via an optical fiber jumper. Furthermore, the optical fiber jumper is exposed to high pressures and potentially harmful fluids in conventional designs. The removal of such a jumper fiber from embodiments of the invention reduces the risks of performance failures.

When axially loading elements of brittle materials, such as glass as in the present example, stresses may be relatively linear across the mating surfaces of the elements before abruptly encountering a region transitioning from "high compression stress" to "no stress" at the end of the mating surface. This abrupt transition may result in a concentration of tensile stress at this region, which may lead to brittle material distortion and, ultimately, breakage. According to certain aspects, however, the magnitude and gradient of the transitional stress distribution may be reduced as shown in <FIG>, by removing (e.g., undercutting) a portion of the mating surface of the housing <NUM>, such that a gap <NUM> is created when the glass plug is seated in a complementary counterbore of the housing. This removal may be performed, for example, by undercutting the housing <NUM> along an inner ring of the bore's mating surface. In this case, the resulting surface of the housing <NUM> opposite the counterbore may have an annular undercut, as illustrated in <FIG>. For other embodiments, the reduction in the magnitude and gradient of the transitional stress distribution may be accomplished by casting or otherwise forming a housing <NUM> initially having an annular undercut opposite the counterbore, such that removal need not be performed. This reduction of the magnitude and gradient of the transitional stress distribution from high compression to no compression may help prevent breakage. In the case of the transducer <NUM>, this modification of the mating surface removes a failure mode, thereby increasing the reliability and lifetime of the transducer.

As illustrated in <FIG>, the feedthrough element <NUM> may also include one or more dynamic seals (commonly referred to as "chevron" seals or v-seals due to their "v" shape in cross section) as a second sealing feature. In an assembled product, these dynamic seals may contact a second portion of the optical waveguide <NUM> and the housing <NUM>, providing backup to the glass-to-metal seal <NUM> (or the glass-to-metal seal could be viewed as providing backup to the dynamic seals). As greater pressure is applied, the dynamic seals are compressed axially and further expanded radially, thereby tightening the seal between the optical waveguide <NUM> and housing <NUM>. Furthermore, the dynamic seals may also centralize the optical waveguide <NUM> within the transducer <NUM>, relative to the bore of the feedthrough housing <NUM> and to the glass-to-metal seal <NUM>.

As previously described, exact materials of various components of the transducer <NUM> may be selected based on desired performance and temperature criteria. For example, the second sealing feature may include a "stack" <NUM> of two or more (possibly alternating) materials <NUM>, <NUM> as shown in <FIG>. The material <NUM>, <NUM> may be selected to achieve desired temperature performance while still maintaining integrity of their shape for adequate sealing. Examples of such materials may include PEEK, Teflon, a polyimide, and other polymers. In some cases, for a relatively high temperature rating (e.g., up to <NUM>° C), a transducer may include a stack of alternating PEEK and Teflon. An even higher temperature rating (e.g., > <NUM>) may be achieved by utilizing graphite, graphite-reinforced polymers, or certain high performance polyimides, such as PMR-<NUM>, in the stack <NUM>. Of course, general substitutions between materials may be made, as appropriate, and materials of other parts may also be replaced to increase the temperature rating and the reliability.

Another feature that increases the temperature rating and the reliability of the transducer <NUM> is the lack of epoxy or other bonding material used in the measurement portion <NUM>. Conventional optical feedthrough designs typically expose epoxy used as a sealing feature in the measurement portion <NUM> to high temperatures. However, the structural integrity of epoxy can fail at such high temperatures, thereby leading to unacceptable leaks in the seal. With the glass-to-metal seal <NUM> and/or the dynamic seals in embodiments of the present invention, epoxy need not be used in the transducer <NUM>.

Material removals to reduce the magnitude and gradient of stress distributions at component interfaces, as described above, may also be utilized in the pre-loaded portion <NUM> of the transducer <NUM> shown in <FIG>. As illustrated, a shape of the waveguide <NUM> is designed to allow an axial force <NUM> to be applied to the waveguide during the assembly process. This pre-loading helps maintain contact in the glass-to-metal seal <NUM> before exposure to operating pressure. However, the stress concentrations that develop in the contact areas between the waveguide <NUM> and one or more members <NUM> (e.g., a clamp) used to apply force during pre-loading may result in damage to the optical waveguide. Therefore, as illustrated in <FIG>, one or more portions <NUM> of a member <NUM> may be removed (e.g., undercut) in an effort to reduce the magnitude and gradient of stress concentrations imposed on the waveguide <NUM> during pre-loading. The members <NUM> may be composed of any suitable material, such as plastic, and may be held in place by a collar in the pre-loaded portion <NUM>.

For some embodiments, an axial pre-loading force may also be applied to the stack <NUM> during fabrication of the transducer <NUM>. This pre-loading force may be used to axially compress and radially expand the dynamic seals and create the seal between the optical waveguide <NUM> and the housing <NUM>. For some embodiments, the pre-loading force may be supplied by a v-seal pre-loader <NUM>, as illustrated in <FIG> and <FIG>.

According to certain aspects, one or more diagnostic sensors (e.g., Bragg gratings) may be utilized to monitor the amount of force applied during pre-loading. In some cases, such a diagnostic sensor may be placed in any suitable position along the waveguide <NUM> that is subject to the pre-loading forces, such as between the pre-loaded portion <NUM> and the sealing portion <NUM> of the optical waveguide <NUM>. Such a diagnostic sensor may, for example, be monitored during the pre-loading and utilize a different wavelength band than the sensors used in the sensing element.

<FIG> illustrates an exterior view of the pre-loaded portion <NUM> depicted in <FIG>. The pre-loaded portion <NUM> includes a pre-loader housing <NUM> that surrounds the optical waveguide pre-loaded with the use of the member(s) <NUM>. A flange <NUM> of the pre-loader housing may be retained axially by one or more retention members of the v-seal pre-loader <NUM>, such as the bayonet-shaped members <NUM> shown in <FIG>. Retention of the pre-loader housing in this manner allows the housing to be radially shifted, such that a center of the housing may be disposed on-axis or slightly off-axis with respect to the bore of the housing <NUM> (and the axis of the v-seal pre-loader <NUM>). With this potential radial shift of the pre-loader housing, a bending force on the optical waveguide <NUM> is avoided, or at least reduced, during assembly of the transducer <NUM>. Minimizing this bending force avoids stressing the optical waveguide, such that shock loads do not crack the optical waveguide and lead to transducer failure.

During transducer assembly, the pre-loader housing may be disposed above the v-seal pre-loader <NUM> to surround the members <NUM>, rotated such that the flange <NUM> is retained by the members <NUM>, and positioned radially in an effort to avoid, or at least reduce, bending forces on the optical waveguide <NUM>. Then, the flange <NUM> of the pre-loader housing may be welded in position above the v-seal pre-loader <NUM>. Should the flange welds fail during operation of the transducer, the members <NUM> prevent the pre-loader housing <NUM> from moving axially away from the v-seal pre-loader <NUM>.

<FIG> illustrates an example final assembly of a transducer <NUM> in accordance with aspects of the present disclosure. Installation of the completed assembly may be relatively straightforward, for example, with the pressure foot of the sensing portion bolted onto a mandrel pressure port in an area to be measured. Connections for instrumentation may be made on the instrumentation side <NUM>, with isolation from the measured environment provided by the sealing features described above.

Claim 1:
A feedthrough assembly comprising:
at least one conductive line (<NUM>); and
a feedthrough element (<NUM>) configured to isolate a first portion (<NUM>) of the feedthrough assembly from a second portion (<NUM>) of the assembly, wherein the feedthrough element comprises:
a housing (<NUM>) having a bore extending therethrough;
a seal pre-loader (<NUM>) and a seal-pre-loader housing (<NUM>);
a first seal (<NUM>) formed by a first portion of the at least one conductive line (<NUM>) in contact with a mating surface of the bore of the housing (<NUM>);
a second seal formed by contact between a stacked arrangement of sealing elements (<NUM>) with a second portion (<NUM>) of the at least one conductive line (<NUM>) and an inner surface of the housing (<NUM>); and
a member (<NUM>) in contact between the pre-loader housing (<NUM>) and a third portion (<NUM>) of the at least one conductive line (<NUM>) and being configured to apply a first pre-loading force (<NUM>) in the axial direction of the conductive line (<NUM>) to promote sealing of at least the first seal (<NUM>) prior to deployment in an operating environment,
characterised in that the third portion (<NUM>) of the at least one conductive line (<NUM>) has a maximum outer diameter greater than a maximum outer diameter of the first portion and greater than an outer diameter of the second portion (<NUM>) of the at least one conductive line (<NUM>) to allow the first pre-loading force (<NUM>) to be applied.