Patent Application
20240209731
Oil and gas wells are harsh environments due to the chemically active materials and elevated temperatures and pressures that are present. Optical fiber-based instrumentation can be a robust and reliable form of instrumentation used in oil or gas wells as long as the optical fiber is sealed for both hermeticity and mechanical protection.
For these reasons, the optical fiber designed for use in oil or gas wells must be sealed from chemical contaminants. Typically, the optical fiber is placed in a capillary tube that isolates the optical fiber from the environment. The capillary tube can be made of metallic material, such as INCONEL® or stainless steel. (INCONEL is a registered trademark of HUNTINGTON ALLOYS CORPORATION.) For instance, INCONEL® 825 is a specific example of an alloy used for manufacturing the capillary tube for a fiber optic cable. INCONEL® 825 is considered to be a high-performance alloy that offers excellent resistance to heat and corrosion while retaining good mechanical properties, such as resistance to stress-corrosion cracking, localized pitting, and crevice corrosion.
For the fiber-based instrumentation, a downhole gauge for use downhole is connected to a fiber optic cable. Typically, the downhole gauge is installed at the end of the fiber optic cable. A mechanical connection is made between the cable to the downhole gauge in which the optical fiber is spliced together and an outer tube is welded between the cable and downhole gauge to enclose the splicing
As is expected, the mechanical connection where optical fiber is joined by fusion splicing can be one of the more common sources of failure in the fiber optical cable. The typical mechanical connection to integrate the gauge with the cable simply uses a large diameter sleeve. As the optical fiber is being fused by splicing, the large diameter sleeve is slid over the cable. Once splicing is complete, the sleeve slides over the splice and affixes to the cable and the gauge. For these reasons, the sleeve is not only larger, but is much stiffer than the surrounding cable, which may not be preferred.
Other methods can be used. For example, the optical fiber can be vibrated out of the cable so there is room for splicing to be performed. The fiber can then be vibrated back into the cable. This method, however, is only useful for a small subset of cable designs.
For these reasons, there is a need in the industry to provide a cable connection that alleviates the drawbacks associated with prior art connections. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
A method is disclosed to connect a termination of a fiber optical cable having optical fiber to a downhole gauge. The method comprises: providing a plurality of tubes including a gauge-end tube, a cable-end tube, and one or more spanning tubes, each of the tubes having ends and defining a passage therethrough; affixing the gauge-end tube to a gauge end of the downhole gauge, the passage of the gauge-end tube permitting a gauge fiber end of the optical fiber to extend therethrough; affixing a cable-end tube to the termination of the fiber optic cable, the passage of the cable-end tube permitting a cable fiber end of the optical fiber to extend therethrough; providing access to the gauge and cable fiber ends of the optical fiber by nesting adjoining ones of the tubes together; splicing the gauge and cable fiber ends of the optical fiber together; and enclosing the splicing of the optical fiber by at least partially unnesting the adjoining tubes and affixing the ends the adjoining tubes together.
A cable connection disclosed herein is assembled according to the method described above to protect the splicing of the optical fiber between the fiber optical cable and the downhole gauge for use in a wellbore.
A cable connection is disclosed herein to protect splicing of optical fiber between a fiber optical cable and a downhole gauge for use in a wellbore. The cable connection comprises a plurality of tubes. Each of the tubes has ends and has a passage therethrough for the optical fiber. The tubes include a cable-end tube, a gauge-end tube, and one or more spanning tubes. The cable-end tube is configured to affix to a termination of the cable, and the gauge-end tube is configured to affix to a gauge end of the downhole gauge. The one or more spanning tubes are configured to position between the cable-end tube and the gauge-end tube. Adjoining ones of the tubes are configured to nest together to provide access to splicing of the optical fiber between the fiber optical cable and the downhole gauge. The ends of the adjoining tubes are configured to affix together nested at least partially inside one another to enclose the splicing of the optical fiber.
A fiber optic cable is disclosed herein for conducing optical fiber in a wellbore. The fiber optic cable comprises a cable section, a downhole gauge, and a cable connection. The cable section is of the fiber optic cable in which the optical fiber passes. The downhole gauge is configured to connect with splicing to the optical fiber. The cable connection as described above is configured to protect the splicing of the optical fiber between the fiber optical cable and the downhole gauge.
The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.
The optical fiber carries optical signals, which can convey measurement information, such as pressure and temperature measurements, from downhole gauges or sensors 50. The gauges 50 are spoolable and are attached by mechanical connections to sections of the fiber optical cable 30. The optical fiber is fused by splicing between the cable and spoolable gauges 50. The cable 30 and spoolable gauges 50 are continuously spooled onto a drum or a reel 40 for later deployment into a well. Therefore, the mechanical connections used between the spoolable gauges 50 and the cable 30 are also spooled onto the drum 40.
The capillary tube and outer protective structure of the cable 30 protects the optical fiber from the environment. Because elevated temperatures and pressures are prevalent in the subterranean formation, the capillary tube of the cable 30 can be made of metallic material, such as INCONEL® 825, to provide mechanical and thermal protection. The cable 30 typically has a circular cross-sectional shape, but other shapes are possible.
Various forms of equipment can be used for installing the optical fiber cable 30 in the wellbore 12. For example, the optical fiber cable 30 arrives at the installation site wound on a drum or a reel 40. Using conventional reel equipment 42, the optical fiber cable 30 is threaded from the reel 40 through a sheave 14 located on a rig (not shown) or the like at a higher elevation than the reel 40. The outgoing run of the optical fiber cable 30 that leaves the sheave 14 can then be inserted into the wellbore 12.
During installation, the optical fiber cable 30 is unwound from the reel 40 and progressively inserted in the wellbore 12 until the desired depth is reached. For example, the cable 30 can be run along the length of a tubing string 20 being inserted in the wellbore 12 as shown in
The insertion of the optical fiber cable 30 in the wellbore 12 is thus a continuous process. Because the optical fiber cable 30 has been completely assembled at the manufacturing site, there is no need to make any cable splices at the installation site, and the optical fiber cable 30 installs by being unwound from the reel 40 and pushed in the wellbore 12 until reaching the intended installation depth.
For this reason, the optical fiber cable 30 has a structure allowing the cable 30 to bend without being damaged. The cable 30 is mostly subjected to bends during the manufacturing and installation process so that the cable 30 need to resist those bending stresses without damage that would otherwise undermine its long-term reliability.
The bend stresses to which the optical fiber cable 30 are subjected during manufacturing occur when the optical fiber cable 30 is wound on the reel 40. Another bend stress arises during the installation of the optical fiber cable 30 when the cable 30 is unwound. The most severe bending stress typically arises when the optical fiber cable 30 passes over the sheave 14 because the sheave 14 can have a radius of curvature that is smaller than the radius of the reel 40 and any elbow radius that may be present in the wellbore 12. For instance, a first bend occurs at the sheave 14 when the optical fiber cable 30 enters the sheave 14 and curves around it, and a second bend occurs when the optical fiber cable 30 exits the sheave 14 and straightens out to enter the wellbore 12.
The external diameter of the cable 30 is preferably as small as possible so the cable 30 takes as little space as possible in the wellbore 12. For example, the optical fiber cable 30 can have a cross-sectional dimension in the range from about 0.1 inch to about 0.625 inch.
The length of the optical fiber cable 30 can vary depending on the installation. The range of lengths can be between several hundred meters to several kilometers. Given such lengths, being able to spool the cable 30 on the reel 40 facilitates transportation of the cable 30. Because the optical fiber cable 30 is spoolable on the spool or reel 40, the cable 30 is sufficiently thin and flexible to be wound on the reel 40 and transported in a wound configuration between the manufacturing facility and the installation site.
At periodic positions along its length, the cable 30 includes the spoolable downhole gauges 50, which can be any suitable sensors or transducers for measuring environmental conditions (pressure, temperature, etc.) in the wellbore 12. For example, the spoolable gauges 50 can be annular gauges and tubing-ported spoolable gauges. As shown in
As discussed above, sections of the cable 30 are spliced together to build up the length required for the installation. The splicing is used to arrange the spoolable gauges 50 in selected positions along the length of the optical fiber cable 30 to meet the needs of the installation so that prefabricated sections of the cable 30 have the spoolable gauges 50 for measuring different parameters, such as temperature and/or pressure, at desired depths in the wellbore 12. The cable 30 is custom built for the installation by splicing the spoolable gauges 50 to plain cable sections that have no sensing capability. With this approach, the optical fiber cable 30 can have the desired sensing capability at the desired location on the cable 30 (the desired position between the cable sections) and over the desired length.
The cable connection 60 of the present disclosure protects the splice of the optical fiber between the spoolable gauge 50 and the adjoining sections of the cable 30. The connection 60 can also be used to protect the splice of the optical fiber between adjoining section of the cable 30. The cable connection 60 affixes to the outer protective structure of the optical fiber cable 30 and affixes to the end of the spoolable gauge 50 to mechanically protect the splice made in the optical fiber of the cable 30.
The cable connection 60a-b includes a plurality of tubes 61 that are nested and affixed together to enclose the passage of optical fiber. In the present implementation, the nested tubes 61 include splice tubes 62a-c and spanning tubes 64a-b. Each of the nested tubes 61 has a longitudinal passageway, such as a throughbore, through which the optical fiber (not shown) can be threaded. The spanning tubes 64a-b have a smaller diameter to nest in the splice tubes 62a-c, and the splice tubes 62a-c have a larger diameter to nest on the spanning tubes 64a-b and terminations of the cable sections 31a-b and ends 52a-b of the spoolable gauge 50.
As specifically shown in
The downhole cable connection 60b in
The order of the nested tubes 61 in the cable connections 60a-b is repeated end-to-end on both ends 52a-b of the spoolable gauge 50 to accommodate how the cable 30 is spooled from the reel (40) and through the sheave (14) and other installation equipment used to insert in the wellbore (12). As noted, most of the bending experienced by the cable connections 60a-b occurs when unwinding the cable 30 from the reel (40) and passing it through the sheave (14) and any other installation equipment. By contrast, winding the cable 30 and the spoolable gauges 50 on the reel (40) during manufacture can be a more controlled process that avoids excessive bending. Therefore, the uphole and downhole connections 60a-b are arranged in the same direction for encountering bending during unspooling and passage through the sheave (14) and the like.
Returning to
The individual lengths L1, L2, L3, L4, and L5 for the splice tubes 62a-c and spanning tubes 64a-b can be varied to define the rigidity and flexibility of the cable connection 60a connect between the cable section 31a and the gauge end 52a. The present example is based on the uphole cable connection 60a used between a 0.25-inch diameter cable 30 and a comparable end 52a of a spoolable downhole gauge 50. The end tubes 64a, 64c have lengths L1, L5 that are about 11 and 14 inches, respectively. The intermediate splice tube 64b has a length L3 of about 6 inches. For their part, the spanning tubes 64a-b have lengths L2, L4 of about 8.5 and 14 inches, respectively. Overlap between the nested tubes 61 can be about 0.5 inch, and the cable-end tube 62a can have an overlap of about 1 inch to cover any hex and roll crimps on the cable 30.
For this implementation, the 11-inch end tube 62a can have an outer diameter of 0.3125 inch and an inner diameter of 0.235 inch. One end is bored with a 0.255-inch diameter to fit over the cable 30 with a depth of 1.25 inch. A step feature can be left on the non-bored end, but a step feature may not be left on bored end of the tube 62a. The 14-inch end tube 62c can also have an outer diameter of 0.3125 inch and an inner diameter of 0.235 inch. One end can be bored with a 0.255-inch diameter to fit over the gauge end 52a for a depth of 0.50 inch. A step feature can be left on non-bored end, but a step feature may not be left on bored end. The 6-inch intermediate tube 62b can have an outer diameter of 0.3125 inch and an inner diameter of 0.235 inch. Outer diameters of the spanning tubes 64a-b can be configured to nest inside the splice tubes 62a-c.
As noted, the protective structure of the cable 30 is typically composed of metal, such as INCONEL or stainless steel. The spoolable gauge 50 is also typically composed of metal, such as INCONEL® 718. The nested tubes 61 are also composed of metal, such as INCONEL® 825.
To protect the optical fiber during manufacture and use, heat sink assemblies can be used inside the nested tubes 61, and in particular inside the spanning tubes 64a-b. For instance,
Nesting of the tubes (61) is done to provide room for performing splicing and the optical fiber can be accessed. Once the splicing is completed, the tubes (61) can be unnested and affixed (welded) together at their joints. Heat sinks are preferably used at least temporarily when the end tubes 62a, 62c are affixed to the gauge end and cable termination. Additionally, heat sinks are preferably used when the intermediate tube 62b is affixed to the other spanning tubes 64a-b. These heat sinks may remain in place after assembly.
The second spanning tube 64b and the intermediate tube 64b are threaded on the pigtail of the fiber 34, and the spanning tube 64b is inserted into the gauge-end splice tube 64c so the optical fiber 34 can pass from the gauge end 52a and through the tubes 62c, 64b, 62b for eventual splicing.
As shown in
In the implementation shown here and as in
As can be seen by the proposed solution, multiple nested tubes 61 slide over one another such that portions of the tubes 61 nest inside one another. This allows the tubes 61 to be withdrawn during assembly so there is room to perform the optical splices of the optical fiber 34. Once the optical splices are complete, the nested tubes 61 can be extended to cover the entire length of optical fiber 34 between the cable section 31 and end 52 of the spoolable gauge 50. The nested tubes 61 are then welded (or mechanically connected) together and to the gauge/cable to provide a continuous structure. Preferably, all of the nested tubes 61 have mechanical properties similar to the downhole cable 30.
Each of the tubes 61 for the cable connection 60 has a length and/or a material configured to flex during bending. Compared to the traditional method of using a single, larger splice tube to protect the splice of an optical fiber, the cable connection 60 with the nested tubes 61 has a much lower bending stiffness allowing it to be more readily spooled onto a drum or reel 40 with the downhole cable 30 and spoolable gauges 50. Compared to the ‘vibrating method’, the proposed solution is compatible with standard downhole cable designs, is easier to implement, and is applicable to a larger number of optical fibers.
The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter.
In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.
