Patent Publication Number: US-10323483-B2

Title: Mitigation of hydrates, paraffins and waxes in well tools

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 USC § 119 of the filing date of International Application Serial No. PCT/US11/64762, filed 14 Dec. 2011. The entire disclosure of this prior application is incorporated herein by this reference. 
     BACKGROUND 
     This disclosure relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in one example described below, more particularly provides for mitigation of accumulation of undesired substances in a well tool. 
     To prevent formation of hydrates, waxes, paraffins and other undesired substances in well tools, the well tools can be positioned at or below a certain depth, with the temperature at that depth being greater than that at which the hydrates, etc. form. However, conditions change over time, and predicting the appropriate depth for certain well tools is an inexact science. 
     It will be appreciated that improvements are continually needed in the art of mitigating accumulation of undesired substances in downhole well tools. 
     SUMMARY 
     In this disclosure, systems and methods are provided which bring improvements to the art of preventing or reducing accumulation of precipitates, hydrates, waxes, paraffins, etc.). One example is described below in which a wall of a flow passage in a well tool is heated to mitigate the accumulation of the undesired substances. Another example is described below in which the wall is vibrated to mitigate the accumulation of the undesired substances. 
     In one aspect, a method of mitigating formation of an undesired accumulation of a substance in a well tool through which a well fluid flows is described below. In one example, the method can include heating a surrounding wall of an interior flow passage through which the well fluid flows. 
     In another aspect, a system for of mitigating formation of an undesired accumulation of a substance in a well tool is described. The system can, in one example, include an interior flow passage having a surrounding wall, and a heater which heats the wall of the flow passage. 
     In yet another aspect, a method of mitigating formation of an undesired accumulation of a substance in a well tool can include monitoring the accumulation of the substance in the well tool, and heating a surrounding wall of an interior flow passage in response to detecting the accumulation. 
     These and other features, advantages and benefits will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the disclosure herein, and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a representative partially cross-sectional view of a system and associated method which can embody principles of this disclosure. 
         FIG. 2  is an enlarged scale representative cross-sectional view of a well tool which can embody principles of this disclosure, and which may be used in the system and method of  FIG. 1 . 
         FIG. 3  is a representative cross-sectional view of another example of the well tool. 
         FIG. 4  is representative partially cross-sectional view of another example of the system and method. 
         FIGS. 5-9  are representative cross-sectional views of additional examples of the well tool. 
     
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in  FIG. 1  is a system  10  and associated method which can embody principles of this disclosure. However, it should be clearly understood that the scope of this disclosure is not limited at all to the details of the system  10  and method described herein or depicted in the drawings, since a wide variety of different systems and methods can incorporate the principles of this disclosure. 
     In the  FIG. 1  example, a production tubing string  12  is installed in a wellbore  14  lined with casing  16  and cement  18 . Various well tools  20 ,  22 ,  24 ,  26  are interconnected in the tubing string  12 . 
     The well tool  20  is a production flow control device (such as a valve or choke), the well tool  22  is a packer, the well tool  24  is a safety valve and the well tool  26  is a side pocket mandrel. These are merely a few examples of the types of well tools which can benefit from the principles of this disclosure. Any other types of well tools, or any other combination of well tools, can be used as desired. 
     In production operations, a well fluid  28  flows through the well tools  20 ,  22 ,  24 ,  26 , for example, to produce the fluid to the earth&#39;s surface. Unfortunately, as the fluid  28  flows toward the surface, its temperature decreases and undesirable precipitates, hydrates, paraffins, waxes, etc. can accumulate in the well tools  20 ,  22 ,  24 ,  26 . This can impede operation of the well tools  20 ,  22 ,  24 ,  26 , and can even cause failure of the well tools, in addition to restricting flow of the valuable fluid  28  to the surface. 
     In one feature of the system  10  described more fully below, a wall of an interior flow passage can be heated to thereby prevent or at least reduce formation of the undesired accumulations of substances in the well tools  22 ,  24 ,  26 ,  28 . Furthermore, in some examples, the interior flow passage can be vibrated and/or inductively heated to further mitigate the accumulations of undesired substances in the well tools  20 ,  22 ,  24 ,  26 . 
     Referring additionally now to  FIG. 2 , an enlarged scale cross-sectional view of a representative well tool  30  is schematically depicted. The well tool  30  may be used in the system  10  and method of  FIG. 1 , or it may be used in other systems and methods. 
     The well tool  30  could be any of the well tools  20 ,  22 ,  24 ,  26  described above, or any other type of well tool. The well tool  30  could be used in addition to any other well tools (such as the well tools  20 ,  22 ,  24 ,  26 ) in other systems and methods. 
     In the  FIG. 2  example, the well tool  30  includes an outer housing  32  and an interior longitudinal flow passage  34  through which the fluid  28  flows. An electrical heater  36  comprises one or more conductors  40  adhered on a surrounding wall  38  of the flow passage  34 . 
     The conductors  40  may be spirally wrapped as depicted in  FIG. 2 , or they may be in any other configuration. The conductors may be evenly, unevenly or randomly spaced. The conductors  40  can comprise electrical resistance heating elements, inductive heating elements, etc. 
     Electrical contacts  42  in the housing  32  provide for connecting the conductors  40  to a line  44  extending to a remote location (such as, a control and power system at the earth&#39;s surface, a subsea location, a downhole generator, etc.). When electrical power is applied to the heater  36 , the wall  38  of the flow passage  34  is heated, thereby preventing (or at least significantly reducing) the accumulation of undesired substances (e.g., precipitates, hydrates, waxes, paraffins, etc.) on the wall. 
     The conductors  40  may be attached in the flow passage  34  using any suitable technique. Adhesives (such as epoxies, etc.) may be used to adhere the conductors  40 . In one example, the conductors  40  could be incorporated into a fiber (e.g., glass fiber, carbon fiber, KEVLAR™ fiber, etc.) and resin matrix composite material which forms the wall  38  of the flow passage  34 . 
     No matter the technique used to attach the conductors  40  about the flow passage  34 , preferably an interior surface of the wall  38  is left smooth, and with minimal dimensional changes. In this manner, adherence of the undesired substances to the wall  38  can be minimized. Note that the heater  36  comprises the surrounding wall  38  of the flow passage  34  in this example. 
     It can now be appreciated that it is not necessary for the bulk of the fluid  28  flowing through the flow passage  34  to be heated in the well tool  30  (although some of the fluid will be heated due to the heating of the wall  38 ). Instead, by heating the surrounding wall  38  of the passage  34 , accumulation of the undesired substances on the wall is mitigated, without having to heat all or most of the fluid  28  itself. 
     In another feature of the system  10  described more fully below, the heating of the wall  38  can be controlled, so that the wall is heated when an accumulation of the undesired substance is detected, or when the accumulation exceeds a predetermined level. In this manner, the heater  36  can be de-energized when it is not needed, or a level of the electrical power (e.g., wattage, frequency, amplitude, voltage, etc.) supplied to the heater can be varied as appropriate for different levels of accumulation of the substance. 
     Referring additionally now to  FIG. 3 , another example of the well tool  30  is representatively illustrated. In this example, the heater  36  is separately installed in the well tool  30 . 
     As depicted in  FIG. 3 , the heater  36  can comprise a sleeve insert  46  having the conductors  40  therein. For example, the conductors  40  could be embedded in a composite material of the sleeve insert  46 , etc. 
     The insert  46  can be installed in the housing  32  when the well tool  30  is manufactured, the well tool could be retrofitted with the heater  36 , or the insert could be installed in the housing after the well tool is installed in the wellbore  14  (e.g., using a running tool conveyed by slickline, wireline, coiled tubing, etc.). 
     Multiple well tools  30  can be interconnected in the tubing string  12  by extending the line  44  in both longitudinal directions from the well tool. If other electrically-operated tools (such as, an electric safety valve, an electric submersible pump, etc.) are in the tubing string  12 , the well tool  30  can be interconnected in the line  44  between the power source and the other electrically-operated tool(s). 
     Referring additionally now to  FIG. 4 , another example of the system  10  and method is representatively illustrated. In this example, the well tool  30  is interconnected in the tubing string  12  upstream of the well tool  24 . 
     As mentioned above, the heating of the wall  38  can also heat the fluid  28  which is adjacent the wall. This effect can be used to mitigate the accumulation of the undesired substances in a well tool (such as the well tool  24  in the  FIG. 4  example) which is downstream of the well tool  30 . 
     If the well tool  24  comprises an electrically-operated safety valve, the line  44  can be used for operation of the well tool  24 , as well as for operation of the well tool  30 . In other examples, the well tool  30  can be connected upstream of well tools other than safety valves (e.g., nipples, other flow control devices, etc.). 
     Referring additionally now to  FIG. 5 , another example of the well tool  30  is representatively illustrated. In this example, a single conductor  40  extends alternately upward and downward longitudinally in the sleeve insert  46 . This demonstrates that a variety of different configurations of conductors  40  may be used, in keeping with the principles of this disclosure. 
     Referring additionally now to  FIG. 6 , another example of the well tool  30  is representatively illustrated. In this example, multiple conductors  40  are connected in parallel, with each of the conductors extending upward and downward longitudinally in the sleeve insert  46 . This demonstrates that a variety of different numbers and arrangements of the conductors  40  may be used, in keeping with the principles of this disclosure. 
     Referring additionally now to  FIG. 7 , another example of the well tool  30  is representatively illustrated. In this example, the well tool  30  comprises a safety valve (such as the well tool  24  in the system  10  of  FIG. 1 ). 
     An operating member  48  (such as an opening prong or flow tube, etc.) is displaced by an actuator  50  (such as, a hydraulic or electrical actuator, etc.) to thereby open or close a closure member  52 . In its closed position, the closure member  52  prevents flow of the fluid  28  through the passage  34  to thereby avoid inadvertent escape of fluid  28  from the well. 
     In the  FIG. 7  example, multiple heaters  36  are used in the well tool  30  to mitigate formation of any accumulation of undesired substances on the surrounding wall  38  of the flow passage  34 . One heater  36  extends about an upper section of the flow passage  34 , another heater is positioned in the operating member  48 , and yet another heater extends about a lower section of the flow passage. Any number and/or positions of the heaters  36  may be used, as desired. 
     Note that, although the operating member  48  displaces during operation of the well tool  30 , the heater  36  can still mitigate accumulation of the undesired substances on the wall  38  in the operating member. In another example, a heater  36  could be attached to the closure member  52 , or to any other member of the well tool  30  which displaces during operation of the well tool. 
     If the safety valve is electrically actuated (e.g., via an electric motor, an electrical linear actuator, etc.), the electrical power supply which is used to actuate the safety valve can also be used to operate the heaters  36 . A suitable electrically actuated safety valve is described in U.S. application Ser. No. 13/196,565 filed on 2 Aug. 2011, the entire disclosure of which is incorporated herein by this reference. 
     Referring additionally now to  FIG. 8 , another example of the well tool  30  is representatively illustrated. In this example, sensors  54  can be used to detect the presence and/or extent of accumulation of the undesired substances on the wall  38 . 
     For example, the sensors  54  could comprise resistivity sensors which detect a change in resistivity due to the accumulation of the undesired substances. Resistivity could be measured across the flow passage  34 , between different components of the well tool  30 , between different locations on the same component, etc. 
     In other examples, the sensors  54  could comprise capacitive or inductive sensors. Changes in capacitance or inductance can indicate a change in wall thickness, which would occur if unwanted deposits are forming on the wall  38 . Resistivity measurements can be augmented with capacitance and/or inductance measurements for enhanced accuracy in detecting accumulation of undesired substances on the wall  38 . 
     In addition, a pressure and/or temperature sensor  56  can be used to detect conditions conducive to formation of the undesired substances on the wall  38 . The heater  36  can be controlled, based on the conditions, parameters, etc. monitored by the sensors  54 ,  56 . 
     Any type(s) of sensors may be used for the sensors  54 ,  56  in keeping with the principles of this disclosure. Any number, positions and/or configuration of sensors may be used, as desired. 
     Referring additionally now to  FIG. 9 , another example of the well tool  30  is representatively illustrated. In this example, the wall  38  can be vibrated to further reduce accumulation of the undesired substances on the wall. 
     The well tool  30  includes a vibrator  58  which, in this example, comprises a stack of annular piezoelectric elements  60  encircling the sleeve insert  46 . The piezoelectric elements  60  are energized as appropriate to cause vibration of the sleeve insert  46  and wall  38 , thereby dislodging or preventing accumulation of undesired substances on the wall. 
     If the conductors  40  comprise one or more inductive heating elements, such inductive heating elements can also be used to induce vibration of the wall  38 . Thus, it is not necessary for the vibrator  58  to be separate from the heater  36 . 
     It may now be fully appreciated that this disclosure provides significant advancements to the art of mitigating accumulation of undesired substances in well tools. 
     In various examples described above, the well tool can have an electric line running from the surface (e.g., from a wellhead) to the well tool. This electric line can provide electrical power to a heating element that is either installed in or is an integral part of the tool. 
     The heating element can be installed as a sleeve insert type device that is fitted in the interior of the tool after normal manufacture of the tool. The well tool can have electrical contacts that connect the tool to the inserted heating element. Any number of contacts may be used. 
     The heating element can be an integral part of the tool. An example of this is a wire wrap or spiral configuration (e.g., a coil that is applied to the interior of the tool components during the manufacturing process). The wires of the heating element could be evenly spaced, unevenly spaced, or randomly spaced or have multiple spiral sections depending on the desired heating effects. 
     The heating element can be a component of a separate well tool that is run directly upstream of another well tool being protected, to impart a temperature increase to the flowing well fluid. This configuration would accommodate any length of heating element(s), without affecting the design of the protected well tool. The well tool with the heating element could be powered independently or in conjunction with power supplied to the protected well tool. 
     The heating element can extend longitudinally (e.g., parallel to a longitudinal axis of the well tool) instead of in a circular or spiral fashion. If longitudinally extending, the heating element could comprise a single continuous element or multiple elements. 
     Any manner of affixing the heating elements to the interior of the well tool may be used. The heating element(s) can be applied as an individual wire, multiple wires, embedded in a tape, etc. In one example, the application process can be a painting-type process where the heating elements are applied at the same time as an adhesive. 
     The heating element and/or adhesive can be made of a relatively short lived material if the life of the feature is not critical. Alternatively, the heating element and/or adhesive can be made of a more durable material (e.g., ceramic, abrasion resistant epoxy, etc.) if the life of the feature is critical. 
     The heating element can be powered continuously or it can be powered as needed. Controls to operate the heating element can be located within the well tool, near the tool, in another device, or at or above the surface (e.g., a wellhead, platform, control room, etc.). 
     As some well tools have internal features that move (e.g., sliding sleeve inserts, flow tubes, etc.) these features can also benefit from prevention of accumulation of undesired substances, and can have similar heating elements provided. A dynamic contact feature can be included that allows continuous contact between the heating element of the moving feature and the power source, or a fixed contact can be included so that the heating element of the moving feature only makes contact at a fixed point or fixed points. 
     As it may not be necessary, beneficial or practical to continuously power the heating element, a sensor that measures accumulation of undesired substances can be included in the well tool. For example, one or more sensors that measure resistance between two points, between the well tool and the fluid  28  flow, two points on the wall  38 , etc. 
     A change in resistance can indicate the onset of accumulation. However, resistance is not necessarily the indicator of accumulation, or the only indicator of accumulation. Other indicators could include changes in other parameters or combinations of parameters (such as, capacitance, pH, inductance, heat capacity, etc.). 
     Other sensors (e.g., pressure and temperature sensors) can be included as part of the system  10 . Temperature sensors can be particularly useful for ascertaining information on the performance and effectiveness of the system  10 . Any number, type or combination of sensors may be used. 
     The well tool can be designed so that when the system  10  is energized the entire heating element of the tool is powered, or it can be designed so that only selected areas or components of the tool receive the heating. Whether the system  10  comprises a single heating element or multiple heating elements, the heating element(s) can be operated together or independently. 
     The composition of the adhesive or internal lining of the heater  36  and/or well tool  30  is also important. The wall  38  of the flow passage  34  is preferably configured so as to prevent or hinder the adhesion of precipitates, hydrates, waxes or paraffin. This can be accomplished, for example, by the adhesive or heating element having a smooth surface finish with minimal imperfections, or being made of a substance that has enhanced lubricity. 
     An electrical connection at the well tool can include a feed-thru connection that will allow the electric lines of other tools to be connected. This will allow multiple tools or valves to be powered by the same electric line and power sources. This also reduces the number of lines that pass through the wellhead and/or tubing hanger, and that need to be run downhole. Circuitry can be included that will protect the system  10  from failures of other devices that are attached electrically to the system. 
     The heater  36  can be a standalone electrical feature of the tool or it can be included as part of a tool that has other electrically operated components (e.g., an electric actuator of an electrically operated safety valve). If included as part of a tool that has other electrically operated components, the tool can include a feature that splits the power at the tool, providing one input source for the tool, but multiple outputs to the electrically operated features (e.g., the heating elements, actuator, sensors, etc.). 
     The system  10  can be powered by direct current (DC) power or alternating current (AC) power. The AC power can be of varying frequency to optimize the power throughput of the electrical lines, and to optimize the heat control over time. 
     AC power would also allow the use of inductive heating when appropriate. Inductive heating elements may also be constructed to vibrate, which would set up vibrations of the wall of the flow passage, allowing the undesired substances to be flowed out of the tool. Heating elements can be combined with piezoelectric elements to vibrate the undesired substances loose after or during heating. 
     A method is described above for mitigating formation of an undesired accumulation of a substance in a well tool  20 ,  22 ,  24 ,  26 ,  30  through which a well fluid  28  flows. In one example, the method includes heating a surrounding wall  38  of an interior flow passage  34  through which the well fluid  28  flows. 
     The method can also include monitoring the accumulation of the substance in the flow passage  34 . The heating may be performed in response to the monitoring including detecting the accumulation, and/or detecting the accumulation being greater than a predetermined level. 
     The monitoring may be performed by at least one sensor  54 ,  56 . The sensor  54  can comprise a resistivity sensor, a capacitance sensor, and/or an inductance sensor. 
     The heating can comprise incorporating a heater  36  about the flow passage  34 . The incorporating may include adhering the heater  36  to an interior of the flow passage  34 , and/or separately installing the heater  36  into an interior of the flow passage  34 . 
     The heater  36  may displace during operation of the well tool  30 . The incorporating can include attaching the heater  36  to a member  48 ,  52  of the well tool  30  which displaces during operation of the well tool  30 . 
     The incorporating may be performed after installing the well tool  30  in a well. The incorporating may include electrically engaging the heater  36  with an electrical line  44  connected to the well tool  30  and extending to a remote location. 
     The heating can be performed by supplying electrical power to one or more electrical conductors  40  adhered to an interior of the well tool  34 , and/or by supplying electrical power to one or more electrical conductors  40  in an insert  46  secured in the well tool  30  after the well tool  30  has been installed in a well. 
     The heating can include inductively heating the wall  38  of the flow passage  34 . 
     The method can include vibrating the wall  38  of the flow passage  34 . The vibrating may include energizing a stack of piezoelectric elements  60 . 
     The well tool  30  may comprise a safety valve. The safety valve can be electrically actuated. 
     The well tool  30  may comprise an actuator  50 . The actuator  50  may be electrically operated. 
     A system  10  for mitigating formation of an undesired accumulation of a substance in a well tool  20 ,  22 ,  24 ,  26 , is also described above. In one example, the system  10  comprises an interior flow passage  34  having a surrounding wall  38 , and a heater  36  which heats the wall  38  of the flow passage  34 . 
     Also described above is a method of mitigating formation of an undesired accumulation of a substance in a well tool, which method includes monitoring the accumulation of the substance in the well tool  30 , and heating a surrounding wall  38  of an interior flow passage  34  in response to the monitoring including detecting the accumulation. 
     Although various examples have been described above, with each example having certain features, it should be understood that it is not necessary for a particular feature of one example to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example&#39;s features are not mutually exclusive to another example&#39;s features. Instead, the scope of this disclosure encompasses any combination of any of the features. 
     Although each example described above includes a certain combination of features, it should be understood that it is not necessary for all features of an example to be used. Instead, any of the features described above can be used, without any other particular feature or features also being used. 
     It should be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of this disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments. 
     In the above description of the representative examples, directional terms (such as “above,” “below,” “upper,” “lower,” etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein. 
     The terms “including,” “includes,” “comprising,” “comprises,” and similar terms are used in a non-limiting sense in this specification. For example, if a system, method, apparatus, device, etc., is described as “including” a certain feature or element, the system, method, apparatus, device, etc., can include that feature or element, and can also include other features or elements. Similarly, the term “comprises” is considered to mean “comprises, but is not limited to.” 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of this disclosure. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the invention being limited solely by the appended claims and their equivalents.