Patent Number: 060268980
Section: summary

FIELD OF INVENTION The within invention relates to a tubing head designed to accommodate a tubing rotator therein such that the tubing head may be retrofit with the tubing rotator. Further, the within invention relates to an apparatus for attachment to a wellhead for suspending and rotating a tubing string within a wellbore, the apparatus comprising a tubing head and a tubing rotator combined to form a single, integral unit. BACKGROUND ART A typical wellhead is often comprised of a casing head or a casing bowl which engages or is otherwise mounted to a casing string contained within a wellbore of a well at the surface. A tubing head or tubing bowl is mounted upon the upper surface of the casing head and provides a support mechanism for a tubing hanger. The tubing hanger is connected to or engages the upper end of the tubing string which is contained within the wellbore. Thus, the tubing hanger and the tubing string connected thereto are supported at the surface of the well by the tubing head. Alternately, the wellhead may not include a casing head. In this case, the tubing head is mounted directly to the casing string at the surface of the well. A reciprocating rod or tube or a rotating rod or tube is then run through the tubing string for production of the well. A typical wellhead may also further include a tubing rotator. Tubing rotators are used in the industry to suspend and rotate the tubing string within the wellbore. By rotating the tubing string, typical wear occurring within the internal surface of the tubing string by the reciprocating or rotating rod string is distributed over the entire internal surface. As a result, the tubing rotator may prolong the life of the tubing string. Further, the constant movement of the tubing string relative to the rod string may inhibit or reduce buildup of wax and other materials within the tubing string. Conventional tubing heads are not typically able to be retrofitted to accommodate the necessary structure of a tubing rotator, including the drive system for causing the rotation of the tubing string. Thus, the tubing head may require replacement in the event the operator of the well chooses to commence the use of a rotator subsequent to the initial completion of the well and the wellhead. Further, when a conventional tubing rotator is used in combination with a conventional tubing head, the rotator is typically mounted on top of the tubing head. This arrangement may increase the overall height of the wellhead and may result in the instability of the wellhead by weakening its overall structure. As well, in order to service the well, the tubing hanger and the connected tubing string must typically be removed from the well. However, any disturbance of the tubing string during servicing may lead to a blowout. To avoid this risk in a conventional well without a tubing rotator, the portion of the wellhead above the tubing head is typically removed and a blowout preventer is mounted to the tubing head. The tubing hanger with the attached tubing string are then removed through the blowout preventer. Where the wellhead includes a tubing rotator, the structure of the rotator tends to interfere with the installation of the blowout preventer. Thus, in order to service the well, the rotator, or at least a portion of it, must typically be removed from the tubing head. Removal of all or a portion of the rotator may require or result in disturbance of the tubing string, which may lead to a blowout. Further, when a rotator is in use in the wellhead, the tubing hanger is typically comprised of a swivel dognut assembly. The swivel dognut assembly is comprised of a rotatable mandrel, which is connected to and suspends the tubing string within the wellbore, and a drive system for rotating the mandrel which results in the rotation of the tubing string. The drive system is conventionally comprised of a system of gears which engages the mandrel either directly or indirectly to cause it to rotate. In order to remove these conventional rotators and tubing hangers for servicing of the well, the gear system must first be removed from the rotator such that the mandrel is no longer directly or indirectly engaged thereby. Where the gear system is not so removed, due to an error or oversight, the rotator and the wellhead may be seriously damaged resulting in the costly replacement of equipment, a loss of production during replacement of the equipment and a potential for the blowout of the well. As well, in order to service the well, a pup joint or servicing tool is typically threaded into the upper end of the inner rotatable mandrel of the swivel tubing hanger. However, upon the removal of the drive system for servicing of the well, the inner mandrel is typically able to freely rotate within the outer supporting structure of the tubing hanger. As a result, connection of the servicing tool may be problematic due to the difficulties encountered in obtaining and ensuring a secure connection between the servicing tool and the inner mandrel of the tubing hanger. This problem is typically addressed by the insertion of a key between the inner mandrel and the outer supporting structure of the tubing hanger during servicing of the well in order to inhibit the rotation of the inner mandrel. There is therefore a need in the industry for a tubing head capable of accommodating the functional structure or elements of a tubing rotator therein such that the tubing head may be retrofit and converted from its use as a conventional tubing head into its use as a combined tubing head and rotator. Further, there is a need for an apparatus which combines the functional elements of a tubing head and a tubing rotator in a single, integral unit. As well, there is a need for such a tubing head and apparatus that are relatively compact and that will facilitate the servicing of the well. More particularly, there is a need for such a tubing head and apparatus that permit the removal of the tubing string from the well therethrough without first requiring the removal of all or a portion of the tubing head or apparatus, including the drive system of the tubing rotator. Further, there is a need for such a tubing head and apparatus which permits the removal of the tubing string through a service blowout preventer mounted thereon without first moving the tubing string connected to the tubing rotator. Finally, there is a need for such an apparatus that facilitates the connection of a servicing tool to the components of the tubing rotator during the servicing of the well. DISCLOSURE OF INVENTION The present invention relates to a tubing head capable of accommodating the functional structure or elements of a tubing rotator therein such that the tubing head may be retrofit and converted from its use as a conventional tubing head into its use as a combined tubing head and rotator. Further, the present invention relates to an apparatus which combines the functional elements of a tubing head and a tubing rotator in a single, integral unit. As well, the present invention preferably relates to such a tubing head and apparatus that are relatively compact and that will facilitate the servicing of the well. In addition, the present invention relates to such a tubing head and apparatus which are configured such that the tubing string is removable from the well therethrough without first requiring the removal of all or a portion of the tubing head or apparatus, including the drive system of the tubing rotator. Further, the present invention preferably relates to such a tubing head and apparatus which are configured such that the tubing string is removable through a service blowout preventer mounted thereon without first moving the tubing string connected to the tubing rotator. Finally, the present invention preferably relates to such an apparatus which facilitates the connection of a servicing tool to the components of the tubing rotator of the apparatus during the servicing of the well. In a first aspect of the invention, the invention relates to a tubing head for accommodating a tubing rotator therein, the tubing head being of the type having an upper end, a lower end for attachment to a wellhead and an internal bore extending between the upper and lower ends, wherein the tubing rotator comprises a drive gear and a swivel tubing hanger for rotatably suspending a tubing string contained within a wellbore, the tubing hanger comprising an external surface for engaging the internal bore of the tubing head such that the tubing hanger may be suspended thereby and a driven gear for engaging the drive gear, the improvement which comprises: (a) the internal bore of the tubing head defining an internal surface for engaging the external surface of the tubing hanger such that the tubing hanger may be suspended by the tubing head; and PA1 (b) the tubing head defining a gear housing for containing the drive gear therein, wherein the gear housing communicates with the internal bore such that the drive gear may releasably engage the driven gear of the tubing hanger when the tubing hanger is suspended by the tubing head; PA1 (a) a tubing head having an upper end, a lower end for attachment to a wellhead and an internal bore extending between the upper and lower ends, wherein the internal bore of the tubing head defines an internal surface and wherein the tubing head further defines a gear housing which communicates with the internal bore; PA1 (b) a swivel tubing hanger for locating within the internal bore and for connecting to the tubing string, the tubing hanger comprising a driven gear and an external surface for engaging the internal surface of the tubing head such that the tubing hanger may be suspended by the tubing head; and PA1 (c) a drive gear for containing within the gear housing and for releasably engaging the driven gear of the tubing hanger; wherein the internal surface, the gear housing, the drive gear and the driven gear are configured such that when the drive gear is contained within the gear housing, the tubing hanger is located in the internal bore and the driven gear is engaging the drive gear, the tubing hanger is capable of being removed from the internal bore by pulling it through the upper end of the tubing head without first disengaging the drive gear from the driven gear. In a second aspect of the invention, the invention relates to an apparatus for attachment to a wellhead for suspending and rotating a tubing string contained within a wellbore, the apparatus comprising: wherein the internal surface, the gear housing, the drive gear and the driven gear are configured such that when the drive gear is contained within the gear housing, the tubing hanger is located in the internal bore and the driven gear is engaging the drive gear, the tubing hanger is capable of being removed from the internal bore by pulling it through the upper end of the tubing head without first disengaging the drive gear from the driven gear. In the first and second aspects, any configuration of the tubing head able to achieve the functions or purpose of the tubing head as described above may be used However, preferably, the internal bore of the tubing head defines a minimum diameter of the bore. Further, the gear housing is preferably configured such that when the drive gear is contained within the gear housing, it does not protrude into the internal bore within the minimum diameter. As well, the internal surface of the tubing head preferably defines a maximum diameter of the internal bore which is about equal to a maximum diameter of the tubing hanger. When a service blowout preventer is mounted on the upper end of the tubing head and the tubing hanger is located in the internal bore, the maximum diameter of the tubing hanger preferably permits the tubing hanger to be removed from the internal bore by pulling it through the blowout preventer in order to service the well. Further, in the preferred embodiment, the drive gear and the driven gear engage each other between the minimum diameter and the maximum diameter of the internal bore. The drive gear and the driven gear may be comprised of any compatible gears suitable for performing their functions or purpose and which engage each other between the minimum and maximum diameters of the internal bore. However, preferably, the drive gear is comprised of a worm and the driven gear is comprised of a worm gear. Further, in the preferred embodiment, the worm and the worm gear are non-enveloping in order to facilitate the removal of the tubing hanger from the internal bore without first disengaging the worm from the worm gear. The worm gear is comprised of a plurality of worm gear teeth and the worm is comprised of a plurality of worm teeth. These worm gear and worm teeth may have any shape or configuration permitting the removal of the tubing hanger from the internal bore without first disengaging the worm from the worm gear. In addition, the shape and configuration preferably facilitate the feeding of the worm gear onto the worm and the feeding of the tubing hanger into the internal bore of the tubing head. In the preferred embodiment, a lower end of each worm gear tooth is tapered inwardly towards a centre of the tooth in order to facilitate the feeding of the worm gear onto the worm. In addition, the lower end of each worm gear tooth is sloped downwardly from a top face to a bottom face of the tooth in order to facilitate the feeding of the tubing hanger into the internal bore of the tubing head. Finally, a crest of each worm tooth is tapered to facilitate the feeding of the worm gear onto the worm. The tubing head is preferably further comprised of any means, structure, mechanism or device for inhibiting the longitudinal movement of the tubing hanger in a direction toward the upper end of the tubing head. Preferably, the upwards longitudinal movement of the tubing hanger is inhibited by the tubing head which is comprised at least one adjustable holddown screw for engagement with the tubing hanger such that when the holddown screw is adjusted for engagement with the tubing hanger, longitudinal movement of the tubing hanger in a direction toward the upper end of the tubing head is inhibited. In the preferred embodiment, the tubing head is comprised of at least two holddown screws located adjacent the upper end of the tubing head. In addition, the tubing head is further preferably comprised of means for mounting the tubing head on the wellhead. Any means, mechanism, structure or device capable of and suitable for temporarily or permanently mounting or connecting the tubing head to the wellhead may be used. Preferably, the mounting means are capable of connecting the lower end of the tubing head on the wellhead. In addition, the mounting means may be suitable for mounting or connecting the lower end of the tubing head to any portion or component of the wellhead, but preferably, the mounting means are compatible with mounting the tubing head to a casing string or a casing head or an existing tubing head. For instance, when the wellhead is comprised of a casing string, the mounting means may be comprised of a mounting portion of the internal bore of the tubing head adjacent the lower end, which mounting portion is adapted for connection to the casing string. When the wellhead is comprised of a casing head or an existing tubing head, the mounting means may be comprised of a lower surface on the lower end of the tubing head, which lower surface is adapted for connection to the casing head or the existing tubing head. Preferably, in this case, the lower surface of the tubing head is comprised of a mounting flange. Finally, the tubing head is further preferably comprised of means for connecting the upper end of the tubing head to other wellhead equipment. Any means, mechanism, structure or device capable of and suitable for temporarily or permanently mounting or connecting the upper end of the tubing head to the other wellhead equipment may be used. The tubing hanger may be comprised of any swivel tubing hanger compatible with its use within the tubing head and which permits the functioning of the apparatus as described herein. However, preferably, the tubing hanger is further comprised of: a supporting member comprising the external surface of the tubing hanger; and a supported member rotatably supported within the supporting member such that the longitudinal movement of the supported member relative to the supporting member in a direction toward the lower end of the tubing head is inhibited, the supported member having an upper end and a lower end for connecting to the tubing string and wherein the supported member is associated with the driven gear such that rotation of the driven gear causes the supported member to rotate within the supporting member. The supported member may be associated with the driven gear in any manner or by any means, mechanism, structure or device which permits the functioning of the tubing hanger as described herein and which permits the drive gear to engage the driven gear. However, in the preferred embodiment, the driven gear is fixedly mounted about the supported member such that the driven gear extends from the supported member towards the gear housing of the tubing head for engagement with the drive gear. The tubing hanger further preferably comprises means for inhibiting the longitudinal movement of the supported member relative to the supporting member in a direction toward the upper end of the tubing head. Any means, structure, mechanism or device for inhibiting the upwards longitudinal movement of the supported member relative to the supporting member may be used. However, preferably, the inhibiting means is comprised of the abutment of the driven gear and the supporting member. Any means, mechanism, device or structure capable of supporting the supported member in the required manner which is compatible with the function of a the tubing hanger, may be used. However, preferably, the supported member is rotatably supported within the supporting member by at least one bearing located between the supported member and the supporting member such that the bearing is seated on the supporting member and the supported member is rotatably supported upon the bearing. Any bearing suitable for, and compatible with, this intended purpose or function may be used. For instance, the bearing may be comprised of a thrust bearing, a radial bearing, a tapered roller bearing or a combination thereof. In the preferred embodiment, the bearing is comprised of a thrust bearing in combination with a bushing sleeve.