Patent Publication Number: US-10323480-B2

Title: Rotating wellhead hanger assemblies

Description:
BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     In order to meet consumer and industrial demand for natural resources, companies often invest significant amounts of time and money in finding and extracting oil, natural gas, and other subterranean resources from the earth. Particularly, once a desired subterranean resource such as oil or natural gas is discovered, drilling and production systems are often employed to access and extract the resource. These systems may be located onshore or offshore depending on the location of a desired resource. Further, such systems generally include a wellhead assembly mounted on a well through which the resource is accessed or extracted. These wellhead assemblies may include a wide variety of components, such as various casings, valves, pumps, fluid conduits, and the like, that control drilling or extraction operations. 
     As will be appreciated, wells are often lined with casing that generally serves to stabilize the well and to isolate fluids within the wellbore from certain formations penetrated by the well (e.g., to prevent contamination of freshwater reservoirs). Such casing is frequently cemented into place within the well. During a cement job, cement can be pumped down a casing string in a well, out the bottom of the casing string, and then up the annular space surrounding the casing string. The cement is then allowed to set in the annular space. 
     SUMMARY 
     Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
     Embodiments of the present disclosure generally relate to wellhead hangers for rotating tubular strings in wells. In some embodiments, running tools are used to rotate casing hangers and attached casing strings during running or cementing of the casing strings in the wells. Locking dogs installed in the running tools engage the casing hangers. These dogs transmit torque from a running tool to a casing hanger so that the casing hanger rotates synchronously with the running tool when the running tool is rotated in one direction, but also allow the running tool to be rotated in an opposite direction to unthread the running tool from the casing hanger. 
     Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  generally depicts various components, including casing and tubing strings and associated hangers, that can be installed at a well in accordance with one embodiment of the present disclosure; 
         FIG. 2  is a perspective view of a casing hanger having angled recesses formed about its circumference in accordance with one embodiment; 
         FIG. 3  is a perspective view of a running tool for use with the casing hanger of  FIG. 2 , the running tool having radial apertures for locking dogs to engage the angled recesses of the casing hanger in accordance with one embodiment; 
         FIG. 4  is cross-section of the casing hanger and the running tool of  FIGS. 2 and 3  shown installed within a casing head in accordance with one embodiment; 
         FIG. 5  is a detail view of a locking dog that can be installed within a radial aperture of the running tool and aligned with an angled recess of the casing hanger in accordance with one embodiment; 
         FIG. 6  is an axial cross-section of the casing hanger and the running tool in  FIG. 4 ; 
         FIG. 7  is a detail view of a landing ring depicted in  FIG. 4 , the landing ring having several gall-resistant rings to facilitate rotation of the casing hanger with respect to the landing ring in accordance with one embodiment; 
         FIG. 8  is a detail view generally depicting a packoff installed in the casing head after removal of the running tool from the casing hanger in accordance with one embodiment; 
         FIG. 9  is a perspective view of a wellhead hanger assembly with a running tool having locking dog assemblies coupled to a casing hanger in accordance with one embodiment; 
         FIGS. 10 and 11  are perspective and sectional views of the casing hanger of  FIG. 9  in accordance with one embodiment; 
         FIG. 12  is a sectional view of the running tool of  FIG. 9  in accordance with one embodiment; 
         FIG. 13  is a cross-section of the wellhead hanger assembly of  FIG. 9  installed in a casing head in accordance with one embodiment; 
         FIG. 14  is a detail view of a locking dog assembly installed in a port of the running tool as depicted in  FIG. 13 ; 
         FIG. 15  is an axial cross-section of the wellhead hanger assembly of  FIG. 9  and shows dogs of the locking dog assembly inserted into recesses in the casing hanger; 
         FIG. 16  is an axial cross-section of the wellhead hanger assembly after the running tool has been rotated to break shear components behind the dogs and cause the dogs to retract away from the casing hanger; 
         FIG. 17  is a perspective view of another wellhead hanger assembly with a running tool having locking dog assemblies coupled to a casing hanger in accordance with one embodiment; 
         FIG. 18  is a cross-section of the wellhead hanger assembly of  FIG. 17  showing dogs of the locking dog assemblies held in a disengaged position away from the casing hanger in accordance with one embodiment; 
         FIG. 19  is a detail view of a locking dog assembly as shown in  FIG. 18 ; 
         FIG. 20  is a cross-section of the wellhead hanger assembly of  FIG. 17  showing the dogs of the locking dog assembly moved into engagement with the casing hanger by rotating handles coupled to the dogs in accordance with one embodiment; and 
         FIG. 21  is a detail view of a locking dog assembly as shown in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, any use of “top,” “bottom,” “above,” “below,” other directional terms, and variations of these terms is made for convenience, but does not require any particular orientation of the components. 
     Turning now to the present figures, a system  10  is illustrated in  FIG. 1  in accordance with one embodiment. Notably, the system  10  is a production system that facilitates extraction of a resource, such as oil, from a reservoir  12  through a well  14 . Wellhead equipment  16  is installed on the well  14 . As depicted, the wellhead equipment  16  includes at least one casing head  18  and tubing head  20 , as well as hangers  22 . But the components of the wellhead equipment  16  can differ between applications, and could include a variety of casing heads, tubing heads, hangers, sealing assemblies, stuffing boxes, pumping tees, and pressure gauges, to name only a few possibilities. 
     The hangers  22  can be positioned on landing shoulders  24  within the tubing and casing heads. These landing shoulders  24  can be integral parts of the tubing and casing heads or can be provided by other components, such as packoffs, other sealing assemblies, or landing rings disposed in the tubing and casing heads. Each of the hangers  22  can be connected to a tubing string  26  or a casing string  28  to suspend such strings within the well  14 . The well  14  can include a single casing string  28  or include multiple casing strings  28  of different diameters. Casing strings  28  are often cemented in place within the well. During a cement job, cement is typically pumped down the casing string. A plug is then pumped down the casing string with a displacement fluid (e.g., drilling mud) to cause the cement to flow out of the bottom of the casing string and up the annular space around the casing string. 
     Rotating the casing string during cementing can increase uniformity of the cement about the casing string and reduce the size or frequency of undesirable cavities or fissures in the cement. Further, rotating the casing string can also facilitate running of the casing string into the well through the wellhead, such as when running the casing string into highly deviated wells. The casing strings can be rotated via casing hangers attached to the casing strings. In various embodiments described below, the casing hangers attached to casing strings can be rotated on a landing shoulder or lifted off of a landing shoulder during rotation. Indeed, to facilitate rotation, in some embodiments an upward force can be applied to the casing hanger to reduce the amount of loading by the casing hanger on a landing shoulder without lifting the casing hanger off of the shoulder. Any suitable devices or machines may be used to rotate the casing hangers (and their attached casing strings) and to run the casing strings into wells. For example, a top drive can be used to run a casing string into a well and to rotate the casing string. 
     One embodiment of a casing hanger assembly is generally depicted in  FIGS. 2-8 . Specifically, a mandrel casing hanger  50  is depicted in  FIG. 2  and a mating running tool  70  is depicted in  FIG. 3 . The casing hanger  50  includes a lower end  52  with internal threads  56  for connecting the casing hanger  50  to a casing string and an upper end  54  that can be received by the running tool  70 . The casing hanger  50  also includes a shoulder  58  for landing the casing hanger  50  within a landing ring  92  ( FIG. 4 ) and an external threaded surface  60  for receiving the running tool  70 . Still further, the casing hanger  50  includes recesses  62  that facilitate locking engagement of the running tool  70  with the casing hanger  50 , as described in greater detail below. The recesses  62  are presently depicted as being arrayed circumferentially about the casing hanger  50  at the same axial distance along the hanger, though other arrangements could be used instead. 
     The running tool  70  includes a lower end  72  for receiving the casing hanger  50  and an upper end  74  for connection to a component for transmitting torque to the running tool  70  (which can then be transmitted to the casing hanger  50  and a connected casing string). The running tool  70  can be threaded onto the external threaded surface  60  of the casing hanger  50  via internal threaded surface  76 , and threads  78  allow connection of the running tool  70  so that it may be driven by another component. The running tool  70  also includes through holes  80  that allow fluid to flow though the running tool  70  when positioned in a casing head. Additionally, the running tool  70  includes holes  84  (also referred to as ports or apertures) that extend from an outer surface of the running tool to an inner surface. In some embodiments, like that shown in  FIG. 3 , the holes  84  extend radially through the running tool  70 . As described in more detail below, the holes  84  are positioned on the running tool  70  so that they can be aligned with the recesses  62  of the casing hanger  50  as the running tool  70  is threaded onto the casing hanger  50 . 
     In  FIG. 4 , the casing hanger  50  is shown as connected to the running tool  70  and installed within a casing head  90 . The casing hanger  50  is received within a landing ring  92  (which may also be referred to as a landing collar) that has an external shoulder that engages an internal shoulder of the casing head  90 . The landing ring  92  has flow-by ports  94  that allow the passage of fluid. Additionally, one or more gall-resistant rings can be provided between the landing ring  92  and the casing hanger  50 . In the presently depicted embodiment, three gall-resistant rings  96 ,  98 , and  100  are so provided. But other embodiments could have a different number of such rings (including embodiments that omit such rings entirely). The running tool  70  is also depicted in  FIG. 4  as including wear bearings  114  about its exterior. 
     Locking pins  104  are also provided in some or all of the holes  84  in the running tool  70 , and one example of such a locking pin  104  is depicted in  FIG. 5 . In this example, the locking pin  104  (which may also be referred to as a dog) is enclosed in a hole  84  with a cap  108 . The cap  108  can be threaded into the hole  84  or retained in any other suitable manner. The depicted cap  108  includes a tool recess  110  to facilitate installation and removal of the cap  108  from the hole  84 . In this embodiment, the locking pin  104  is spring-loaded in that a spring  112  is provided between the cap  108  and the locking pin  104  so as to provide a biasing force (directed radially inward) to the pin  104 . 
     The running tool  70  translates axially along the casing hanger  50  as it is threaded onto the casing hanger  50  via threaded surfaces  60  and  76 . The locking pins  104  are biased inwardly by springs  112  into engagement with the outer surface of the casing hanger  50  as the running tool  70  is first rotated along the threaded surface  60  until the axial translation of the running tool  70  brings the holes  84  (with the locking pins  104 ) into alignment with the recesses  62 . Upon such alignment, however, the locking pins  104  extend inwardly into the recesses  62  due to the bias applied by the springs  112 , as generally depicted in  FIG. 6 . While only two pins  104  are depicted in  FIG. 6  for the sake of clarity, it will be appreciated that in at least some embodiments a locking pin  104  is provided in each of the holes  84  for engaging a mating recess  62 . But in other embodiments, fewer than all of the holes  84  include a locking pin  104 . And while the depicted embodiment includes ten recesses  62  and ten holes  84 , other embodiments can differ from such a configuration. 
     Each recess  62  in  FIG. 6  is shown as having an angled profile with a stop surface or shoulder  118  and an angled (return) surface  120 . In at least some embodiments, such as that depicted here, the stop surfaces are radial stop surfaces that are formed orthogonal to the outer circumference of the casing hanger  50 . In the present embodiment, the running tool  70  is rotated clockwise (via right-handed threads on surfaces  60  and  76 ) down onto the casing hanger  50  until the locking pins  104  are aligned with the recesses  62 . 
     When aligned in this manner, the locking pins  104  are pushed into the recesses  62  by the springs  112  and engagement of the pins  104  with the stop surfaces  118  inhibits further rotation of the running tool  70  about the casing hanger  50  in the clockwise direction. Rather, once the locking pins  104  extend into the recesses  62 , further rotation of the running tool  70  in the clockwise direction causes synchronous movement of the casing hanger  50  in the clockwise direction. That is, the locking pins  104  transmit torque on the running tool  70  to the casing hanger  50  via the stop surfaces  118 . Through this engagement, the running tool  70  can rotate the casing hanger  50  and an attached casing string, such as during cementing of the casing string. Using the locking pins  104  in this way prevents the running tool  70  from being excessively tightened onto the casing hanger  50  via the threaded surfaces  60  and  76 , and allows rotation of the casing hanger  50  by the running tool  70  without transmitting torque directly through the threads of surfaces  60  and  76  (which could cause the threads to stick and prevent removal of the running tool  70  from the casing hanger  50 ). It also permits easy removal of the running tool  70  from the casing hanger  50 , such as after cementing the casing. Particularly, the running tool  70  can be threaded off the casing hanger  50  (e.g., by rotating it counterclockwise in the present embodiment) with little or no break-out torque required. The angled surfaces  120  push the locking pins  104  against the springs  112  and back into the holes  84 , allowing the running tool  70  to rotate freely off of the casing hanger  50 . 
     Additional details of the rotation of the casing hanger  50  with respect to the landing ring  92  may be better appreciated with reference to  FIG. 7 . In this illustration, the landing ring includes strips  124  that reduce friction between rotating components (here the casing hanger  50 , the landing ring  92 , and the gall-resistant ring  96 ) and a wiper seal  126  to inhibit entry of fluid (e.g., cement) into the recesses  62  or holes  84 . As noted above, the present embodiment includes three gall-resistant rings  96 ,  98 , and  100 . Such gall-resistant rings can be made from any suitable material, such as nitrided chromoly steel. As depicted, the ring  96  has a tapered upper edge that engages the shoulder  58  of the casing hanger  50 , and the ring  100  includes a tapered lower edge that engages a mating shoulder of the landing ring  92 . The ring  98  in the present embodiment is provided with two parallel surfaces for engaging mating surfaces of the rings  96  and  100 . Again, the inclusion of one or more gall-resistant rings reduces wear on the casing hanger  50  and the landing ring  92 , while allowing the landing ring  92  to support some or all of the load from the casing hanger (and attached casing) during rotation of the casing while cementing. Of course, the casing hanger  50  could instead be lifted off of the landing ring  92  such that the full load of the casing hanger  50  and the casing is supported in some other way (e.g., by a top drive). Once the casing is cemented into place, the running tool  70  can be removed from the casing hanger  50  and a packoff  132  with a rubber sealing component  134  can be installed in the casing head  90 , as generally depicted in  FIG. 8 . 
     Another embodiment of a wellhead hanger assembly is generally depicted in  FIGS. 9-17 . As shown in  FIG. 9 , a wellhead hanger assembly  138  includes a wellhead hanger, in the form of casing hanger  140 , coupled to a running tool  142 . Locking dog assemblies  144  installed in the running tool  142  engage the casing hanger  140  to facilitate rotation of the casing hanger  140  by the running tool  142 . 
     Additional details of the casing hanger  140  are generally depicted in  FIGS. 10 and 11  in accordance with one embodiment. As shown in these two figures, the casing hanger  140  includes a lower end  146  with an internal threaded surface  148  for mating with a casing string. The lower end  146  also includes a flange with a chamfered edge, forming a shoulder  150 , and flow-by ports  152 . In other embodiments, the flange could include flutes in addition to, or instead of, the flow-by ports  152 . The casing hanger  140  is shown here as having a lower neck portion or box connection extending downwardly from the flange for receiving a casing string at its lower end  146 . But in other embodiments, the body of the casing hanger  140  could be provided in a different form. For example, the lower neck portion could be omitted and the lower end  146  of the casing hanger  140  could terminate with the flange having the shoulder  150  and the flow-by ports  152 . In this instance, the internal threaded surface  148  could be axially aligned with the flange at the bottom of the casing hanger  140 . 
     The casing hanger  140  also includes a threaded surface  154 , which allows the running tool  142  to be threaded onto the casing hanger  140 , and recesses  156  formed in its exterior surface. As described in additional detail below, the recesses  156  receive dogs of locking dog assemblies to facilitate synchronous rotation of the casing hanger  140  with the running tool  142 . The casing hanger  140  further includes an upper end  160  with a seal neck  158  and an internal threaded surface  162 , which allows other components (e.g., a back pressure valve or a two-way check valve) to be threaded to the casing hanger  140 . 
     Certain aspects of the running tool  142 , according to one embodiment, are illustrated in  FIG. 12 . For instance, the depicted running tool  142  includes a threaded surface  164  for mating with the threaded surface  154  of the casing hanger  140 . In this embodiment, the threaded surface  164  is provided below the locking dog assemblies  144 , though other arrangements are possible (see, e.g.,  FIG. 4  with locking dogs  104  below threaded surface  76 ). The locking dog assemblies  144  are provided in an upper end of a running tool (i.e., closer to the top of the running tool  142  than to the bottom of the tool  142 ) in some embodiments. And in some cases, the threaded surface  164  could be provided in the upper end of the running tool  142  (e.g., along with the locking dog assemblies  144 ), with the mating threaded surface  154  of the hanger  140  accordingly repositioned further from the flange. In one such embodiment, the bottom of the running tool  142  could be lengthened (compared to that shown in  FIG. 12 ) so that the threaded surface  164  is closer to the top of the running tool than to the bottom. The depicted running tool  142  also includes a threaded surface  166  (e.g., for receiving a landing joint), seal grooves  168  for receiving seals, and a test port  170  for testing proper sealing between the running tool  142  and the casing hanger  140  by seals in the seal grooves  168 . 
     A casing string  174  can be coupled to the casing hanger  140  (e.g., via threaded surface  148 ) and the running tool  142  can be used to run the casing hanger  140  into a casing head  172 , as generally depicted in  FIG. 13 . Although omitted in  FIG. 13  for the sake of clarity, it will be appreciated that the casing hanger  140  can be run into the casing head  172  through other components (e.g., a blowout preventer) attached to the wellhead stack above the casing head  172 . In at least some embodiments, the locking dog assemblies  144  are installed in the running tool  142  after the running tool is threaded onto the casing hanger  140 . For example, to assemble the casing hanger  140  and the running tool  142  in one embodiment, a landing joint is threaded into the running tool  142  to engage threaded surface  166 . The running tool  142  can then be lifted via the landing joint, positioned over the casing hanger  140 , and then rotated (e.g., clockwise) as it is lowered onto the casing hanger  140  to thread the running tool  142  and the casing hanger  140  together via threaded surfaces  154  and  164 . The running tool  142  can continue to be rotated about the casing hanger  140  until radial ports in the running tool  142  for receiving the locking dog assemblies  144  are axially and radially aligned with the recesses  156  in the exterior surface of the casing hanger  140 . 
     Once the radial ports are aligned with the recesses  156 , the locking dog assemblies  144  can be installed in the radial ports of the running tool  142 . One example of a locking dog assembly  144  is shown in  FIG. 14  as including a dog  176 , a biasing component (e.g., spring  178 ), a shear component  180 , and a retaining cap  182 . Any suitable biasing component could be used in the locking dog assembly  144 . When provided as a spring, the biasing component could include a compression spring, a disc spring, or a tapered spring, to name only a few examples. The spring  178  can be inserted into a radial port in the running tool, followed by the dog  176 . The inserted dog  176  can be pushed inwardly to extend through the radial port and into the recess  156  in the casing hanger  140 . The shear component  180  is installed behind (i.e., radially outward from) the dog  176 , and a retaining cap  182  is inserted into the radial port behind the shear component  180 . The shear component  180  is provided here as a shear washer, but could be provided in other forms (e.g., one or more shear pins). The retaining cap  182  includes a recess  184  for receiving the dog  176 , as described in greater detail below. The cap  182 , which can be threaded into the radial port or retained in any other suitable manner, also includes tool recesses that facilitate installation and removal. 
     As shown here, the radial port includes a first counterbore for receiving the spring  178  and the dog  176  and a second, larger counterbore for receiving the shear component  180  and the retaining cap  182 . But the radial port could be configured differently in other embodiments. Indeed, although presently described as radial ports, the ports through the running tool  142  into which the locking dog assemblies are installed could be formed at an angle with respect to a line normal to the inner and outer surfaces of the wall of the running tool  142  at which the port is formed. In such cases, it will be appreciated that dogs installed in the ports may still move inwardly and outwardly (i.e., closer to and further from the center, rotational axis of the casing hanger  140  and the running tool  142 ) to engage and disengage the casing hanger  140  and be used to transmit torque as described herein, even if the path of movement of the dogs is not actually radial with respect to the center axis. 
     With the locking dog assembly  144  installed in the radial port depicted in  FIG. 14 , the compressed spring  178  biases the dog  176  radially outward. The shear component  180  and the retaining cap  182  resist the biasing of the spring  178  and hold the dog  176  in its locked (i.e., engaged) position, in which the dog  176  extends radially inward from the running tool  142  into the recess  156  of the casing hanger  140 . An axial cross-section of the hanger assembly  138  is generally depicted in  FIG. 15  with the locking assemblies  144  installed in the radial ports of the running tool  142  and the dogs  176  engaging the recesses  156  of the casing hanger  140 . The running tool  142  can be rotated in one direction (clockwise in  FIG. 15 ) so that the dogs  176  bear against stop surfaces or shoulders  188  of the recesses  156 , preventing relative rotation of the running tool  142  with respect to the casing hanger  140  and causing the dogs  176  to transmit torque from the running tool  142  to the casing hanger  140 . This allows the dogs  176  to drive synchronous rotation of the casing hanger  140  with the running tool  142 . The hanger assembly  138  can then be lifted (e.g., via the landing joint) and threaded to the casing string  174 . In some instances, this may include attaching a casing pup joint to the casing hanger  140  (before or after connecting the running tool  142  to the casing hanger  140 ), aligning the hanger assembly  138  and the attached pup joint over a casing string in the well, and rotating the hanger assembly  138  to thread the pup joint to the casing string. The casing hanger  140  can then be lowered into the wellhead (e.g., into the casing head  172 ). In some instances, the casing hanger  140  and its attached casing string  174  can be rotated while running the casing hanger  140  into the wellhead. In one embodiment, the casing hanger  140  and the attached casing string  174  are rotated while running the casing string  174  into a deviated well. Rotation of the casing hanger  140  can also facilitate cementing of the attached casing string  174  within the well. 
     After desired rotation of the casing hanger  140  is completed and the hanger  140  is landed, the running tool  142  can be rotated in the opposite direction (e.g., counter-clockwise) to disconnect the running tool  142  from the hanger  140 . When the running tool  142  is rotated in this opposite direction with sufficient break-out torque (enough to break shear components  180 ), the return surfaces of the recesses  156  drive the dogs  176  radially outward and cause the shear components  180  to shear. The biasing springs  178  then cause the dogs  176  to automatically retract from the recesses  156  to their disengaged positions, out of contact with the casing hanger  140  and into the recesses  184  in the retaining caps  182 , as generally shown in  FIG. 16 . The running tool  142  can be further rotated to unthread the running tool  142  from the casing hanger  140 . Because the dogs  176  are automatically retracted out of engagement with the casing hanger  140 , the dogs  176  will not scratch or otherwise mar the seal neck  158  of the casing hanger  140  as the running tool  142  is unthreaded from the casing hanger  140 . Consequently, the present arrangement reduces the risk of damage to sealing surfaces along the casing hanger  140  above the recesses  156 . Once disconnected from the casing hanger  140 , the running tool  142  can be pulled from the wellhead. Other components, such as a packoff, can then be installed above the casing hanger  140  in the wellhead. 
     Another wellhead hanger assembly is generally depicted in  FIGS. 17-21 . As shown in  FIGS. 17 and 18 , a wellhead hanger assembly  190  includes the casing hanger  140  and the running tool  142  coupled together, with locking dog assemblies  192  installed in radial ports of the running tool  142  so as to engage the casing hanger  140 . Like the locking dog assemblies  144 , the locking dog assemblies  192  can transmit torque between the running tool  142  and the casing hanger  140  and facilitate rotation of the casing hanger  140  and any attached casing string  174 , such as during run-in or cementing processes. The locking dog assemblies  192  can also be provided in the upper end of the running tool  142 , as described above for locking dog assemblies  144 .  FIGS. 17, 20, and 21  generally depict the locking dog assemblies  192  in their locked positions (in which the dogs engage recesses  156  of the casing hanger  140 ), while  FIGS. 18 and 19  depict the locking dog assemblies in their unlocked positions (with dogs retracted from the recesses  156 ). 
     An example of a locking dog assembly  192  is depicted in  FIG. 19  as including a dog  196 , a biasing component (e.g., spring  198 ), a retaining cap  200  threaded into the radial port, and a handle  202 . The handle  202  includes a stem  204  threaded through the retaining cap  200  and coupled to the dog  196 . The locking dog assemblies  192  can be installed in radial ports of the running tool  142  before or after threading the running tool  142  onto the casing hanger  140 . 
     The handle  202  can be rotated to radially move the dog  196  into or out of engagement with the casing hanger  140 . The spring  198  is compressed between the dog  196  and the retaining cap  200  and biases the dog  196  radially inward. The handle  202  is accessible at the outer surface of the running tool  142  and is shown in  FIG. 19  as holding the dog  196  in a retracted position away from the casing hanger  140 . In one assembly technique, the dogs  196  are kept in this retracted position as the running tool  142  is threaded onto the casing hanger  140 . The handles  202  are then turned to the engaged positions depicted in  FIGS. 20 and 21 , allowing the biasing springs  198  to push the dogs  196  into engagement with the casing hanger  140 . If the radial ports of the running tool  142  are aligned with the recesses  156  when the handles  202  are turned to their engaged position, the springs  198  will push the dogs  196  radially inward into the recesses  156 . If the radial ports of the running tool  142  are offset from the recesses  156  when the handles  202  are turned to their engaged position, the springs  198  will push the dogs  196  radially inward into contact with the exterior surface of the casing hanger  140 . The running tool  142  can then be rotated about the casing hanger  140  to align the dogs  196  with the recesses  156 , at which time the biasing springs  198  will push the dogs  196  into the recesses  156 . 
     Once the dogs  196  extend into the recesses  156 , the running tool  142  can be rotated to drive synchronous rotation of the casing hanger  140  (via engagement of the dogs  196  with the stop surfaces  188  of the recesses  156 ) as described above with respect to hanger assembly  138 . To disconnect the running tool  142  from the casing hanger  140  (e.g., after running the casing hanger  140  into the casing head  172 , cementing an attached casing string  174 , and landing the casing hanger  140 ), the running tool  142  can be rotated to unthread the running tool  142  from the casing hanger  140 . The return surfaces of the recesses  156  push the dogs  196  radially outward against the biasing of the springs  198  when the running tool  142  is unthreaded from the casing hanger  140 , allowing the dogs  196  to exit the recesses  156  and the running tool  142  to be freely removed. With no shear components  180  to break, little or no break-out torque is needed to unthread the running tool  142  from the casing hanger  140 . 
     Each of the hanger assemblies described above can be used to rotate a casing string during running of the casing hanger into a well or cementing of the casing string within the well. In at least some embodiments, the load due to the weight of the casing hanger and its attached casing string can be carried entirely by the mating threads of the casing hanger and the running tool (e.g., surfaces  60  and  76 ; surfaces  154  and  164 ), while the applied torque used to rotate the hanger is carried entirely by the dogs of the running tool. Further, while certain embodiments may be described in the context of casing hangers, it is noted that the presently disclosed techniques could also be used to rotate other kinds of hangers, such as those connected to other tubular strings or to rods. The running tools described herein can be used to transmit torque to the hangers (whether casing hangers or some other types of hangers), causing the hangers to rotate synchronously with the running tools. Once rotation is completed and the hangers are landed, the running tools can be removed from the hangers. 
     While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.