FIELD OF INVENTION

The present invention broadly relates to a casing hanger for installation of a casing in a wellhead, and to a method of fabricating a casing hanger.

BACKGROUND

Wellheads are used in oil and gas drilling to suspend casing strings, seal the annulus between casing strings, and provide an interface to a blow out preventer ("BOP"). In drilling a well, it is a standard practice to pass a number of concentric tubes, or casings, down into the well to support the borehole and/or isolate the borehole from fluid producing zones. The wellhead is used to support a number of casing hangers that support the weight of the casing.

Figure 1 shows a cross-sectional view of a conventional slip-type casing hanger 100, hereinafter also referred to as slip hanger 100. Figure 2 shows a cross-sectional view of a wellhead 200 having the slip hanger 100 of Figure 1 disposed therein.

Typically, the functions of the slip hanger 100 include suspending one or more casing strings (not shown), and sealing off pressure from the annulus area 202 (Figure 2). In the slip hanger 100, slips 102, which are disposed adjacent a slip bowl 106 and a casing 204 (Figure 2), are friction wedges that "grip" the casing string and use "teeth" 104 to bite into the casing 204 when subjected to the weight of the casing. Seals, e.g. in the form of a deformable packing layer 108, are used to seal the annulus 202 between the casing 204 and the wellhead 200. For example, the packing layer 108 is made of a rubber ring and is disposed below the slips 102 and above a lower plate 110. When the slip hanger 100 is in use, the lower plate 110 rests inside the wellhead 200, and the packing layer 108 is compressed by the downward casing weight that is first transferred to the slips 102 then to the packing layer 108. As the packing layer 108 expands laterally under the weight, it seals the annulus 202 between the casing 204 and the wellhead 200. There are several drawbacks with the existing packing and seal configuration described above. For example, in some instances, the slip hanger 100 may become stuck onto the casing 204, resulting in large amounts of remedial work to correct. In addition, with the position of the packing layer 108 below the slips 102, hanging capacity is limited, as the packing layer 108 may be compressed above its compressible ratio. Thus, the conventional slip hanger 100 may not be suitable for high load and high pressure applications, e.g. in deep wells, where the packing layer 108 may become over compressed and extruded. Test results on a standard 7-inch casing hanger have shown that it fails to hold at a pressure of 10,000 pounds per square inch (psi) with a 800,000 pound-force (Ibf) casing load under temperatures of -20° to 350°F. Also, as the packing layer is disposed below the slips, the packing layer cannot be replaced unless the casing is also pulled out from the well.

There have been some attempts at solving the above problems. Figure 3 shows a cut-away perspective view of an existing casing hanger 300. In the casing hanger 300, as slips 302 bite onto the external surface of a casing (not shown) and moves downward, the slips 302 push a slip bowl 304 downward. The slip bowl 304 is directly connected to an upper plate 306 via screws 308. Thus, in turn, the slip bowl 304 pulls the movable upper plate 306 downward such that the upper plate 306 compresses a packing layer 310 disposed directly below it against a fixed housing 312. As the packing layer 310 is above the slips 302, replacement can be carried out without having to pull out the casing. However, the compression distance of the packing layer 310 is equal to the travelling distance of the slips 302 and the travelling distance of the slips 302 is limited. This means that the packing layer 310 must be very sensitive, i.e. capable of expanding laterally and sealing with very little compression. This kind of packing layer is typically not cheap.

A need therefore exists to provide a slip-type casing hanger that seeks to address at least one of the above problems.

SUMMARY

In accordance with a first aspect of the present invention, there is provided a casing hanger for installation of a casing in a wellhead, the casing hanger comprising a support structure comprising a tubular inner surface; an annular lower plate disposed axially above a top portion of the support structure; a deformable annular packing layer disposed axially above the lower plate; and an annular upper plate disposed axially above the packing layer and connected to the top portion of the support structure; wherein the lower plate is axially movable relative to the upper plate for compressing the packing layer against the upper plate, thereby sealing annular spaces between the casing hanger and the casing, and between the casing hanger and the wellhead.

The casing hanger may further comprise a slip bowl disposed within the tubular inner surface, the slip bowl further defining a hollow centre portion; and a plurality of slip segments disposed within the hollow centre portion of the slip bowl and movable relative to the slip bowl for suspending the casing in the wellhead.

The casing hanger may further comprise a plurality of activator elements, wherein respective top faces of the activator elements abut a bottom surface of the lower plate, and respective bottom faces of the activator elements slidingly contact a top surface of the slip bowl.

The top surface of the slip bowl may be chamfered at an angle corresponding to the angle that the bottom faces of the activator elements make with a horizontal plane.

The activator elements may be restrained from radial movement by the tubular inner surface of the support structure.

The slip bowl may be configured sit on an annular supporting surface of the support structure such that the slip bowl is radially slidable relative to the support structure.

In an unloaded state, an outer surface of the slip bowl and the tubular inner surface of the support structure may be separated by a gap. In a loaded state, the slip bowl may be configured to slide radially outward for partially closing the gap. In the loaded state, the slip bowl may push the activator elements to slide axially upward relative to the support structure and push against the lower plate, thereby compressing the packing layer.

The packing layer may be compressed by a highest amount when a lower chamfered face of the slip bowl engages an inner slanted face of the support structure. The highest amount may be determined based on the chamfer angle of the top surface of the slip bowl and a horizontal distance travelled by the slip bowl before the lower chamfered face engages the inner slanted face of the support structure. The highest amount may be selected to be lower than a compression capacity of the packing layer. The lower plate may be coupled to the upper plate by screws inserted from a bottom surface of the lower plate, and only ends of said screws engaging the upper plate may be threaded.

The casing hanger may comprise two equal halves coupled to each other by screw means.

The support structure may be configured to abut a shoulder of the wellhead for transferring the casing weight to the wellhead.

In accordance with a second aspect of the present invention, there is provided a method of fabricating a casing hanger, the method comprising the steps of providing a support structure comprising a tubular inner surface; disposing an annular lower plate axially above a top portion of the support structure; disposing a deformable annular packing layer axially above the lower plate; disposing an annular upper plate axially above the packing layer; and connecting the upper plate to the top portion of the support structure such that the lower plate is axially movable relative to the upper plate for compressing the packing layer against the upper plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figure 1 shows a cross-sectional view of a conventional slip-type casing hanger.

Figure 2 shows a cross-sectional view of a wellhead having the slip hanger of Figure 1 disposed therein.

Figure 3 shows a cut-away perspective view of a prior art casing hanger.

Figure 4 shows a cut-away perspective view illustrating a slip-type casing hanger according to an example embodiment.

Figure 5a shows a top view (i.e. along an axial direction) of the slips of Figure 4 according to an example embodiment.

Figure 5b shows a sectional view along a line A-A in Figure 5a.

Figure 5c shows an enlarged view of detail A in Figure 5b.

Figure 5d shows an enlarged view of detail B in Figure 5b. Figure 6a shows a top view (i.e. along an axial direction) of the lower plate of Figure 4 according to an example embodiment.

Figure 6b shows a sectional view along a line A-A in Figure 6a.

Figure 6c shows a sectional view along a line B-B in Figure 6a.

Figure 7a shows a top view (i.e. along an axial direction) of the support structure of Figure 4 according to an example embodiment.

Figure 7b shows a sectional view along a line A-A in Figure 7a.

Figure 7c shows a bottom view of the support structure shown in Figure 7a.

Figure 7d shows a sectional view along a line B-B in Figure 7c.

Figure 8a shows a top view (i.e. along an axial direction) of the slip bowl of Figure 4 according to an example embodiment.

Figure 8b shows a sectional view along a line A-A in Figure 8a.

Figure 9a shows a top view (i.e. along an axial direction) of the upper plate of Figure 4 according to an example embodiment.

Figure 9b shows a sectional view along a line A-A in Figure 9a.

Figure 9c shows a sectional view along a line B-B in Figure 9a.

Figure 10a shows a top view (i.e. along an axial direction) of the activator elements of Figure 4 according to an example embodiment.

Figure 10b shows a sectional view along a line A-A in Figure 10a.

Figure 11a shows a cross-sectional view of a wellhead.

Figure 11 b shows a cross-sectional view of the wellhead of Figure 11a together with a casing inserted therein.

Figure 11c shows a partial cross-sectional view illustrating the assembly of the casing hanger of the example embodiments around the casing of Figure 11 b.

Figure 11d shows a cross-sectional view illustrating a resting position of the slip hanger in the wellhead according to an example embodiment.

Figure 11e shows a cross-sectional view illustrating the slip hanger in a loaded state inside the wellhead according to an example embodiment.

Figure 11f shows a cross-sectional view of the wellhead, casing hanger and casing illustrating operation of iockdown screws according to an example embodiment.

Figure 12 shows a flow chart illustrating a method of manufacturing a casing hanger according to an example embodiment. DETAILED DESCRIPTION

Figure 4 shows a cut-away perspective view illustrating a slip-type casing hanger 400 (hereinafter also referred to as a slip hanger 400) according to an example embodiment. In this view, the slip hanger 400 is upright in the same orientation as its orientation during normal deployment. The slip hanger 400 includes a plurality of slip segments 402 (hereinafter also referred to as slips 402), which have contact members in the form of inner teeth 401 for gripping, i.e. biting onto, a cylindrical casing (not shown) passing through its hollow centre. The slips 402 are disposed inside of a slip bowl 404, and outer teeth 403 of the slips 402 contact with an inner surface 405 of the slip bowl 404. The inner surface 405 is slightly tapered downward, e.g. at an angle of about 7°. As would be appreciated by a person skilled in the art, the slip segments 402 may be moveable, at some resistance due to the outer teeth 403, relative to the slip bowl 404. For example, slips 402 may slide downward due to the weight of the casing, thereby tightening their grip on the casing. As can be seen in Figure 4, the slip bowl 404 rests on a support structure 406 such that a bottom surface 424 of the slip bowl 404 can slide radially outward relative to a supporting surface 425 of the support structure 406. Additionally, the support structure 406 is shaped such that it can fit into a cylindrical portion of a wellhead and rest against a wellhead shoulder. For example, an outer side surface 426 of the support structure 406 is substantially tubular, while a bottom surface 428 is chamfered at an angle corresponding to the angle of the wellhead shoulder 802 (as can be seen in Figures 8 and 9). A top surface 407 of the slip bowl 404 is disposed at an angle, e.g. 45°, to a horizontal plane and contact respective slanted faces 409a-b of a plurality of activator elements 408a- b. In the example shown in Figure 4, four activator elements 408 are used in the casing hanger. However, it will be appreciated that different numbers of activator elements 408 may be used in alternate embodiments. In preferred implementations, the activator elements 408 are evenly distributed around a top portion 444 of the support structure 406.

In example embodiments, the activator elements 408a-b are prevented from radial movement by the support structure 406, but may be movable vertically relative to the support structure 406. Top faces 411a-b of respective activator elements 408a-b abut a bottom surface 430 of a lower plate 410, Which is disposed beiow an elastic packing layer 412. The packing layer 412, in turn, is disposed below an upper plate 414, i.e. the packing layer 412 is sandwiched between the upper plate 414 and the lower plate 410. The lower plate 410, packing layer 412 and upper plate 414 define substantially cylindrical inner surfaces 450, 452 and 454 respectively. In addition, the lower plate 410 is connected to the upper plate 414 by a plurality of mechanical fasteners, e.g. screws 416a-c. The screws 416a-c are threaded only at respective ends 417a-c that engage with the upper plate 414, such that the lower plate 410 and the packing layer 412 are moveable relative to the upper plate 414, as will be described in detail below. It will be appreciated that other types of fasteners that achieve the same function can be used in alternate embodiments.

The upper plate 414 is fixed to the support structure 406 by fastening means in the form of a plurality of screws 418a-c which can be inserted from a top surface 432 of the upper plate 414. While not shown in Figure 4, it will be appreciated that only end portions of the screws 418a-c are threaded and engage with the support structure 406. Other types of fasteners can also be used. Thus, the upper plate 414 and the support structure 406 together define an overall stationary structure of the casing hanger 400, in which other parts are moveable relative to this structure. In a preferred embodiment, the packing layer 412 is made of rubber, while other parts of the casing hanger 400 described above are typically made of steel alloys of respective grades, as will be understood by a person skilled in the art. However, it will be appreciated that other materials may be used in alternate embodiments. Figures 5a-5d show various views of the slips 402 of Figure 4 according to an example embodiment. Figure 5a shows a top view (i.e. along an axial direction) of the slips 402. Figure 5b shows a sectional view along a line A-A in Figure 5a. Figures 5c-5d show enlarged views of details A and B in Figure 5b respectively. As can be seen in Figure 5a-5b, a plurality of slip segments 502a-d form the slips 302. While 4 slip segments 502a-d are used in the example embodiment, it will be appreciated that a different even number of segments may be used in alternate embodiments. The slips segments 502a-d may be coupled to each other by fastening means, e.g. screws, that engage respective hole pairs 504a-d. Moreover, as can be seen in Figures 5c-d, the inner teeth 401 , which grip the casing, are sharper than the outer teeth 403, which can slide against the inner surface 405 of the slip bowl 404 (Figure 4).

Figures 6a-6c show various views of the lower plate 410 of Figure 4 according to an example embodiment. Figure 6a shows a top view (i.e. along an axial direction) of the lower plate 410. Figure 6b shows a sectional view along a line A-A in Figure 6a. Figure 6c shows a sectional view along a line B-B in Figure 6a. The lower plate 410 includes plurality of through holes, e.g. 602a, 602b, for receiving the screws 418a-c (Figure 4), and a plurality of counterbore holes, e.g. 604a, where the screws 416a-c (Figure 4) are inserted. The lower plate 410 also includes a chamfered edge 440, as shown in Figure 6b. Figures 7a-7d show various views of the support structure 406 of Figure 4 according to an example embodiment. Figure 7a shows a top view (i.e. along an axial direction) of the support structure 406. Figure 7b shows a sectional view along a line A-A in Figure 7a. Figure 7c shows a bottom view of the support structure 406. Figure 7d shows a sectional view along a line B-B in Figure 7c. As can be seen in Figure 7a, a plurality of slots, e.g. 438a-b, are formed on a top portion 444 of the support structure 406 for receiving the respective activator elements 408a-b (Figure 4). In addition, a plurality of threaded holes, e.g. 702a-c, are disposed on the top portion 444 for engaging with the screws 418a-c (Figure 4). The support structure includes a slanted face 704 at the corner between the supporting surface 425 and the tubular inner surface 436 (Figure 4). Figures 8a-8b show various views of the slip bowl 404 of Figure 4 according to an example embodiment. Figure 8a shows a top view (i.e. along an axial direction) of the slip bowl 404. Figure 8b shows a sectional view along a line A-A in Figure 8a. Similar to the slips 402, the slip bowl is formed by a plurality of segments coupled to each other by screws that engage with respective hole pairs 802a-d, as shown in Figure 8a. Additionally, the slip bowl 804 includes a chamfered face 804 formed at the corner between the outer surface 435 and the bottom surface 424 (Figure 4). In a preferred embodiment, the chamfered face 804 has the same angle as the slanted face 704 (Figure 7) for engaging with the slanted face 704.

Figures 9a-9c show various views of the upper plate 414 of Figure 4 according to an example embodiment. Figure 9a shows a top view (i.e. along an axial direction) of the upper plate 414. Figure 9b shows a sectional view along a line A-A in Figure 9a. Figure 9c shows a sectional view along a line B-B in Figure 9a. The top plate 414 includes a plurality of counterbore holes, e.g. 902a-c, for receiving the screws 418a-c (Figure 4), a plurality of threaded holes, e.g. 904a-c, for engaging with the screws 416a-c (Figure 4), and a plurality of threaded blind holes, e.g. 906a-b, for engaging and mounting the eyelets 422a-b (Figure 4).

Figures 10a-10b show various views of the activator elements 408a-d of Figure 4 according to an example embodiment. Figure 10a shows a top view (i.e. along an axial direction) of the activator elements 408a-d. Figure 10b shows a sectional view along a line A-A in Figure 10a. Slanted faces 409a-b are disposed at lower ends of respective activator elements 408a-b for slidingly engaging with respective top faces 407a-b of the slip bowl 404.

With reference to Figure 4, to assemble the casing hanger 400, a first sub assembly comprising the upper plate 414, the packing layer 412 and the lower plate 410, in this order, is formed. Screws 416a-c are then inserted from the bottom surface 430 of the lower plate 410, and fastened such that the threaded ends 417a-c engage with the upper plate 414. Separately, a second subassembly comprising the slips 402, the slip bowl 404, the support structure 406 and the activator elements 408a-b is formed. The slips 402, slip bowl 404 and support structure 406 are held together by alignment means in the form of pins or screws 420a-b (Figure 4). In addition, the activator elements 408a-b are inserted into respective slots 438a-b on the top portion 444 of the support structure 406 (Figure 4). In some embodiments, the slots 438a-b may be formed such that the activator elements 408a-b are held in place, instead of tipping into the hollow center 421. In the assembled but not yet operational state, a gap 433 exists between an outer surface 435 of the slip bowl 404 and a tubular inner surface 436 of the support structure 406 (Figure 4). The first and second sub-assemblies are then attached to each other by fastening the screws 418a-c. In some implementations, mounting means in the form of a plurality of eyelets 422a-b are affixed to the top surface 432 of the upper plate 414 for lifting and suspending the casing hanger 400 later using external means (not shown). As described, the slip hanger 400 forms a hollow cylinder capable of gripping a casing running through its center portion 421 , as well as resting on a shoulder 1120 of the wellhead (Figures 1 1d-e). The slip hanger 400 thus helps to suspend the casing inside the bore hole. Typically, the slip hanger 400 is formed of two equal halves joined by fastening means (not shown). In other words, the two halves can be closed and securely fastened to each other, e.g. using screws or bolts or other mechanical fasteners. It will thus be appreciated that the assembly process described above applies to each half of the slip hanger 400 first, before the two halves are joined.

During operation, the bottom surface 428 of the support structure 406 rests on the shoulder 1 120 of the wellhead (Figures 1 1d-e), while the outer surface 426 of the support structure 406 is adjacent a cylindrical portion 1122 of the wellhead (Figures 11 d-e). Under the weight of the casing 1 106 (Figure 11d), the slip segments 402 may slide downward relative to the slip bowl 404. The inner teeth 403 bite onto the casing 1106 while the outer teeth 405 frictionally slide against the inner surface 405 of the slip bowl 404. The weight of the casing 1106 is thus transferred to the slip bowl 404, causing the slip bowl 404 to slide radially outward relative to the support structure 406, i.e. the gap 433 is partially closed as the lower chamfered face 804 (Figure 8) of the slip bowl 404 finally engages the inner slanted face 704 (Figure 7) of the support structure. The slip bowl 404 is then prevented from further sliding by the engaging faces 704, 804. As the slip bowl 404 slides outward under the weight of the casing 602, the top face 407 slide against slanted faces 409a-b of the activator elements 408a-b, thus pushing the activator elements 408a-b upward.

Further, as the activator elements 408a-b are pushed to move vertically upward, the top faces 411a-b push against the bottom surface 430 of the lower plate 410. As a result, the bottom plate 410, being not restricted by the screws 416a-b and 418a-c, moves upward and compresses the deformable packing layer 412, causing the packing layer 412 to expand laterally to seal the space between the casing hanger 400 and the casing, and between the casing hanger 400 and the wellhead.

With reference to Figures 11a-11f, an example deployment of the slip hanger 400 (Figure 4) for installation of a casing in a wellhead is now described. Here, the same numerals are used to denote the respective elements already described in previous Figures.

In the first step, a wellhead is prepared. Figure 11 a shows a cross-sectional view of a wellhead 1100 having a bowl 1102. In some instances, lock down screws 1 104a-b may be retracted in this step.

In the second step, a casing string (also referred to as casing) is run (i.e. lowered) to the required depth in the bore hole. Figure 11 b shows a cross-sectional view of the wellhead 1100 of Figure 11a together with a casing 1106 inserted therein. At this point, the casing 1106 may be suspended by external means (not shown).

In the next step, the slip-type casing hanger 400 (Figure 4) is assembled around the casing 1 06. Figure 11c shows a partial cross-sectional view illustrating the assembly of the casing hanger 400 of the example embodiments around the casing 1106 of Figure 11 b. Supporting boards 1108a-b, which are typically made of wood, are placed on top of the wellhead 1100. The casing hanger 400 is split open and placed above the supporting boards 1108a-b, which prevent the hanger 400 from dropping uncontrollably into the bore hole. The two halves of the hanger 400 engage the casing 1106 such that the inner teeth 401 of the slips 402, and inner surfaces 450, 452, 454 (Figure 4) of the lower plate 410, packing layer 412 and upper plate 414 respectively (Figure 4) are adjacent, but movable relative to, the casing 1106. The two halves are then locked to each other by fastening screws 1110, 1112, 1114. At this point, the alignment pins or screws 420a-c (Figure 4) are still in place. The casing hanger 400 can be lifted by external lifting means (not shown) attached to the eyelets 422a-d (Figure 4). As can be seen in Figure 11c, bottom slots 11 6 may be optionally formed on the support structure 406 for injecting material, e.g. a fluid, from the annulus of the wellhead 1100 to the annulus space around the casing 1106 after the casing hanger 400 has been installed in the wellhead 1100.

Next, with the supporting boards 1108a-b withdrawn and the alignment screws 420a-c removed, the slip hanger 400, which now wraps around a portion of the casing 1106, is lowered into the bowl 1102 of the wellhead 1100. Figure 11d shows a cross-sectional view illustrating a resting position of the slip hanger 400 (Figure 4) in the wellhead 1100 according to an example embodiment. In this position, the outer surface 426 (Figure 4) of the support structure 406 (Figure 4) is adjacent a cylindrical portion 1122 of the wellhead 1100, while the bottom surface 428 (Figure 4) of the support structure 406 abuts a wellhead shoulder 1120 and is prevented from dropping further. Typically, the wellhead shoulder 1120 is slanted at an angle, e.g. 45°, corresponding to the chamfered bottom surface 428 on the support structure 406.

In the resting position shown in Figure 11d, the casing 1106 is initially still suspended by the external means. Thus, the inner teeth 401 (Figure 4) of the slips 402 just contact an outer surface 1122 of the casing 1106 while the outer teeth 403 (Figure 4) just contact the inner surface 405 (Figure 4) of the slip bowl 404, without loading or stress. The gap 433 still exists between the outer surface 435 (Figure 4) of the slip bowl 404 and the tubular inner surface 436 (Figure 4) of the support structure 406. The activator elements 408 are at the lowest position and the packing layer 412 is uncompressed. In some implementations, the casing 1106 may be pulled upward slightly to initiate the slips 402 to slide downward and start contact with the casing 1106. Next, the casing 1106 is released from the external suspension means and allowed to travel vertically downward due to its own weight. As a result, the slips 402 are dragged downward and slide against the inner surface 405 of the slip bowl 404. In the process, the inner teeth 401 of the slips 402 "bite" into an external surface 1124 of the casing 1106 for suspending the casing 1106. Additionally, as the slips 402 are in cooperative contact with the inner surface 405 of the slip bowl 404 via the outer teeth 403, the weight of the casing 1106 is transferred to the slip bowl 404, causing it to slide radially outward to compress the packing layer 412.

Figure 11e shows a cross-sectional view illustrating the slip hanger 400 (Figure 4) in a loaded state inside the wellhead 1100 according to an example embodiment. As shown in Figure 11e, the activator elements 408 and the lower plate 410 are pushed upward as the top surface 407 (Figure 4) of the slip bowl 404 slidingly pushes against the slanted faces 409 (Figure 4) of the activator elements 408. The packing layer 412 is thus compressed against the upper plate 414, as the upper plate 414 is fixed. As a result, the packing layer 412, being made of an elastic material, expands laterally and seals the gaps between the casing 1106 and the slip hanger 400, and between the slip hanger 400 and the wellhead 1100.

As described, both suspending and sealing functions are achieved by the casing hanger 400 of the example embodiments. The maximum upward movement (i.e. vertical displacement) by the activator elements 408 is reached when the lower chamfered face 804 of the slip bowl 404 contact the inner slanted face 704 of the support structure 406, and can thus be determined based on the horizontal distance travelled by the slip bowl 404 and the slant angle of the slanted faces 409. For example, in embodiments where the slanted faces 409 are at an angle of 45° to a horizontal plane, the maximum vertical displacement by the activator elements 408 is equal to the distance travelled by the slip bowl 404. In alternate embodiments, the relationship between the maximum vertical displacement and the horizontal distance travelled by the slip bowl 404 is based on the following formula:

Y = Xx tanA (1) where Y is the maximum vertical displacement, X is the horizontal distance and A is the slanted angle of the slanted faces 409 to the horizontal plane.

Thus, even if the weight of the casing 1106 is increased, e.g. in applications with longer casings in deeper wells, the activator elements 408 cannot be moved further upward beyond the maximum vertical displacement Y (Equation (1)). In other words, the packing layer 412 is not further compressed in such applications, thereby avoiding the risk of being compressed beyond its compression ratio (capacity). Once the maximum vertical displacement is reached, any additional casing weight is directly transferred downwardly to the wellhead 1100 via the slips 402, slip bowl 404 and the bottom portion of support structure 406, and not to the activator elements 408.

Also, if the maximum allowable vertical displacement is known (e.g. based on material properties of the packing layer), the horizontal distance to be travelled by the slip bowl 404 can be calculated using Equation (1) such that the chamfered face 804 contact the slanted face 704 before the compression capacity of the packing layer 412 (Figure 4) is reached. For example, in one implementation, if the packing layer 412 can be compressed to a maximum of 3mm, the distance to be travelled by the slip bowl 404 can be determined accordingly. Figure 11f shows a cross-sectional view of the wellhead 1100, casing hanger 400 and casing 1106 illustrating operation of Iockdown screws 104a-b according to an example embodiment. The support structure 406 includes a chamfered top edge 446, and the lower plate 410 includes a chamfered bottom edge 440, as can be seen more clearly in Figures 4 and 6. The edges 446, 440 are shaped such that they correspond to, and are thus capable of receiving respective chamfered ends 1132a-b of the Iockdown screws 1104a-b. The vertical level of holes 1130a-b on the wellhead 1100 that receive the Iockdown screws 1104a-b is determined based on the vertical position of the lower plate 410 after loading. In some embodiments, by further tightening the Iockdown screws 1104a-b after the chamfered ends 1132a-b abut the chamfered edge 440 of the lower plate 410, the lower plate 410 can be further pushed upward. As a result, the packing layer 412 may be further compressed, if desired, to provide additional sealing, e.g. in high-pressure applications.

The example embodiments provide a slip mechanism that allows the packing layer to be placed above the slip. Thus, advantageously, the packing may be replaceable without pulling out the suspended casing. Also, the pressure applied by the packing layer and the slip on the casing is more widely distributed, thus reducing the risk of the casing being collapsed. The slip mechanism of the example embodiments may also allow higher casing loads to be transferred to the wellhead (and not to over compress the packing layer) as soon as the lower chamfered face 804 of the slip bowl 404 engages the inner slanted face 704 of the support structure 406. As the casing hanger of the example embodiments is capable of greater casing loads, it may be suitable for applications in deep wells.

Figure 12 shows a flow chart 1200 illustrating a method of manufacturing a casing hanger according to an example embodiment. At step 1202, a support structure comprising a tubular inner surface is provided. At step 1204, an annular lower plate is disposed axially above a top portion of the support structure. At step 1206, a deformable annular packing layer is disposed axially above the lower plate. At step 1208, an annular upper plate is disposed axially above the packing layer. At step 1210, the upper plate is connected to the top portion of the support structure such that the lower plate is axially movable relative to the upper plate for compressing the packing layer against the upper plate.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.