CA2254391C - Oil well tubing string hanging device and lifting assembly - Google Patents

Abstract

An oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well, and a method of retaining an oil well tubing string in tension within an oil well. The device includes a hanger shell suspended within or connected to the oil well casing, a lifting assembly, and may include a mandrel mounted within the hanger shell. The lifting assembly is connected to the tubing string and is securable to the hanger shell or the mandrel. When the lifting assembly is disengaged from the hanger shell or the mandrel, the lifting assembly and the production tubing string that is attached thereto may be independently lifted within the oil well without removal or lifting of the mandrel or the hanger shell.

Description

TITLE: Oil Well Tubing String Hanging Device And Lifting Assembly FIELD OF THE INVENTION
This invention relates generally to devices used to hang a tubing string within the casing of an oil well.
BACKGROUND OF THE INVENTION
Even a slight deviation from the vertical will cause the sucker rod in an oil well to contact the inner wall surface of the production tubing string resulting in wear to the tubing string through rod movement. Such wear can form small holes in the side of the production string, or can reduce the tensile strength of the string to a point where it will fail under load. For that reason others have developed a variety of different tubing string rotators that slowly rotate the production tubing string about the sucker rod in order to more evenly distribute any frictional wear around the inside circumference of the string.
Traditionally, the production tubing string has been supported within the well casing by the rotator. However, that particular structure was found to suffer from a variety of limitations, not the least of which was a requirement to lift the entire tubing string in order to remove or service the rotator. As a result, more recently tubing string hanging devices have been developed that permit the production tubing string to be, in effect, hung from the well casing independently from the rotator. In such cases the tubing string is attached to a tubing string hanging device, which is itself then hung or held within the well casing. A variety of different mechanical structures can be utilized to transfer rotational movement from the rotator to the production tubing string.
While such tubing string hanging devices have proved useful in allowing for the independent removal of a rotator without the necessity of pulling the entire production tubing string from a well, they have not addressed all of the short comings of prior devices and suffer from their own inherent limitations. For example, a tubing string hanging device typically includes an outer shell, that is suspended from the well casing, and some form of inner rotatable mandrel or coupling device to which the production tubing string is attached. Between the inner and outer portions is usually situated a variety of different bearing mechanisms and seals. In the event that it becomes necessary to remove or lift the tubing string from the well those bearings and seals often become exposed to the elements of the well and can become clogged with sand and other debris which will significantly reduce their life span and operating efficiency. In addition, there are a large variety of devices or down-hole tools that are employed at the bottom of a production tubing string, deep within the well. Such devices include anchoring mechanisms, no-turn tools, and packers. Typically these devices are attached to the bottom end of the production tubing string and lowered into the well.
Once in place down-hole tools are usually "set" through either rotating, or pulling the tubing string, or through a combination of rotational and pulling movements, to cause arms or other forms of engagement mechanisms to be deployed such that the tool becomes locked to the well casing. At that point it often becomes necessary to lift the production tubing string in an upward direction so as to place the entire string, and the tool, in tension to complete the "setting" operation and allow proper functioning of the down-hole tool. The ability to set oil well tools in this manner, and to maintain a production tubing string in tension, is not available through use of current tubing string hanging devices.

SiIMMARY OF THE INVENTION
The invention therefore provides a tubing string hanging device and lifting assembly which overcomes the shortfalls of such prior devices through the incorporation of a structure that allows for the production tubing string to be rotatably hung from the well casing, enables the string to be retained in tension, and in some instances permits the tubing string to be lifted within the oil well independent from the tubing string hanging device. The invention further provides for a mechanism to allow down-hole oil tools to be set while maintaining well control.
Accordingly, in one of its aspects the invention provides the invention provides an oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well casing, the device comprising a hanger shell suspended within or connected to the oil well casing, a mandrel mounted within said hanger shell, and, a lifting assembly releasably securable to said mandrel, said lifting assembly having means for connecting to and for hanging a production tubing string therefrom, said lifting assembly including engagement means for releasably securing said lifting assembly to said mandrel such that said lifting assembly, and a production tubing string attached thereto, may be independently lifted within the oil well without removal or lifting of said mandrel or said hanger shell.
In a further aspect the invention provides an oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well casing, the device comprising a hanger shell suspended within or connected to the oil well casing, and, a lifting assembly releasably securable to said hanger shell, said lifting assembly having means for connecting to and for hanging a production tubing string therefrom, said lifting assembly including engagement means for releasably securing said lifting assembly to said hanger shell such that said lifting assembly, and a production tubing string attached thereto, may be independently lifted within the oil well without removal or lifting of said hanger shell.
In a further aspect the invention provides an oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well casing, the device comprising a hanger shell suspended within the oil well casing, a lifting assembly releasably suspendable from said hanger shell, said lifting assembly containing means to hang a production tubing string therefrom, and, engagement means to releasably suspend said lifting assembly from said hanger shell, said engagement means allowing said lifting assembly to be suspended from hanger shell and allowing said lifting assembly, and a production tubing string attached thereto, to be independently lifted within the oil well casing without removal or lifting of said hanger shell.
In a yet further aspect the invention provides a method of retaining an oil well tubing string in tension within an oil well casing, the method comprising (i) lowering an oil well tubing string, having a lifting assembly attached to its upper end, into an oil well casing; (ii) anchoring a lower portion of the oil well tubing string within the oil well casing; (iii) applying a lifting force to the tubing string to place the tubing string in tension and bringing the lifting assembly into engageable contact with a tubing string hanger such that engagement means on the lifting assembly are releasably securable to the tubing string hanger; and, (iv) releasing the lifting force applied to the tubing string and causing the engagement means to secure the lifting assembly within the tubing string hanger thereby causing the tubing string to be held and retained in tension.

Further objects ands advantages of the invention will become apparent from the following description taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings which show the preferred embodiments of the present invention in which:
Figure 1 is a side elevational view in longitudinal section of an oil well tubing string hanging device and lifting assembly in accordance with the present invention;
Figure 2 is a side elevational view in longitudinal section of the lifting assembly of the 1 S device shown in Figure I ;
Figure 3 is a side elevational view in longitudinal section of the mandrel portion of the device shown in Figure I ;
Figure 4 is a sectional view of the lifting assembly of Figure 2 taken along the line 4-4 of Figure 2;
Figure 5 is a side elevational view in longitudinal section of an alternate embodiment of the device shown in Figure 1;
Figure 6 is a side elevational view in longitudinal section of an alternate embodiment of the lifting assembly of the device shown in Figure I;
S

Figure 7 is a side elevational view in longitudinal section of a further alternate embodiment of the present invention;
Figure 8 is a side elevational view in longitudinal section of a further alternate S embodiment of the present invention having a modified rotator design; and, Figure 9 is a side elevational view in longitudinal section of yet a further embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention may be embodied in a number of different forms. However, the specification and drawings that follow describe and disclose only some of the specific forms of the invention and are not intended to limit the scope of the invention as defined 1 S in the claims that follow herein.
The oil well tubing string hanging device and lifting assembly pursuant to the present invention is shown in the attached drawings and noted generally by reference number 1. Device 1 is comprised generally of a hanger shell 2, a mandrel 3 and a lifting assembly 4. Hanger shell 2 includes means to engage an oil well casing S such that the hanger shell is retained or suspended within the casing. While it will be appreciated that a variety of different structures could be utilized to engage the well casing so as to suspend the hanger shell therein, in the preferred embodiment, and as shown in Figure 1, hanger shell 2 has an inwardly tapered exterior surface 6 that engages an inwardly tapered shoulder 7 on the inner surface of well casing 5. Since the diameter of hanger shell 2 is greater than the internal diameter of well casing 5, hanger shell 2 effectively acts as a plug and engages the side of the well casing to suspend itself therein.

Mandrel 3 may be constructed so as to be either stationary or rotatably mounted within hanger shell 2. In the attached drawings the mandrel is rotatably mounted within the hanger shell and has an upper end 8 and a bottom or lower end 9. In the embodiment shown in Figure l, mandrel 3 further includes, at or near its upper end, an outwardly extending radial flange 10 that bears against bearing means 11 disposed between the hanger shell and the mandrel. Bearing means 11 facilitates in the rotation of mandrel 3 within hanger shell 2 through a reduction in friction between the respective parts.
Bearing means 11 preferably comprises both a thrust bearing 12 and a radial bearing 13, and is configured such that vertical loading of the mandrel is transferred through thrust bearing 12 to hanger shell 2. Radial bearing 13 facilitates in the rotational movement of the mandrel and carries side loading where the mandrel is subjected to non-vertical loading in deviated well situations.
Mandrel 3 also includes means to engage a tubing string rotator 17 so as to impart a rotational movement to the mandrel. In the embodiment shown in Figure 1, the engagement with tubing string rotator 17 is accomplished through the use of a series of inwardly directed splines 14 situated at the upper end 8 of mandrel 3. Splines 14 mesh with similarly shaped splines on a coupling member 1 S that is attachable to the shaft 16 of tubing rotator 17. As shown in Figure I, coupling member 15 is preferably of a dimension that allows it to be inserted into the upper opening of mandrel 3 such that the splines on the coupling member mesh with splines 14 on mandrel 3 to effectively "lock"
the structures together. It will therefore be appreciated that when coupling means I S is inserted into the upper portion of mandrel 3, rotation of tubing rotator shaft 16 will result in the transmission of rotational movement through coupling member 1 S
to splines 14, and thus cause the rotation of mandrel 3 within hanger shell 2. It will also be appreciated that a variety of other mechanical structures could equally be used to rotate the mandrel.

To hold mandrel 3 securely within hanger shell 2, a retaining nut 18 is preferably threaded onto the top portion of hanger shell 2. When retaining nut 18 is threaded onto hanger shell 2 it is positioned in close proximity the exterior surface of the mandrel such that the mandrel is effectively held within the hanger shell and yet is still able to freely rotate. In order to prevent the seepage of dirt or debris into bearing means 11, a seal 19 is positioned near the top of hanger shell 2, and between retaining nut 18 and mandrel 3. Similarly, seals 20 are positioned between hanger shell 2 and mandrel 3 at a point below bearing means 11. To help ensure full well control a further set of seals 21 is preferably positioned on the exterior surface of hanger shell 2 such that they bear against the interior of oil well casing 5. Seals 21 will help to preventing the escape of oil and gases from between the hanger shell and the well casing.
Referring specifically to Figures l, 2 and 4, lifting assembly 4 is shown as comprised of a generally cylindrical structure having an upper end 22 and a lower end 23. Lower 1 S end 23 of lifting assembly 4 includes means for connecting the lifting assembly to a production tubing string and hanging the tubing string therefrom. In the preferred embodiment the production tubing string is threadably received within a threaded internal bore 24 within lower end 23 of lifting assembly 4, however, it will be appreciated that other forms of connections between the lifting assembly and the production tubing string could equally be employed. Lifting assembly 4 further includes engagement means 25 for releasably securing the assembly within mandrel 3.
Engagement means 25 operates such that when lifting assembly 4 is releasably secured to mandrel 3 rotational movement of the mandrel results in rotational movement of the lifting assembly, and hence the production tubing string attached thereto.
When engagement means 25 is disengaged from the mandrel, lifting assembly 4, and a production tubing string attached thereto, may be independently lifted, through a limited vertical range, within oil well casing 5 without the removal or lifting of either the mandrel or the hanger shell. That is, through hanging lifting assembly 4 from mandrel 3 by way of the interaction of engagement means 25 with the mandrel, lifting assembly 4 may be releasably secured to the mandrel so as to enable the entire production tubing S string to be quickly and easily lifted or lowered within the well casing without interfering, lifting or disturbing hanger shell 2 or mandrel 3. In this way well control can be maintained. In addition, the raising or lowering of lifting assembly 4 will not expose any of the internal mechanisms of device 1, including bearing means 11, to contamination from dirt and debris that may otherwise be present within the oil well.
At all times the bearings will remain sealed between the hanger shell and the mandrel regardless of the position of lifting assembly 4.
Raising or lowering lifting assembly 4 within the well is facilitated through the use of lifting threads 26 positioned at upper end 22. Lifting threads 26 permit a rod, pipe or 1 S other tool to be threadably received within lifting assembly 4 to enable the assembly to be lifted or lowered. In the preferred embodiment seals 27 are positioned between lifting assembly 4 and mandrel 3 and prevent the by-pass of oil and gases between the lifting assembly and the mandrel to maintain full well control.
It will be appreciated by those skilled in the art that a wide variety of different engagement means 25 could be utilized in order to releasably secure lifting assembly 4 within mandrel 3 while staying within the scope of this invention. However, for purposes of explanation the particular embodiments shown in the attached drawings will now be described and discussed in more detail. Referring again to Figures I, 2 and 4, engagement means 25 is shown as comprising outwardly extending pins 28. Pins 28 are located on the outer surface of the lifting assembly and are releasably receivable within slots 29 on mandrel 3. Slots 29 may be either positioned on the interior surface of mandrel 3 and recessed into the mandrel body or may extend completely through the mandrel. Preferably slots 29 are positioned at or near lower end 9 of mandrel 3 in order that they provide no interference to the operation of bearing means 11 or the numerous seals positioned on the lifting assembly, mandrel and hanger shell.
Through receipt of pins 28 on lifting assembly 4 into slots 29 within mandrel 3, the lifting assembly may be hung from the mandrel in such a manner that the weight of both the lifting assembly and the production tubing string attached thereto is fully transferred to the mandrel and borne by bearings means 11. Typically the weight will be supported by thrust bearings 12, however, in the event of a deviated well a portion of the load will be transferred to radial bearings 13 as well. When pins 28 are received within slots 29 there will also be a transference of rotational movement from the mandrel to the lifting assembly when the mandrel is rotated by tubing string rotator 17. Slots 29 are preferably configured so as to enable the mandrel to be rotated in either a clockwise or 1 S counter clockwise direction while transferring rotational movement to the lifting assembly. In this manner the production tubing string may also be rotated in a clockwise or counterclockwise manner. To accomplish this function, slots 29 are of a generally "J"-shaped configuration having an open longitudinal portion 30, and a hook portion 31 that defines an open bowl portion 32.
As shown in Figures 2 and 4, when pins 28 are received and secured within bowls 32 of slots 29, the disengagement of the pins will require the application of both a lifting and rotational force. That is, to remove pins 28 from open bowls 32 of slots 29, lifting assembly 4 will first have to be lifted in an upward manner until pins 28 are able to clear the ends of hook portions 31. At that point either lifting assembly 4 and/or mandrel 3 may be rotated to allow the pins to move rotationally beyond the ends of hook portions 31 and to enable lifting assembly 4 to the lowered downwardly, past the mandrel and into the well casing. Where the lifting assembly is rotated locking keys are inserted into slots 24 on the upper end of the mandrel to hold the mandrel stationary and allow independent rotation of the lifting assembly. Engaging pins 28 within slots 29 will require the exact opposite series of movements. That is, the lifting assembly is first pulled upwardly to a point where pins 28 are raised above hook portions 31 of slots 29.
Thereafter rotational movement of the lifting assembly and/or the mandrel will allow the pins to pass around the ends of hook portions 31. Lifting assembly 4 may then be lowered downwardly so as to seat pins 28 within open bowls 32.
Rather that being formed as a single unit, as shown in Figure 3 the mandrel may be comprised of upper and lower portions, 41 and 42 respectively, that are threaded together. In this manner manufacture and assembly of the parts of the invention may be simplified. Further, mandrel 3 may also include an external sleeve 36 that both encloses slot 29 and helps to support hook portion 31. To this extent, sleeve 36 is preferably fixed to the outer surface of the mandrel through pinning or by use of plug welds 43.
In the attached drawings pins 28 are shown as positioned on the exterior surface of lifting assembly 4 with slots 29 situated within mandrel 3. A reversed structure, where the slots are positioned on the exterior surface of the lifting assembly and the pins extend outwardly from a sleeve 35 attached to the lower portion 9 of the mandrel (see Figure 5), could equally be utilized and would function and operate generally in the same manner as that described above. Regardless of which configuration of pins and slots is utilized, engagement and disengagement of the lifting assembly from the mandrel will require the application of both a lifting and a rotational force.
For that reason, it will be understood that other configurations of slots may be used while performing the same functions. For example, a "U" or "L" shaped slot could be used in the substitution for the "J"-shaped slot depicted in the attached Figures.
By way of the foregoing structure, lifting assembly 4 can be utilized to help set down-S hole oil tools within the well casing. Doing so generally requires lowering lifting assembly 4 such that pins 28 are no longer engaged within slots 29, and then "setting"
the down-hole tool within the well casing. The method of "setting" the down-hole tool will be dependant upon the tool itself but typically will require the tubing string to be dropped below the lifting assembly by the amount of desired string stretch and thereafter setting the tool through a rotational and/or lifting movement. Once the tool has been "set", lifting assembly 4 can be pulled upwardly within mandrel 3 until pins 28 have sufficiently cleared the ends of hook portions 31 of slots 29 to enable the lifting assembly and/or the mandrel to be rotated so that the pins are vertically aligned with open bowl portions 32. At that point the lifting assembly can be lowered back downwardly into the well casing until the pins rest within bowl portions 32.
In this manner lifting assembly 4 will effectively be hung from mandrel 3 such that rotation of the mandrel will cause rotation of the lifting assembly and the production tubing string attached thereto. At the same time, the entire production tubing string may be held in tension since it will be anchored at the bottom of the well casing by the down-hole tool and will be hung from and secured to the mandrel through the engagement of pins 28 within slots 29. Accordingly, the described structure will readily allow for down-hole tools to be set and reset as required, without having to pull the tubing string from the well, remove or disturb the hanger shell or mandrel, and without losing well control.

In the further alternate embodiment as shown in Figure 6, lifting assembly 4 is releasably secured directly to hanger shell 2. To accommodate and support lifting assembly 4, hanger shell 2 contains slots 33 on its interior surface that releasably receive pins 28 of the lifting assembly. The function and operation of lifting assembly 4 will thus be essentially the same as that described above for the other embodiments of the invention except that, as the lifting assembly is secured directly to the hanger shell, once in place within the well casing it will remain stationary such that neither the lifting assembly nor a production tubing string attached thereto will be rotated.
In Figure 7 a variation to the embodiment of Figure 1 is show. Here external sleeve 36 is positioned around the lower portion 9 of mandrel 3 so as to enclose slots 29. As discussed previously, sleeve 36 serves to help prevent the ingress of debris into slots 29 and may also be fixed, by way of welding, pinning, or otherwise, to hook portion 31 of slot 29 and to the upper and lower portions of the mandrel to increase the load bearing capabilities of the assembly. In Figure 7, mandrel 3 is comprised of upper and lower portions that are threaded to together.
In Figure 8 a variation of the present invention is shown having a modified rotator design. In this embodiment rotator 17 includes a worm gear 37 which drives a radial gear 38 connected to mandrel 3. It will thus be appreciated that in this embodiment the means for driving or rotating mandrel 3 are somewhat different, however, the function and the operation of lifting assembly 4 will be the same.
In yet a further embodiment of the invention as shown in Figure 9, lifting assembly 4 is releasably suspendable from hanger shell 2 and contains means to hang a production tubing string therefrom. In the preferred form of this variation, lifting assembly 4 supports mandrel 3, to which the production tubing string is connected. There may be positioned between mandrel 3 and lifting assembly 4 thrust and radial bearings, 12 and 13 respectively, to assist in rotational movement of the mandrel and the transference of axial and radial loading from the mandrel to the lifting assembly. A retaining nut 18 secures the mandrel within lifting assembly 4. As in the case of the previously described embodiments, a tubing rotator 17 may be utilized to supply rotational energy to the mandrel.
The embodiment of Figure 9 further includes engagement means to releasably suspend lifting assembly 4 from hangerlshell, 2., The engagement means preferably comprise a series of slots 39, on the exterior surface of the lifting assembly, that are engaged by pins 40 extending outwardly from~the interior surface of hanger shell 2. As shown in Figure 9, pins 40 are preferably threadably engaged within the walls of the hanger shell.
It will therefore be appreciated that through the interaction of pins 40 and slots 39, lifting assembly 4 may be releasably suspended within the hanger shell.
Furthermore, formation of slots 39 such that they have a generally "J"or "L"-shaped configuration will enable the lifting assembly, and a production tubing string attached thereto, to be independently lifted within the well casing without lifting or disturbing the hanger shell.
In a similar fashion as described previously with respect to slots 29 and pins 28, it will equally be appreciated that slots 39 and pins 40 of Figure 9 will enable the tubing string to be held in tension following the setting of a down-hole tool or anchor.
It is to be understood that what has been described are the preferred embodiments of the invention and that it may be possible to make variations to these embodiments while staying within the broad scope of the invention. Some of these variat;~"~ have 1,PP., discussed while others will be readily apparent to those skilled in the art.
For example, whereas the attached drawings show the use of three pins 28 upon lifting assembly 4, it will be understood that if desired four or more pins could equally be employed. In addition while "J"-shaped slots 29 are described and shown in the drawings a wide range of alternate slot configurations could equally be used.

Claims (28)

1. An oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well casing, the device comprising:
a hanger shell suspended within the oil well casing, a mandrel mounted within said hanger shell, and, a lifting assembly releasably securable to said mandrel, said lifting assembly having means for connecting to and for hanging a production tubing string therefrom, said lifting assembly including engagement means for releasably securing said lifting assembly to said mandrel such that said lifting assembly, and a production tubing string attached thereto, may be independently lifted within the oil well without removal or lifting of said mandrel or said hanger shell.

2. A device as claimed in claim 1 wherein said engagement means permits said lifting assembly, and an attached production tubing string with its lower end secured to the oil well casing, to be independently lifted within the oil well and thereafter releasably secured to said mandrel so as to maintain said lifting assembly, and a production tubing string attached thereto, in tension.

3. A device as claimed in claim 2 wherein said mandrel is rotatably received with said hanger shell.

4. A device as claimed in claim 3 wherein rotational movement of said mandrel results in rotational movement of said lifting assembly when said lifting assembly is releasably secured to said mandrel.

5. A device as claimed in claim 2 wherein said engagement means comprises pins on said lifting assembly that are releasably receivable within slots in said mandrel.

6. A device as claimed in claim 5 wherein receipt of said pins on said lifting assembly into said slots in said mandrel permits said lifting assembly to be hung from said mandrel and allows for the transference of rotational movement from said mandrel to said lifting assembly.

7. A device as claimed in claim 6 wherein said slots in said mandrel are of a generally J-shaped configuration such that disengagement of said pins from said slots requires the application of a lifting force to said lifting assembly and the rotation of said lifting assembly relative to said mandrel.

8. A device as claimed in claim 6 wherein said slots in said mandrel are generally parallel to the longitudinal axis of said mandrel.

9. A device as claimed in claim 2 wherein said engagement means comprises slots positioned on said lifting assembly, said slots receiving pins on said mandrel and thereby permitting said lifting assembly to be releasably secured to said mandrel.

10. A device as claimed in claim 9 wherein receipt of said pins on said mandrel into said slots on said lifting assembly permits said lifting assembly to be hung from said mandrel and allows for the transference of rotational movement from said mandrel to said lifting assembly.

11. A device as claimed in claim 10 wherein said slots on said lifting assembly are of a generally J-shaped configuration such that disengagement of said pins from said slots requires the application of a lifting force to said lifting assembly and the rotation of said lifting assembly relative to said mandrel.

12. A device as claimed in claim 10 wherein said slots on said lifting assembly are generally parallel to the longitudinal axis of said lifting assembly.

13. A device as claimed in claim 6 wherein said lifting assembly includes lifting threads that threadably receive a lifting tool to enable said lifting assembly to be independently lifted within the oil well without removal or lifting of said mandrel or said hanger shell.

14. A device as claimed in claim 13 including sealing means between said lifting assembly and said mandrel.

15. A device as claimed in claim 14 wherein said mandrel includes means to receive a drive member from a tubing rotator such that the drive member may impart rotational movement to said mandrel.

16. A device as claimed in claim 15 including sealing means between said mandrel and said hanger shell and sealing means between said hanger shell and the oil well casing.

17. A device as claimed in claim 16 including bearing means between said mandrel and said hanger shell to facilitate in the rotational movement of said mandrel.

18. A device as claimed in claim 17 wherein said bearing means includes thrust and radial bearings.

19. A device as claimed in claim 6 wherein said mandrel includes longitudinal slots extending along its interior surface to permit a tubing string with said lifting assembly secured thereto to be lowered into the oil well through both said hanger shell and said mandrel.

20. An oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well casing, the device comprising:
a hanger shell suspended within the oil well casing, and, a lifting assembly releasably securable to said hanger shell, said lifting assembly having means for connecting to and for hanging a production tubing string therefrom, said lifting assembly including engagement means for releasably securing said lifting assembly to said hanger shell such that said lifting assembly, and a production tubing string attached thereto, may be independently lifted within the oil well without removal or lifting of said hanger shell.

21. A device as claimed in claim 20 wherein said engagement means permits said lifting assembly, and an attached production tubing string with its lower end secured to the oil well casing, to be independently lifted within the oil well and thereafter releasably secured to said hanger shell so as to maintain said lifting assembly, and a production tubing string attached thereto, in tension.

22. A device as claimed in claim 21 wherein said engagement means comprises pins on said lifting assembly that are releasably receivable within slots in said hanger shell.

23. An oil well tubing string hanging device and lifting assembly to hang a tubing string within an oil well casing, the device comprising:
a hanger shell suspended within the oil well casing, a lifting assembly releasably suspendable from said hanger shell, said lifting assembly containing means to hang a production tubing string therefrom, and, engagement means to releasably suspend said lifting assembly from said hanger shell, said engagement means allowing said lifting assembly to be suspended from hanger shell and allowing said lifting assembly, and a production tubing string attached thereto, to be independently lifted within the oil well casing without removal or lifting of said hanger shell.

24. A device as claimed in claim 23 including a mandrel rotatably mounted within said lifting assembly, said mandrel including means to hang a production tubing string therefrom.

25. A device as claimed in claim 24 where said engagement means comprises pins on said hanger shell that are releasably received within slots in said lifting assembly.

26. A method of retaining an oil well tubing string in tension within an oil well casing, the method comprising:
(I) lowering an oil well tubing string, having a lifting assembly attached to its upper end, into an oil well casing;
(ii) anchoring a lower portion of the oil well tubing string within the oil well casing;
(iii) applying a lifting force to the tubing string to place the tubing string in tension and bringing the lifting assembly into engageable contact with a tubing string hanger such that engagement means on the lifting assembly are releasably securable to the tubing string hanger; and, (iv) releasing the lifting force applied to the tubing string and causing the engagement means to secure the lifting assembly within the tubing string hanger thereby causing the tubing string to be held and retained in tension.

27. The method as claimed in claim 23 wherein the step of causing the engagement means to secure the lifting assembly within the tubing string hanger includes rotating the lifting assembly relative to the tubing string hanger.

28. The method as claimed in claim 24 wherein the tubing string hanger includes a rotatable mandrel and the step of securing the lifting assembly within the tubing string hanger includes securing the lifting assembly to the rotatable mandrel.