LINER HANGER

Abstract

Liner hanger to be placed in an existing casing with a flexible expansion seal (180) and a metallic gripping element (190) disposed on inclined surfaces such that they are moved radially when a leadscrew nut (130) is moved axially relative to an inner, hollow shaft (150). The lead screw nut is moved axially when a lead screw is rotated therein, and the lead screw is rotatably disposed around the inner, hollow shaft (150).

Description

BACKGROUND

1. Field of the Invention

This invention concerns a liner hanger for use in wellbores.

2. Related and Prior Art

For retrieving oil and/or gas, hydro carbons, from subterranean formations, a borehole is drilled to a predetermined depth. Then the drill bit is retrieved, and a section of pipes is assembled from pipes that are threaded together at their ends. The section, known as a casing, is inserted into the borehole and typically cemented to the formation by pumping cement into the annular space between the casing and the formation. The cement is allowed to cure, and a smaller diameter drill bit is inserted through the casing to drill a new section through the formation to a second predetermined depth. The next section of pipes, called a ‘liner’, is inserted through the casing to a depth where the top of the liner overlaps the lower part of the existing casing. In this position, the liner is suspended from the casing using a liner hanger. The liner may in turn be cemented to the formation, and the process may be repeated until the wellbore has reached its intended depth. For practical reasons, the term ‘casing’ as used herein refers to an upper section of pipes, usually cemented to the formation, and the term ‘liner’ as used herein refers to a lower section of pipes. However, there is no clear distinction between a ‘casing’ and a ‘liner’ as both comprise strings of pipes, and as the liner of one section will be the casing of the next.

The liner hanger is mounted at the top of the new string of pipes, and will have to carry the weight of it, which often is several tens of tons. It is usual to dimension the elements for a weight of 150 tons.

The problem to be solved by the present invention is to provide a liner hanger that can be attached to an existing casing for a shorter or longer period of time, without it necessarily being cemented.

Another objective of the invention is to provide a liner hanger that can be set without rotating the entire section of pipes that is suspended from it.

Yet another purpose of the invention is to avoid leakage to occur in the annular space between existing and new casing as the rubber becomes old.

SUMMARY OF THE INVENTION

According to the invention, this is solved by a liner hanger to be placed in an existing casing with a flexible expansion seal and a metallic gripping element disposed on inclined surfaces such that they are moved radially when a leadscrew nut is moved axially relative to an inner, hollow shaft, the lead screw nut being moved axially when a lead screw is rotated therein, and the lead screw being disposed around the inner, hollow shaft 150.

When the new section is suspended from the inner shaft 150, which does not rotate, it is still simple to rotate the sleeve 110.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be disclosed in greater detail in the following with reference to the accompanying drawings, where similar reference numerals refer to similar elements, and where:

FIG. 1 is a partial cross section through a liner hanger according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a partial cross section through a liner hanger according to the invention. The liner hanger has an inner, hollow shaft 150 disposed within an outer housing. The shaft 150 is at one of its ends, to the left on FIG. 1, connected to a lead screw having outer threads on a torque transmitting sleeve 110. The lead screw can have conventional Acme-threading, and is disposed within a lead screw nut 130 having corresponding internal threading. The lead screw is part of the outer housing of the liner hanger. The lead screw is rotated in the nut 130 by an external drive shaft 120 which is rotation locked using first latching dogs 121 in the sleeve 110, while second latching dogs 141 are rotation locked to the lead screw nut 130. The external drive shaft rotates the first latching dogs 121 relative to the second latching dogs 141, and thus the lead screw on the sleeve 110 relative to the lead screw nut 130.

The lead screw nut 130 is axially slidably disposed around the inner shaft 150. Thus, when the lead screw is rotated in the lead screw nut 130, the nut 130 will be moved axially along the shaft 150. When the liner hanger is set, the drive shaft is rotated such that the lead screw nut 130 is moved downward relative to the inner, hollow shaft 150, i.e. to the right in FIG. 1.

Thereby, the lead screw nut 130 will push against the other parts of the outer shell, which, starting from the lead screw nut, are in order: Belleville springs 160, expandable seal 180, Belleville springs 170 and a slip section having slips 190.

The slips 190 are disposed on inclined surfaces that are pulled closer to each other by the axial displacement. Thereby, the slips will be moved radially outward and be the first elements to engage the wall of the well. When the lead screw is rotated further, the seal 180 will expand radially until it engages the wall of the well and seals the annular space between the shaft 150 and the existing casing (not shown).

When the seal 180, which conventionally is made from a rubber blend, has been disposed in the well for a while, its characteristics are expected to change, and it is expected to seal less well. The purpose of the Belleville springs 160 and 170 is to preload the seal 180, such that it continues to seal after this occurs. The Belleville springs can e.g. be preloaded with a force around 200 kN. Depending on the rubber blend and well conditions, it is expected that the force from (the less compressed) Belleville springs is half of the original force after a while. However, the seal will still seal. If the seal was not compressed by the Belleville springs, a leak would have been expected at this point in time.

The inner, hollow shaft 150 is in one of its ends connected to the external drive shaft through milled out grooves and the second latching dogs 141. In its other end, the shaft 150 is preferably provided with pipe threads. Thereby, the liner hanger can be threaded to the upper part of a new section of pipes before the entire assembly is lowered into the well. The shaft 150 thereby becomes part of the new section of pipes.

When the hanger is to be attached to the lower or outer end of the existing casing, the entire weight of a section of pipes, possibly in the order of hundreds of tons, will thereby be suspended from the second dogs 141 and the shaft 150, while the sleeve 110 with the lead screw is rotated around the shaft 150. Hence, it is not necessary to rotate a mass of several tens of tons to set the liner hanger.

When the slips 190 has a firm grip in the casing and the seal 180 engages the inner surface of the casing, the new section of pipes is suspended from the shaft 150, and the weight is removed from the second dogs 141. When the external drive shaft is to be removed, the part 140 can be used to release the latching dogs in different ways, e.g. by moving a ring over inclined faces of the dogs to retract them from their latching position.

The first latching dogs 121 are not subject to any substantial axial load in the above description. As long as they provide the required rotational locking, nothing prevents them from being pulled axially out from the sleeve 110 when the liner hanger is attached to the existing casing.

When the drive shaft is pulled back and the new section of pipes is suspended from the liner hanger, the new section of pipes can optionally be cemented to the formation, be penetrated and/or be treated like other steel pipes in the well.

Claims

1-4. (canceled)

5. A liner hanger to be placed in an existing casing, the liner hanger comprising an inner, hollow shaft, having, in a first end, grooves configured to receive second latching dogs for latching to an external drive shaft and having, in a second end, threading for connecting a section of pipes, wherein the inner shaft is supported coaxially in an outer housing comprising a flexible expansion seal and a radially movable metallic gripping element disposed on inclined surfaces configured to be moved axially by a leadscrew nut which is axially movable relative to the inner shaft, and wherein the leadscrew nut is provided with lead screw threading on an inner surface, characterized in that

the inner shaft is rotation locked relative to the outer housing,

that the liner hanger further comprises a torque transmitting sleeve rotatably disposed around, and axially locked relative to, the inner shaft, and

that the torque transmitting sleeve has external lead screw threads disposed in the lead screw nut and additional grooves adapted to first latching dogs for rotational locking against a separate part of the external drive shaft.

6. The liner hanger according to claim 5, wherein the flexible expansion seal is preloaded by spring elements.

7. A method for suspending a section of pipes from an existing casing, comprising:

connecting an inner hollow shaft to a section of pipes,

suspending the shaft from a drive shaft using second latching dogs and corresponding grooves,

lowering the inner shaft until its upper end overlaps the lower end of the casing,

rotating a leadscrew on a torque transmitting sleeve around the inner hollow shaft using first latching dogs rotatably fixed to the leadscrew, the leadscrew having threads engaging corresponding threads on a lead screw nut rotationally locked to the shaft, thereby moving the leadscrew nut axially along the shaft, the leadscrew nut causing a metallic gripping element and an expandable seal to engage the inner surface of the casing,

transferring the weight of the section of pipes from the second latching dogs to the metallic gripping element,

releasing the latching dogs, and

retracting the drive shaft axially from the assembly comprising the inner hollow shaft.