This invention relates generally to setting liner hangers during well completion or maintenance operations. In particular, the invention is directed to a liner hanger in which the cones of the liner hanger are non-integral to the barrel and attached by mechanical means without welding.
Generally, in a producing well, casing (lengths of steel pipe joined together) runs from the surface to a specified depth in the wellbore. The casing generally has a large diameter. It is installed and cemented in place to seal off drilling and circulating fluids from the borehole and prevent commingling of well fluids, and to prevent the walls of the borehole from caving. The casing string is generally hung from a hanger on the surface.
A liner is a length of casing that is hung inside existing casing. Unlike the casing string, the liner generally does not extend to the surface, but is anchored, suspended, and supported by a liner hanger that is installed near the bottom of the casing in which the liner is suspended, or near the location where the liner string is desired to isolate problems such as from other zones such as lost circulation or high pressure. The liner also provides capital savings in reducing the cost of the steel pipe needed since it does not run to the top of the well.
A liner hanger holds the liner in place once the liner is in the desired location in the well, and carries the weight of the liner after it is hung off. Mechanical or hydraulic slips on the hanger hold the liner in place by gripping the inside wall of the casing in which the liner is suspended. Hangers may be set hydraulically by creating pressure in the hanger, activating hydraulic pistons that move the slips against the casing. During the running process the slips are retained in a retracted position. Once the liner is in the desired position, the slips are driven across the cones by the activation mechanism, which may be mechanical or hydraulic, thereby increasing the diameter of the slips and forcing the teeth on the outer surface into the casing. Liner hangers generally include one or more sets of cones and slips.
The cones are wedge-shaped sections on the liner hanger's outer wall. Generally in the past, the cones have been integral to the barrel of the liner hanger. For example, in a common type of prior art liner hanger the barrel is made of two piece construction, as shown in FIGS. 1A and 1B. A lower portion of the barrel is threaded onto an upper portion and acts as a hydraulic cylinder. The entire assembly contains a longitudinal throughbore that allows for the passage of fluids during the running process. The slips and cones are slotted to allow the passage of fluid in the annulus around the liner hanger during the running in/removal or cementing processes.
With the hydraulic version, when the liner hanger is in the desired position, the operator creates an increased pressure, generally by dropping a ball or dart into a ball seat or other receptacle in a landing collar below the liner hanger. At a particular increased pressure a setting piston moves upward to an extended position. The setting piston drives a setting sleeve, connected by one or more slip arms to the slips. This drives the slips, which expand out over the wedge-shaped cone pads until fully gripping the inside of the casing. Downward motion transfers the full liner weight through the cones and slips into the supporting casing.
Alternatively, the hanger can be mechanically set. In one such hanger, the work string attached to the liner hanger is rotated. Rotation may be right-hand set or left hand set depending on the desired embodiment. The rotation causes a J-Cage mechanism in contact with the casing to disengage a lug from the short leg of the J-Cage and allows the slips to align with the cones. Downward motion then allows the slips to expand over the cones and grip the casing's inner wall, transferring the weight of the liner to the supporting casing.
A disadvantage of such prior art liner hangers is that they must be constructed using a very thick-walled steel tube stock, for example a six inch inner diameter might require an eight inch outer diameter, in order for the wall to have sufficient thickness in the area of the cones and the cylinder once the steel tube is machined inside and out. This creates expense in the material, in the machining time, and in the construction.
Other liner hangers have been constructed with a single-piece mandrel or barrel. In this case, the cylinder or J-Cage is connected to the barrel using mechanical means such as set screws, wirelocks, or welding. The cones are generally integral to the barrel as described above, but in some prior art embodiments the cones may have been welded to the barrel, which adds cost and time to the production. In addition, because of the complexity and cost of the tool construction, it is impractical to create stock items.
Welding the cones or the cylinder to the barrel or casing mandrel requires multiple welds. These welds add time and expense to the manufacture of the liner hanger. More importantly, welding can affect the metallurgy of the barrel, making the welded area subject to attack, for example by corrosive well fluids. As such, welding to the barrel or to a casing mandrel is at minimum undesirable, and may be prohibited under certain industry standard regulations. As such, mechanical connections are preferable.
The disadvantages of two-piece liner hanger, and the single-piece welded liner hanger, are overcome by the present invention.