Spider Plug

In general, the Spider Plug forms a mechanical abutment upon which a bridge, made up of various fractions of bulk solids which, as a rule, are inserted from a coarse to a fine grain size. This is then followed by the development of a hydraulic plug in the form of one or more cement bridges. Depending on the requirements, it is also possible to use chemical cleaning and scrubbing additives and fillers (e.g. granulates) or sealants (e.g. synthetic resin).

On behalf of UGS, the Fraunhofer Institute for Applied Polymer Research (IAP) and the TU Freiberg carried out extensive tests to improve the efficiency of the hydraulic plug. When repairing storage wells, it is often necessary to plug the well from the actual storage volume. This can be very problematic in a salt cavern where the cavern neck has a very large diameter or where the salt within the neck section has sharp edges.

The use of conventional plug technologies is often not possible in such cases. This is where the Spider Plug can help.

What is Spider Plug?

The Spider Plug is a mechanical plugging device, developed and patented by UGS, which works on the principle of a cavity dowel. Such a dowel is usually only a few millimetres in diameter. But when it is screwed in, its spreading fingers take up a diameter many times greater than its original width. This principle has been applied to the design of the Spider Plug, which can support a very large load once it has been set. This allows cement bridges to be built and the cavern neck to be completely plugged.

Development requirements

The technical requirements for the development of the Spider Plug are derived from the experience gained over the past years in the use of standard subsurface equipment:

• The secure and reliable plugging of a large-diameter, unlined drill hole or cavern neck area.
• The need for deviations in the setting profile of a circular form to be manageable to a high degree.
• No special preparation of the setting area before introducing the Spider Plug.
• The running down and setting of the Spider Plug through the existing casing string without any additional technological measures.

The following plug dimensions have been successfully tested and are currently available as standard:

Other dimensions can be achieved upon customer request.

Advantages of the Spider Plug

• Lower costs than other products or technologies
• No conditioning of the borehole and/or cavern neck necessary
• The use does not dependent on contour formation in the setting area
• Deployable in all liquid media
• Easily re-millable after the repair work

Use of the Spider Plug

Special devices have been developed for inserting the Spider Plug. These setting tools are brought to the setting level with a standard drill pipe. The plug is set in five steps:

1. Carrying out a pressure test.
   The tightness of the setting assembly is necessary as the indication of the successful completion of the respective setting step is shown in certain pressure curves.
2. Pumping of the plug out of a protective tube by pressurising the setting device.
3. Compression of the plug until the “spider legs” are spread out and rest against the well or cavern wall. Successful setting is indicated by the behaviour of the hook load as the rig or workover winch attempts to raise or lower the string.
4. Disconnection of the plug from the setting tool:
   Cutting off equalises the pressure between the drill string and the well. This means that the string can be removed dry.
5. Placement of gravel:
   The introduction of differently fractionated bulk material creates a load-bearing, mechanical basis for the cement slurry to be applied later. After curing, this forms the hydraulic barrier between the storage facility and the well.

Once the repair work in the well has been completed, the Spider Plug can be drilled out without any problems because all components are made of aluminium and are structurally secured against twisting.