Sometimes conventional devices and technologies will not work when it comes to the plugging of wide-diameter cavern necks. In such cases, the Spider Plug developed by UGS can provide the remedy.
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).
At the behest of UGS GmbH, extensive test series were carried out to improve the effectiveness of the hydraulic plug at the Fraunhofer Institute for Applied Polymer Research and the Freiberg University of Mining and Technology. For carrying out repair work on storage wells it is often necessary to plug the well from the actual storage volume. This can prove to be highly problematic if this is in a storage cavern in salt rock where the cavern neck has a very wide diameter or if the salt in the neck has sharp edges.
The deployment of conventional plugging technologies is often not possible in such cases – but this is where the Spider Plug can come to the rescue.
What is a Spider Plug?
The Spider Plug is a mechanical plugging device, developed and patented by UGS GmbH, 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 spread-out fingers occupy a diameter that is a multiple of its original width. This principle has been constructively applied to the Spider Plug, which can bear a very large load after it has been set. This then enables cement bridges to be built and, consequently, complete plugging of the cavern neck.
The demands for its development
The technical demands for the development of the Spider Plug came from experience gained in years gone by when deploying standard subsurface equipment. These were:
The following plug dimensions were tested successfully and are currently available as standard::
Diameter of the casing string through which the Spider Plug is introduced | Maximum diameter of the plugged area |
≥ 6 5/8″ | 14″ |
≥ 11 3/4″ | 24″ |
≥ 13 3/8 “ | 2,5 m (100″) |
Further dimensions can be realised on request.
What are the advantages of the Spider Plug?
Deployment of the Spider Plug
Special devices were developed for setting the Spider Plug. These setting devices are brought to the setting depth on a standard drill string. The setting of the plug then takes place in five stages:
1. Carrying out a pressure test.
The tightness of the setting assembly is necessary, as this indication of the successful conclusion of the particular setting stage shows itself in certain pressure curves.
2. Pumping the plug out of a protection pipe by applying pressure to the setting device.
3. Compressing the plug until the “spider’s legs” moor against the well or cavern walls by spreading apart. Successful setting is shown through the behaviour of the hook load, when the drilling rig or workover winch tries to raise or lower the string.
4. Separating the plug from the setting device.
The separation causes a pressure compensation between the drilling string and the well. The dry running up of the string can now take place.
5. Introducing the gravel.
A sound mechanical basis for the later introduction of cement slurry is developed by introducing different fractions of bulk solids. After hardening this forms the hydraulic barrier between the storage volume and the well.
After finishing the repair work in the well, it is no problem to mill out the plug as all the components are made from aluminium and deliberately designed not to twist.