HWO / Snubbing
Hydraulic Workover, HWO, or Snubbing as it is sometimes referred to, is a well intervention method which has been in existence for many years.
Largely pioneered in the US on land-based operations it gained popularity in the North Sea during the late 80's early 90's and is still used albeit less frequently. However, with the acceleration in offshore P&A activity in the North Sea snubbing has been very successfully deployed on several P&A campaigns in preference to re-activating mothballed rigs/derricks.
Principle of Operation:
HWO is a live well intervention service using 'jointed pipe' through a mini rig and using a hydraulic 'jacking ram' to push or 'snub' the pipe into the well against the well pressure. Once the weight of pipe exceeds the well pressure acting upon the pipe trying force it out of the hole, the jack is then used to effectively lower the pipe / BHA to the desired depth. Just as with a drilling rig the pipe can be rotated and large volumes of fluids circulated through the pipe.
HWO is generally used for 'heavy duty' well operations and typically include:
- Large cleanout, sand bailing and scale milling operations
- Tubing repair / change out operations (where well kill may not be desired)
- Heavy duty fishing operations (where large forces / pulling weights are forecast)
- Large perforating operations (where perf guns exceed the weight limits of wireline)
Modern HWO equipment is of modular design and comparatively light weight in consideration of aging infrastructure and attendant crane limitations, transportation, storage and rig up and rig down operations. The 'package' will consist of:
- Mast unit including guying system
- Work basket and hydraulic jacking ram assembly
- BOPS including stripper rams and work rams
- High pressure riser assembly
- Pipe handling / pipe make up equipment
- Pipe rack / laydown area
- Fluid pumping system / storage tanks & surface pipework