What is Workover ?
Operations to a completed production well to clean, repair and maintain the well for the purposes of increasing or restoring production ( or injection ).
When is Workover Chosen ?
When all other rig-less options are not successful, or when the severity of the problem is too high. This also depends on the economical perspective.
Estimate cost of operation –
- Cost for Rig-less Operations : up to USD 50K/day
- Cost for Workover : USD 100K/day
- Cost for Drilling : USD 250K/day
- The term workover is used to refer to any kind of oil well intervention involving invasive techniques, such as wireline, coiled tubing or snubbing. More specifically though, it will refer to the expensive process of pulling and replacing a completion.
- Some may simply call it as maintenance of old well
Hydraulic Workover Unit (HWU)
Hydraulic Workover Unit (HWU) may be self contained or skid mounted. Components are modular for ease of transport and rig up.
Typical HWU consists of:
- Hydraulic Jack Assembly
- Traveling Slips
- Stationary Slips
- Rotary Table
- Power Tongs
- Work Basket
- Counter Balance
- Control Panel
- Power Pack
- Hydraulic Hoses
- Pumps, Kelly Hose, Circulating Swivel
- BOP Stack
- A snubbing rigup is a very tall structure. It consists of a hydraulically powered snubbing unit, which provides the force on a pipe, above string of multi-layered pressure control components.
- At the top of the snubbing unit is the basket, which serves as the control post for the rigup. Below the basket are the hydraulic jacks, which powers the pipe into an out of the hole. It consists of two mechanisms for applying force to the pipe in either direction. Each mechanism consists of travelling and stationary slips. The travelling slips are used to move the pipe, while the stationary slips are used to hold the pipe while the travelling slips are repositioned between strokes.
- Primary pressure control during snubbing operations is provided by a self-energizing stripper and through an assembly of stripping rams. The stripping rams consists of two sets of rams, one on top of the other. There are opened one at a time to allow the collar of the connections between joints of pipe to pass through the rams. Below the stripping rams are the safety rams, which may consist of a shear/blind blowout preventer and an annular BOP. The tertiary barrier, a shear/seal BOP, sits below this directly above the Xmas tree.
- Snubbing – Snubbing is the process of running and pulling tubing, drill-pipe, or casing with surface pressure present on the wellhead. Snubbing also describes a force-balance condition where an external force is required to prevent the work-string from being force out of the hole. HWU may be used to trip tubulars into and out of wells with no existing or anticipated surface pressure.
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