A METHOD FOR INSERTING TOOLS AND TUBULARS INTO WELLS UNDER PRESSURE

Thanks to the snubbing method, wells can be serviced without having to kill the well with fluids and the pipe can be tripped into and out the well with a wellhead pressure present.

The two operational modes consist of snubbing (pipe light) and stripping (pipe heavy). While in the snubbing mode the combination of well head pressure and the work string weight, if unrestrained, would eject the pipe out of the hole (snubbing is forcing the pipe down), in the stripping mode the weight of the pipe is greater than the pressure acting on the cross-sectional area of the pipe (the pipe falls lowers into the well by gravity).

Well control is key!

BOPs are the only barrier between the well and the snubbing unit crew.

Pipe handling for efficiency!

Gin pole: telescoped out 50 ft above the snubbing unit (for work in the basket).
Pipe winches: dual winches allow multiple joints of pipe to be handled simultaneously.

Smaller Footprint, Smaller Modules, Lighter Weight, Easier To Move.

Execution

Requirements

• The tubular / work string needs to be plugged.
• The stripping BOPs are closed around the outside of the tubing or work string providing a pressure seal around the pipe, hence containing the well bore pressure.

Pipe movement control

• Inverted stationary slips ( Counteract the upward force that is exerted on the cross-sectional area of the tubular )
• Travelling snubbing slips ( Force the tubulars into or out of the well through closed BOPs in a controlled manner )

Snubbing unit powered by hydraulic system operating the snubbing jack (i.e. a multi cylinder jack)

• Snubbing units get denoted in size by lifting / pulling capacity.
• Example: 460 K units can pull 460 K LBS and has snubbing capacity of 230 K LBS.
• Example: 10,000 psi and snubbing 2 3/8” tubing requires 51,000 LBS including friction forces. The requirement will be for a 120 K unit with 60,000 snub force as a minimum (normally a higher system e.g. 150 K is taken).

Snubbing Jack

The stationary and travelling slips are operated in sequence to grip the pipe as it is snubbed in the well.

Travelling heavy slipsThis set is used during stripping operations. The pipe is hold from falling down the hole during transition from pipe light to pipe heavy.

Stationary snubbing slips : This set holds the pipe from ejecting from the well during snubbing operations. The stationary slips are engaged in order to release the travelling slips and allow the jack to be stroked for the next bit.

Hydraulic cylinders : he cylinders provide the necessary force to jack the pipe into and out the hole during snubbing operations. The bore and ratio of these cylinders dictate the maximum snubbing force.

Work Basket : Used during tripping operations and it is the mounting point of the control panel of the unit.

Hydraulic control panel : BOPS, slips, jack cylinders are all controlled from this position. Closing pressures for the annular, the slips and stripping rams can be set to match the operational conditions.

Hydraulic rotary : It enables the rotation of the string in the pipe light or pipe heavy mode, while giving the unit the capability to set tools requiring rotation or perform drilling / milling operations.

Benefit of the snubbing unit

• Smaller footprint.
• Smaller modules.
• Lighter weight.
• Easier to move.
• Designed for tripping and well bore working under pressure.
• Works with closed systems.
• Savings made on cost of kill fluids / brines.
• Avoids killing the well in workover.
• Always reaches the target depth (push, rotate) and can put weight on mill.