Hydraulic Workover Unit • A ‘Snubbing System’ is basically a well

servicing system capable of running and

retrieving jointed pipe under live well

conditions (but not necessarily high pressure).

• A snubbing unit or Hydraulic Workover (HWO)

unit can be used for:

– drilling new wells (underbalanced if

required)

– side-tracking existing wells (underbalanced

if required)

– completion (underbalanced if required)

– fishing (underbalanced if required)

– gravel packing (underbalanced)

– perforating (underbalanced)

– clean-out (underbalanced)

• Advantage is that the well does not require

killing.

• Can carry out some work as a rig as long as

tubulars are less than 103/4” OD.

• HWO Unit useful for pulling CT completions

Live Well Workovers

• less fluids lost to formation = less damage

• shorter time with well off-line

• less problems with kill fluids

Hydraulic Workover Unit

‘Snubbing’ = process of tripping pipe in well

which as a surface pressure

great enough to eject the pipe

from the well if no restraining

force is applied.

‘Stripping’ = relates to the same operation,

but where the surface pressure

and workstring combination

would result in the workstring

failing into the well under its

own weight if unrestrained.

‘Lubrication’ = process of inserting and

removing BHA and toolstrings

from the well.

‘Hydraulic Workover’

(HWO) = Unit to run/pull tubulars in/out

of well (with or without

surface pressure), using

hydraulic power to transmit

the required forces to the pipe.

• HWO Definitions

Snubbing - An Introduction

• Snubbing is a live well workover process

that uses standard jointed tubulars

• Rig (cable) assisted snubbers date from the

1930’s

• Hydraulic snubbers a later addition.

Components

• A pipe movement system - cable assisted or

rig assisted

• A sealing stack of pipe rams that allows

passage of tool joints and equipment into

and out of a well under pressure.

A view of the pressure connection

tube between the upper isolation

chamber and the well.

Schematics

from Cudd

Pressure

Control

Hydraulic snubber - top

of stroke.

Pipe slip

elements in

hydraulic

snubber

1. Close upper or

traveling slips.

2 Open lower or

stationary slips.

3. Activate hydraulic

pressure to pull down

on pipe and force it

into the well.

Weight Necessary to Pull Wire into a Wellhead

Under Pressure

0

50

100

150

200

250

300

350

400

450

500

0 2000 4000 6000 8000 10000

Well Head Pressure, psi

Weig

ht

Necessary

to

Pu

ll

Wir

elin

e in

to t

he W

ell, lb

s

0.072" Wire

0.092" Wire

0.108" Wire

0.125" Wire

3/16" Wire

5/16" Wire

Snubbing Pressure vs. WHP and Wire or

Tubing Size

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

0 1000 2000 3000 4000 5000

Well Head Pressure, psi

Sn

ub

bin

g F

orc

e o

r W

eig

ht

Re

qu

ire

d t

o E

nte

r W

ellh

ea

d,

lbs

0.108" Wire

3/16" Wire

1.5" CT

2-3/8" Tbg

2-7/8" Tbg

3-1/2" Tbg

4-1/2" Tbg

Hydraulic snubber

nearing bottom of

stroke.

1. Close lower or

stationary slips.

2. Open upper or

traveling slips.

3. Activate hydraulics

to extend cylinders.

Tool joint nearing

slips.

Stop tool joint

immediately above top

pipe ram on snubbing

stack.

Pipe seal

elements

Tool joint above top

ram. System

pressurized below.

Middle pipe seal closed

Ready to bleed

off upper

straddled area.

Upper straddled area

bled off.

Open upper ram and

pass tool joint into

upper straddled area.

Close upper ram and

prepare to pressurize

upper straddled area.

Upper straddled area

pressurized, prepare to

open middle ram.

Open middle ram

and pass tool joint

into well.

Rig assisted

snubbing using

rig draw works

and snubbing

stack below the

table.

Braided line

and pulleys

on the rig

floor.

Traveling

slips

Stationary

slips

Description of job

Length of

guns

Location

Depth of well

Surface PSI

TCP guns 33/8” using DHSV

1,200’

Valhall/ N. Sea

13,123

2900

TCP guns 33/8” w/auger system using DHSV

250’

Valhall/ N. Sea

12,467

2755

TCP guns 41/2” w/ aligning knobs using DHSV

500’

Valhall/ N. Sea

14,108

3190

Halliburton Deployment system TCP guns 41/2”

850’

Statfjord B

13,123

1957

Halliburton Deployment system TCP guns 41/2”

1,100’

Statfjord C

14,108

1812

TCP guns 41/2” using DHSV

450’

Gulfaks B

15,420

1595

TCP guns 41/2” using DHSV

600’

Gulfaks C

15,092

1740

Halliburton Deployment System TCP guns 4 ½”

2,800’

Statfjord B

16,076

3552

TCP guns 4 ½” using DHSV

1,800’

Sleipner

13,780

3045

TCP guns 4 ½” using DHSV

3,200’

Gulfaks B

17,717

2755

TCP guns 4 ½” Using FIV Valve

1,400’

Veslifrik

12,795

2610

Halliburton Deployment System TCP guns 4 ½”

950’

Gulfaks C

13,780

3190

Halliburton Deployment System TCP guns 4 ½”

1,100’

Gulfaks A

13,451

2682

Perforating Guns Run Under Pressure