Hydraulic Workovers, HWO

• A hydraulic workover is an intervention accomplished under well pressure and without killing the well. Some snubbing operations, most wireline work and most coiled tubing work is done under pressure, through isolation barriers. The difference with HWO is that the conveyance system allows circulation at higher rates than CT, rotation and heavier pulls than wireline or CT.

• The ability to move pipe under pressure elimiates well kills, damage, cleanup time and loss of production.

• Snubbing is a larger well work segment that may include rig draw-works assistance (mechanical) pipe movement and hydraulic units as well.

– Snubbing – moving pipe against pressure that would push it from the well.

– Stripping – moving pipe when its weight would pull it into the well if released.

Other HWO Operations

• Hot Tapping – drilling through pipe with isolation and barriers to provide a circulation port to an area with trapped pressure.

• Gate Valve Drilling – provides an opening through a stuck gate valve

• Related Operations

– Freezing the wellhead

– Sealant injection

Rig Assistance

• Rig draw-works assistance

– Rig or hydraulic jacks

– Slower than hydraulic

– Used for larger pipe – typically casing when running in against a kick or a flow drilled well.

Draw works

Traveling Slips

Floor Sheaves

Tube being moved

BOP and stripper seal

Bottom plug

Hydraulic Workover Equipment

• Provide pressure and load control of tubulars run in and removed from the well.

• Usually have three or more barriers with contingencies for repair while the job is in progress.

• The bottom of the pipe is plugged while running.

HWO Job Procedure/Equipment Illustrations

1. Operate within load, pressure and component ratings.

2. Modifications to critical components require engineering authorization and redesign.

3. Pipe guides (or braces) are required when snubbing.

4. BOP stack must meet minimum specific requirements for pressures, repair options and spacing required by couplings and tools.

5. Slips must include both traveling and stationary slips to hold both pipe light and pipe heavy operations. Multiple slips are required for specific operations – pulling stuck pipe, milling, pulling shallow plugs, etc.

6. Daylight may limit operations.

HWO Job Procedure/Equipment Illustrations

7. Max pull set by safety factor and pipe condition – usually 80% of minimum yield.

8. Max wellhead working pressure is 80% of rated pressure at equipment condition.

9. Modifications to critical components require engineering authorization and redesign.

10. Use hydraulic lock when milling. Do not use clamps when moving pipe or transmitting torque.

11. Pressure test BOP stack and all lines and valves before entering well.

12. Have an open stabbing valve with wrench in the basket.

13. Pumping units must have a relief valve (manned while operating).

14. Kill lines must have a check valve close to the BOP stack.Part of a list from Halliburton

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

04/11/23 © BP presentation name

Live Well Workovers

• less fluids lost to formation = less damage

• shorter time with well off-line

• less problems with kill fluids

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.

Normal tubulars used for HWO

A view of the pressure connection tube between the upper isolation chamber and the well.

Equipment in the stack

A HWO stack involves several pressure control surfaces and spacer tubes between the pipe rams to allow the passage of tool joints and equipment such as packers and pumps.

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

100150

200

250

300

350400

450

500

0 2000 4000 6000 8000 10000

Well Head Pressure, psi

Wei

gh

t N

eces

sary

to

Pu

ll W

irel

ine

into

th

e W

ell,

lbs

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

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ht

Re

qu

ire

d t

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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

Drill pipe pushed out of a well by pressure.

Hydraulic snubber nearing bottom of stroke.

Tool joint nearing slips.

1. Close lower or stationary slips.

2. Open upper or traveling slips.

3. Activate hydraulics to extend cylinders.

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.

Sealing against the pipe

• Stripper Friction has several variables – pipe OD, pipe surface condition, lubrication, type of packing, length of packing, etc. In general, for a good seal:

– 500 lb per square inch on a stripper packing

– 1000 lb per square inch on an annular

General rules of thumb

• It takes about 1 second per 1000 feet (MD) each way for a change in the choke setting to be see as a change in pressure at the pump.

• Max Flow Rate in BPM = 2 x (ID in inches)2

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