Wellheads and Casing

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TAMU - PemexOffshore Drilling

Lesson 3

Wellheads and Casing

Drilling with a Riser

Temporary and Permanent Guide Bases

Fracture Gradients

Subsea Cementing

Casing Seals

Drilling Procedures - An Example

Conventional Riser Drilling

SEAFLOOR

SEA WATERHYDROSTATIC

PRESSURE

MUD HYDROSTATIC

FLOATER

DRILLING RISER

CHOKE LINE

Conventional Riser Drilling- Install 30-in Conductor -

FLOATER

DRILLPIPE

Jet 30-in Conductor to ~ 200 ft below mudline

No riser - “Mud” returns to seafloor

No annulus - no cementing (in GOM)

~200 30”

Conventional Riser Drilling- Install 20-in Conductor

FLOATER

DRILLING RISER

CHOKE LINE

Drill 26-in hole to 1,050 ft below mudline

Riser optional - Mud returns to surface or seafloor

Run 20-in Conductor to ~ 1,000 ft below mudline

Cement to mudline

~1,050

Conventional Riser Drilling - Install 13 3/8-in Surface Csg.

FLOATER

DRILLING RISER

CHOKE LINE

Run Riser and BOP Stack

Drill 17 1/2-in hole to 4,050 ft BML

Drill with Mud returns to surfaceRun 13 3/8-in Surface Casing

to ~ 4,000 ft below mudline

Cement to mudline

Now, finally, we can close the BOP if necessary

13 3/8”

A subsea wellhead, like a land wellhead:

Must support the BOP‟s while drilling Must support the suspended casing

while cementing, and

Must seal off between casing strings

during drilling and production

operations.

Wellheads and Casing, cont.

In floating drilling, the casing hangers,

casing seals and cementing heads

differ

from land and platform operationsin the following manner:

1. The first and second casing strings

are cemented with returns to the

seabed.2. Casing is run with the last joint made-

up on a casing hanger and

permanently suspended prior tocementing. Mud returns flow

through fluting in the hanger.

3. Usually, cementing plugs are

located at the wellhead and

released remotely. Thecementing string from the vessel

to the wellhead is drill pipe.

4. Casing seals are run and set

remotely.

5. Special test tools are required for

remotely testing the casing seals.

6. Wear bushings are essential for

protecting the wellhead.

Fig.4-10.Typicalsealing

arrangement

for subseawells.

Depth BML

240 ft

1,100 ft

4,100 ft

8,600 ft

10,100 ft

PermanentGuide

Structure.

Temporary

Guide Base

Hole Opener

TemporaryGuide Base

Utility

Guide Frame

Procedure for Starting a Well

1. To get the well started, place a heavy

steel template on the seafloor.

Run on drillpipe.2. Four guidelines guide bit, casing, etc to

the right location on the seafloor.

3. Run 36” hole opener (with guide frame)and drill 36” hole to ~240 ft BML

with returns to the seafloor.

4. Run 30” casing and cement with returns

to the seafloor. With the 30” casing

also run the permanent guidestructure and the wellhead housing.

(3 & 4 alt. Sometimes the 30” casing is

jetted or driven in. - instead of drilling).

5. Drill 26” hole to 1,050 ft below mudline.

6. Run 20” conductor casing.

With the 20” casing, run the high

pressure wellhead. Cement the casing.

NOTE: The 26” hole may be drilled with

returns to the seafloor, or with returns

to the surface using the marine riser.

Note the guide posts on the permanent

guide structure. These are for the BOP stack

Fig. 4-5. Estimated Fracture gradients at

100 ft below seabed (Santa Barbara Channel).

Fracture gradient at

100 ft. below seabed

(Santa BarbaraChannel).

Why drill with returns to the seafloor?

With this low fracture gradient it is difficult to

drill with returns to the surface.

No shallow gas would be expected at this

depth below the mudline.

Fig. 4-5. Estimated Fracture gradients at

1000 ft below seabed (Santa Barbara Channel).

Drill with Diverter to theSurface Casing Point

ShallowGas

Blowout

Gasreduces

buoyancy!

Typical specific gravity variations in ablowout boil have increasing effect nearer

the water‟s surface.

Fortunately for a semi-submersible, therig‟s primary flotation members are

situated below the zones where specific

gravity has been reduced the most.

Gas in theWater Column

If there is sufficient length to the mooringsystem cables/ chains, the rig will be

pushed off location and out of harm‟s way.

However, the plume can also cause the rig

to list, which reduces its freeboard and

makes it more susceptible to capsizing.

Gas in theWater Column

Increasing the water depth reduces

the total overburden gradient and

consequently the formation fracturegradient. This can be expressed as:

ppobf gF)gg(g

Fracture Gradients in Deep Water

Where:

ratiostressvertical / horizontalF

psi/ftgradient,pressureoverburdeng

psi/ftgradient,pressureformationg

psi/ftgradient,fractureg

ppobf gF)gg(g

For offshore drilling:

)ddd(p4335.0d44.0d

1g FKBf KB

g/cmdensity,bulk formation

ftwater,theaboveflowlineof heightd

ftdepth,waterd

ftbushing,kellythefrommeasureddepthd

Where:

0.44 d is the overburden due to water,

or simply the hydrostatic pressure at theseafloor.

(dKB - d - dF) is merely the penetrationinto the seafloor.

)ddd(p4335.0d44.0d

g FKBf KB

Formation bulk density vs. horizontal to verticalstress ratios for the Santa Barbara Channel.

Get f fromdensity log.

Get F fromthis plot.

Calculate gf

Get gp

Fig. 4-7. An example of onshore andoffshore fracture gradients.

Cumulative average (BML)

formation bulk density

= 5.3 * (TVDBML)0.1356

e.g. = 5.3 * (3,000)0.1356 = 15.70 lb/gal

J. W. Barker and T. D. Woods“Estimating Shallow Below Mudline Deepwater

Gulf of Mexico Fracture Gradients” Presented at the 1997 Houston AADE Chapter

Annual Technical Forum, April 2-3, 1997.

At 1,000 ft below mudline, avg. OB. Density,

= 5.3 * (TVDBML)0.1356

gob = 5.3 * (1,000)0.1356 = 13.52 lb/gal

gf = 0.9 * ob = 12.17 lb/gal = 0.663 psi/ft

gp = 0.8 * ob = 10.82 lb/gal = 0.563 psi/ft

NOTE: These are gradients relative to

the mudline!

J. W. Barker and T. D. Woods cont’d

At 1,000 ft below mudline, in 1,500 ft water:

Total overburden = 0.44 * 1,500

+ 0.052 * 13.52 * 1,000 psi

gob = 1,363/2,500 psi/ft = 10.48 lb/gal !!

pf = 0.44 *1,500 + 0.052 * 12.17 * 1,000 psi

gf = 1,293/2,500 psi/ft = 9.94 lb/gal

gp = 0.44 * 1,500 +0.052 * 10.82 * 1,000 psi= 1,223/2,500 psi/ft = 9.40 lb/gal

NOTE: These are gradients relative to SURFACE!

J. W. Barker and T. D. Woods cont’d

Fracture gradient equation:g =

Poisson‟s

from Text

Ben A. Eaton and Travis L. Eaton“Fracture Gradient Prediction for the new

generation” World Oil, October 1997, pp. 93-100.

ppobf gF)gg(g

Fig. 4-8. Plot of a leak-off test.

Mud Weight 9.5 PPGCasing 13 inchesSet to 3,340 ft-KB

Frac. Grad. = ?

Fracture Gradient Calculation

Fracture Pressure = 0.052 * 9.5 * 3,340 + 650= 2,300 psig

Frac. Grad. = 2,300/3,340 = 0.6886 psi/ft= 0.6886/0.052 = 13.24 ppg

Casing

Drillpipe

Leak-Off Test

Fig. 4-9.

Sub-seacementing

system.

Fig.4-10.Typical

sealingarrangement for subsea

wells.

Metal-to-Metal Casing Annulus Seal

Assures maximum seal over

extended periods, even in high-

pressure holes Eliminates dependence on seal

materials that deteriorate or “cold

flow”.

Available on systems up to 15,000

psi pressure integrity.

1 Actuating force is transferred to the

Upper MetalSeal Lips

Resilient

CompressionElement

Lower MetalSeal Lips

1. Actuating force is transferred to the2. Resilient compression element

which expands, forcing the3. Metal seal lips into contact

with the surface of the4. Wellhead housing and the5. Casing hanger

Casing Hanger and Pack-offAssembly

Single trip installation

The pack-off seal assembly is runsimultaneously with the casing hanger

body. All operations - installing the casing

hanger, cementing the casing string and

actuating and testing the pack-off seal areperformed in a single trip of the running

string.

Large Flow-By Areas

Large flow-by areas can handle most

drilling fluid applications with a minimal

drop in pressure.

Deep 2" wide flow-by slots in the casing

hanger body, and ample porting through

the pack-off nut assembly, provide clear passage for cuttings and mudcake

without plugging.

Liquid Compressibility

The volume required to compress a liquid

is defined by the equation:

Where:

Vi = volume of system, bbl

Cp = compressibility = 3 * 10-6 per psi for water = 6 * 10-6 per psi for mud

DP = test pressure, psi

DV = Vi * Cp * P

Seal Test - Example

Water depth = 500 ft (all depths are KB)

Casing string = 13 3/8” OD

Volume of system above the seal = 11 bblTest pressure = 3,000 psi

Test fluid = water

Previous casing string = 20”, J-55, 94.0 lb/ftPrevious casing seat = 1,500 ft KB

Cement top = 996 ft

Seal Test - Example

V = 11 bbl

500 „ KB Mud Line

996‟ 20”

1,500‟

13 3/8”

4,000 ft

With no leak, the system will require

DV = 3 * 10-6 * 11 * 3,000 = 0.1 bbl water

to reach test pressure.

If the seal leaks, the volume will be more,but how much more?

Obviously, 0.1 bbl would be difficult to

measure. The annular volume between the

seal and the cement is

(996 - 500) ft * 0.1815 bbl/ft = 90 bbl of mud

DV = 6*10-6 * 90 DP + 3*10-6 * 11 DP bbl

= ( 5.4 * 10-4

+ 3.3*10-5

) DP bbl= ( 5.73 * 10-4 ) DP bbl

What should the maximum pressure be?

Pressure in the annulus must always be

less than the collapse pressure of the inner

casing, and less than the internal yield of the outer casing.

This will depend on both volume andpressure. Table 4-2 shows the relationship

for four grades of casing.

Also, the internal yield of the 20-inch casing

is reached at 2,110 psi when V = 1.24 bbl.

Plug fortesting

casing seal

to fullworking

pressure.

Test Procedure

1. Set seal

2. Land test plug in wellhead,

sealing off below the seal3. Displace mud with water for test

4. Close pipe rams

5. Pump slowly down the choke line,preferably in stages, to protect the

casing in case of leaks

Test Evaluation

During the test, if the wellhead system

being tested will not sustain test

pressure, several possible causesshould be considered:

1. Leak in the surface manifold2. Leak in the test plug (detected by

returns through the drillpipe)

Test Evaluation, cont.

3. Leak in the casing seal

4. Leak in the BOPs5. Leak in the hydraulic wellhead

connector

When the well does not sustain

pressure, it is obvious that there is a

problem.

There is also a problem if the well

takes too much fluid to reach testpressure, just as we have discussed.

Test Evaluation, cont.

Drilling Proceduresfrom a floater

Install 30” Structural Csg.

Install 20” Conductor

Install 13 3/8” Surface Casing

D illi P d

Drilling ProceduresTentative Hole and Casing Sizes

8 1/2” Pilot Hole to 180‟ BML

26”x36” Hole Opener to 180‟ BMLInstall 30” Structural Csg.

8 1/2” Pilot Hole to 1040‟ BML

17 1/2” Pilot Hole to 1040‟ BML 17 1/2”x26” Under reamer to 1040‟

Install 20” Conductor

Drilling Procedures

Drilling ProceduresTentative Hole and Casing Sizes

12 1/4” Pilot Hole to 3,830‟ BML

12 1/4”x17 1/2” Hole Opener to 3,830‟ BMLInstall 13 3/8” Surface Csg.

12 1/4” Hole to TD (8,530‟ BML)Install 9 5/8” Production Csg.

8 1/2” Hole if Required 7” ContingencyLiner

General Rules

1. Do not change the tension on the

anchor lines until the 30” casing

has been run and cemented.

2. Have all the 30” casing and all of the

wellhead equipment on board

prior to spudding.

3. There will be an SLM prior to any

logging or coring run.

General Rules

4. All casing strings will be strapped

and drifted prior to running.

5. Casing will not be run until thehole is in the best possible

condition and a trouble free

wiper trip can be made.6. Cement densities will be

monitored with a mud balance.

G l R l

General Rules

7. The rig will be moved 50‟ off location

whenever the riser is being run or

pulled.

8. No smoking or open flames arepermitted on deck whenever the

riser is connected to the well.

9. Welding permits (authorized by thedrilling supervisor and tool pusher)

will be required at all times.

General Rules

10. Coring will be at the the discretion of the

well site geologist, but only after

approval from the task force Manager and the Exploration Coordinator.

11. All information concerning the well will

be kept strictly confidential. Anydiscussions will be held in a secure

area in the quarters or on the rig.

General Rules

11. Confidentiality - cont‟d.

Only contractors with “a need to

know” will be allowed access to wellinformation.

12. All personnel on board and all visitors

will be instructed with the necessaryenvironmental and safety films and

instructions.

General Rules

13. No one will be allowed on the

helicopters, work boats, or drilling

vessel without the proper authorization or identification.

14. The rotary table must be positioned

within a 200 foot radius of theproposed location.

G l R l

General RulesAnchoring

1. Place anchors on sea floor 5800‟ from

the desired final location.

2. Anchor lines should be equally

deployed around the rig with an

angular spacing of 45 degreesbetween adjacent lines.

General Rules

3. Pull in opposing lines to set anchors.

An indicated line tension of 125

kips is necessary for the anchor toreceive any load.

4. A tension level of 440-460 kips

should be reached before 600‟ of line is taken in with the rig

remaining stationary.

General Rules

5. If a line tension of 440-460 kips has

not been reached before 800‟-

1000‟ of line has been retrieved,

then it may be necessary to use

piggy-back anchors.

6. The following Western KDC planoutlines the mooring procedure.

Shallow Gas Plan

After the rig is properly anchored the

following steps will be followed as

there is a potential for shallow gas in

this area:

Shallow Gas Plan

1. Leave mooring line pawls or stoppels

unset until the 20” casing has been

set and cemented.

2. Mooring winches will be manned while

the 8 1/2” pilot holes for the 30” and20” casings are being drilled.

Shallow Gas Plan

3. Mooring winches will be manned

while the 8 1/2” pilot holes for the

30” and 20” casings are being

opened up or under-reamed.

4. The moonpool and seafloor will be

observed for gas bubbles until the20” casing is set and cemented.

36” H l Pl

36” Hole Plan

1. Premix 600 barrels of 11.5 ppg kill mud

prior to spudding the well.

2. PU and TIH with an 8 1/2” bit, 6 - 6 1/2”

drill collars, 6 jts of 5” Hevi-Wate drill

pipe, and sufficient 5” drill pipe.

36” H l Pl

36” Hole Plan

3. Tag bottom with the pilot bit, and

note and report the following:

a. RKB to water level

b. RKB to mud line

c. Water depthd. Time of day (tide allowance)

36” Hole Plan

4. Lower TV camera, and observe bit

entering guide base. Retrieve

universal guide frame back to surface.

5. Upon spudding, space out drill string with

pup joints so that it will not be

necessary to pull the bit above theguide base to make the first

connection.

36” Hole Plan

6. Drill an 8 1/2” hole to +/- 30‟ below

the setting depth of the 30”

casing (estimated at 180‟ BML).

Circulate returns to the sea floor,

and monitor returns with the

TV camera.

36” H l Pl

36” Hole Plan

7. If there are no problems with shallow

gas, pull out of hole, PU 26” bit and

36” hole opener, 6-9 1/2” DC‟s, 6 jts5” Hevi-Wate DP, and sufficient 5” DP.

Drill 36” hole to set 150‟ (4 joints) of 30” OD structural casing.

36” H l Pl

36” Hole Plan

Drill with sea water as follows:

a. Circulate viscous sweeps as

required to clean the hole.b. Survey hole at 30‟, 60‟, and

150‟ BML.

c. At TD of 36” hole, displacehole to the mud line with

viscous mud.

36” Hole Plan

Drill with sea water cont.:

d. Make a wiper trip.e. Circulate the hole to the mud

line with viscous mud.

f. Penetration rate should notexceed 100 ft/hr overall.

36” H l Pl

36” Hole Plan

8. Run 30” structural casing per procedure.

9. If there are problems with shallow gas,

displace the 8 1/2” hole with kill mud

until the gas stops or the hole is full of

kill mud.

Monitor returns with the TV camera for

evidence of gas or flow, and if after

one hour the hole is stable, proceed

as in steps 7 and 8.

36” H l Pl

36” Hole Plan

10. If the kill mud in step 9 does notstabilize the well and it appears that

heavier mud will not stabilize the well

or will break down the formation, thenprepare to cement.

Mix and pump, sufficient 15.8 ppg

cement slurry to circulate cement tothe mud line, and monitor returns for

gas with the TV camera.

36” H l Pl

36” Hole Plan

10. Make sure that the hole is stable

POH with BHA

Retrieve TGB

Move rig as required

26” H l Pl

26” Hole Plan

1. Have 600 barrels of 11.5 ppg kill mud

prior to drilling out below the 30”

casing.

2. PU and TIH with an 8 1/2” bit, 9-6 1/2”

DC‟s, 9 jts of 5” Hevi-Wate DP, andsufficient 5” DP.

26” Hole Plan

3. Drill an 8 1/2” hole to +/- 40‟ below the

setting depth of the 20” casing

(estimated at 1040‟ BML).

Circulate returns to the rig shakers, and

monitor returns for indications of gas or

26” Hole Plan

4. Displace the hole with viscous

spud mud, make a wiper trip,displace the hole with viscous

spud mud, POH, and log well

as required.

26” Hole Plan

26 Hole Plan

5. If there are no problems with shallow

gas, pull the riser, PU & TIH with a

17 1/2” bit, 26” hole opener, monel

DC, 6-9 1/2” DC‟s, 6-8” DC‟s, 9 jts 5”

Hevi-Wate DP, 26” stabilizer at 60‟,

qand sufficient 5” DP.

Drill a 26” hole to set 1040‟ of 20” OD

conductor casing as follows:

26” Hole Plan

a. Circulate viscous pills as

required to clean the hole.

b. Circulate returns to the sea floor with sea water.

c. Maintain inclination at less than

three degrees.

d. Spot viscous mud at TD of 26”

26” Hole Plan

e. Make a wiper trip.

f. Spot viscous mud as required.

g. Drop multishot and POH.

6. Run 20” OD conductor casing and

cement per procedure.

26” H l Pl

26” Hole Plan

7. If there are problems with shallow gas in

Step 5, circulate the hole with viscous

spud mud and slowly increase theweight until the flow has stopped or

until the active system is depleted.

If the flow continues, pump the killmud at the maximum rate until the

active system is depleted.

26” Hole Plan

7. (Cont.) Then pump sea water at themaximum rate until the hole bridges.

8. If the flow rate is significant, and the hole

will not bridge, prepare to move the rig.Cement the hole to just below the sea

floor with 15.8 ppg cement. POH with

the BHA. Cut or shoot the 30” casing,and pull the TGB and PGB. Move rig

as required.

26” Hole Plan

26 Hole Plan

9. If the gas in step 7 depletes or the

density is sufficient to control the

well, then casing can be run or the

well can be drilled ahead.

10. Drill 8 1/2” hole to +/- 40‟ below the

setting depth of the 20” casing

(estimated at 1040‟ BML).

26” H l Pl

26” Hole Plan

11. Circulate and condition for logs. Pull out

of hole, and log well per procedure.

12. PU & TIH with 17 1/2” bit, Monel DC, 6-9

1/2” DC‟s, stabilizers at 60‟ amd 90‟, 6-8”

DC‟s, jars, 9 jts 5” Hevi-Wate DP.

26” Hole Plan

13. Drill a 17 1/2” hole to sufficient depth

to set 1040‟ of 20” conductor casing.

Drop multishot, and POH.

14. PU & TIH with 17 1/2” bit and 26”

underreamer, 6-9 1/2” drill collars, 6- 8” drill collars, 9 jts 5” Hevi-Wate DP,

and 26” stabilizer at 60‟.

26 Hole Plan

15. Underream to sufficient depth to set

1040‟ of 20” conductor casing.

16. Circulate and condition the hole for

casing. Care must be taken to have a

balanced mud weight all the wayaround with no heavy slugs.

26” Hole Plan

17. Displace hole from TD to the sea floor

with sufficient weight mud to balance

the hydrostatic when the riser is

removed.

Again, care must be taken to have a

balanced mud weight while displacing,

and the riser may have to be voidedwith sea water as the heavier mud is

circulated.

26 Hole Plan

26” Hole Plan

18. POH, run the 20” casing and 18 3/4” -

10,000 psi wellhead housing, and

cement per procedure.

19. If there is evidence that the hole

cannot be drilled deeper safely in

step 9, the well will be underreamedat the depth reached in step 9 and

20” casing will be set.

26 Hole Plan

20. It will then be determined whether

future casing settings need to be

changed.

etc. etc. etc.

26” Hole Plan

Wellheads and Casing

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