wellheads and casing
TRANSCRIPT
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TAMU - PemexOffshore Drilling
Lesson 3
Wellheads and Casing
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Wellheads and Casing
Drilling with a Riser
Temporary and Permanent Guide Bases
Fracture Gradients
Subsea Cementing
Casing Seals
Drilling Procedures - An Example
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Conventional Riser Drilling
SEAFLOOR
SEA WATERHYDROSTATIC
PRESSURE
D E
P T H
MUD HYDROSTATIC
BOP
FLOATER
DRILLING RISER
CHOKE LINE
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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”
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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
D
~1,050
30”
20”
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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
D
BOP
Now, finally, we can close the BOP if necessary
13 3/8”
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Wellheads and Casing
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.
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Wellheads and Casing, cont.
In floating drilling, the casing hangers,
casing seals and cementing heads
differ
from land and platform operationsin the following manner:
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Wellheads and Casing
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.
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Wellheads and Casing
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.
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Wellheads and Casing
5. Special test tools are required for
remotely testing the casing seals.
6. Wear bushings are essential for
protecting the wellhead.
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Fig.4-10.Typicalsealing
arrangement
for subseawells.
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Depth BML
240 ft
1,100 ft
4,100 ft
8,600 ft
10,100 ft
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PermanentGuide
Structure.
Temporary
Guide Base
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Hole Opener
TemporaryGuide Base
Utility
Guide Frame
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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.
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Procedure for Starting a Well
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.
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Procedure for Starting a Well
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
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Fig. 4-5. Estimated Fracture gradients at
100 ft below seabed (Santa Barbara Channel).
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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.
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Fig. 4-5. Estimated Fracture gradients at
1000 ft below seabed (Santa Barbara Channel).
Drill with Diverter to theSurface Casing Point
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ShallowGas
Blowout
Gasreduces
buoyancy!
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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
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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
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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
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Where:
ratiostressvertical / horizontalF
psi/ftgradient,pressureoverburdeng
psi/ftgradient,pressureformationg
psi/ftgradient,fractureg
ob
p
f
ppobf gF)gg(g
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For offshore drilling:
)ddd(p4335.0d44.0d
1g FKBf KB
ob
3f
F
KB
g/cmdensity,bulk formation
ftwater,theaboveflowlineof heightd
ftdepth,waterd
ftbushing,kellythefrommeasureddepthd
Where:
f
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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
1
g FKBf KB
ob
f
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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
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Fig. 4-7. An example of onshore andoffshore fracture gradients.
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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.
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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
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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
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Fracture gradient equation:g =
Poisson‟s
Ratio
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
D
p
1D
p
D
S
D
F
g
g
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Fig. 4-8. Plot of a leak-off test.
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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
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BOPs
Casing
Drillpipe
Leak-Off Test
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Fig. 4-9.
Sub-seacementing
system.
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Fig.4-10.Typical
sealingarrangement for subsea
wells.
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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
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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
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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.
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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.
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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
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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
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Seal Test - Example
V = 11 bbl
500 „ KB Mud Line
996‟ 20”
1,500‟
13 3/8”
4,000 ft
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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?
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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
Now,
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?
?
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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.
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Plug fortesting
casing seal
to fullworking
pressure.
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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
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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)
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Test Evaluation, cont.
3. Leak in the casing seal
4. Leak in the BOPs5. Leak in the hydraulic wellhead
connector
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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.
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Drilling Proceduresfrom a floater
Install 30” Structural Csg.
Install 20” Conductor
Install 13 3/8” Surface Casing
etc.
D illi P d
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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
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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
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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.
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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
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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.
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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.
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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.
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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
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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
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General RulesAnchoring
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
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General RulesAnchoring
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.
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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:
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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
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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
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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
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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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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36” Hole Plan
10. Make sure that the hole is stable
POH with BHA
Retrieve TGB
Move rig as required
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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
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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
flow.
26” Hole Plan
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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
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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
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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”
hole.
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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.
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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
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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
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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).
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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
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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
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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
26” Hole Plan
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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
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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.
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20. It will then be determined whether
future casing settings need to be
changed.
etc. etc. etc.
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