Petroleum Engineering 406 Floating Drilling

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Petroleum Engineering 406Floating Drilling

• Lesson 9c
• Wellheads and Casing

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Lesson 9c - Wellheads and Casing

• Temporary and Permanent Guide Bases
• Subsea Cementing
• Casing Seals

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Wellheads and Casing

• A subsea wellhead, just like a land wellhead
• Must support the BOPs 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 operations in 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 to cementing. 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. The
  cementing 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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Depth BML 240 ft
1,100 ft 4,100 ft
8,600 ft 10,100 ft
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Permanent Guide Structure.
Temporary Guide Base
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Utility Guide Frame
Hole Opener
Temporary Guide Base
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Fracture gradient at 100 ft. below seabed
(Santa Barbara Channel).
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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Gas reduces buoyancy!
Shallow Gas Blowout
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Typical specific gravity variations in a blowout
boil have increasing effect nearer the waters
surface.Fortunately for a semi-submersible, the
rigs primary flotation members are situated
below the zones where specific gravity has been
reduced the most.
Gas in the Water Column
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If there is sufficient length to the mooring
system cables/ chains, the rig will be pushed off
location and out of harms way. However, the
plume can also cause the rig to list, which
reduces its freeboard and makes it more
susceptible to capsizing.
Gas in the Water Column
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Fig. 4-9. Sub-sea cementing system.
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Fig.44-10. Typical sealing arrangement 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.

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1. Actuating force is transferred to the2.
Resilient compression element which
expands, forcing the 3. Metal seal lips into
contact with the surface of the4. Wellhead
housing and the5. Casing hanger
Upper Metal Seal Lips Resilient Compression
Element Lower Metal Seal Lips
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Casing Hanger and Pack-off Assembly

• Single trip installation
• The pack-off seal assembly is run simultaneously
  with the casing hanger body. All operations -
  installing the casing hanger, cementing the
  casing string and actuating and testing the
  pack-off seal are performed 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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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 and 20 casings are
  being drilled.

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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 the 20 casing is set and
  cemented.