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Petroleum Engineering 406 Floating Drilling


Title: General Rules Author: Sara Kabell Last modified by: Ghost Created Date: 8/10/1998 4:06:58 PM Document presentation format: Skjermfremvisning – PowerPoint PPT presentation

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Title: Petroleum Engineering 406 Floating Drilling

Petroleum Engineering 406 Floating Drilling
  • Lesson 9c
  • Wellheads and Casing

Lesson 9c - Wellheads and Casing
  • Temporary and Permanent Guide Bases
  • Subsea Cementing
  • Casing Seals

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.

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

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.

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.

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
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
Gas reduces buoyancy!
Shallow Gas Blowout
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
Fig. 4-9. Sub-sea cementing system.
Fig.44-10. Typical sealing arrangement 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 2.
Resilient compression element which
expands, forcing the 3. Metal seal lips into
contact with the surface of the 4. Wellhead
housing and the 5. Casing hanger
Upper Metal Seal Lips Resilient Compression
Element Lower Metal Seal Lips
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.

Large Flow-By Areas
  • Large flow-by areas can handle most drilling
    fluid applications with a minimal drop in
  • 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.

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 and 20 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 the 20 casing is set and