1, Heave Compensation Diag, Low Max
1, Heave Compensation Diag, Low Max
2, Heave Compensation Diag, Low Mid
2, Heave Compensation Diag, Low Mid
3, Heave Compensation Diag, High Mid.
3, Heave Compensation Diag, High Mid.
4 Heave Compensation Diag, High Max
4 Heave Compensation Diag, High Max
Sub Sea Reservoir
Sub Sea Reservoir
Supports, All From 2e
Supports, All From 2e
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Index, Section  4 Modules Offshore
General
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Level 2
a general understanding
MODULEitus
of Modules 
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Level 1
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Level 3
Level 2
Heave Compensation Diag Parts
Heave Compensation Diag Parts
Heave Compensation. Any item that floats
suffers Heave (Rise and Fall) from Sea
Surface displacwmwnta (waves). Some hulls
more than others are prone to this. Drilling
is an operation where heave is a movement
that must be removed or mitigated. To do
this most floating drilling applications require
heave compensation (hence the attraction
of a fixed platform).
These Heave Compensation Diagrams show the displacement of a Semi Sub. 1 Low Max, 2 Low Mid, 3 High
Mid, 4 High Max Wave Heigh. The blue arrow heads in the Diag show the area of maximum buoyancy for a
semi sub, the pontoon/sponson area. The transverse stiffeniner having minimal effect. Two problematical
areas of interelation between the Semi Sub , Drill String and Riser Casing exist. a) the Drilling Riser Casing
(and eventually the production Riser Casing) need to be in tension to avoid buckling (they are long and thin
and would eaily buckle if not in tension.. The contact point for this interface is the casing swivel. b) the
second point of contact is the Drill String head. This also needs to be in tension to either support its weight
or provide load to the drill bit also again to prevent buckling. The diagrams show the movement of the
component parts as the ship moves. Initially the sides of the compensation bottle are in equilibrium with
sufficient force to hold the drill casing in tension. the Semi Sub marginally moves up or down from the fixed
point, the swivel. In doing this it creates a disparity in the compensation bottles, increasing the pressure on
one side of the diaphragm over the other. As the pressures are allowed to stabilize the condition returns
where sufficient force holds the drill string in equilibrium but the correlation semi sub to swivel has changed.
These displacements contiue and increase or decrease but still holding the drill casing in a constant
tension.4d_3 West Navion shows the type of equipment in this operation. The same diagram Heave Diagrams
also show compensation at b) however they use a pantgraph style of arrangenment to accomodate heave
but at this point they also have toaccomodate the fact that the drill string is in the proces of drilling down or
being recovered at the same time. Here theforce in the Drill String must be sufficient to enable the tool bit to
drill. This is accomplished by paying out the drill winch cable sufficintly to progress drilling withoutletting the
drill string buckle. cd_3 West Navion is slightly different to this since the Rig know as a Ram Rig uses two
special long cylinders to raise or lower the drill string. Other compensation systems exist, some are all
hydraulic and some work has been undertaken for linear motor style of actuaters to contain the movements
but still ensure tension of the strings.
Fixed or Floating Support Main Feature Controlling Type of Drilling Rig Used. In Section 2 SUPPORTS Offshore the above from 2e Diagram indicates the general contolling guideline that as water depth Deepens then the preference to support a facility moves from a structure with sea bed foundations to a suitable Floating Design. Sea Bed Structures remove the complexity of Sea State on the Drilling Operation. We thus see that the range of Structures used to support Drilling are those that have direct sea bed support , see 4d-1 and 4d 5, and in deeper waters use  a floating structure, usually ship shape see 4d 3, have other typoes of hulls such as Sevan see 2e, some have a purpose provided Drilling Platform adjacent to its Production Platform.
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Go to 4d Continued, for more.
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