Malampaya DCP - AOG · Malampaya DCP DESIGN FOR THE RELAXATION OF SEABED PREPARATION TOLERANCES...
Transcript of Malampaya DCP - AOG · Malampaya DCP DESIGN FOR THE RELAXATION OF SEABED PREPARATION TOLERANCES...
Background
• Malampaya field, offshore Palawan,
Philippines
• Malampaya gas to power project - Shell,
Chevron, PNOC – Shell operators
• Existing platform at site – Shallow Water
Platform (SWP) – concrete gravity structure
installed in 2000
• Supplies gas to four power stations
providing ~45% of Luzon’s power needsSource: malampaya.com
Depletion Compression Platform
• Field requires depletion compression to continue operating
effectively i.e. for future expected decrease in well pressure
• Depletion Compression Platform – DCP
• Maintain flow of gas to shore at acceptable rate to end of
field life
• Topside equipment (above deck): 3500 – 5000t, +/- 2m COG
variation
ACE Platform Range
• 5 - 140m water depth range
• Up to 15,000te topsides equipment payload (equivalent to 30,000te integrated deck)
• Wellhead / Minimum Facilities Platforms
• Drilling / Workover & Production
DCP – Key Project Drivers• Form suited to local
construction capability → steel
• No special transport vessel resident in the region → Self-installing
• Ground conditions → gravity based foundation
• Resists typhoon and earthquake events
• Safety
DCP – Key Structural Elements
• Four 21 x 19 x 4m stiffened
hexagonal pad footings
linked by horizontal truss
• Four Φ 3.8m stiffened
cylindrical legs
• 62 x 42 x 7.5m stiffened
rectangular barge
Geotechnical Aspects• In-Situ Ground
Conditions• 0.5 – 6m of carbonate
sand (partially cemented)• 3 – 15m of reef limestone• 35m of calcarenite
• Relatively poor cyclic characteristics of insitusoil
• Remove and replace approach
• Material sourced locally
Geotechnical Aspects• Challenge: Eliminate
dedicated scour protection
layer i.e. size seabed
preparation to resist scour
Soil-Structure Interaction• Develop a solution to accommodate platform installation on
an undulating seabed
• Globally accommodate differential vertical levels in the
prepared seabed at footing locations
• Perform plastic analysis to assess local behavior of the
structure for a range of potential seabed undulations
• Relax tolerances for undulation shape and location – resulting
in reduced installation time
Pad Footing Design
• Four individual hexagonal pad
footings, integral with leg
• Six compartments
• Filled with iron ore slurry to
provide weight
• Connected by pin ended
horizontal truss to
accommodate relative levels
during installation and allow
lateral load share
Pad Footing Design
• Prepared seabed includes possibility
for local mounds of finite stiffness
• Mound squash loads quantified –
associated pressure/contact area
• Local mounds apply high localised
pressure to underside of base
• Base stiffened to resist
Pad Footing Design
Radial T-stiffeners
Concentric T-stiffeners
Tubular leg
Vertical propping
columns between
top and bottom plateHorizontal T-
stiffeners on
external walls
Vertical T-
stiffeners on
bulkheads
Bottom Plate
Critical Load Cases
• Environmental and seismic in-place loading
• 10,000 year Abnormal Level Earthquake (ALE)
• Identify possible mound types
• Steep mounds (1:2 slope)
• Small gradual mounds (1:10 slope, up to 100mm)
• Large gradual mounds (1:10 slope, 100-300mm height)
• One or two discrete mounds most critical
Local EquilibriumAxial N*
Uniform lateral pressure from seismic inertia
Ballast applied as distributed pressure load
Moment M*
Shear V*
Lever arm determined from moment equilibrium
Equivalent mound reaction applied as distributed pressure over squash area
Design Cases
Case 1: Single mound
Case 2: Two mounds (opposite edges)
Case 3: Two mounds (near edge)
Case 1: Single mound
Case 2: Two mounds (opposite edges)
Case 3: Two mounds (near edge)
Case 1: Single mound
Case 2: Two mounds (opposite edges)
Case 3: Two mounds (near edge)
Case 1: Single Mound Case 2: Two mounds
(opposite edge)
Case 3: Two mounds
(near edge)
Mound Parameters
VERTICAL
FORCE (KN)
DISPLACEMENT
(MM)
AREA (M2) PRESSURE (KPA)
2506 60 5.655 443.1
8640 120 11.310 763.9
17928 180 16.965 1056.8
29437 240 22.619 1301.4
46027 300 28.274 1627.9
• 300mm height, 10H:1V
• Mound located away from edge of footing
• Vertical load and area halved for mound at edge
• Limit max pressure based on complete squash load
yLoad in-line with bulkhead
x
Squashed mound footprint
Load perpendicular to face
Squashed mound footprint
y
x
Case A - load in line with bulkhead
Case B - load perpendicular to face
Mound Parameters
yLoad in-line with bulkhead
x
Squashed mound footprint
Load perpendicular to face
Squashed mound footprint
y
x
Case A - load in line with bulkhead
Case B - load perpendicular to face
Case A: Load in-line with bulkhead Case B: Load perpendicular to face
Structural Analysis
• Linear analysis in DNV
SESAM
• Non-linear analysis in Strand7
• Plate - 2D quad-8 shell
elements
• Stiffeners – beam elements
• Fixed boundary conditions at
tubular leg
Structural Analysis
• Plastic behaviour acceptable
• Plastic strain limits from ISO
19902 and API-RP-2A• Base plate 5%
• Compact stiffener flange/web
5%
• Non-compact stiffener
flange/web 1%
Structural Analysis
• Buckling assessment of stiffened
plates and girders using GeniE
PULS (Part 2 DNV-RP-201)
• Longitudinally stiffened panels
• Local elastic buckling and non-
linear post-buckling behaviour
• Define initial imperfections to
account for permanent plastic set
Stiffener
Girder
Axial / Longitudinal direction
Longitudinally Stiffened Panel
GeniE 'sub-panel '
Transverse direction
Secondary stiffenerLongitudinally Stiffened Panel
Transverse direction
Axial/longitudinal direction
Primary girder
GeniE sub-panel
Girder being checked
Stresses averaged over highlighted panels
Assessment for primary girder
In-plane stresses averaged over highlighted sub-panels
• In-situ material removed within nominated footprint
• Backfilled with rock fill material
• Local surface tolerances achieved
Offshore Work – Seabed Preparation
Offshore Work - DCP Installation
• DCP successfully installed
February 2015
• Self-installing system
performed as anticipated
• Barge jacked into position
within 2 days, allowing
rapid access to commence
weld-outSource: Shell Philippines Exploration B.V.