Malampaya DCP DESIGN FOR THE RELAXATION OF SEABED PREPARATION TOLERANCES EMMA STEER ARUP

Transcription

1 Malampaya DCP DESIGN FOR THE RELAXATION OF SEABED PREPARATION TOLERANCES EMMA STEER ARUP

2 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 needs Source: malampaya.com

3 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): t, +/- 2m COG variation

4 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

5 DCP Key Project Drivers Form suited to local construction capability steel No special transport vessel resident in the region Selfinstalling Ground conditions gravity based foundation Resists typhoon and earthquake events Safety

6 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

7 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 insitu soil Remove and replace approach Material sourced locally

8 Geotechnical Aspects Challenge: Eliminate dedicated scour protection layer i.e. size seabed preparation to resist scour

9 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

10 Seabed Preparation Contractor Consultation

11 Mound Squash Bounding Shapes Legend 2:1 radius to height ratio 10:1 radius to height ratio

12 Mound Squash cont.

13 Mound Squash cont.

14 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

15 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

16 Pad Footing Design Tubular leg Vertical T- stiffeners on bulkheads Bottom Plate Horizontal T- stiffeners on external walls Vertical propping columns between top and bottom plate Concentric T-stiffeners Radial T-stiffeners

17 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, mm height) One or two discrete mounds most critical

18 Local Equilibrium Axial N* Moment M* Shear V* Uniform lateral pressure from seismic inertia Ballast applied as distributed pressure load Equivalent mound reaction applied as distributed pressure over squash area Lever arm determined from moment equilibrium

19 Design Cases Case 1: Single mound Case 2: Two mounds (opposite edges) 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) Case 2: Two mounds (opposite edges) Case 3: Two mounds (near edge)

20 Mound Parameters 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 VERTICAL FORCE (KN) DISPLACEMENT (MM) AREA (M 2 ) PRESSURE (KPA)

21 Load in-line with bulkhead Mound Parameters y x Squashed mound footprint ase A - load in line with bulkhead Case B - load perpendicular to face Squashed mound footprint Load in-line with bulkhead y x y x Squashed mound footprint ase B - load perpendicular to face Squashed mound footprint Load perpendicular to face Case A: Load in-line with bulkhead y Case B: Load perpendicular to face x

22 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

23 Structural Analysis Strength - Von Mises stress

24 Structural Analysis Plastic behaviour acceptable Plastic strain limits from ISO and API-RP-2A Base plate 5% Compact stiffener flange/web 5% Non-compact stiffener flange/web 1%

25 Structural Analysis Buckling assessment of stiffened plates and girders using GeniE PULS (Part 2 DNV-RP-201) Longitudinally stiffened panels Local elastic buckling and nonlinear post-buckling behaviour Define initial imperfections to account for permanent plastic set GeniE GeniE 'sub-panel ' Secondary Stiffener stiffener Longitudinally Stiffened Stiffened Panel Panel Primary Girder girder Transverse direction direction Axial Axial/longitudinal / Longitudinal direction direction Girder Assessment being checked for primary girder

26 Offshore Work Seabed Preparation In-situ material removed within nominated footprint Backfilled with rock fill material Local surface tolerances achieved

27 Offshore Work Seabed Preparation

28 As-built Prepared Seabed

29 As-built Prepared Seabed South-East Pad Footing South-West Pad Footing

30 Offshore Work Prepared Seabed

31 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-out Source: Shell Philippines Exploration B.V.

32 Questions? Source: Shell Philippines Exploration B.V.