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A Functional Method for the
Optimization of Offshore Platform
Orientation Utilizing CFDGerard Reynolds
March 16, 2015
STAR Global Conference
16 March 2015 STAR Global Conference 2015 1
Introduction
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Background Information
• Type: Tension Leg Platform (TLP)
• Size: 300 ft x 300 ft x 100 ft
• Personnel on Board: 180
• Access: 90 min by Helicopter
• Cost: $3.5 bn
• Production: $10 MM/day
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Incidents – Why We Care
• Deepwater Horizon – 11 fatalities
• Piper Alpha – 167 fatalities
• Thunderhorse – 0 fatalities (close call)
• Petrobras 36 – 11 fatalities
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Problem Statement
Considering:
• Ventilation
• Helideck Impairment
• Wind Chill
• Lifeboat Drift-off
• Tendon Stress
Find:
• Optimum Platform Orientation
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Ventilation
Higher ventilation rates
typically translate to
smaller flammable gas
clouds if leaks were to
occur.
• Regulations
– Institute of Petroleum
(IP) 15
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Increased
Ventilation
.
Exhaust
The helideck is considered impaired if there is a temperature increase of 2 ºC above ambient within a 30 m operational zone above the helideck.
• Regulations
– Civil Aviation Protocol (CAP) 437
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Helideck Operational Zone
Exhaust Outlets
Wind Chill
Quantified by the
perceived decrease in
temperature felt by the
body on exposed skin.
• Working conditions
• Regulations
– NORSOK S-002
16 March 2015 STAR Global Conference 2015 8http://www.thedrillingman.com/2015/02/cold-weather-oilfild-clothing-quick-guide/
Lifeboat Drift-off
If a lifeboat is deployed
and loses power, the
lifeboat should drift
safely away from the
platform.
• Regulations
– Safety of Life at Sea
(SOLAS) 1974
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Tendon Stress
Fatigue estimated from
wave impact and drag
loading.
• Regulations
– American Petroleum
Institute (API)
Recommended Practice
(RP) 2T
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Goals – Orientation Determination
Current Practice:
• Basis for platform orientation is previous experience and qualitative judgment
Design Objective:
• Maximize Ventilation
• Minimize Helideck Impairment from Exhaust
• Minimize Wind Chill Effects
• Minimize Tendon Stress
• Minimize Adverse Lifeboat Drift-off
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Why Use CFD?
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Accura
cy
Effort
CFD
Expert
Judgment
Tetlock, Philip E. Expert Political Judgment: How Good is It? How Can We Know?
CFD Technical Challenges
• Large platforms with
extremely complex geometry
• Difficult to explicitly resolve
all objects
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CFD Project Challenges
• Projects are schedule driven
• In early design stages
information is scarce
• HSE portion of a project is
usually 1% of the project
cost
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Methodology
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CFD Setup - Physics
Physics Parameters:
• Steady-State
• Two Layer Realizable K-
Epsilon Turbulence Model
• Segregated Multi-
Component Gas for Exhaust
• Buoyancy Driven Flow:
Gravity Model Used
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CFD Setup - Mesh
Mesh Parameters:
• Large scale objects are explicitly resolved
• Small scale objects are represented by sub-grid drag terms
• 2-5 million hexahedral cells
• Locally refined on platform and helideck
• Refined exhaust outlets
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Methodology – Step 1
Simulate wind from 16 direction and 2 wind speeds.
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Methodology – Step 2
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Calculate helideck impairment from exhaust.
Helideck
Operational Zone
Methodology – Step 3
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Calculate mean air speed through the platform.
SW Wind E Wind
Fast
Slo
w
Methodology – Step 4
Calculate wind chill on the platform.
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Cold
Hot
Methodology – Step 5
Determine lifeboat drift collision probability.
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Methodology – Step 6
Calculate drag loading
on hull as a surrogate
for tendon stress.
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Methodology – Step 7
Combine all results
using annual wind and
current probability
distributions.
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Results
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Results - Ventilation Objective
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Results – Exhaust Objective
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Ventilation
Results – Wind Chill Objective
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Ventilation
Exhaust
Results – Lifeboat Drift-Off Objective
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Ventilation
Exhaust
Wind Chill
Results – Tendon Stress Objective
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Ventilation
Exhaust
Wind Chill
Drift-Off
Results – Combined Objective
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Ventilation
Exhaust
Wind Chill
Drift-Off
Tendon Stress
Future Considerations
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Future Considerations
Optimization of facility layout.
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