A Functional Method for the Optimization of Offshore...

A Functional Method for the

Optimization of Offshore Platform

Orientation Utilizing CFDGerard Reynolds

March 16, 2015

STAR Global Conference

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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

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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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www.atkinsglobal.com

Email: gerard.reynolds@atkinsglobal.com

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