Elin CrombieTord Mongstad28.01.2021

Operational limitations in Odfjell Drilling

Ptil - Webinar om værbetingede operasjonskriterier for operasjoner på flyttbare boreinnretninger

Contents

• Rig designs

• Development and implementation of air gap limit curves

• Operational limitations

• Operational compliance

• The way forward

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Heave [

m/m

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Period [s]

The hull design dilemma

All year wave energy and occurrence

Typical waves for operation condition

Little motion may give large upwell

Steep curve inside wave periods may give unpredict-able motions

Large still water air gap reduces VDL

Large displacement and wind area increase station keeping requirements

Large motion may give low operability. Good motion compensation required

Rig Designs

• Aker H-3.2

• Aker H-4

• Aker H-6

• BINGO9000

• CS50E/60

• CS60E

• GM4000-D/WI

• GG5000

• GM4-D

• GVA7500

• GVA4000-NCS

• Still water air gap

• Displacement, Hydrodynamic effects, Column & Pontoon design

• Motions-RAOs-natural periods

• Extent of deck box (cantilever)

• Windows vs port holes & positions

• Deck box openings (engine room inlet/outlets)

• Positions of (ventilation) structures

Parameters influencing air gap limits

Understanding the rig specific motions,

responses, capacities and

limitations

Development of air gap limit curves

• Early 2016 investigations/evaluations

Development of rules and guidance

• NMA Construction Regulation, Section 10 - 2018

• DNV-OS-C103

Review of motion and air-gap analysesReview of operational practices Wave case study for various rig designs to investigate potential slamming

Draupner (freak) waveUndisturbed wave

Overall rig comparisonsVarious analyses / investigationsAnalyses according to OTG-13

Probability & Consequence

• Letters to industry

– DNVGL Sep 21st 2016

– NMA Sep 28th 2016

– PSA Sep 30th 2016

• OTG13

– Draft Jul2016, Draft Sep2016, Mar2017, Jun2019

• OTG14

– Draft Sep2016, Apr2017, Jun2019

• New rules opens up for negative air gap in non-critical area in operations, ref.

Revised air gap limit curves for Deepsea Nordkapp- the process

• Re-analysis

– acc. to DNV-OS-C103 July 2020

• MOC

• Class approval

• Update procedures, AoC part 3, Class certification

• Other actions (from MOC):

– Review original Hazid (negative air gap)

• Identify gaps

– Access restrictions

• i.w.o. columns & underhull guiding

• Signs/barriers & PtW

• Adhere to original limits

Assess both integrity & HSE

Implementation of air gap operational limitations

• Content of Internal guidance notes:

– Background/info

– Applicable regulations

– Applicable procedures

– Even keel ballasting

– Analysis results & technical documentation

– Limit curves presented

– Weather forecast; sea states, wave periods

– Example use of curves

• Operational compliance

– How to ensure/achieve?

Definitions & coordinate systems:

Scientific (right hand coordinate system) vs Marine navigators;

e.g. are waves/wind coming from or going to direction?

Generic operational limitations

Location specific limitations

Location specific limitations• Limitations from mooring analysis• Limitations from DP capability analysis• Limitations from riser analysis

• Riser running, operational analysis, conductor analysis, disconnect and recoil, transit with riser/BOP suspended, storm hang-off.

The way forward

Operational dashboard incorporates analyses results

and uses sensor data and weather forecast to calculate the environmental forces and

currently valid operational limitations.

Intention is to provide the operator with tools to assist in decision-making during

challenging and changing operational conditions.

Compliance to governmental requirements

The way forward

• Improve presentation of limitations:

– (In-house) expertise for marine analyses and data management

– Develop dashboard presentation

– Presentation of critical limitations

– Dynamic limitations

• Operational compliance:

– How to ensure/achieve?

• Multi-discipline expertise; academic and operational

• Enhance culture and organisation

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