field development & construction

Field Development & Construction

Michael Cowie

Technical Director

Ecosse Subsea Systems Ltd

Ambient Lifting:A Real Alternative to Heavy Lift Vessels

4th February 2016, AECC, Michael Cowie

Presentation Overview

• Ecosse Subsea Systems

• ESS Ethos

• Installation and Recovery of Subsea Structures Without the Use of

Heavy Lift Vessels

• Ambient Lifting Technology – theory and examples

• Current Project Status

• Summary

Ecosse Subsea Systems

ESS is a Technology Based Company:

• Established in 1996

• 100% Scottish owned

• Initially O & G focused, diversified into Offshore Renewables

• Core business:

Subsea engineering consultancy

Offshore contracting

SCAR Seabed System

Route clearance, pre-cut trenching, backfilling

Technology development and implementation

ESS Ethos

Provision of Subsea Services that are focused on being:

• Safe

• Simple

• Robust

• Cost-effective

Off-the Shelf Components

Installable by local people and vessels

Recoverable, recyclable

Negate the requirement for specialist vessels

Installation and Recovery of Subsea Structures Without the Use of Heavy Lift Vessels

• Image installing a 400Te Foundation utilising Multicat Vessels inextreme environmental conditions……

• Imagine recovering a 600Te+ structure using an Anchor Handlervessel in remote locations……

This can be achieved with Ambient Lifting and Ballast Technology where:

Spread cost is more than halved

Weather risk is significantly reduced

Vessel choice is increased

Ambient Lifting

Ambient Lifting – General Overview

• Ambient lifting is a flexible mechanism that allows you

to control the ascent, descent and underwater

positioning of offshore structures.

• Utilisation of off-the-shelf pressure containment

vessel/receptacle and a mechanism to accurately

control ballast/buoyancy.

• Ambient lifting can be used in a variety of industries

including Oil & Gas, Decommissioning, Offshore Wind,

Wave & Tidal Energy.

• Innovative subsea lifting without use of heavy-lift

vessels.

Ambient Lifting:

Theory Examples

11

Te

250Te

0kg

• In air structural weight

Structure FOUNDATION Example

Low Friction Gel Pig

Liquid Gas

Te

12

250Te

Neutrally Buoyant

250Te

250Te

• In-water structural weight

• Buoyancy in receptacle

designed to ensure structure is

neutrally buoyant


13

Te

250Te

250Te

0-200Te

250Te

• In-water weight increased by adding

ballast material

• Structure sinks to floor in a very

controlled manner


14

Te

250Te

250Te

250Te

200Te

• Gas is replaced or compressed by

fluid

• Now in-water structural weight plus

weight generated by water in

receptacle

• Design ensures sufficient for

temporary stability


15

Te

250Te

250kg

250Te

3 x Wt

=600Te

• Fluid is be replaced by denser fluid

• Fluid has SG = 3.0 and is pump-able

• On-bottom weight is trebled

• Structure is fit for extreme environmental

loading


16

Te

• Reverse process for recovery

• Fluid replaces heavy fluid


17

Te

• Structure is neutrally buoyant

• Structure is returned to surface in a

very controlled manner


Te

18

250Te

Neutrally Buoyant

• Structure on surface

• Can be towed to quayside for recovery


19

Te

300Te

Neutrally Buoyant

• Structure is designed to be buoyant

when flooded with fluid

• Structure is positioned over structure

to be recovered

Structure INSTALLATION / RECOVERY Example

20

Te

• Structure is neutrally buoyant

• Structure encloses over top of structure

and is locked in

300Te


21

Te

• Fluid in receptacle is replaced by gas

• Structure is recovered to surface in a

very controlled manner


300Te

Foundation Installation/Recovery Example

Ambient Lifting – Typical Configuration

Steel Frame (Lower Section)

Lower pipework section

First pipe section loaded to Steel Frame on quayside and secured

Lower section steelwork and pipework loaded in to water

Mass Buoyancy Net Uplift

Second pipework section loaded into Steel Frame in Quayside water


Third pipework section loaded into Steel Frame in Quayside water


Upper steelwork attached to Steel Frame in Quayside water


Bottom third of ABL pipework filled with SG 3.0 fluid prior to tow out.


External ballast added to frame prior to tow out.


Second vessel arrives in the field to assist in ballasting operations.

ABL unit is attached to both vessel winches. The unit is ballasted via the control umbilical until it has a negative buoyancy and both winches are showing a weight of 5-10Te.

Vessels simultaneously pay out on winches to lower the foundation to the seabed.

Upon laydown on the seabed, the ABL unit can be fully water ballasted and then disconnected.

On bottom weight when fully water ballasted with bottom third filled with SG 3.0 fluid

For recovery of unit the removal of heavy fluid from top two HDPE sections gives a net uplift for tow back to port. Reverse Process to installation.

Subsea Structure Recovery Example

Two AHTS vessels are implemented for the removal of the subsea Structure

19m

4m

Lift connection points to be located in Structure600Te

The ABL unit is constrained by tow chains from the vessels.

The ABL unit ballasted down to connect to the Structure.

ABL attached to the Jacket Footing using the mechanical connectors shown on following slide.

Male portion attached to underside of Ambient Lifting frame

Female portion to be placed on the foundation.

Ambient Lifting – Innovative Mechanical Connection Option

Upon connection, buoyancy is added to ABL unit to lift Structure from the seabed.

The unit can be towed by a single vessel to port for decommissioning.

Ambient Lifting – Current Status

• Prototype constructed, 1:10 model

• Test tank procured for ESS Workshop

• Successful prototype trials undertaken

• Trials witnessed by potential Clients

• Secured 1st Project

• Installation of gravity based foundation

• 400Te foundation – on-bottom weight

• Detailed design complete Q4 2015

• Installation Q1/Q2 2016 – using multi-cats in extreme currents

• Evaluating and implementing feedback on system e.g. contingency measures

Ambient Lifting – Detailed Design Renewables

Summary

• Overview of Ecosse Subsea Capabilities

• Ambient Lifting theory has been summarised along with lifting and foundation examples

• Ambient lifting is shown to be a cost effective way of install/recover/relocate small to large subsea structures using:• simple construction methods• local companies/people• local vessels,

• Current status of Ambient Lifting presented for most recent project

• Had hoped to show Case Study of 450Te foundation installation without the use of Heavy Lift Vessel – installation will hopefully be in 2016

Thank you.

Michael Cowie – Technical Director

[email protected]

field development & construction

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