The wonders of Wheatstone - atteris.com.au · On the overall Wheatstone Project timeline, the shore...
Transcript of The wonders of Wheatstone - atteris.com.au · On the overall Wheatstone Project timeline, the shore...
and construction of the tunnel. Atteris was
also involved with providing engineering
support throughout the execution phase
of the shore crossing, as well as for the
trunkline and flowline phases elsewhere in
the Wheatstone Project.
Upon completion at the end of 2013,
the shore crossing set new benchmarks in
Australia, It is both the first microtunnelled
shore crossing in the oil and gas industry
and the longest pipe-jacked tunnel in the
Southern Hemisphere to date. The project
had a very short duration of eight months
from mobilisation to demobilisation, with
daily advance rates of 55 m achieved in two
ten-hour shifts.
“The microtunnelling method had never
been used as a conduit across a shoreline
to pull a trunkline through within Chevron,
or indeed within the oil and gas industry in
Australasia,” said the Chevron spokesperson.
Deciding on microtunnellingDuring the early stages of the Wheatstone
Project’s assessment process, a number of
options were considered for the trunkline
shore crossing, including open trenching,
rock groyning, above ground shore-
pulling, horizontal directional drilling (HDD)
and microtunnelling.
“For each shore crossing option,
senior Chevron decision-makers carefully
considered Chevron’s key commitment
to reduce potential impacts to the
environment alongside the logistical, cost,
schedule and technical considerations,”
said the Chevron spokesperson.
Examples of such considerations included
the size of the Wheatstone trunkline
(44 inch), as well as the very shallow
water depth along the Onslow nearshore
area (a pipelay barge was unable to come
within several kilometres from the beach,
for example). These factors steered Chevron
to pursue microtunnelling for the shore
crossing. Microtunnelling was favoured
over HDD because, compared to HDD,
the technique was deemed less sensitive
to difficult geotechnical conditions. Other
potential major HDD risks included the very
large diameter open borehole (in combination
with the length of an HDD), the possibility of
borehole collapse, the volume of drilling
fluid release and a complex interaction with
offshore construction equipment.
“Based on these circumstances,
microtunnelling was recognised as
an innovative solution and the senior
management team selected it as the preferred
option,” said the company spokesperson.
Environmental benefitsThe microtunnelling methodology for
the shore crossing delivered a number
of environmental benefits without
compromising safety or constructability.
These benefits included avoiding a
physical surface presence, reducing the
need to access mangroves or beaches,
greatly reducing both onshore and marine
disturbance footprints, avoiding potential
sediment disturbance activities in the highly
dynamic and sensitive Ashburton Delta,
removing the need for machinery on the
surface of the shore crossing, and reducing
risk associated with leaks and spills.
“In selecting the method for the shore
crossing, the primary environmental
considerations were the potential impacts
on the Ashburton River Delta and its
habitats, and the potential impact on
coastal processes,” commented the
Chevron spokesperson.
THE MULT I - B I L L ION -DOLLAR
WHEATSTONE PROJECT is a flagship
project in Australia’s liquefied natural
gas (LNG) industry. Developed following
an extensive period of environmental
assessment and community engagement
– including liaising with local government,
independent experts and local communities
– the project’s planning and construction
is being carried out with explicit attention
to minimising impacts to the surrounding
environment and native wildlife.
Recognising these important values,
Chevron commissioned a technically
impressive microtunnelling campaign at the
project’s shore crossing – connecting the
onshore and offshore segments of the
development via a 1.2 km pipe jacked
tunnel. Completed in only eight months, the
project achieved many milestones and sets
a new standard for Trenchless Technology
in the oil and gas industry.
Project backgroundLocated near Onslow in the Pilbara Region,
the Chevron-operated Wheatstone Project
is now in its fourth year of construction.
At almost 60 per cent complete, first gas
is expected by late-2016. Wheatstone’s
onshore LNG and domestic gas plants will
be fed from four offshore natural gas fields.
Gas will be gathered using subsea wells
and manifolds and transported via flowlines
to the offshore Wheatstone Platform.
The platform will partially treat gas and
condensate and transport it to onshore
processing facilities via the newly-installed
225 km trunkline (pipeline). The 112 cm
diameter trunkline, Australia’s largest
diameter gas pipeline, passes through a
1.2 km long microtunnelled and pipe jacked
shore crossing.
Called the “critical link” by a Chevron
spokesperson, the use of microtunnelling
provided an innovative and cost-effective
solution to cross the shoreline by tunnelling
under the coastal environment to reduce
impacts. The shore crossing begins behind
the coastal dune system, extends seaward
and terminates under the ocean floor.
For the crossing’s design and installation,
Chevron tapped Australian companies
including Perth-based subsea and pipeline
consultancy Atteris for the concept
development and front-end engineering
design (tunnel), and Thiess Tunnelling – now
Leighton Tunnelling – for the detailed design
Innovative use of microtunnelling on Chevron Australia’s Wheatstone Project smashes industry records
and minimises environmental effects.
ThewondersofWheatstone
“The microtunnelling method had never been used as a conduit
across a shoreline to pull a trunkline through within Chevron,
or indeed within the oil and gas industry in Australasia.”
Aerial view of the microtunnel exit pit.
Computer rendering of the tunnelling installation.
PROJECT UPDATE
Click here to watch the
First Quarter 2015 update
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Wheastone Project
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On the overall Wheatstone Project timeline,
the shore crossing tunnel was one of the
earliest scope items for the project because
it needed to be installed prior to the trunkline
installation and during the weather window
of May-November 2013. According to
Chevron, missing this 2013 weather window
would have pushed the trunkline installation
out by one year, which could have impacted
the project time schedule.
The microtunnel execution team, led by
Thiess Tunnelling (Leighton Tunnelling) used
an innovative tunnelling method and shaft
design which allowed the team to pipe-jack
three pipes in a complete push, reducing
the number of times service pipes had to
be manually handled and improving cycle
times – something relatively uncommon in
pipe-jacking. Additionally, by utilising the
latest and most advanced microtunnelling
guidance system, the tunnelling team was
able to drive the tunnel to within 135 mm of
the design location.
“This was an excellent result considering
the specification requirements were
to finish within 1,000 mm,” said the
Chevron spokesperson.
Thiess Tunnelling (Leighton Tunnelling)
also designed a special lifting mechanism
for the rotation of the concrete pipes and
the movement of the jacking pipes around
the project site.
“The rotation of the concrete pipes was
a safety risk that required an engineering
solution,” continued the spokesperson.
“Together with the supplier, Thiess
Tunnelling designed a clamp that meant
that the concrete pipes could be rotated
in a controlled manner without the use of
multiple cranes.”
For the movement around site, a specific
set of forks and lever was designed. This
allowed the concrete pipes to be moved
around the site easily and be picked up
and placed in a controlled manner, thus
reducing the risk of working at heights and
men next to moving equipment.
Following the tunnelling procedure,
the team formed a partnership with
Independent Offshore Solutions (IOS) to
develop a new methodology for recovering
the Herrenknecht-supplied tunnel boring
machine (TBM) from the ocean floor.
According to a Herrenknecht spokesperson,
recovering TBMs from oceans is difficult
due to their size, with the feat only achieved
about a dozen times in the world.
A watershed trenchless project“Completed within a short turnaround
and with surgical precision, the scope and
ambition of the Wheatstone Project’s shore
crossing microtunnelling work illustrates
what can be achieved when a collaborative
approach brings together the community,
government and industry to work on
innovative and mutually beneficial solutions,”
concluded the Chevron spokesperson.
“The innovative application of
microtunnelling technology demonstrated
that with the appropriate level of
commitment, passion and responsibility,
we can safely access and develop much
needed energy resources while minimising
environmental impacts and preserving
important habitats.”
“The development of the entire shore
crossing concept, including selection of
microtunnelling as a method, defining the
tunnel entry/exit points and alignment,
design of the subsea exit pit, the pipeline
within the tunnel, and the pipeline cathodic
protection, are all ground-breaking
innovations in their own right.”
Looking ahead, microtunnelling for shore
crossings of this scale – and in such
delicate environments – is now a proven
technology and could be implemented
globally, both by Chevron and the wider oil
and gas industry.
With the trunkline needing to cross
the shoreline at the lagoon system at the
eastern entrance to the Ashburton River,
the decision to use microtunnelling
technology was based on extensive
research showing the environmental
objectives of protecting coastal processes,
the creek system, mangrove habitats and
listed species could be achieved.
“As evidenced by the environmental
monitoring results pre- and post-
construction, the decision to tunnel under
this area significantly reduced potential
impacts to this environment, while still
providing a solution that met Wheatstone
requirements, continued the spokesperson.
“Ultimately, the decision to construct
a microtunnel underneath the sensitive
chenier and lagoon system demonstrated
excellent environmental outcomes.”
Project timelineThe concept and front-end engineering
design of the shore crossing tunnel
was performed from 2010-2011 by a
combined Chevron/Atteris team. Chevron
subsequently awarded the microtunnelling
contract to Thiess Tunnelling (Leighton
Tunnelling) in January 2012, with work
beginning onsite in April 2013. The tunnel
was completed in October 2013 and the
site was demobilised two months later
in December.
Key Wheatstone shore crossing facts
Total tunnel length: 1,242 m
Tunnel pipe material: Reinforced concrete
External tunnel pipe diameter: 2.5 m
Internal tunnel pipe diameter: 2 m
Tunnel pipe segment length: 3 m
Number of tunnel pipe types: 6
Tunnel pipe segment weight: 12-16 tonnes
Bird’s-eye view of the shoreline crossing
showing the nearby Ashburton Delta.
The Herrenknecht-supplied tunnel boring machine was later retrieved from the ocean floor following
the tunnel procedure.
Close-up of the microtunnel construction area.
The decision to use microtunnelling technology was based
on extensive research showing the environmental objectives
of protecting coastal processes, the creek system, mangrove
habitats and listed species could be achieved.
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