52 Offshore December 2013 • www.offshore-mag.com
ASIA/PACIFIC
Patience pays off for Macedon partners
Field provides vital domestic gas supply
while region gears up for LNG megaprojects
In August, BHP Billiton turned on the taps at the Macedon gas development, a four-well subsea tieback to an onshore plant near Onslow, Western Australia. Thefeld, inthe Exmouthbasin WA-42-L
lease area, is in water depths of 170-180 m
(558-591 ft) and is estimated to hold between
400 and 750 bcf in recoverable reserves – a
small feld, relative to the LNG megaprojects nearby, but one that is expected to feed
as much as 20% of the state’s daily gas demand. And in many respects, the $1.5-billion
project was a milestone for BHP Billiton.
It was also a long time coming. BHP Bil-
liton, operator of the WA-42-L block, which
includes the Pyrenees FPSO project, made
the gas discovery in 1992; sanction would
wait nearly two decades. “This was our third
attempt to commercialize Macedon gas,”
says Garry Walker, who was BHP Billiton’s
Macedon project director before recently re-
locating to Houston to serve as senior man-
ager of shale projects. The problem was the
gas itself: lean, with 94% methane content
and no ethane, characteristics that made it
ineligible under the regulations at the time
to travel through the Dampier to Bunbury
Natural Gas Pipeline, WA’s main transmis-
sion route. “The heating value didn’t meet
the pipeline requirements,” Walker says.
“To get our gas into that pipeline, we needed
the regulations governing what could be
carried through that pipeline to be changed,
and they were changed in 2009. That really
was the green light for Macedon.”
The regulations were changed in the
aftermath of the 2008 explosion at Apache
Corp.’s Varanus Island gas plant, which cut
off about 30% of WA’s domestic gas sup-
ply for several months. “The government
rightly recognized that it was a good idea
to have some depth in supply, and there we
were with Macedon. Macedon gas was the
only new gas that could come on in this pe-
riod between 2010” and the startup of WA
production from big LNG projects such as
Gorgon, Wheatstone, and Pluto for domestic
use, Walker says.
With one hurdle out of the way, there still
remained the task of getting the gas from
the feld to the Dampier to Bunbury line.
BHP Billiton had a plant in the area – the
idle Griffn Gas Plant – but there was little
else in the way of infrastructure at the pro-
posed landfall, south of Onslow. Macedon
is about 100 km ( 62 mi) offshore; BHP Bil-
liton considered bringing the gas ashore at
the nearest landfall, the town of Exmouth.
But the area lies in a protected zone around
the World Heritage-listed Ningaloo Marine
Park.
“We looked at an offshore platform,”
Walker says. “But the feld is quite spread
out, so we’d still need subsea tieback to the
platform, and the cost was prohibitive. It’s a
relatively small accumulation, quite a long
way away. The beneft of building a plat-
form would be that we could downsize the
pipeline, but the platform cost outweighed
the benefts.” The company also considered
developing Macedon as a tieback to the Pyr-
enees feld, which is in a different geological
structure, but opted instead to bring the gas
directly to shore.
“Once we decided on the subsea tieback
to the beach, we looked at either control-
ling it from the beach, through an extended
reach umbilical, or to have a local buoy,”
Walker explains. “And based on the envi-
ronmental and safety risks associated with
having surface facilities out on the ocean in
a cyclone-impacted area, we decided to go
with the extended reach umbilical – 66 km
[ 41 mi] single length of umbilical, tied into a
13-km [8-mi] nearshore umbilical.”
BHP Billiton and its WA-42-L partner,
Apache Corp., submitted a plan to WA au-
thorities that included a pipeline route tra-
versing the shortest distance to shore. But
there was a hitch, in the unassuming guise
of an endemic species of cowry found only
in a stretch of the Indian Ocean next to Peak
Island, where the proposed route would
run. “So we had the choice of managing our
impact on that species of shellfsh, or mov-
ing the pipe. We moved the pipe, and took
a more northerly route, which got us into
deepwater quicker, and then we doglegged
across.” The change meant an additional 3
km ( 1. 9 mi) of pipe and umbilicals would
be needed. Oceaneering was contracted to
provide umbilicals, related hardware, and a
subsea pig launching system (see sidebar).
Cameron supplied the Macedon trees and
subsea control system; the fowlines were
Russell McCulley
Senior Technical Editor
A map of the Macedon project, a joint venture of BHP Billiton (operator, 71.43%) and Apache
Northwest ( 28.57%).
