trunkline - Woodside

Making scents
Oil and gas exploration could be
described as a blind man’s game.
We can’t actually see what is below
the surface, so we have to use other
“senses” to predict where there may
be hydrocarbons.
Over the past 90 years we have
become very good at “listening”
through seismic surveys for the
geological conditions where
hydrocarbons might be. Now there
is another sense that Woodside is
using to discover hydrocarbons and
subsequently monitor them.
Controlled Source ElectroMagnetics
(CSEM or EM) is a new technique that
effectively “sniffs out” hydrocarbons.
Through Woodside’s Strategic
Technology Plan, senior geophysicist
Andrew Lockwood has been working
on CSEM – understanding how to best
use it and how to interpret and display
the data so it is easily read by our
geoscientists and reservoir engineers.
“CSEM is like smell because the
physics of smell is all about diffusion
and with EM we are measuring the
diffusion of the electromagnetic
signal through the earth, whereas
the physics of seismic is all about
reflection,” Andrew says. “That’s
why we can’t form an image with
EM like we can with seismic, but it
can give us information that seismic
can’t.”
Seismic can indicate the structure
of a reservoir, but isn’t as clear as
Whiff of success: Senior geophysicist Andrew Lockwood, Greater Western Flank
subsurface manager Tom Ridsdill-Smith and vice president reservoir development
Tammie Sebire get a clearer picture
8 trunkline | Q1 2011
to what might be in the reservoir.
CSEM surveys measure how quickly
an electro-magnetic signal passes
through the earth, so it can indicate
the presence of hydrocarbons (which
give out a strong signal as they are
natural insulators) or water (which the
signal will travel through slowly as it is
a conductor).
The surveys are acquired by towing a
transmitter sending out high-powered,
low frequency electromagnetic radio
waves close to electric and magnetic
field antennae placed on the seafloor.
The antennae are incredibly sensitive
– they can detect 0.0000000001V
– so not only can a survey indicate
the presence of hydrocarbons, it can
indicate the ratio of hydrocarbons to
water for example. This has obvious
benefits for exploration, but may be an
even more powerful tool for reservoir
monitoring.
“When you extract oil and gas from a
reservoir, water flows in to replace the
hydrocarbons,” Andrew says. “There
is a point at which the water enters the
producing wells, and you need to have
the facilities installed to deal with it.
That’s a very significant investment in
CAPEX, which you don’t want to make
earlier than you need to.
“We can use CSEM to spot early water
movement because it is so sensitive.
Seismic can spot water, but can’t
detect how much. When you combine
the two techniques, seismic and EM
are incredibly powerful.”
of oil and gas
To get an idea of how sensitive it is, if
0.0000000001V is equivalent to the
height of a person, 1V is the equivalent
of the distance to the sun. That means
it can pick up a lot of noise, and how
to filter that out is part of our learning
curve. “We are basically using labgrade
equipment in one of the most
hostile environments in the world,”
Andrew says.
Woodside, which is already an
accomplished user of 4D (time lapse)
seismic surveys, will be one of the first
companies in the world to conduct 4D
CSEM surveys for reservoir monitoring.
Elsewhere CSEM has been used as an
exploration tool – particularly to narrow
down exploration drilling where there
may be a large number of prospects.
Woodside chief geophysicist Tom
Ridsdill-Smith says Woodside is taking
the right approach in investing in this
technology early.
“We conducted trials over Pluto prior
to production start-up and have a lot
of experience in exploration CSEM,”
Tom says. “Both seismic and CSEM
can throw up false positives and
negatives, but when you have the two
techniques saying the same thing, you
are likely to be onto something as they
are measuring completely different
properties.”
Tammie Sebire, vice president of
reservoir development, is also excited
about CSEM’s potential.
“We are at the forefront of using
CSEM for reservoir monitoring and
that’s where we need to be right
now,” Tammie says. “This is an area
of technology where getting a baseline
is extremely important and so you
have to effectively preinvest. It is
very exciting because it gives us the
potential to save CAPEX in the future
by understanding our reservoirs better
to enable effective decision making.”
Woodside will follow up the baseline
CSEM surveys on Pluto with more
CSEM surveys once production starts.
CSEM research is being partially
funded through Woodside’s Strategic
Technology Plan which aims to
respond to the challenges and
opportunities facing Woodside now
and in the future.