Chapter 20
Interpretation of Marine CSEM and Marine MT Data for
Hydrocarbon Prospecting
Sta ˚le Emil Johansen and Pa ˚l T. Gabrielsen
20.1 Introduction
Remote sensing techniques record variations in
petrophysical parameters such as acoustic or electric
properties. Seismic sounding is by far the most common
of such tools. Seismic techniques can detect strata and
structure in the subsurface that are potential hydrocarbon (HC) traps. By interpreting the seismic a detailed
geological model can be constructed, but seismic data
has limitations in direct prediction of pore fluid composition. Given detection of a structural geometry that
may contain HC within porous sedimentary rocks, the
main remaining uncertainty is normally whether the
pore space is filled with saline water or HC. For this
reason only 10–30% of exploration wells penetrate
commercial oil or gas reserves in many areas.
Controlled source electromagnetic (CSEM) data
has been used for several years for general mapping
of electrical properties of the subsurface. In the late
1990s Statoil scientists Svein Ellingsrud, Terje
Eidesmo and Sta ˚le Johansen developed the use of
the CSEM method for remote identification of
hydrocarbons in a marine setting. The early tests of
the method were positive and in co-operation with
NGI, Statoil established EMGS that further developed
and commercialised the CSEM technique for hydrocarbon exploration.
Controlled source electromagnetic (CSEM) sounding uses EM energy transmitted by a horizontal electric dipole (HED) source to detect contrasts in
subsurface resistivity. Although EM techniques have
been used for many years, detection of subsurface
hydrocarbons by CSEM sounding is still a new discipline within HC prospecting.
A full scale CSEM sounding research test was first
done offshore Angola in 2000 by Statoil, and showed
that the CSEM technique could detect deeply buried
hydrocarbons. The first commercial test was done in
2002 by EMGS on the Ormen Lange Field offshore
Norway. For some time the interpretation of CSEM
data was hampered by the lack of statistically significant calibration data demonstrating that deeply buried
HC accumulations were detectable by the method.
However, development of new equipment opened the
way for improved acquisition, processing and interpretation of CSEM data, and in 2003 the Troll CSEM
data was collected by EMGS. This data was the first
irrefutable evidence for direct detection of a deeply
buried hydrocarbon accumulation by subsea CSEM
sounding. The technique has later shown very good
results when applied correctly in the prospecting work
flow. These results have opened a new frontier in
hydrocarbon exploration.
In recent years different types of CSEM acquisition
have evolved including horizontal dipole source with
seabed nodes, horizontal dipole source with cable
towed receivers, and vertical dipole source with seabed
nodes. Here we will describe the seabed node receiver
method using a horizontal towed dipole source.
The marine magnetotelluric method (MMT) is
another offshore geophysical method measuring subsurface resistivity. This method is using the Earth’s
S.E. Johansen (*)
NTNU, Trondheim, Norway
e-mail: stale.johansen@ntnu.no
P.T. Gabrielsen
EMGS (ElectroMagnetic GeoServices ASA), Trondheim,
Norway
e-mail: ptg@emgs.com
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_20, # Springer-Verlag Berlin Heidelberg 2015
515
Interpretation of Marine CSEM and Marine MT Data for
Hydrocarbon Prospecting
Sta ˚le Emil Johansen and Pa ˚l T. Gabrielsen
20.1 Introduction
Remote sensing techniques record variations in
petrophysical parameters such as acoustic or electric
properties. Seismic sounding is by far the most common
of such tools. Seismic techniques can detect strata and
structure in the subsurface that are potential hydrocarbon (HC) traps. By interpreting the seismic a detailed
geological model can be constructed, but seismic data
has limitations in direct prediction of pore fluid composition. Given detection of a structural geometry that
may contain HC within porous sedimentary rocks, the
main remaining uncertainty is normally whether the
pore space is filled with saline water or HC. For this
reason only 10–30% of exploration wells penetrate
commercial oil or gas reserves in many areas.
Controlled source electromagnetic (CSEM) data
has been used for several years for general mapping
of electrical properties of the subsurface. In the late
1990s Statoil scientists Svein Ellingsrud, Terje
Eidesmo and Sta ˚le Johansen developed the use of
the CSEM method for remote identification of
hydrocarbons in a marine setting. The early tests of
the method were positive and in co-operation with
NGI, Statoil established EMGS that further developed
and commercialised the CSEM technique for hydrocarbon exploration.
Controlled source electromagnetic (CSEM) sounding uses EM energy transmitted by a horizontal electric dipole (HED) source to detect contrasts in
subsurface resistivity. Although EM techniques have
been used for many years, detection of subsurface
hydrocarbons by CSEM sounding is still a new discipline within HC prospecting.
A full scale CSEM sounding research test was first
done offshore Angola in 2000 by Statoil, and showed
that the CSEM technique could detect deeply buried
hydrocarbons. The first commercial test was done in
2002 by EMGS on the Ormen Lange Field offshore
Norway. For some time the interpretation of CSEM
data was hampered by the lack of statistically significant calibration data demonstrating that deeply buried
HC accumulations were detectable by the method.
However, development of new equipment opened the
way for improved acquisition, processing and interpretation of CSEM data, and in 2003 the Troll CSEM
data was collected by EMGS. This data was the first
irrefutable evidence for direct detection of a deeply
buried hydrocarbon accumulation by subsea CSEM
sounding. The technique has later shown very good
results when applied correctly in the prospecting work
flow. These results have opened a new frontier in
hydrocarbon exploration.
In recent years different types of CSEM acquisition
have evolved including horizontal dipole source with
seabed nodes, horizontal dipole source with cable
towed receivers, and vertical dipole source with seabed
nodes. Here we will describe the seabed node receiver
method using a horizontal towed dipole source.
The marine magnetotelluric method (MMT) is
another offshore geophysical method measuring subsurface resistivity. This method is using the Earth’s
S.E. Johansen (*)
NTNU, Trondheim, Norway
e-mail: stale.johansen@ntnu.no
P.T. Gabrielsen
EMGS (ElectroMagnetic GeoServices ASA), Trondheim,
Norway
e-mail: ptg@emgs.com
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_20, # Springer-Verlag Berlin Heidelberg 2015
515