Marine EM, the Past, the Present, and the Future

Steven Constable

Scripps Institution of Oceanography

Acknowledgements

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Marine EM, the Past, the Present, and the Future

Steven Constable

Scripps Institution of Oceanography

On Tuesday 17th August, 2004 the front page of the Wall Street Journal had a lead article about a new geophysical technique. Marine CSEM was suddenly in the news…

On Tuesday 17th August, 2004 the front page of the Wall Street Journal had a lead article about a new geophysical technique. Marine CSEM was suddenly in the news…

… except is wasn’t new. Over 23 years earlier an oceanographer called Charles Cox had suggested marine CSEM for hydrocarbon exploration…

On Tuesday 17th August, 2004 the front page of the Wall Street Journal had a lead article about a new geophysical technique. Marine CSEM was suddenly in the news…

… except is wasn’t new. Over 23 years earlier an oceanographer called Charles Cox had proposed using marine CSEM for hydrocarbon exploration…

… to Exxon.

Outline:• Basics of the EM methods• Early history of marine EM• Commercialization• 10 things you need to know• The future

grounded wire (E)

horizontal loop (B) Ex

By

Bz

Bx

Ey

Transmitters Receivers

I

V

V

I

Controlled Source ElectroMagnetic sounding has been used since the 1930’s to map sub-surface geology through the proxy of electrical conductivity. On land it is mainly used for mining exploration (shallower, conductive ore bodies), but has been used for map geological structure for oil exploration.

What is CSEM?

Natural-source Magnetotelluric fields

grounded wire (E)

horizontal loop (B) Ex

By

Bz

Bx

Ey

Transmitters Receivers

I

V

V

I

CSEM is related to another EM technique called MagnetoTelluric (MT) sounding, which uses similar receivers to measure Earth’s natural magnetic field variations and the induced electric currents. MT signals are either part of a useful complementary method or a source of noise for CSEM.

What is MT?

Both can be used in the marine environment:

100-300 m dipole,100-1000 amps

25-100 m

CSEM Transmitter

Oil, Gas (resistive)

Seawater (very conductive)

Air (resistive)

Salt, carbonate,volcanics (resistive)

Natural-source Magnetotelluric fields

Electric and magnetic field recorders

Seafloor (variable conductivity)

Marine CSEMmore sensitive to

resistive rocks

Marine MTmore sensitive toconductive rocks

But both methods can detect contrasts

Both MT and CSEM sounding use electromagnetic induction, which describes what happens around a time-varying primary magnetic field: primary magnetic

field

Faraday’s Law says that a time varying (or moving) magnetic field will induce electric fields:

( is magnetic flux).

CE · dl = d

dt

primary magnetic field

electric field

Faraday’s Law says that a time varying (or moving) magnetic field will induce electric fields:

( is magnetic flux).

Ohm’s Law says that E will generate a current J in a conductor:

CE · dl = d

dt

J = E

primary magnetic field

electric field and current

Faraday’s Law says that a time varying (or moving) magnetic field will induce electric fields:

( is magnetic flux). Ohm’s Law says that E will generate a current J in a conductor:

Ampere’s Law says that the current will generate a secondary magnetic field:

CE · dl = d

dt

CB · dl = µI

J = E

primary magnetic field

electric field and current

secondary

magnetic

field

The secondary field opposes the changes in the primary field. The consequence of this is that conductive rocks absorb variations in EM fields more than resistive rocks.

Half-space

Depth —

>

The secondary field opposes the changes in the primary field. The consequence of this is that conductive rocks absorb variations in EM fields more than resistive rocks.

This absorption is exponential:

The rate of absorption is given by the skin depth, which depends on rock resistivity and period:

High resistivity, long periods = large skin depths, greater penetration.

Low resistivity, short periods = small skin depths, greater attenuation.

E(z) = Eoez/zs

Half-space

Depth —

>

Secondary fields are different in amplitude, phase, and direction than the primary magnetic and electric fields. Electric fields can also be distorted galvanically, as in DC resistivity methods.

CRIP

PS I N

ST

ITUTION OF OCEANOGRA

PHY

UCSD

Primary fields

Secondary fields

Induced magneticfields

Galvanic distortion of electric currents

water

sediments

mantle

basaltic melt

ice, hydrate

hydrocarbons

basalt, salt,carbonates

marine

lower mantle

0.1 1

110 0.1 0.01 10-3 10-4

10Resistivity, Ωm

Conductivity, S/m

100 1,000 10,000

10%

0°C20°C

1%3%

peridotite

partial melt

land14

00°C

1200

°C110

0°C

seawater fresh water

MT and CSEM are methods to measure electrical conductivity. Conductivity varies over 5 orders of magnitude in common Earth materials, and provides the ideal mechanism for studying fluids, water, and geology, including hydrocarbons.

The Past

GEOPHYSICS, VOL 18, NO. 3 (JULY 1953), P. 605-635.

Interestingly, Cagniard proposed adaption to the marine environment in the 1953 paper that first presented the MT method.

Tucson mag

seafloor mag

seafloor E

Charles (Chip) Cox and Jean Filloux of Scripps Institution of Oceanography made the first marine MT measurements in 1965, in 4300 m water offshore California.

Cox, Filloux, and Larsen, 1968

Charles Cox

Jean Filloux

Tucson mag

Theory pre-dates practice, but even so marine CSEM is a young field. The earliest marine CSEM work was carried out by the British and US navies. This 1968 paper out of the US Navy Underwater Sound Lab appears to be the first proposal for marine CSEM as we now know it.

The same Chip Cox (1922-2015) developed practical deepwater CSEM in the early 1980’s, partly under funding by DARPA to improve understanding of seafloor communications, and ONR for submarine noise studies.

In 1979 Chip carried out an experiment in nearly 3,000m water with transmissions of 80 amps on an 800 m antenna. Frequencies of 0.25 - 2.25 Hz were detected 19 km away. His target was a mid-ocean ridge.

Young and Cox, 1981

Transmitter

Tow cable

Receiver

Cox et al, 1981

Electrodes

Antenna

Remarkably, within 2 years, in March 1981, Chip proposed the CSEM method for oil exploration to Exxon:

In the proposal, Chip explicitly described the direct detection of a hydrocarbon reservoir.

Fields measured 2500 m from a 104 Am CSEM transmitter

I checked Chip’s calculations and they are basically correct. However, the proposal was declined - Chip was too far ahead of the times.

Fields measured 2500 m from a 104 Am CSEM transmitter

10−1

100

101

10210

−1

100

101

102

Hz

Am

plitu

de (

nV

/m)

Meanwhile, in the late 1980’s Martin Sinha of Cambridge (later Southampton) developed a UK CSEM capability based on Scripps’, but with an “flown” transmitter capable of working over mid-ocean ridges.

(From Sinha et al, 1990)

Current industry funding for marine EM started in 1995 in order to develop MT imaging of salt in the Gulf of Mexico. Clearly, the price of oil was not a factor (adjusted for inflation, 1998 was the lowest price in history).

What drove interest in such an expensive, non-seismic method?NW

SW

Conductive (0.3 Ohm-m)

Resistive (4 Ohm-m)

4 k

m6 k

m

2 km

1 km

thin resistive layerthin resistive layer overhangoverhang

NW

SW

Conductive (0.3 Ohm-m)

Resistive (4 Ohm-m)

4 k

m6 k

m

2 km

1 km

thin resistive layerthin resistive layer overhangoverhang

First, the seismic method was having great difficultly imaging beneath salt…

Current industry funding for marine EM started in 1995 in order to develop MT imaging of salt in the Gulf of Mexico. Clearly, the price of oil was not a factor (adjusted for inflation, 1998 was the lowest price in history).

What drove interest in such an expensive, non-seismic method?

NW

SW

Conductive (0.3 Ohm-m)

Resistive (4 Ohm-m)

4 k

m6 k

m

2 km

1 km

thin resistive layerthin resistive layer overhangoverhang

But probably the biggest factor was the development of the tension leg platform, which enabled production of oil and gas from deepwater prospects…

… but deepwater drilling is very expensive.

Current industry funding for marine EM started in 1995 in order to develop MT imaging of salt in the Gulf of Mexico. Clearly, the price of oil was not a factor (adjusted for inflation, 1998 was the lowest price in history).

What drove interest in such an expensive, non-seismic method?

Commercial marine MT was offered starting in 1996. The first oilfield CSEM tests were done in late 2000 - early 2002, by Statoil and ExxonMobil. They both used Scripps receivers and the Southampton transmitter.

Again, the driver was the high cost of drilling combined with limitations in the seismic method.

First oilfield CSEM surveys, Angola

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

20

40

60

80

100

120

140

160

180

Year

We

lls;

Oil p

rice

Gulf of Mexico, wells >1,000 m water depth and oil price

Wells drilled

Oil price, nominal $

First Scripps industry funding

starts

First Scrippsindustry funding

stops

Current industryfunding starts

0 0.10.4

0.8

1.2

1.6

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Gas saturation

P-w

ave

velo

city

, km

/s

Seawater/gas in 50% porous sandstone

Velocity

Fizz-gas

Archie’s with fizz-gas

The seismic method has the problem that small gas saturations produce big velocity changes.

0 0.10.4

0.8

1.2

1.6

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1100

101

102

103

104

Gas saturation

Res

istiv

ity, Ω

m, l

og s

cale

P-w

ave

velo

city

, km

/s

Seawater/gas in 50% porous sandstone

HS lower bound

Arc

hie

’sVelo

city

Fizz-gas

Least resistivity contrast easily

detected with EM

Archie’s with fizz-gas

However, electrical resistivity does not change until the gas saturation gets large. This means that marine CSEM can be used to assess targets prior to drilling.

Air

Sea

Sediment

movie © Kerry Key, SIO.

Oil and gas reservoirs are too thin to be sensed with MT - now we need to use a man-made source of energy. Again, EM energy propagates best through the more resistive rocks.

In this movie, the electric fields are absorbed more rapidly in seawater:

Air

Sea

Sediment

Oil layer

If we add a thin resistive layer to the model (an oil or gas reservoir?), then energy propagates even better through this layer than the surrounding sediments.

Then we add a transmitter and receivers to actually collect these data.

CRIP

PS IN

ST

ITUTION OF OCEANOGRAPHY

UCSD

movie © Kerry Key, SIO.

The effect can be up to an order of magnitude for a large oil or gas reservoir. This is what I call the “canonical model”, and is similar to the target chosen by Statoil for the first test of the marine CSEM method, and very similar to the model that Chip used in his proposal.

0 2 4 6 8 10

10 -14

10 -12

10 -10

10 -8

Source-receiver offset, km

In-li

ne e

lect

ric fi

eld,

V/m

/(Am

)

oil, gas

no oil, gas

1000 m, 0.3 Ωm

1000 m, 1 Ωm

100 m, 100 Ωm

E-field amplitudes larger overhydrocarbon reservoirs

Statoil’s tests were made in November 2000 over the Girasoll oil field off Angola:

-6000 -4000 -2000 0 2000 4000 6000 N 10

-15

10-14

10-13

10-12

10-11

10-10

Radia

l E

lectr

ic F

ield

, (V

/m)/

(sourc

e d

ipole

mom

ent)

Source-Receiver Offset, m

InfiniteReservoir

No Reservoir

Terminating Reservoir

Oil Reservoir

V

10

5

15

20

25

30

35

50 10 15 20 21

tow A

approximate extent of reservoir

Distance East (km)

Dis

tanc

e N

orth

, (km

)

http://www.oilpro.com/

Constable and Srnka, 2007

Over a known discovery

Prior to drilling

Constable and Srnka, 2007

Similar studies were carried out by ExxonMobil in Jan 2002, also off Angola.

These studies used 30 new instruments designed and built by Scripps for ExxonMobil, operated by AOA Geophysics.

Brine Filled

Distance East (km)

noise level

00

3

6

9

12

15

3 6 9 12 15 Distance (km)0 3 6 9 12 15

10-15

10-14

10-13

10-12

10-11

10-10

Radi

al E

lect

ric F

ield

, (V/

(Am

2 ))

Oligocene HC FilledMio + Olig HC Filled0.25 Hz Data

Rotated Inline E FieldReceiver 21, Tow Line 3Oligocene

Miocene

Salt

Salt

tow 3

well

receiver 21

Dist

ance

Nor

th (k

m)

Distance along line (km)

noise level

0 3 6 9

Distance (km)

0

0

3

3

6

6

9

9

12 1512 15

10-15

10-14

10-13

10-12

10-11

10-10

No

rma

lize

d f

ield

(V

/(A

m2

) )

Backgound

With Reservoir

2 min. Stacked Data

Inline E Field, 0.25 Hz

Receiver 21, Tow Line 2

Salt

tow 2Well B

Well A

receiver 21

seismic O/W

contact

reservoir limits

Dis

tan

ce

(km

)

At least 3 main contractors offering marine EM data collection and interpretationservices

Then things got interesting...

By the end of 2002 three contractors were formed to offer marine MT/CSEM as a commercial product.

Several special-purpose ships have been built since then.

Much based on early academic science and technology.

Since then more companies have joined the party…

The Present10 things you should know about marine CSEM

that are not likely to change

1. EM does not map oil or gas, or even rock type. We cannot tell the difference between an evaporite, a basalt, or an oil sand based on resistivity alone.

-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

pyrrhotite

graphite

groundwater

clays

evaporites

drywet

drywet

intrusive igneous rocks

basalts/lavas

quartz

limestones

sandstones, quartzites

seaw

ate

r

OIL SANDS

Log 10 (Resistivity, Ωm)

Resistivity of Rocks and Minerals (Data from Telford et al.)

Thus, to manage false positives you need additional data - seismics, geology, magnetics, gravity, … Integration with other data sets is perhaps the only safe way to use marine EM data.

2E = µEt

+ µ2Et2

2E = 0

Radar

DC Resistivity

High frequency(megahertz)

Mid frequency(0.001 - 1000 Hz)

Zero frequency

2. The resolution of EM induction is between wave propagation and potential fields:

2E = µEt

r2U = 0

r2u = @u

@t+

1c2

@2u

@t2

Wave equation: Resolution ~ wavelength

Diffusion equation: Resolution ~ size/depth

Laplace equation: Resolution ~ bounds only

µ

= electrical conductivity ~

= magnetic permeability ~ = electric permittivity ~ 109 1011

104 106

3 106 S/mH/m

F/m

Inductive EM

Seismics

Gravity/Magnetism

E(z) = Eoez/zs+i(tz/zs)

zs =

2/µ

3. Frequency is too low for wave propagation in rocks, but does constrain length scale through skin depth :zs

2E = µEt

At a single frequency becomes 2E = iµE

which for uniform fields has solutions of the form

where we have defined a skin depth

For every skin depth the fields decay by 1/e (~37%) and phase lags by one radian (~57°).

= 2f( )

In 1 Ωm sediments:

frequency skin depth0.1Hz 1,600 m0.25 Hz 1,000 m1.0 Hz 500 m5.0 Hz 225 m

degrees

degrees

degrees

degrees

7785

7790

7795

7800

7805

7810

7815

7820

7825

7830

Nort

hin

g, km

3000m, Erad

0.25Hz

N = 623 rms = 4°

−90

−80

−70

−60

−50

−40 3000m, Erad

0.75Hz

N = 642 rms = 3°

−190

−180

−170

−160

−150

−140

710 720 730 740 750 760

7785

7790

7795

7800

7805

7810

7815

7820

7825

7830

Easting, km

Nort

hin

g, km

3000m, Erad

1.75Hz

N = 602 rms = 5°

−330

−320

−310

−300

−290

−280

710 720 730 740 750 760

Easting, km

3000m, Erad

3.25Hz

N = 348 rms = 8° −460

−450

−440

−430

−420

−410

Although you need a low enough frequency to reach your target, sensitivity can increase with frequency (Eradial, 3,000 m, phase):

0.25 Hz 0.75 Hz

1.75 Hz 3.25 Hz

(But your signal size gets smaller.) These are data over the Scarborough gas field offshore NW Australia, collected by Scripps with support from BHP Billiton.

Single frequency - 0.25 Hz

Single frequency - 0.75 Hz

Multiple frequencies

Single frequency - 1.75 Hz

4. Good inversion technology is key to getting the most out of EM data, and inversions of multiple frequencies are much better than single frequency inversions.

10−1 100 101 102

1

1.5

2

2.5

3

3.5

4

4.5

Resistivity (ohm−m)

Dep

th(km)

Truth1 Hz0.1, 1 Hz0.1, 0.3, 1, 3, 10 Hz

y transmitter

Key, 2009

Constable, Orange, and Key, 2015

With a single frequency and no phase data, a shallow resistor (say, hydrate) has an almost identical response to a deep hydrocarbon reservoir. This led to actual drilling errors.

Receiver

Shallow slab

Reservoir

Ey

1 ohm-m

0.33 ohm-m

1 ohm-m

0.33 ohm-m

Reservoir Shallow slab

Courtesy Arnold Orange

5. Transmitter fields have a dipole geometry. The radial (inline) and azimuthal (broadside) fields behave differently. The greater vertical component of the radial fields creates greater sensitivity to thin, sub-horizontal resistors (reservoirs). You can use this to tell thick from thin resistors. The modes also behave differently to anisotropy.

Transmitter

Receiver

Azimuth

Radial fieldEr

Azimuthal fieldEø

0 AzimuthField purely radial(in-line geometry)

o

90 AzimuthField purely azimuthal(broadside geometry)

o

,

log10

(V/Am2) degrees

log10

(V/Am2) degrees

7785

7790

7795

7800

7805

7810

7815

7820

7825

7830

No

rth

ing

, km

4000m, Erad

0.75Hz

N = 690 rms = 10% −13.25

−13.2

−13.15

−13.1

−13.05

−13

−12.95

−12.9

−12.85

−12.8 4000m, Erad

0.75Hz

N = 690 rms = 4°

−250

−240

−230

−220

−210

−200

710 720 730 740 750 760

7785

7790

7795

7800

7805

7810

7815

7820

7825

7830

Easting, km

No

rth

ing

, km

4000m, Eaz

0.75Hz

N = 297 rms = 9% −13.65

−13.6

−13.55

−13.5

−13.45

−13.4

−13.35

−13.3

−13.25

−13.2

710 720 730 740 750 760

Easting, km

4000m, Eaz

0.75Hz

N = 297 rms = 6°

−150

−140

−130

−120

−110

−100

0.75 Hz amplitude, 4km Tx-Rx offset

log10

(V/Am2) degrees

log10

(V/Am2) degrees

7785

7790

7795

7800

7805

7810

7815

7820

7825

7830

No

rth

ing

, km

4000m, Erad

0.75Hz

N = 690 rms = 10% −13.25

−13.2

−13.15

−13.1

−13.05

−13

−12.95

−12.9

−12.85

−12.8 4000m, Erad

0.75Hz

N = 690 rms = 4°

−250

−240

−230

−220

−210

−200

710 720 730 740 750 760

7785

7790

7795

7800

7805

7810

7815

7820

7825

7830

Easting, km

No

rth

ing

, km

4000m, Eaz

0.75Hz

N = 297 rms = 9% −13.65

−13.6

−13.55

−13.5

−13.45

−13.4

−13.35

−13.3

−13.25

−13.2

710 720 730 740 750 760

Easting, km

4000m, Eaz

0.75Hz

N = 297 rms = 6°

−150

−140

−130

−120

−110

−100At intermediate azimuths the data are a trigonometric mixture of the radial and azimuthal fields.

10−1

100

101

102

1

1.5

2

2.5

3

3.5

4

4.5

Resistivity (ohm−m)

De

pth

(km

)

TruthExBy

Bz

Ex,By,Bz

TruthBxEy

Ez

Bx,Ey,Ez

TruthBxEy

Ez

Bx,Ey,Ez

x transmitter

10−1

100

101

102

1

1.5

2

2.5

3

3.5

4

4.5

Resistivity (ohm−m)

De

pth

(km

)y transmitter

10−1

100

101

102

1

1.5

2

2.5

3

3.5

4

4.5

Resistivity (ohm−m)

De

pth

(km

)

z transmitter

y

x

E

BB

y

x

B

EE

y

x

Bx

EyEz

1D Inversions of synthetic 0.1 and 1.0 Hz data with 1% noise added:

Inline Tx Vertical TxCrossline Tx

Inverting either inline Bx or Ey provides best resolution to reservoir targets. Note Ez: don’t confuse sensitivity with resolution.

Key, 2009

6. CSEM works best in deep water, where the “air wave” is small. But, it works OK in shallow water because the air wave and target response are coupled. Don’t try to remove the air wave.

Flood from left - Water depth 1500 & 3000 m

Flood From: Orange, Key and Constable, Geophysics, 2009

'Air wave'

Seawater propagation

host rock propagation

target signal

CRIP

PS IN

ST

ITUTION OF OCEANOGRAPHY

UCSD

Orange, Key, and Constable, 2009

7. Depth sensitivity in CSEM is largely determined by geometry. Sensitivity is always greatest right below the Tx and Rx. Depth sensitivity is about half Rx-Tx spacing, and so is sensitivity to off-line structure.

inline (m)

Plan

Section0.25 Hz and perturbationof 1 Ωm halfspace

Constable, 2010

1000 2000 3000 4000 5000 6000 7000 8000 -18

-17

-16

-15

-14

-13

-12

-11

-10

-9

-8

Radial mode fields (1 Hz)

Range, m

log10(E

fie

ld m

agnit

ude, V

/m/(

Am

))

100 m, 100 Ωm

1000 m, 1 Ωm

5 km diameter

4 km

3 km

2 km

1 km

1D layer

1D halfspace

(3D calculation courtesy C. Weiss)

Targets have to be bigger than their depth of burial to be detected (note that this has nothing to do with transmitter power!).

Constable and Weiss, 2006

8. Anisotropy is important. Aligned crystals and inter-bedding can produce anisotropy on microscopic to macroscopic scales.

CSEM cannot tell micro- from macro-anisotropy until the layers get very thick.

http://www.sleepingdogstudios.com/NR O’Brien, J. Sed. Res. 1987

0 1 2 3 4 5 6 7 8 9 10-18

-17

-16

-15

-14

-13

-12

-11

-10

-9

-8

Horizontal Range (km)

AZIMUTHAL: Frequency: 0.25 Hz

0 1 2 3 4 5 6 7 8 9 10-18

-17

-16

-15

-14

-13

-12

-11

-10

-9

-8

Horizontal Range (km)

RADIAL: Frequency: 0.25 Hz

Am

plitu

de (

log

10 V

/m/(

Am

), T

/(A

m))

Am

plitu

de (

log

10 V

/m/(

Am

), T

/(A

m))

Bx: Anisotropy

Ey: Anisotropy

Bx: HS_half

Ey: HS_half

Bx: HS_one

Ey: HS_one

By: Anisotropy

Ex: Anisotropy

By: HS_half

Ex: HS_half

By: HS_one

Ex: HS_one

Radial Azimuthal

1 Ωm 0.5 Ωm

To a good approximation (10% or so), the anisotropic response follows the vertical resistivity for the radial mode, and the horizontal resistivity for the azimuthal mode.

Inverting the modes separately using isotropic models may give reasonable results, but joint inversion of both modes will fail without anisotropy.

Red - magnetic fieldsBlue - electric fields Anisotropic

Horizontal Vertical Constable, 2010

9. Seawater conductivity matters. Getting it wrong can introduce spurious structure into CSEM models (red = correct, black = 1-layer approximation). Expensive mistakes have been made...

Key, 200910 −1 10 0 10 1 10 2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Resistivit y (ohm−m)

Dep

th(km)

TruthFree sea, 1 layer, rms 3.6Fixed sea, 20 layers

10 1 10 2 10 3 10 4

10 0

101

Electrode Spacing

App

aren

t Res

istiv

ity

100 m, 1 Ωm

10 m, 100 Ωm

100 m, 1 Ωm

1 m, 1000 Ωm

VI

VI

10. Like DC resistivity, CSEM is mainly sensitive to the resistivity-thickness product of thin resistive layers. This is called T-equivalence, where “T” = transverse resistance (i.e. resistivity times thickness).

If resistivity is proportional to net pay, this may not be much of a problem.

The Future

Marine EM was almost certainly over-sold between 2002 and 2007 or so. WesternGeco pulled out of the marine EM business in 2010 and OHM was absorbed into EMGS in 2012.

The marine EM market was recently worth around $200m/year, or about 5% of the marine seismic market. Marine EM is a capital-intensive business and there is a persistent fear of patent lawsuits, so it is difficult for smaller, innovative companies to enter the market. On the other hand, there probably isn’t enough profit for the big companies to care. But there is some progress.

EM contractor share price

PGS’ surface towed streamer system is providing good data in water depths up to 400 m or so, and allows data collection co-incident with 2D seismics.

PGS website

Petromarker website

Petromarker has a novel vertical-vertical system which can operate in deep water, but has limited lateral capabilities.

However, the custom vessel, large (3D) survey model has made CSEM a relatively expensive commodity.

On the other hand, there is only one contractor offering the standard approach that works so well in deep water.

EMGS website

Hesthammer et al., First Break, 2012; Hesthammer pers. comm. 2015

Does it work? Jonny Hesthammer thinks so. False positives have been drilled (mostly lithological resistors), but false negatives are very rare. That is, without a CSEM signature the likelihood of a commercial discovery is very low - but industry just keeps drilling and providing more data for Jonny’s plot - without more confidence in the method it is difficult to realize its value.

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85

NAR=15%

Weak EM response (NAR<15%)Strong EM response (NAR>15%)

Discovery - ExplorationDiscovery - Calibration

Dry well - ExplorationDry well - Calibration

Recent CSEM wells

Discovery – Non-commercial

Mostly discoveries (76%) Mostly dry wells (68%)(2.9% commercial discovery rate)

Incr

easi

ng E

M s

igna

ture

350%

300%

250%

200%

150%

100%

50%

0

-50%

Norvarg – 189 mmboeSkrugard – 286 mmboe

Havis – 250 mmboe

Bønna - Dry

Wisting – 132 mmboe

Skavl – 35 mmboe

Byrkje - Dry

Hanssen – 18-56 mmboe

Goliat 238 mmboeIvory 32 mmboe

Darwin - DryWisting Alt. - Dry

Eik - Dry

Heilo - DryBreiflabb

Storbarden - Dry

Phoenix – Dry*Apollo - Dry*

Atlantis – Minor gasMercury – 6-12 mmboe

Salina – 38 mmboe

Discovery – Unknown commerciality

Much of the CSEM data is collected by the majors (ExxonMobil, Shell, Chevron, etc.) and the large NOCs (Petrobras, Pemex, etc.). These companies keep their success rate statistics fairly confidential. But they are still collecting data… I think the future lies in smaller, portable, ship-of-opportunity systems (like the ones academics must use), expanding the market to smaller client companies. This may take the passing of a few years and a rise in oil prices, but I think we can count on both of these.

Thank you!

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