Note: Descriptions are shown in the official language in which they were submitted.
CA 02531944 2006-01-04
MARINE OIL AND GAS EXPLORATION SYSTEM
This application is based on a provisional patent application filed in the
U.S. Patent and
Trademark Office on November 19, 2003 having Serial Number 60,524,020 by the
subject
inventor.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The subject invention relates to a marine exploration system and more
particularly, but
not by way of limitation, to a marine exploration system using a ship with a
towed "fish". The
fish used for measuring telluric currents as a natural electromagnetic energy
source flowing
beneath an ocean or sea floor.
(b) Discussion of the Prior Art
Heretofore, ground and airborne electromagnetic systems have been in use for
natural
resource exploration from about 1950 onwards. These systems depend mainly upon
the
measurement of the magnetic and conductive properties of the underlying
ground. Airborne
magnetic survey systems, that employ magnetometers with advanced stages of
development,
provide very satisfactory results. However, airborne conductivity measurements
of the underlying
terrain made with airborne electromagnetic systems that currently exist, leave
a great deal of
room for improvement.
Electromagnetic systems typically operate at a minimum terrain clearance with
respect to
safety and employ electromagnetic transmitters operating in the frequency
range from about 20
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Hz. to 50 kHz with limited ground penetration. The ground currents and their
related secondary
magnetic fields as induced in the underlying ground by these transmissions are
detected by
receiving coils mounted in a tail boom on an aircraft or in an airborne survey
bird towed behind
the aircraft. Either fixed wing aircraft or helicopters are used for these
surveys. The response
from the underlying ground is related to it's conductivity and the depth of
penetration of the
transmitted fields. The latter is primarily a function of the frequency
employed and the field
strength of the electromagnetic field that is generated by the equipment.
Typical maximum
penetrations are in a range of 400 to 1000 ft.
The only exception to the above description was an airborne system known as
"AFMAG"
that was developed by S.H. Ward and others in the 1960's. (S.H. Ward et al.
AFMAG-
Applications and Limitations. Geophysics, Vol. XXXI, No. 3 (June 1966), pp.
576-605.) This
system utilized the natural electromagnetic fields generated by lightning
events occurring in
distant electrical storms. These storms can provide a source for
electromagnetic energizing of the
ground, primarily in the frequency range of 20 Hz. to 500 Hz. Useable
frequencies down to about
3 Hz. exist but high quality receiving coils and coil anti-vibration mountings
are required for the
lower frequencies. These were apparently not available in the AFMAG system.
Although the AFMAG system showed some promise, it did not achieve sufficient
commercial acceptance to survive for more than a short period. Amongst the
various problems of
the system was the absence of the sophisticated instrumentation and digital
data acquisition and
processing systems that were not available at that time. Also and very
importantly, there was a
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lack of adequate technology for suppressing the prime sources of noise, such
as angular vibration
of the detection coils in the presence of a strong magnetic field in the
earth. The latter is
associated with a motor generator effect that can detect a millionth of a
degree of angular
vibration.
The AFMAG system was also restricted to the use of audio frequency fields and
did not
employ extremely low frequency and much more powerful natural magnetotelluric
fields, as used
in the present invention. Just as importantly, the AFMAG system as well as all
other airborne
electromagnetic systems, past or present, did not make use of the valuable
data available in the
electric field components of electromagnetic fields.
The subject marine exploration system demonstrates that electric field data,
as measured
by methods that do not make contact with an ocean or sea floor, can be more
important than the
magnetic component of electromagnetic fields. Experience with the invention
has also shown
that, for specific reasons, the measuring of the electric field data is
particularly valuable at
frequencies below 3 Hz. This type of information is completely missing in the
old AFMAG
system as well as current marine, ground and airborne electromagnetic systems.
The field data
lies in the range of frequencies from 0.01 Hz. to 3 Hz. and is used in the
present invention for the
marine detection of an induced polarization phenomena. Also, related response
of dielectric
interfacial polarization effects can be detected over oil and gas fields.
These low frequency
polarization effects, which are particularly important in the electric fields,
are discussed herein.
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In U.S. Patent 6,765,383 issued to the subject inventor, a magnetotelluric
geophysical
survey system is described using an aircraft survey bird. The survey system
uses natural
electromagnetic EM fields as an energy source. The system includes the survey
bird with electric
dipoles, an angular motion detector and an airborne data recording system. The
subject marine
exploration survey system described herein is similar to the survey system
described in U.S.
Patent 6,765,383 and provides a unique marine exploration system using a
combination of non-
contact electric field EM techniques for oil and gas exploration under an
ocean and sea floor.
The marine exploration system is dependent upon certain effects associated
with a deep
flow of natural telluric currents in a frequency range of 0.01 to 3 Hz. These
currents are induced
in the earth by an action of magnetotelluric (MT) fields. These MT fields are
well known and are
generated by the interaction of solar wind with the outer reaches of the
earth's magnetic field.
The solar wind is a stream of positively charged particles that are emitted by
the sun. The MT
fields that are relevant to the subject exploration system cover a frequency
range from
approximately 30 Hz down to 0.01 Hz and lower. These MT fields increase
progressively in
field strength with decreasing frequency, which is a fact that provides for
penetrations into an
ocean and sea floor at frequencies of 1 Hz. and lower down to depths of 10,000
feet and deeper.
SUMMARY OF THE INVENTION
A primary object of the subject invention is to provide a unique marine
exploration
survey system using a combination of non-contact electric field techniques for
deep exploration
employing natural telluric currents as an energy source. The system operates
in a frequency
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range from 0.01 Hz to 3.0 Hz. The telluric currents are induced within the
earth by the action of
magnetotelluric (MT) fields.
Another object of the marine exploration system is develop both deep and
shallow ocean
and sea exploration information induced by polarization effects or dielectric
polarization effects
related to oil and gas.
Still another object of the exploration system is to operate offshore with a
survey ship and
a towed fish exploring and surveying ground depths of 10,000 feet or more
below the ocean and
sea floor.
Yet another object of the marine exploration system is through it's use,
exploration costs
are greatly reduced when compared to current offshore oil and gas exploration
systems using a
seismic ship with elaborate installations and a towed array of marine
geophones. The use of the
subject system is close to direct detection of oil and gas and greatly
improves the odds of
detecting a new underwater oil and gas field.
The subject marine exploration system includes a towed fish adapted for being
pulled
behind a survey ship. The coordinates of the ship and the towed fish can be
controlled by a GPS
satellite and time data. The fish is a streamlined waterproof container,
somewhat reminiscent of
a shape of a fish. Metal sheet electrodes of electric field sensors are
mounted on the surface of a
tubular nose of the fish. The electric field sensors are in direct contact
with the sea water.
Typically, the fish is towed approximately 100 feet above the sea floor. The
positioning of the
CA 02531944 2006-01-04
fish is maintained by the use of an acoustic "pinger" on the fish. The pinger
transmits signals up
a towed cable to the survey ship. The fish can also include a cesium
magnetometer connected to
the electric field sensors. The magnetometer provides for detecting low
frequency magnetic
components of the electromagnetic fields generated by the telluric currents
flowing under the sea
floor. A filtering of the magnetic component signals is used to provide a
phase and amplitude
references for the electric fields. The amplitudes of the electric field at
each frequency are
ratioed against the amplitudes of similarly filtered components of the
magnetometer.
These and other objects of the present invention will become apparent to those
familiar
with marine, ground, and airborne geophysical oil and gas survey systems when
reviewing the
following detailed description, showing novel construction, combination and
elements as
described herein, and more particularly defined by the claims, it being
understood that changes in
the embodiments in the disclosed invention are meant to be included as coming
within the scope
of the claims, except insofar as they may be precluded by the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates magnetic and telluric field data before and after frequency
filtering.
FIG. 2 is a world map illustrating the flow of telluric currents in the oceans
and seas of
the world and across land masses.
FIG. 3 illustrates charges developed by telluric currents flowing through an
oil and gas
reservoir and showing dielectric interfacial boundary charges at boundaries of
sandstone grains,
water and gas.
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FIG. 4 illustrates the response of an airborne exploration system flown across
a major,
deep-seated gas field, Rulison Gasfield, Piceance Basin, Colorado.
FIG. 5 illustrates the subject marine exploration system with a survey ship
with tow cable
pulling a towed fish disposed above an ocean and sea floor. The fish is shown
disposed directly
above an oil and gas reservoir below the sea floor.
FIG. 6 is a perspective view of the towed fish with an outwardly extending
tubular nose
carrying electric field sensors.
FIG. 7 is a perspective view of the electrical wiring connections to dipoles
making up the
field sensor mounted on the tubular nose shown in FIG. 6.
FIG. 8 illustrates an oil reservoir below a sea floor and showing an
associated negatively
charged gas leakage plume and low frequency alternating telluric currents
flowing beneath the
ocean and sea floor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, magnetic and telluric field data is shown before and after
frequency filtering of
a wide frequency band and the same frequency band filtered.
In FIG. 2, a world map is shown illustrating a flow of telluric currents in
the oceans and
seas of the world and also across land masses in the northern and southern
hemispheres.
In FIG. 3, illustrates charges developed by telluric currents flowing through
an oil and gas
reservoir and showing dielectric interfacial boundary charges at boundaries of
sandstone grains,
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water and gas. It is extremely important to note that the electric fields
detected by the marine
exploration system described herein are associated with the dielectric charge
effects at
hydrocarbon/water contacts as shown in this drawing. The hydrocarbon/water
contacts exhibit
very high contrast in both dielectric constant and conductivity giving rise to
electric charges in
the presence of telluric currents. These currents are shown as arrows and are
extremely strong at
very low frequencies. The telluric currents are induced by magnetotelluric
fields and are
measured in the 0.05 to 3 Hz range by the dipoles and magnetometers as
discussed above
In FIG.4, an example of the type of data acquired in a flight across a major
gas field is
shown. The field is the Rulison Gas Field, Piceance Basin, Colorado. The data
was obtained by
dividing the electric field response (E) by the magnetic field response (H).
The highly directional
response of the field is due to the presence of oriented fractures that make
the field productive.
In FIG. 5, the subject marine exploration system is shown having numeral 10.
The
system 10 includes a towed fish 12 disposed above a sea floor 14. The fish 12
is shown in this
drawing disposed directly above an oil and gas reservoir 16 below the sea
floor 14. The towed
fish 12 is connected to a tow cable 20 attached to and pulled behind a survey
ship 22.
In FIG. 6, a perspective view of the towed fish 12 is shown with an
aerodynamic
waterproof housing 24 and an outwardly extending tubular nose 26. The tubular
nose 26
includes an electric field sensor, having general reference numeral 28. The
electric field sensor
28 includes three orthogonal dipoles 30, 32 and 34. The field sensor and
dipoles are shown more
clearly in FIG. 7. The housing 24 and tubular nose 26 are designed to minimize
drag as it is
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pulled underwater at various depths. The sensor 28 is used in association with
a 3-axis angular
motion detector 36 installed in the fish housing 24. The motion detector 36 is
based on the use
of vibrating quartz tuning forks and has an angular sensitivity of 0.003
degrees. The motion
detector 36 is fully adequate for use in compensating for noise produced by
the angular motions
of the electric field sensor 28 in the presence of the telluric currents from
the sea and under the
sea floor 14.
An optically pumped cesium vapor magnetometer 38 is mounted inside the housing
24
and electrically connected to the motion detector 36 via electric lead 40.
Also, the magnetometer
38 can be connected to a data processing unit 42 via the electric lead 40 in
the housing 24.
Optionally, the data processing unit 42 can be installed on the survey ship 22
for gathering the
signals and data from the fish 12 via the electric lead 40.
The magnetometer 38 has a sensitivity of 1 picoTesla and provides a very
sensitive
measurement of the magnetotelluric fields. However, the sensitivity of the
magnetometer 38 lies
in a direction of the earth's magnetic field. Therefore, the MT frequency
measurements are
made in this direction. But, the derivative of the output of the magnetometer
38 provides data
that is proportional to a horizontal gradient of the MT fields. The use of the
optically pumped
magnetometer 38 in the subject marine exploration system 10 has two important
applications.
The first is the magnetometer's immunity to noise from angular motions
encountered when
towed underwater and the second is the high sensitivity and stability of the
magnetometer 38.
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Also, the magnetometer 38 provides a critical function of detecting low
frequency
magnetic components of the electromagnetic fields generated by the telluric
currents flowing
beneath the sea floor. The filtered components of these signals are used as a
phase and amplitude
reference of the electric fields measured by the dipoles 30, 32 and 34. The
electric field data
from the dipoles is presented as a set of selected frequencies in each of the
orthogonal directions
along the X axis, Y axis and Z axis, shown in FIG. 7. The amplitudes of the
electric field at each
frequency are ratioed against the amplitude of the similarly filtered
components of the
magnetometer 38. These amplitudes of the magnetic field are then resolved in
the direction of
the earth's magnetic field, which has operationally been proven to provide a
very convenient and
satisfactory reference.
The above mentioned procedure of using the ratio of the electric fields
against the
magnetic fields automatically compensates for fluctuation in the field
strengths of the MT fields.
This is due to the fact that the MT fields are the source of the telluric
currents. Therefore, the
telluric currents track these fluctuations.
In FIG. 7, a perspective view of the electrical wiring connections to dipoles
is shown
making up the field sensor 28 mounted in the tubular nose 26. The X dipole 30,
disposed along
the X axis is connected to electric leads X1 and X2. The Y dipole 32, disposed
along the Y axis
is connected to electric leads Y1 and Y2. The Z dipole 34, disposed along the
Z axis is
connected to electric leads Zl and Z2. The electric leads are all connected to
the motion detector
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36. The electric field sensor 28 and the magnetometer 38 are designed to
operate below 30 Hz.
and more specifically in a range of 0.01 to 3 Hz and less.
In should be mentioned that lower natural field frequencies, termed
magnetotelluric (MT)
fields, cover a typical range of 0.01 Hz to 3 Hz. As mentioned above, the MT
fields originate
from an interaction between the solar wind and the outer reaches of the
earth's magnetic field
into space. The field strength of these fields increases by factor of 100
times from 1 Hz down to
0.1 Hz and about 1000 times down to 0.05 Hz. These very strong and extremely
low frequency
fields can provide penetrations down to 10,000 feet and deeper below the sea
floor, which makes
them uniquely effective for oil and gas exploration.
In FIG. 8, an enlarged view of the oil and gas reservoir 16 below the sea
floor 14 is
illustrated. In this drawing, a negatively charged gas leakage plume 44 is
shown moving
upwardly through 2000 to 15,000 feet below the sea floor 14. Also shown in
this drawing are a
plurality of low frequency alternating telluric currents 46 flowing
underground and beneath the
sea floor 14.
While the invention has been particularly shown, described and illustrated in
detail with
reference to the preferred embodiments and modifications thereof, it should be
understood by
those skilled in the art that equivalent changes in form and detail may be
made without departing
from the true spirit and scope of the invention as claimed except as precluded
by the prior art.
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