U.S. patent application number 14/214003 was filed with the patent office on 2014-07-17 for seismic data acquisition using self-propelled underwater vehicles.
This patent application is currently assigned to WESTERNGECO L.L.C.. The applicant listed for this patent is WESTERNGECO L.L.C.. Invention is credited to JULIAN EDWARD KRAGH, KENNETH E. WELKER.
Application Number | 20140198610 14/214003 |
Document ID | / |
Family ID | 44507519 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140198610 |
Kind Code |
A1 |
WELKER; KENNETH E. ; et
al. |
July 17, 2014 |
SEISMIC DATA ACQUISITION USING SELF-PROPELLED UNDERWATER
VEHICLES
Abstract
The present disclosure generally relates to the use of a
self-propelled underwater vehicle for seismic data acquisition. The
self-propelled underwater vehicle is adapted to gather seismic data
from the seafloor and transmit such data to a control vessel. The
self-propelled underwater vehicle may be redeployed to several
seafloor locations during a seismic survey. Methods for real-time
modeling of a target zone and redeployment of the self-propelled
underwater vehicle based on the modeling are also described.
Inventors: |
WELKER; KENNETH E.; (OSLO,
NO) ; KRAGH; JULIAN EDWARD; (GREAT BARDFIELD,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WESTERNGECO L.L.C. |
HOUSTON |
TX |
US |
|
|
Assignee: |
WESTERNGECO L.L.C.
HOUSTON
TX
|
Family ID: |
44507519 |
Appl. No.: |
14/214003 |
Filed: |
March 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12880445 |
Sep 13, 2010 |
8717844 |
|
|
14214003 |
|
|
|
|
61307153 |
Feb 23, 2010 |
|
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Current U.S.
Class: |
367/16 |
Current CPC
Class: |
B63G 8/001 20130101;
B63C 11/52 20130101; B63B 27/36 20130101; G01S 5/0027 20130101;
G01S 11/14 20130101; G01V 1/38 20130101; G01V 1/3808 20130101; G01S
5/26 20130101; G01V 1/3852 20130101 |
Class at
Publication: |
367/16 |
International
Class: |
G01V 1/38 20060101
G01V001/38 |
Claims
1. A system for surveying subterranean formations, comprising: a
flotation element; a surface control unit disposed on the flotation
element; and at least one self-propelled underwater vehicle, the
vehicle having a control unit; whereby the surface control unit and
the vehicle control unit are adapted to communicate with one
another during surveying of subterranean formations.
2. The system according to claim 1, wherein the flotation element
comprises a vessel, an autonomous sea surface vehicle or a
buoy.
3. The system according to claim 2, wherein the flotation element
is an autonomous sea surface vehicle, the autonomous sea surface
vehicle having a net-like device operatively connected thereto for
collecting the at least one self-propelled underwater vehicle.
4. The system according to claim 1, wherein the vehicle includes a
sensor for gathering seismic data.
5. The system according to claim 4, wherein the sensor is a seismic
sensor.
6. The system according to claim 5, wherein the seismic sensor is a
hydrophone, a geophone or an accelerometer.
7. The system according to claim 4, wherein the sensor is an
electromagnetic sensor.
8. A method for retrieving self-propelled underwater vehicles,
comprising: providing an autonomous sea surface vehicle; attaching
a net-like device to an underwater portion of the autonomous sea
surface vehicle; and using the net-like device to capture one or
more self-propelled underwater vehicles.
9. The method according to claim 8, further comprising providing
the autonomous sea surface vehicle with a surface control unit, and
issuing positioning commands to the surface control unit to
position the autonomous sea surface vehicle for retrieval of the
one or more self-propelled underwater vehicles.
10. The method according to claim 9, wherein issuing positioning
commands comprises positioning the autonomous sea surface vehicle
to minimize total travel distance of the self-propelled underwater
vehicles to be retrieved.
11. The method according to claim 8, further comprising disposing a
sensor on or near the net-like device, and upon sensing entry of
the one or more self-propelled underwater vehicles, signaling
closure of the net-like device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/880445 filed Sep. 13, 2010; which claims the benefit of
U.S. Provisional Patent Application Ser. No. 61/307153 filed Feb.
23, 2010; both of which are incorporated herein by reference in
their entireties.
BACKGROUND
[0002] Seismic exploration involves surveying subterranean
geological formations for hydrocarbon deposits. A seismic survey
typically involves deploying seismic source(s) and seismic sensors
at predetermined locations. The sources generate seismic waves,
which propagate into the geological formations creating pressure
changes and vibrations along their way. Changes in elastic
properties of the geological formation scatter the seismic waves,
changing their direction of propagation and other properties. Part
of the energy emitted by the sources reaches the seismic sensors.
Some seismic sensors are sensitive to pressure changes
(hydrophones), others to particle motion (e.g., geophones), and
industrial surveys may deploy only one type of sensors or both. In
response to the detected seismic events, the sensors generate
electrical signals to produce seismic data. Analysis of the seismic
data can then indicate the presence or absence of probable
locations of hydrocarbon deposits.
[0003] Some surveys are known as "marine" surveys because they are
conducted in marine environments. However, "marine" surveys may be
conducted not only in saltwater environments, but also in fresh and
brackish waters. One type of marine survey, called a "seabed"
survey, involves the deployment of seismic sensors, either cables
or nodes on the seafloor. Seabed nodes may include both hydrophones
and/or geophones for use in acquiring seismic data. Conventional
seabed surveys typically involve the use of a deployment vessel
from which seismic sensors are dropped to the seafloor and may be
positioned with a remote operating vehicle (ROV). Deployment is
especially difficult in deep water where currents can cause units
dropped at the sea surface to travel horizontally and away from the
desired location. After deployment, the node positions must be
accurately determined before a source vessel passes over the seabed
sensors. The source vessel then generates seismic waves, which in
turn generate data captured by the sensors on the seafloor. Once a
particular region is surveyed, the nodes must be retrieved, the
recorded data extracted, and redeployed by the deployment vessel.
Conventional seabed surveys are thus inefficient due to the time it
takes to deploy, position and retrieve the ocean bottom nodes and
to download the data captured by the nodes.
SUMMARY
[0004] This disclosure generally relates to seafloor acquisition of
seismic data, and more particularly to the use of a self-propelled
underwater vehicle to assist in the acquisition of such data. A
recently developed self-propelled underwater vehicle, referred to
herein as a sub-surface glider, is now widely used in oceanographic
data collection. Such devices rise and fall in the water column
with efficiency, taking advantage of the pressure and temperature
differentials available in the water column. The self-propelled
underwater vehicle, according to the present disclosure, may be
used to acquire seismic data and then to transmit such data to a
surface control unit, which may conduct further processing of the
data. The surface control unit may be associated with any flotation
element, such as a surface vessel, a buoy or other autonomous sea
surface vehicle, such as a wave glider on the sea surface. Wave
gliders are similar in some respects to sub-surface gliders that
travel through the water column in that they harvest energy from
their environment, both solar and wave, and communicate via
satellite with remote sites, such as a mother vessel. The gliders
are different, however, in that the sub-surface glider requires
vertical travel in the water column while the wave glider remains
on the sea surface. Sub-surface and wave gliders can be used
together to conduct seabed type surveys with far greater efficiency
than today's conventional types of surveys. Additional types of
surface control units are contemplated. For example, while some
types of wave gliders rely on self propulsion, any sea surface
vehicle, either propelled by the mechanical method peculiar to the
wave glider or propelled by a more conventional method, such as by
a propeller driven by a combustion or electrical engine, may be
used as a surface control unit in coordination with a sub-surface
glider.
[0005] Sub-surface gliders that include seismic geophones and/or
other seismic sensors and adequate data storage media can swim in
order to reposition themselves from one survey line position to the
next as directed by the vehicle control unit. As the source vessel
traverses down a line, those sub-surface gliders (or "nodes") that
are no longer within the planned offset position with respect to
the source can move to the next source line acquisition position
while the source vessel continues along its planned trajectory. At
the end of the line, the last nodes swim into position during the
vessel line change and are ready for the next acquisition. In
addition, as sub-surface gliders need to ascend in the water column
in order to fully realize the pressure and temperature gradients
that make their lateral motion possible, they can come within range
of the wave gliders and be positioned acoustically relative to the
wave gliders. In turn, the wave gliders may contain GNSS type
antennas and receivers that give their position in an earth
centered earth fixed (ECEF) reference frame such as WGS-84. The
sub-surface gliders are equipped with a vehicle control unit that
communicates with a surface controller. Control critical
information such as location of surface unit, location of source
vessel, vehicle health checks, and survey plan updates, can be
exchanged between the surface unit controller and vehicle unit
controller to coordinate the survey in an efficient manner. When
the sub-surface gliders are within range of the wave gliders,
seismic recording data downloading can be performed. This data may
be stored in the wave glider for download when retrieved by the
mother vessel, or transmitted via satellite link to the mother
vessel for near real time processing.
[0006] Additional embodiments are disclosed, such as the use of the
wave gliders in performing efficient retrieval of the
self-propelled underwater vehicles. The wave gliders may include
net-like devices that capture the self-propelled underwater
vehicles for retrieval purposes.
[0007] Still further, the self-propelled underwater vehicles may be
used for time lapse survey operations adjacent to a drilling rig,
thus offering on demand seismic surveying without the danger that
towed streamers present when towed adjacent to a drilling rig.
[0008] Advantages and other features of the present disclosure will
become apparent from the following drawings, description and
claims.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a schematic view of a self-propelled underwater
vehicle deployed along a trajectory underwater to collect data,
according to an embodiment of the present disclosure;
[0010] FIG. 2 is a schematic view of another example of a
self-propelled underwater vehicle, according to an alternate
embodiment of the present disclosure;
[0011] FIG. 3 is a schematic illustration representing the transfer
of data between the self-propelled underwater vehicle and a surface
vessel, according to an embodiment of the present disclosure;
[0012] FIG. 4A is a schematic illustration representing the
transfer of data between the self-propelled underwater vehicle and
a surface vessel, according to another embodiment of the present
disclosure;
[0013] FIG. 4B is a schematic illustration representing the
transfer of data between the self-propelled underwater vehicle and
a surface vessel, according to another embodiment of the present
disclosure;
[0014] FIG. 4C is a schematic illustration representing the
transfer of data between the self-propelled underwater vehicle and
a wave glider, according to another embodiment of the present
disclosure;
[0015] FIG. 5 is a schematic illustration representing the use of
the self-propelled underwater vehicle to conduct a time lapse
survey adjacent to a drilling rig;
[0016] FIG. 6 is a schematic diagram of a data processing system
for carrying out processing techniques according to the present
disclosure;
[0017] FIG. 7 is a schematic diagram illustrating one embodiment of
a method for retrieving the self-propelled underwater vehicles
using wave gliders;
[0018] FIG. 8 is a schematic illustration representing ongoing
adjustment to the trajectories traveled by the self-propelled
underwater vehicle, according to an embodiment of the present
disclosure; and
[0019] FIG. 9 is a schematic illustration representing the
deployment of a fleet of self-propelled underwater vehicles.
DETAILED DESCRIPTION
[0020] In the following description, numerous details are set forth
to provide an understanding of the present invention. However, it
will be understood by those of ordinary skill in the art that the
present disclosure may be practiced without these details and that
numerous variations or modifications from the described embodiments
may be possible.
[0021] The present disclosure generally relates to a technique that
can be used in seabed seismic data acquisition. The system and
methodology utilize a self-propelled underwater vehicle (e.g.,
self-propelled or remotely controlled) to position seismic devices
on the seafloor. The self-propelled vehicle includes seismic
sensors (e.g., hydrophone, geophone, accelerometer and/or
electromagnetic receiver) for detecting seismic signals reflected
from subterranean structures. The self-propelled underwater vehicle
is not physically coupled to any surface seismic vessels and moves
independently underwater to desired regions of the seismic survey
area. In some embodiments, the vehicle is connected to other
vehicles via a cable such that several vehicles can cooperate to
act as a seismic cable, either a seabed or towed cable. In
combination with the self-propelled underwater vehicle, an
autonomous sea surface vehicle may provide a near real time link to
a mother vessel, and an acoustically determined distance from an
ECEF reference frame. In some embodiments, the autonomous sea
surface vehicle may be a wave glider, such as described in U.S.
Pat. No. 7,371,136, which is incorporated herein by reference. In
near real time, the position of the self-propelled underwater
vehicle can be determined and compared to the planned position for
use in a control method such as a proportional-integral-derivative
(PID) controller that corrects the trajectory of the self-propelled
underwater vehicle in order to position it closer to the bottom
coordinates planned for seismic acquisition.
[0022] The self-propelled underwater vehicle can be preprogrammed
and/or programmed during operation to follow desired trajectories
underwater. The underwater trajectories are selected to position
the vehicle and accompanying seismic sensors optimally on the
seafloor to achieve various seismic surveying objectives. These
trajectories can be updated and adjusted in reference to the wave
glider ECEF reference frame during operations. Data can be
transferred from the self-propelled underwater vehicle to a desired
collection location, e.g., to a processing/control system on a
surface vessel, such as via a wave glider/satellite link.
Similarly, data can be transferred from the surface vessel either
directly or via a wave glider/satellite link to the self-propelled
underwater vehicle. The transfer of data from the surface vessel to
the self-propelled underwater vehicle may be used to iteratively
program the self-propelled underwater vehicle to follow new paths
through the water column to other survey regions. For example,
based on seismic coverage plots, or near real time geophysical
imaging, the self-propelled underwater vehicle may be iteratively
programmed to continually reposition itself at different areas of
the seafloor in order to fill gaps identified in the coverage or
image analysis.
[0023] According to one embodiment, the self-propelled underwater
vehicle is a sub-surface glider programmed to glide along desired
trajectories. Another example of a self propelled underwater
vehicle is the Sounding Oceanographic Lagrangrian Observer Thermal
RECharging (SOLO-TREC) autonomous underwater vehicle. The SOLO-TREC
uses a thermal recharging engine powered by the natural temperature
differences found at different ocean depths. Sub-surface gliders
differ from wave gliders in that sub-surface gliders are able to
travel within the water column, whereas wave gliders are for sea
surface use only. Individual sub-surface gliders or groups of
sub-surface gliders can be deployed in a seismic survey area and
programmed to position themselves on the seafloor. In some
embodiments, data from the sub-surface gliders is collected during
surfacing, and data may also be downloaded to the sub-surface
glider during the same surfacing activity. In one embodiment, data
is transmitted between the sub-surface glider and a surface vessel
via a satellite communication system, such as the Iridium satellite
system. One example of a suitable type of sub-surface glider is the
"Seaglider" developed by the Applied Physics Laboratory-University
of Washington in cooperation with the University of Washington
School of Oceanography. In other embodiments, the sub-surface
gliders remain underwater during communication with the
processing/control system. Typically such sub surface self
propelled devices are equipped with dead reckoning systems that
combine information from velocity meters, such as Doppler shifted
acoustics referenced to the sea bottom or water particles. Such
dead reckoning systems measure heading, pitch and roll through
integrated magneto-inductive compasses and inclinometers. The
velocities in the instrument frame are converted to Cartesian
velocities in the ECEF frame using a transformation computed from
the sensor values of roll, pitch and heading. The ECEF velocities
can then be integrated to compute bottom track position and
compared to a desired trajectory.
[0024] In another embodiment, the sub-surface glider transmits data
and other useful information such as health checks and coordinates
acoustically or by physical coupling to a wave glider positioned on
the sea surface. Subsequently the wave glider transmits such
information to the processing/control vessel for analysis such as
seismic survey coverage, geophysical imaging and vehicle
diagnostics. The sub-surface glider can calibrate its inertial
guidance system periodically by comparing its non wave glider
computed coordinates with those computed with reference to a
geometrically adequate set of wave gliders through acoustic
distance measuring, typically referred to as long baseline
positioning or lbl. Further, short, ultra short and super short
baseline positioning methods (sbl, usbl, ssbl respectively) can
also be employed to locate the sub-surface glider relative to one
or more wave gliders.
[0025] By way of example, the positioning trajectory selected for
the sub-surface glider may be determined from a Global Navigation
Satellite System (GNSS) (e.g., Global Positioning System (GPS)
owned and operated by the U.S. Department of Defense) with a
determined starting point and by dead reckoning, inertial
navigation measurements, altimeters, compasses, and with a surface
survey vessel or wave glider platforms for performing acoustic
methods, such as lbl and sbl measurement methods, or any
combination of such methods. In an alternate embodiment,
communications also can be achieved through underwater acoustic
and/or optical telemetry to either the survey vessel or wave
glider. Obtaining a position for the sub-surface glider through
active or passive acoustic distance measurement and subsequent
communication to the sub-surface glider allows an operator on the
surface survey vessel to control the trajectory of the sub-surface
glider. The history of descent or ascent enables an operator to
download information regarding an updated desired path for the
sub-surface glider. The process of updating the sub-surface glider
path also can be automated according to specific objectives for
changing the glider trajectory. For example, objectives for
changing the glider trajectory may include avoiding obstructions
and other vehicles, e.g., surface vessels, which may be moving
through the survey area during a scheduled surfacing of the
glider.
[0026] Referring generally to FIG. 1, a self-propelled underwater
vehicle 20 is illustrated according to an embodiment of the present
disclosure. In this embodiment, vehicle 20 is illustrated as
following a desired trajectory 22 through a water column 24 of a
seismic survey area 26. Although self-propelled underwater vehicle
20 may be designed in a variety of configurations, one example is
the illustrated glider 28 that can be programmed to glide along the
desired trajectory 22.
[0027] In the embodiment illustrated, the self-propelled underwater
vehicle 20, e.g., sub-surface glider, comprises an outer shell or
hull 30 that is hydrodynamically designed to have a low coefficient
of drag as the vehicle moves through the water. The self-propelled
underwater vehicle 20 also may comprise a control unit 32, such as
a processor based control system, powered by a suitable battery 34.
By way of example, battery 34 may comprise a battery pack movable
along an internal structure 36 to adjust the balance/inclination of
the self-propelled underwater vehicle 20. Additionally, wings 38
are mounted to extend from shell 30 in a manner that helps control
the gliding of vehicle 20 along trajectory 22. A plurality of
stabilizer fins 40 may be attached to a tail section 42 of shell 30
to further stabilize the movement of vehicle 20 along desired
trajectories 22. Additionally, further control over self-propelled
underwater vehicle 20 can be achieved by selectively inflating and
deflating a bladder 44 to change the buoyancy of vehicle 20. The
bladder 44 may be inflated, for example, to cause vehicle 20 to
surface for transmission of data to or from a surface vessel, a
wave glider or other surface platform.
[0028] Transmission of data from self-propelled underwater vehicle
20 to a surface location, e.g., a surface vessel or wave glider,
and transmission of data to vehicle 20 can be accomplished via an
antenna 46 coupled to a suitable transceiver 48 which, in turn, is
connected to control unit 32. By way of example, antenna 46 may be
mounted to extend from tail section 42. Accordingly, when bladder
44 is inflated to cause vehicle 20 to surface, antenna 46 extends
above the water line to facilitate transmission of data. It should
be noted, however, that underwater data transmission techniques
also can be utilized. Additionally, control unit 32 can be designed
to exercise automatic control over the movement of vehicle 20. In
other applications, a PID controller or other suitable controller
is used to position the vehicle 20 at multiple locations for
gathering seismic data.
[0029] The vehicle 20 further includes sensors 50 useful for
acquiring seismic data in marine environments such as at the
seabed. The sensors 50 are coupled to the control unit 32. In one
embodiment, the sensors 50 include one or more seismic sensors,
such as hydrophones 54 and/or particle motions sensors (e.g.,
accelerometers) 56. In some embodiments, the sensors 50 may include
electromagnetic sensors or combinations of seismic and
electromagnetic sensors. The sensors 50 are able to record pressure
and shear wave data at the seabed to thus facilitate the mapping
and analysis of subsea hydrocarbon deposits.
[0030] The self-propelled underwater vehicle is optimally designed
to couple the seismic sensor 50 to the sea floor and locate other
seismic sensors optimally to record the seismic source signal in
either the pressure wave, shear wave, or particle motion domain.
Such optimization aims to isolate the signal from other sources of
pressure waves, shear waves or particle motion.
[0031] The vehicle 20 is equipped with a clock 57 that can be
calibrated through various methods of communication. Clock
calibration facilitates keeping the recording and source events
synchronized, thus enabling the migration of travel times to depth
via sound velocity models. In one embodiment, the vehicle 20
surfaces and receives GPS satellite signals (e.g., from satellite
communication system 68 in FIG. 3) that contain time information.
These are compared to the vehicle's local clock and the local clock
is calibrated to the GPS time. The same satellite time is recorded
at a source vessel (e.g., surface vessel 66 in FIG. 3) and a record
of the time difference is maintained to allow for clock drift
models. These models are then applied to the recorded data in order
that the differences between clocks in the recording vehicle and
source vessel are accounted for. In an alternate embodiment, clock
calibration is achieved by sending a time stamped message of the
clock time to the vehicle 20 from the source vessel, wave glider,
or other surface platform acoustically or by other methods such as
with a light source, e.g., lasers.
[0032] The self-propelled underwater vehicle 20 may have a variety
of other configurations and incorporate additional or alternate
components. In FIG. 2, for example, an alternate embodiment of
self-propelled underwater vehicle 20 is illustrated with a charging
system 58 designed to enhance the life of battery 34. In this
example, an impeller 60 is coupled to a generator 62 to charge
battery 34. As self-propelled underwater vehicle 20 descends along
a desired trajectory 22, water flows through impeller 60 to rotate
the impeller and power generator 62. The generator 62 outputs
current to battery 34 to charge the battery for longer battery life
during operation of the various systems on self-propelled
underwater vehicle 20. However, charging system 58 also facilitates
the use of battery 34 to power an optional propulsion system that
can be used to move vehicle 20 through water column 24.
[0033] Additional electrical power generation mechanisms may also
be incorporated into the self-propelled underwater vehicle 20 and
surface platform such as those described in U.S. Patent Publication
No. 2009/0147619, which is incorporated herein by reference. Power
generated by this method can be used for charging the battery 34 in
the self-propelled underwater vehicle 20. Power uses include radio
and satellite communications systems as well as acoustic ranging
systems.
[0034] As illustrated in FIG. 3, self-propelled underwater vehicle
20 can be designed to communicate with a surface control unit 64
located on, for example, a surface vessel 66. Surface vessel 66 may
comprise one of the seismic survey vessels or an independent vessel
for use in obtaining data from vehicle 20 and for controlling the
movement of vehicle 20 through water column 24. In the embodiment
illustrated, self-propelled underwater vehicle 20 communicates with
surface control unit 64 via a satellite communication system 68. As
described above, the bladder 44 may be inflated to increase the
buoyancy of vehicle 20 and to move the vehicle to the surface such
that antenna 46 extends through the surface of the water, as
illustrated.
[0035] In other embodiments, as illustrated in FIG. 4A, the
self-propelled underwater vehicle 20 need not surface to
communicate with a surface vessel 66 or other surface platform.
Rather, the vehicle 20 may ascend to a position proximate the
surface platform, yet still underwater, and communicate with the
surface control unit 64, for example via light or acoustic
communication. In an alternative embodiment, as illustrated in FIG.
4B, the surface control unit 64 may be disposed on a float 65
associated with the surface vessel 66. In still further
embodiments, as illustrated in FIG. 4C, the surface control unit 64
may be disposed on a wave glider 72. It is to be appreciated that
the surface control unit 64 may be associated with any flotation
element. Such an arrangement provides flexibility in transferring
data from the vehicles 20 as the wave glider 72 or other surface
float 65 (or other flotation element) may be closer to certain
vehicles 20 deployed throughout the survey area. Several such wave
gliders 72 or other surface floats 65 having surface control units
64 may be deployed throughout the survey region. Indeed, the wave
gliders 72 may not be operatively connected to the surface vessel
66, but rather function as autonomous buoys at strategic locations
throughout the survey area. The wave gliders 72 may include an
antenna 74 for data transmission. In embodiments where multiple
surface control units 64 are deployed, the surface control unit 64
on the vessel may function as the master surface control unit such
that it receives data from and transmits data to the deployed
surface control units. Towed float communication may occur through
tail buoys at the end of towed streamers if the survey methods
combine towed streamer technology with bottom nodes. Alternatively,
the towed source can also be equipped with a communications device
on the source float. Both of these platforms may be already
equipped with a communications line back to the towing vessel.
[0036] In still further embodiments, as illustrated in FIG. 5, the
self-propelled underwater vehicles 20 may conduct a time lapse
monitor survey around a drilling rig or near a production
reservoir. The vehicles 20 can be deployed from the rig whenever a
4D type of monitor survey is conducted. The vehicles 20 can be
positioned as described above for larger surveys or can be
positioned relative to the rig or rigs via long baseline or short
baseline types of acoustic methods. In such embodiments, the
positioning acoustic devices may be located on the rig or rigs. The
acoustic devices are referenced to an ECEF reference frame
established onboard the rig by, for example, a GNSS receiver
antenna and positioning system. The vehicles 20 may seek to occupy
the positions they had during the base survey or other past surveys
in order to reduce the normalized root mean squared (nrms) noise
that can occur due to changes in azimuth and offset of the energy
through a non homogeneous overburden region. With the vehicles 20
located in the same positions as the previous or base survey, a
source vessel (not depicted) can position the center of the source
in the same positions occupied during the base survey such that any
difference measured by analyzing (differencing) the two survey
records can be attributed to changes in the reservoir and
overburden as a result of production rather than from changes in
the source and receiver locations.
[0037] In some embodiments, the self-propelled underwater vehicles
20 may be stored on or near the rig as part of a suite of source
and receivers easily deployable for reservoir monitoring whenever
recent seismic survey data is needed for production decisions. This
enables the production team to conduct a local seismic survey on
demand with reduced operational effort. Processing of the data and
image interpretation may also be performed locally on the rig. A
further advantage to this type of survey system is that the
self-propelled underwater vehicles 20 may be deployed close to
and/or directly under the rig with reduced risk of accident as no
vessel is required to retrieve the vehicles 20. Rather, the
self-propelled underwater vehicles 20 can travel away from the rig
or towards the location where they will be retrieved. For example,
in some embodiments, the vehicles 20 may travel to a water surface
location adjacent the rig for safe retrieval.
[0038] Referring to FIG. 6, in some embodiments, the surface
control unit 64 and/or the vehicle control unit 32 may take the
form of a data processing system 100 that includes a processor 102
constructed to execute at least one program 104 (stored in a memory
106) for purposes of processing data to perform one or more of the
techniques that are disclosed herein (e.g., processing the seismic
data received from the vehicles 20 or identifying and issuing
positioning commands to the vehicles 20 with respect to the surface
control units 64 and processing data, such as positioning commands,
received from the surface control units 64 with respect to the
vehicle control units 32). The processor 102 may be coupled to a
communication interface 108 for purposes of receiving and
transmitting data at the surface control unit 64 and/or vehicle
control unit 32. In addition to storing instructions for the
program 104, the memory 106 may store preliminary, intermediate and
final datasets involved in the techniques (data associated with
techniques 110) that are disclosed herein. Among its other
features, the data processing system 100 may include a display
interface 112 and display 114 for purposes of displaying the
various data that is generated as described herein. The data
processing system 100 may further include a data collection
platform 116 (e.g., a database) configured to receive and store
data from the vehicles 20 and/or surface control units 64.
[0039] It is to be appreciated that communication between the
underwater vehicle 20 and the surface control unit 64 may be
one-way or two-way. That is, the vehicle 20 may transmit recorded
seismic data to the surface control unit 64 for additional
processing and/or storage. The surface control unit 64 may transmit
positioning commands to the vehicle 20 in order to direct the
vehicle 20 to its next location (e.g., seafloor position). Of
course, embodiments are contemplated in which only one-way
communication takes place. For example, the vehicle 20 may be
provided with sufficient data storage such that data transmission
to the surface control unit 64 during deployment is unnecessary. In
such scenarios, the vehicle 20 would only receive communication
from the surface control unit 64. Providing the vehicles 20 with
data storage capacity allows the vehicles 20 to obtain seismic data
at one region of the seafloor and be repositioned to other regions
of the seafloor for additional data gathering prior to
surfacing.
[0040] In some embodiments, the vehicle 20 may be used with
permanent seafloor nodes such that the vehicle 20 collects seismic
data from the nodes and delivers the data to the surface control
unit 64 either at the sea surface or from underwater.
[0041] The self-propelled underwater vehicle 20 also can be moved
to the surface to facilitate retrieval. Retrieval may be
accomplished by monitoring movement of vehicle 20 with onboard
positioning systems, as described above. Additionally, or in the
alternative, the vehicle 20 can utilize the satellite communication
system 68 to send a GNSS fix via satellite after surfacing. A
homing beacon signal system also can be incorporated into the
vehicle 20 and the homing beacon signal can be used as a primary or
backup locator. In addition to being a locator, the relationship
can be reversed so the retrieval platform emits a homing beacon
signal to bring the self-propelled underwater vehicle 20 home. This
allows the retrieval platform to continue with its primary mission
profile until the self-propelled underwater vehicle is close enough
to be retrieved.
[0042] In some embodiments, retrieval may be facilitated by
gathering the vehicles 20 into a certain area using homing devices
installed in the vehicles. By congregating the vehicles 20 into a
strategically convenient area, a surface vessel may retrieve many
such vehicles in a quick manner. Alternatively, the vehicles 20 can
communicate with each other via satellite, conveying their surface
coordinates to a central controller (e.g., on vessel 66) that
computes the optimum point for retrieval based on factors such as
retrieval vessel location and the geometric center for some number
of units to be retrieved. The central controller then transmits the
best retrieval point determined by an optimization algorithm back
to the individual units via satellite. Such an algorithm may
attempt to limit the distance the vessel will have to transit to
retrieve the seismic recording units. Other inputs to the
optimization algorithm may be seismic survey lines yet to be
completed, turn radius of the vessel and others.
[0043] In still other embodiments, with reference to FIG. 7, the
underwater vehicles 20 can be captured by the wave gliders 72 or
other sea surface autonomous vehicle in a net-like device 90
extending from the wave gliders. As the underwater vehicles 20 and
wave gliders 72 approach each other, their relative orientation can
be determined so that the wave glider can open the mouth of the
towed net-like device 90 that is hydrodynamically designed to open
in the direction of the approaching sub-surface vehicle. After the
underwater vehicle 20 has entered the net 90, a sensor 92 may
detect its presence, thus signaling the net to close until the next
sub-surface vehicle 20 approaches the wave glider 72. It is to be
appreciated that the net-like device 90 may be disposed on the wave
glider 72 in various manners. For example, the net-like device 90
may be disposed in or on the umbilical portion of the wave glider
72 and can be deployed during the retrieval process. In other
embodiments, the net-like device 90 may hang from the fin portion
of the wave glider 72.
[0044] Moreover, other surface platforms may be utilized in
retrieving the underwater vehicles 20 using the net-like device 90
described herein. The collected sub-surface vehicles 20 may be
towed back to the survey vessel 66 (FIG. 3), drilling rig (FIG. 5),
or other location where they can be retrieved, where the acquired
data can be downloaded, and where the vehicles may be maintained
and stored until the next deployment.
[0045] In embodiments where satellite systems are used with the
underwater vehicles 20, satellite communications system 68 or
another suitable communication system may be used such that data
can be repeatedly sent to self-propelled underwater vehicle to
adjust the trajectory or trajectories of vehicle 20 during
operation without retrieval of the vehicle, as illustrated in FIG.
8. For example, surface control unit 64 may be used in cooperation
with communication system 68 to send new program instructions to
self-propelled underwater vehicle 20 at each surfacing location 70.
The updating of program instructions and the changes to trajectory
can be conducted on an iterative basis to pursue different seafloor
regions.
[0046] Alternatively, communications can be conducted through the
wave glider 72 or other surface platform which communicates with
the mother vessel via satellite or surface radio.
[0047] Tracking of the self-propelled underwater vehicle 20 by the
surface vessel 66 or other surface platform can be achieved with
various acoustic positioning systems, including lbl systems, sbl
systems, usbl systems and other suitable systems. The trajectory of
the vehicle 20 also may be transmitted back to the vessel during
surface or underwater visits as described above. In the latter
application, the trajectory can be determined by dead reckoning
between GNSS fixes.
[0048] In some of these applications, and with reference again to
FIG. 1, the processing system 32 of vehicle 20 can be used to
compute the coordinates of the vehicle. For example, hydrophones 54
can be positioned on the self-propelled underwater vehicle 20 at
specific geometries and separation distances to enable operation of
a short baseline system or an ultra short baseline system type of
positioning system. If the depth measurement is known, two or more
hydrophones 54 can be used to enable determination of position.
Otherwise, three or more hydrophones are positioned on vehicle 20
with sufficient separation to measure the phase difference between
an acoustic wave transmitted by a transmitter on a home platform,
such as a transmitter on surface vessel 66. If the acoustic signal
has the ECEF or other reference frame coordinates of the
transmitter modulated on it, the internal processing system 32 of
the vehicle 20 can compute its own coordinates in the reference
frame of the transmitters and compare them to the planned
trajectory or final survey position coordinates in the same or
other reference frame after the appropriate reference frame
conversion. The coordinates can be stored and/or used in making
steering decisions. For example, decisions can be made to steer
toward the transmitter or to steer according to a planned
trajectory.
[0049] In seabed applications, a relative positioning network can
be built up on the survey area seafloor. Once any one vehicle 20
has an accurately determined position, it may remain at that point
to serve as a control point. Other vehicles 20 can determine their
position relative to the control points and dead reckon to their
position. As the source/acquisition vessel passes over the newly
assembled vehicles on the sea bottom, it can use one or more of the
above mentioned acoustic positioning methods to determine a new set
of control points. In addition, during data acquisition, methods
can be used to position the nodes both with reference to the source
and to each other. See, e.g., U.S. Pat. No. 5,757,722, which is
incorporated herein by reference.
[0050] Referring to FIG. 9, the vehicles 20 may be grouped in an
array or fleet 120 to carry out seismic data acquisition. For
example, the vehicles 20 can be separated into one of two
acquisition lines 122, 124, thus permitting one set to be sent for
data download (either at the surface or underwater) while the other
set(s) are being deployed for seismic data acquisition. Of course,
the fleet could be made up of several acquisition lines depending
on the size and scope of the survey. The fleet 120 may be
programmed to respond to certain parameters. In one embodiment, the
vehicles 20 may be pre-programmed to receive a message from the
surface control unit 64 when the seismic mission has been
completed. This message may be in the form of an acoustic signal
transmitted from the vessel 66 or other transmitter associated with
the survey. The message may be a dedicated message or, in some
embodiments, it may be associated with a certain survey parameter,
such as source strength, indicating the distance between the source
and vehicle. In this example, the vehicles 20 may be programmed to
discontinue survey efforts once the strength of the direct arrival
or reflected source signal as measured by the vehicle falls below a
certain threshold level. In other embodiments, the vehicle 20 may
include a clock that has a specified time window for the
survey.
[0051] During deployment of the fleet 120, the survey target zone
may be analyzed through various onboard processes. For example,
survey coverage may be tracked with conventional binning processes,
which generally form a cell (bin) grid over the target zone. The
bins may be populated with data acquired by the vehicle 20 when
positioned on the seafloor. This active tracking of the target zone
coverage could thus facilitate re-positioning of the vehicles 20 to
areas where additional bin data coverage is needed. In other
embodiments, a model of the target zone may have been created
according to a previous survey. Accordingly, the model may be
altered in the current survey by using real-time feedback from the
vehicles 20. In this manner, target zone coverage can be assessed
using a real-time updated model and thus the vehicles 20 can be
repositioned according to any coverage holes identified.
[0052] Seismic data acquisition using the fleet 120 may be combined
with other seismic data acquisition methods. In some embodiments,
the acquisition cycle can include towed streamer acquisition
simultaneous to seafloor node recording in order to integrate both
datasets. As well as providing multi-component data, this dual
acquisition scenario may have significant advantages for increasing
the crossline sampling of the towed streamer data, improving the
azimuthal coverage and enabling coverage where obstacles obscure
the path of the vessel and streamers. Further to this, the vehicles
20 can record very low frequencies because of their ability to
deghost the seismic signal through a combination of P+Vz and their
location in a quiet low-noise seabed environment. In this manner,
only sparse spatial sampling is required compared to the towed
streamer acquisition in cases where processing of the low
frequencies from the vehicles 20 takes place. Integration with the
towed streamer data could then provide a considerably improved
broadband data set. Another exploration application can be the
inclusion of EM receiver antenna recording the signal of a source
being towed by the master acquisition vessel.
[0053] While the present disclosure has been described with respect
to a limited number of embodiments, those skilled in the art,
having the benefit of this disclosure, will appreciate numerous
modifications and variations therefrom. It is intended that the
appended claims cover all such modifications and variations as fall
within the true spirit and scope of this present disclosure.
* * * * *