Westerngeco patents glider operations

December 8, 2010 - via WesternGeco

Patent Application: Westerngeco  E. L. L. C. (10001 Richmond Avenue, Houston, TX, 77042, US)
Title: SYSTEM AND METHOD OF USING AUTONOMOUS UNDERWATER VEHICLE TO FACILITATE SEISMIC DATA ACQUISITION
Document Type and Number:
United States Patent Application 20100302901 Kind Code: A1


Abstract:

A technique facilitates the use of seismic data. The technique utilizes an autonomous underwater vehicle to obtain data on water column characteristics in a seismic survey area. The data can be used to adjust aspects of the seismic survey data and/or the seismic survey technique.


Inventors:
Welker, Kenneth E. (Nesoya, NO)   
Kristiansen, Ottar (Oslo, NO)   
Svendsen, Morten (Voyenenga, NO)   
Kragh, Julian Edward (Finchingfield, GB)   
Application Number:
12/473667
Publication Date:
12/02/2010
Filing Date:
05/28/2009
Primary Class:  367/21
Other Classes: 701/23
International Classes: G01V1/38; G05D1/00

BACKGROUND
In a variety of marine environments, seismic surveys can be taken to gain a better understanding of geological formations beneath a body of water. Relatively large marine regions can be surveyed by a surface vessel or vessels towing seismic streamer cables through the water. Another vessel, or the same vessel, can be employed in providing a seismic source, such as a compressed air gun utilized to generate acoustic pulses in the water. The seismic source is used to generate energy that propagates down through the water and into the geological formation. Marine survey data on the geological formation can be obtained by detecting the energy reflected from interfaces between geological formations. Hydrophones are connected along the seismic streamer cables to detect the reflected energy.

Accurate collection of data by the hydrophones is affected by changes in characteristics of the water column, such as changes in sound velocity between regions of the water column in the survey area. The travel time of the reflected energy/signal through the water column is needed to accurately establish, for example, the depth of the target reflecting surface. In some applications, sound velocity probes are dropped with varying frequency from a survey vessel during the seismic survey to collect data on sound velocity. The usefulness and frequency of the drops, however, can be limited by several factors, including operational safety considerations, risk of tangling the sound velocity probe line with the seismic spread equipment, requirements of the survey client, type of survey, e.g. 4D versus 3D, and knowledge of the survey space and time rate of sound velocity variation.

Current methods to measure sound velocity in the water column during a seismic survey operation include the use of both retrievable and expendable probes. The probes can be deployed either by conventional drop systems or advanced continuous drop systems. However, the approaches can be relatively expensive, cumbersome, and limited in adaptability.

SUMMARY
In general, the present invention provides a methodology and system for enhancing the usefulness of seismic data. The technique utilizes an autonomous underwater vehicle (auv) to obtain data on water column characteristics in a seismic survey area. The data can then be used to aid in the analysis of seismic data and/or to adjust aspects of the seismic survey.

DETAILED DESCRIPTION
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 invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

The present invention generally relates to a technique that can be used to improve the usefulness of seismic survey data. The system and methodology utilize an autonomous underwater vehicle to obtain data on water column characteristics in a seismic survey area. The data is then used, e.g. processed, with corresponding seismic data obtained during a seismic survey to improve, for example, the accuracy of the seismic data. In one embodiment, the autonomous underwater vehicle is programmed to sample water column characteristics that enable estimation of the time and space varying sound velocity of the water column in the seismic survey area.

The autonomous underwater vehicle is not physically coupled to any surface seismic vessels and moves independently underwater to desired regions of the seismic survey area. The autonomous underwater vehicle can be preprogrammed and/or programmed during operation to follow desired trajectories underwater. The underwater trajectories are selected to obtain data on the desired water column characteristics, e.g. sound velocity characteristics, which may vary throughout different regions of the water column. Data is transferred from the autonomous underwater vehicle to a desired collection location, e.g. to a processing/control system on a surface vessel. Similarly, data can be transferred from the surface vessel to the autonomous underwater vehicle. The transfer of data from the surface vessel to the autonomous underwater vehicle may be used to iteratively program the autonomous underwater vehicle to follow new paths through the water column. For example, the autonomous underwater vehicle may be iteratively programmed to follow water column characteristic interfaces, such as sound velocity interfaces.

According to one embodiment, the autonomous underwater vehicle is a glider programmed to glide along desired trajectories. Individual gliders or groups of gliders can be deployed in a seismic survey area and programmed to sample the water column. For example, the gliders may be programmed to detect water column characteristics indicative of sound velocities in the survey area. In some embodiments, data from the gliders is collected during surfacing; and data also can be downloaded to the glider during the same surfacing activity. In one embodiment, data is transmitted between the glider and a surface vessel via a satellite communication system, such as the Iridium satellite system. One example of a suitable type of glider is the “Seaglider” developed by the Applied Physics Laboratory—University of Washington in cooperation with the University of Washington School of Oceanography.

By way of example, the sampling trajectory selected for the glider may be directed from a global positioning system (e.g. Global Navigation Satellite System GNSS) starting point and by dead reckoning, inertial navigation measurements, altimeters, compasses, and with surface survey vessel acoustic methods, such as long baseline and short baseline measurement methods. In an alternate embodiment, communications also can be achieved through underwater acoustic and/or optical telemetry. Obtaining a position for the glider through active or passive acoustic distance measurement and subsequent communication to the glider allows an operator on the surface survey vessel to control the trajectory of the glider. The history of descent or ascent enables an operator to download information regarding an updated desired path for the glider. The process of updating the 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 or seismic spread equipment deployed to acquire the survey data, which may be moving through the survey area during a scheduled surfacing of the glider.

In one embodiment, the autonomous underwater vehicle, e.g. glider, is used to map the sound velocity of the survey area for geophysical signal propagation. Because the autonomous underwater vehicle can be redirected by updating its program, the glider may be used to follow water column characteristic interfaces, such as sound velocity (density) interfaces detected during an earlier survey to define the boundaries of these interfaces and to monitor movement of the interfaces. For example, the autonomous underwater vehicle enables sound velocity gradients to be followed so as to obtain the most information from the shortest travel distances. In many applications, the programmed trajectory may be updated iteratively based on local feedback from the survey vessel.

In another embodiment, the autonomous underwater vehicle can be used to follow a sound velocity gradient or a water mass boundary based on internal local measurements. The measurements are translated to steering commands that drive the autonomous underwater vehicle in a direction that is desired. For example, if the wall of an eddy is to be mapped, the autonomous underwater vehicle can be used to seek the water column salinity and temperature interface values that define the wall or boundary. The autonomous underwater vehicle also can be used to monitor the presence and location of marine mammals in the survey area to conform to local regulations that may affect seismic operations. For example, the autonomous underwater vehicle can be programmed to move up and down at edges of the survey area or at other/additional strategic locations to detect marine mammal sounds by hydrophones. Data on the marine mammals can then be relayed back to a surface vessel or other collection location.

Attorney, Agent or Firm:
Jeffrey, Griffin Ip Dept Westerngeco E. L. L. C. (10001 Richmond Avenue, Houston, TX, 77042, US)

Claims:
What is claimed is:

1. A method for facilitating seismic data acquisition, comprising: utilizing an autonomous underwater vehicle to obtain data on water column characteristics in a seismic survey area; transmitting the data to a collection location; and employing the data to correct inaccuracies of seismic data obtained during a seismic survey of the seismic survey area.

2. The method as recited in claim 1, wherein utilizing comprises utilizing a glider programmed to glide underwater along a desired trajectory.

3. The method as recited in claim 2, further comprising updating the desired trajectory iteratively.

4. The method as recited in claim 1, wherein utilizing comprises utilizing the autonomous underwater vehicle to obtain sound velocity data in the seismic survey area.

5. The method as recited in claim 4, wherein utilizing comprises automatically directing the autonomous underwater vehicle to sound velocity interfaces.

6. The method as recited in claim 1, further comprising utilizing an onboard generator system to charge the autonomous underwater vehicle.

7. The method as recited in claim 1, wherein transmitting comprises transmitting data via satellite communication.

8. The method as recited in claim 1, wherein transmitting comprises transmitting data from the surface vessel to the autonomous underwater vehicle.

9. The method as recited in claim 1, wherein employing comprises computing static corrections to account for changes in sound travel time during the seismic survey.

10. The method as recited in claim 9, further comprising using the static corrections to facilitate the processing of time-lapse data.

11. The method as recited in claim 1, wherein employing comprises using the data to create a water-sound velocity model.

12. The method as recited in claim 1, further comprising mounting at least one hydrophone and at least one accelerometer to the autonomous underwater vehicle to obtain and record seismic data.

13. A method, comprising: obtaining data in a marine survey area with an autonomous underwater vehicle; using the data to determine a water column characteristic at multiple locations in the marine survey area; and employing the water column characteristics to improve the usefulness of seismic data obtained during a seismic survey of the marine survey area.

14. The method as recited in claim 13, wherein obtaining comprise obtaining sound velocity data with a glider that glides underwater according to programmed instructions.

15. The method as recited in claim 13, wherein employing comprises computing static corrections to account for changes in sound travel time during the seismic survey.

16. The method as recited in claim 15, further comprising using the static corrections to facilitate the processing of time-lapse data.

17. The method as recited in claim 14, further comprising employing the glider to obtain and record supplemental seismic data; and comparing the supplemental seismic data to the seismic data obtained during the seismic survey.

18. The method as recited in claim 13, wherein obtaining comprises obtaining data on the location of marine mammals proximate the marine survey area.

19. The method as recited in claim 13, wherein obtaining comprises utilizing at least one hydrophone to capture a range of frequencies expected from marine mammals.

20. A system, comprising: an autonomous underwater vehicle having trajectory control features of that are adjustable to control the trajectory of the autonomous underwater vehicle when underwater, the autonomous underwater vehicle further comprising at least one detector to collect data related to sound velocity; and a processing system selectively placed in communication with the autonomous underwater vehicle to collect the data, wherein the processing system uses the data to create a map of sound velocity in a marine survey area.

21. The system as recited in claim 20, further comprising a surface ship, wherein the processing system is located on the surface ship.

22. A method, comprising: obtaining data related to characteristics of a water column in a seismic survey area with an autonomous underwater vehicle; and performing a seismic survey throughout the seismic survey area.

23. The method as recited in claim 22, further comprising adjusting seismic data obtained through the seismic survey based on data obtained with the autonomous underwater vehicle.

24. The method as recited in claim 22, wherein obtaining data comprises obtaining data on the location of marine mammals.

25. The method as recited in claim 22, further comprising updating autonomous underwater vehicle control data to locally adjust the trajectories of the autonomous underwater vehicle while the autonomous underwater vehicle is deployed to obtain data through a local controller that seeks a sensor detected gradient.

26. The method as recited in claim 22, further comprising: obtaining the coordinates of the autonomous underwater vehicle; processing data collected by the autonomous underwater vehicle to separate current direction and amplitude of force from lift induced forces; and based on the processed data, adjusting steering control spread elements to optimize a spread element trajectory.

27. The method as recited in claim 22, further comprising optimizing trajectories of the autonomous underwater vehicle to anticipate current ahead of a seismic spread to provide a recent current regime.

External link: http://www.freepatentsonline.com/y2010/0302901.html

Tags:
Author:Jeffrey Griffin