Patent Application
20140086008
Embodiments of the invention are generally directed to timing and time synchronization methods, apparatus utilizing these methods, and applications of said methods and apparatus, and more particularly to said methods, apparatus, and applications directed to precisely and accurately creating a seismic data record, most particularly a marine seismic data record.
The ability to generate meaningful and commercially valuable seismic surveys critically relies on the accuracy and precision of the timing relationships between source and signal generation and recordation events. This is particularly challenging in the marine seismic environment. Referring to the illustration in
To effect a marine seismic record, a surface vessel equipped with a GPS-, atomic clock-, or other precision timing device-synchronized seismic source (e.g., air gun) shoots a signal towards the ocean bottom in the vicinity of the node array at a precisely known time; however, the local (resident in) node clock (referred to hereinafter as the ‘node clock’) may not and likely will not be synchronized to any ‘true’ time (e.g., world time, called Coordinated Universal Time (UTC)) regardless of the precision of the timing device (e.g., a voltage controlled oscillator, atomic clock, others; due to, e.g., clock warm-up/stabilization, time drift, and other known factors); thus it will be difficult to accurately determine the real (true) start time and the precise recording times of a nodal seismic record. Moreover, even if a true source (signal) time is known, water temperature variations, salinity, turbidity, and other factors may uncontrollably affect the ability to know a precise relationship between source time and record time events.
Conventional practices including, but not limited to, node clock synchronization prior to node (sensor) deployment, or node clock synchronization prior to establishing the seismic record consume considerable resources and time. For example, when an atomic clock (AC) is used as a node clock, clock stabilization characteristics may not be accurately known during some warm-up duration after starting the clock. If an AC, for example, is remotely restarted, there may be an unknown offset time from true time that can adversely affect precise recording. The effects of quickly changing environmental conditions such as the change in temperature between the air and the water into which a running, pre-synchronized clock is deployed may also alter the ability to precisely and accurately obtain a seismic record.
Applicant's pending US Published Application 2009/0080290 entitled Method and Apparatus for Correcting the Timing Function in a Nodal Seismic Data Acquisition Unit provides additional pertinent background and inventive solutions in the seismic timing field. The subject matter of the '290 published application is incorporated herein by reference in its entirety to the fullest extent allowed by applicable laws and rules.
It would be highly advantageous to provide solutions to the above mentioned and related known challenges and problems associated with precisely and accurately creating a seismic record. It would be particularly advantageous to provide a solution in which node clock synchronization occurred after acquisition of the seismic data record, such that a ‘true’ time could be assigned to the timing schedule of the local node clock for the newly recorded data. Embodiments and aspects of the invention described herein set forth advantageous and beneficial novel solutions to these and related challenges and problems known in the art.
Embodiments of the invention include apparatus, and method(s) and applications utilizing the embodied apparatus and/or method(s) pertaining to the timing, acquisition, synchronization, precision, accuracy, recordation, transfer, etc. of data to, by, and/or from one or more autonomous nodal seismic data acquisition units (‘nodes’), particularly but not limited to autonomous, marine seismic (mid- and deep-water) nodes. As used herein, ‘true’ time refers to the precise real world clock time used as a standard, which may be, e.g., ‘world time’ or Coordinated Universal Time (UTC). As used herein, ‘record’ or ‘seismic record ‘refers to a recording of seismic data, which may include a plurality of sequenced data records obtained after each of a plurality of shot sets or a continuous recording of seismic data over a selected time interval. As used herein, ‘synchronization’ time will refer to that instant of time of the recording of seismic data that is to be synchronized to true time and from which point the data-record timing prior to the synchronization time can precisely be determined. The synchronization may, but need not be a final or intermittent ‘stop’ time of the record.
A non-limiting embodiment of the invention is a timing method referred to herein as ‘inverse timing.’ The method may advantageously be utilized for, e.g., marine seismic applications involving one or more autonomous nodes. The inverse timing method involves the step of synchronizing the timing of newly recorded and/or prior recorded data with a ‘true’ time whereby the synchronizing of timing is performed in a non-traditional ‘reverse’ manner rather than the traditional manner that is performed prior to recording the seismic survey data.
An illustrative inverse timing method includes the steps of establishing a running condition of a local node clock in each of one or more nodes, including generating a local timing schedule; recording seismic data with the node while the timing schedule is running to generate a seismic record; selecting a time of the seismic recording with a discrete value of the timing schedule of the running node clock to establish a synchronization time; associating a true time with the synchronization time; and assigning the true time to the discrete value of the timing schedule of the running node clock, wherein the timing schedule of the running node clock prior to the discrete value of the timing schedule can be accurately associated the true time. In various exemplary, non-limiting aspects the inverse timing method may include one or more of the following further steps or characterizations:
In conjunction with the embodied inverse timing method, an embodied inverse timing system includes a true time source; a node operatively, wirelessly coupled to the true time source, wherein the node includes a local clock characterized as being in one of a non-running/sleep mode and a running mode and further characterized by a timing schedule and a time stamp in the running mode, further wherein the node includes a data recorder and a data record file operatively coupled to the timing schedule, wherein the data record file contains new recorded seismic data or does not contain new recorded seismic data; at least one of a transmitter, a receiver, and a transceiver operatively coupled to the true time source and the node, wherein the local node clock is in an unsynchronized running condition for a given time after the data record file contains new recorded seismic data prior to being in a synchronized running condition after the data record file contains new recorded seismic data.
Additional information including that in regard to nodes and synchronization between the timing of seismic sensor data acquisition and the initiation of a seismic source signal is disclosed in co-owned U.S. Pat. No. 7,310,287, the subject matter of which in herein incorporated by reference to the fullest extent allowed by applicable laws and rules.
In all aspects of the invention, ‘true’ time is available from a true time source as is known in the art. For the purpose of understanding the invention and, in particular, the claim terminology, the following terms have the identified meanings as follow: Running condition of a local node clock means that the local clock has appropriately been ‘woken-up,’ started, and has been determined to be running in a stabilized timing state/condition. Local timing schedule means a time stamp data stream in the node. Seismic record means a record or set of records of seismic data recorded by the node. Selected time of the seismic data record means a particular point in the seismic data record to be associated with a time stamp value. Synchronization time means assigning the time stamp value to the selected time of the seismic data record. A stabilization characteristic, parameter, or metric for the node clock means a substantial assurance that the local clock is running in a time-stabilized (i.e., predictable) condition. Source signal start time means the firing time of a seismic source (gun) signal. Metacontent means data about data content; e.g., offset timing; timing data of the recorded seismic data. A new seismic data record (survey) and a prior recorded seismic data record (survey) mean time-stamped data being recorded or time-stamped data previously recorded and stored in the node database, which has not yet been synchronized with true time.
The steps of an illustrative, non-limiting, exemplary ‘inverse timing’ method are shown in
The synchronization may be assigned a known time offset as appropriate. The illustrative steps (209, 211) of transferring true times/node times to/from an external true time platform and a node for ultimately associating a true time with the synchronization time may be done without any physical contact with the deployed node. An RF, electrical, inductive, or acoustic communication link may be made with the node. In an advantageous aspect, an ROV or AUV, for example, may be brought into proximity with the node and a high bandwidth optical communication link established there between to transfer time values and survey data. Data could also optically be transferred between adjacent nodes for collection by, and transmission from, one or more primary nodes such that, for example, a data transfer between a primary node and an AUV would encompass recorded data from a plurality of non-primary nodes optically coupled to the one or more primary nodes.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening.
The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed.
The instant application claims priority to U.S. provisional application Ser. No. 61/704,814 filed on Sep. 24, 2012, the subject matter of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61704814 | Sep 2012 | US |
