Clock drift

Abstract

In some examples, the present disclosure provides a method for determining drift in clock data provided by a clock of a seismic sensor. The sensor is exposed to a varying ambient temperature over time. The method includes obtaining temperature data associated with the ambient temperature as a function of time. The method also includes obtaining clock data. The method also includes obtaining timestamp data provided by a Global Navigation Satellite System. The method also includes determining drift data that minimizes a time drift difference in the clock data based on the timestamp data and the temperature data. The method also includes outputting correction data based on the determined drift data.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, methods for determining drift in clock data and methods for processing clock data. The present invention also relates to corresponding devices, computer programs or computer program products. Background Art

[0002] This section is intended to introduce the reader to various aspects of the art that may be relevant to various aspects of the present disclosure, which are described and / or claimed below. This discussion is considered to be helpful in providing background information to the reader to facilitate a better understanding of various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read from this perspective and not as an admission of prior art.

[0003] A seismic survey involves generating an image or map of a subsurface area of the earth by sending acoustic energy down into the ground and recording the reflected acoustic energy returning from geological formations within the subsurface area.

[0004] During a seismic survey, energy sources are placed at various locations on or above an area of the earth's surface that may include hydrocarbon deposits. Whenever a source is activated, the source generates seismic (e.g., acoustic) energy that travels downward through the earth, is reflected, and is recorded upon return using one or more seismic sensors placed on or above the subsurface area of the earth. Seismic data is recorded by the seismic sensors, where each seismic sensor includes a clock configured to provide clock data. The seismic data can then be used to create an image or profile of the corresponding subsurface area. Summary of the Invention

[0005] An overview of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide a brief overview of these certain embodiments to the reader and are not intended to limit the scope of the present disclosure. Indeed, the present disclosure may include aspects that may not be set forth below.

[0006] The clock data provided by the clock of a seismic sensor should be accurate so that the seismic data (synchronized with the clock data) can be accurately interpreted. However, the seismic sensor may be exposed to environmental temperatures that vary over time, which may cause drift in the clock data.

[0007] Accordingly, current embodiments of the present disclosure can achieve determination of drift in clock data (provided by the clock of a seismic sensor), where the seismic sensor is exposed to environmental temperatures that vary over time.

[0008] In some embodiments, the determined drift in the clock data can be corrected so that the clock data of the seismic sensor is accurate and so that the seismic data can be accurately interpreted even when the seismic sensor is exposed to environmental temperatures that vary over time.

[0009] Aspects and embodiments of the invention are set forth in the appended claims. These and other aspects and embodiments of the invention are also described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments of the present disclosure will now be described by way of example with reference to the accompanying drawings, in which:

[0011] Figure 1 Schematically illustrate a plurality of example seismic sensors disposed in or above a survey area during a seismic survey;

[0012] Figure 2 Schematically illustrate an example control system and a plurality of example seismic sensors;

[0013] Figure 3 Schematically illustrate an example seismic sensor;

[0014] Figure 4 Schematically illustrate an example amount of clock drift that occurs over time for a clock;

[0015] Figure 5 Schematically illustrate an example graph of a drift rate (expressed as a function of ambient temperature) exhibited by clock data;

[0016] Figure 6 Show an example graph of temperature data that is a function of time and is obtained, for example, by a thermometer of a seismic sensor and reflects ambient temperature;

[0017] Figure 7 Show an example graph of the determined integral of the ambient temperature T(t) between time t0 (associated with the start of the recording period of the sensor) and time t; and

[0018] Figure 8 Show a flowchart schematically illustrating an example method according to the present disclosure;

[0019] Figure 9 Show schematically illustrate Figure 8 a flowchart of the detailed steps of an example method;

[0020] Figure 10 Show schematically illustrate Figure 8 a flowchart of other detailed steps of an example method;

[0021] Figure 11 Show a flowchart schematically illustrating another example method according to the present disclosure.

[0022] In the drawings, like elements have the same reference numerals. DETAILED DESCRIPTION

[0023] Figure 1 Schematically illustrate a plurality of exemplary seismic sensors 15 disposed in or above a survey area 16 of the Earth during a seismic survey. The sensors 15 are configured to record reflected seismic energy returned from geological layers within the survey area 16.

[0024] A Global Navigation Satellite System (GNSS) 20 provides timestamp data to the sensors 15 during the seismic survey to assist in creating an image or profile of the corresponding survey area 16.

[0025] Before the start of the seismic survey, the sensors 15 can be initialized, for example, calibrated. After completion of the seismic survey, the seismic data recorded by the sensors 15 can be collected and used to create an image or profile of the corresponding subsurface area.

[0026] In some embodiments, the sensors 15 can operate in conjunction with a control system 10 to perform initialization of the sensors 15 and / or to perform collection of the seismic data recorded by the sensors 15.

[0027] Figure 2 Schematically illustrate an exemplary control system 10 and a plurality of exemplary seismic sensors 15.

[0028] The control system 10 includes a docking station 14 in which a plurality of sensors 15 can be detachably docked, as illustrated by the Figure 2 arrow.

[0029] The control system 10 can also include a processor 11, a memory 12, and / or a communication module 13, which are configured to communicate with the communication module of the sensors 15, for example, when the sensors 15 are docked in the docking station 14 of the control system 10. The processor 11, the memory 12, and the communication module 13 can implement initialization of the sensors 15 (e.g., during calibration). The processor 11, the memory 12, and / or the communication module 13 can also implement collection / retrieval of the seismic data already recorded by the sensors, for example, when the sensors 15 are docked in the docking station 14 of the control system 10. In other words, by an example embodiment, the sensors 15 can be initialized by being docked in the docking station 14 before being deployed in the survey area 16. Next, when the sensors 15 are deployed in the survey area 16, the sensors 15 can record seismic data. Finally, when the sensors 15 are deployed in the survey area 16, the sensors 15 can be collected from the survey area 16 and redocked within the docking station 14 in order to collect the data recorded by the sensors 15. For one or more embodiments, when the sensors 15 are redocked within the docking station 14, clock drift caused by varying environmental temperatures can be corrected.

[0030] As Figure 2As described, each sensor 15 can have at least two configurations. In a first configuration, the sensor 15 can be docked in the docking station 14 of the control system 10, for example, for performing initialization and / or for being transported to the survey area. In a second configuration, the sensor 15 can be deployed in the survey area for measuring seismic data.

[0031] As Figure 3 described, the sensor 15 includes a communication module 151 configured to communicate with the communication module 13 of the control system 10.

[0032] The sensor 15 further includes a processor 152 and a memory 153. In some examples, the sensor 15 can include a thermometer 154.

[0033] The sensor 15 can further include a clock 155 configured to provide clock data.

[0034] The sensor 15 can include an antenna 156 configured to receive timestamp data provided by the GNNS 20. In some examples, the timestamp data provided by the GNNS 20 can be used by the sensor 15 to correct time irregularities in the period of the clock data provided by the clock 155 (of the sensor 15). The time irregularities can be considered as the deviation between the clock data of the clock 155 and the received timestamp data. As described above, for one or more embodiments, the time irregularities can be corrected when the sensor 15 is redocked within the docking station 14.

[0035] One or more embodiments of the present invention can consider the timestamp data (received from the GNNS 20) as a reliable / authoritative source of time data. Thus, to correct the above time irregularities, one or more embodiments can compare the clock data (provided by the clock 155) with the received timestamp (provided by the GNNS 20). In the case where there is a deviation / difference between the clock data and the timestamp data, one or more embodiments can consider such deviation / difference as time irregularities. The above clock drift can be evidenced by such time irregularities. After comparing the received timestamp (provided by the GNNS 20) with the clock data (provided by the clock 155), the sensor 15 can correct the time irregularities, as described in more detail below.

[0036] Figure 4 Schematically illustrates an example amount of clock drift that occurs over time. As Figure 4 described, the clock data provided by the clock during a seismic survey may be affected by drift that generates time irregularities over time. During Figure 4In [the figure], the circled curve corresponds to drift measurements over a period of approximately 8 days (as determined by comparing received clock data with received timestamp data). As reflected by the circled curve of ( Figure 4 ), the drift can vary dynamically over an 8-day period. For example, between days 1 and 5, the amount of drift tends to further become negative until it reaches an amount of approximately -25 milliseconds. After day 5, the amount of drift tends to increase to positive until it reaches an amount of approximately 90 ms on day 8. As shown above, the trend of the amount of drift is dynamically changing, and the dynamically changing trend cannot be accurately represented by a simple two-point trend line. For example, assume a two-point trend line is drawn between the first measurement at the start (day 1) and the second measurement at the end of day 8. This two-point trend line only reflects an upward, increasing drift and cannot accurately reflect the actual, dynamically changing amount of drift. One or more embodiments can accurately account for the dynamically changing amount of drift, and one or more embodiments can correct this dynamically changing amount of drift.

[0037] Figure 5 An example graph schematically illustrating the drift rate exhibited by clock data (such as expressed as a function of ambient temperature). As Figure 5 illustrated, during a seismic survey, the drift rate of clock data can be a function of the ambient temperature around a seismic sensor during seismic data collection. Figure 5 An example graph schematically illustrating the drift rate in clock data as a function of ambient temperature. In the example of Figure 5 , the drift rate varies linearly with temperature over a temperature range of about 20°C (e.g., between -40°C and -20°C in Figure 5 ), but the change in the drift rate is non-linear above a certain temperature (e.g., temperatures above -20°C in Figure 5 ).

[0038] In some examples, during a seismic survey, the temperature range of the ambient temperature around the sensor can be very large, such that the sensor may not be able to adjust its clock with sufficient regularity using timestamp data provided by GNSS.

[0039] Accordingly, one or more embodiments of the present disclosure can determine the drift in clock data, where the clock data is provided by the clock of a seismic sensor and where the seismic sensor is exposed to a time-varying ambient temperature.

[0040] In some embodiments, the determined drift in the clock data can be adjusted / corrected such that the clock data of the seismic sensor is accurate and such that seismic data can be accurately interpreted even when the seismic sensor is exposed to a time-varying ambient temperature.

[0041] One or more embodiments of the present invention may determine the amount of drift by using the received temperature data, and one or more embodiments may use the received temperature data to correct / adjust the drift.

[0042] Figure 6 An example graph showing temperature data that reflects the ambient temperature, e.g., obtained by a thermometer of a seismic sensor, as a function of time. Figure 6 An example of the obtained temperature data T(t) is shown, which reflects the ambient temperature around the sensor during a seismic survey as a function of time. The obtained temperature data T(t) may be provided, for example, by a thermometer of the sensor. As Figure 6 illustrated, in some examples, the temperature data may be represented by a representative curve, where the representative curve is determined by performing a smoothing function on the temperature data.

[0043] Figure 7 An example of the integral of the ambient temperature T(t) between a time t0 associated with the start of a recording period (e.g., at the start of a seismic survey) and the current time t (e.g., during a seismic survey) is shown.

[0044] Figure 8 A flowchart illustrating an example method 100 according to the present disclosure by using the above-received clock data and received temperature data is shown. As described in more detail below, the example method 100 may output correction data that may be used to correct the drift in the clock data.

[0045] Figure 8 The method 100 illustrated in may include obtaining, at S1, temperature data that reflects the ambient temperature (around the sensor) as a function of time. As described above, the temperature data may be provided, for example, by a thermometer. The method 100 may also include obtaining, at S2, clock data provided by a clock of the sensor.

[0046] In some examples, the temperature data obtained at S1 may be provided by a thermometer of the sensor. Alternatively or additionally, the temperature data may be provided in other ways, e.g., by other thermometers, such as a thermometer provided in a control system. As described above, the control system may operate in conjunction with the sensor when initializing the sensor or when retrieving / collecting seismic data from the sensor.

[0047] An example of the obtained temperature data is illustrated in Figure 6 and has been discussed. The obtained temperature data may be used to correct the drift, as described in more detail below.

[0048] In addition to the clock data obtained (at S2), one or more embodiments may also obtain timestamp data provided by GNSS (at S3). As described above, by comparing the timestamp data with the clock data provided by the sensor's clock, and by determining the difference between the clock data (provided by the clock) and the timestamp data (provided by GNSS), one or more embodiments may determine drift data (at S4) that reflects the time drift in the clock data. The difference between the clock data and the timestamp data may indicate that drift has occurred.

[0049] Method 100 may also include determining and outputting correction data at S5. One or more embodiments may use the determined correction data to correct the clock data, as explained below. As described below, the correction data may be determined based on received temperature data.

[0050] In some examples, determining the correction data at S5 includes parameterizing drift D(t), where:

[0051] D(t) = [a x θ(t)]+(b x t) (E)

[0052] In the above equation (E), is the integral of the ambient temperature T(t) between the time t0 associated with the start of the sensor's recording period and the current time t during the sensor's recording period, such that:

[0053]

[0054] An example of Figure 7 is illustrated in and has been discussed.

[0055] In some examples, the recording period may correspond to, for example, several hours or days. In some examples, the recording period may correspond to the duration of a seismic survey during which a seismic sensor is deployed to measure seismic data.

[0056] In the drift D(t) of the above equation (E), the parameters (a, b) are parameters determined to minimize the difference between D(t) and the measured time drift (as determined by comparing the clock data and the timestamp data). Thus, for one or more embodiments, determining the correction data at S5 may include determining the parameters (a, b). D(t0) may be such that:

[0057] D(t0) = 0.

[0058] Thus, it should be understood that at S5, one or more embodiments determine correction data that minimizes the difference between the determined drift data and the measured time drift.

[0059] In other words, for one or more embodiments, by determining the parameters (a, b) that minimize the above differences, a best-fit curve describing the drift D(t) can be determined.

[0060] Figure 8 Method 100 further includes outputting correction data at S5 based on the determined drift data. The drift in the clock data can be corrected based on the output correction data. In some examples, determining the correction data includes determining the parameters (a, b) for equation (E).

[0061] For one or more embodiments, once the correction data is determined, the correction data can be used to correct the occurrence of drift in the clock data. For example, such correction may occur when data recorded by a sensor is being collected via a docking station. In other words, for one or more embodiments, after all the data has been received by the sensor, the correction data corrects the occurrence of drift.

[0062] In some examples, outputting the correction data (at S5) can include performing at least one of the following:

[0063] (1) storing the correction data in the memory of the seismic sensor and / or the memory of the control system (e.g., for further reference); and / or (2) providing the correction data to the processor of the seismic sensor and / or the processor of the control system (e.g., for immediate use, such as for correcting drift).

[0064] As Figure 5 and Figure 6 (discussed above) illustrates, during one or more recording cycles, the ambient temperature can vary within one or more temperature ranges. In Figure 5 an example, for instance, the ambient temperature varies between a first range (e.g., a temperature range below -40°C), a second range (e.g., a range between -40°C and -20°C), and a third range (e.g., a range above -20°C). Thus, the method can include determining correction data corresponding to each temperature range of the ambient temperature.

[0065] In some examples, determining the correction data includes determining the parameters (a, b) of equation (E), as described above.

[0066] Alternatively or additionally, in some examples, the correction data can include temperature data. As described above, the correction data can correspond to different temperature ranges of the ambient temperature. The temperature data associated with the correction data can include data associated with at least one of the following:

[0067] the highest temperature of each temperature range; and / or

[0068] The lowest temperature of each temperature range; and / or

[0069] The average temperature of each temperature range.

[0070] In some examples, outputting the calibration data at S5 can include storing the calibration data corresponding to each temperature range in a library associated with the plurality of temperature ranges. The library can be located in the memory of the sensor and / or in the memory of the control system.

[0071] As Figure 9 illustrated, at S5, one or more embodiments can output the calibration data by performing at least one of the following: Method S5 includes, at S51, determining one or more calibration data for one or more calibration periods and / or one or more seismic survey periods. Method S5 can further include, at S52, updating the determined one or more calibration data (previously determined). Method S5 includes, at S53, outputting the updated calibration data.

[0072] As Figure 10 illustrated, in some examples, updating the determined one or more calibration data (previously determined) at S52 can include at least one of the following. As described above, the calibration data can include at least the parameters (a, b) that allow the calculation of temperature drift. Method S52 includes, at S521, comparing the determined one or more calibration data (e.g., comparing the previously determined calibration data with the newly determined calibration data). Method S52 can further include: at S522, selecting the determined one or more calibration data based on the comparison. In other words, the newly determined calibration data can be selected as the applicable calibration data. Method S52 can further include, at S523, averaging the determined one or more calibration data. In other words, the previously determined calibration data can be combined and / or averaged with the newly determined calibration data.

[0073] In some examples, selecting the determined one or more calibration data (at S522) can include: outputting the calibration data output during the previous one or more recording periods of the sensor and / or at least one other sensor.

[0074] In some examples, method 100 can be at least partially implemented by Figure 2 system 10 and / or Figure 3 sensor 15.

[0075] Method 100 can achieve reducing the presence of timing errors in the seismic data, where the seismic data is provided by the sensor and where the sensor cannot adjust its clock with sufficient regularity using the timestamp data provided by GNSS 20.

[0076] Figure 11 Schematically illustrate a method 200 for processing clock data provided by a clock of a seismic sensor, where the seismic sensor has been exposed to a time-varying ambient temperature.

[0077] Figure 11 The method 200 illustrated in may include one or more of the following: obtaining clock data and timestamp data at S10 (where the timestamp data is provided by a Global Navigation Satellite System). The method 200 may also include determining at S20 whether the obtained timestamp data includes at least one time gap greater than a predetermined threshold.

[0078] Using one or more embodiments, a time gap may be defined as the duration between continuously receiving timestamp data from GNSS. For one or more embodiments, the predetermined threshold may be a duration between 1 hour and 10 hours, such as 6 hours. In the example, a time gap greater than 6 hours means that the sensor has not received timestamp data from GNSS for at least 6 hours.

[0079] If it is determined at S20 that the obtained timestamp data includes at least one determined time gap greater than a predetermined threshold, the method 200 may further include estimating correction data associated with the drift in the clock data at S30, the drift being a function of time and ambient temperature. In some examples, the correction data may be determined at least in part by the method 100 according to the present disclosure for the sensor and / or at least one other sensor.

[0080] The method 200 may also include, for each time gap greater than a predetermined threshold, correcting the corresponding clock data based on the obtained correction data at S40.

[0081] The method 200 may achieve reducing timing errors in seismic data provided by the sensor, where the sensor cannot adjust their clocks with sufficient regularity using the timestamp data provided by GNSS 20.

[0082] In some examples, the method 200 may be at least partially implemented by Figure 2 the system 10 and / or Figure 3 the sensor 15.

[0083] Modifications and variations

[0084] In some examples, alternatively or additionally, Figure 3 the communication module 151 of may be configured to communicate wirelessly with the communication module 13.

[0085] In some examples, the communication between the communication module 13 and Figure 3 the communication module 151 of may include at least one of the following:

[0086] (1) Configuration data from the control system 10 to the sensor 15, such as for setting the recording gain of the sensor 15; and / or

[0087] (2) Seismic data from the sensor 15 to the system 10, such as during and / or after a seismic survey; and / or

[0088] (3) Temperature data from the sensor 15 to the system 10 / from the system 10 to the sensor 15, such as during and / or after a seismic survey; and / or

[0089] (4) Drift data from the sensor 15 to the system 10 / from the system 10 to the sensor 15, such as during and / or after a seismic survey; and / or

[0090] (5) Calibration data from the sensor 15 to the system 10 / from the system 10 to the sensor 15, such as during and / or after a seismic survey.

[0091] Other data can also be contemplated.

[0092] In some examples, the effects of clock aging and / or hysteresis can be negligible, or there can be sufficient timestamp data to characterize them. For one or more embodiments, for a given clock, the main determinant of clock drift variation is the change in ambient temperature. In some examples, the temperature of the sensor can be continuously recorded during the deployment of the sensor.

Claims

1. A method for determining drift in clock data provided by a clock of a seismic sensor, wherein the sensor is exposed to a time-varying ambient temperature, the method comprising: Obtaining temperature data from a seismic sensor exposed to the surrounding environment, wherein the temperature data is associated with the ambient temperature as a function of time; Obtaining the clock data; Obtaining timestamp data provided by a Global Navigation Satellite System; Determining the time drift in the clock data based on the difference between the timestamp data and the clock data; Modeling the drift data based on the temperature data obtained from the seismic sensor; And Determining correction data for correcting the clock data by minimizing the difference between the modeled drift data and the time drift in the clock data.

2. The method according to claim 1, wherein The temperature data and / or the clock data are obtained over at least one recording period, and wherein determining the correction data includes parameterizing the drift data in the form of a drift D(t) such that: D(t) = [a × θ(t)]+(b × t) where Θ is the integral of the ambient temperature T(t) between a time t0 associated with the start of the at least one recording period and the time t, such that: where the parameters (a,b) are determined to minimize the difference between D(t) and the time drift, and D(t0) = 0.

3. The method according to claim 1 or 2, wherein, The temperature data and / or the clock data are obtained over at least one recording period corresponding to a calibration period, and wherein determining the correction data includes determining the correction data based on the time drift in the clock data observed over a recording period of at least one day, wherein the timestamp data includes timestamp data completed during the recording period, and wherein the timestamp data is obtained periodically and the temperature data is obtained continuously.

4. The method according to claim 1, further comprising: Storing the correction data in a memory of the seismic sensor and / or a control system; And / or Providing the correction data to a processor of the seismic sensor and / or the control system.

5. The method according to claim 1, wherein The ambient temperature varies within at least one temperature range during one or more recording periods, and wherein determining the correction data includes determining correction data for each temperature range.

6. The method according to claim 1, wherein, The correction data includes temperature data.

7. The method according to claim 5, wherein The correction data associated with the temperature data includes data associated with at least one of the following: The highest temperature of each temperature range; and / or The lowest temperature of each temperature range; and / or The average temperature of each temperature range.

8. The method according to claim 6, wherein Outputting the correction data includes: Storing the correction data corresponding to each temperature range in a library associated with a plurality of temperature ranges.

9. The method according to claim 2, wherein The correction data includes the parameters (a,b).

10. The method according to claim 2, wherein, At least one recording period corresponds to a measurement period, wherein the seismic sensor is deployed for measuring seismic data, and / or wherein the temperature data and / or the clock data are obtained over at least one recording period corresponding to a calibration period, and wherein determining the correction data includes: Determine one or more correction data for one or more calibration cycles and / or one or more measurement cycles; Update the determined one or more correction data; and Output the updated correction data.

11. The method according to claim 10, wherein, Updating the determined one or more correction data includes at least one of the following: Selecting the determined one or more correction data; or Averaging the determined one or more correction data.

12. The method according to claim 1, wherein, Obtaining the temperature data includes filtering the temperature data to smooth the temperature data.

13. The method according to claim 1, further comprising: Applying the correction data to the clock data so that the time drift in the clock data is minimized.

14. The method according to claim 1, further comprising: Determining whether the clock data includes at least one time gap greater than a predefined threshold in the provided timestamp data; If the clock data includes at least one predefined time gap, determining the correction data; And For each of the at least one determined time gap, correcting the clock data based on the correction data.

15. An apparatus comprising a processor and a memory, the memory including instructions that, when executed by the processor, enable the processor to perform the method according to any one of claims 1 to 14.

Images