Ocean Bottom Node Seismic Data Analysis Using Travel Time Inversion
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Solution Overview
Problem
In underwater seismic exploration, accurate shot and receiver positions, receiver timing, and water column velocity models are crucial for deep water time-lapse monitoring, but existing methods struggle to simultaneously correct for clock drift and water velocity variations, leading to uncertainties and errors in data processing.
Innovation Solution
A travel time inversion process that minimizes errors between actual and modeled direct arrival times to determine shot and receiver positions, receiver clock drift, and water column velocity, using angular designature and conjugate gradient methods to iteratively refine RMS error, accounting for tide height and clock drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If nodes remain on the seafloor for extended periods (30+ days) to cover full tidal cycles, then data coverage and tidal cycle completeness are improved, but clock drift uncertainty and timing errors increase
Solution Approach 1:
The system performs preliminary actions by recording GPS synchronization time and tide height data at the moment of node deployment, and stores these as reference values. During retrieval, these pre-recorded reference values are used to calculate clock drift and correct timing errors, allowing the node to maintain accurate timing even after extended deployment periods
Solution Approach 2:
The system establishes a feedback mechanism where clock drift is calculated by comparing the node's internal clock time with the recorded GPS synchronization time, and tide height corrections are applied based on recorded reference tide heights. This feedback loop enables continuous timing correction despite long deployment durations
2Device complexity
If traditional separate correction methods are used for clock drift and water velocity, then processing complexity is reduced, but positioning accuracy and timing precision deteriorate
Solution Approach 1:
The system merges the correction of clock drift and water velocity variations into a unified processing framework. By simultaneously applying GPS-based clock drift correction and tide height-based velocity correction using correlated reference data, the system achieves accurate positioning and timing without requiring complex separate correction procedures
Solution Approach 2:
The system uses recorded GPS time and tide height data as intermediary reference values that mediate between the node's internal measurements and external reality. These intermediaries enable accurate correction of both timing and velocity effects without requiring complex direct measurements
3Device complexity
If clock drift is corrected using only GPS synchronization time, then timing correction is simplified, but accuracy deteriorates under varying water velocity conditions
Solution Approach 1:
The system records GPS synchronization time and tide height data at deployment as preliminary reference values. During retrieval, these pre-recorded references are used to calculate corrected clock drift that accounts for both timing offset and water velocity variations, providing accurate correction without complex real-time measurements
Solution Approach 2:
The system changes the approach to clock drift correction by incorporating tide height variations as an additional parameter. Instead of using only GPS synchronization time, the corrected clock drift calculation includes tide height differences that reflect water velocity changes, thereby improving timing correction accuracy under varying environmental conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate shot and receiver positioning, timing, and water column velocity models, significantly reducing RMS errors and enabling reliable 4D seismic mapping by accounting for dynamic water column conditions, thus improving the accuracy of hydrocarbon reservoir assessments.
Implementation Method 1
A source, such as a vibrator unit, dynamite shot, or an air gun, generates acoustic or elastic vibrations that travel into the Earth
Implementation Method 2
pass through strata with different seismic responses and filtering effects, and return to the surface to be recorded as seismic data
Implementation Method 3
placing geophones in a wellbore (as in a vertical seismic profile) to record the seismic signal
Data Source
Figure 1~2
Figure 3a~3b
Figure 3c
AI summary
The present invention permits RMS traveltime error in a seismic data acquisition to be minimized. Field measurements of source and receiver coordinates, speed of sound in water as a function of depth and time, receiver timing, and clock drift are first collected. The seismic data is then examined to measure travel time from each source to each reciever. A model travel time can then be computed based on the field measurements. By iteratively perturbing at least one of the field measured data using a look-up table and calculating the travel time after each perturbation until an acceptable RMS error has been achieved, conditioned seismic data that takes into account the dynamic nature of the water column will provide the basis for creating an accurate seismic map that is unaffected by the changing water conditions.