DAS Data Conversion to Geophone Velocity Response
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Solution Overview
Problem
Distributed Acoustic Sensing (DAS) data, used in well drilling and completion operations, measures integrated strain rather than particle velocity, making it less compatible with existing geophone seismic monitoring systems, which require particle velocity measurements at specific locations rather than averaged over a gauge length.
Innovation Solution
Converting DAS data into equivalent geophone response data by processing it to match particle velocity measurements at specific locations, eliminating the need for prior knowledge of wave velocities and allowing for full-spectrum particle velocity output independent of formation velocity, thus aligning with geophone response characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If DAS data is used directly for seismic monitoring, then measurement coverage is improved, but measurement precision deteriorates because DAS measures integrated strain over a gauge length rather than particle velocity at specific locations
Solution Approach 1:
The patent segments the DAS measurement data by dividing the continuous fiber optic cable into discrete measurement intervals corresponding to geophone locations. By processing the integrated strain measurements and differentiating with respect to position, the system extracts particle velocity information at specific locations rather than averaged values, thereby resolving the contradiction between coverage and precision.
Solution Approach 2:
The patent introduces an intermediate processing step that acts as a mediator between DAS measurements and geophone response requirements. This intermediary process involves mathematical operations (differentiation and filtering) that transform the DAS strain data into equivalent particle velocity measurements, enabling compatibility with existing geophone-based seismic monitoring systems.
2Adaptability or versatility
If DAS data is converted to equivalent geophone response, then adaptability to existing systems is improved, but device complexity increases due to additional processing requirements
Solution Approach 1:
The patent replaces the need for physical geophone devices with a computational approach. Instead of deploying actual geophones, the system uses optical fiber DAS measurements combined with signal processing algorithms to simulate geophone responses. This substitution reduces physical device complexity while maintaining adaptability to existing seismic monitoring systems.
Solution Approach 2:
The patent changes the measurement parameters from integrated strain (DAS native output) to particle velocity (geophone native output) through mathematical transformation. By applying differentiation operations and frequency-domain filtering, the system transforms the data parameters to match geophone response characteristics, enabling seamless integration with existing systems despite the increased processing complexity.
3Measurement precision
If full-spectrum particle velocity output is provided independent of formation velocity, then measurement precision is improved, but loss of information increases due to noise in raw DAS data
Solution Approach 1:
The patent applies preliminary filtering actions to the DAS data before converting to particle velocity. By pre-processing the strain measurements with appropriate filters and applying windowing functions, the system reduces noise content in advance, preserving more useful information during the subsequent differentiation and velocity calculation steps, thereby reducing information loss while maintaining precision.
Solution Approach 2:
The patent converts the harmful effect of noise in DAS data into a benefit by applying sophisticated signal processing techniques. Through techniques such as frequency-domain filtering, spectral analysis, and noise characterization, the system identifies and removes noise components while preserving the actual seismic signals, thereby transforming the noisy raw data into high-quality particle velocity measurements with minimal information loss.
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 conversion enables more accurate seismic monitoring by providing particle velocity data that is independent of formation velocity and phase shift, enhancing the sensitivity and accuracy of seismic data interpretation without requiring assumptions about wave velocities, thereby improving hydrocarbon recovery operations.
Implementation Method 1
Distributed acoustic sensing (DAS) data is detected from a seismic wave traversing the subsurface formation via the optical fiber. The DAS data comprises measurements of a relative displacement of light over a gauge length of the optical fiber.
Data Source
AI summary
Systems and methods relate to borehole seismic studies. Traditionally, borehole seismic studies are conducted using geophones. Seismic acquisition can be performed using fiber optic Distributed Acoustic Sensing (DAS). Because DAS measures dynamic relative displacement over a gauge length, which is different from particle velocity, DAS data can be converted into an equivalent geophone output response. Operations include converting DAS data into distributed velocity, and then, converting the velocity output into an equivalent geophone response. Various aspects include separating the data into interleaving subsets, integrating each subset along the spatial coordinates, selecting a window width over which the median of each subset will be calculated and subtracted from the data, performing a spatial average or low-pass filtering over contiguous values, performing a time-domain low-pass filtering, and performing the velocity-to-geophone conversion operation.