Distributed Acoustic Sensing VSP Modeling via Reciprocity
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Solution Overview
Problem
Conventional methods for modeling and processing seismic data are not effective for distributed acoustic sensing (DAS) data, which measures strain or strain-rate, leading to inaccurate results in borehole seismic surveys for reservoir characterization.
Innovation Solution
A method is developed to generate DAS vertical seismic profile (VSP) data by receiving synthetic DAS acquisition parameters, modeling synthetic pressure-field data, augmenting it using reciprocity, sorting into pressure-field common shot gathers, and converting these to strain-rate DAS VSP data through spatial and temporal derivatives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional seismic data processing methods are used for DAS data, then processing can be performed with existing tools, but the results are inaccurate because DAS measures strain or strain-rate rather than pressure or particle motion
Solution Approach 1:
The patent replaces conventional pressure-based seismic processing methods with a specialized processing system designed for strain-rate measurements. The system uses fiber optic cables with distributed acoustic sensing technology to measure strain or strain-rate along the cable, and implements a processing workflow that specifically handles these measurements through spatial derivatives and temporal integrals to convert strain-rate data into displacement data suitable for seismic imaging.
Solution Approach 2:
The patent changes the measurement parameter from pressure or particle motion to strain or strain-rate. The processing method accounts for this fundamental parameter change by implementing specific mathematical operations (spatial derivatives to convert strain-rate to velocity, temporal integrals to convert velocity to displacement) that transform the strain-rate measurements into seismic-compatible data.
2Productivity
If reciprocity is implemented for DAS VSP modeling, then computational efficiency improves given the large number of shots versus receivers, but implementing strain or strain-rate as a reciprocal source is not straightforward
Solution Approach 1:
The patent uses an intermediary approach by first modeling with pressure sources and then converting the results to strain-rate measurements through mathematical transformations. This intermediary step allows the use of conventional reciprocity-based modeling techniques while ultimately producing the correct strain-rate data format required for DAS processing.
Solution Approach 2:
The patent segments the modeling process into distinct computational stages: (1) forward modeling of pressure fields from multiple shots, (2) application of reciprocity principles to reduce computational load, (3) conversion of pressure-field data to strain-rate measurements through spatial derivatives, and (4) temporal integration to obtain displacement data. This segmentation allows efficient processing while maintaining accuracy.
3Measurement precision
If DAS VSP surveys are conducted for reservoir characterization, then subsurface imaging quality improves, but accurate determination of acquisition parameters requires sophisticated modeling that is currently unavailable
Solution Approach 1:
The patent implements a self-service modeling system that generates synthetic DAS VSP data using the newly developed processing methods. The system uses the same strain-rate measurement and conversion techniques that will be applied to field data, allowing acquisition parameters to be optimized based on realistic synthetic examples rather than conventional pressure-based models.
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 allows for more accurate DAS VSP synthetic data, enabling better determination of acquisition parameters for field surveys, which improves the quality and resolution of subsurface images and reduces uncertainty in subsurface models.
Implementation Method 1
An acoustic signal 18 encountering the fiber-optic cable 12 is recorded as a change in strain or strain-rate along the cable and may be considered to be a seismic event.
Implementation Method 2
A laser pulse 14 propagates through the fiber-optic cable 12, shown as light stream 16.
Data Source
AI summary
A method is described for generating distributed acoustic sensing (DAS) vertical seismic profile (VSP) data including receiving, at one or more processing cores, synthetic DAS acquisition parameters; modeling synthetic pressure-field data; augmenting the synthetic pressure-field data using reciprocity to generate an augmented dataset; sorting the augmented dataset into pressure-field common shot gathers; and converting the pressure-field common shot gathers to strain-rate DAS VSP data. The converting may be done by taking a spatial derivative of pressure along a DAS cable; performing a temporal integral to find particle velocity along the DAS cable; and taking a spatial derivative of the partial velocity along the DAS cable to convert the pressure-field common shot gathers to strain-rate DAS VSP data.