DAS Depth Calibration Using Multi-Gauge VSP Impedance Matching
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Solution Overview
Problem
Existing DAS systems struggle to accurately pinpoint the exact physical depth of DAS receiver channels in relation to geology, necessitating improved depth calibration for precise vertical seismic profiling.
Innovation Solution
A method involving multi-gauge length measurements and data manipulation techniques, including shifting and stretching/squeezing DAS seismic data to align DAS impedance with well log data, using a misfit functional to optimize correlation and determine a calibrated VSP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DAS systems use backscattered signals from fiber-optic cables for depth calibration, then seismic data acquisition is enabled, but the exact physical depth of vibrations cannot be precisely determined due to external conditions affecting the signals
Solution Approach 1:
The patent introduces an intermediary calibration process that uses well log data (density and acoustic slowness logs) as a mediator to bridge the DAS seismic data and the subsurface geological formations. By computing impedance curves from both DAS data and well log data, and optimizing the match between them, the system indirectly determines the correct depth calibration without relying directly on the unstable backscattered signals alone.
Solution Approach 2:
The patent applies parameter changes by introducing depth adjustment parameters (shift and stretch/squeeze) that modify the depth axis of the DAS seismic data. These parameters are optimized to maximize the correlation between the DAS impedance curve and the well log impedance curve, thereby adjusting the depth calibration to compensate for signal instability and external conditions.
2Measurement precision
If multiple gauge lengths are used for VSP data acquisition, then subsurface feature delineation is improved, but the complexity of depth calibration increases
Solution Approach 1:
The patent merges the calibration information from multiple gauge lengths by computing impedance curves for each gauge length and combining them through a misfit functional optimization. This approach integrates the advantages of multiple gauge lengths for better subsurface feature delineation while managing the calibration complexity through a unified optimization framework that simultaneously adjusts depth parameters for all gauge lengths.
Solution Approach 2:
The patent creates a universal calibration approach that works across multiple gauge lengths using a common misfit functional and depth adjustment parameters. The same calibration parameters (shift and stretch/squeeze) are applied universally to all gauge lengths, allowing the system to handle multiple gauge lengths without proportionally increasing calibration complexity.
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
Enhances the accuracy of depth calibration in DAS systems, allowing for precise localization of seismic vibrations and improved seismic imaging, facilitating better subsurface feature delineation and well planning.
Implementation Method 1
The backscattering occurs along the cable and can be analyzed to record a seismic wavefield impinging upon it
Data Source
AI summary
Systems and methods are presented for determining a calibrated vertical seismic profile (VSP) with a distributed acoustic sensing (DAS) system in a borehole. The methods include obtaining a density log and an acoustic slowness log for the borehole; determining a first impedance, a DAS impedance from well log (DIL) curve, from the density log and the acoustic slowness log; obtaining a VSP dataset in the borehole; for each of the plurality of gauge lengths: determining a second impedance, a DAS from vibrations (DIV) curve, from the VSP dataset for the plurality of gauge lengths, and determining a fit between the DIV curves and the DIL curve by using a misfit functional for each of a plurality of depth adjustments. The method further includes determining the calibrated VSP by applying a preferred depth adjustment to the VSP dataset.