Microseismic Localization Using Head-Wave Arrivals
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Solution Overview
Problem
Current microseismic event localization techniques are adversely affected by multipath arrivals, particularly head waves, which can cause false positive detections and erroneous localizations due to complex wave propagation in unconventional shale plays, leading to limited depth estimation accuracy and mislocalization across high-velocity layers.
Innovation Solution
The method involves analyzing both direct-path and head-wave arrivals to improve microseismic event localization accuracy, utilizing a probabilistic framework based on the Cramér-Rao bound, which combines the information from direct-path and head-wave arrival times to enhance depth estimation by treating head waves as complementary to direct-path information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only direct-path arrivals are used for microseismic event localization, then the analysis is simpler, but depth estimation accuracy is limited and mislocalizations occur across high-velocity layers
Solution Approach 1:
The patent converts the previously harmful head-wave arrivals into beneficial information sources. By identifying and analyzing both direct-path and head-wave arrivals, the system transforms the problematic multipath energy into complementary data that improves depth estimation accuracy by a factor of about 10, preventing mislocalizations across high-velocity layers while maintaining practical analysis complexity through automated arrival identification
Solution Approach 2:
The patent adds the temporal dimension of wave arrival analysis by examining multiple arrival types (direct-path and head-wave) at different times. This multi-dimensional approach to analyzing seismic energy arrivals provides additional constraints for localization, improving depth accuracy without proportionally increasing analysis complexity through efficient use of existing array data
2Reliability
If monitoring arrays are designed to avoid head waves, then false positive detections are reduced, but localization accuracy is compromised
Solution Approach 1:
The patent segments the seismic signal analysis into distinct arrival components - direct-path arrivals and head-wave arrivals. By separately identifying and analyzing each arrival type with appropriate detection criteria, the system maintains high detection reliability while utilizing both arrival types to improve localization accuracy, avoiding false positives through proper classification
Solution Approach 2:
The patent merges information from both direct-path and head-wave arrivals into a unified localization framework. This combination of multiple independent observations improves localization accuracy and reliability simultaneously, as each arrival type provides complementary information about the microseismic event location
3Measurement precision
If head waves are analyzed in combination with direct-path arrivals, then depth estimation accuracy improves, but the complexity of identifying and processing multiple arrival types increases
Solution Approach 1:
The patent implements automated arrival identification algorithms that self-adapt to the specific seismic data characteristics. The system automatically distinguishes between direct-path and head-wave arrivals based on their inherent temporal and amplitude patterns, eliminating manual intervention and keeping processing complexity manageable while achieving depth estimation accuracy improvement
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 significantly reduces event location uncertainty, particularly in the depth dimension, by providing additional depth accuracy and preventing mislocalizations, as demonstrated in the Montney formation, where depth estimation errors are reduced by a factor of about 10 compared to conventional methods.
Implementation Method 1
complex wave propagation where energy from a single microseismic event will reach an array of geophones near target depth through multiple indirect propagation paths such as reflections and head waves
Implementation Method 2
head waves are radiated by critically refracted waves that travel at a higher velocity than the direct path for events occurring within the target layer
Data Source
AI summary
The present invention relates to methods and apparatuses for using head waves to greatly improve microseismic event localization accuracy, particularly in the depth dimension, by analyzing them in addition to direct path arrivals whenever they are observed. Embodiments of the invention also include techniques known as multipath analysis.