Microseismic Event Location via Rock Physical Model Inversion
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Solution Overview
Problem
Current microseismic monitoring techniques face challenges in accurately locating microseismic events due to ambiguities in event-time versus event-depth interdependence, especially in the presence of noise, and uncertainties driven by errors in the velocity model and bandwidth limitations, leading to significant location uncertainties in both horizontal and vertical directions.
Innovation Solution
A system and method utilizing a rock physical model with spatial volume elements that include attributes for position, extension, velocity, density, and attenuation, allowing for improved data inversion and reduced uncertainties in velocity models, enabling more accurate matching of microseismic events to observed data and providing physically meaningful output for human operators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional microseismic monitoring techniques are used, then the system is simple and easy to operate, but the location accuracy of microseismic events deteriorates due to ambiguities in event-time versus event-depth interdependence and uncertainties in velocity models
Solution Approach 1:
The patent applies preliminary action by performing full-waveform inversion to establish an accurate velocity model before microseismic event location. The system pre-processes seismic data to create a detailed velocity model that accounts for subsurface heterogeneities, which then serves as a foundation for accurate event location. This preliminary modeling step resolves the ambiguity in event-time versus event-depth interdependence by providing a more accurate propagation velocity framework.
Solution Approach 2:
The patent introduces full-waveform inversion as an intermediary process between raw seismic data and microseismic event location. This intermediary step creates a detailed velocity model that mediates the relationship between observed waveforms and source parameters, resolving the ambiguities in event location. The velocity model acts as a mediator that translates complex waveform data into accurate spatial and temporal source characteristics.
2Reliability
If conventional event location methods are used, then the processing is fast and simple, but the bandwidth limitations and velocity model errors cause significant location uncertainties in both horizontal and vertical directions
Solution Approach 1:
The patent replaces conventional mechanical event location methods (which rely on simplified travel-time tomography and assumed velocity models) with a physics-based full-waveform inversion approach. This substitution uses complete wavefield information and rigorous wave propagation physics to resolve event parameters, eliminating the limitations of bandwidth constraints and velocity model errors that plague conventional methods. The physics-based approach naturally accounts for all frequency components and propagation effects.
Solution Approach 2:
The patent fundamentally changes the parameter estimation approach by moving from direct inversion of simplified travel-time equations to iterative full-waveform inversion. This parameter change transforms the location problem from a geometric calculation based on assumed velocities to a physics-based inversion that simultaneously optimizes velocity model parameters and event source parameters, thereby resolving the interdependence ambiguities and improving location reliability.
3Measurement precision
If simplified velocity models are used, then the computation is faster and less complex, but the event location accuracy deteriorates due to ambiguities in event-time versus event-depth interdependence
Solution Approach 1:
The patent performs preliminary full-waveform inversion to establish an accurate velocity model before microseismic event location. This pre-processing step creates a detailed velocity model that accounts for subsurface heterogeneities, which then serves as a foundation for accurate event location. The preliminary modeling resolves the ambiguity in event-time versus event-depth interdependence by providing a more accurate propagation velocity framework.
Solution Approach 2:
The patent introduces full-waveform inversion as an intermediary process between raw seismic data and microseismic event location. This intermediary step creates a detailed velocity model that mediates the relationship between observed waveforms and source parameters, resolving the ambiguities in event location. The velocity model acts as a mediator that translates complex waveform data into accurate spatial and temporal source characteristics.
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
The rock physical model enhances the accuracy of microseismic event location and reduces uncertainties, providing reliable spatial mapping and physically interpretable results, thereby improving the reliability of microseismic monitoring and reducing errors in event depth and horizontal location.
Implementation Method 1
seismic sensors arranged in known positions in a sensor array... detected by seismic sensors... data representing seismic signals from microseismic events that are caused by changes in stress in an underground formation
Implementation Method 2
setting off a powerful seismic source that provides acoustic energy sufficiently powerful to penetrate to a desired depth... The source wave components are reflected and refracted from interfaces in the formation
Implementation Method 3
The source wave components are reflected and refracted from interfaces in the formation
Data Source
AI summary
A system (400) for processing microseismic data comprises an array (330) of seismic sensors (331, 332) at known locations, means (331, 332; 410) for enhancing SNR in a seismic signal output from a seismic sensor, means (331, 332; 410) for detecting a microseismic event in the seismic signal and inverting means (410) for adapting a rock physical model (255) to microseismic data that are acquired at least partially from the seismic signal representing a microseismic event. The rock physical model comprises a set of spatial volume elements mapping a set of physical volume elements (320) within a volume (300) to be monitored, wherein each spatial volume element comprises attributes for the position and extension of the physical volume element (320), a velocity and an attenuation. Data of various kinds, e.g. pore geometry, and from numerous sources, e.g. laboratory measurements, can be incorporated in the rock physical model (255).