Buried Seismic Arrays for Microseismic Event Localization
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Solution Overview
Problem
Current microseismic monitoring techniques face challenges in accurately detecting and locating microseismic events in high-noise environments, particularly due to significant variability in subsurface formations, which affects production uniformity and the ability to characterize reservoirs effectively.
Innovation Solution
An integrated seismic acquisition and monitoring system that combines surface and buried arrays of sensors, with buried sensors deployed in shallow boreholes, to enhance signal detection and noise reduction through beam steering and data processing techniques, allowing for improved imaging of subsurface structures and microseismic event localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If surface-based sensor arrays are used for microseismic monitoring, then the coverage area is large and no observation well is needed, but the signal-to-noise ratio is poor due to large surface noise compared to small downhole events
Solution Approach 1:
The patent transitions from surface-based 2D array monitoring to 3D distributed fiber optic sensing within boreholes, adding the vertical dimension. This enables sensors to be positioned at multiple depths, creating a volumetric monitoring capability that improves signal detection while maintaining broad coverage through strategic borehole placement.
Solution Approach 2:
The patent introduces fiber optic cables as an intermediary medium that couples sensors to the borehole wall and surrounding rock formation. This intermediary enables efficient transmission of微弱 seismic signals from downhole events to the fiber optic sensors, overcoming the signal weakness problem while allowing surface-based data acquisition.
2Measurement precision
If observation wells are drilled close to the target well for microseismic monitoring, then the signal detection capability is improved, but the drilling cost increases and suitable wells may not be available
Solution Approach 1:
The patent enables existing boreholes and wellbores to serve dual purposes: their original function plus microseismic monitoring. The fiber optic sensing system can be deployed in any existing borehole within the monitoring area, eliminating the need for dedicated observation wells and reducing deployment complexity while maintaining detection accuracy.
Solution Approach 2:
The distributed fiber optic sensing system utilizes the existing borehole infrastructure and rock formation itself as part of the sensing mechanism. The fiber optic cable acts as both the transmission medium and the sensor, detecting seismic waves directly through the borehole wall and formation, thereby simplifying the overall system architecture.
3Measurement precision
If beam steering is applied to surface sensor arrays to detect microseismic events, then points of greatest energy can be identified, but the polarity of events may not be uniform across the array causing detection failures
Solution Approach 1:
The patent implements localized sensing zones along the fiber optic cable at different borehole depths, with each segment independently detecting seismic events. This local quality approach ensures that sensors closest to the event dominate the signal, maintaining consistent polarity detection regardless of array geometry, and enabling reliable event characterization through depth-dependent signal analysis.
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 enhances the accuracy of microseismic event detection and localization, improves the characterization of subsurface properties, and optimizes reservoir production by reducing noise interference and providing detailed near-surface models.
Implementation Method 1
seismic sensors deployed on the earth's surface or in boreholes to detect seismic energy from microseismic events
Implementation Method 2
The array 10 is beam steered so points of greatest energy in the subsurface can be identified. To do this, travel time corrections for subsurface target points are calculated, and the trace data of the surface sensors 12 is time shifted.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Microseismic mapping using buried arrays with the integration of passive and active seismic surveys provides enhanced microseismic mapping results. The system is initially set up by recording signals in response to seismic energy with the buried array installation, while shooting a significant portion of the 3D surface seismic survey. The input analog signal at a sensor are amplified by a downhole gain and the amplified analog signal is sent to an uphole recording unit via a transmission line. The 3D surface seismic survey provides the following data: shallow 3D VSP data from the buried arrays; P-wave and converted wave data for the area covered by the buried array that benefits from a planned data integration processing effort; and microseismic data and associated analysis.