Downhole GPR Fracture Length Mapping via Diffraction Timing
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Solution Overview
Problem
Current methods for characterizing fracture length and orientation in unconventional reservoirs, such as microseismic monitoring, are limited by noise, require nearby monitoring wells, and are ineffective for deep formations, leading to high costs and variability in results.
Innovation Solution
A ground penetrating radar system is deployed in a wellbore to emit and sense electromagnetic energy, utilizing the knife-edge effect to determine fracture length by measuring the time difference between direct and diffracted pulses, eliminating the need for nearby wells and surface sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microseismic monitoring is used to characterize fracture length, then fracture characterization can be performed, but the method is limited by acoustic noise and requires nearby monitoring wells
Solution Approach 1:
The patent replaces acoustic-based microseismic monitoring with electromagnetic radar technology. The radar system emits electromagnetic pulses that travel through the formation and reflect off fractures, allowing fracture characterization without being affected by acoustic noise. This substitution of physical domain (acoustic to electromagnetic) eliminates the harmful acoustic environmental noise factor.
Solution Approach 2:
The patent introduces electromagnetic waves as an intermediary medium to characterize fractures. Instead of using acoustic waves that are attenuated and noisy in the wellbore environment, the radar system uses electromagnetic waves that can propagate through the formation without being affected by acoustic noise, serving as a cleaner intermediary for fracture detection.
2Measurement precision
If microseismic monitoring is used for deep formations, then fracture characterization can be performed, but the microseismic signal is attenuated and becomes indistinguishable from noise
Solution Approach 1:
The patent substitutes acoustic microseismic monitoring with electromagnetic radar technology. Electromagnetic waves experience different attenuation characteristics compared to acoustic waves in geological formations. The radar system can penetrate deeper formations effectively, allowing fracture characterization at greater depths where acoustic signals would be completely attenuated.
Solution Approach 2:
The patent changes the fundamental propagation parameter from acoustic wave speed to electromagnetic wave speed. This parameter change enables the system to operate effectively at deeper formations where acoustic signals fail, as electromagnetic waves can maintain sufficient signal strength through the formation to detect fractures at considerable depths.
3Measurement precision
If nearby monitoring wells are required for microseismic monitoring, then fracture characterization can be performed, but the cost and complexity increase
Solution Approach 1:
The patent extracts the fracture characterization capability from the wellbore environment and places it in the formation itself. By using downhole radar tools that can be positioned within the wellbore to emit and detect electromagnetic waves, the system eliminates the need for separate nearby monitoring wells. The fracture information is obtained directly from the formation through electromagnetic wave interaction.
Solution Approach 2:
The patent makes the wellbore environment multi-functional. The wellbore serves both as the access point for drilling and as the deployment location for the radar measurement system. This eliminates the need for separate monitoring wells, as the same wellbore structure is used for both production/access and fracture characterization.
4Measurement precision
If conventional fracture characterization methods are used, then fracture length can be estimated, but the results vary greatly depending on the model used
Solution Approach 1:
The patent replaces model-based estimation methods with direct electromagnetic wave interaction. Instead of using pseudo-3D fracture propagation models that make assumptions about fracture geometry and properties, the radar system directly measures fracture characteristics through electromagnetic wave reflection and diffraction, providing more reliable and consistent results.
Solution Approach 2:
The patent enables the formation itself to provide the measurement data. The electromagnetic waves interact with the fractures in the formation, and the reflected/diffracted waves carry direct information about fracture length and orientation. This self-service approach eliminates the need for complex external models and provides direct, reliable measurements.
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 method allows for accurate mapping of fracture length without nearby monitoring wells, is less affected by acoustic noise, and can be used for deep reservoirs, providing more reliable and cost-effective fracture characterization compared to existing techniques.
Implementation Method 1
Electromagnetic energy is emitted from a ground penetrating radar transmitter in a wellbore at a depth of interest. The ground penetrating radar electromagnetic energy is sensed after emission with a radar receiver in the wellbore at a distance from the ground penetrating radar transmitter.
Implementation Method 2
detecting return signals reflected from the near-borehole region; generating an image of the near-borehole region based on the return signals
Implementation Method 3
sensing arrival of a second break pulse indicating presence of a fracture as a secondary electromagnetic energy source
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
Ground penetrating radar (GPR) measurements from a downhole well tool in a wellbore are obtained to identify length of fractures adjacent the wellbore. A ground penetrating radar transmitter of the downhole tool emits an electromagnetic pulse. The electromagnetic wave of the ground penetrating radar is diffracted on encountering an end or tip of a fracture, which acts as a secondary source. The diffracted signal is then collected by downhole receiver(s) of the downhole tool. Length of the fracture is determined based on the time of travel of the electromagnetic wave from its emission until its collection as a diffracted signal by the downhole receiver(s).