Fracture Characterization Using Refracted Seismic Travel Time
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Solution Overview
Problem
Current methods for characterizing fractures and stress in subsurface reservoirs using seismic data have limited spatial resolution and rely heavily on reflected energy, which does not effectively capture the pronounced anisotropy effects of refracted waves, making it difficult to accurately detect and analyze fractures and stress states in hydrocarbon reservoirs.
Innovation Solution
A method is developed to estimate azimuthal anisotropy properties using refracted seismic data, involving the processing of multi-azimuth refracted data to derive anisotropic parameters and fracture strike directions, utilizing techniques such as linear move-out correction, dipping signal removal, and extraction of refraction travel times, with the concept of Common Refraction Point (CRP) to enhance the characterization of fractures and stress states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reflected seismic energy is used to characterize fractures, then the method is commonly practiced and relatively simple, but the spatial resolution is limited and anisotropy effects are not effectively captured
Solution Approach 1:
The patent inverts the conventional approach by using refracted seismic energy instead of reflected seismic energy for fracture characterization. Refracted waves travel longer distances through the target layer, sampling a significantly larger area and providing better spatial coverage while capturing more pronounced anisotropy effects for improved fracture detection accuracy
Solution Approach 2:
The patent introduces azimuthal dimension to the refracted wave analysis by measuring travel times and amplitudes across multiple azimuths. This multi-azimuth approach enables characterization of azimuthal anisotropy and provides comprehensive spatial sampling of the target layer, transforming the detection capability from single-point to area-wide coverage
2Measurement precision
If refracted seismic energy is used to characterize fractures, then spatial coverage and anisotropy detection are improved, but the methodology is uncommon and more complex to implement
Solution Approach 1:
The patent applies preliminary processing steps including linear move-out correction, dipping signal removal, and refraction travel time extraction before azimuthal anisotropy analysis. These preparatory actions simplify the subsequent interpretation of refracted wave data and make the methodology more implementable by reducing data complexity early in the workflow
Solution Approach 2:
The patent uses Common Refraction Point (CRP) binning as an intermediary step to organize multi-azimuth refracted data. By binning data according to CRP geometry, the complex multi-azimuth measurements are structured into a manageable format that facilitates azimuthal anisotropy parameter extraction while maintaining the benefits of extended spatial sampling
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 provides a more comprehensive understanding of fractures and stress states, enabling better detection of oil reservoirs, identification of high production zones, optimal well placement, and monitoring of induced directional stress changes, thereby improving the economic viability of conventional and unconventional resource plays.
Implementation Method 1
refraction energy samples significantly more area of the target layer as it travels long distances in the target layer
Implementation Method 2
azimuthal variation of refracted travel time is used as a method to detect and show influence of azimuthal anisotropy
Data Source
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AI summary
Refracted energy travel time can help to derive anisotropic parameters in a target layer. These anisotropic parameters allow us to both explore for new reservoirs and to understand stress and fracturing in existing reservoirs. This information can be used to i) detect oil reservoirs, ii) spot naturally fractured, hence high production zones, iii) detect dominant natural stress directions, iv) better place horizontal wells to optimize production, v) monitoring man made fractures or induced directional stress changes. The method is demonstrated using synthetic and real data.