Seismic Mono-Frequency Workflow for Gas Reservoir Detection
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Solution Overview
Problem
Current seismic methods for gas detection are unreliable due to the numerous variables affecting reflection amplitude, making it difficult to accurately derive gas or fluid content from seismic data, and often misidentify gas reservoirs with similar frequency responses from loose sands, porous sandstone, gas clouds, and gas chimneys.
Innovation Solution
The method involves spectrally decomposing seismic data into mono-frequency volumes, generating low and high-frequency maps, calculating a frequency ratio map by dividing the low-frequency map by the high-frequency map, and using this ratio to identify subsurface gas reservoirs by designating areas with high amplitude frequency ratios as gas-bearing regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If reflection amplitude analysis is used for gas detection, then the method is simple and widely applicable, but the accuracy and reliability of gas content derivation is poor due to multiple affecting variables
Solution Approach 1:
The patent segments the seismic frequency spectrum into multiple mono-frequency volumes (e.g., 10-20 Hz, 20-30 Hz, 30-40 Hz bands) and processes each frequency band separately. This segmentation allows the system to isolate and analyze specific frequency characteristics that are indicative of gas reservoirs, filtering out the confounding effects of multiple variables that affect overall reflection amplitude.
Solution Approach 2:
The patent changes the analysis parameter from overall reflection amplitude to frequency-specific amplitude ratios. By calculating the ratio of amplitudes at different frequency bands (e.g., low-frequency amplitude divided by high-frequency amplitude), the system creates a frequency ratio map that highlights gas-bearing formations based on their distinctive frequency response characteristics, thereby improving measurement precision.
2Ease of operation
If reflection amplitude is used to identify gas reservoirs, then the approach is straightforward, but it leads to misidentification with similar frequency responses from loose sands, porous sandstone, gas clouds, and gas chimneys
Solution Approach 1:
The patent divides the seismic data into multiple frequency bands and analyzes each band separately, then combines the results through ratio calculation. This segmented approach allows the system to distinguish between different subsurface formations based on their unique frequency responses across multiple bands, rather than relying on a single amplitude measurement that can be misleading.
Solution Approach 2:
The patent introduces an intermediary parameter - the frequency ratio - that mediates between the raw seismic amplitude data and the final gas reservoir identification. This frequency ratio serves as a discriminative intermediary that filters out false positives from loose sands, porous sandstone, gas clouds, and gas chimneys by highlighting formations with characteristic frequency amplitude relationships.
Data Source
AI summary
The present disclosure describes methods and systems, including computer-implemented methods, computer program products, and computer systems for direct gas reservoir detection using frequency amplitude. One computer-implemented method includes spectrally decomposing seismic data associated with a target area into a plurality of mono-frequency volumes. Further, the method includes based on a low-frequency volume of the plurality of volumes, generating a low frequency map of the target area. Yet further, the method includes based on a high-frequency volume of the plurality of volumes, generating a high frequency map of the target area. Additionally, the method includes dividing the low frequency map by the high frequency map to generate a frequency ratio map. The method also includes using the frequency ratio map to identify a subsurface gas reservoir in the target area.