AVO Cross-Plot for Hydrate and Gas Differentiation
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Solution Overview
Problem
Current methods for identifying shallow gas and gas hydrate using seismic amplitude variation with offset (AVO) techniques are not as effective as those for direct hydrocarbon indication, particularly in differentiating between hydrate-bearing sediments and hydrate-over-gas sediments, which are critical for drilling hazards and resource evaluation.
Innovation Solution
A novel AVO modeling technique that uses well log data and rock physics models to generate and cross-plot AVO responses for free gas charged sands, hydrates over free gas, and hydrates not over free gas, allowing for the estimation of gas and hydrate concentrations from seismic data by analyzing AVO intercept and gradient pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AVO techniques are used for identifying shallow gas and gas hydrate, then the method is simple and widely applicable, but the ability to differentiate between hydrate-bearing sediments and hydrate-over-gas sediments is insufficient
Solution Approach 1:
The patent segments the AVO analysis by creating separate classification schemes for different geological scenarios: hydrate-bearing sediments, hydrate-over-gas sediments, and free gas charged sands. By dividing the problem into distinct categories with specific AVO response patterns, the method achieves better differentiation capability while maintaining manageable complexity through targeted modeling for each scenario.
Solution Approach 2:
The patent utilizes changes in AVO parameters (intercept and gradient) at different offsets to differentiate between gas hydrate and free gas. By analyzing how reflection coefficients vary with offset and incorporating density changes, the method transforms the detection approach from simple amplitude analysis to a multi-parameter characterization that enhances differentiation precision.
2Measurement precision
If detailed AVO modeling is performed to differentiate hydrate types, then the identification accuracy improves, but the processing time and computational complexity increase
Solution Approach 1:
The patent performs preliminary AVO modeling to establish expected response patterns for different gas hydrate and free gas scenarios before analyzing actual seismic data. By pre-characterizing the AVO responses for various concentration levels and geological configurations, the method creates reference frameworks that accelerate the interpretation phase while maintaining high identification accuracy.
Solution Approach 2:
The patent replaces complex mechanical drilling testing with seismic AVO analysis to estimate gas and hydrate concentrations. By substituting direct physical measurement with remote seismic characterization, the method reduces time and cost while providing sufficient accuracy for resource evaluation and drilling hazard assessment.
3Adaptability or versatility
If AVO analysis is extended to deepwater environment for gas hydrate detection, then the resource evaluation capability is enhanced, but the reliability of identification decreases due to complex geological conditions
Solution Approach 1:
The patent introduces rock physics models as intermediaries between seismic AVO data and geological interpretation. These models provide the theoretical framework to translate observed AVO anomalies into reliable estimates of gas hydrate saturation and type, even in complex deepwater environments. The rock physics relationships serve as mediators that connect seismic observations with subsurface conditions, enhancing identification reliability.
Solution Approach 2:
The patent develops a universal AVO analysis framework that can be applied across different deepwater settings and geological conditions. By creating classification schemes and modeling approaches that work across various scenarios (hydrate-bearing, hydrate-over-gas, free gas), the method achieves both broad adaptability to deepwater environments and consistent reliability through standardized interpretation procedures.
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 robustly differentiates between hydrate-bearing sediments and hydrate-over-gas sediments, providing accurate indicators for drilling hazards and resource potential, enhancing the ability to design effective drilling strategies and production strategies for gas hydrate deposits.
Implementation Method 1
seismic amplitude variation with offset (AVO) techniques
Implementation Method 2
In Shuey's two-term approximation to the Zoeppritz equations, the P-wave reflection coefficient can be approximately written as a function with two parameters
Data Source
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AI summary
A method for indicating the presence of free gas charged sands, and/or hydrates over free gas, and/or hydrates not over free gas, the method using well log data and a rock physics model. Velocity and density of background clays and sands are extracted from the well log data. The extracted velocities and densities are used to build a rock physics model. An AVO response is generated that is representative of free gas-charged sands. An AVO response is generated that is representative of hydrates over free gas-charged sands. An AVO response is generated that is representative of hydrates devoid of free gas. The generated AVO responses are used to construct an AVO crossplot diagram that is further used to distinguish deposits of free gas charged sands from hydrates over free gas, from hydrates not over free gas.