4D Seismic Data Inversion for Fluid Saturation and Pressure Change
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Solution Overview
Problem
Current methods for deriving fluid saturation and pressure changes from 4D seismic data face challenges due to uncertainties in rock parameter estimations and interference from side-lobe energy, especially in multi-cycle reservoirs, which complicates the interpretation of fluid movement and pressure changes.
Innovation Solution
A method that inverts 4D seismic data at well locations using well log data and rock physics models to directly estimate formation pressure and fluid saturation changes, then extrapolates these changes away from well locations, combining rock physics and reservoir simulation results to generate a well-tied fluid saturation and pressure change model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If current transformation methods using AVO attributes are used to derive saturation and pressure change, then the interpretation process is simplified, but uncertainties in rock parameter estimations (shale volume and porosity) become overwhelming relative to fluid and pressure change signals
Solution Approach 1:
The patent inverts the traditional approach by not transforming seismic data to derive rock parameters, but rather using well-constrained rock parameters to transform seismic data directly into fluid saturation and pressure change. This inversion eliminates the need to estimate uncertain rock parameters from seismic data, thereby resolving the contradiction between ease of operation and measurement precision
Solution Approach 2:
The patent introduces an intermediary step using well log data and rock physics models to establish reliable rock parameters at well locations, which then serve as constraints for the transformation. This intermediary approach provides accurate rock parameter inputs without requiring direct seismic-based estimation, thus improving measurement precision while maintaining operational simplicity
2Ease of manufacture
If AVO attribute transformations are used to infer saturation and pressure change, then near and far difference amplitudes can be combined, but side-lobe energy in multi-cycle reservoirs generates apparent difference events that complicate interpretation
Solution Approach 1:
The patent extracts and removes the harmful side-lobe energy through a low-pass filtering step before performing the transformation. By separating and eliminating this interfering component, the method prevents apparent difference events from complicating the interpretation, thus resolving the contradiction between ease of data processing and reliability of reservoir differences interpretation
Solution Approach 2:
The patent performs preliminary filtering to remove side-lobe energy before the main transformation process. This preliminary action prevents interference from affecting subsequent interpretation steps, thereby maintaining both ease of manufacture and reliability in multi-cycle reservoir environments
3Loss of information
If rock parameter estimations are performed from seismic data, then rock properties can be derived, but uncertainties in shale volume and porosity estimations are overwhelming relative to fluid and pressure change signals
Solution Approach 1:
The patent inverts the traditional workflow by not deriving rock parameters from seismic data, but rather using well-constrained rock parameters to directly transform seismic data into fluid and pressure change. This eliminates the source of uncertainty in rock parameter estimation while preserving all necessary information, resolving the contradiction between information availability and measurement precision
Solution Approach 2:
The method uses well log data to self-constrain rock parameters at well locations, eliminating the need for uncertain seismic-based rock parameter estimation. This self-service approach provides accurate rock properties without introducing overwhelming uncertainties into the fluid and pressure change signals
Data Source
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AI summary
The invention is a method for inferring the saturation and pressure change of a reservoir by combining the information from 4D (time-lapse) seismic and time lag data volumes (7) derived from the 4D seismic, well logs (4), and reservoir simulation results (when simulator results are available) and featuring one or more 4D well ties (1) for a quantitative 4D interpretation. The inventive method uses model-based inversion incorporating rock physics (2) at well locations (5), and is statistical-based (6) away from wells. The method thus allows integration (8) of rock physics model and reservoir simulation and honors 4D seismic change.