4D Seismic Inversion Using Geological-Dynamic Constraints
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Solution Overview
Problem
4D seismic techniques face challenges in accurately estimating elastic parameters of subsoil, particularly in hydrocarbon exploration, due to limitations in accounting for geological and dynamic constraints, which affect the precision of saturation and pressure variations in geological layers.
Innovation Solution
A method that measures base and monitor seismic traces, assumes variations in elastic parameters, and numerically evaluates these assumptions to estimate elastic parameter variations using geological-dynamic a priori information, allowing for the estimation of density and propagation speed changes in permeable layers along a predefined direction, such as a well or arbitrarily chosen direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 4D seismic techniques are used to estimate elastic parameters, then the process is relatively simple, but the accuracy is insufficient due to lack of geological and dynamic constraints
Solution Approach 1:
The patent applies preliminary action by incorporating geological and dynamic constraints (a priori information) before performing the inversion process. This pre-establishment of constraints guides the inversion toward geologically realistic solutions, improving accuracy without requiring complex post-processing adjustments
Solution Approach 2:
The patent implements feedback by using an objective function that compares observed seismic data with synthetic data generated from the model. The inversion process iteratively adjusts elastic parameters to minimize the misfit between observed and synthetic data, creating a feedback loop that continuously improves estimation accuracy
2Adaptability or versatility
If model-based inversion with statistical methods is used, then saturation and pressure variations can be directly estimated, but the method lacks geological constraints and relies on correlation computations
Solution Approach 1:
The patent applies local quality by allowing different types of constraints to be applied to different regions of the subsurface model. Geological constraints such as layer continuity, permeability zones, and fault structures can be incorporated locally where relevant, while maintaining flexibility in other areas
Solution Approach 2:
The patent uses parameter changes by transforming the inversion problem to work with logarithms of elastic parameters rather than the parameters themselves. This transformation linearizes the relationship between parameters and seismic observables, improving the stability and convergence of the inversion process
3Loss of information
If inversion methods that account for both time offsets and amplitude changes are used, then comprehensive parameter variations can be captured, but the computational complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the inversion process into distinct stages: preprocessing of seismic data, construction of the forward model, computation of the objective function, and iterative optimization. This segmentation allows each stage to be optimized independently and facilitates parallel computation where possible
Solution Approach 2:
The patent uses an intermediary approach by introducing a forward modeling step that generates synthetic seismic data from the current model parameters. This intermediary model acts as a bridge between the elastic parameters and the observed seismic data, enabling the inversion to account for both amplitude and timing changes through a unified physical framework
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 enhances the accuracy of 4D parameter estimation on a reservoir scale by accounting for geological and dynamic constraints, improving the estimation of saturation and pressure variations in hydrocarbon reservoirs, even in the absence of well data, by using seismic traces and reservoir grids for a priori information.
Implementation Method 1
measuring at least one base seismic trace in a first phase; measuring, in a second phase, at least one monitor seismic trace corresponding to the base seismic trace
Implementation Method 2
making assumptions of variation of elastic parameters in permeable layers... the elastic parameters including a density and a speed of propagation of pressure waves
Data Source
AI summary
A 4D seismic technique, where a base seismic trace is measured at a first time in a region of the subsoil, and then a monitor seismic trace corresponding to the base seismic trace is measured at a second time. To interpret the 4D measurements, assumptions are made about the variation of elastic parameters in permeable layers at predefined positions in one direction between the first and the second time. Elastic parameters include the density (ρ) and the speed of propagation of the pressure waves (VP) in the permeable layers. Numerical evaluation is performed for a capability of each assumption about the variation of elastic parameters to give an account of a change between the measured base seismic trace and the measured monitor seismic trace, and the variation of the elastic parameters is estimated in accordance with an assumption of optimum capability.