VSP Data Inversion Without Shear Wave Velocity
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Solution Overview
Problem
Existing methods for analyzing vertical seismic profile data are limited by the need for prior information on shear wave velocity, which can introduce errors in anisotropy parameters and reduce the accuracy of regression values.
Innovation Solution
A method that extracts P-wave slowness-polarization data and selects a function relating P-wave polarization angle to slowness, using at least three free parameters where information of shear wave velocity is absorbed along with anisotropy parameters, allowing for independent inversion without prior knowledge of shear wave velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior information on shear wave velocity is used in the inversion process, then the inversion can be executed, but errors in the ratio would generate proportional errors in the anisotropy parameters and reduce measurement precision
Solution Approach 1:
The patent extracts and removes the dependency on prior shear wave velocity information from the inversion process. By reformulating the inversion to solve for both P-wave velocity and anisotropy parameters simultaneously without requiring VS0/VP0 ratio as input, the method eliminates the source of error propagation while maintaining inversion feasibility.
Solution Approach 2:
The patent changes the parameterization of the inversion problem by absorbing shear wave velocity information into the anisotropy parameters themselves. This reparameterization allows the system to be solved with fewer external constraints, transforming the input requirements and eliminating the need for independent shear wave velocity measurements.
2Ease of manufacture
If the ratio VS0/VP0 is fixed at 0.5, then the inversion can proceed with realistic assumptions, but any error in this fixed ratio generates proportional errors in the anisotropy parameters
Solution Approach 1:
The patent removes the fixed ratio assumption from the inversion framework entirely. By designing an inversion that does not require VS0/VP0 as input, the method eliminates the constraint that limits accuracy while preserving computational feasibility through the simultaneous solution approach.
Solution Approach 2:
Instead of fixing the velocity ratio and solving for anisotropy parameters, the patent inverts the approach by solving for both P-wave velocity and anisotropy parameters simultaneously without any fixed velocity ratio, allowing the data to determine the actual velocity relationships rather than imposing predetermined values.
Data Source
AI summary
A P-wave slowness-polarization data set resolving P-wave slowness against P-wave polarization angle is extracted from a multi-offset vertical seismic profiling data set. A function relating P-wave polarization angle to P-wave slowness, and being dependent on at least three free parameters, wherein in at least two of these free parameters information of shear wave velocity is absorbed together with one or more anisotropy parameters that characterize formation anisotropy is selected, and regression values found for the at least three free parameters by fitting the selected function to the P-wave slowness-polarization data set. The regression values may be utilized in a method of producing a mineral hydrocarbon fluid from an earth formation.