Adaptive Inversion for Vertical Resistivity Logs
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Solution Overview
Problem
Conventional methods for measuring formation properties in wellbores, such as triaxial induction tools, face limitations in obtaining accurate vertical resolution of vertical resistivity (Rv) logs, particularly in 3D formations, leading to poor resolution and incorrect resistivity readings in thin beds, which affects hydrocarbon volume prediction.
Innovation Solution
An adaptive inversion method using a selected subset of conductivity tensor measurements and zero-dimensional (ZD) inversion results to derive a sharper Rv log, constraining the inversion model with horizontal resistivity (Rh), dip, and azimuth logs, and utilizing sensitive components of the conductivity tensor to improve Rv measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional triaxial induction tools are used to measure formation properties, then formation conductivity measurements can be obtained, but the vertical resolution of Rv logs is poor especially in thin beds
Solution Approach 1:
The patent applies parameter changes by modifying the inversion approach from conventional full-tensor inversion to a selective inversion method that uses only the zz-component of the conductivity tensor. This parameter change in the inversion strategy enables achieving sharper vertical resolution for Rv measurements while maintaining computational efficiency and reducing shoulder bed effects that plague conventional methods
Solution Approach 2:
The patent extracts and utilizes only the zz-component of the conductivity tensor for Rv inversion, separating this specific component from the full tensor measurements. By taking out and focusing on this particular component that is most sensitive to vertical resistivity variations, the method achieves improved vertical resolution without being constrained by the limitations of conventional full-tensor inversion approaches
2Reliability
If conventional inversion methods are used, then Rv logs can be generated, but shoulder bed effects cause incorrect resistivity readings in thin beds
Solution Approach 1:
The patent changes the inversion parameter selection by using exclusively the zz-component of the conductivity tensor for Rv calculations. This parameter change fundamentally alters the inversion behavior, reducing sensitivity to adjacent bed effects and improving the accuracy of Rv measurements in thin bed scenarios where conventional methods fail due to shoulder bed effects
3Loss of information
If full conductivity tensor measurements are used for inversion, then comprehensive formation data is obtained, but computational complexity and processing time increase
Solution Approach 1:
The patent extracts and utilizes only the essential zz-component of the conductivity tensor for Rv inversion, discarding the unnecessary complexity of processing all nine tensor components. This extraction approach maintains the critical formation property information needed for accurate Rv measurements while dramatically simplifying the computational inversion process and reducing processing time
Solution Approach 2:
The patent inverts the conventional approach by not using all available tensor components for inversion. Instead of performing a comprehensive full-tensor inversion, it selectively inverts only the zz-component, which is the most sensitive to vertical resistivity variations. This inverted strategy reduces computational complexity while preserving the most important formation information
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
The method provides higher resolution Rv logs that are closer to true formation resistivity values, especially in thin beds, improving the accuracy of hydrocarbon volume prediction and reducing shoulder bed effects.
Implementation Method 1
measuring 9 component apparent conductivity tensors (σm(i,j,k), j,k=1,2,3), at multiple distances between an electromagnetic transmitter and the respective receivers
Data Source
AI summary
A method for logging a formation or sample includes obtaining a plurality of multiaxial conductivity measurements from the formation or sample. A horizontal resistivity measurement, a dip measurement and a dip azimuth measurement are derived from the plurality of multiaxial conductivity measurements. A sharp vertical resistivity measurement is derived from a subset of the plurality of multiaxial conductivity measurements.