Two-Step Inversion for Electromagnetic Logging Accuracy
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Solution Overview
Problem
Current electromagnetic logging methods face challenges in accurately measuring subterranean formation properties due to tool vibration and the complexity of multi-layer formations, as existing inversion methods are impractical with current computer processing capabilities and are limited by the need to account for borehole effects and tool vibrations.
Innovation Solution
A two-step inversion methodology is employed, where electromagnetic voltage measurements are processed to compute borehole-corrected gain compensated measurement quantities, followed by a second inversion using a point dipole model and multi-layer formation model to accurately determine multi-layer anisotropic formation properties, effectively removing borehole effects and accounting for tool vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-step inversion including detailed tool/borehole model and multi-layer formation model is used, then measurement precision would be improved, but computer processing speed becomes insufficient
Solution Approach 1:
The inversion process is divided into two separate steps: first inverting for borehole properties using a tool/borehole model, then inverting for formation properties using a multi-layer formation model. This segmentation allows each inversion to be computationally manageable while maintaining overall accuracy.
Solution Approach 2:
The borehole properties are determined first as a preliminary step before performing the formation property inversion. This preliminary action removes borehole effects from the measurements, simplifying the subsequent formation inversion problem and reducing computational complexity.
2Ease of operation
If borehole effects are not corrected, then processing simplicity is maintained, but measurement precision deteriorates
Solution Approach 1:
Borehole correction is performed as a preliminary step before formation property inversion. The first inversion computes borehole properties (borehole radius, mud resistivity) that are then used to correct the measurements, removing borehole effects before the formation inversion occurs.
Solution Approach 2:
The borehole properties (borehole radius, mud resistivity) act as intermediaries that bridge the raw measurements and the formation properties. These intermediate parameters are computed first and then used to correct the measurements for accurate formation property determination.
3Device complexity
If tool vibration is not accounted for, then processing complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
Tool position variations due to vibration are accounted for in the first inversion step along with borehole properties. The system computes effective borehole properties that inherently account for tool motion, removing the need for separate vibration correction and simplifying the overall process.
Solution Approach 2:
The inversion process itself accounts for tool vibration effects through the computation of borehole properties. The first inversion automatically handles the complexities of tool motion by determining effective borehole parameters, making the system self-correcting without additional complex processing.
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 enables the computation of multi-layer formation properties with improved accuracy and reliability, overcoming processing limitations and eliminating errors related to gain drift and cumbersome procedures, thus providing more precise subterranean formation data.
Implementation Method 1
electromagnetic logging measurements may need to be corrected for borehole effects
Data Source
AI summary
A two-step inversion method for computing multi-layer subterranean formation properties includes processing gain compensated electromagnetic measurement quantities using a first inversion to compute a corresponding set of borehole corrected gain compensated measurement quantities. The first inversion includes a mathematical model of the tool and the borehole in a uniform, anisotropic formation. The set of borehole corrected gain compensated measurement quantities are then processed using a second inversion to compute multi-layer anisotropic formation properties. The second inversion includes a 1D inversion employing a point dipole model and a multi-layer formation model.