Multi-Step Inversion for Resistivity Anisotropy in LWD
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Solution Overview
Problem
Current well logging technologies, particularly multi-axial LWD instruments, lack a real-time inversion procedure for determining formation resistivity anisotropy and dip during drilling, relying on one-dimensional parametric inversion methods that are not applicable to multi-axial measurements.
Innovation Solution
A multi-step inversion procedure using a combination of electromagnetic measurements from tilted and transverse dipole antennas to determine horizontal and vertical resistivity, formation dip, and layer thicknesses, allowing for real-time interpretation of resistivity anisotropy and bedding attitude during drilling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If one-dimensional parametric inversion is used for wireline 3D induction measurements, then interpretation is available, but real-time inversion during drilling is not achievable
Solution Approach 1:
The inversion process is divided into multiple sequential steps: first inverting for horizontal resistivity using longitudinal measurements, then inverting for vertical resistivity using transverse and tilted measurements, and finally inverting for dip and azimuth. This segmentation allows real-time processing during drilling by breaking down the complex multi-parameter inversion into manageable stages that can be executed sequentially with available data at each step.
Solution Approach 2:
The method performs preliminary inversion steps using available measurement data before the complete dataset is available. Horizontal resistivity is inverted first using longitudinal measurements, then vertical resistivity is inverted as transverse and tilted measurements become available, enabling progressive real-time interpretation during the drilling process rather than waiting for complete data acquisition.
2Loss of information
If multi-axial LWD measurements are taken, then more formation parameters can be determined, but inversion procedures are not yet available
Solution Approach 1:
The invention extends traditional one-dimensional inversion methods by incorporating multi-axial measurement dimensions. It uses longitudinal, transverse, and tilted dipole measurements in three-dimensional space to invert for horizontal resistivity, vertical resistivity, dip angle, and azimuth simultaneously. This dimensional extension enables complete formation evaluation from multi-axial LWD measurements by adding angular dimensions to the traditional radial measurement approach.
3Device complexity
If traditional inversion methods are used, then processing is simpler, but borehole effect and shoulder-bed effect cannot be removed
Solution Approach 1:
The method uses an intermediary formation model that incorporates borehole geometry, invasion zone, and shoulder-bed effects as intermediate parameters. By modeling these interfering effects as separate components in the forward model, the inversion can explicitly account for and remove their influences on the measured data, isolating the true formation anisotropy signal from contamination by borehole and adjacent formation effects.
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
Enables accurate and real-time determination of formation resistivity, anisotropy, and dip, improving the precision of well placement and reservoir evaluation by processing measurements from multi-axial LWD instruments, potentially reducing the borehole effect and enhancing the reliability of inversion results.
Implementation Method 1
electromagnetic measurements with three dimensional (3D) sensitivities. In so called 'wireline' measuring systems... 3D electromagnetic induction measurements are designed primarily for detecting resistivity anisotropy
Data Source
Figure 1A
Figure 1B~2
Figure 3
AI summary
A method is provided for determining formation resistivity, anisotropy and dip from wellbore measurements includes moving a well logging instrument through subsurface formations. The instrument includes longitudinal magnetic dipoles and at least one of tilted and transverse magnetic dipoles. Formation layer boundaries and horizontal resistivities of the formation layers are determined from longitudinal magnetic dipole measurements. Vertical resistivities of the formation layers are determined by inversion of anisotropy sensitive measurements. Improved vertical resistivities of the formation layers and dips are determined by inverting symmetrized and anti-symmetrized measurements. Improved vertical resistivities, improved boundaries and improved dips are determined by inversion of the all dipole measurements. Improved horizontal resistivities, further improved layer boundaries and further improved dips are determined by inversion of all dipole measurements.