Multiaxial Well Logging in Dipping Formations
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Solution Overview
Problem
Current electromagnetic well logging technologies face challenges in accurately determining formation resistivity anisotropy and complex formation structures, such as cross bedding, due to insufficient data and limitations in existing inversion models, particularly in deviated wells.
Innovation Solution
A method and system for multiaxial electromagnetic well logging that uses a tri-axial induction instrument to measure nine-component transimpedance coupling voltages, converting them into apparent conductivity tensors, and employing a generalized reflection/transmission method for electromagnetic field decomposition in cross-bedded formations, allowing for the determination of horizontal and vertical conductivities, bedding dip, and cross-bed dip and azimuth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional electromagnetic well logging instruments are used, then basic formation resistivity measurements can be obtained, but accurate determination of formation resistivity anisotropy and complex formation structures such as cross bedding cannot be achieved
Solution Approach 1:
The patent transitions from traditional single-axis or triaxial measurements to multiaxial electromagnetic field measurements, adding measurement dimensions by incorporating multiple transmitter and receiver antenna orientations. This enables capture of full tensor conductivity information (nine components) necessary for resolving formation anisotropy and cross-bedding structures that cannot be detected with conventional instruments.
Solution Approach 2:
The patent decomposes the complex electromagnetic field into distinct components using vector wave equations and separates the formation conductivity tensor into isotropic and anisotropic parts. This segmentation allows independent determination of vertical resistivity, horizontal resistivity, and resistivity anisotropy parameters, improving measurement precision for each individual formation property.
2Measurement precision
If existing inversion models are used, then basic formation parameters can be obtained, but accurate resolution of complex formation structures and resistivity anisotropy is limited due to model simplifications
Solution Approach 1:
The patent extends inversion models to accommodate complex formation structures by introducing additional parameters including cross-bedding dip angle, cross-bedding azimuth, and resistivity anisotropy ratios. The model transforms from simple layered formations to those incorporating tilted beds and anisotropic properties, allowing accurate representation of real-world complex formation geometries.
Solution Approach 2:
The patent develops a unified inversion framework that can handle multiple formation types (vertically isotropic, horizontally isotropic, anisotropic, cross-bedded) using a single set of multiaxial measurement equations. This universal model applies to both vertical and deviated wells, replacing the need for separate specialized models for different formation conditions.
3Loss of information
If multiaxial electromagnetic measurements are implemented, then full tensor conductivity information can be obtained, but computational complexity and data processing requirements increase significantly
Solution Approach 1:
The patent extracts and measures all nine components of the formation conductivity tensor using multiaxial electromagnetic fields with multiple transmitter and receiver antenna orientations. By systematically measuring each tensor component (three transmitter axes × three receiver axes), the full anisotropic conductivity information is captured without requiring complex post-processing to derive missing components.
Solution Approach 2:
The patent performs preliminary decomposition of the multiaxial measurement data into isotropic and anisotropic components before inversion. Vector wave equations are solved in advance to separate ordinary and extraordinary wave modes, and measurement data is pre-processed to isolate conductivity tensor elements, simplifying the subsequent inversion process and reducing computational burden.
4Measurement precision
If conventional well logging methods are used in deviated wells, then basic measurements can be obtained, but accurate determination of formation properties is compromised due to tool orientation and formation dip effects
Solution Approach 1:
The patent explicitly accounts for the asymmetric effects of tool orientation relative to formation bedding planes in deviated wells. The measurement model incorporates wellbore inclination angle and azimuth, and formation dip angle and azimuth, to correct for the asymmetric response patterns that arise when the tool is not vertically oriented. This allows accurate formation property determination regardless of wellbore trajectory.
Solution Approach 2:
The patent employs dynamic coordinate transformation that adapts to arbitrary wellbore orientations and formation dips. The measurement and inversion system dynamically adjusts to the relative geometry between tool axes and formation layers, using rotation matrices and coordinate system transformations to maintain measurement accuracy in any well configuration, from vertical to highly deviated trajectories.
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 provides more accurate and efficient determination of formation properties in both vertical and deviated wells, improving the resolution of resistivity anisotropy and formation structure analysis, and is more efficient than existing methods by avoiding repetitive computation of reflection and transmission matrices.
Implementation Method 1
A method and system for multiaxial electromagnetic well logging is disclosed. In the computer, expected transimpedance responses due to the initial model are calculated. The input measurements made at a plurality of axial spacings from a position of the inducing are compared to the expected transimpedance responses
Data Source
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AI summary
A method for determining resistivity of subsurface formations includes generating an initial model of the formations from multiaxial electromagnetic transimpedance measurements, the model comprising values of vertical resistivity, horizontal resistivity, crossbed dip, crossbed azimuth, and bedding dip and azimuth. Expected measurements generated from the initial model measurements are decomposed into ordinary and extraordinary components. The actual tool measurements are compared to the summation of the expected decomposed measurement components. The initial model is adjusted, the expected decomposed components are recalculated and the foregoing are repeated until the difference between the actual tool measurements and the summation of the expected decomposed components falls below a selected threshold.