Transient EM Geosteering Mandrel Conductivity Correction
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Solution Overview
Problem
Current electromagnetic induction well logging technologies face limitations in accurately determining earth formation properties at ultra-deep scales, particularly in high conductive environments, due to assumptions invalid for metal mandrels and inefficiencies in multi-frequency acquisition and signal processing.
Innovation Solution
The method involves conveying a logging tool into a borehole, inducing a current in the formation, receiving a transient signal, transforming it into the frequency domain, and estimating the distance to an interface using Fourier transforms and multifrequency focusing techniques that account for finite conductivity of the mandrel, enabling more accurate and efficient data interpretation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If multi-frequency acquisition is used to increase depth of investigation, then depth of investigation is improved, but acquisition time and device complexity increase
Solution Approach 1:
The patent applies periodic action by using transient electromagnetic signals with multiple frequencies in a time-domain measurement sequence. The system sends electromagnetic signals at different frequencies sequentially and records the transient response over time, allowing depth of investigation to be increased through multi-frequency analysis without requiring simultaneous multi-frequency acquisition, thus reducing overall measurement time.
Solution Approach 2:
The patent employs preliminary action by pre-processing the transient signals through Fourier transformation to extract frequency-domain information before final interpretation. This preliminary frequency analysis allows the system to identify and separate signals from different frequencies, enabling depth of investigation to be enhanced while maintaining efficient acquisition timing through optimized signal processing rather than extended physical measurement.
2Length of stationary object
If conventional electromagnetic induction tools are used for deep-looking measurements, then depth of investigation is improved, but measurement precision deteriorates in high conductive environments
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional steady-state electromagnetic induction to transient electromagnetic measurements with time-varying currents. The system uses changing current parameters (frequency, amplitude over time) to excite the formation and analyze the transient response, which allows accurate measurement in high conductive environments where conventional methods fail due to skin effect and proximity effects.
Solution Approach 2:
The patent replaces the conventional frequency-domain electromagnetic induction system with a time-domain transient electromagnetic system. Instead of using steady-state sinusoidal currents and analyzing impedance at a single frequency, the system uses pulsed or modulated currents and analyzes the time-decaying electromagnetic response, substituting the measurement approach to overcome limitations in high conductive formations.
3Strength
If metal mandrels are used in logging tools, then device strength is improved, but measurement precision deteriorates due to finite conductivity effects
Solution Approach 1:
The patent uses an intermediary approach by introducing a computational model that acts as a mediator between the metal mandrel's finite conductivity and the formation measurement. The system accounts for the mandrel's electromagnetic effects through correction algorithms and modeling that separate the mandrel's influence from the formation signal, allowing accurate formation property measurement despite the presence of the conductive metal structure.
Solution Approach 2:
The patent applies feedback by using measured transient electromagnetic responses to iteratively correct for mandrel effects. The system analyzes the time-decaying signal characteristics and uses this feedback information to distinguish between signals generated by the formation versus those attenuated or distorted by the metal mandrel, enabling precise formation measurement despite the interfering presence of the conductive tool structure.
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 enhances the depth of investigation and accuracy in determining formation properties, including resistivity and anisotropy, while reducing acquisition time and maintaining transmitter circuits, effectively addressing the limitations of existing technologies.
Implementation Method 1
An alternating current is passed through the transmitter coil. Voltages which are induced in the receiver coils as a result of alternating magnetic fields induced in the earth formations are then measured.
Implementation Method 2
receiving a transient signal resulting from the induced current in the formation
Data Source
AI summary
A transmitter on an instrument is used to induce currents in an earth formation when it is turned on or off. A Fourier transform is applied to transient measurements made in the receivers. A multifrequency focusing of the transformed data is used for applications like determination of a distance to an interface in the formation, controlling the drilling direction, determination of formation resistivities and formation strike directions.