Downhole Tool Signal Correction for Deep Transient Resistivity
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Solution Overview
Problem
Deep transient logging while drilling (LWD) operations face challenges due to parasitic signals generated by conductive drill collars, which overwhelm formation signals, even with ferrite and copper shielding, making accurate measurement difficult, especially at depths up to 50 meters.
Innovation Solution
A downhole tool with a conductive carrier, a transmitter, and two axially spaced receivers processes electromagnetic signals by applying a linear transformation to the signal from the closer receiver to generate a transformed signal, which is then subtracted from the signal from the farther receiver to correct for parasitic signals, effectively isolating the formation signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ferrite and copper shielding are used to reduce conductive collar signal, then the parasitic signal is reduced, but the formation signal remains overwhelmed by the conductive collar signal which is more than two orders of magnitude greater
Solution Approach 1:
The patent segments the signal reception function by using multiple receivers at different axial distances from the transmitter. The first receiver is positioned closer to the transmitter while the second receiver is positioned farther away. This spatial segmentation allows the system to separately capture signals at different depths, enabling the closer receiver to pick up primarily the conductive collar signal while the farther receiver captures both collar signal and formation signal, thus allowing for signal separation and improving measurement precision.
Solution Approach 2:
The patent introduces an intermediary processing step using a linear transformation algorithm that acts as a mediator between the raw signals from the receivers and the final corrected formation signal. The linear transformation uses parameters derived from the closer receiver's signal to calculate and subtract the conductive collar signal component from the farther receiver's signal, thereby eliminating the harmful parasitic signal and isolating the formation signal for accurate measurement.
2Measurement precision
If multiple receivers at different axial distances are used to separate signals, then the conductive collar signal can be isolated and subtracted, but the device complexity increases
Solution Approach 1:
The patent extracts the conductive collar signal information from the composite signal by using the closer receiver to capture primarily the collar signal. This extracted collar signal is then used as a reference to calculate and remove the collar signal component from the farther receiver's signal, thereby isolating the formation signal. This extraction approach allows for signal separation without requiring complex multi-receiver configurations.
Solution Approach 2:
The patent changes the parameter of receiver positioning by placing receivers at specific axial distances from the transmitter. The first receiver is positioned at a shorter axial distance to optimize capture of conductive collar signal, while the second receiver is positioned at a longer axial distance to capture formation signal. This parameter optimization enables effective signal separation with minimal additional complexity.
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 method significantly reduces parasitic signals from downhole components, enhancing the accuracy of formation property measurements by isolating the formation signal from the conductive collar signal, even at deep investigation ranges, without requiring data extrapolation.
Implementation Method 1
transmitting an electromagnetic (EM) signal from the transmitter into the formation
Implementation Method 2
the generation of a parasitic signal due to conductive drill collars or other downhole components
Data Source
AI summary
A method of processing data includes: disposing a downhole tool in a borehole in an earth formation, the downhole tool including a conductive carrier, a transmitter, a first receiver disposed at a first axial distance from the transmitter, and a second receiver disposed at a second axial distance from the transmitter that is less than the first axial distance; performing a downhole electromagnetic operation, the operation including transmitting an electromagnetic (EM) signal from the transmitter into the formation and detecting a first EM response signal by the first receiver and a second EM response signal by the second receiver; applying a linear transformation to the second EM response signal to generate a transformed signal, the linear transformation having parameters associated with a set of data corresponding to a signal representing the conductive carrier; and subtracting the transformed signal from the first EM response signal to generate a corrected EM signal.