Nonconductive Inserts in MWD Drill Pipe for Parasitic Signal Reduction
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Solution Overview
Problem
Existing electromagnetic well logging methods face challenges in reducing parasitic signals caused by eddy currents in drill pipes without increasing the distance between transmitter and receiver, which limits the accuracy and convenience of Measurement-while-drilling (MWD) applications.
Innovation Solution
The use of a carrier with a conductive tubular and a non-conductive insert in the drill pipe, along with at least two spaced-apart receiving antennas, to reduce parasitic signals by activating the transmitter and processing first and second transient signals to estimate the resistivity properties of the earth formation, employing a bucking mechanism to diminish the impact of eddy currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the distance between transmitter and receiver is increased to reduce parasitic signals from eddy currents in the drill pipe, then the influence of parasitic signals is reduced, but the tool length increases to 10-15 m which is not desirable for MWD applications
Solution Approach 1:
A non-conductive insert is introduced as an intermediary element within the drill pipe to block eddy current paths. This insert acts as a mediator that interrupts the conductive path of the drill pipe, thereby reducing parasitic signals without requiring increased transmitter-receiver distance or tool length
Solution Approach 2:
The drill pipe is segmented by introducing non-conductive inserts at specific locations, dividing the continuous conductive path into separate segments. This segmentation disrupts eddy current flow while maintaining the overall structural integrity and compactness of the MWD tool
2Reliability
If measurements are taken at late stage when formation signal dominates parasitic signals, then the measurement reliability improves, but the formation signal becomes very small making reliable measurement difficult
Solution Approach 1:
The non-conductive insert converts the harmful effect of eddy currents into a beneficial signal characteristic. By blocking eddy current paths, the insert causes the parasitic signals to decay more rapidly, allowing formation signals to become dominant at earlier time stages when they are still strong enough for reliable measurement
Solution Approach 2:
The system uses transient electromagnetic excitation with periodic on-off cycling of the transmitter. The non-conductive insert modifies the decay characteristics of each transient cycle, creating a distinct signal pattern that enhances the ability to distinguish formation signals from residual parasitic signals
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 effectively reduces the dominance of parasitic signals from the drill pipe, allowing for more accurate and reliable measurement of earth formation resistivity properties, even at closer transmitter-receiver distances, thereby enhancing the resolution and practicality of MWD tools.
Implementation Method 1
current in the transmitter coil drops from its initial value I0 to 0 at the moment t=0. Subsequently, measurements are taken while the rotating tool is moving along the borehole trajectory. The currents induced in the drilling pipe and in the formation (i.e. eddy currents) begin diffusing from the region close to the transmitter coil
Implementation Method 2
The currents induced in the drilling pipe and in the formation (i.e. eddy currents) begin diffusing from the region close to the transmitter coil in all the directions surrounding the transmitter. These currents induce electromagnetic field components which can be measured by induction coils placed along the conductive pipe. Signal contributions due to the eddy currents in the pipe are considered to be parasitic
Data Source
AI summary
A three-coil bucking system is used for determination of a formation resistivity property ahead of the drill bit. The conductive drill pipe is provided with non-conductive inserts in the proximity of at least one transmitter and at least two receivers. Transient electromagnetic signals are processed to give the estimate of the resistivity property and for geosteering.