Abstract
The telemetry drill string transmits the measured drilling and formation parameters near the bit to the ground at high speed through the transmission line in the wired drill pipe and the inductive coupler formed by the coil embedded in the drill pipe joint. The voltage transfer function of the inductive coupler seriously affects the signal transmission characteristics of the telemetry drill string. Present research methods cannot accurately and quantitatively describe the influence of the electromagnetic parameters of the inductive coupler on its voltage transfer function. This paper quantitatively analyzes the effects of the electromagnetic parameters of the inductive coupler on signal transmission through reasonable high-frequency circuit modeling. The generation mechanism of eddy current in the magnetic core and the interaction mechanism between eddy current and coupling coils are studied using the electromagnetic detection analysis method of nondestructive testing (NDT) technology. Then, the high-frequency circuit model of the coupler containing eddy current loss is established. The mathematical model of input impedance and signal transmission characteristics of the inductive coupler is established through circuit analysis. The influence of the electromagnetic parameters of the magnetic core and the load resistance of the coupler on the voltage transmission characteristics and power transmission characteristics of the coupler is studied. The research results show that the relative permeability of the magnetic core, load resistance of the coupler, and signal frequency seriously affect the signal voltage transmission. When the relative permeability of the magnetic core material reaches 50, the voltage transmission of the inductive coupler is effectively improved. The electromagnetic simulation results are consistent with the theoretical analysis of the circuit model, which proves the correctness of the circuit model. This paper provides theoretical guidance for the electromagnetic design of inductive couplers and the improvement of signal transmission characteristics of telemetry drill string.
Highlights
Measurement while drilling/logging while drilling (MWD/ LWD) technology can transmit formation information to the surface in real time during drilling, but, limited by the transmission rate, the current formation sampling spacing is larger than that of conventional logging technology, which is not conducive to the discovery and exploitation of thin reservoirs [1]
When two wired drill pipes are connected, the coil in the pin nose of the wired drill pipe and the coil in the box joint of the wired joint form an inductive coupler, and the high-frequency signal is transmitted between the wired drill pipes through electromagnetic induction
Some theoretical studies [20,21,22] are conducted on the characteristics of the coupler based on the equivalent high-frequency transformer model, but this model needs to be further improved to adapt to the research of inductive coupler in wired drill pipe
Summary
Measurement while drilling/logging while drilling (MWD/ LWD) technology can transmit formation information to the surface in real time during drilling, but, limited by the transmission rate, the current formation sampling spacing is larger than that of conventional logging technology, which is not conducive to the discovery and exploitation of thin reservoirs [1]. Some theoretical studies [20,21,22] are conducted on the characteristics of the coupler based on the equivalent high-frequency transformer model, but this model needs to be further improved to adapt to the research of inductive coupler in wired drill pipe. E high-frequency circuit modeling of the inductive coupler needs to consider the influences of the eddy current loss of the magnetic core material, magnetic field leakage, and distributed capacitance of the coupler on signal transmission and ensure they are equivalent to the influences of the corresponding circuit elements. Is paper uses the electromagnetic detection and analysis method of nondestructive testing (NDT) to study the generation mechanism of eddy current in magnetic core material and the interaction mechanism between eddy current and the coupling coil; on this basis, a high-frequency circuit model of the coupler considering eddy current loss is established. Is paper uses the electromagnetic detection and analysis method of nondestructive testing (NDT) to study the generation mechanism of eddy current in magnetic core material and the interaction mechanism between eddy current and the coupling coil; on this basis, a high-frequency circuit model of the coupler considering eddy current loss is established. e input impedance mathematical model and signal transmission characteristic mathematical model of the coupler are established through theoretical analysis. e relevant circuit parameters of the coupler are determined according to the calculation results of the mathematical model and the electromagnetic field finite element simulation analysis, and the voltage transmission characteristics and power transmission characteristics of the coupler are studied
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