Development of nuclear magnetic resonance downhole logging tool for hydrocarbones search

Alexey A Tyshko

Doctoral dissertation

Dissertations are not being sold



This thesis presents a new development in the design of Nuclear Magnetic Resonance (NMR) downhole logging tools for the oil and gas industry and operates in a high temperature environment. Two main improvements of this tool is suggested and analyzed in this thesis. They are a new NMR antenna containing a Faraday shield placed between the antenna coil and the analyzed fluid and an improved NMR transmitter operating at 175 °C ambient temperature. This is based on multi-module, multilevel topology, which combines the outputs of several identical power modules, which operate at a 50% duty cycle at its fundamental frequency.

The NMR antenna equipped with Faraday shield decreases the resonant frequency shift to less than 1%, which makes it possible to perform measurements without engaging a special tuning system for the compensation of antenna detuning. It was shown experimentally that the implementation of the Faraday shield makes the NMR echo signal less dependant on the type of the well fluid being measured. For the multi-module NMR transmitter, a method of DC/AC conversion based on the multi-vector synthesis of the sinusoidal voltage with sequential elimination of the higher harmonics in the output voltage was used. This was done in order to decrease the power dissipation occurring in the resonant loads.

The present study reevaluates the prior investigations of a silicon MOSFET’s drain-to-source resistance (Rdson) in a temperature range of up to 200 °C as a function of the temperature and the drain current (Id). An improved Rdson behavioral model in which Rdson and power index (P) of Rdson dependence on the temperature proposed as a function of Id was tested and validated for the temperature range from 25 °C to 200 °C.

The multilayer X7R type capacitors, used as the high power NMR transmitter’s filters, were investigated for excessive losses and ways to mitigate these losses were suggested. It was demonstrated that these capacitors behave as piezoelectric resonators when biased with DC voltage and that their mechanical resonances increase the capacitors’ losses and propability of failure.

The multimodule NMR transmitter, which uses a combination of the fixed phase shift method for the cancellation of the higher harmonics an increase of the NMR tool signal to noise ratio and NMR transmitter life expectancy. The higher harmonics cancelation in the multimodule NMR transmitter was validated experimentally by testing transmitters with different topologies.

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Imprint No:
145×205 mm
130 p.
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