Design Of Experimental Device And Receiving Circuit For Nuclear Magnetic Resonance Logging While Drilling

Petroleum is a hugely significant non-renewable resource.With the rapid development of the Chinese economy,the shortage of petroleum resource has become increasingly severe,restricting the growth of the national economy and,somewhat,threatening national security.Therefore,there exists an important realistic significance to develop petroleum logging and exploration technology vigorously.NMR logging while drilling technology,compared with other logging technologies,not only has the characteristics of the precise target,fast inversion,the high degree of reduction,but also can effectively avoid the pollution caused by the radioactive logging fluid.Although the relatively complete commercial instrument based on this technology has been developed on the international level,little domestic research into this domain has been conducted.This paper focuses on the following research on the NMR logging technology while drilling:1.The in-depth understanding of the nuclear magnetic resonance phenomenon;the analysis of the principle of the nuclear magnetic resonance logging technology;the determination of the overall design of the relative experimental device by carrying out the detailed investigation and analysis of the relevant domestic and international technology.The experimental device can be divided into two segments,including a probe system,which consists of a permanent magnet and an antenna,and an electronic circuit system.The electronic circuit system contains a master control circuit,a transmitting circuit,a receiving circuit and an acquisition circuit.2.The probe system of the device applies the "inside-out" structure to generate a stable uniform static magnetic field with a Larmor frequency of about 500 k Hz.The antenna generates a radio frequency signal and receives the original nuclear magnetic resonance signal via a parallel resonant circuit;The transmitting circuit adopts a double full-bridge structure using eight RF MOSFETs,forming a power amplifier which can double the input voltage;In terms of the acquisition circuit,an eight-channel 14-bit synchronous acquisition system based on the 100 M Ethernet has been used to read and analyze the data.3.In order to address the issue of the small amplitude of the received nuclear magnetic resonance signal,a low-noise receiving circuit has been designed.It includes the power supply circuit,the isolation and absorption circuit,the low-noise front-end amplifier,the active filter,the calibration circuit,the attenuation measurement circuit.4.Having done the PCB design of the whole circuit,mainly the receiving circuit,the main functional circuit and the overall system has been tested.For receiving circuit,the gain of the front-end amplifier,the passband of the active filter,the bandwidth,the maximum gain within the passband and the working temperature have been tested.In addition,the probe is subjected to the static magnetic field test.Furthermore,the transmission circuit is subjected to power amplification test.The high-temperature test has also been carried out for the key components of the system.