Development Of Detection Circuit For High Temperature NMR Logging

In view of the design requirements of conventional NMR logging tool(EMRT), the working environment temperature can only reach 150°C. With the reduction of oil resources, oil and gas exploration depth is increasing, the more deep and higher temperature logging environment requires the instrument to have a better performance. In this paper an application to the weak signal detection circuit for high temperature of 200 °C is developed. In the realization of the project mainly in the following two problems, one is weak voltage amplification problem in high temperature well logging environment, and another is the thermal stability problem of the circuit in the high temperature environment.In this paper, based on the problem of weak voltage signal amplification in high temperature logging environment, a low noise amplifier circuit is designed and realized by using the matching method of complex source impedance noise. In order to verify amplification circuit temperature reliability, respectively from the frequency characteristics and signal amplifier linearity and noise voltage angles, amplifying circuit performance testing under high temperature. The experimental results show that, under the environment of 200 °C and temperature of 25 °C, circuit performance meet the above 90 d B gain, the noise spectrum density 3nv/(?) design requirements.In view of the problem of circuit thermal stability in the high temperature environment, based on COMSOL simulation software, EMRT data acquisition circuit and high temperature acquisition circuit model are simulated, and take this as the basic design for system in package high temperature signal acquisition circuit. Through the high temperature experiment, the experimental results of the EMRT signal acquisition circuit are compared, the thermal performance and electrical performance of the high temperature signal acquisition circuit are verified.Finally, the high temperature well logging instrument machine are tested, compared with EMRT test results, the signal to noise ratio and echo data and echo inversion verified the high temperature weak signal detection circuit performance.