Research And Design Of DSP Module For Multi - Frequency Nuclear Magnetic Resonance Logging Tool

Nuclear Magnetic Resonance (NMR) logging, Through the observation of the NMR signals of the hydrogen nuclei in the formation of pore fluid, this method can get information required for formation evaluation, such as porosity, permeability, pore size distribution, and the fluid nature and content, and it has played an important role in the identification and evaluation of oil and gas.NMR logging has high accuracy without complex calibration, and it can avoid the mud pollution and obtain more logging parameters. Based on the study of the basic principles of NMR and the fully understanding of the structure and function of the NMR logging instrument, this article discusses and and designs a multi-frequency DSP module of NMR logging instrument.This paper details the principle of NMR logging and the composition of the NMR logging instrument, and then puts forward the overall design of DSP module of the NMR logging instrument. The DSP module including digital signal processor (DSP), field programmable gate array (FPGA) and other interface circuit is used to monitor the working status of the entire instrument, control working time and sequence, generate and release the CPMG pulse sequence, collect and process the echo signal speedily and communicate with CPL remote in real time, etc. As to the hardware circuit design, the DSP module’s feature of bearing high-temperature and high-pressure is fully considerated to select the key device so that it can work normally and stably in the harsh environment of the underground. As to the system software design, on the basis of detailed analysis of the logging process of instrument, the article shows the design of operating mode of logging, sweep, determining the 90-degree pulse and so on.Finally, DSP Module acquisition experiment and modified time-sequence control experiment are made, which show good performance of DSP module acquisition. After the modification of time-sequence control, the quality of the echo signal has been greatly improved, and the signal quality of the key points becomes better.