Design And Implementation Of Main Control System For Downhole Scanning NMR Logging Tool

As an accurate and effective detection technology,NMR has important applications in petroleum exploration.At the present stage,in the face of complex oil and gas reservoirs,lithology,physical properties,and oil-bearing properties are inhomogeneous in the spatial range.Qualitative and quantitative analysis with multi-component and multi-dimensions is essential for the exploration of complex oil and gas reservoirs.At present,the probes of NMR logging tools at home and abroad can not detect different azimuths in 360 degrees around the well;their main control systems also do not involve the 360 degree measurement and control of array probes and array antenna.The Downhole Scanning NMR Logging Tool has the capability of detecting radial,axial and circumferential multi-azimuth sensitive areas,and has profound significance for complex reservoirs with strong heterogeneity,among which the main control system is an important part of the logging tool.At the same time,with technical blockades and restrictions of foreign countries on China,we urgently need to develop our own high-tech nuclear magnetic resonance instruments.Therefore,the self-developed main control system that meets the requirements of the technical characteristics of our instrument and implements circumferential scan is the core issue of the paper.Using Intel-Altera's FPGA chip as a single master chip,this paper designed and implemented a digital master control system for NMR logging tool.This system can meet the basic requirements for the Downhole Scanning NMR Logging Tool,It is suitable for probes with circumferential scanning function,complete experimental tests with analog circuits,and laid a certain foundation for the design and development of NMR logging tool to laboratory.The main control system includes emission control module,main Q-switch control module,auxiliary Q-switch and De-coupler control module,receiver control module,DDS(Direct Digital Synthesizer)module and antenna selection control module,etc.,which can achieve flexible generation of various timing pulses,generate control signals for analog circuits according to timing requirements,acquire,process,and storage of NMR echo signals,control array antenna to select and switch,and complete measurement for circumferential multi-zone with multi-frequency.The main control system designed in this paper has passed the timing simulation test with the simulation software and the actual waveform test under the laboratory environment.The design of the main control system has achieved good experimental results and proved that the system can achieve the radio frequency pulse emission,echo signals reception,control of analog circuits and other functions,shows that the entire system is feasible.