Optimization Design Of Energy Spectrum Acquisition And Processing Module Of High Temperature Density LWD Tool

Density Logging While Drilling(LWD)technology belongs to the branch of radioactive logging technology field,and is one of the important technologies in the field of petroleum exploration.The principle is to use the gamma rays radiated into the formation to have a Compton effect and photoelectric effect with the formation medium,and then measure the energy of the attenuated gamma rays to obtain energy spectrum data,thereby calculating the formation density and photoelectric absorption index.Based on the measurement principle and structural composition of the density LWD tool,this thesis takes the density logging tool of an oilfield services company as the object,analyzes the logging data of the tool in field logging,and summarizes the defects and flaws of the energy spectrum acquisition and processing module in the logging process as follows: 1)The energy spectrum acquisition and processing module still has temperature drift after gain control of the all-energy peak at 0.662 Me V,which cannot meet the logging needs of high-temperature wells;2)The dead time of the energy spectrum acquisition and processing module for sampling a single gamma ray pulse is too long,which is prone to accumulation effect..In view of the above defects,the thesis optimizes the design of the high temperature energy spectrum acquisition and processing module.First of all,the thesis establishes a mathematical model for the circuit of the energy spectrum acquisition and processing module and conducts theoretical analysis,and on this basis,conducts high-temperature experiments on the energy spectrum acquisition and processing module.The mutual influence relationship among ambient temperature,peak time and charging current in the module,so as to locate the existing problems of the current energy spectrum acquisition and processing module,and determine the root cause of such problems.Secondly,on the basis of the successful positioning of the problem,the thesis further optimizes the parameters of the energy spectrum acquisition and processing module,and designs an high-temperature adaptive energy spectrum acquisition and processing module,which can adaptively adjust circuit parameters as the ambient temperature changes,so that it can offset the negative impact of temperature on the instrument,fundamentally solve the problem of temperature drift;the adaptive circuit can compress the width of Gaussian like signals at low temperature,so that there is a shorter dead time at low temperature,thereby reducing the overall dead time of the system.At the same time,use Multisim software to build a circuit model for simulation,verifying the feasibility of the design.Finally,the thesis describes the laboratory high-temperature testing and instrument testing on the high-temperature adaptive energy spectrum acquisition and processing module.The test results show that the maximum operating temperature of the optimized module is raised from 80°C to 150°C,and the nonlinear error is less than 1%;the dead time is reduced from 1500 ns to 1000 ns,and the dead time is shortened to 66.7% of the original,which can meet the requirements of actual measurement.