Development Of Motion Detection Circuit Module For Drilling NMR Logging Tool

In an actual project of the Logging While Drilling,nuclear magnetic resonance logging-while-drilling(LWD-NMR)tool measures reservoir fluid properties real-time in the drilling process.In the process of drilling,due to the collision between the drill bit and the rock,the instrument moves randomly and results of Carr-Purcell-Meiboom-Gill(CPMG)pulse sequence logging have no good quality.One important way of improving the accuracy of logging and drilling efficiency is to obtain equipment vibration displacement data.In the logg-ing while drilling,by installing the biaxial acceleration sensors in the drill site to obtain the vibration acceleration signal of the instrument.In theory,the vibration displacement data can be obtained by the double integration of the vibration accele-ration signal.However due to the effect of the dc bias and noise existing in the vibration acceleration signals,if the acceleration signal is directly integrated to obtain the displacement signal,it will produce relatively large trend items and random noise items.The trend items can be removed by frequency domain or polynomial fitting,but random noise items remove more difficultly.In this thesis,based on the comprehensive analysis of the mechanism of the drill and the causes of random noise,the new methods were discussed.The main contents are as follows:(1)In this thesis,the mechanism of the instrument movement was discussed and analyzed.Firstly,analyzed the force of the drilling tool,and expounded the mechanism of the four kinds of motion forms of the instrument.Based on the principle of nuclear magnetic resonance logging,established the main motion form of the drill bit lateral vibration as the logging quality.Then discussed the principle of measuring the transverse motion of the biaxial accelerometer with the magnetometer,and the algorithm of the displacement from the vibration acceleration with angle.(2)The initial motion detection circuit consisted of two two-axis accelerometer anda three-axis magnetometer with its corresponding signal conditioning circuit.Due to the previous signal sampling resolution was low,the conversion rate was low and other shortcomings,the signal acquisition circuit was improved and the schematic diagram of the motion measurement circuit and the pcb were drawn.After the vibration test,the relative error of the acceleration power spectrum collected by the motion measurement circuit was controlled within the range of 5%.Achieved the drilling Acceleration Measurement Requirements.(3)Kalman filter algorithm was used to process the acceleration signal.Firstly,the Kalman filter algorithm was implemented in Matlab and the Kalman coefficient was determined.Then,FPGA hardware was selected and the Kalman filter model was established by FPGA tool.Through model simulation,functional simulation,the error analysis of the two methods showed that the Kalman filter algorithm implemented by FPGA could achieve the filtering effect of Matlab program.