Probe Design Of Eccentric Nuclear Magnetic Resonance Logging Tool

As the most advanced downhole oil and gas exploration method,the development and application of nuclear magnetic resonance logging tools have become an important symbol to measure the level of logging technology in a country.Due to the particularity of the marine environment,offshore oil exploration work has strict requirements on the performance of nuclear magnetic resonance logging tools.At the same time,domestic oil exploration and development technology started late,and foreign oil service giants have implemented strict blockades on core technologies such as logging tool probes.It is urgent to solve the problem of " neck sticking " in the oil and gas field.Therefore,it is of great significance to accelerate the research on the probe technology of nuclear magnetic resonance logging tool to support the high-quality development of the oil industry chain and ensure national energy security.In this paper,an eccentric NMR logging tool probe suitable for offshore oil exploration is designed.The magnet,antenna and shell of the probe are simulated and optimized.The main research contents and conclusions are as follows:(1)The finite element analysis of CMR,MREx,MR Scanner and MRIL-P probes was carried out by ANSYS software.Through the simulation of the magnet,it is found that an eccentric NMR logging tool probe suitable for offshore oil exploration is designed.The detection range should be 7～12 cm,the magnetic field strength should be 120～200 Gs,and the detection frequency should be 500～1000 k Hz.(2)The magnet is selected and optimized from four aspects: magnet material,magnet shape,magnet length and magnet spacing.The results show that the magnetic induction intensity of samarium cobalt material can reach 229 Gs at 180 °C,which is more suitable for underground high temperature environment.The magnetic field intensity of the cylindrical magnet is 30 % higher than that of the prismatic magnet,and the magnetic field line distribution is more uniform.The length of the pre-polarized magnet is at least 60 cm to ensure that the polarization degree of the formation proton reaches more than 95 % when the logging speed reaches 200 m/h.At the same time,the influence of model shape,model size and unit type on the error of data simulation is analyzed.The simulation data show that the data accuracy of the circular boundary model is 12.5% higher than that of the square boundary model.The magnetic field strength calculated using a circular boundary with a diameter of 3 m increases by 42～30Gs;the magnetic field distribution calculated by triangular mesh subdivision is smoother,and the error of static magnetic field distribution is less than 1%,which improves the accuracy of probe simulation design.(3)Comparing three classical antenna models,according to the probe detection requirements,the planar coil is selected as the antenna structure.When the opening angle of the planar antenna is 80°,the orthogonal matching effect is the best,and the signal-to-noise ratio can reach 2.4.When the antenna length is 70 cm,the velocity of the logging tool can reach 400 m / h,and the detection accuracy can reach more than90%.Solid Works software is used to design and model the probe shell.Aiming at the special environment at sea,a portable shell is designed to shorten the longitudinal size of the probe by 50 mm in the process of storage,reduce the area by 20%,and improve the quality and efficiency of logging.(4)Through the simulation and verification of the probe,it is found that the average magnetic field strength in the range of 7～12 cm from the probe is 153.8 Gs,and the maximum value is 154.22 Gs.Through the actual verification of the probe model machine,it is found that the magnetic field of the probe magnet is the largest in the middle,up to 157.5 Gs,and the intensity is uniform in the detection range,reaching the magnetic field strength required for nuclear magnetic resonance logging,which meets the logging requirements.At the same time,the magnetic field curve obtained by experimental verification is consistent with the trend of the magnetic field curve obtained by simulation verification,and the design results are real and effective.