Research Of Two-dimension QT Inversion Method Based On Array Loop For Surface Magnetic Resonance Sounding

Surface nuclear magnetic resonance sounding（MRS） technology has become a rapidlyrising modern geophysical method for groundwater exploration with the advantages ofdirect detection and quantitative assessment. In recent years it is widely used in theexploration of underground freshwater and prevention of water disaster. However, there isstill a lot of work to do for two-dimensional nuclear magnetic resonance sounding methodusing on complicated geological structure and non-layered inhomogeneous distributedgroundwater. The main problems are, on the one hand, the method that repeatedly usingseparate transmitter/receiver coils to measure for integrated imaging is too time consumingand low work efficiency, on the other hand, the two-dimensional initial value inversion (IVI)has a low signal data utilization rate and poor stability and only gets the inversion results ofwater content. In order to solve these problems, this paper carried out the research onresolution and imaging results of the measurement with array coil. In addition, thetwo-dimensional mono-exponential QT inversion method and two-dimensionalmulti-exponential QT inversion method are also proposed, which use all MRS envelopesignals derived from all the pulse moments and the record time to participate in theinversion and accomplish the double parameter imaging of the relaxation time and watercontent. At last, using different two-dimensional inversion methods, the two-dimensionalinitial value inversion、the two-dimensional mono-exponential QT inversion method andtwo-dimensional multi-exponential QT inversion, for numerical simulations and fieldmeasurement data based on the measurement with array loop, imaging results are given anddiscussed.For the low efficiency of repeatedly using separate transmitter/receiver coils to measuremoving along the profile when doing the two-dimensional MRS, according to the theory ofthe measurement with array coil that one large elongated coil as transmitter and a few smallembedded coils as receiver, three groups of laying schemes of different size and differenttype are proposed. Through constructing the water-bearing structure model, the resolution and imaging effects are calculated and analyzed, respectively. The conclusion is confirmedthat the measurement with array coil can improve the work efficiency. Moreover, differentarray coil of size and type have respective advantages and according to the practicalsituation, the different measurement scheme should be made adjustment.For that the two-dimensional initial value inversion only use fitted initial amplitude datato do interpretation, which ignores the relaxation time information. The two-dimensionalmono-exponential QT inversion method aiming at a single relaxation time andtwo-dimensional multi-exponential inversion method aiming at multiple relaxation timesare proposed basing on all MRS envelope signal data and the solving method is deduced byusing a matrix transformation to convert into the general matrix form. The doubleparameter imaging relating to the relaxation time and water content is accomplished, whichcan give more accurate information of the groundwater. Then imaging results are comparedand analyzed by adopting a numerical model and respectively using the two-dimensionalinitial value inversion method, two-dimensional mono-exponential QT inversion methodand two-dimensional multi-exponential QT inversion method.Finally, these three different two-dimensional inversion methods are used to process themagnetic resonance sounding data based on the measurement with array loop in Eddelstorf,northern Germany. Then comparing the imaging effects with geological data, theeffectiveness of two-dimensional QT inversion method is demonstrated.The measurement with array loop and two-dimensional QT inversion method proposed inthis paper excellently achieve the objectives of shortening the detection time, improving themeasurement efficiency and the high precision imaging for a complex water-bearingstructure with multiple relaxation times. Moreover，the measurement and inversion methodhave been verified the superiority and practicability by a practical application and it has aguiding significance for the application of two-dimensional nuclear magnetic resonancesounding technology.