【作者】 孙淑琴；

【导师】 林君；

【作者基本信息】 吉林大学 ， 地球探测与信息技术， 2005， 博士

【摘要】 本论文对地面核磁共振找水技术中影响地面核磁共振信号的因素进行了详细的研究,建立了层状大地单一含水层及多个含水层仿真模型,并针对所建立模型对理想情况下及实际地电条件下单一含水层进行仿真计算,分析两种情况下核磁共振信号的关系;根据理论表达式中存在的等价的问题,对单一含水层进行仿真计算,得出多个模型仿真结果一致的结论。对于层状大地存在多个水平含水层的情况下,分析了理想情况及多个含水层上方存在不同导电性介质时平均电阻率的计算方法,给出多个含水层核磁共振信号的计算方法,仿真对比理想情况及实际地电条件下多个含水层总信号与各个单一含水层信号的贡献关系,为数据反演奠定基础。针对实际找水仪器野外工作时出现的反演解释勘探深度与钻孔获得的勘探深度存在误差的情况,仿真分析几种参数变化时的最大勘探深度,结合野外实测地点的数据与钻孔资料提出增大勘探深度的有效办法。分析地层岩性对钻孔出水量的影响,利用野外实测地点的数据与钻孔资料验证地层中平均含水量大而且地层弛豫时间较长的地点才能得到较大的出水量。更多还原

【Abstract】 The nuclear magnetic resonance (NMR) technique is mainly known in geophysics for well logging and laboratory applications. In recent years, Surface NMR (SNMR) has become available for hydrogeological applications, NMR is observed with nuclei of certain atoms which are immersed in a static magnetic field and exposed to a secondary oscillating magnetic field, The amplitude of the signal is proportional to the amount of spinning nuclei, e.g. H-proton and the decay of the signal contains information on the pore space. The power of SNMR lies in the fact, that it is the only available geophysical technique which provides direct information of the water content and structural parameters, like porosity or pore size. These abilities of SNMR make it a promising tool for much broader applications in near surface geophysics than for hydrogeophysical exploration alone, like ground water quality, waste disposal, site exploration, soil physics, dam wetness/stability or agriculture (agro-geophysics) research. Since 1992, there are few personnel to develop scientific research on SNMR for groundwater in China, though abundant investigations have already developed in foreign country, so it has science importance to develop research of theoretics and method based on SNMR groundwater, and it will promote grow of SNMR technology in our country. Application research of SNMR miss quite mature, datum exist error tested by France NUMIS Instrument, the depth of water-saturated layers from the NMR data interpretation and the depth of bore is not coherent, the depth of theory and the antenna diameter have corresponding relationship, but certain parameters should be simulated and analyzed the influence factors about depth of investigation in order to present appropriate model. Otherwise, there are some problems to evaluate underground abnormity and provide appropriate explaination accord with geologic structure. SNMR Method was initially developed for the detection of free water in aquifers. SNMR capability of separation of groundwater into free and bound water is based on the measurement of signal relaxation time constant. Generally speaking, in some rock, bound water is characterized by shorter relaxation time constant (<30 ms) and longer time constant(>30 ms) corresponds to free water, when water in the unsaturated zone(bound water) is the target, the relaxation time of the NMR signal is usually longer, so the bound water can be detected and the errors between water content and water yield of substratum can appear during the NMR data inversion. It is important that the manifold factors should be considered to detect the water-saturated layers which water can be detected. Based on numerical simulation on surface NMR for groundwater, focusing on influence factors on surface NMR technique for groundwater exploration, linking fund projects of Jilin University “Study on key technique of SNMR -instrument for groundwater”, “Coal mine sap water circumstance detection on NMR method”, “TEM and NMR amalgamation”and outspreading research work. The main research work and achievements are as following: 1. The basic theory of NMR is introduced, the relaxation mechanism of atom nuclei is particular analyzed, relaxation process of hydrogen proton-containing at subterranean liquids is calculated. 2. The electromagnetic theory is introduced and the Maxwell equations based on transient electromagnetic field and frequency electromagnetic field are presented, the basic method of SNMR for groundwater is analyzed, calculation method of NMR signal based on single water-saturated earth layers homogeneous half-space model is particular deduced。The ideal homogeneous model and actual conductive homogeneous half-space model are founded, the NMR signal is computed used by up to date math softwareMAPLE, the relationship of NMR signal amplitude and excited pulse moment is studied when the depth, thickness, water content of water-saturated layers and antenna area are changed. There are equivalence problem about NMR signal from different models through calculating single water-saturated layers, it means that the same NMR signal tested at surface may be come from the different models which in the same depth, different thickness and water content, and it means that inversion may lead to several models, which in turn means that different models may fit equally well a given SNMR experimental data. 3.The multi-water-saturated layers model is founded based on the results of the single water-saturated layer model, the method of calculation about multi-water-saturated layers is given from ideal homogeneous half-space model, and the NMR signal of multi-water-saturated layers is calculated at the same time the contribution from every single layers to total signal is analyzed. The practical conductive homogeneous half-space model is presented according to ideal homogeneous half-space model. The computation method of the average resistance ratio is studied from several layers which in the different medium, and the relationship between the amplitude and the pulse moment of the total NMR signal is calculated when the layer is in the same and the different medium, and the electrical conductivity of the layers above the water-saturated layer will decrease the amplitude of NMR signal, in contrary, the electrical conductivity of the layers under the water-saturated layer has not influence to the amplitude of NMR signal. 4. The maximum depth at which water can be detected is calculated used the model of ideal free and the conductive homogeneous half-space based on the NMR signal from the stratum medium, the relationship between the amplitude versus pulse moment and the amplitude versus depth of investigation of NMR signal is contrasted, the errors between depth of investigation from instrument and depth of investigation from the full theoretical description are analyzed. The maximum depth of investigation is calculated when there are the electrical conductivity of the layers above the water-saturated layer, it is proved that the depth of investigation is decreased when there are the electrical conductivity of the layers above the water-saturated layer, this information is then used toestimate the depth range over which most of the NMR signal is obtained at the field experiment. 5. The testing results from NMR instrument made by our work group are given in Chang Chun suburb, there are coherence through the corresponding data obtained from NMR instrument compared with the calculated data obtained from the simulation model. The data obtained from a nearby boring are compared with the data from interpretation by NUMIS instrument (France) and the results from computer modeling, It can be seen that the NMR signal calculated using a conductive homogeneous half-space model is in fair agreement with the NMR data obtained Experimentally, the validity of model calculation is validated. 6.There are disagreement between the water content from the NMR data interpretation and the yield from the boring of stratum, it can be found from the data of Hydrogeological Department in Mongolia that borehole data only 20% compared with the NMR data interpretation are creditability. Based on analyzing the relaxation property of hydrogen protons of water in a porous medium and linking NMR method for well logging, the relationship between water-saturated rocks lithology and the relaxation time is studied, the method of calculation about the porosity, the permeability and the yield of layers are presented, it shows that the relaxation mechanism of liquid in a porous medium depends on not only relaxation property but also the porous structures and components, and the difference lithology of water-saturated layers will influence the yield of borehole. 7. The influence on groundwater-saturated layers lithology to yield of borehole is analyzed by several experimental data in field from China and France, there are good agreements between the yield of borehole and layers lithology. It is also established that the borehole can offered the more yield when the average free water content is great and the layers lithology is good (its relaxation time is long). The results also provide a theoretical reference to NMR experiments for groundwater in field. Based on the above research findings, focused on “Study on SNMR theory and method for groundwater and develop SNMR instrument system”the problems that need further study are as follow: 1. The testing data from SNMR instruments should be analyzed and processed integrated, the accurate interpretation if there is free water exploited from subsurface更多还原