【作者】 王艳；

【导师】 林君；

【作者基本信息】 吉林大学 ， 测试计量技术及仪器， 2011， 博士

【摘要】 中国矿产资源经过几十年的大力开采,已造成浅部(<500 m)矿山资源枯竭,后备接替资源匮乏的局面,目前,矿山危机问题已成为重要的经济和社会问题。成矿理论研究和国际找矿经验表明我国存在第二采矿空间,即地下500-1500 m大陆深部蕴藏着潜力巨大的矿产资源。深部矿产资源的开发利用可缓解我国的矿山危机问题。然而,深部矿产资源勘探由于浅部采空、环境噪声严重等特殊情况,给勘探技术提出了巨大挑战。频域CSAMT和时域LOTEM电磁方法勘探深度大、场源大小和方向可控、信噪比较高,且对低阻敏感,具有探测深部矿产资源的潜力。为此,本文提出采用时频(CSAMT和LOTEM)联合电磁探测方法进行深部(500-1500 m)矿产资源的探测,缩短与国际探测深度的差距,并解决我国面临的矿产资源危机问题。基于此,本文首先对频域CSAMT法和时域LOTEM法分别进行了数值模拟,研究了单独采用两种方法进行探测时的优势和不足,发现两种方法在单独探测时均存在不可避免的难题。然而,若两种方法联合,则可取长补短,突出优势,从而突破探测深度瓶颈,提高探测的成功率。随后,将两种方法进行联合,并对时联合探测方法的方案设计及数据处理方法等进行了深入研究,证实了采用时频联合电磁探测方法进行深部矿产资源探测的可行性,可为我国深部矿产资源的探测提供有效的解决方案和方法保障。本论文研究过程中主要获得如下研究成果和结论：(1)基于麦克斯韦方程组阐述了频域CSAMT法和时域LOTEM法探测深部矿产资源的基本原理,从理论上探讨了时、频两种方法探测深部矿产资源的可行性。采用均匀半空间模型,通过对发射频率和激发场强的研究,发现电偶极子更适合作为两种方法深部探测的发射场源；通过电阻率、接发距和时域电磁场的关系研究,深入探讨了时域信号的特点。(2)采用层状大地模型,对CSAMT法的优势和不足进行了数值模拟研究。首先,通过几种方法的仿真结果对比,确定了大收发距下的贝塞尔函数收敛问题的解决方法；随后,通过不同模型电磁场曲线的对比分析,得出高、低阻的电磁场曲线特征及CSAMT法分辨高、低阻的能力；并研究了妨碍CSAMT法深部探测的各种效应(非平面波效应、假极值效应和静态效应)的特征及其对探测结果影响。(3)采用层状大地模型,对LOTEM法的优势和不足进行了数值模拟研究。首先,利用Guptasarma数字滤波法稳定、高精度的频一时域电磁场转换优势,解决了大收发距下电偶极LOTEM法电磁场的计算问题；随后,分析了高、低阻在感应电动势和磁(?)曲线上的特征反映以及LOTEM法分辨高、低阻的能力；LOTEM法由于数据量庞大、电磁场及电阻率计算过程复杂、数据反演理论不成熟等问题,直接降低了其深部探测的效率。(4) CSAMT和LOTEM法的分别研究表明：LOTEM法相对CSAMT法曲线光滑无假极值效应,且由于其接收磁场或磁场的变化率,因而不存在静态效应和趋势项；其次,CSAMT法横向分辨能力高、穿透高阻能力强,而LOTEM法纵向分辨能力高、且无高阻屏蔽现象；另外,CSAMT法的理论和反演方法成熟,可为LOTEM法的数据反演提供有效借鉴；最后,两种方法的观测装置相近,具备联合应用的条件。因此,两种方法联合可提高CSAMT法深部探测结果的可信度和LOTEM法的反演效率,从而达到深部资源成功探测的目的。(5)针对深部矿产资源探测,对时频联合电磁探测方法的观测装置进行了研究。研究结果表明,为提高深部微弱信号的提取能力,可采用电偶极发射并在转折频率前采集信号；其次,不断加密频率并不能无限制提高频域纵向分辨率,但采用基频小于或等于最佳发射频率的3或5频的伪随机发射方式,可在分辨出深部异常的同时,提高工作效率和接收信号幅度(提高了△fmin1.5倍)；另一方面,时域可通过发射周期性和双极性方波,并大容量存储原始数据,从而实现双极性阈值叠加压制尖峰和其它噪声的目的；最后,设计了环阵列固体不极化电极,可同时实现高效、高精度的深部资源探测。(6)针对深部探测中电极性能低的问题,进行了接收电极极差和稳定性研究。通过对净反应速度、环境浓度、环境温度、扩散速率等电化学因素与极差和稳定性的关系研究,得出了降低极差、提高稳定性的方法；另外,采用电阻网络元模拟法,对接地电阻进行了仿真研究,提出了低接地电阻的电极设计方法和野外施工要求；最后,研究了电极中趋势项电化学噪声对CSAMT法视电阻率值的影响,结果表明该噪声可显著降低CSAMT法对深部矿产资源的探测能力。(7)针对时频联合电磁探测的数据处理,进行了时域和频域的全区视电阻率计算、人机联合反演以及联合LOTEM数据校正等方法研究。结果表明全区视电阻率计算结果能够客观反映地下地质信息,尤其是深部地电信息,从而可降低计算的复杂度,提高解释结果的可信度；其次,人机联合反演方法(频域包含自动迭代功能)能快速获取地电模型,并在一定程度上减少LOTEM法的工作量,提高其在深部探测中的效率；另外,LOTEM联合校正对时频转换方法和修正反演法进行了研究,结果表明时频转换方法可以用来识别CSAMT法中存在的假极值、静态效应和趋势项,但由于逼近能力的不同而导致其校正误差大；而修正反演法则可以成功识别并校正CSAMT法中的静态效应和趋势项。本论文通过上述研究,主要在如下三个方面取得了突破和创新：(1)发现电极中低频趋势项对CSAMT法的深部探测结果存在明显影响,并提出了校正方法。研究表明正值趋势项会导致低频对应的深部电阻率值迅速增大,而负值趋势项则可导致低频对应的深部电阻率值迅速降低,从而屏蔽了深部真实的地质信息；联合LOTEM数据的反演修正法,可成功校正趋势项,还原低频真实信息,提高频域CSAMT和时频联合电磁探测结果的可信度；(2)提出环阵列固体不极化电极的设计方法。该方法采用电解法、固体电解质均匀包裹制作成锥形一体化固体不极化电极,并运用环阵列设计电极结构和叠加压噪法处理信号,从而同时实现金属电极的高效和不极化电极的高精度,为深部微弱电场信息的获取提供了技术支持；(3)深部矿产资源探测的时频联合电磁探测方法研究。基于CSAMT法和LOTEM法的优势和不足,对联合探测方法的观测方案和数据处理进行了深入研究,论证了联合探测方法可扬长避短,实现深部矿产资源探测的目的。综上,本研究表明,时频联合电磁探测方法可突破目前深部矿产资源探测深度的技术瓶颈,为深部矿产资源探测提供了理论基础和方法指导,对缓解我国矿山危机具有重要意义,同时可缩短与国际发达国家深部探测技术的差距。更多还原

【Abstract】 The results of exhaustion of mineral source, deficiency of substitution source and declination of economy have been produced with the expliotion of several decades. The crisis ore problem brought becomes the economic and social problem. Metallogenic studies and the international exploition experiences ores show that there exists the second exploring space in China, in which large mineral sources deposit below 500～1500 meters depth. This foundation provides basis guarantee for solving the problem of crisis mines. However, the environment in mining area is very unfavorable for the geophysical exploration, so the large improvement of prospecting techniques is needed.CSAMT and LOTEM methods have those advantages such as:artificial source, controlled source direction, large signal strength, and sensitive to low resistivity. Thus both methods are the good choices for deep mine resource prospecting. Therefore, on the basis of the numerical modeling of these two time frequency methods, this article proposed the joint time-frequency electromagnetic method, and payed the main attention to the research of observation scheme and data process method. The conclusions are as follows:(1) The principles of CSAMT and LOTEM for deep mine prospecting have been introduced based on Maxwell’s equations, and the principles confirm the feasibility of those methods. The electric dipole transmitting source is determined by the research of transmitting equency and excited field. The relationship between resistivity, offset and electromagnetic field makes the knowledgement of signal characteristics of time domain.(2) In the CSAMT modeling simulation, the precise and fast method for the electromagnetic calculation is determined by analysis and comparision of several methods for the convergence problem of Bessel function under the large offset condition. The different reflections in electromagnetic curve of low and high resistivity provide theoretical knowledge for recognization of geologic characteristics. In addition, the resolution ability for low and high resistivity bodys is drawn from the characteristics of electromagnetic curves. Non-pl ne wave effect, false peak effect and static effect are found in the far-zone and all-zone electromagnetic curves, by the analysis of their characteristics and influences, the conclusions are obtained as follows:the existence of those effects shields the ture geologic information, especially the medi and deep information, adds the interpretation difficulty, lowers the reliability of results, and finially hinders the development of CSAMT in the deep detecting space. This problem lays the foundation for the effects correction by joint LOTEM data.(3) Guptasarma digital linear filter method with stability and high precision solves the elelctromagnetic field calculation in time domain using the frequency domain method. In the modeling simulation of LOTEM method, different reflections of high and low resistivity in induced voltage and magnetic curves are enduced. The sensibility of induced voltage to resistivity and offset makes the curve complicated, and non-sensibility of magnetic field make the curve simple and smooth. There are no false peak effect, and no static effect and trends in LOTEM curves because of magnetic field or induced voltage collection. The large storage by long period observation, complex calculation of time domain, overloaded early-late apparent resistivity calculation separately and immature data interpretation problems lower the utilization ratio of LOTEM method directly. Those advantages and disadavantages of LOTEM method further the combination of CSAMT and LOTEM in deep mine resources detection.(4) The joint time-frequency electromagnetic method for deep mine resources detection is proposed by the similar observation configuration, complementation of two methods. In frequency domain, the frequency lower than the optimal transmitting frequency can be taken as the minimum transmitting frequency, taking this frequency as the base frequency, and transmitting with 3 or 5 pseudo-random frequency will make the electric field increase byΔfmin1.5. In time domain, in order to improve the data quality by bipolar preset stacking methods, transmitting bipolar period wave, acquiring repeated, and enlarging the storage volume are needed. Combining with the convience of metal electrode and high performance of nonpolarized electrode, the "dumbbell" enclosing solid nonpolized electrode forms taper metal electrode integration construction. The electrode is plated by electrolysis, and then is enclosed by solid electrolyte uniformly, and this method can improve the stability of electrode. The taper electrode is like a needle, can penetrate easily with high efficiency. Several electrode needles forming ring array electrodes can suppress noises using digital signal processing method.(5) The stability and precision of electrodes are affected by the volecity of net reaction, circumstance concentration, circumstance temperature, pH, and diffusion potential. The influence to the potential difference of the factors will be lowered if the electrolytic solution is at the saturated or oversaturated situation. At the same time, increasing the length will extend the use life of the electrode. The calculation by resistivity network simulation method has the results as followings:different type, radius, bury and resistivity of soil will have different grounded resistivity. The bigger radius, the deeper bury, the smaller soil resistivity, and the smaller grounded resistivity, and this is good to the collection of weak signal. The potential difference will change by the influence factor, named as trends. The curve characteristic is near linear or nonlinear, and the spectrum focuses on zero or low frequency as the presence of drift. The drift will make the calculated resistivity at low f(?)equency change abruptly, shield the real information at deep depth, and lead to wrong inversion results.(6) In the data procession method research, the all-zone apparent resistivities of CSAMT and LOTEM methods are calculated, and the results can reflect the geologic information objectively, reproduce the deep geologic imformation, lower the work load and complexities, and improve the reliability of results. Man-machine combination (auto-iteration for CSAMT method) inversion can obtain the geo-electric model quickly, and thus improves the competitive power of LOTEM method in deep resources prospecting. Besides, the effects of CSAMT method can be revised by the LOTEM data, and the methods are f=186/t time-to- frequency transform and inversion correction method. The static effect and trends can be revised effectively, and the false peak effect can be recognized. Those data processing methods make the reflection of deep information more reality, and improve the interpretation effiency and reliability.The innovations of this paper are as followings:(1) The influence to CSAMT results by trends of electrode is found, and the correction method is then proposed. The positive trends will make the resistivity in depth increase abruptly, and vice versa. This kind of change can shield the real information in depth. However, the inversion correction with LOTEM data can reveal the true geologic information in depth, and finally improves the reliability of CSAMT and joint time-frequency electromagnetic results.(2) The design method of ring array solid non-polarized electrode is proposed. Those methods adopted overcome the problems of low stability in metal electrode and inconvience in non-polarized electrode such as, electrolysis in electrode manufacture, electrode enclosed by solid electrolyte uniformly in solid non-polarized electrode manufacture, ring array and taper design structure, and iteration suppression method. The realization of electrode with high precision and effiency provides technical support for weak electric signal acquisition in deep mine resource detection.(3) Joint time-frequency electromagnetic method for deep mine resources is proposed. Those methods such as,3 or 5 pseudo-random transmitting with the base frequency lower than the optimal transmitting frequency, bipole preset iteration method, all-zone apparent resistivity calculation, man-machine joint inversion, time-frequency transform and inversion correction method etc., are used to improve the prospecting ability and effiency of deep resources.Those results show that, joint time-frequency electromagnetic method can break the technique bottleneck of deep mine resources prospecting, provide guarantee for the successful detection of deep mine resources, is very important for the solving of mine crisis, and can shorten the gap of deep prospecting level between our country and developed countries.更多还原