火山地区二维自然电位异常反演

将线性反演理论与正则化法相结合，提出一个火山地区二维自然电位（ＳＰ）异常反演方法．地下岩浆活动（对流体）是引起自电异常的极化源，反演的目的是计算地下视极化强度分布和极化源中心位置．可以通过用已知的各种资料改变地下极化源区域（简称源区）的方式来进行多次反演，以便获得一个比较合理的地下视极化强度分布模型．最后，分别给出意大利和墨西哥的两个火山地区的自然电位异常分析结果．     

磁化强度矢量反演新方法及其在卡拉塔格铜多金属矿床找矿中的应用

磁异常的反演是地球物理勘探的重要手段,三维磁化率反演是磁异常定量解释中的一种重要方法.由于剩磁的存在使得磁化方向与地磁场方向产生偏差,从而影响了磁异常反演与解释的精度.本文基于磁异常模量反演和磁化强度矢量反演方法得到了一种新的磁化强度矢量反演方法.与以往的磁化强度矢量反演方法相比,该方法以磁异常模量反演得到的磁化率模型为约束,采用Lp范数正则化方法求解,提高了磁化强度矢量反演的精度和效率.本文通过模拟试验的反演计算,验证了这种磁化强度矢量反演方法的有效性.最后,将本文方法应用于新疆东天山卡拉塔格地区航磁数据的解释,获得了地下空间不同磁性差异的磁性体的空间分布特征,为进一步分析研究区隐伏矿床提供了重要信息.     

庐枞矿集区矾山-将军庙地区AMT三维反演及地质结构解释

庐江-枞阳矿集区是长江中下游成矿带内的一个重要的多矿种成矿区.为揭示矾山-将军庙地区的地质结构以指导找矿,首先,在庐枞矿集区北部的矾山-将军庙地区开展了三维音频大地电磁数据采集工作,采用Rhoplus方法进行AMT数据死频带校正保证数据质量,利用相位张量分析地下介质的维性特征;其次,利用模块化三维反演并行代码ModEM开展了实测数据的三维反演,获得了一个典型的具有双层结构特征的火山岩盆地三维地下电性模型;最后通过电性模型及其他地质资料的综合解释,依据反演模型中近地表的低阻层和深部的高阻隆起区,分别勾画出了火山岩地层的厚度和深部侵入岩的分布范围,并在小岭地区发现地表浅部下方存在一个含矿次级火山机构的高导体.     

不同激励源井地电位成像技术三维正反演方法研究（英文）

井地电位成像是通过套管向井中供电或将电源放在井中,在地表观测电位异常的一项技术,其供电源有线源和点源两种类型。为了研究这两种电源对地下异常体产生的电位异常特征,本文针对不同激励源,采用有限差分方法进行数值模拟研究,在线性方程组求解电位时引入不完全Cholesky共轭梯度(ICCG)迭代方法,分别实现了点源和线源井地电位成像技术的三维正演。最后,基于阻尼最小二乘法实现了井地电位成像技术的电阻率三维反演。设计不同地电模型分别进行正演和反演试算,正演结果表明,供电电源的类型不同,异常体在地表的电位异常特征也不同;反演结果表明,低阻体的反演结果要好于高阻体,点源置于异常体下方时反演的电阻率对异常体边界的识别比线源更加准确。     

基于COMSOL Multiphysics的长白山天池多物理场耦合响应研究

采用COMSOL Multiphysics建立长白山天池2D多物理场模型,模拟长白山天池流场、自然电位分布及其磁场响应.研究结果表明:天池和大气降水入渗补给地下水,地下水在重力作用下向下流动时,产生电位差,形成自然电场,进而产生磁场.在火山通道外侧,电流密度方向由地表指向地下,通道周边地区磁通量密度呈现高值;在火山通道/断层破碎带内,向下运移的地下水遇到致密岩体后向上补给天池或涌出地表成泉,该过程产生向上运移的电流,电流密度方向由地下指向地表,磁通量密度呈现低值.研究长白山天池多物理场响应,有助于进一步理解长白山天池地区地下水循环过程及电磁异常出现的机理,亦可用于指导火山地区勘查、监测与开发.     

基于最小二乘正则化的自然电场场源反演成像

自然电场对多种地下污染物敏感,开展相应的场源反演成像研究可帮助有效监测污染源活动.把目标区域内的多种自然电场场源进行统一处理,利用有限单元构建二维地电模型,实现自然电位正演的高精度计算.采用最小二乘正则化反演迭代,实现自然电场场源的二维反演.在设计二维自然电场场源反演算法的基础上,利用加入高斯噪声的合成模拟数据,对反演算法进行测试.测试结果表明:基于有限单元二维模型的最小二乘正则化反演算法能有效地实现对自然电场场源的反演成像,并能准确地确定自然电位异常源的位置和深度,且算法收敛快速稳定,具有一定的抗噪声能力.     

高频电磁测深在地下热水勘探中的应用

高频电磁测深法是一种利用天然高频电磁场作为场源的电磁勘探方法,具有高分辨率和相对直流电法较深的勘探深度的特点,特别适合中浅层地热和地下水勘探。本文介绍了一个应用高频电磁测深评价地下热水资源的一个成功实例。野外数据采集采用了高频电磁测深系统MT-U5A,采用远参考技术,以保证数据采集质量。高频电磁测深资料二维反演成像处理结果较好地描述了地下热水的空间分布范围,为查明该区的地下热水的来源提供了较有利的证据。     

跨孔电磁波层析成像在岩溶三维空间分布上的应用

灰岩地区岩溶发育对城市建设有着极大的威胁,一般岩溶探测主要采用钻探勘探,很难充分反映地下岩溶发育规模与特征,而跨孔电磁波层析成像方法,能查明工区地下岩溶发育及延伸情况.对钻孔间地层进行电磁波层析成像正演,表明电磁波层析成像对岩溶勘察的准确性与可行性.结合地铁轨道交通岩溶勘察实例,应用电磁波层析成像技术反演电磁波吸收系数...     

油气勘探新领域:火山岩油气藏——松辽盆地大型火山岩气田发现的启示

通过观念转变和理论与技术创新,大庆油田在松辽盆地徐家围子断陷深层火山岩天然气勘探获得重大突破,使火山岩由原来的油气勘探"禁区"变为"靶区".从而带动了全国的火山岩油气勘探,促使国内油气储量的不断增长.研究表明,各类火山岩均有可能成为良好的储层.与沉积岩相比,火山岩在盆地深层具有体积大、储层物性受埋深影响小、孔渗条件好等...     

地面磁共振与瞬变电磁横向约束联合反演方法研究

大地电阻率分布信息是影响磁共振地下水探测反演结果准确性的重要因素.在众多电磁法勘探技术中,瞬变电磁法具有高分辨率、高效率和大探测深度等优势,能准确探测地下几百米范围内的电阻率分布信息.因此磁共振与瞬变电磁联合解释方法具有重要意义.然而,利用单一测点拼接的磁共振与瞬变电磁联合解释方法进行模拟二维反演时存在解释结果不唯一,容易出现错误异常体等问题,尤其在复杂地质情况下,同一测线上相邻测点探测结果连续性差,解释结果偏离实际.基于此,本文提出磁共振与瞬变电磁横向约束联合反演方法（Laterally Constrained Inversion,简称LCI）,重点引入外推积分法（quadrature with extrapolation,简称QWE）,解决了传统正演过程中基于直接数值积分方法引起的求解效率低的问题,保证了联合反演方法的顺利实施,进而以相邻测点地下结构应具备连续性为依据,引入横向约束反演思想,通过在联合反演目标函数中加入相邻测点间各模型参数约束矩阵,提高磁共振解释结果准确性,加强探测剖面地质结构和含水模型连续性.经过理论模型证实,本文提出的LCI方法能有效提高传统一维反演结果的稳定性和唯一性.最后,对安徽黄山野外实际探测数据进行横向约束联合反演,验证了磁共振与瞬变电磁LCI联合反演方法的实用性.本文的研究成果将为磁共振与瞬变电磁空间约束联合反演奠定基础.     

Using temperature to test models of flow near Yucca Mountain,Nevada

Ground water temperatures in the fractured volcanic aquifer near Yucca Mountain, Nevada, have previously been shown to have significant spatial variability with regions of elevated temperatures coinciding roughly with near-vertical north-south trending faults. Using insights gained from one-dimensional models, previous investigators have suggested upwelling along faults from an underlying aquifer as a likely explanation for this ground water temperature pattern. Using a three-dimensional coupled flow and heat-transport model, we show that the thermal high coinciding with the Paintbrush fault zone can be explained without significant upwelling from the underlying aquifer. Instead, the thermal anomaly is consistent with thermal conduction enhanced slightly by vertical ground water movement within the volcanic aquifer sequence. If more than approximately 400 m3/day of water enters the volcanic aquifer from below along a 10 km fault zone, the calculated temperatures at the water table are significantly greater than the measured temperatures. These results illustrate the potential limitations in using one-dimensional models to interpret ground water temperature data, and underscore the value in combining temperature data with fully coupled three-dimensional simulations.     

SPONTANEOUS POTENTIALS AND RESISTIVITY SURVEYS APPLIED TO HYDROGEOLOGY IN A VOLCANIC AREA: CASE HISTORY OF THE CHAÎNE DES PUYS (PUY-DE-DÔME,FRANCE)1

Two geophysical methods [resistivity soundings and spontaneous potentials (SP)] are used to investigate aquifers in the Quaternary volcanic formations of the Chaîne des Puys (France). The interpretation of the resistivity soundings required a specific work of determination of the resistivity of the formations concerned. The basement topography, characterized by axial horst and graben structures and perpendicular palaeovalleys, was revealed. SP was developed experimentally in the field and theoretically. It is shown that the SP anomalies can be considered as double-layer potentials, with their source on the aquifers' interfaces. The most significant of them is the water table, which creates an SP anomaly of similar but inverted form. SP anomalies due to flows in unconfined aquifers, in palaeovalleys, and in volcanic ranges are computed and compared with the observed ones. These two methods have determined the extent and the boundary conditions of the different hydrogeological basins and have determined the major drainage axes and the groundwater flow pattern.     

APPLICATION OF 3D HIGH PRECISION GRAVITY METHOD TO THE EXPLORATION OF DEEP BURIED HILL

Due to the influence of volcanic rock or weathering crust coverage, the quality of deep seismic data is often not reliable and it is difficult to identify small deep buried hill structure beneath the cover. However, the gravity exploration technology can use the remarkable density differences between the object and the overlying strata to identify this special geological reservoir. Although recently several rounds of seismic exploration have been carried out in Raoyang depression, Huabei Oilfield, North China to determine the existence of Hu 8 north deep buried hill, whether the buried hill really exists or not as well as its scale is still in controversial. In this paper, based on the information of seismic data and formation density, deep processing of 3D high precision ground gravity data has been carried out for 3D forward and inversion computation. The dimensional gravity forward calculation results show that the density of the deep anomaly body forms a relatively low gravity anomaly in the earth's surface. By using the potential processing method of vertical second derivative, and sliding filtering, the residual anomaly is separated from regional or background field, which illustrates the existence of a local high gravity anomaly at Hu 8 north area. According to the amplitude of residual gravity anomaly and formation density difference modeling, through a number of 3D forward calculations and 3D inversion of gravity data, the existence of Hu 8 north buried hill and its possible scale are basically determined. The results prove that the 3D high precision gravity method is effective in determining the deep buried hill structure in case that seismic data is not reliable.     

A NOTE ON THE USE OF A NOMOGRAM FOR SELF-POTENTIAL ANOMALIES*

A nomogram has been devised for situations, in which the source of a self-potential anomaly can be approximated by an obliquely polarized sphere or horizontal cylinder embedded in a homogeneous half space. The nomogram can be used for rapid determination of three parameters of the target: (1) depth to the centre, (2) angle between the axis of polarization and the horizontal, (3) shift of the point vertically above the centre of the body from zero potential value. The nomogram has been tested and the parameters determined for SP results obtained over ore bodies Weiss and Süleymanköy in the Ergani Copper district, Turkey. The curves computed for the estimated parameters match the field curves well.     

Classification of self-potential anomalies on volcanoes and possible interpretations for their subsurface structure

Self-potential (SP) surveys were conducted on 10 island-arc-type volcanoes in Japan. Large-scale SP anomalies that covered entire volcanic edifices and had simple shapes were observed. Neglecting the local fluctuations, we named the SP anomaly that shows voltage gradients anywhere on the flank a long spatial wavelength (LSW) SP anomaly. We first classified these anomalies into three types: 1) no anomaly (SP profile is flat): 2) “W”-shaped profile: and 3) “V”-shaped profile. In some volcanoes, one flank with a flat SP profile and another with half of the W-shaped SP profile coexist. Next, we compared LSW-SP anomalies with various factors that may be related to SP generation and found that the SP profile is approximately flat on the flank where geothermal manifestations exist. This relationship, which is new aspect of the SP data on volcanoes, is important because it can impose a constraint on the model for SP generation and the subsurface structure. Based on the discussion that SP is generated by an electrokinetic mechanism, we propose that resistivity, zeta potential, and hydraulic radius are the possible parameters that control the existence of LSW-SP anomalies. The new relationship between SP and geothermal manifestation are understood in terms of the presence of hydrothermal system. Although the structure of volcanic edifice is probably spatially complicated, the insight into the SP data presented in this study implies that the flanks with flat SP profiles are relatively weak and have high potential for sector collapse.     

连续电磁剖面法在古潜山构造勘探中的应用

随着电磁法勘探技术的发展 ,其应用已由传统的矿产普查工作过渡到地下异常体的目标勘探上 ,构造勘探精度也由提供构造大框架的粗放式阶段向较精细的刻画构造阶段发展。在简单介绍高密度连续电磁剖面法 (CEMP)的基础上 ,重点展示了该方法在古潜山构造勘探中的应用效果     

Three-dimensional interpretation considering the static and the sea-effects of magnetotelluric data obtained in Jeju,Korea

Three-dimensional (3D) magnetotelluric (MT) surveys have been performed in Jeju, the largest volcanic island in Korea to figure out any possible structures or potential anomaly for remnant deep geothermal resources. Various approaches have been applied to interpret MT data observed in Jeju. MT dataset shows generally simple stratigraphy of four layers, though contains the severe static and the sea-effects. In our previous works, the induction vectors and 3D inversion results have commonly indicated the existence of a conductive anomaly in central parts of the island, beneath Mt. Halla. The 3D inversion dealt the static shifts as inversion parameters. The Jeju MT dataset, however, still contains the effect of conductive sea water surrounding the island.The sea-effect on MT impedance can be represented as a distortion tensor and excluded from the Jeju MT dataset by an iterative sea-effect correction. In this study, 3D inversion incorporating static shift parameterization was conducted using MT dataset corrected using 1D resistivity model obtained from the iterative scheme. Reasonably reconstructed images are obtained through the 3D inversion and using the MT dataset with sea-effect correction. The inversion result still shows the conductive anomaly in a similar depth. RMS misfits converged to a lower value than that of inversion using MT data before the sea-effect correction. From the fact, it is highly possible that the conductive anomaly is not an artifact but a real underground structure. Further investigation about the anomaly including exploration drilling is needed to see if it is from a fracture containing conductive sea water or related to the old volcanic activities.     

Review on Morphological Insights of Self-Potential Anomalies on Volcanoes

Energy and thermal transfers in active volcanoes can play an important role incontrolling their dynamics depending on the hydrothermal state. Much geothermalenergy is released through the groundwater circulation, hot gas emission and thermalconduction. Therefore, it is very important to know the hydrological and thermalenvironments associated with volcanoes from the volcano-energetic point of view.However, it is difficult to evaluate these because of the availability of only a fewborehole data on the summit of volcanoes. Recent studies reveal that self-potential(SP) anomalies (up to some hundreds of mV) are observed on volcanoes, activefissure zones and/or fumarolic areas, suggesting that the SP anomalies are closelyrelated to heat-triggered phenomena such as thermoelectric and electrokinetic effectsdue to hydrothermal circulations. Therefore, SP studies can be appropriate for sensingthe thermal and hydrothermal states of volcanoes. In addition, monitoring SP anomaliescan be an efficient method for describing the change of thermal state and the evolutionof the hydrothermal (and volcanic) activities.In this paper, we have reviewed the origin of the SP anomalies associated withvolcanic phenomena theoretically as well as experimentally. Subsequently, wehave presented the results of many case studies and have classified the types ofanomalies in accordance with possible mechanisms. We have also described theresults of time variations of SP anomalies associated with volcanic activities. Timevarying SP fields exhibit the dynamic aspects of volcanic activities correspondingto the evolution of hydrothermal activity, changes in ground water circulation andmagma displacement. These morphological insights should lead to a quantitativeinterpretation of SP anomalies in volcanic regions.     

ON THE ORIGIN AND INTERPRETATION OF SELF-POTENTIAL ANOMALIES*

The renewed interest in the self-potential method of exploration for mineral deposits gives an understanding of the self-potential mechanism new importance. The cause of SP anomalies in general lies in the interference between simultaneously occurring nonequilibrium phenomena. However, theories of the mechanism of mineral SP anomalies generally relate the SP anomaly to the equilibrium potential of the chemical reaction supposed to occur on the ore body surface. In this paper, I reformulate these equilibrium mechanisms in terms of nonequilibrium thermodynamics. The result is that the SP anomaly depends not on the equilibrium potential alone, but also on the potential resulting from current transferred across the ore body—electrolyte interface. It is not possible to calculate the overpotential theoretically because of the number of complicating factors, and experimental data are not available. This does not imply that SP data are uninterpretable quantitatively. SP data may be interpreted similarly to other potential field data.