Forward Coupled Modeling and Assessment of Gravity Anomalies Caused by Pumping Tests in Unconfined Aquifers Under Unsteady-State Conditions

Analysis of drawdown data from pumping tests is the most common method for identification of aquifer properties and estimation of hydraulic parameters in hydrogeology. Limited hard hydraulic data from wells, expensive and intrusive, can be supplemented with geophysical spatially distributed information. Gravity, sensible to mass variations, can provide information about hydraulic parameters and storage coefficients of aquifers. A satisfactory use of gravity requires the computation of temporal evolution of gravity anomalies related with the dynamic hydraulic process. For simplified and ideal problems, the calculation can be accomplished with analytical solutions. However, the limitations of analytical solutions in capturing some relevant characteristics, like heterogeneities, that require the use of numerical models, are well known. This article shows how the time-dependent gravity anomaly caused by a pumping test can be calculated in a unique code, in a coupled manner and in a single run. The methodology avoids the use and transference of data between various codes and can be utilized in a coupled hydrogeophysical inversion procedure. Additionally, it is flexible enough to include a wide range of characteristics that can be encountered in any pumping test, and is an adequate framework for field survey planning via analysis and study of time-dependent gravity curves.     

大比例尺重力调查与成矿预测：以江西朱溪钨矿外围为例

江西塔前-赋春成矿带近年发现了世界上最大的钨矿—朱溪钨铜矿。该矿床发育在富含钨铜元素的新元古代泥砂质岩基底之上,产在燕山期花岗岩与石炭纪-二叠纪灰岩接触带,阐明其覆盖区花岗岩与石炭纪-二叠纪灰岩的三维空间分布结构,是寻找该类矿床的关键问题。塔前-赋春成矿带控矿地层、花岗岩仅有微弱磁性,但是密度差异明显,这为本区开展重力工作提供了良好的前提。本文利用最新的1:5万重力调查成果,结合航磁建立了本区构造格架,使用重磁三维反演建模技术建立本区三维地质模型,取得了以下成果：（1）对区内控矿地层进行立体识别划分,推断了塔前-朱溪、双田-大游山和临港-乐河镇石炭-二叠系条带深部延展形态,推断红梅岭-排前村和刘家滩-珍珠山深部存在两条隐伏石炭-二叠系条带;（2）发现本区岩体具有环形重力低夹局部重力高的异常特征,结合磁法区分岩浆岩岩性,圈定了本区隐伏岩体;（3）根据朱溪钨铜多金属矿物化探异常特征,圈定了两类深部成矿有利靶区：一类位于地表出露石炭纪-二叠纪灰岩沿断裂延伸与隐伏岩体接触带;一类位于推断的隐伏石炭纪-二叠纪灰岩与隐伏岩体接触带。（4）塔前-赋春成矿带重力工作较少,通过分析本次重力调查成果,发现在地形复杂、具有明显密度差异的推覆构造发育地区开展1:5万重力调查可取得较好的勘查成果。重力调查工作成本低,工作周期短,在圈定的成矿有利靶区内开展大比例尺综合物化探异常查证和矿产调查工作,能有效提高矿产勘查效率;在地形、构造复杂地区推广应用1：5万重力调查并建立三维地质模型对开展深部找矿预测具有重要意义。     

重力方法在祁连山地区构造特征与岩体解释中的应用

依据地质、航磁等资料,结合实测岩石物性资料,以1∶250 000重力资料为基础对祁连山地区(张掖、刚察地区)进行综合研究。研究地质构造与地球物理特征,划分了大地构造单元,探讨了隐伏与半隐伏岩体分布。该区域经多年的重力工作,勘探面积已近3万多km²,根据重力资料研究布格重力场特征并进行分区; 对地质构造单元重新划分,对主要断裂进行探讨; 圈定隐伏与半隐伏岩体,推断其空间展布特征,并对其解释。结果表明: 祁连山地区地壳密度结构横向分区、纵向分层明显,布格重力异常场的分区特征与地质构造分区特征基本一致。结合2.5D重力剖面反演印证了新的推测结果,为综合地质、地球物理找矿提供参考。     

重力高阶方向导数的可视化拟合及其应用

针对目前人们所使用的交互式重力剖面拟合软件多以正演布格重力异常为主,在应用效果方面存有欠缺的情况,提出了在作重力剖面布格异常拟合的同时,增加高阶方向导数的拟合。其目的是发挥布格重力异常的高阶方向导数在突出浅部地质体的特征,压制区域性深部地质因素,区分相邻地质体引起的叠加异常等方面的优势。这里采用最小二乘法演算了布格重力异常高阶方向导数的计算过程,对计算程序编制和使用中涉及的相关问题进行了阐述,并例举了在地球物理勘探中,利用高阶方向导数提高重力资料解释效果的实例。并在最后对重力剖面进行可视化拟合解释时应注意的要点做了分析,强调了兼顾布格重力异常及其高阶方向导数二者拟合曲线均基本相似,而不应追求其中某一方面精确拟合的解释原则。     

豫西寨凹隐伏岩体地球物理场特征与深部找矿预测

寨凹隐伏岩体是豫西南地区利用重磁资料解释推断的8个隐伏、半隐伏岩体之一,分布面积约310km2。豫西南地区主要钼（钨）铅锌银（金）矿床均分布于这8个隐伏、半隐伏岩体区及其边部附近,二者具有非常明显的时空关系。研究隐伏岩体分布形态、深度、产状和深大断裂构造分布,对指导深部找矿勘探具有重要意义。通过研究寨凹隐伏岩体重、磁场变化特征和分布规律,并通过相关定量计算,确定了隐伏岩体的侵入模型。将全区隐伏岩体分为三个区,Ⅰ区隐伏岩体顶面深度0~0.8km,分布面积约71km2,Ⅱ区隐伏岩体顶面深度0.8~2.0km,分布面积约153km2,Ⅲ区隐伏岩体顶面深度2~4km,分布面积约86km2。根据隐伏岩体侵入模型和典型矿床物探异常特征,建立了立体成矿模型（从浅至深从中低温成矿元素到高温成矿元素的过渡模型）和综合地球物理找矿模型（包括隐伏岩体、隐伏岩体顶上带、岩钟和斑岩体、矿体矿化体的地球物理异常标志）;预测了找矿潜力,总结了勘查方法技术组合;指出在Ⅰ、Ⅱ隐伏岩体分布区银（金）铅锌矿床的下部有寻找斑岩型钼、钨、铜矿产的潜力。     

物化探测地工作采用GPS定位时进行高程异常改正的研究探讨

本文叙述了我国现行高程系统与ＧＰＳ高程系统垢区别,介绍了ＧＰＳ求解的大地高转换为正常高的几种方法,具体提出了１：２０万区域重力调查中用ＧＰＳ定位时所求测点高程应进行高程异常改正及高程异常对区域重力调查精度的影响。对区域重力调查及其它物化探测地工作有一这的指导意义。     

Structural framework of the Jaibaras Rift,Brazil, based on geophysical data

The Cambro-Ordovician Jaibaras Rift is a NE–SW trending elongated feature, controlled by the Transbrasiliano lineament, locally known as Sobral-Pedro II shear zone (SPIISZ). An integrated study of geophysical data (gammaspectrometry, magnetometry and gravimetry) was undertaken in the Jaibaras Rift area, between Ceará Central (CCD) and Médio Coreaú domains (MCD), northwest Borborema Province. Geophysical data were interpreted qualitatively and quantitatively in order to understand the tectono-magmatic relations and rift formation based on the main geophysical lineaments, source geometry and depth, and separation of geophysical domains. In addition, a 2D gravity model was generated. The results show a structural partition characterized by NE–SW lineaments and E–W inflexions, where CCD presents a relatively mild magnetic field, whilst the MCD field is more disturbed. The Jaibaras Rift is characterized by positive magnetic and gravity anomalies. The SPIISZ, which corresponds to the SE fault edge of the Jaibaras Rift, is marked by strong magnetic dipoles and strong gravity gradients in the profile, showing the deep character of the Transbrasiliano lineament in the region. The Café-Ipueiras fault, at the NW edge of the rift, is well marked in gravity profiles, but displays low contrast of the magnetic field. Interpretation of the gravimetric anomaly map allowed to recognizing the main NE–SW axis, with alternation of maxima and minima in MCD. A regional gravity gradient reveals significant lateral density variation between the MCD and CCD perpendicular to the SPIISZ, emphasizing it as a main continental suture zone between crustal blocks.     

综合物探在新疆1∶50000矿产普查中的应用

为了在新疆1∶50000矿产普查中研究成矿地质条件圈定成矿远景区域,在普查过程中通过重、磁、电等多种物探手段的综合应用,来探测深部和隐伏矿,效果明显。通过采集标本对其工作区的物性特征加以归纳分析,指导物探方法(重、磁、激电)的运用,为后续开展物探工作提供借鉴。首先在工作区利用重力和航磁资料,查明勘探区内地质构造特征及岩体分布规律,得到重、磁高值异常区多与岩体、岩体接触带及断裂带有关,而该区域的成矿与接触带或断裂构造密切相关,在接触带及断裂构造带上有利于硫化物发育,再利用大功率激发极化法的低阻高极化特征圈定含硫化物的有利区域,最后优选重、磁、电综合物探异常特征明显、成矿部位有利地段,并结合地质、化探异常特征对工作区定性的综合评价,指导寻找含硫化物的岩(矿)体,最终圈定找矿靶区一处,为矿产普查工作提供基础资料和找矿依据。     

物探方法探测煤矿区岩浆岩侵入体探讨

针对煤矿区岩浆岩侵入体,分析了如磁化率、密度、顶面埋深、水平展布范围、垂直延伸长度等参数条件下岩浆岩侵入体引起的重力、磁力异常;介绍了现有重力勘探仪器和磁法勘探仪器的分辨能力;结合岩浆岩侵入体引起的物探异常,提出了重力勘探和磁法勘探工作布置的具体要求及其仪器的操作方法。研究显示,物探方法尤其是重力勘探、磁法勘探探测煤矿区岩浆岩侵入体能获得有意义的异常,可圈定岩浆岩侵入体的分布范围。      

MATLAB programs for the synthetic models

The separation of residual gravity anomaly from regional gravity has considerably been studied for many years in gravity explorations. In addition, it is considered as a critical step in gravity data inversion. Some techniques have been developed for regional–residual anomaly separation both in space and frequency domains. One of these techniques for computing the regional anomaly is nonlinear filtering. In this paper, some techniques such as low-pass filtering, Butterworth, upward continuation, and nonlinear filtering are used to on synthetic gravity data in present of random noise and noise free for the purpose of residual–regional anomaly separation. The obtained results of techniques are compared with each other. The results have shown that separation methods are so efficient where synthetic models are located in shallow depth. Moreover, it is found that in comparison with other separation techniques, nonlinear filtering is more efficient in residual–regional anomaly separation and upward continuation technique is more efficient than Butterworth filter and low-pass filter. In addition, all of the obtained results have shown that Butterworth and low-pass filters are the same.     

西藏林周县轮郎铅锌矿区地球物理异常特征评价及找矿意义

林周县轮郎铅锌矿区位于拉萨-林周-墨竹工卡铅锌成矿区中部,属雅鲁藏布江巨型铜多金属成矿带北亚带。根据该区地球物理测量成果,共圈出重力异常区10个、磁力异常区18个。通过对重力异常特征及磁力异常特征综合评价,分析出其中5个磁力异常区和重力异常有明显的对应关系,属矿致异常,具良好的找矿前景;并且得出该区高磁区、局部磁异常与局部重力高的结合部和重、磁双高地带均为找矿潜力区。     

基于并行预处理算法的三维重力快速反演

随着地球物理设备和探测技术的不断发展,快速处理大规模地球物理数据的需求也随之增长。为了解决三维重力数据密度反演的耗时问题,提出一种并行的预处理共轭梯度算法来提高计算效率。本文分别采用两种不同的预处理算子通过组合模型数据反演进行测试比较,并利用迭代残差和计算用时共同评价其加速效果。结果表明：对称逐次超松弛预处理方法比对角预处理方法反演计算速度快,密度结果更贴近实际模型;与传统串行的共轭梯度算法相比,本文并行预处理快速算法可以获得近19倍的加速比。将该算法应用于美国Vinton盐丘的实测重力数据中,反演结果能够很好地圈定出岩体的位置,验证了本文并行预处理共轭梯度法在三维重力数据快速反演中的高效性和可行性。     

综合找矿方法在覆盖区的应用——以山东省单县大刘庄铁矿勘查为例

山东省铁矿分布广泛,在鲁西南广大覆盖区产有许多铁矿床,其中在菏泽市单县地区发育沉积变质型铁矿。简要介绍了单县大刘庄铁矿区的地质特征：该矿床埋藏于第四系-古近系巨厚层（覆盖厚度达458～549 m）以下,赋存于新太古代泰山岩群山草峪组中;区内铁矿体总体呈层状、似层状、透镜状,产状与围岩一致,走向为NW-SE,总体倾向SW,倾角为45°～60°;铁矿中全铁平均品位约25%,磁性铁平均品位约20%。详细介绍了运用地质、物探等勘查方法进行找矿的过程：通过对区内的物探数据进行分析,解译了矿区基岩的地质特征和隐伏断层的重要信息;根据大比例尺地质、物探示矿信息特征,建立了包含地质环境、矿床特征和地球物理特征（明显高磁异常和高重力异常及其梯度带）的预测模型;通过对大刘庄铁矿的勘查,总结出了在厚大覆盖层下铁矿床的勘查流程:“航磁异常选区→资料全面系统收集→工作区优选→磁法测量和重力测量→地质信息分析→大比例尺高磁和重力剖面、CSAMT和SIP测量→通过优选成矿有利部位→深部钻探施工→井中磁测”。     

基于EIGEN-6C2重力场模型反演青藏高原地壳结构

重力数据是地下场源产生的重力场的叠加, 包含了地下从浅部到深部的丰富信息.高阶卫星资料的丰富为青藏高原深部构造研究提供了重要资料.基于EIGEN-6C2模型作为原始数据, 首先对青藏高原布格重力异常和均衡重力异常分别作1~5阶尺度分解, 得到不同尺度重力异常的分布特性, 探讨不同空间尺度反映的地壳构造意义.其次, 基于径向对数功率谱估计平均深度方法理论, 进一步研究1~5阶细节反映的场源深度.再次, 利用Canny算子的多尺度边缘检测识别和分析重力异常中表现不明显的断裂, 定位断裂在地表的位置, 识别青藏高原内部断块边界, 完成活动块体和次级块体的划分.最后, 对布格重力异常进行沉积层及岩石圈改正, 采用Parker-Oldenbarg三维位场反演法反演青藏高原莫霍界面起伏.      

Three-Dimensional Gravity Model Applied to Underwater Navigation

At present, new integrated navigation, which usesthe location function of reference gravity anomaly map to control the errors of the inertial navigation system (INS), has been developed in marine navigation. It is named the gravity-aided INS. Both the INS and real-time computation of gravity anomalies need a 3-D marine normal gravity model. Conventionally, a reduction method applied in geophysical survey is directiy introduced to observed data processing. This reduction does not separate anomaly from normal gravity in the observed data, so errors cannot be avoided. The 3-D marine normal gravity model was derived from the J2 gravity model, and is suitable for the region whose depth is less than 1000 m.     

选择法在红旗岭矿区重力G8异常评价中的应用

为评价引起红旗岭矿区G8重力异常的原因,采用解重力勘探反演问题的选择法对其进行重新解释评价。根据剩余重力异常,结合异常地段及其外围地质、地球物理条件建立正演计算模型,进行正演计算并与实测重力异常曲线进行拟合。结果表明G8重力异常并非是由镁铁-超镁铁岩体引起,而是由地层密度局部增大及重力高背景场的局部重力低G11的衬托效应引起。     

Integrated geophysical studies to elicit the subsurface structures associated with Uranium mineralization around South Purulia Shear Zone,India: A review

South Purulia Shear Zone in India is an important zone that hosts uranium mineralization. Since detailed geophysical studies have not been carried out in this region, an integrated geophysical study using self-potential, resistivity, very low frequency electromagnetic and radiometric methods was performed to identify the subsurface structures that could host the hydrothermally altered uranium deposits in the area. The study reveals the wide and large magnitude of negative self-potential anomaly across the South Purulia Shear Zone. The peak negative self-potential anomalies are correlated with the low gravity and low resistivity anomalies measured along various profiles. The low self-potential, gravity and low resistivity anomaly zones are also correlated with conducting zones inferred from very low frequency electromagnetic measurements. Interpretation of self-potential data reveals multiple thick sheet-type vertical and/or inclined structures which might be associated with uranium mineralization. Schlumberger resistivity sounding data reveals an increasing trend of apparent resistivity with current electrode separations/depth. Apparent conductance measured simultaneously with resistivity measurement reveals an increase in current flow of current as depth increases. This exhibits the presence of thin conducting layers at these depths, which is not reflected in resistivity sounding data due to suppression problem. Also this conducting layer is consistent in various soundings and is connected from Raghunathpur to the South Purulia Shear Zone. Correlation of very low frequency and self-potential data shows that the structures are comparable and a radiometric profile also advocate that the conducting structure is associated with radioactive minerals. These structures are likely to be mineralized zones as hydro-uranium anomaly has also been reported from various locations in the area. Moreover, drilling results at a specific mine near the study area also confirms the presence of uranium mineralization. The hydrothermal activity associated with uranium mineralization seems to be still active in the area. Such combined geophysical studies are essential to understand this highly complex shear zone for the economic exploitation of its natural resources.     

地球物理在三维地质调查中的应用——以本溪-临江勘查区为例

以本溪-临江勘查区为例,通过对勘查区航磁、重力以及电法剖面数据的解译,为深部地质地层、构造、岩体、矿体等信息推断提供地球物理依据,绘制地质图切剖面,服务三维地质建模.在地球物理信息处理的过程中,结合鞍山式铁矿成矿机制,在勘查区内研究发现若干潜力矿床.     

综合物探剖面揭示松辽盆地基底地质与地球物理特征——以过松科二井剖面为例

松辽盆地是中国东北部中—新生代陆相沉积盆地,本文在深入分析东北地区古生代地层特征、沉积环境及构造演化基础之上,以过松科二井地区综合地球物理资料解译为基础,开展基底的属性和地球物理特征研究。松科二井南北剖面发现:布格重力异常具有中间高两边低的特点;磁异常呈现出与重力异常负相关的趋势;电性表现为浅部分层、高—低阻交叉重叠和深部分区的特征。东西剖面发现:布格重力异常具有西高东低的趋势;磁异常形态呈"碗状";电性结构与南北剖面相比深部出现了高阻异常。结合地球物理特征与岩相古地理分析,得到以下结论:(1)上古生界晚石炭世至晚二叠世期间,具有浅海相、陆相、河湖相多种沉积环境,相应岩性组合具有不同的物性特征;(2)重磁电地球物理特征揭示了研究区基底主要由泥砂岩、大理岩和侵入岩组成,基底顶面埋深位于7 km左右,上古生界和侵入岩共同组成了研究区基底;(3)识别出了滨州断裂带、孙吴—双辽断裂带、海伦—任民断裂带以及深层次断裂体系的位置和走向,断裂构造主要以SN和EW向为主,它们作为构成古生代构造骨架的重要组成部分,控制着深部油气运移和贮藏。     

赣东北塔前-赋春成矿带画子山地区地球物理特征及找矿启示

画子山地区隶属于赣东北塔前-赋春成矿带,其具有地质条件复杂,深部成矿条件优越等特点。在复杂的地质条件情况下,对多种地球物理方法进行有机的结合,可较为客观的反映地下深部信息。而物性差异是地球物理方法的应用研究前提,首先对画子山地区的岩石标本进行物性分析。基于物性分析结果,在画子山地区针对性的布设两条（8 线和11 线）重力、磁法及可控源音频大地电磁法综合地球物理剖面,然后结合地质、物性、钻孔等资料对综合剖面进行解译,解译得到重力高值和低阻异常区是由矿化引起,磁异常带由蚀变所引起。最后通过分析综合剖面反映出地下的高密度体、高磁性体和低阻高极化体的分布规律,圈定出找矿的重点区域为万年群牛头岭组上段地层的西南方向,为画子山地区的下一步工作指明方向。