MULTIPARAMETER GEOPHYSICAL LOGGING AT THE YAVA LEAD DEPOSIT: A STATISTICAL APPROACH1

The present study describes multiparameter geophysical logging carried out at the Yava sandstone lead deposit, Nova Scotia, Canada. Statistical analysis of the multiparameter data set shows that the spectral gamma-gamma ratio log (SGG ratio) is the most useful technique for characterizing the disseminated sulphide mineralization. Principal component analysis (PCA) indicates that the apparent chargeability (IP parameter) responds to the presence of clay minerals in the sandstone in addition to disseminated sulphides, so that the induced polarization method (IP) does not accurately delineate the disseminated galena content as was originally assumed in the preliminary log interpretation. PCA has also confirmed that the SGG ratio and density are related to lead content and that lithological variations can be delineated with natural radioactivity and resistivity. The zinc content of the deposit was poorly characterized by geophysical logs. Sphalerite occurrences seem to be localized as narrow bands (< 1 cm) which were not geophysically detectable.     

松科2井东孔营城组高放射性异常层测井响应特征及成因初探

松科2井东孔是松辽盆地科学钻探工程的主体钻孔,按照计划在全井段进行地球物理测井资料采集,为深部资源勘探及白垩纪古气候、古环境研究提供准确和全面的地球物理信息.在诸多测井方法中,自然伽马测井和自然伽马能谱测井能够测量地层的天然放射性强度和铀、钍、钾元素含量等参数,被有效地应用于放射性矿床勘查,尤其是铀资源的勘查与研究;电阻率、声波、密度和中子测井等常规测井和核磁共振成像、电阻率成像、元素俘获谱测井等特殊测井能够获取地层岩性和物性参数等信息,为铀矿勘查提供有力支持.本文利用松科2井东孔自然伽马测井资料来识别高放射性异常层;基于常规测井与特殊测井资料,结合前人的地质研究成果,分析放射性异常层的特征和成因.核测井曲线指示营城组存在两段高放射性异常层,深度分别为3096.8~3102.8 m（I号层）、3168.3~3170.9 m（Ⅱ号层）.I号层自然伽马值最高达360 API,铀含量范围20.5~29.3 ppm,综合测井和岩心资料判断该层为砾岩,具有铀成矿潜力;分析表明,构造条件和后生改造作用是影响I号层铀富集的关键因素,推测断裂-火山活动和盆地抬升剥蚀为含铀地下水及油气运移至I号层提供了通道,油气的后生还原作用最终导致了I号异常层的铀富集.Ⅱ号层自然伽马值最高达250API,钍含量22.4~37.3 ppm,铀含量5.9~11.0 ppm,为集块熔岩及凝灰岩,高放射性异常可能是高钍含量的流纹质成分和粘土矿物对铀的吸附作用导致的.松科2井东孔营城组高放射性异常层具有埋藏深度深、铀含量高等特点,表明松辽盆地深部具有找铀矿前景.     

庐枞盆地科学钻探地球物理测井及深部铀异常的发现

庐枞盆地砖桥科学钻探ZK01孔为深部探测技术与实验研究专项在庐枞盆地施工的钻探验证孔,全井段实施了连续取心和地球物理测井工作.测井工作分三次完成,测井总深度1994.02m.测井项目包括视电阻率、极化率、磁化率、纵波速度、超声成像、自然伽马、密度、井斜、井径、井温、泥浆电阻率、井中三分量磁测等10多种方法,获得了钻孔剖面原位物性参数、钻孔几何形态及井壁超声图像.通过对地球物理测井和钻孔岩心编录等资料的研究,完成了岩性的人工识别与支持向量机判别,建立了钻孔测井解释岩性剖面;通过对矿化地层的测井响应分析,将电阻率和磁化率作为粗安岩矿化的识别标识;根据超声成像测井资料推断本地区深部地层最大水平主应力方向为南北走向.在ZK01孔1500~1900m发现放射性异常,对铀当量大于万分之一的21处异常进行了定量解释,铀矿化段累积厚度93.02m,为庐枞地区深部找铀矿提供了重大线索.     

Walsh列率域中多维分形模型与GIS环境下地球物理信号处理

地球物理信号通常在多个尺度段表现尺度不变性,这些不变性起因于不同的地质、地球物理或成矿过程的自相似性. 利用这种在多个尺度段的尺度不变性可以设计多维分形滤波器,滤波所得信号表征了具尺度不变性的地质地球物理或成矿过程,可以用于成矿预测或环境评价. 本文研究了Walsh变换列率空间地球物理信号的列率功率谱密度与列率之间的分形与多维分形关系, 试验证实了大洋钻探、石油以及煤系地层地球物理测井资料在Walsh域的多维分形性质,提出了用于分解地球物理场,提取有用信号并用于矿产资源勘探或环境评价的多维分形W-A模型. 利用波列率域中的多维分形关系构造了W A图解(W-A Plot). 借助W-A图解可以确定最小平方误差（LS）意义下Walsh功率谱变化的不同自相似性的频率分界点,从而用于设计W-A分形滤波器. 这种滤波器可将地球物理场分解成具有不同自相似性的局部场,并且保留原场的各向异性结构. 与通常使用的基于Fourier变换的滤波技术相比,W-A模型具有许多优点：W-A适用于检测地球物理信号中的突变、线性、环状、局部与纹理结构等弱信号. 同时,由于Walsh变换中只有简单的变号(加法与减法),其计算速度远快于建立在复数乘法之上的Fourier变换,所以W-A计算速度远快于Fourier域的滤波方法,可以用于地球物理信号的现场实时处理. 用加拿大Nova-cotia省西南地区的布格重力异常进行了W-A方法的试算,处理结果反映了地质、矿产分布规律,能够很好地进行矿产预测.     

空间自相似性与地球物理和地球化学场的分解方法

场的分解是应用勘查地球物理和地球化学数据所必不可少的数理处理工作，这项工作往往是为了分解不同的场来研究和了解不同的地质以及相应的地质过程，比如划分不同岩石类型以及识别和圈定矿化蚀变睡.闰定地质过程所产生的同类型的地质体并不简单地对应于相同的场值和频率，场的分布特征往往还与地质体的几何形态，。埋藏深度以及与其周围地质体的相对差异有关。然而，由于地质过程往往具有多期次和空间相关性等特点，所产生的地质体或者相应的场往往会呈现空间自相似性或统计自相似性。这种自相似性可以帮助分解不同地质过程所产生的同类地质体，文中所介绍的多重分形（multifractal)滤波方法（S－A）根据场的能谱分布的不同空间自相似性形成不规则甚至分形滤波器，并将场分解为不同同的组份，如局部异常和背景场，应用该方法对多处地球化学和地球物理场的处理结果表明，该方法对区分与矿有关的局部异常与背景场是很有效的，对加拿大NOVA SCOTIA省西南部航空放射性铀钍钾（U-Tn-K)数据处理所分解的异常对反映岩体中与铀－钨－锡（U－W－Sn)矿化有关的围岩饰变具有明显的效果。     

地球物理信号能量(密度)多维分形及应用

地球物理信号代表的地质地球物理过程在多种尺度上和尺度之间表现为自相似性（self-affinity)或尺度无关性（Scale Invariant)，称为地球物理信号的分形性质，多个分形地球物理信号叠加在一起表现为多维分形特征，研究多维分形地球物理信号的能量或能量密度特征，可以进行时间或空间地球物理信号的校正、奇异性研究分析，或进行不同地球物理动力学过程的分解，本文描述了地球物理时间（空间）信号的多维分形过程和功率谱密度（能量密度）与波数以及重磁场能谱密度及面积（能量）与能谱密度的多维分形关系，并用地球物理测井与重磁资料作了试算。     

地层水矿化度检测的地球物理测井方法

传统的水文地质研究方法在进行地下水的矿化度评价时，是通过地层水的取样进行室内分析化验，确定含水岩组中地层水的矿化度，目前，在利用已有的地质、地球物理资料进行西部地下水资源评价的研究中，鉴于大多数石油井不含有浅层地层水的水样化验资料，因而本文介绍一种利用石油测井数据（主要为自然电位曲线）计算地层水矿化度的方法，并将之应用于鄂尔多斯白垩系自流水盆地地层水的矿化度估算，方法研究和应用实例证明这种方法是较为可靠的，虽然求取的地层水的矿化度的数值存在一定的误差，但完全可以满足地层水矿化度分级评价的需求，从而开发了石油测井数据在水文地质中的应用，也降低了单纯利用水文取样，由于样点少，矿化度预测精度低的缺点。     

Ellog Auger Drilling: Three-in-One Method for Hydrogeological Data Collection

The Ellog auger drilling method is an integrated approach for hydrogeological data collection during auger drilling in unconsolidated sediments. The drill stem is a continuous flight, hollow-stem auger with integrated electrical and gamma logging tools. The geophysical logging is performed continuously while drilling. Data processing is carried out in the field, and recorded log features are displayed as drilling advances. A slotted section in the stem, above the cutting head, allows anaerobic water and soil-gas samples to be taken at depth intervals of approximately 0.2 m. The logging, water, and gas sampling instrumentation in the drill stem is removable; therefore, when the drill stem is pulled back, piezometers can be installed through the hollow stem. Cores of sediments can subsequently be taken continuously using a technique in which the drill bit can be reinserted after each coring. The Ellog auger drilling method provides detailed information on small-scale changes in lithology, sediment chemistry, and water, as well as gas compositions in aquifer systems–data essential to hydrogeological studies.     

Targeting of Gold Deposits in Amazonian Exploration Frontiers using Knowledge- and Data-Driven Spatial Modeling of Geophysical,Geochemical, and Geological Data

This paper reports the application of weights-of-evidence, artificial neural networks, and fuzzy logic spatial modeling techniques to generate prospectivity maps for gold mineralization in the neighborhood of the Amapari Au mine, Brazil. The study area comprises one of the last Brazilian mineral exploration frontiers. The Amapari mine is located in the Maroni-Itaicaiúnas Province, which regionally hosts important gold, iron, manganese, chromite, diamond, bauxite, kaolinite, and cassiterite deposits. The Amapari Au mine is characterized as of the orogenic gold deposit type. The highest gold grades are associated with highly deformed rocks and are concentrated in sulfide-rich veins mainly composed of pyrrhotite. The data used for the generation of gold prospectivity models include aerogeophysical and geological maps as well as the gold content of stream sediment samples. The prospectivity maps provided by these three methods showed that the Amapari mine stands out as an area of high potential for gold mineralization. The prospectivity maps also highlight new targets for gold exploration. These new targets were validated by means of detailed maps of gold geochemical anomalies in soil and by fieldwork. The identified target areas exhibit good spatial coincidence with the main soil geochemical anomalies and prospects, thus demonstrating that the delineation of exploration targets by analysis and integration of indirect datasets in a geographic information system (GIS) is consistent with direct prospecting. Considering that work of this nature has never been developed in the Amazonian region, this is an important example of the applicability and functionality of geophysical data and prospectivity analysis in regions where geologic and metallogenetic information is scarce.     

Integrated geophysics for mineral exploration in drift-covered volcanic terrains: examples from northern Vancouver Island,Canada

Known mineral occurrences in northern Vancouver Island are typically hosted in volcanic units of the Bonanza Group. At a local scale, the mineralization is associated with advanced argillic bedrock alteration and is often intimately related to porphyry intrusions. On a larger scale, faults are thought to exert the most significant control on the distribution of mineralized host rocks. Poor exposures and a complex glacial history limit the use of traditional methods of geological mapping and mineral exploration in this region and to date geophysical methods have been under-utilized. Here we present findings from four standard geophysical (gravity, magnetics, electromagnetics and seismic refraction) methods, recently deployed here to elucidate the subsurface geology, as well as to identify new targets for base metal exploration. Results at two different sites show that the integrated interpretation of geophysical data, constrained by physical rock property measurements, yields detailed images of the subsurface at a fraction of the cost of drilling. At one site, east of Rupert Inlet, the final subsurface model shows that the Bonanza Group is not nearly as extensive as previously presumed. An extension of the Holberg Fault is identified some 50 km east of the visibly mapped outcrop and an extensive zone of alteration around the fault is recognized. Furthermore, a number of the methods provide support for the existence of a porphyry dike at this site. At the second site, north of Rupert Inlet, magnetic and electromagnetic data prove effective at mapping alteration and locating shear zones beneath a relatively thin drift cover. Together, these results help outline a strategy for exploration in drift-covered terrains and show that a redirection of exploration effort is warranted in the case of northern Vancouver Island.     

国内外地震科学钻探与测井技术应用

大地震发生后, 在断裂带开展科学钻探是研究地震发震机理的快速反应和科学计划手段。 测井技术是重要的井中地球物理探测方法。 本文结合日本Nojima断层科学钻探、 美国San Andreas科学深钻、 台湾车笼埔钻探和中国汶川地震科学钻探研究成果, 综述了国内外地震科学钻探计划实施和研究进展, 对比和分析了测井技术在其中发挥的作用和取得的成果。 最后, 对地震科学钻探井中观测研究提出了建议, 并展望了测井技术在地震科学钻探中的应用。     

Magnetic signatures related to orogenic gold mineralization,Central Lapland Greenstone Belt,Finland

A number of lode–gold occurrences are hosted by hydrothermally altered greenstones along the southern boundary of the Palaeoproterozoic Central Lapland Greenstone Belt. The hydrothermally altered and mineralised zones are related to a major thrust and shear zone system that extends much across northern Finland. Spatial correlation between mineralized zones, brittle structural features and chemical alteration was explored and identified from high-resolution aeromagnetic data, in combination with airborne electromagnetic and gamma-ray spectrometric data and coupled with petrophysical and palaeomagnetic studies. The most prominent magnetic, ductile signatures formed during the Svecofennian Orogeny (1900–1800 Ma), resulting in elastic, curved, continuous magnetic patterns. These elastic anomaly patterns were disturbed by tectonic stress from S–SW, resulting in parallel, regularly oriented fracture families and thrust faults normal to the main stress direction. According to aeromagnetic, palaeomagnetic and structural evidence, the thrust zone was active during the latest stage of the orogenic event, but was also reactivated at a later date. Airborne gamma-ray data reveals zones of potassic alteration in the ultramafic rock units in the vicinity of cross-sections of these two fault sets. Chemical and mineralogical changes during alteration and metamorphism strongly affected the mafic and ultramafic host rocks throughout the deformation zone. The strong potassium enrichment and coinciding destruction of magnetic minerals resulted in enhanced potassium concentration and reduction of magnetic anomaly amplitudes. Palaeomagnetic results indicate that the remanent magnetization for the altered ultramafic rocks along the thrust zone is of chemical origin (CRM) and was acquired at 1880–1840 Ma, which is presumed also to be the age of the chemical alteration related to gold mineralization.     

综合电磁法在矿区深部成矿机制中的应用研究——以皖南乌溪多金属矿区为例

乌溪矿区介于长江中下游多金属成矿带与华南成矿带之间,是江南造山带上的一个找矿新区.本文在这一找矿新区开展了有效的电磁方法综合勘探,试图对该区深部成矿机制进行研究.我们收集了该区的地质地球化学资料,从地质地球化学资料中分析了区域成矿背景;我们还采集了区域出露的主要岩石类型,在实验室开展物性测定,在此基础上选择了三种电磁方法开展研究区的野外测量.通过地面高精度磁测、激发极化法和可控源音频大地电磁法(CSAMT)三种地球物理方法,开展了研究区的磁化率、极化率和电阻率的分布特征研究.深入分析了地质、地球化学和地球物理三种资料与成矿的关系,相互约束,探讨成矿模型、成矿机制和成矿的可能性,推测可能的矿体赋存位置和深度范围.在地球物理研究结果基础上,结合地质和地球化学背景资料,构建了研究区的成矿动力学模型,推测了研究区成矿机制,揭示了矿区的成矿潜力.综合所得结果布设了钻孔,钻探结果揭示了研究区深部存在强烈矿化蚀变和强蚀变斑岩,初步确认为斑岩型矿床,与CSAMT剖面的解释结果基本一致,也与推测的测区内深部成矿机制相吻合.钻孔结果和地球物理结果的一致性以及对已构建的成矿动力学模型的支持,充分证明了综合电磁方法在斑岩型多金属矿床的发现和预测中的重要作用,同时斑岩型矿床的确认进一步印证了华南成矿带与俯冲作用形成的成矿带的相似性,从而推动整个华南地区的成矿地质研究.     

Integrated geological and geophysical exploration for concealed ores beneath cover in the Chaihulanzi goldfield, northern China

An integrated geological and geophysical investigation was carried out in the near‐mine areas of the Chaihulanzi gold‐field, Inner Mongolia, northern China, to determine the south‐eastern strike extension of the principal mineralized shear system, in the search for new resources. In this case study, surface geophysical surveys played an important role in defining the mineralized structures beneath cover. A re‐investigation of the mine geology by observing the underground exposures of mineralization and its hosting structures, coupled with re‐evaluation and re‐examination of previous exploration data, revealed that the mineralization style at the Chaihulanzi gold‐field is not the skarn‐type as previously assumed, but is structurally controlled by an oblique‐sinistral shear structure. Moreover, a south‐eastward shallow‐plunging mineralized corridor within the principal mineralized shear system was also identified, implying that the ore‐forming fluid‐flow might move through the mineralizing system, from the south‐east at depth to the north‐west. These new geological findings imply that the mineralized shear system should extend much farther south‐eastwards along strike beneath cover, and thus a conceptual target area was proposed. A detailed geophysical survey program, involving the application of VLF‐EM, Stratagem EH4, CSAMT and gradient IP measurements, was carried out to test the validity of the conceptual target. Orientation surveys on the geologically known Line‐18 traverse revealed that VLF‐EM and Stratagem EH4 were the most effective methods of detecting the unseen mineralized system, whereas CSAMT could only provide low‐resolution data, and IP proved to be unsuitable in this environment due to the ubiquitous presence of graphite‐bearing schists in and around the mineralized system. A follow‐up systematic VLF‐EM survey highlighted the principal mineralized shear system as a linear conductive belt, tracing the principal mineralized system for a further 750 m of strike length beneath cover from the previous exploration limit (Line 18). Stratagem EH4 soundings over six parallel traverses perpendicular to the mineralized trend revealed that the principal mineralized shear structure extends for more than 500 m in the dip direction, a strong indication of the presence of potential deep mineralization under the surveyed area. Detailed modelling of the Stratagem EH4 sounding images provided well‐defined targets for test drilling. Subsequent test drilling on some of these targets returned encouraging results as several core‐intercepts of economic gold mineralization were encountered. This led to a more extensive drilling and underground prospecting program, focusing on deep mineralization south‐eastwards along the mineralized trend.     

地球物理测井在多年冻土厚度和地下冰调查中的应用

基于青藏高原多年冻土区三个钻孔的地球物理测井数据和钻孔编录资料,我们对多年冻土厚度和多年冻土层内地下冰与地球物理测井数据之间的关系进行了相关的分析研究.研究表明,当地层为土壤类型时,可以使用井径和侧向测井曲线来判断多年冻土层厚度;而当地层为致密的基岩时,不能使用上述两种测井曲线来判断多年冻土层厚度.此外,还可以使用长源距伽马-伽马曲线和侧向测井曲线来识别多年冻土层内部分地下冰层的位置,其前提条件是地下冰层具有一定的厚度,或即使厚度较薄,但连续出现.这一研究结果对于利用地球物理测井曲线来调查多年冻土情况具有一定的应用价值.     

Geological and geochemical characteristics of the Baogudi Carlintype gold district(Southwest Guizhou,China) and their geological implications

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province,China,where there are numerous Carlin-type gold deposits.To better understand the geological and geochemical characteristics of the Baogudi gold district,we carried out petrographic observations,elemental analyses,and fluid inclusion and isotopic composition studies.We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou.Three mineralization stages,namely,the sedimentation diagenesis,hydrothermal(main-ore and late-ore substages),and supergene stages,were identified based on field and petrographic observations.The main-ore and late-ore stages correspond to Au and Sb mineralization,respectively,which are similar to typical Carlin-type mineralization.The mass transfer associated with alteration and mineralization shows that a significant amount of Au,As,Sb,Hg,Tl,Mo,and S were added to mineralized rocks during the main-ore stage.Remarkably,arsenic,Sb,and S were added to the mineralized rocks during the late-ore stage.Element migration indicates that the sulfidation process was responsible for ore formation.Four types of fluid inclusions were identified in ore-related quartz and fluorite.The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4±N2system,with medium to low temperatures(180–260℃)and low salinity(0–9.08%NaCl equivalent).The late-ore stage fluids featured H2O–NaCl±CO2±CH4,with low temperature(120–200℃)and low salinity(0–7.48%Na Cl equivalent).The temperature,salinity,and CO2and CH4concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage.The calculated δ^13C,d D,and δ^18O values of the ore-forming fluids range from-14.3 to-7.0%,-76 to-55.7%,and 4.5–15.0%,respectively.Late-ore-stage stibnite had δ^34S values ranging from-0.6 to 1.9%.These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids,with minor contributions from strata.Collectively,the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou.It is likely that the Baogudi gold district,together with other Carlin-type gold deposits in southwestern Guizhou,was formed in response to a single widespread metallogenic event.     

Fuzzy inference system for identification of geological stratigraphy off Prydz Bay, East Antarctica

The analysis of well logging data plays key role in the exploration and development of hydrocarbon reservoirs. Various well log parameters such as porosity, gamma ray, density, transit time and resistivity, help in classification of strata and estimation of the physical, electrical and acoustical properties of the subsurface lithology. Strong and conspicuous changes in some of the log parameters associated with any particular geological stratigraphy formation are function of its composition, physical properties that help in classification. However some substrata show moderate values in respective log parameters and make difficult to identify the kind of strata, if we go by the standard variability ranges of any log parameters and visual inspection. The complexity increases further with more number of sensors involved. An attempt is made to identify the kinds of stratigraphy from well logs over Prydz bay basin, East Antarctica using fuzzy inference system. A model is built based on few data sets of known stratigraphy and further the network model is used as test model to infer the lithology of a borehole from their geophysical logs, not used in simulation. Initially the fuzzy based algorithm is trained, validated and tested on well log data and finally identifies the formation lithology of a hydrocarbon reservoir system of study area. The effectiveness of this technique is demonstrated by the analysis of the results for actual lithologs and coring data of ODP Leg 188. The fuzzy results show that the training performance equals to 82.95% while the prediction ability is 87.69%. The fuzzy results are very encouraging and the model is able to decipher even thin layer seams and other strata from geophysical logs. The result provides the significant sand formation of depth range 316.0- 341.0 m, where core recovery is incomplete.     

Quantitative geophysical pore‐type characterization and its geological implication in carbonate reservoirs

This paper discusses and addresses two questions in carbonate reservoir characterization: how to characterize pore‐type distribution quantitatively from well observations and seismic data based on geologic understanding of the reservoir and what geological implications stand behind the pore‐type distribution in carbonate reservoirs. To answer these questions, three geophysical pore types (reference pores, stiff pores and cracks) are defined to represent the average elastic effective properties of complex pore structures. The variability of elastic properties in carbonates can be quantified using a rock physics scheme associated with different volume fractions of geophysical pore types. We also explore the likely geological processes in carbonates based on the proposed rock physics template. The pore‐type inversion result from well log data fits well with the pore geometry revealed by a FMI log and core information. Furthermore, the S‐wave prediction based on the pore‐type inversion result also shows better agreement than the Greensberg‐Castagna relationship, suggesting the potential of this rock physics scheme to characterize the porosity heterogeneity in carbonate reservoirs. We also apply an inversion technique to quantitatively map the geophysical pore‐type distribution from a 2D seismic data set in a carbonate reservoir offshore Brazil. The spatial distributions of the geophysical pore type contain clues about the geological history that overprinted these rocks. Therefore, we analyse how the likely geological processes redistribute pore space of the reservoir rock from the initial depositional porosity and in turn how they impact the reservoir quality.     

盆地超压地层识别方法--以四川盆地通南巴构造带为例

在四川盆地通南巴构造带,首先以井芯、录井资料和钻井泥浆比重资料为约束条件,利用泥岩段声波测井资料建立区域“正常压实趋势线”;然后用精细速度处理获得的地震层速度剖面减去区域“正常压实趋势线”建立速度差值剖面,速度差值剖面上的异常低速带定性指示了地层超压范围;再采用速度一压力变换技术,建立压力系数剖面,定量分析地层超压,地层压力计算结果与实际钻井采用的泥浆比重较好吻合,说明利用地球物理资料、钻井资料及地质资料不但可以定性识别超压地层,而且可以定量预测地层压力;对不同压力封存箱的认识有助于分析地层含油气性延展方向,指导下一步勘探部署。     

Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods

Abstract

The resolution of the freshwater and saline water aquifers in a coastal terrain (Mahanadi Basin, India) is updated. We analysed electrical borehole log data at four sites and compared the water resistivity regime of the freshwater and saline water zones obtained from electrical borehole logging, with the resistivity regime obtained by interpreting vertical electrical sounding (VES) data. The multilayer VES data interpretation is modified to a simple model, containing only the freshwater zone and the saline water zone. The composite geophysical parameters of the freshwater and saline water zones, in particular the resistivity and longitudinal unit conductance regime, are identified. The resolution obtained from the composite geophysical data analyses is very clear and convincing. The composite longitudinal unit conductance regime of the saline water zones is very high compared to that of the freshwater zones. This makes the identification of the two aquifers easy and increases its reliability. A technique which enables analysis of composite geophysical data of freshwater and saline water zones at VES sites in the vicinity of the borehole log sites is proposed. The significance of longitudinal unit conductance in resolving the freshwater and saline water aquifers is illustrated graphically. The proposed technique is validated by correlating the longitudinal unit conductance and resistivity with the total dissolved solids. The efficiency of the technique is validated by carrying out discriminant function analysis.

Citation Hodlur, G. K., Dhakate, R., Sirisha, T. & Panaskar, D. B. (2010) Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods. Hydrol. Sci. J. 55(3), 414–434.