A Study of the Method for the Recognition of Anomalies in Geochemical Hydrocarbon Exploration

The greatest difficulties in recognizing geochemical hydrocarbon anomalies are: (1) how to objectively and accurately separate anomalies from background; (2) how to distinguish hydrocarbon pool related apical anomalies from lateral anomalies controlled by faults; and (3) how to eliminate interferences. These uncertainties are serious obstacles for the wide acceptance and use of geochemical techniques in hydrocarbon exploration. In this paper, the features of hydrocarbon anomalies were analyzed based on the micro migration mechanisms. In most cases, there are two anomalous populations or point groups, which are produced by two distinct mechanisms: (1) a population that directly reflects oil and gas fields, and (2) one that is related to structures such as faults. Statistical studies show that background anomalous populations and the boundaries between them can be described by the population means, prior probabilities, which are the proportions of population sizes, and covariance matrices, when background and anomalous populations have normal distributions. When this normality condition is met, a series of formulas can be derived. The method is designed on the basis of these allows: (1) univariate anomaly recognition, (2) elimination of interferences, (3) multivariate anomaly recognition, and (4) multivariate anomaly combination which depicts a more representative picture of morphology of the anomalous target than individual anomalies. The univariate and multivariate anomaly recognition can not only separate anomalies from background objectively, but also simultaneously distinguish the two types of anomalies objectively. This method was applied to the hydrocarbon data in Yangshuiwu region, Hebei Province. The interferences from regional variation of background were eliminated, and the interpretation uncertainty was reduced greatly as the anomalous populations were separated. The method was also used in Daxing region within the confines of Beijing City, and Aershan and Jiergalangtu regions in Inner Mongolia.

Ore-controlling Regularities of Thrust-fold structures and features of Tectono-geochemical Anomalies at the Xiaozhuqing Exploration Area in the Huize Zn-Pb District

1 Introduction The huize Zn-Pb ore district in Yunnan province is locatedinthecentralsouthernofthe Sichuan—Yunnan—GuizhouPb-ZnPoly-metallic Mineralization Area in the southwestern margin of the Yangtze Block,and is strictly controlled by fault structures.It has developed to one of the famous production bases of lead&zinc and germanium in China.

Application of Wavelet Analysis toInterference Elimination for Geochemical Hydrocarbon Exploration

Interference in the data of geochemical hydrocarbon exploration is a large obstacle for anomaly recognition. The multiresolution analysis of wavelet analysis can extract the information at different scales so as to provide a powerful tool for information analysis and processing. Based on the analysis of the geometric nature of hydrocarbon anomalies and background, Mallat wavelet and symmetric border treatment are selected and data pre-processing (logarithm-normalization) is established. This approach provide good results in Shandong and Inner Mongolia, China. It is demonstrated that this approach overcome the disadvantage of backgound variation in the window (interference in window), used in moving average, frame filtering and spatial and scaling modeling methods.

Geochemical and Geophysical Data Processing Aided by“Multifractal-Spectrum”Filters for GIS-Based Mineral Exploration

A recently developed method, on the bases of “multifractal spectrum” filters for mineral exploration, is introduced in this paper. The “multifractal spectrum” filters, a group of irregularly shaped filters that are constructed on each processed datum, can be used to separate various types of geochemical and geophysical anomalies. The basic model, with an emphasis on the GIS based implementation and the application to the geochemical and geophysical data processing for mineral exploration in southern Nova Scotia, Canada, indicates its advantage in the separation of multiple anomalies from the background.

Ion Exclusion at the Ice-Water Interface Differs from That at the Hydrate-Water Interface: Consequences for Methane Hydrate Exploration

When water-ice grows into salt solutions ion species are excluded by the ice differentially due to non-identical solubility in the ice lattice. This causes an electrical potential across the interface during the ice growth process, initially named the Workman Reynolds Freezing Potential, and may be one of the causes for lightning. However, by measuring the voltage between the ice and water, we have found that when tetrahydrofuran hydrate crystals are grown into salt solutions all ion species are excluded equally and the potential does not manifest. When considered together, this marked difference in ion exclusion scenarios may have ramifications for hydrate exploration because of the chlorine anomaly, which is often used as an indicator of the presence of hydrate reserves.

Application of GISto Geo-anomaly-Based Delineation of Mineral Resources

In this paper, the Dongchuan type copper deposits are taken as an example to illustrate the application of GIS to the geo anomaly based delineation of mineral resources. The following eight steps are listed in this paper to delineate the permissive and preferable ore finding areas: (1) the analysis of favorable prospecting index using linear and planar geo anomalies; (2) the analysis of favorable prospecting index using combined anomalies; (3) the construction of a GIS based spatial model for mineral prognosis; (4) the delineation of the permissive ore finding area; (5) the determination of the synthetic anomalies and numerical range for the prediction of the favorable prospecting areas, and the determination of the weights of these two variables; (6) the superimposition of all the selected anomalies and the construction of the superimposition map; (7) the determination of unifying criterion of favorable prospective areas at various levels, and (8) the delineation of favorable prospective areas. Finally, this paper offers a detailed discussion of the results in the forecasting of Dongchuan type copper deposits.

Evaluation and extraction of weak gravity and magnetic anomalies

In this paper, I introduce what are called weak gravity and magnetic anomalies and propose standards for estimating their reliability. I also introduce new techniques for processing this kind of weak anomaly. These techniques consist of interference elimination and weak signal extraction. Practical applications have proved their effectiveness, Weak gravity and magnetic anomalies will get more attention with the development of targeted exploration.

Gold anomaly ranking based on stream sediment geochemistry in the Fariman–Kashmar axis, NE Iran

One of the essential tasks accelerate the decision-making process in mineral exploration projects is ranking anomalous areas.In this study,we used fourteen geologic maps(at scale 1:100,000)in areas where systematic geochemical explorations were conducted in the Fariman-Kashmar axis in northeast Iran to conduct the anomaly ranking.On all these maps,samples were consistently prepared to be analyzed through statistical and geostatistical methods.At first,anomaly separation was carried out by fractal methods that resulted in the detection of 308 anomalous samples in 128 areas.These samples were classified into three groups of first,second,and thirdorder anomalies,whose number of anomalous samples were calculated based on this ranking technique.Three factors,including the average concentration of each anomaly,its surface area,and the number of its samples,were used to rank the areas.According to this technique,the maximum anomaly score obtained was 172 for the Taknar area,and the minimum score was 3 for several areas.To validate the ranking results,some exploration operations were carried out in some of these anomalous areas in which mining operations started later.Several significant gold anomalous areas were introduced,which is considered an important result of this study.

Interpretation of residual gravity anomaly caused by simple shaped bodies using very fast simulated annealing global optimization

A very fast simulated annealing（VFSA） global optimization is used to interpret residual gravity anomaly.Since,VFSA optimization yields a large number of best-fitted models in a vast model space;the nature of uncertainty in the interpretation is also examined simultaneously in the present study.The results of VFSA optimization reveal that various parameters show a number of equivalent solutions when shape of the target body is not known and shape factor ＇q＇ is also optimized together with other model parameters.The study reveals that amplitude coefficient k is strongly dependent on shape factor.This shows that there is a multi-model type uncertainty between these two model parameters derived from the analysis of cross-plots.However,the appraised values of shape factor from various VFSA runs clearly indicate whether the subsurface structure is sphere,horizontal or vertical cylinder type structure.Accordingly,the exact shape factor（1.5 for sphere,1.0 for horizontal cylinder and 0.5 for vertical cylinder）is fixed and optimization process is repeated.After fixing the shape factor,analysis of uncertainty and cross-plots shows a well-defined uni-model characteristic.The mean model computed after fixing the shape factor gives the utmost consistent results.Inversion of noise-free and noisy synthetic data as well as field data demonstrates the efficacy of the approach.

东北太平洋Explorer Ridge热液羽状流位温浊度异常和物质能量通量估算

深海热液流体与周围海水之间存在明显的物理和化学差异,通过检测海水的位温浊度异常是探测深海热液活动的重要手段之一。本文采用"海底火山带项目(Submarine Ring of Fire 2002)"拖曳式温盐深测量仪数据资料,研究了东北太平洋Explorer Ridge热液场的水文特征及物质能量通量的释放。结果表明Explorer Ridge热液场热液羽状流中性浮力层所在深度范围约为1 600~1 900m,距离海底的高度约为200m,最大位温、盐度和浊度异常分别为0.04℃、0.004和0.18NTU;中性浮力层热液羽状流帽呈椭圆结构,其长轴与洋中脊线重合,羽状流帽总面积约为27km^2;热液羽状流在中性层范围内存在明显的分层现象,通过经验公式计算得到Explorer Ridge热液场观测范围内热液喷口的总的浮力通量为6.19×10^(-2)m^4/s^3,平均值为2.063×10^(-2)m^4/s^3;总的体积通量为9.884×10^(-2)m^3/s,平均值为3.295×10^(-2)m^3/s;总的热通量为194.9MW,平均值为64.967MW。

Artificial intelligence-based anomaly detection of the Assen iron deposit in South Africa using remote sensing data from the Landsat-8 Operational Land Imager

Most known mineral deposits were discovered by accident using expensive,time-consuming,and knowledgebased methods such as stream sediment geochemical data,diamond drilling,reconnaissance geochemical and geophysical surveys,and/or remote sensing.Recent years have seen a decrease in the number of newly discovered mineral deposits and a rise in demand for critical raw materials,prompting exploration geologists to seek more efficient and inventive ways for processing various data types at different phases of mineral exploration.Remote sensing is one of the most sought-after tools for early-phase mineral prospecting because of its broad coverage and low cost.Remote sensing images from satellites are publicly available and can be utilised for lithological mapping and mineral exploitation.In this study,we extend an artificial intelligence-based,unsupervised anomaly detection method to identify iron deposit occurrence using Landsat-8 Operational Land Imager(OLI)satellite imagery and machine learning.The novelty in our method includes:(1)knowledge-guided and unsupervised anomaly detection that does not assume any specific anomaly signatures;(2)detection of anomalies occurs only in the variable domain;and(3)a choice of a range of machine learning algorithms to balance between explain-ability and performance.Our new unsupervised method detects anomalies through three successive stages,namely(a)stage Ⅰ–acquisition of satellite imagery,data processing and selection of bands,(b)stage Ⅱ–predictive modelling and anomaly detection,and(c)stage Ⅲ–construction of anomaly maps and analysis.In this study,the new method was tested over the Assen iron deposit in the Transvaal Supergroup(South Africa).It detected both the known areas of the Assen iron deposit and additional deposit occurrence features around the Assen iron mine that were not known.To summarise the anomalies in the area,principal component analysis was used on the reconstruction errors across all modelled bands.Our method enhanced the Assen deposit as an anomaly and attenuated the background,including anthropogenic structural anomalies,which resulted in substantially improved visual contrast and delineation of the iron deposit relative to the background.The results demonstrate the robustness of the proposed unsupervised anomaly detection method,and it could be useful for the delineation of mineral exploration targets.In particular,the method will be useful in areas where no data labels exist regarding the existence or specific spectral signatures of anomalies,such as mineral deposits under greenfield exploration.

Surface geochemical anomaly pattern of medium-to-high temperature geothermal systems in South China and its application

The existence of thermal storage will correspondingly increase the temperature of surrounding strata and promote the continuous expansion,volatilization,upward migration,and loss of gas in the strata.As a result,a low-concentration gas field will be formed in the strata above geothermal reservoirs.Geothermal reservoirs could in turn heat formation water and increase the solubility of soluble inorganic salts in the surrounding rocks and the total dissolved solids(TDS)content in the formation water.Since water can strongly wet and permeate strata,the dissolved inorganic salts migrate into upper strata along with water,giving rise to the formation of a high-concentration inorganic salt field in the strata above geothermal reservoirs.A higher geothermal reservoir temperature corresponds to more significant characteristics mentioned above.Therefore,a medium-to-high temperature geothermal system has a surface geochemical anomaly pattern of high inorganic salt concentrations and low gas concentrations(also referred to as the high-salt and low-gas pattern).This pattern is applied to the surface geochemical exploration of the two geothermal fields in Guangdong Province,i.e.,the Huangshadong geothermal field in Huizhou City and the Xinzhou geothermal field in Yangjiang City,revealing low-concentration gas fields above both.The application results also show that the exposed thermal spring water in both geological fields has higher concentration of dissolved inorganic salt than the surface water and nearby seawater,forming high-amplitude anomalies on the surface above geothermal reservoirs.These characteristics,as well as the measured temperature at known geothermal wells,verify the validity of the high-salt and low-gas pattern of medium-to-high temperature geothermal systems proposed in this study.Moreover,the high-salt and low-gas pattern proposed predicts three favorable medium-to-high temperature geothermal zones in the surface geochemical exploration of the Shiba Basin near the Huangshadong geothermal field.

自相关滤波法提取弱异常方法在油气勘查中的应用

在论述自相关滤波法理论的基础上,通过对各种理论模型进行实验,由实验效果分析方法的优势,并以我国某区域重力资料为例,对该区域内重力资料进行了自相关滤波计算,计算结果压制了区域场的影响,提取出油气藏相关的局部弱异常,并与布格重力异常、垂向导数以及剩余异常等资料相互验证,取得了很好的应用效果。基于该地区的计算结果,证明自相关滤波法可应用于油气勘查中,可为其他油气勘查区圈定油气藏的有利局部构造提供可靠并且准确的研究方法,从而达到辅助油气勘查的效果。

综合物化探在内蒙古鄂伦春某铅锌多金属矿勘查中的应用及找矿效果

以内蒙古鄂伦春某铅锌多金属矿勘查为例,研究不同勘查阶段的有效物化探组合方法。通过1∶1万土壤地球化学扫面圈定多元素组合异常,根据磁测工作证实了火山口的存在,以火山机构边部受NE-NNE向断裂带控制的铅锌矿体为重点研究对象,兼顾火山堆积型铅锌矿体,在激电中梯异常见矿不理想的情况下,开展复电阻率法剖面测量工作,通过二维电性剖面指导深部钻探工作部署,最终取得找矿突破。通过小比例尺物化探异常结合地质背景选区-大比例尺物化探扫面圈定找矿有利部位-二维物探剖面进一步确定目标体的埋深和产状以指导钻探,该套有效勘查方法组合对其他地区的找矿具有借鉴意义。

高斯混合模型在水系沉积物地球化学异常圈定中的应用:以湖南省溆浦地区为例

化探数据的正确处理和解译对于区域矿产勘查工作具有重要意义。然而,由于不同类型的岩石具有不同的元素丰度,在处理复杂岩性区化探数据时如果采用统一的异常下限,会导致高背景区被误判为异常区,而部分低弱地球化学异常被忽略。所以复杂岩性区的化探数据需按岩性分类后再划分地球化学背景与异常,从而更准确地圈定化探异常。提出了基于因子得分高斯混合模型的化探异常圈定方法,首先将化探数据做对数比转换后进行因子分析,然后利用因子得分完成高斯混合模型岩性分类,再进行分类标准化处理以消除岩性背景的影响,最后使用处理后的数据圈定化探异常。利用该方法对湖南溆浦地区1∶20万水系沉积物化探数据进行研究,结果表明,成矿元素在研究区不同岩性中的含量存在一定差异,若采用统一的异常下限是不合理的;而本研究提出的方法能准确地进行岩性分类、消除不同岩性的背景和强化低弱异常,且异常位置与已知矿点相吻合。因此,高斯混合模型方法可以准确地圈定复杂岩性区的化探异常,并为研究区下一步的矿产勘查工作提供一些参考依据。

高精度磁法测量在矽卡岩型铜锌矿床深部找矿预测中的应用——以大兴安岭南部浩布高铜锌矿床为例

高精度磁法测量是矿产预测的重要手段之一,其结果包含丰富的浅源信息和深源信息,在推断隐伏地质构造方面效果良好。根据不同岩性的磁性特征,可以识别地质体的形态产状及空间分布特征,进而间接指导找矿。浩布高铜锌矿床位于大兴安岭南部黄岗—甘珠尔庙锡多金属成矿带,矿体主要赋存于二叠系大石寨组大理岩与粉砂质板岩层间滑动带的矽卡岩中,部分产于大理岩和隐伏黑云母花岗岩接触带的矽卡岩内,具有典型矽卡岩型矿床特征。通过对高精度磁测数据的精细地质构造解译,对比地质勘查结果,分析总结控矿构造的产状变化和成矿地质体的形态规模变化特征,确定控矿因素及找矿标志,对深部及外围的找矿方向进行评价,为探矿工程布置提供依据。

巷道前方地质异常八点电源电法随掘探测响应

为可靠探查掘进巷道前方地质异常体情况,提出了八点电源随掘超前探测方法。从巷道迎头向后沿巷帮中线布置32道电极,电极间距5m。近工作面8个电极顺次做为点电源电极,采集整条测线单极-偶极装置视电阻率值。根据微分电测深探测原理,每个点电源所测得的视电阻率值可视为该点电测深结果,得到电测深曲线图和视电阻率成像图。巷道每掘进20m,将最后4个电极滚动布置到新测线前4个电极,再进行八点电源电测深数据采集,得到连续变化的电测深曲线和电测深成像结果。根据单极-偶极装置视电阻率响应公式计算了工作面超前方向地质异常球体的响应,研究结果表明:对同一地质异常球体,距离掘进工作面由远到近,电阻率响应越来越明显;低阻球体边缘到点电源距离不大于球体半径时,可以探查;高阻球体边缘到点电源距离不大于1/2球体半径时,可以探查;低阻球体的响应强于高阻球体。地质异常体半径越大,能够被探查出的超前距离越大。因此,超前0~50m范围地质异常探测精度高;超前50~100m范围地质异常探测可靠性低,适宜解释是否有较大范围的地质异常区。八点电源电法随掘超前探测能够可靠探测工作面前方地质异常的赋存情况,为工作面安全快速掘进提供地质保障。

羌塘盆地白云湖凹陷航空重磁异常特征及其油气勘探意义

航空重磁数据是揭示盆地深部构造的有效手段,本文通过最新测量的航空重磁数据结合野外实测物性资料,阐述了白云湖凹陷航空重、磁异常特征及其地质成因,利用航空重磁资料识别出白云湖凹陷断裂与岩浆岩的分布情况,采用人工切线法、功率谱分析法和Parker-Oldenburg迭代反演算法,计算了白云湖凹陷基底埋藏深度与中生界底面构造形态,并通过重点剖面重磁综合解释,对构造分层结果进行了验证。研究结果表明白云湖凹陷中生界、古生界沉积层的起伏变化是引起重力异常的主要因素,区域航磁异常则主要反映了前寒武纪基底展布特征。白云湖凹陷基底埋深较深,中生界分布连续且厚度较大,区域断裂—岩浆活动不发育,整体受构造运动影响较少,具有较好的油气勘探前景。

磁电异常联用技术在矿井火区勘探中的应用

针对新柳矿业周边小煤窑数量众多及小煤窑破坏漏风、引发自燃等问题,致使柳湾煤矿井田产生破坏,研究采用磁电异常联用技术和测温杆红外热像测温反演技术。研究表明:通过磁电异常联用技术和测温杆红外热像测温反演技术的联合应用,可以准确地探测和定位火源,从而实施有效的灭火程序。

水文地球化学方法在地热资源勘查中的应用:以湖北省应城市为例

地热流体水文地球化学研究在指示地热资源的形成机制、赋存环境以及预测地热资源有利勘查区等方面具有广泛应用。为了探究湖北省应城市地热系统的热源以及成因机制,并对其地热异常区进行圈定。基于研究区内地热水与浅层地下冷水的水化学及同位素特征,探讨了地热流体中主要组分的地球化学起源,评估了地热流体的热储温度。结合区内浅层地下冷水的温度与水化学数据,对地热异常区进行了圈定。研究结果表明,地热水水化学类型主要为SO 4-Ca型,地热系统主要的热储围岩为海相碳酸盐岩,通过地热温标计算热储温度约112.2℃。大气降水入渗和碳酸盐岩热储层中的水-岩相互作用是地热水中化学组分的主要来源。地热水的水化学和氢氧同位素特征指示地热水的补给来源为研究区西部山区的大气降水,大气降水由补给区入渗后向东南盆地中心不断运移,循环深度为3436.7~5030.2 m。通过与典型岩浆热源型地热系统的对比以及岩石样品中放射性元素的数据结果,得出应城地热系统是由地温梯度正常加热而形成的。结合区内浅层地下冷水的温度与水化学数据,最终圈定地热异常区位于应城市区西南陈河镇以北地区,但仍需考虑井深、人为污染等客观限制因素对圈定结果的影响。