Geoscience

Distribution and Migration of Gold in Gobioverlay of Arid Desert Terrain：Take the Jinwozi 210 Gold Belt in Xinjiang as an Example

YE Rong1，ZHANG Bimin2，WANG Yong3

2013, 27(6): 1265-1274.

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The deeppenetrating geochemistry methods for geogas and mobile elements survey were evaluated in Jinwozi 210 gold belt, Xinjiang. The experimental results in this paper confirm that these methods can effectively indicate the concealed ore bodies under the regolith cover. The drilling investigations revealed the “Cshape” distribution patterns of the mobile gold. The geogas and soil samples in surface anomalies were collected, in which the size, morphology and component of the particles were characterized by transmission electron microscope. Goldcopper and goldbismuth nanoscale particles were observed in the geogas and soil samples. It is believed that the nanoscale particles sourced from the underlying concealed ore bodies are likely to cause the surface geochemical anomalies. The nanoscale particles could travel upwards to the surface, during which the geogas and soil anomalies were developed in pore space and soil. The dissociation and desorption of the nanoscale particles from soil particles’ surface during their migration upwards probably created the “Cshape” distribution patterns of the mobile gold in vertical profiles in drilling holes.

Geochemical Characteristics of Stream Sediments and Prospecting Prediction of Dongan-Tangwanghe Region, Heilongjiang, China

ZHU Lian1, GU Xuexiang1, ZHANG Yongmei1, ZHAO Honghai2, DONG Shunli3

2013, 27(6): 1275-1282.

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Based on the 1∶200,000 geochemical data of stream sediments in Dongan-Tangwanghe region, Heilongjiang Province, correlation analysis, cluster analysis and principal factor analysis conducted on 13 elements show systematic and regular element distributions. Anomalies of hightemperature elements and lowtemperature elements occur in the western and eastern parts of the study area, respectively. Though computing the threshold by fractal analysis, it is proposed that the eastern area has substantial potential for exploring Au deposits associated with middleto lowtemperature elements. Combining the information of geology, geophysics and known deposits, this paper delineates 34 element anomaly associations and 4 potential prospecting areas.

he Evolution of the Continental Margin Rift Basin and Its Relationship to VMS Deposit: A Case Study of the Luchun Copper Deposit, Yunnan Province

HAN Siyu1,2,3, LIU Jiajun1,2, YANG Xian1,2, CHEN Siyao1,2, CHENG Wenbin4

2013, 27(6): 1283-1296.

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The Luchun massive sulfide deposit is located in the LuchunHongponiuchang rift basin. The Luchun copper deposit occurs in a series of bimodal volcanic rocks which are dominated by acidic volcanics. There are upper and lower orebodies in the ore district: the upper is black and lower is yellow. The assemblage of minerals, with higher contents of sphalerite, galena and chalcopyrite, is simple. Trace elements and REEs geochemical data on the minerals are similar to the volcanics. The result of sulfur isotopic analyses shows that the 34S values vary from 115‰ to 178‰. Ore lead isotopic compositions are rather uniform, as evidenced by the Pb isotopic ratios: 206Pb/204Pb=18498 to 18626；207Pb/204Pb=15588 to 15760；208Pb/204Pb=38430 to 38974. It is clear that the evolution history of the rift basin. And the bimodal volcanics in the basin are typical of oceanic ridges or intraplate extensional settings and island arc, it suggests that the tectonic setting in this area is extensional and rifting. The deposit was associated with the bimodal volcanic rocks in the extensional setting, which was favoured to the formation of the hydrothermal fluids circulatory system. The hydrothermal fluids exhaled and precipitated to form the Luchun VMS deposit.

The Geological Characteristics and Metallogenesis Analysis of Faults in Haojiahe Copper District in Chuxiong Basin，Yunnan

LIANG Xuwen1,2，HAN Runsheng1, WU Haizhi1, WU Peng1, LIN Bingxia1

2013, 27(6): 1297-13074.

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Haojiahe copper deposit is a typical representative of sandstone deposits in Chuxiong Basin, Yunnan. On the basis of large scale tectonic geological mapping, this article uses the theory and method of ore fields of geomechanics to select the typical fractures to identify the mechanical properties of fracture surface, divides the construction period of time and set the tectonic systems, and also makes a detailed description on the relationship between the geological characteristics of the faulted geology and the oreforming in different period time and from different direction. Since Yanshanian, this area has experienced the transition from NE-SW trending→near EW trending→NW-SE trending→near S-N trending to the main constructional compressive stress. In late Yanshanian, NW trending structure has control function on the inchoate metallogenic material activation, migration and reconfiguration and enrichment of copper; between late Yanshanian and early Himalayan, near S-N trending structure prompted into enrichment of metallogenic material. The morphology of ore body emerged to be lamellar and stratoid; in the early Himalayan, NE trending structure promoted the ore fluid to extract a great number of mineral substance then enriched them again and formed rich ore body; in the middlelate Himalayan, near EW trending structure caused damage to the ore body.

Geochemical Characteristics of Dishuigou Diorite in Inner Mongolia and Its Geological Significance

HU Hongfei1, 2 ，ZHANG Yongquan3，HU Huabin4，ZHANG Chao1, ZHANG Lizhong5

2013, 27(6): 1308-1315.

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The Dishuigou dioritic intrusion is located in the Langshan arc at the northern margin of the North China Craton (NCC), Inner Mongolia. It is emplaced in the Late CarboniferousEarly Permian according to the previous zircon UPb dating data. In this paper, the major and trace (including rare earth) elements composition of the Dishuigou diorite are reported. The result shows relatively enriched in large ion lithophile elements (LILE) such as the Rb, Ba, Th, K, and P, and depleted in high field strength elements (HFSE) such as the Nb, Ta, and Ti, and high Rb/Sr (005-010) and Ba/Rb (1145-2216) values, and low A/CNK (<11). In combination with the strong fractionation REE (LREE/HREE=297-331) and LREE (La/Sm=275-357), and insignificant Eu anomalies (δEu=092-113), suggesting the dioritic intrusion formed in an arc environment and derived from mantle melt mixed with crust material during ascending. It is concluded that the southward subduction of the paleoAsian oceanic slab in Late CarboniferousEarly Permian resulted in the formation of the Dishuigou dioritic intrusion based on the regional evolution the Langshan arc.

Key Issues and Solution of Analysis Support Software for Petrogeochemical Diagrams

XUE Tao1, DIAO Mingguang1, Lu Zhicheng2

2013, 27(6): 1316-1322.

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Petrogeochemical diagrams are effective and common tools in current pertrogeochemical research, used for rock classification, genetic discrimination of rocks and ore deposits, tectonic environment discrimination, and evaluation of the geological evolutionary history.This paper examines the analysis support softwares for petrogeochemical diagrams and identifies the key issues related to the softwares.These issues include the limitations of available diagram types and quantity, the lack of automation, the weakness of software independence, and so on.By collecting 232 diagrams, which show 8 different categories of petrogeochemical fields, we used the postfix expression to calculate and plot diagrams of these fields automatically and used XML to define and extend the diagrams.A program based on experts workflow in the field of petrogeochemistry is designed, which can be used to draw, plot, and compute petrogeochemical diagrams, and also can be used in common methods of calculation, such as CIPW.

Geochemical Characteristics of Trace Elements of Sediments from drillhole SFK1 in the Continental Shelf of the East China Sea and the Source Implication

LAN Xianhong1,2，ZHANG Zhixun1,2，GUO Xingwei1,2，WANG Zhongbo1,2

2013, 27(6): 1323-1331.

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The geochemical information from trace elements of the continental shelf sediment from East China Sea is a significant indicator to the stratigraphic division and provenance analysis. The trace elements of sediments derived from drillhole SFK1(82.90 meters in depth) which was located at Xihu depression in the continental shelf of East China Sea were analyzed and their provenances were discriminated. According to the changing law of trace element contents and their ratios，the sediments from drillhole SFK1 can be divided into eight layers, which reflect the fluctuation of sea level and the change of sediment sources in East China Sea since the late last interglacial cycle (warm period). Combined with factor analysis, the scatter diagrams of U/Th vs. (Zr+Hf)/(Al2O3+TiO2) and Th/Co vs. TiO2/Zr were drawn to determine the material source of sediments from drillhole SFK1. The results revealed that the material sources of sediments mainly come from the Changjiang River, and sediments in the middle part of the drillhole were apparently influenced by materials from the Yellow River. The results also indicated that in the case of unchanging sediment sources, the changes of climate and sedimentary environment had little effect on transformation and redistribution of chemical elements of sediments in the study area.

Characteristics of Carbon and Oxygen Isotopes of Carbonate Rocks in Riganpeicuo Formation of Upper Triassic in Ｒenacuo Ａrea of Gaize, Tibet and Its Geological Significance

HOU Engang, GAO Jinhan, WANG Xunlian, WANG Genhou, HU Xinrui, MA Zhanchuan

2013, 27(6): 1332-1339.

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The Ｒenacuo area of Gaize, Tibet, in the southern Qiangtang Basin, shows a series of strikingly thick carbonate layersResearch on C and O isotopes in the area plays an important role in the reconstruction of the paleoenvironment and the identification of the sedimentary characteristicsBased on the geological map of the lithostratigraphy (1∶2,000), the numerous samples collected in the field and analysis of the C and O isotopes, the Z values of salinity from 12632 to 13537, which indicates that the paleoseawater in the Ｒenacuo area of Gaize ranges from normal marine to hypersalineIn addition, the average temperature of the paleoseawater is 224 ℃, firm evidence of a warm climateBoth the rates of δ18O and δ13C vary with respect to the sea level： the deeper the seawater, the higher the δ18OThe paleotemperature and paleosalinity from the determination of C and O isotopes closely reflect the related sedimentary facies

Sedimentary Environments and Geochemical Characteristics of Early Permian Carbonate Platform in the Western Henan ProvinceYAO Xu

YAO Xu, ZHOU Yaoqi, LI Su

2013, 27(6): 1340-1347.

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This paper presents the study of the sedimentary facies of Taiyuan Formation in typical sections from Jiaozuo area to Yuzhou area, mainly focusing on the platform sedimentary characteristics and evolution of epicontinental sea. Sedimentary facies of Taiyuan Formation, which is mainly featured by limestones along with interlayered siltstones, mud shales and coal seams, can be divided into five facies including open carbonate platform, limited carbonate platform, barrier island, lagoonswamp and tidalflat facies. The storm depositional events widely developed in the carbonate platform, which can be divided into several sedimentary cycles. Open carbonate platform (mainly in Yuzhou area) mainly contain amount of bioclastic, featured by substantial broken fossils, high content of trace elements and rare earth elements, much higher content of LREE than that of HREE, the respectively positive correlations between the value of ∑REE and the content of Fe as well as between that of LREE/HREE and Fe. Compared with open carbonate platform, restricted carbonate platform (mainly in Jiaozuo area) is featured by the widespread micrite, which infer that the ancient ocean in the restricted carbonate platform contained less fossils and colloids, and became much more restricted and quieter than that of open carbonate platform. The bottom limestones of the Lower Limestone Section of Taiyuan Formation, which is formed in transgressive systems tract(TST) during the early phase of first transgression, are featured by high content of biodetritus, Sc, Ba and ∑REE, low value of Sr/Ba, low differentiation between LREE and HREE. The top limestones of the Lower Limestone Section formed in highstand systems tract (HST), which reflected the sedimentary environment of the limited carbonate platform in the research area evolving from the previous turbulent water into confined and quite surroundings with biodetritus and collides diminishing and evaporation strengthening. It aims to put implications on the research of the characteristics and evolution by comparing with the sedimentary characteristics of Taiyuan Formation limestones in different stage of the system tracts in restricted carbonate platform.

Study of Sequence and Lithofacies Paleogeography of the Xujiahe Formation in the LargeScale Central Sichuan

ZHANG Bing1，WANG Xuben1，WU Chaorong1，LIU Pengbo2，ZHAO Wenlong1

2013, 27(6): 1348-1355.

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The oil and gas exploration began in the 1940s in the Xujiahe Formation,Upper Triassic, Sichuan Basin, of which the second, the fourth and the sixth members are not only main aim strata, but also one of the most favorable horizons in search for new gas sources. According to core of drilling observation, the actual measurement of field section, the identification and analysis of microscope thin sections, and combined the research of sedimentary facies marks with petrology, well logging and seismology, it is indicated that fan delta, braid river delta and lakes are developed in the Xujiahe Formation, largescale Central Sichuan,and further are divided into several subfacies and microfacies. Through the theory and technology of high resolution sequence stratigraphy, we identify two super longterms and five longterms of datum baselevel cycles sequences in the Xujiahe Formation. Using the sedimentary theory as a guidance, we choose the longterm baselevel cycle sequences as isochronal stratigraphic units to map sequencelithofacies paleogeography of Sichuan basin. The result of maping diagram makes it clear that five longterm lithofaciespaleogeographic subsidence center, migration direction and the distribution rule of sedimentary facies are strictly controlled by the Longmen orogenic belt and Micang Mountains with the nonsynchronous tectonic framework.

Characteristics of C and O Isotopes of Carbonates Associated with Gas Hydrate in the Qilian Mountain Permafrost and Their Geological Significance

CAI Junjun1, LU Zhenquan2, 3, SUN Qing4， LIU Hui3,WANG Ting3, SUN Xiai3

2013, 27(6): 1356-1364.

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It is a universal phenomenon for gas hydrate associated carbonates in seafloor sediments, but it is rarely reported in the permafrost. Based on microscopic observations and mineral analyses on carbonates associated with gas hydrate, mineral species and occurrence modes of carbonates are determined in the Qilian Mountain permafrost. The results show that occurrence modes of carbonates can be divided into four types according to mineral compositions and geological features. Characteristics of C and O isotopes in different occurrence modes of carbonates indicate that the smoky gray rhombic calcite crystals or microcrystalline calcites may be related to gas hydrate decomposition. The variation of C and O isotopic compositions in carbonates with depth suggests that there probably exist hydrocarbon seepage activities within a certain depth, namely decomposition of gas hydrate, resulting in carbonate formation.

Semiquantitative Research on the Relationship between Thickness of Marine Gas Hydrate Stability Zone and Its Influencing Factors

XU Hao, LEI Xinhua, LI Pengfei, ZHANG Xin, FU Jun

2013, 27(6): 1365-1372.

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There are a large number of natural gas hydrate resources in marine sediments. The hydrate stability zone (HSZ) is an important factor to reflect gas hydrates mineralization and distribution, and the thickness of HSZ is a decisive factor for the resource of gas hydrates, thus the study of HSZ and its influencing factors is of guiding significance to the mineralization rule, distribution pattern and resource assessment of gas hydrates. The previous studies show that there are a lot of factors which can affect the HSZ, but their influencing degrees are different. In this paper, the phase equilibrium of natural gas hydrate was firstly analyzed, and then the important factors affecting HSZs thickness were emphatically discussed, ie. gas component, geothermal gradient, seawater depth, temperature in seafloor and salinity of pore water. With program CSMGem, the influencing degree of these factors were simulated and calculated. Moreover, these calculated data were used to do curve fitting for a more accurate curve of phase equilibrium. According to this accurate curve, combined with the geothermal gradient the thickness of HSZ was obtained. With the regression analysis method, the relationship among the HSZs thickness and these influencing factors are semiquantitatively analyzed in detail.

Experimental Study on Formation Behavior of Methane Hydrate in Sea Mud from South China Sea

JIA Jialin1, 2, 3, ZHANG Yu1, 2, LI Gang1, 2, CHEN Zhaoyang1, 2,

2013, 27(6): 1373-1378.

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The formation behaviors of methane hydrate in the sea mud from South China Sea were studied. The sea mud with mean pore diameter of 12178 nm and total pore volume of 4997×10-2 ml/g, surface area of 16412 m2/g was used for the experiments. The mass fraction of water in the sea mud is 40%. The experiments were carried out at the temperature range of 27415-28115 K and the initial formation pressure range of 102-144 MPa. The experiment results show that the formation rate of methane hydrate in the sea mud and the gas consumption increase with the increase of initial formation pressure and increase with the decrease of temperature. The complex pore structure of the sea mud can promote the nucleation of the hydrate, but reduce the final conversion of the water,and this effect will be strengthened with the increase of the temperature and the decrease of the initial formation pressure.

Experimental Investigation of Gas Hydrate Dissociation by Hot Brine Injection with Different Temperatures

LI Shuxia1,2，XU Xinhua1，WU Jinjin1，LI Xiaosen2

2013, 27(6): 1379-1383.

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As a new clean energy, natural gas hydrate (NGH) has attracted much more attention in recent years. Thermal stimulation is one of the effective ways to dissociate natural gas hydrate. To dissociate NGH by hot brine injection economically, a onedimensional experimental system is designed to form NGH with the same initial conditions in sandpacked tube, and then hot brine with different temperatures was injected to analyze the NGH dissociation performance. The results show that the higher the hot brine temperature is, the earlier the NGH dissociation begins, and the higher the average gas production rate is during the hot brine injection stage. With hot brines in different temperatures injected, the relationship of the thermal front vs. time is close to linear. When the temperature increases from 40 ℃ to 100 ℃, the average speed of thermal front movement increases from 015 cm/min to 02 cm/min, indicating that the hot brine temperature has a little effect on the thermal front movement. Early in the heat injection period, the higher temperature results in higher energy efficiency; however, later in the heat injection period, the higher temperature results in lower energy efficiency. Under these experimental conditions, with the hot brine temperature increasing from 40 ℃ to 100 ℃, the energy efficiency decreases from 67 to 24, while the movement speed of thermal front stays stable. It is proposed that, to dissociate NGH economically, hot brines with high temperature should be injected in early stage and lowtemperature brines should be injected in middle and later periods.

Source Rock Potential of Permian in Wuli Permafrost Zone in QinghaiTibetan Plateau

LI Xiaoyu1, GONG Jianming2, CHEN Xiaohui3, WANG Huidong1,

2013, 27(6): 1384-1391.

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In order to find out the hydrocarbongenerating potential of Permian source rocks in Wuli permafrost zone, QinghaiTibetan Plateau, the cores from gashydrate trial hole (ZK1) and its adjacent drilling holes were analyzed. The results show that the organic matter abundance of upper member source rocks of Nayixiong Formation in Upper Permian is poor, while the abundance of the lower member is fair to good. The organic type is mainly constituted by Ⅲ kerogen, which is in favor of generating gas. The thermal evolution degree of Permian source rocks is very high, reaching to excessive maturity. Considering that the maturity of mudstone and metamorphic grade of coal bed are very high in Wuli Permafrost zone, it can be drawn a conclusion that the hydrocarbongenerating potential of Permian source rocks is general good in Wuli permafrost zone,QinghaiTibetan Plateau.

Discussion about the CO2 Origins of Wuli Permafrost Zone in QinghaiTibetan Plateau

YANG Deshou1, GONG Jianming2, HE Xingliang2, WANG Huidong1,

2013, 27(6): 1392-1398.

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In order to understand the component and origin of gases from gashydrate drillhole (ZK1) in Wuli permafrost zone, QinghaiTibetan Plateau, the gas components and the carbon isotopes of headspace gas samples and resolving gas samples from hole ZK1 and its adjacent drillholes and gas samples from lake water are analyzed. At the same time, the carbon isotopes of carbonate rocks from cores are also analyzed. The results show that more than 98% natural gas is composed of carbon dioxide with a little hydrocarbon gas(mainly methane),the main maximum values of δ13CCO2 are between-4‰ and-6‰(VPDB), the main maximum values of δ13CCH4 from a few richmethane samples are between -3238‰ and -2782‰(VPDB), while the mean value of δ13CCaCO3 is -387‰(VPDB).Integrated with regional geology, it could be drawn a conclusion that the CO2 of Wuli permafrost zone is mainly of volcanic mantle type, which is related with strong tectonic movement and magma activities.

Presentday Geothermal Structure of Lithosphere and the Cenozoic Tectonothermal Evolution of Bohai Basin

PENG Bo，ZOU HuaYao

2013, 27(6): 1399-1406.

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Based on 2,706 static temperature measurements in 236 boreholes and system temperature measurements in 25 boreholes, the geothermal gradient and heat flow of Bohai basin were calculated. By setting up typical crustal structure models in this area, the mantle heat flow, deeper temperature and thermallithosphere thickness were calculated by the “stripping” method. Based on the dynamic model of the Earth, the heat flow evolution in this area was reconstructed. The results show that the background geothermal gradient is 322 ℃/km, and the heat flow is 648 mW/m2. The presentday lithosphere thickness ranges from 61 km to 69 km, and the ratio of mantle heat flow in the surface heat flow is about 60%, while the type of lithosphere geothermal structure is “hot mantle and cold crust”, and the temperature of the bottom of crust ranges from 548 ℃ to 749 ℃. The heat flow evolution coincides with the tectonic subsidence history. After three phases of heating and thinning of lithosphere, the heat flow reached the maximum (70-83 mW/m2） at the end of Dongying depositional duration. It is suggested that the basin has experienced the process of synrift phase involving the mantle and combining with multiphase alkaline basalt in the basin. As the heat flows decreasing in thermal subsidence phase, the type of basin transforms into depression.

Characteristics of GeotemperaturePressure System and Their Influence on Hydrocarbon Distribution in Zhuyi Depression, Pearl River Mouth Basin

WU Yan1, LIU Zhen1, DAI Yiding2, QUAN Zhizhen2, HUANG Yanhui1, CHENG Haohua1

2013, 27(6): 1407-1413.

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Geotemperature and pressure have a great controlling function on hydrocarbon generation, migration and accumulation. The characteristics of geotemperaturepressure system in Zhuyi Depression, Pearl River Mouth Basin are underresearched. By theory of geotemperaturepressure system, the geotemperature, formation pressure and geotemperaturepressure system in three typical sags are characterized and their relationship with hydrocarbon distribution is explored based on measured data. Research shows that Zhuyi Depression is characterized by rising geothermal gradient from top to bottom and rising overpressure extent with Enping Formation developing slight overpressure and Wenchang Formation developing moderate overpressure. Overpressure composite geotemperaturepressure system develops in Zhuyi Depression, namely normal geotemperaturepressure system of shallow layers and overpressure system of deep layers. So far the reservoirs discovered in Zhuyi Depression are mainly fault reservoirs distributed in shallow and middle layers. However, it is highly possible that overpressure lithological reservoirs are developed in deep layers, which is predicted according to the basic characteristics of overpressure composite geotemperaturepressure system. Finding out the characteristics of geotemperaturepressure system is quite instructive in predicting hydrocarbon distribution and making exploration deployment in Zhuyi Depression.

Comparison of Petroleum Geology and Exploration Potential of Three Foreland Basins in Peru

WANG Qing，ZHAO Xu，LIU Yaqian

2013, 27(6): 1414-1424.

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Maranon, Ucayali and Madre de Dios basins are SubAndean foreland basins.The key results of study show that: (1)The tectonic events at the end of Tertiary formed the basementinvolved thrusts and reverse structures in Ucayali basin, while the effects on Maranon basin are less intensive. (2)During the Triassic period, most Paleozoic formations in Maranon and Ucayali basins are uplifted and eroded, while in Madre de Dios basin, Paleozoic formations are unaffected and relatively well preserved. (3)Generally, the main source rocks and reservoirs for the three basins become older from north to south. And the reservoir quality of foredeep region are relatively poor due to deep burying and diagenesis. (4)Anticlinal and faultedanticlinal traps are formed in the western and middle parts of the foreland basins because of compressive tectonic events, while stratigraphic traps developed in the east of the basin. Basementinvolved thrusts predominated in the Maranon basin and the northern part of Ucayali basin,which were caused by the Tertiary compression and uplift, while thinskinned thrusting are characterized in the southern part of Ucayali basin. Finally, the exploration targets are pointed out with the comparison results of the three basins. Three exploration targets exist in Maranon basin, including thrustfoldforedeep belt, carbonate reservoir in Pucara Formation as well as Cretaceous reservoir without the background of hydrocarbon accumulation in Paleozoic, and reservoir below Chonta Formation. Four types of exploration leads exist in Ucayali basin: traps in thrustfoldforedeep belt, Carbonate reservoir in Pucara Formation, as well as gas prospects of Permian formation in North Ucayali subbasin, and Cretaceous stratigraphic traps in the eastern part of the basin. And structures with inherited Paleozoic uplift in the foreland slope are main exploration targets in Madre de Dios basin.

Analysis of Seismic Acquisition Technology in Bare Carbonate Outcrop in Southern Complex Mountainous Area

LI Guilin1，KANG Jiaguang2，FENG Minggang2，WANG Tao3

2013, 27(6): 1425-1433.

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The quality of seismic data collected in complicated southern area with mountains and bare carbonates, is hard to reach the desired effect. This paper does a series of comparative analyses about technologies and methods for seismic data acquisition based on thorough understanding of the geological characteristics and the key exploration technical difficulties of seismic. (1) Using various surface survey techniques to fulfill fine surface structure survey, and to set up relative accurate nearsurface structure model and velocity model for computing statics, choosing the best well site and designing well depth. (2) Dynamic observation system is used widely in the southern complex terrain. For example, long arrangement and wide shot distance is utilized to deal with imaging of high and steep structure, observation system with increased density is employed in limestone district, and wideline observation system is adopted in the special region with caverns and fissures. (3) The conditions of excitation and reception are improved to meet the sophisticated exploration needs of multilayer lithology with naked rocks. The position of shot is optimized to adapt the lithology changing and to avoid caverns and thick pure limestone district. Double well combined excitation is often used in the limestone district, and large combined reception need more than two strings of detectors per channel. Of course, the reception effect of detector in the well is better than those on the ground. Applying the above techniques and methods to processing and analyzing the collected seismic data, the quality of the seismic profiles and single shot records are improved, and both seismic reflection wave energy and SNR are all heightened

Study on Evaluation of Effective Hydraulic Fracture Length of Gas Well and Its Influencing Factors

XIAO Hui1, GUO Jianchun1，REN Shan2

2013, 27(6): 1434-1439.

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In order to accurately determine effective hydraulic fracture length and its influencing factors of gas well,to improve the pertinence of hydraulic fracturing in Xujiahe Reservoir, West Sichuan, the relationship between effective length obtained from the gas wells and propped length obtained from net pressure fitting is determined.The degree of the parameters influence on effective length is analysed by grey correlation analysis theory, and its implication to fracturing design is also analysed.Calculation results showed that there is a noticeable correlativity between effective length and propped length (Le=0.0584 Lp13593), and effective length is shorter obviously than propped length; construction parameters (especially fracturing fluid volume) is the primary determinant of effective length in Xujiahe Reservoir,and the stress difference between barrier and interbed is the key objective factor.This research provides a reference for postfracturing evaluation and improvement of hydraulic fracturing design level.

Analysis of Production Decline for Horizontal Well in Dual Porosity Media

LUO Erhui1,HU Yongle1,WANG Lei2，CAO Chen3

2013, 27(6): 1440-1444.

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Horizontal wells have advantages for the development of particular reservoirs. In order to solve the complicated seepage flow problem of horizontal wells in dual porosity media, based on WarrenRoot model, the 3D transient model was established in this paper. The solutions of dimensionless bottomhole pressure at constant rate condition were obtained by modern mathematical methods including the Laplace transformation, finite Fourier cosine transform, and superposition integral. The solutions of rate at constant bottomhole pressure were solved by Duhamel convolution principle. McCray integral average production decline equation was built based on redefined dimensionless groups. Dimensionless production integral average decline and its derivative at constant pressure condition were programmed and plotted by Stehfest numerical inversion. The results show that type curves of production integral average decline derivative exhibit characteristics of dual porosity media. Applications of type curves matching production data can predict rate and calculate reservoir parameters.

Application of Satellite Remote Sensing in Regional Hydrogeological Investigation：Taking Cenozoic Strata in Wenquan Sheet (1∶250,000) of Karakoram Range as an Example

AN Guoying

2013, 27(6): 1445-1453.

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Using the remote sensing image of ETM+ data, this paper carried out the scale 1∶250,000 hydrogeology investigation of Wenquan sheet in Karakoram Range. The vital interpreting indexes were adequately identified on the basis of the image of various geological units, combined with comparison of the previous field investigation researches. Accordingly, the primary visual interpretations to major sediments, geomorphology and water system were studied and the scale 1∶250,000 RS interpretation map of Cenozoic strata was obtained. Moreover, the genetic type and distribution of Quaternary sediments, geomorphologic characteristics and hydrogeology signs, i.e. rivers, lakes, spring spots, groundwater overflow zones, wetlands and so on, were discussed respectively. The different forming environments of the groundwater resources reveal that the systems have two types, i.e. the alluvium and diluvium groundwater of river vale in the south and the flowsin lake basin groundwater in the north. The alluvium and diluvium groundwater system has better reserve condition, and the supplement of water resources is abundant，so that its groundwater and surface water resources constitute a unified system; but the flowin lake basin area mostly consists of lacustrinefacies sediments and is affected by the weather, so the groundwater resources are indigence except the giant several alluvialpluvial sediment fans with enough groundwater resources. The results indicate that the remote sensing technique is efficient and lowcost in hydrogeological investigation of plateau region, and it can play an important role in regional hydrogeological mapping in Tibetan Plateau.

Hydrochemical Characteristics, Origin and Evolution of the Subsurface Brines in Western Qaidam Basin

HAN Jiajun1, ZHOU Xun1,2, JIANG Changlong1, HU Liangjun3, FANG Bin1,2,SUN Qi4

2013, 27(6): 1454-1464.

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Basement rocks occur in the northwestern corner of the Qaidam Basin and piedmont deposits and alluvial and lacustrine sediments prevail in the western basin.Several NWSE trending anticlines of different sizes occur in the Cenozoic sediments in the western basin.K+rich brines have been found in the Neogene sediments in the western Qaidam Basin.In this paper, statistic methods are used to examine the enrichment of TDS, K+ and B2O3 of the subsurface brines.The results show that the TDS of the brines are of bipeak values and the brines are rich in K+ and B3+ with enrichment probabilities of 628% and 6129%, respectively.When the Piper diagram is used to study brine samples, the data points are usually too concentrated to show the changes of the main ions.The previous methods are modified to express hydrochemistry of subsurface brines.Ratios of Na+ to Cl-, Cl- to Br-, Cl- to I-, K+ to Cl-, SO2-4 to Cl- and Ca2+ to Mg2+ are employed to analyze the brine samples, indicating that most of the brine samples are not saturated with respect to halite and only a small number of the brine samples are saturated with respect to halite.The δ18O and δD of the brine samples in the study area show both the 18O shift and the D shift, indicating a long time evaporation and concentration of the brines.The subsurface brines originated from the paleometeoric water of Neogene age.The Qaidam Basin uplifted and its subsidence center moved eastwards due to the quick uplift of the QinghaiTibet Plateau after Pliocene.The basin received sediments and the caprocks of the brinebearing formations formed.In the meanwhile, the change in atmospheric circumfluence led to an arid climate.As a result, the subsurface brines become the presentday brines after a long time evaporation, concentration and under a sealed state.

Numerical Modeling of Groundwater Level Oscillations in a Coastal Leaky Confined Aquifer Induced by the Tide

CHEN Ruige1, ZHOU Xun2,3, SONG Chao2, ZHANG Huan2，XIAO Rui2

2013, 27(6): 1465-1470.

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Groundwater levels in a coastal leaky confined aquifer may fluctuate as a result of the induction of the tide.A numerical model describing 1D groundwater flow in a coastal leaky confined aquifer is established in this paper based on the finite element method.By simplifying the fluctuation in the tide as a sinusoidal wave, groundwater level oscillations in a coastal leaky confined aquifer with horizontal and linear slope initial groundwater levels are modeled.Comparison of the modeling results of these two cases shows that the groundwater level oscillations induced by the tide in the coastal confined aquifer are similar to those of the tide but the fluctuation ranges of groundwater levels are smaller than those of the tide.The degree of effect by the tide is related to distance from the coast.The fluctuation range of groundwater levels and the tidal efficiency decrease negatively exponentially with the distance from the coast.The fluctuation range, tidal efficiency and time lag of groundwater levels in the confined aquifer with horizontal initial groundwater level are smaller than those of the aquifer with linear slope initial groundwater level.The time lag of the groundwater levels to the tide increases linearly with the distance from the coast.

Determination of Coastal Aquifer Parameters Based on Measurements of Asymmetrical Tidal Fluctuations in Groundwater Levels

SONG Chao1, ZHOU Xun1,2, ZHAO Jingbo1, CHEN Ruige3, ZHANG Huan1, LI Jingwei1

2013, 27(6): 1471-1476.

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Because of the influence of tidal fluctuations, determination of aquifer parameters by using methods of pumping tests and recovery of groundwater levels becomes difficult and costs more in coastal areas. In this paper, through the study of the dynamic data of groundwater levels in the coastal aquifer in Beihai, Guangxi, we find that the rising and falling sections of the tide are asymmetrical. Based on the theory of the propagation of the sinusoidal tidal wave in confined aquifers, we provide a segmentation method to calculate the parameter of the aquifer, and compare the result with the those of the swing attenuation method and the time lag method. The ratios of storativity to transmissivity calculated with the three methods are close. This shows that the segmentation method is effective. The S/T of the rising section is larger than that of the falling section in the coastal aquifer in Beihai. The mechanism needs further analyses.

Model of Basalt Dissolution Rate Under CO2 Mineral Sequestration Conditions

LI Xiaoyuan, CHANG Chun, YU Qingchun

2013, 27(6): 1477-1483.

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Implementation of CO2 capture and sequestration has currently been proposed as an effective way to reduce CO2 emissions and alleviate greenhouse effect.CO2 mineral sequestration is the most secure and stable way among all the geological storage types and basalt has been identified as a potential host formation.Moreover, the process of rock dissolution is the basis of mineral precipitation and CO2 mineral sequestration.Therefore, it is necessary to study the dissolution rate of basalt.Previous researches concentrate on rate models for individual primary minerals in basalts under buffer solution.In this paper, we propose a dissolution rate model of basalt in supercritical CO2 solution under different temperatures.The basalt samples used in the experiments were taken from Linqu County, Shandong Province.The laboratory experiments were conducted under a range of temperatures (45-100 ℃) and 10 MPa.The related parameters in the model were calculated through least square method.Model verification were conducted using the model predicted value and experimental value under 57 ℃, 72 ℃, 92 ℃, respectively. Results show that the model is accurate and reliable, which can be directly applied for calculating basalt dissolution rate under CO2 geological sequestration conditions.

Removal of Chromium (VI) in Water by Carboxymethyl Cellulose Stabilized Nano Zerovalent Iron

JI Hang, HE Xian,CAO Xi, CHEN Jiawei

2013, 27(6): 1484-1488.

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Nano zerovalent iron (NZVI) is an attractive material for insitu groundwater remediation due to its high activity. However, oxidation and aggregation are easily happened on NZVI and lower its reduction ability. Therefore, researchers try to use environmentfriendly materials to do surface modification on NZVI. A kind of carboxymethyl cellulose (CMC) coating NZVI is synthesized (CNZVI). Its dispersity and reactivity was studied in this paper. The results showed that stabilization of CNZVI is obviously better than commercial RNIP. The higher proportion CMC coating has, the greater stabilization and dispersity CNZVI has. CNZVI also has a good performance on Cr(VI) removal in water.

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