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    22 February 2012, Volume 26 Issue 1
    Stratigraphy
    Zircon Dating of the Baiyinduxi Group in Inner Mongolia and Its Tectonic Interpretation
    GU Cong, ZHOU Zhi-An, ZHANG Wei-Kuan, LIU Chang-Feng, LIU Wen-Can, WU Yang-Sen
    2012, 26(1):  1-9. 
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    A set of medium metamorphic clasolite exposing in the area, sandwiched by the Bainaimiao arc magmatic and Wenduermiao complex rock zones in the middle Inner Mongolia, is known as the Baiyinduxi Group.   Analysis of zircon (detrital grains) by using LA-MC-ICP-MS, sampled from the quartzsand stone of the group indicates that the apparent age is dated by 206Pb/238U technique, ranging from 294 Ma to 518 Ma and coinciding with the zircon dating from the Paleozoic arc magmatite of the northern margin of the North China block.  It is suggested that the Paleozoic arc magmatite might be a sedimentsource of the Baiyinduxi Group. Protolith of the group is likely a set of forearc depositional sequence, forming throughout the process of both the subduction of the
    PaleoAsian Ocean floor and the Paleozoic magmatism, and was undergone with deformation and metamorphism due to orogenesis. Furthermore, obvious characters of the zircon samples showing magma genesis indicate that the protolith would be weathered sediments of either contemporaneous or slightly early magmatites. In addition, the fact that the Baiyinduxi Group was intruded by the endPermian granites suggests that the forming, deformation and metamorphism of the protolith should take place in the
    period from 294 Ma to 254 Ma. Therefore, a collision along the Solonker suture zone should occur in the Early and Middle Permian. 

    Geological Age, Paleoclimate and Petroleum Geological Characteristics of the Upper Part of the Suowa Formation in the North Qiangtang Basin
    CENG Qing-Jiang, WANG Jian, CHEN Meng, FU Xiu-Gen, TUN Tao, XIONG Xin-Guo
    2012, 26(1):  10-21. 
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    The upper part of the Suowa Formation in the central district of the North Qiangtang depression is the sediment during the latestage evolution of the Qiangtang basin, which deposits in tidal flatlagoonal environment. By strata correlation of the upper part of the Suowa Formation, it is found that its lithology is different in the eastern, western and southern areas, and the places where the oil shale exposed only aligned around the epicontinental restricted gulflagoon areas
    e g. Shengli River area, Changshe Mountain area and Tuolamu area in the southern margins of the North Qiangtang basin. The deposition of the oil shale is obviously controlled by differential palaeotopography. Based on the fossil assemblages in the upper part of the Suowa Formation and its underlying strata, and combined with the Re-Os dating of the Shengli River oil shale, the geological age of the upper part of the Suowa Formation is suggested to be Early Cretaceous. The Cretaceous spores and pollen assemblages and silicified wood reveal that the climate during the early period of the upper part of the Suowa Formation was warm and humid, while the climate during the later period was hot and arid. Furthermore, the vertical changed climate may be not restricted to the Shengli River region, but the whole North Qiangtang basin. The discovery of the oil shalegypsum sedimentary associations is of important implications for our knowledge of the hydrocarbon accumulation and preservation of the Qiangtang basin during the late stage evolution.

    Microfacies and Sedimentary Environments of Cretaceous Fossil Carbonate in Gamba, Southern Tibet
    LIU Yun-Long, LI Guo-Biao
    2012, 26(1):  22-35. 
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    Cretaceous marine strata are well exposed in Gamba, southern Tibet, and the study of which may provide abundant information about the evolution of TibetTethyan ocean before the collision between Indian and Asian plates. This research carried out a detailed study on the Cretaceous fossil carbonate microfacies of Gamba. Twelve types of microfacies (MF1MF12) and seven types of biofacies had been recognized. On the basis of these, the research made a preliminary discussion on the environmental evolution of TibetanTethys during Cretaceous, which could be concluded as follows: a transgression took place during the BarremianAptian; in the early of Albian, Gamba area was generally in a regressive environment; from the Late Albian to Cenomanian the seawater had a deepening trend; there was a big transgression which took place during the Turonian and lasted to SantonianConiacian; the seawater became shallow rapidly during the Maastrichtian.

    Petrology and Study of Ore Deposits
    Characteristics of Geochemistry and Tectonic Significance of Caledonian Granite in the Maerzheng Region in the South Area of East Kunlun
    LIN Er-Feng, ZHANG Gui-Lin, QIU Wei, LI Huan-Hua, SUN Zhao-Hua
    2012, 26(1):  36-44. 
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    Caledonian intrusive rock body is newly discovered in the Maerzheng region in the south area of East  Kunlun. Based on zircon U-Pb dating,the age is determined to be Early Ordovician. The lithology is composed of some tonalite, a few of anorthosite and dioriteporphyry. According to research on petrologic and geochemical characteristics of intrusive rocks, the content of Na2O is much richer than that of K2O in basic and acid rocks, which shows characteristics of rich Na. The content of  Al2O3 s from 13.21% to 16.03%, and increases gradually from basic rocks to acid rocks. The content of Al2O3 is higher than the total content of K2O, Na2O, and CaO, showing that the rock belongs to an aluminium saturation type. The rock body is characterized by obvious fractionation of REE, enrichment of LREE,weak nagative Eu anomaly (δEu values are 0.61-0.94); the rock body is characterized by richment of Ba, Th, Zr and depletion of Nb. The lithologic combinations show the  characteristics of representative TTG. Combining with the geotectonic environment map of granite in the Maerzheng region, the intrusive rock body formed as a result of Tethys ocean subduction from south to north in Early Ordovician. The age of Maerzheng Formation in Earlymiddle Permian is redefined to be Early Ordovician according to the age of the intrusive rock body and field investigation.

    orming Process of Dongguashan Stratabound Skarn Cu Deposit in Tongling, Anhui Province—Evidence from Pyrrhotite
    YANG Shuang, DU Yang-Song, CAO Yi, ZHANG Zhi-Yu, LIU Chao-Feng
    2012, 26(1):  54-60. 
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    Dongguashan copper deposit is one of representative stratabound skarn Cu deposits in Tongling, Anhui Province, and pyrrhotite is a type of ore minerals widely distributed in the deposit. Field investigation and microscopic observation indicate occurrence of sedimentary, thermally metamorphic, and hydrothermal metasomatic textures and structures in pyrrhotite ores from the deposit. Mineralogic study shows large difference in composition of pyrrhotite from the different ores, with Fe content ranging from 57.78% to 60.67%. There occur hexagonal (high temperature) and monoclinic (lowtemperature) pyrrhotite mainly formed by desulfurization of pyrite. A complex metallogenic process of early sediment and middle thermal metamorphism followed by late magmatic hydrothermal metasomatism may be responsible for the formation of the Dongguashan copper deposit.

    Discussion on the Formation of Jianchaling Gold Deposit in Lüeyang,Shaanxi Province
    JIANG Xiu-Dao, WEI Gang-Feng, ZHANG Meng-Beng, NIE Jiang-Chao, ZHANG Ying
    2012, 26(1):  61-70. 
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    Jianchaling gold ore deposit, located in the northeast edge of MianxianLüeyangNingqiang triangle
    area, is associated with ultrabasic rock and the ore bodies occur in the goldbearing altering belt round the ultrabasic rock. Since the contentious understanding of mineralization, the subsequent exploration was influenced. Beginning with the geologic characteristics, orecontrolling factors and mineralization mechanism are discussed by measurement of major, trace and rare earth elements as well as S, H and O isotopic composition. The result shows that the deposit is controlled by ductilebrittle shear zone developed in the contact belt of ultrabasic rock and Sinian dolomite, and the mineralization is not only related with the ultrabasic rock, but also tightly with the granophyres. The emplacement of granophyres results in thorough alteration of the ultrabasic rock and the metallogenic elements to be released. Since δ34S of pyrites in the ore, ultrabasic rock and dolomite is approximate to that in the granophyres, and shows definite regularity spatially, it is believed that sulfur in the ores is derived from the granophyres. Hydrogen and oxygen isotope composition of the ores lies between magmatic and meteoric water, and most of them gather together near the meteoric water line, which suggests that the hydrothermal solution originated from the granophyres and gradually turned into mixed water with the meteoric water added successively in. In view of the close relation between the deposit and granophyres and the appearance of fuchsite, it is considered that the deposit is formed between intermediate Indosinian and intermediate Yanshanian according to the isotopic ages.

    Composition in Solid Potash Deposits of Qarhan Salt Lake, Qinghai Province and Its Significance
    LI Bo-tao, ZHAO Yuan-Yi, YE Rong, HAO Ai-Bing, WANG Shi-Jun, et al
    2012, 26(1):  71-84. 
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    At present,Qarhan salt lake is the largest potash producing area in China.
    Based on the principle that
    mineral composition in potash deposits could determine potassium mining process, and that chemical composition could determine potassium-rich layers and estimate the amount of K resources, mineral composition, chemical composition and physical parameters of solid potash strata were studied by analyzing the samples from the field of Bieletan section and Qarhan section in Qarhan salt lake. Results show that the characteristics are as following: the main potassium mineral from Bieletan is polyhalite, and crystals of salt minerals are shaped perfectly and arranged closely, which indicates that the middle phase of liquefaction is available,and the resource quantity is about 250 million tons above the 22.42 m in Bieletan section, and there are five main occurrence layers for 0-0.4 m, 2.9-8.1 m, 8.90-9.70 m, 11.4-12.4 m and 15.99-16.33 m,respectively; the main potassium minerals are carnallite, and crystals of salt minerals are  loosely arranged, which indicates that the last phase of liquefaction is available, and the average concentration of KCl is 1.68% above the 3.55 m, and the main layer of potash is located above 60 cm, the resource quantity is about 89 million tons above the 3.55 m in Qarhan salt lake except Bieletan section. The research provides new data for the further research and the exploitation of solid potash.

    Hydrogeology and Environmental Geochemistry
    DeepCirculation Hydrothermal Systems Without Magmatic Heat Source in Fujian Province
    LIAO Zhi-Jie
    2012, 26(1):  85-98. 
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    In recent years, the voice that Fujian has hightemperature geothermal systems with magmatic heat source is very high. So it is a must to answer the important question. The author reviews the researched achievements of predecessors and discusses following topics: the geological setting of geothermal activity in Fujian, distribution of thermal springs, types of geothermal systems, magmatic heat source in the depth and heat structure of crust in this paper. According to the setting of geological tectonics in Fujian Province, a large number of mediumtemperature (90-150 ℃) and lowtemperature (<90 ℃) hydrothermal systems are controlled by faults and become the warm water reservoir by means of deep circulation. The limited hot water systems with higher temperature (>150 ℃)formed through deep circulation in the depths of earth crust. The author thinks that Fujian Province does not have the tectonic setting to form hydrothermal systems with magmatic heat sources.

    Evolution Process of the Downstream of Qingjiang River Since Late Middle Pleistocene in Western Hubei Province
    CHANG Hong, JIN Wei-Qun, WANG Shi-Chang, XIAO Chang-Bin
    2012, 26(1):  99-106. 
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    With the development of water resources, hydropower and tourism economy, the study on Qingjiang river has become a hot spot in many disciplines, and the formation and evolution of Qingjiang river
    were also paid academic attention to. The study on Qingjiang river evolution can contribute to investigate the pathogenesis of geological disaster, and thus provide theoretical support for local disaster prevention and mitigation. There are many ancient valleys represented by doublebottom valleys in some reaches of the downstream of Qingjiang river, which show linear continuous distribution, and the connection of these ancient valleys parallel to the current river. These doublebottom valleys are the direct evidences of river bed change of Qingjiang river. The ages of the river terraces can date the time series of the river evolution accurately. Based on analysis of the characteristic doublebottom valleys, and dating of the river terraces in the key locations, series of migration of valley in the downstream of Qingjiang river since late Middle Pleistocene were evaluated. Furthermore, the paper points out that mountain rivers may be characterized by abandoning line to choose curve, and merging each other, and transferring gradually. The result shows that difference in crustal uplift is the main reason of the valley change, and underground river communication may be another capture mode. The paper also points out that
    the slope stability should be discussed based on river evolution. 

    Features and Formation Mechanism of Debris Flow in Dabaiyang Gully  in Upper Reaches of Minjiang River
    TUN Yu-Fu, TU Bin, QI Xing, CHU Qing-Ming, LI Li
    2012, 26(1):  107-113. 
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    The Dabaiyang gully is located at the Jiaochang epsilontype structure in the north of Diexi town, Maoxian County, Sichuan Province, which is in upper reaches of Minjiang River. Two largescale flow debris events occurred in the gully in 1935 and 1991, and the flow debris in 1935 was caused by the 1933 Diexi Earthquake
    (Ms=7.5) which is huge with peak flow of 557 m3/s. After the analysis of the landform, available loose materials and water conditions of two tributaries(Dagou and Xiaogou gullies) in Dabaiyang gully, it was obtained that there are sufficient conditions for the formation of tributary debris flow, which explains the intense activity of debris flow in the Xiaogou gully:(1)the average longitudinal gradient is 275‰ in the Dagou gully and 398‰ in the Xiaogou gully, and the relative altitude is 2,023 m;(2)the total amount of loose materials is 292,100 m3  in the Dagou gully and 420,100 m3 in the Xiaogou gully, and the source of materials is abundant. The formation mechanism of debris flow was also analyzed. It reveals that  the formation of debris flow caused by the fire hose effect in the Dagou gully, and by the fire hose effect and the burst of barrage body in the Xiaogou gully. The flux of historical debris flow was calculated by mud trace investigation method,and the flux of future debris flow was appropriately forecasted, which provides valuable data for preventing debris flow disaster in Dabaiyang gully.

    Distribution, Sources and Impact Factors of Arsenic in the Major Rivers of Eastern China
    LIU Jing-Jing, YANG Zhong-Fang, ZHOU Guo-Hua, JIA Hua-Ji, HOU Jing-Xie, TU Chao, DI Da-Xin
    2012, 26(1):  114-124. 
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    This paper aims to investigate the concentration, partitioning and sources of As in the major rivers of eastern China.Samples of filtered water and suspended particulate matter were sampled, from more than 30 rivers at the lower reaches in 2007 and 2008.The results indicated that the concentration of dissolved As is averaged to 3.1 μg/L, significantly higher than most other rivers in the world.The frequency distribution histogram with more than one peak showed that most of the rivers have been obviously polluted by anthropogenic activities, which was also confirmed by the enrichment factors (EF) of the suspended particulate matter samples.The partitioning of As in the river was dominated by the dissolved phase other than the particulate one.The distribution of As in the two phases was controlled by water pH and temperature.The concentration of As is also influenced by rock type in the river basins and is significantly higher in the rivers whose catchments were mostly covered by volcanic and pyroclactic rocks, whereas the content was relatively lower in the rivers with their catchments covered by the granite and metamorphic rocks.The sources of anthropogenic pollution of typical rivers were presumed mainly coming from industrial and domestic waste water. The order of main four rivers contribution was that, Haihe(46.7%)>Huanghe(18.7%)>Changjiang(13.5%)>Zhujiang(8.3%)

     

    Eco-geochemical Characteristics of the High quality Shatang Citrus Producing Area in Sihui, Guangdong
    LI Xu-Rong, SHU Xin, ZHANG Gao-Jiang, WEN Dun
    2012, 26(1):  125-130. 
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    This study carried out an ecogeochemistry investigation on Shatang citrus plantation field in Weizheng and Didou of Sihui, Guangdong Province. Soils, leaves and fruits of citruses were sampled from Shatang citrus plantation field, and the contents of their nutritional, beneficial and harmful elements were measured. The measurements revealed the following results: (1)in the high quality Shatang citrus producing area in Sihui, the content of beneficial and nutritional elements is suitable, and the content of harmful elements, such as Cd, Cr and Hg is in accord with the environmental demand of the unpollutedfruit producing area; (2)in the ecological system of soil Shatang citrus, the variation regularity of total and effective contents of beneficial and nutritional elements is similar to each other from the depth to the surface; (3)in different organs of Shatang citrus , i.e. leaves, pericarps and fleshes, elements are enriched mostly in leaves, and harmful elements are enriched a little in fleshes, and the content of beneficial and nutritional elements in leaves are higher than that in fleshes; (4)the crimson soil with the parent materials from granites or sandstones(especially sandstones), is relatively suitable for planting Shatang citrus.

    Petroleum geology
    Controlling of Tectonic Evolution on Hydrocarbon Occurrence of Maracaibo Basin, Venezuela
    HONG Wei-Guang, YU Lian, SONG Cheng-Feng, JU Liang
    2012, 26(1):  131-138. 
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    Maracaibo Basin has experienced four tectonic phases including rifting, passive continental margin, foreland basin and Maracaibo syncline since Mesozoic, which played a significant role in the controlling of oil generation, migration and accumulation. Based on the response of hydrocarbon geologic condition to tectonic events, the author discussed the controlling of tectonic evolution on the formation of source rock, reservoir, traps as well as oil migration and accumulation. Impacted by tectonic activities, the thickness of source rock interval varied, with thicker to the north and thinner to the south. Depocentre transferred as well, formed three clastic wedges thickening in different directions, which comprised the major reservoirs of Maracaibo Basin. Besides, the change of buried depth led to the multiphase oil generation of source rock. Also, tectonic activities controlled the trap types of different layers. The revival and reversal of faults related to early rifting during the later tectonic activities offered the main pathway for oil migration. In addition, regional tilt of the layers set up a basinal structural framework for the oil migration.

    Fracture Description and Geological Modeling of Kc Formation in Ombu District, Columbia
    WANG Wei
    2012, 26(1):  139-144. 
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    Fractures play a very important role in the improvement of lowpermeability clastic reservoir properties. A research of the fracture patterns and controlling factors has a direct effect on the planning of the development program and reservoir development. On the basis of basin analysis and reservoir studies, both the relationship between fracture of the Kc Formation and regional tectonic stress cracks, and the relationship between sedimentary facies and lithology are studied through sequence stratigraphy and geological statistical analysis. The research findings reveal that there are NE and NW direction stresses that influence fracture in the work area, which form highangle fractures of NE direction. Different facies and lithology also affect fracture development. Fractures in middle fan and fringe fan facies are more developed than those in root fan, and fractures in sandstone are more developed than those in conglomerate. On the basis of geological understanding, fracture network model is established.

    Microcosmic Characteristics and the Effect of Diagenesis on the Siegenian Formation Reservoir of Devonian in X Block, Algeria
    ZHANG Chun-Meng, JIANG Zai-Xin, ZHANG Yuan-Fu, CHEN Qi, DIAO Wei
    2012, 26(1):  145-153. 
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    The microcosmic characteristics of the Siegenian Formation reservoir in X block are analyzed by studying the effect of lithology, diagenesis, pore types and clay minerals on pore structure based on cores, welllogs, and formation test data including the rock thin sections and cast thin sections, the observation of scanning electron microscopy, pressuredmercury testing and X-ray diffraction analysis of clay minerals. Reservoir lithology is mainly quartz fine sandstone with high compositional maturity. Six pore types including primary intergranular pores, intragranular dissolved pores, intergranular dissolved pores, moldic pores, cement dissolved pores and microfractures, are identified in the Siegenian Formation reservoir. The quartz intergranular dissolved pores and the quartz overgrowth cement dissolved pores are found for the first time in this area. The secondary dissolution pore is the main pore type in X block. Pore structure is mainly micropore with thin to microthroat association, beside a few medium pores with thin throat and micropores with microthroat. The diagenesis types are various. Compaction and cementation is the main reasons for the pores and pore throats decreasing. In the opposite, dissolution is important in improving the quality of reservoir. This study of the reservoir will guide the future exploration of this area.

    Comparative Study of North and South Subbasins ofGabon Coastal Basin
    QIU Chun-Guang, LIU Yan-Chi
    2012, 26(1):  154-159. 
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    The Gabon coastal basin is the passive margin basin whose sedimentary cover includes the Cretaceous, the Paleogene and the Neogene. The sedimentary strata are divided into three parts: presalt strata, salt strata and postsalt strata. According to the exploration status, postsalt petroleum system is mainly located in the north of subbasin and presalt petroleum system in the south of subbasin. The paper compares the two subbasins in the fields of the geology background, petroleum geology parameter, size and the exploration potential. The research result is that the key for the south subbasin exploration is trap identification and the key for the north subbasin exploration is sand prediction. 

    Fluid Pressure Evolution and Accumulation Effect of the Cao 113-Zhengqi 2 Area in Dongying Sag
    HAN Shuang-Biao, CENG Jian-Hui, SONG Xiu-Yan, LI Ji-Ting, TANG Xuan
    2012, 26(1):  160-167. 
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    According to the measured formation pressure and typical profile pressure distribution characteristics,we find that the overpressure occurs in the lowermiddle third Member and the fourth Member of Shahejie Formation in Dongying Sag. In vertical it is divided to three pressure systems: normal pressure, high pressure abnormal and abnormal high pressure. We analyze the paleopressure evolution using the Basin Modeling. Research shows that the overpressure evolution mainly experiences three stages:original formation, metadeclining and latestraising.Based on former analysis,overpressure is mainly caused by undercompaction, hydrocarbon generation and clay mineral transformation.The evolution of overpressure not only is well related with the hydrocarbon accumulation stages but also provides enough power.

    Reservoir Characteristics and Control Factor of Feixianguan Formation in Northern Sichuan
    TUN Bin, WANG Xin-Zhi, ZHANG Fan, YANG Ti-Meng, LI Fen
    2012, 26(1):  168-174. 
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    Research on oolitic beach reservoir of Feixianguan Formation in northern Sichuan, with a combination of macro and micro methods,shows that the main reservoir rocks are oolitic dolomite and oolitic limestone, reservoir space is dominated by secondary pores and the reservoir property is relatively poor
    appearing as fracturepore type and porefracture type with low porosity and low permeability. Reservoir of Feixianguan Formation in the study area was formed by eustatic sea level fall. Development and evolution of the reservoir were controlled by deposition and diagenesis. The generation of ancient highland of Permian Changxing reef and Longmenshan island chain provided Feixianguan Formation with high energy sedimentary condition. Relative sea level fall promoted the formation of highenergy beach, and the high energy oolitic beach on platform margin is the advantageous part for reservoir development. On the other hand, secondary pores, which markedly promoted the reservoir properties, were produced by mixing zone dolomitization and burial dissolution.

    Study on Heterogeneity of Putaohua Reservoir in Block Zhao 35 of Songfangtun in Daqing Oilfield
    CHEN Wei, LIU Da-Meng, BANG Cheng-Wen
    2012, 26(1):  175-183. 
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    Based on the theory of reservoir heterogeneity, this study researched the characteristics of intralayer heterogeneity, interlayer heterogeneity, plane heterogeneity and microheterogeneity, and analyzed the controlling factors. The results showed that the intralayer heterogeneities were controlled by the sedimentary structures, the permeability rhythms and the distribution of interbed. The distribution characteristics of physical property and interlayer were analyzed and the heterogeneities changed from weak to strong then to weak from bottom to top within Putaohua reservoir. The plane heterogeneities were mainly affected by the distribution of sandstones and sedimentary microfacies. Along the extending direction of underwater distributary channel, the heterogeneity was good. The primary intergranular pore, secondary intergranular dissolved pore and intragranular dissolved pore developed well in the study area, and the micropore structures were fine. The distribution of remaining oil was influenced by the heterogeneity in different aspects. The sedimentary facies types and diagenesis were considered as the main controlling factors of reservoir heterogeneity. Finally, this study predicted the developing area and distribution range of favorable reservoir for the main productive layers of Putaohua reservoir, and the result provided a certain foundation for the future exploration in the study area.

    Experimental Study on Controlling Factors of Foamy Oil Stability
    TUN Yong-Ban, LI Xiao-Ling, DIAO Xin, LI Song-Lin, LI Xiu-Luan
    2012, 26(1):  184-190. 
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    In the process of natural energy depletion, particularly, the foamy oil is a characteristic of “high oil viscosity, low produced gas & oil ratio, high level of oil rate, low production decline rate, and high natural depletion recovery factor”, and the foamy oil stability is a crucial factor to determine the time of “foamy oil phenomenon”. Aimed at quantifying the controlling factors affecting the foamy oil stability, the hightemperaturehighpressure (HTHP) visualized foamy oil stability test model is designed and used to test foamy oil stability under conditions of different temperature, original dissolved gas & oil ratio (GOR), pressure decline rate and pore size. Experimental results indicate that the highest temperature for stable existence of foamy oil is 60 ℃, the least original dissolved gas & oil ratio (GOR) is 5 m3/m3, the lowest pressure decline rate is 0.08 MPa/min; and it is found that the stability time of foamy oil becomes longer where porous media gets similar to the real reservoir condition, which indicates that during practical natural energy depletion phase, the “foamy oil phenomenon”  will exist for a long time. The findings above effectively guided the development of MPE3 reservoir by natural energy depletion, and played an important guidance for choosing rational operation strategy and realizing economic and efficient development for similar heavy oil reservoirs.

    Lunar geology
    Regional Structure of the Northern Land of the Lunar Mare Imbrium and the Implication
    WANG Min-Pei, CHEN Jian-Beng
    2012, 26(1):  191-197. 
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    The northern land of the lunar Mare Imbrium is the second mountain ring around the Imbrium multiring basin, and the average elevation is about -1 km. Masses of the ejecta from Sinus Iridum and Crater Plato caused severely nonuniform elevation of this area, which is clearly shown by the DEM. The craters located in this area are counted and divided into four groups based on the depth/diameter ratios. The craters with less depth/diameter ratio and larger oblateness are regarded as older craters. The distributions of older craters are more close to the Mare. The mapping of lineaments in this area reveals three preferred orientations, i.e. EW, NEESWW and NW-SE direction. The style of lineament distribution is roughly matched with the Lunar Grid System and likely formed before the Imbrium event. These lineaments, including fractures and rills, had supplied tunnels for the intrusion of basaltic magma during the period of mare basalt flooding. Some intruded basaltic magma extruded onto the surface of this land in several places with lower elevations. The average content of FeO of extruded magma is close to but lower than that of mare basalt. The features of the geological structure and evolution history of this area were summarized, and it could be concluded that there do exist marelike lands on the Moon.

    Formation Mechanism of Lunar Ridges and the  Correlation Analysis with Tidal Forces
    HUI Wei, LIU Shao-Feng, WANG Kai, XI Xiao-Xu, LI Li, JIAO Zhong-Hu, TUN Zhi-Yuan
    2012, 26(1):  198-204. 
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    As a common linear structure on the surface of the Moon, lunar ridges have certain distribution regularity. The maps of lunar ridges obtained from the DEM data of LRO(Lunar Reconnaissance Orbiter) were analyzed, and the result revealed that most lunar ridges are of compressional formation mechanism as a combination of drag folds on the surface and thrust faults underneath. The former study always explained the dynamic origin of lunar ridges by a combination of the basalt subsidence of the mare basin and the thermal shrink of the Moon, but it cannot explain the preferred NS orientation of these lunar ridges in the central area of the mare basin. This phenomenon is probably influenced by the regional compressional stress oriented to the eastwest, which is corresponding to the stress state of the tidal forces at low and middle latitudes of the Moon, and it can be inferred that tidal forces may be the main factor for the formation of these lunar ridges. According to the CCD images of Change I and panchromatic images of Lunar Orbiter and LRO,1,464 pieces of lunar ridges at low and middle latitudes of the Moon were identified, and the orientations of them were analyzed. It reveals that the overall trend of these lunar ridges is roughly consistent with the tectonic pattern predicted with tidal forces by Melosh. It can be concluded that there is a strong correlation between tidal forces and the distribution styles of lunar ridges. Furthermore, this study proves that the formation of lunar ridges is related to tidal forces.