Geoscience

Tectonic Origin Type of the Low Amplitude Uplifted Structure and Its Role in the Control of the Distribution of Oil and Gas in Mesozoic, the Ordos Basin

2013, 27(4): 755-764.

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The oil and gas exploration of Ordos Basin in Mesozoic was mainly in the range of hydrocarbon source rocks for the main sandy belt, and little attention was paid to the control of the construct reservoirs in the past.But in recent years, within the Ordos Basin, it was found that a considerable number of oil and gas reservoirs were controlled by the low amplitude uplifted structure. In this paper, on the basis of the latest seismic exploration and drilling data, outcrop survey, observation of drilling cores and seismic profiles interpreted, we conduct indepth analysis on the distribution of low amplitude structural space, formation mechanism and hydrocarbon accumulation relationship in Mesozoic of the Ordos Basin. The results show that: (1) In the east and west slopes of Tianhuan Depression, Ordos Basin, there are a large number of lowamplitude uplift structures with regular distribution, in which the largescale distribution of low amplitude noseshaped uplift structure nearly eastwest along the rows is mainly controlled by paleoprotuberance in Yanchang Formation, and the local uplift structures of Yanchang and Yanan formations are mainly controlled by the faultrelated fold, differential compaction and composite geneses; (2)The low amplitude structures affects both east and west slopes of the Mesozoic oil and gas accumulation in the Tianhuan Depression, in which large lowamplitude noseshaped uplift structure provides a large area of the oil and gas gathering tectonic setting, and near the locals, the uplift structure and nonstructural traps are favorable parts of the oil and gas accumulation. The article also pointed out that seismic exploration and basic geological research should be vigorously strengthened.

Balingshan-Huayuan Multilayer Salt and Salt Mud Tectonics in Jiangling Depression and Its Formation Mechanism

SHE Xiao-yu1, 2，GONG Xiao-xing1, 2，L Peng1, 2，LIANG Bin3，

2013, 27(4): 765-773.

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New discovery of oil and gas in the flank of Balingshan-Huayuan anticline structure in the recent years makes it necessary to have a further understanding of its structural nature. Based on the interpretation of seismic profiles, it is considered that K2y-Ex is the superimposition of salt and mud tectonics, and can be divided into salt dome salt pillar multi layered superimposed structure, salt mud dome salt mud pillar structure and salt mud dome structure. The formation of salt mud tectonics was the superposition effect of plasticized salt mud stone bedding creep which led to thickening of the single layer and the multi layer cumulation. Reverse fault was formed by the salt mud intrusion along the early hanging wall of fault and the diapirism, thus the fault had the characteristics of the upper bed showing reverse and the lower showing normal. Differential loading and volcanic thermal convection were the dominant dynamic mechanisms. The salt dome-salt pillar of K2y Lower Es occurred at the Middle Eocene with the main formation stage of the Late Oligocene, the salt mud tectonics of upper Es-Ex occurred at the Late Oligocene, and both of them finalized basically in Pleistocene. The salt mud tectonic wing strata-salt mud sealing barrier trap and the lithologic updip pinch out salt mud sealing barrier trap are the potential oil and gas reservoir exploration types.

Deformation of the Lowermiddle Jurassic Series and Their Trap Characteristics in the AmuDarya Right Bank Area

LU Shi-kuo, BAO Zi-he, YANG Jun-sheng

2013, 27(4): 774-782.

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The AmuDarya right bank area is one of the important overseas cooperative areas of the China National Petroleum Corporation. The structural feature of the Lowermiddle Jurassic series in this area is not understood well currently, which restricts the next exploration activity. In this paper, making full use of existing geological and drilling data as well as latecollective 3D seismic data, we investigate the structural feature of the Lowermiddle Jurassic series in the middle of the AmuDarya right bank area by tracing and matching of the strata surfaces, and further analyze the style of the structural trapping and their effectiveness in the formation of hydrocarbon reservoirs. The investigation indicates that four groups of faults develop in the Lowermiddle Jurassic series in this area with their strike being NWSE, nearly EW,NEESWW and NESW direction respectively, and there are obvious differences among their formation time, kinetic characteristics, evolutionary process and spatial distribution. Similarly, in this area develop three groups of fold structures with their strikes being NWSE, NESW and NNESWW, respectively. Under the influence of the structural development, the main type of structural trapping is anticline trap, which is often cut by faults and is remolded to form faultanticline composite trap. According to the main controlling factors of the trap development, the anticline traps could be classified into the anticline trap (Type A)that develops on the palaeohigh of the basement rock, and the compressive anticline trap(Type B) that develops in the Neogene era and is independent of the palaeohigh of the basement rock. The type A is drape fold in the early period and is reformed during the subsequent compressional movement, with being formalized in the Neogene era. There are obvious differences in the effectiveness of the formation of hydrocarbon reservoirs between various types of structural traps. The type A develops on the palaeohigh of the basement rock so that the reservoir of the Lowermiddle Jurassic series develops well. Contrarily, the type B is mainly located at the east of the research area, where the depositional water was so deep in the Earlymiddle Jurassic that the reservoir of the Lowermiddle Jurassic series develops badly. According to reconstruction extent of the subsequent compressional movement, the type A could be further divided into type A1 and type A2. The type A1 was reconstructed weakly during the after compressional movement, so the reactivity of the faults being located at the edge of the palaeohigh of the basement rock in the early stage couldnt destroy the primary oil gas pools of the Lowermiddle Jurassic series that were formed before Neogene completely with some native reservoirs saved. The type A2 was remolded so intensely during the after compressional movement that the reactivity of the existing faults or neogenic faults activity almost eliminate the primary oil gas pools of the Lowermiddle Jurassic series. As a whole, the effectiveness in the formation of hydrocarbon reservoirs in the Lowermiddle Jurassic series of the type A1 is better than that of the type A2, which is better than the type B.

Application of Outcrop Sequence Stratigraphy on the Initial Exploration of Shale Gas in Upper Yangtze Region：Taking Niutitang Formation in Lower Cambrian as an Example

ZHANG Jun-peng1,2 ，FAN Tai-liang1,2 ，ZHANG Jin-chuan1,2 ，LI Yi-fan1,2，WU Yue1,2

2013, 27(4): 778-985.

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In this article, with the basic principle and method of sequence stratigraphy, the discrimination and contrast of Cambrian sequence in the Upper Yangtze region were made, and the plane and spatial distribution of sedimentary facies were studied within three-order sequences in Early Cambrian. During Early Cambrian, transgression happened continuously on the passive continental marginal side of Yangtze platform, so the systems tracts mainly included TST and HST, missing LST. Therefore, two sedimentation models of two stages, i.e. transgression stage and high stand stage were identified, which revealed the sedimentary characteristics of Cambrian sequence. Taking the black shale of Niutitang Formation in Lower Cambrian as an example, the shale reservoir was evaluated, and the result indicated that the sequence stratigraphy of outcrops was evaluable in the initial exploration of shale gas.

Seismic Geomorphology, Evolution and Genesis of Shelf Sand Ridge, East China Sea

LI Lei1, WANG Xiao-gang2, CAO Bing3, SHEN Wen-long3, YANG Lin4

2013, 27(4): 783-790.

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The study on linear shelf sand ridges is always a hot topic in the field of marine geology and sedimentology. On the base of nearseafloor 3D seismic data which covers an area of 1 700 km2, the seismic geomorphology, sedimentary architecture, genesis and evolution of the shelf sand ridges were discussed in this paper. The following conclusions have been drawn from this study: (1) 7 NWSE oriented shelf sand ridge systems have developed in this study area. The seafloor in the study area is characterized by a ridgeandswale topography. Sand waves oriented NESW have been observed in the surface of the sand ridges. The ridge 1, ridge 2, ridge 4 and ridge 6 were composed of 2 to 3 crosscombining sand ridges. While the ridge 3, ridge 5 and ridge 7 were revealed as a single sand ridge in the study area. (2)The linear sand shelf ridges are asymmetric in cross section and are oriented parallel to the current direction. The sand ridges have a length between 2 km and 11km. Their heights are from 3 m to 31 m. The angle of dip of the slope is mostly less than 1°. (3) In this study area, the stage of the sand ridges between active sand ridge and moribund sand ridge have been indicated by the change of water depth and the velocity of tidal current. Investigation of sand ridges on the Quaternary shelf is of critical importance for predicting tidal sand reservoirs.

River Terraces Development and Significance of Neotectonic Movement on the Southern Margin of Taihang Mountains since Late Pleistocen

2013, 27(4): 791-798.

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The responding to neotectonic movement in Wujiawan River, which runs through transition area of two geomorphic units of Taihang Mountains and the North China Plain, is more sensitively than other water systems in Taihang Mountains, so it can record the history of uplift better. By the field investigation of sequence and sedimentary features, dating of optical stimulated luminescence(OSL), the conclusions can be reached that there are four levels of river terraces in Pingdian River, the lower reaches of Wujiawan River, T4, T3, T2 and T1 terraces heights are 61-96 m, 35-54 m,19-43 m and 3-5 m, and ages are 97.4 kaBP, 73.9 kaBP, 48.3 kaBP and 2.3 kaBP respectively. After investigation the causes of river terraces, T4, T3, T2 terraces should be the results of tectonic uplift, otherwise T1 is climatic terrace. It reveals that the amplitude of uplift of the area is 90 m at least after three stages of stable sedimentation and rapid uplift since Late Pleistocene(Qp3), the amplitude and the rate of uplift are 26-42 m and 1.11-1.79 mm/a, 11-27 m and 0.43-1.05 mm/a, 16-39 m and 0.35-0.85 mm/a. This study is of great value, which provides actual material for the research of river terrace and neotectonic movement on the southern margin of Taihang Mountains.

Application of Radon Measurement to Prospecting for Buried Faults in No.3 Anticline of Muli Antimony Deposit in Yunnan, Southwest China

SHEN Xiao-ming1, LUO Xian-rong2

2013, 27(4): 799-808.

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The Muli antimony ore bodies in Yunnan have close relationship with the faults. To solve the deep and edge prospecting problem of the deposit, the FD-3017 RaA radon measuring instrument was used to detect the buried faults in No.3 anticline of Muli antimony ore bodies. The data indicate that all of the known faults (including faults of Xiaopunong, F1, F2 and F3) and ore bodies show clear radon anomaly. It is suggested that the radon measurement may be an effective method to search for buried faults and an auxiliary method to search for buried deposits which have close relationship with the fracture structure including faults, joints and cleavages. The results reveal that there are two large buried faults in the core of the anticline and the northeastern study area, respectively, and there are many secondary faults of the known faults and the predicted faults. In the end, the radon anomaly model of the study area is summarized

Fracture Characteristics and Main Controlling Factors of Ordovician Outcrop Zones of Taihang Mountains in the North-west of Henan Province

NIU Yong-bin1,2,DONG Xiao-bo1, ZHU Xin-sheng1, ZHOU Shuo1, GAO Wen-xiu1

2013, 27(4): 809-818.

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Based on the summarizing of previous studies and the field observation of five outcrop zones of Taihang Mountains in the north-west of Henan Province, the fracture characteristics and main controlling factors were studied by using methods of geostatistics and tectonic stress analysis. The results show that high-angle fractures are the main type in the research area, which can be divided into four groups, i.e.NNW, NWW, NNE and NEE directions. The down-cutting depth of fractures changes greatly from 0.15 m to 1.4 m. The linear density is 1 to 10 per meter and the fracture opening width is usually between 0.1 cm and 3 cm. The fracture filling degree includes unfilled, half-filled and completely filled types, which is characterized by the dominance of unfilled type. The fracture fillings include calcite, plaster mass and irony materials, which are mainly calcites. By analyzing the main controlling factors and the genetic mechanism, it is deduced that the fractures formed in four periods, i.e.Paleogene, Miocene epoch, Pliocene epoch to Early Pleistocene, later Middle Pleistocene. Tectonism, lithology and layer thickness are three main factors that affect the fracture development; the tectonism has a significant influence on the trend, dip, opening width, down-cutting depth and filling condition; the linear density is closely related to lithology and layer thickness; the fractures is developed with the growth of dolomitic content, and the mean value of linear density has a good linear relationship with the mean value of layer thickness.

Research on U-Pb Chronology in Xitian Pluton of Hunan Province

CHEN Di，MA Ai-jun，LIU Wei，LIU Yao-rong，NI Yan-jun

2013, 27(4): 818-830.

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In this paper, the U-Pb geochronology of zircon of the 8 samples in Xitian pluton of Hunan Province has been measured, using SHRIMP and LA-ICP-MS technique. All zircons from Xitian granite pluton have the oscillatory zoning and high Th/U ratio revealed by the cathodoluminescence (CL) images, which suggest that zircons are magmatic zircons. Based on the new data and the latest reported high-precise dating of the related granites, the magmatic activities in the study area can be ascribed to four stages as follows: The first stage of Indosinian(230-224 Ma)，the peak was about 228 Ma;The second stage of Indosinian was about 215 Ma; The first stage of Yanshanian(160-147 Ma),the peak was about 151 Ma; The second stage of Yanshanian was after 141 Ma.

REE Geochemical Characteristics and Genesis of Granites in Baoyintu Molybdenum Deposit, Inner Mongolia

YANG Fan1, XIAO Rong-ge1, LI Na1, QU Yun-yan1, HE Zhong-yin2, FENG Gang2

2013, 27(4): 831-840.

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The Baoyintu molybdenum deposit, located in western Inner Mongolia, is a large scale porphyry molybdenum deposit which is discovered in recent years. This paper focuses on discussing REE geochemistry of ore-forming granites and genesis of granites. Based on analyses of REE distribution patterns, characteristic value (including ∑REE-LREE/HREE and δEu-LREE/HREE) and petrochemical compositions, comparisons with REE compositions of mantle-derived magma and Nanling granites, authors deduce that genesis of ore-forming granites is related to melting of the continental crust.The compositions of granites vary in the sequence of plagiogranite→monzoniticgranite→K-feldspar granite→graniteaplite. The chemical variation during the magmatic evolution process is in favour of mineralization,especially the late-stage K-feldspar granites.

Research on REE Geochemical Characteristics of the Xiaba Pb-Zn Ore Deposit, Guangxi

OU Zheng1，2, WEI Chong-tao1, MO Shao-wen2, GAO He-feng3, Santigie Kekuda Sesay1,

2013, 27(4): 841-846.

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This paper used inductively coupled plasma mass spectrometry (ICP-MS) to determine the concentration of rare earth elements (REE) and the composition of ore and surrounding rocks of Pb-Zn deposit from Xiaba, Guangxi Province, and discussed the geochemical characteristics and the source of ore-forming fluid of the deposit. The results show that the total rare earth content is quite low, ranging from 0.51×10-6 to 36.53×10-6, while LREE/HREE is about 3.06 to 6.05. In different types of ore body, the content and distribution patterns of REE vary in a quite wide range, and negative anomaly for Ce and both positive and negative anomaly for Eu are presented in the samples. Combined with the REE parameters and geological features of the ore, it can be deduced that the metallogenic fluid source of Xiaba deposit is a hybrid of ore-bearing brine and deep circling underground water under special physical-chemical condition.

Research on the Mineralogical Characteristics of Metallic Mineral and Mineralization of Huajian Gold Deposit，Eastern Hebei Province

KONG De-xin1，YIN Jing-wu1，HU Jian-zhong1，LI Jiao1，GUO Yuan1，

2013, 27(4): 847-858.

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Huajian gold deposit is located in the eastern part of Hebei Province where contains abundant iron and gold resources.In order to decipher the mechanism of this gold deposit and guide the future mineral deposit exploration，we have studied the metallic mineral characteristics and compositional variations. In this paper，field investigations，microscopic identification and electron microprobe analysis are complished on the metallic minerals in Huajian gold deposit. Hydrogen，oxygen and sulfur isotopes are also analyzed to confirm the source of hydrothermal solution and sulfur of the ore-forming stage. The results suggest that pyrite and quartz are the main gold-bearing minerals in Huajian gold deposit and Au mainly exists as silver-bearing native gold.In this case，silver-bearing native gold generally occurs in the micro-fissures of pyrite or as inclusions in pyrite.The average sulfur value of pyrite is 52.11% and it is lower than the theoretical value，indicating a magmatic hydrothermal genesis.The δD and δ18O values of the fluid vary from-77.9‰ to-68.1‰，and from 9.9‰ to 15.7‰，respectively.The δ34S values of pyrite vary from 3.2‰ to 6‰.They indicate that the sources of ore-forming solution are mainly magmatic fluid and sulfur is derived from deep-seated magma.We argue that the Huajian gold deposit is a magmatic hydrothermal deposit.

Geological-Geochemical Characteristics and Genesis of Kalagailei Copper-Gold Deposit in Zhaosu County, Xinjiang

LI Xiao-fei1,2, GE Wen-sheng1, XUE Yun-qing3, JIA Qi3, GUO Peng-zhi3, FU Qiang1,

2013, 27(4): 859-868.

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Kalagailei copper-gold deposit, located in the western Nalati tectonic belt of Western Tianshan Mountains, Xinjiang, is the first Cu-dominated volcanic hydrothermal deposit accompanied by Au and Co etc. in this metallogenic belt. The hydrogen and oxygen isotope compositions show that ore-forming fluids were mainly made up of magmatic water in the early period and added by rainwater in the later period. The characteristics of sulfur isotope show that the sulfur sources originate from the deeper crust and upper mantle, accompanying with the interfusion of strata sulfur. The lead isotope compositions indicate that lead sources are mixture of crust and mantle. The Re-Os isotopic model age of molybdenite is (259.6±9.7) Ma, indicating that early stage mineralization age of the deposit falls into the mid-late Permian. The authors probe into the genesis and consider the volcanic rocks of Dahalajunshan Formation are the source beds. At the collision-extensional stage of late Carboniferous, mineral-enriched magmatic hydrothermal fluids originating from the deep crust migrate through regional and large faults, volcanic vents and shallow faults system, and extract early mineral elements, forming the orebody in the favorable tectonic positions.

Discussion on Material Sources of Jincheng Gold Deposit, Luoshan County, Henan Province

LIU Hong1,2, Lyu Xin-biao2,3, SHANG Shi-chao2, WANG Yu-qi2,4, LI Chun-cheng2,

2013, 27(4): 869-878.

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The Jincheng gold deposit, in the Luoshan County, Henan Province, lies in south of Tongbai-Shangcheng ductile shear zone. The ore deposit, which occurs in the east side of Lingshan granitic mass, is hosted in the lower stratum of Huwan formation complex in the upper Proterozoic. Based on the geologic feature, we conducted the comparative study on REE and trace element characteristics of granite-porphyry dyke and Lingshan granitic mass, moreover we further investigated the oxygen isotope compositions of the paragenous quartz and the carbon isotope compositions of fluid inclusions within paragenous quartz, as well as the sulfur and lead isotope compositions of the paragenous pyrite. We found that the REE and trace element characteristics of granite-porphyry dyke is similar to those of the Lingshan granitic mass, and that the granite-porphyry dyke originated in the magmatic hydrothermal activities in the late Yanshanian stage. The δ34S value of pyrite in the main orebody ranges from -6.9‰ to +5.5‰ with a mean of +2.3‰. The lead isotope composition show the typical characteristics of the lower crust lead isotope, similar to those of Huwan formation complex. The δ18O values in the ore range from +5.5‰ to +11.4‰ with a mean of +2.3‰; the δ13CCO2PDB values of fluid inclusions within paragenous quartz range from +6.3‰ to +2.8‰ with a mean of +4.4‰. The δ18O-δ13C results suggest that ore fluids mainly came from magmatic hydrothermal fluids with participation of small amounts of atmospheric water. According to our research，we consider that the ore-forming materials are mainly derived from the Huwan formation complex, and secondly derived from the magmatic hydrothermal activities in the late Yanshanian stage.

Origin of Metallogenic Materials of the Chang'an Gold Deposit in the Southern Ailaoshan Belt: Evidence from Sulfur and Lead Isotopic Composition

LI Shi-hui1，2, ZHANG Jing1, YANG Li-qiang1, WANG Huan1

2013, 27(4): 879-887.

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The Changan deposit is one of large gold deposits in the Southern Ailaoshan metallogenic belt in Sanjiang region, and the occurrence of ore bodies is controlled by the brittle fractured zone of Ganhe fault. The ore-hosted rocks are dominated by Lower Ordovician sandstone and clastic rocks. The δ34S values of pyrites in the magmatite and ores range from-3.49‰ to +3.57‰, concentrating between +1‰ and +3‰. The comparative study on sulfur isotopic compositions of the ores, wall rocks and magmatic dikes suggests that the sulfur in ore-forming fluid was most probably sourced from the ore-hosted strata and partly mixed with that in the Himalayan period magmatic hydrothermal fluid. The Pb isotopic values of the ore vary in a narrow range, i.e., 208Pb/204Pb=38.722-40.649, 207Pb/204Pb=15.604-15.813 and 206Pb/204Pb=18.788-19.761, respectively, showing that the gold ores are relatively rich in radiogenic lead. It is suggested that the ore lead was sourced from the upper crust with higher maturity, indicating that the lead and other ore-forming elements should be mainly derived from the Devonian dolomite and clastic rocks, the Ordovician sandstone in mining area. At the same time, the lead isotopic compositions of altered rock and magmatite mainly show the characteristics of orogenetic belt. Comprehensive research proves that the metallogenic materials only have a little relationship to the magmatite. That is to say, the ore-forming materials were mainly sourced from the ore-hosted wall rocks, and the Cenozoic magmatism provided the heat source and part metallogenic materials for the further enrichment of the Changan gold deposit.

ESR Dating of Quartz from Linxi Fluorite Deposits, Inner Mongolia and Its Geological Implications

CAO Hua-wen, ZHANG Shou-ting, ZOU Hao, FANG Yi, ZHANG Peng, WANG Guang-kai

2013, 27(4): 888-894.

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The Linxi fluorite deposits, Inner Mongolia, are mainly hosted in the vocanic-sedimentary stratum and acidic intrusions in the Late Paleozoic-Mesozoic, controlled by the NS and the NNE trending fault zone. Quartzs (quartz vein) are massively formed within the same period in the deposit. The ESR dating was used to study the fluorite-forming time by measuring the 8 pieces of paragenetic quartz samples in the deposits. The results show that the ESR dating of quartzs from Linxi fluorite deposits ranges from 126.6 to 157.3 Ma, with an average of 137 Ma, indicating that the metallogenic hydrothermal fluid mainly formed in the Late Jurassic-Early Cretaceous. Combined with geological characteristics of deposits and the global fluorite deposits, Linxi fluorite deposits are of hydrothermal origin, and of fracture-filled metasomatic type, which are formed in the conversion period of the middle Yanshanian stage intraplate tectonic regime.

Research on Oil Accumulation Process of Lithologic Reservoir in Chang 8 Member of Yanchang Formation, Xifeng Oilfield

LIU Zhen1,ZHU Wen-qi2,XIA Lu3,PAN Gao-feng1,WU Xun-da4,GUO Yan-ru1

2013, 27(4): 895-906.

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Using quantitative methods, the evolution process of formations, geothermal field, hydrocarbon generation and drainage, diagenesis, porosity, accumulation times, traps and the driving force window are simulated, and the space-time matching of key accumulation factors are further analyzed. Results show that beginning form the Early Cretaceous, the regional structural subsidence and incidental significant geothermal event triggered the generation and drainage of source rocks. Dissolution of organic acid before accumulation period dramatically improved the porosity of Chang 8 reservoir which provides enough space for oil accumulation. Following time-space evolution, the increasing pressure difference between source rocks and reservoirs makes the oil injected into reservoirs possible. Beginning at the accumulation period, the steady development of driving-force window and trap window not only promotes the efficiency of oil injection but also makes those already accumulated oil preserved safely. The time-space matching of key conditions of oil accumulation shows that oil accumulation in Xifeng oilfield is a natural process, namely, the porosity in Chang 8 reservoirs is perfect before the oil accumulation period, and after which, becomes denser and denser under compaction and cementation.

Enriched Mechanism of Natural Gas in the Feixianguan-Changxing Formations in the Northeast Sichuan Basin

FENG Chong1， GUO Tong-lou2，ZOU Hua-yao1，CHENG Xiao-zhuan1

2013, 27(4): 907-914.

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In Northeast Sichuan Basin, the accumulation elements of different areas of Feixianguan-Changxing Formations are the same, but the enriched degrees of the nature gas vary from region to region. In order to disclosure the enriched mechanism of the nature gas, this paper analyzed the origin of the nature gas in Feixianguan-Changxing Formations, the hydrocarbon generating density of main resource rocks, the characteristics and the scales of the reservoirs, the conservation condition of the natural gas, the history of hydrocarbon generation and the adjusting process of the oil and gas reservoirs with the analyzed and examined data of resource rocks, the data of the cores and lamellas, and the data of the well logging and cutting logging, etc. Results show that: (1)the Northeast Sichuan Basin is in the center of hydrocarbon generation or its vicinity , and the primary migration distances of the oil and gas are short; (2)the lithologic gas reservoirs of reefs and sands are independent, and the distribution of the reservoirs controls the scales of the oil and gas reservoirs; (3)several gypsum mantles cover the natural gas reservoirs and the conservation condition of the natural gas is good; (4)the high temperature made the early oil reservoirs cracked to the present gas reservoirs; (5)with the tectonic movement, the accumulating processes of gas are separated into three steps, the formation of the early oil reservoirs, the cracking of the early oil reservoirs with the formation of the gas reservoirs and the formation of the present gas reservoirs. Discussing the enrichment mechanism of natural gas is useful for finding the beneficial target areas in the Northeast Sichuan Basin when natural gas is explored.

Sedimentary Characteristics of Fan Deltas and the Dominated Factors in W11 Area of 1st Member of Liushagang Formation in Weixinan Depression, Beibuwan Basin

LI Mao1，2, LI Sheng-li3, JIANG Ping1，2, YU Xing-he3, ZENG Xiao-ming2,3, DAI Ming

2013, 27(4): 915-924.

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Fan deltas of the abrupt slope and the gentle slope areas, were developed in the W11 area of 1st Member of the Liushagang Formation in Southwestern Weizhou Depression, Beibuwan Basin. Based on the lithology, logging and seismic data, the different characteristics between these two kinds of fan deltas were analyzed and the main controlling factors of the fan delta were discussed. The fan deltas at abrupt slope area, which were mainly distributed at the steep slope zone of the middle part of 1st Member of the Liushagang Formation in the northern of the study area, were comparatively coarse grain-sized and were mainly thick-layer sandstone rock deposited from the gravity flow, with large depositional thickness and small scale planar distribution. However, the fan deltas at gentle slope, which were widely distributed in the lower part of 1st Member of the Liushagang Formation at Southwestern Weizhou Salient in the southern of the study area, had a mixed gravity flow and tractive current with relatively fine grain-sized, a small depositional thickness and a wide range of planar extension. The development and distribution of these two kinds of fan deltas were mainly controlled by structural framework, paleotopography and basal level change.

Contrast Experiment about Dissolution of Feldspar in Different Freshwater Diagenetic Systems

XU Mei-gui1,2,ZHANG Shao-nan1,3,FU Mei-yan1,2,FAN Xiao-cong1,2,

2013, 27(4): 925-933.

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In the same conditions of temperature and pressure(25 ℃,101,325 kPa), the interaction of atmospheric water-sandstone by comparative experiment of feldspar dissolution under different systems is explored in this paper, and it is confirmed that atmospheric water can eluviate aluminosilicate minerals. Feldspar dissolution by natural fresh water is simulated by comparative experiments among open system with sludge, open system without sludge and closed system without sludge. After the reaction, the change in the concentrations of Al3+,Si4+,Ca2+,K+ and HCO-3 ions in solution and scanning electron microscopy (SEM) observation showed that feldspar in the three systems have different levels of dissolution. Dissolution of different degree is open system with sludge＞open system without sludge＞closed system without sludge. Not only feldspar dissolution but also the quartz micro-dissolution phenomena are observed in open system without sludge and closed system without sludge. Degree of feldspar dissolution has relation with organic matter content and pH value. The phenomenon of feldspar dissolution in open system is more obvious than in the closed system.

Logging Identification for the Tight Sandstone Reservoir Fractures of Yanchang Formation in Zhenjing Oilfield of Southwestern Ordos Basin

ZHAO Yong-gang1 ，PAN He-ping2，LI Gong-qiang1，LUO Miao2

2013, 27(4): 934-940.

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It is very difficult to evaluate low porosity and low permeability sandstone reservoirs and to develop these reservoirs using logging data. The fracture development could affect the production of this type of reservoir and is very important. In order to take advantage of conventional logging data to evaluate tight sandstone reservoir fracture development, in this paper, based on the caliper, resistivity, density and sonic logging curves, eight fracture indication parameters were calculated. Then an integrated recognition parameter of fracture was constructed by using the eight parameters.The integrated parameter for recognizing fractures was more correct. This method was used for the identification of tight sandstone reservoir fracture in Zhenjing oilfield of southwest of the Ordos Basin and the correct rate is 81.4% for all samples. Therefore, this paper provides a way for the use of conventional logging data to evaluate the fracture development and effectiveness of tight sandstone reservoirs, and it is valuable to the exploration and development of tight sandstone reservoirs.

Solid-Fluid Interaction in Glutenite Reservoirs of the Upper Submember, Fourth Member, Shahejie Formation in Northern Slope of Dongying Sag

DONG Guo-guo1,2, HUANG Wen-hui1,2, WAN Huan1,2，WANG Hua-jun1,2

2013, 27(4): 941-948.

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In northern Dongying Sag, the reservoir formation and distribution of upper submember of the fourth member in the Shahejie Formation is the study focus in recent years. It is an important oil-bearing sequence. The solid-fluid interaction mechanism and its influence on physical properties of reservoirs could be studied by the observation of polarizing and fluorescence microscope and the analyses of SEM on thin sections in combination with regional tectonic evolution and thermal history of organic matters. Conclusions are drawn as follows. There are seven active fluid episodes in the variation of diagenetic environment, namely, alkaline, acidic, alkaline, acidic, alkaline, acidic and alternating alkaline and acidic setting, respectively. The interaction of acidic fluid and solid presents significant dissolution of carbonate minerals and feldspar, and quartz overgrowth to enhance the reservoirs; while the interaction of alkaline fluid and solid is characterized by quartz dissolution, feldspar overgrowth and the precipitation of ferrocalcite, ankerite and anhydrite, which largely infill pores and destroy the reservoirs. There are two hydrocarbon expulsion episodes, namely, the deposition period from the second member of Shahejie Formation to Dongying Formation, and the latest one of Guantao Formation. These two events are in correspondence with the development of two secondary pore zones.

Changes of Sedimentary Environment Since Late Middle Pleistocene of Qingtu Lake in Northwestern Margin of Tengger Desert

WANG Li-yuan, CHENG Jie, XIN Wei, ZAN Li-hong

2013, 27(4): 949-958.

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Based on the analyses of sediment, OSL dating, grain size, magnetic susceptibility of lake sediments from core ZK1 in Qingtu Lake, the northwestern margin of Tengger desert, this paper reconstructs the history of lake evolution since late Middle Pleistocene. The results indicate that Qingtu Lake experienced dry-cold and warm-wet climates in Middle Pleistocene, warm-wet and dry-cold climates in Late Pleistocene, which is accorded with climate cycle characteristics of the last glaciation and last interglaciation in MIS. Meanwhile, Qingtu Lake experienced the evolutions of the dry-cold and warm-wet climate in the Holocene. Therefore, this study reflects the evolutions of climate in the northwestern margin of Tengger desert during Late Quaternary and provides the basis for Qingtu Lakes climatic and environmental evolutions since late Middle Pleistocene.

Sedimentary Characteristics and Stratigraphic Correlation of the Late Precambrian Strata in Guozigou of Yili，Xinjiang

FENG Bo1,2，LIN Jin-yan1,2，NIE Li1,2，MA Shang-wei1,2，LI Ying1,2

2013, 27(4): 959-967.

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Guozigou in Yili of Xinjiang is located at the west margin of north Tianshan. The Precambrian strata in Guozigou are exposed relatively completely，which can be subdivided into Kayingdi Formation，Tarqiate Formation and Talisayi Formation from bottom to top. Kayingdi Formation and Tarqiate Formation are interglacial deposits，and Talisayi Formation is a glacial deposit. Kayingdi Formation mainly consists of argillaceous siltstone，silty mudstone，lithic sandstone and feldsarenite，in which sedimentary structures are developed，including parallel bedding，horizontally laminated bed，flaser bedding，sand lens and trough cross stratification. Kayingdi Formation can be subdivided into littoral subfacies (mixed flat microfacies and sand flat microfacies) and neritic shelf subfacies (normal neritic microfacies and storm deposit microfacies). Tarqiate Formation consists of argillaceous siltstone and silty mudstone with high shale content，in which a great quantity of horizontally laminated beds are developed，and this formation is a shallow-marine detrital deposit with three sedimentary sequences from deep to shallow. Talisayi Formation is a tillite deposit and can be subdivided into basal till subfacies，proglacial littoral subfacies and typical ice rafting-marine subfacies. According to sedimentation type，depositional combination，sedimentary facies and stratigraphic correlation with Quruqtagh area in Xinjiang，and combined with previous research results，it is inferred that these strata belong to Nanhua System. Meanwhile, Kayingdi Formation and Tarqiate Formation can be correlated with Huangyanggou Formation in Quruqtagh area，and Talisayi Formation can be correlated with Teruiaiken Formation. The existence of the ancient land in the study area is also discussed by analysis of Nanhua System petrology, and the evidence is provided in the end.

Relationship between Sequence Stratigraphic Framework and Petroleum of Shahezi Formation in Qikeshu Oilfield

CHEN Xian-liang1, JI You-liang1, FAN Tai-liang2, WANG Hong-yu2, HAO Yue-juan2

2013, 27(4): 968-977.

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On the basis of the sequence stratigraphy and sedimentology, the sequence stratigraphic framework and sedimentary facies of Shahezi Formation in Qikeshu oilfield, Songliao Basin were established, and the distribution characteristics of sandstone and the rules of hydrocarbon accumulation within the sequence stratigraphic framework were analyzed, then the type and distribution of lithologic reservoir were predicted. The results show that Shahezi Formation is a third-order sequence and can be subdivided into two fourth-order sequences, experiencing an evolution process from rapid regression to slow transgression. The development of sand bodies is controlled by the tectonic effect, lake-level change and sediment supply, and the sand bodies mainly grow in the descending base-level cycles of the fourth-order sequence, which are favorable exploration zones for lithologic reservoirs.

Land Quality Geochemical Assessment in Guanzhong Area, Shaanxi Province

LU Ting, WANG Ming-xia，REN Rui，WANG Hui-feng，YIN Zong-yi， WANG Xian-wei

2013, 27(4): 986-992.

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About 30,000 km2 in Guanzhong area had been done during the muti-target reginal geochemical survey of Shaanxi Province. The geochemical assessment of land quality in Guanzhong area was taken according to beneficial elements, harmful elements, healthy elements and pH etc. P,N,Mo,Zn,Cl,Si,Na,Cd,F,I,Se contents and pH were chosen as index of assessment, based on the oil environmental and oil fertility quality evaluation. Land of Guanzhong area was divided into five levels: high, better, good, middle and low grades. The high grade is mainly distributed in Sanyuan, Gaoling and Fengxiang, which accounts for 1.8% of the whole area; the better grade accounts for 66.1% of the whole area; the good land accounts for 11.2%, which is distributed in Qian County-Chunhua-Bin County；the middle grade is dispersedly distributed in loess rough terrain and loess plateau, which accounts for 13.9%; the low grade is mainly distributed in Dali-Hua County，Xian urban area and Tongguan,which accounts for 7% of the whole area.

Surveys on Radon Concentration and Distribution in Soil and Air in Aba, Sichuan

ZHOU Yun-long1, CEN Kuang1, SHI Ze-ming2

2013, 27(4): 993-998.

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By using an IED-3000 portable emanometer produced by Beijing Nuclear Instrument Plant, this paper conducted a preliminary investigation on the radon concentration of soil and air in Aba, Sichuan. The results reveal three aspects as follows: (1) the radon concentration of air in the study area is around background value of 185 Bq/m3; (2) the radon concentration of soil ranges from 2,736 Bq/m3 to 93,486 Bq/m3 with average value of 26,021 Bq/m3, which is higher than the average value of the other domestic cities of 7,300 Bq/m3, and the average values of radon concentration in 91 measured points are over 20,000 Bq/m3 among 156 measured points; (3) the radon concentration of soil in five districts is sorted in descending order as Heishui＞Maerkang＞Rangtang＞Aba＞Hongyuan. The radon concentration of soil in Aba is affected by geological environment, soil porosity, geotechnical properties, moisture content of soil, and the radon concentration of soil in most districts of the study area is extremely high, thus it is necessary to take measures to control and lower indoor radon concentration of the study area.

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