Geoscience

Late Early Cretaceous Magmatic Event in Hongliuxia in Eastern Sector of the Altyn Tagh Fault, and Its Regional Tectonic Implications

WANG Xunlian, ZHOU Hongrui, WANG Zhentao, GAO Zhengsheng, YANG Lichao, ZHANG Haijun, YU Zidong, JU Pengcheng

2018, 32(01): 1-15. DOI: 10.19657/j.geoscience.1000-8527.2018.01.01

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This paper made a comprehensive study on the petrology, zircon morphology and LA-ICP-MS U-Pb geochronology of the Hongliuxia and its peripheral volcanic rocks in the eastern sector of the Altyn Tagh Fault. The results show that there are two types of zircons in the samples. One is a type of long-columnar magmatic zircons sampled from the volcanic neck, whose weighted average age is (109.0±1.6) Ma (late Early Cretaceous), and it represents the formation age of Hongliuxia volcanic rocks. This age agrees well with previous results through different approaches. The other is a type of sub-rounded or oval inherited zircons sampled from the peripheral basalts, and most of them have the core mantle structure. The age distribution ranges from (138±2) to (2,376±74) Ma, which show the diverse age peaks. These inherited zircons are all captured from the Lower Cretaceous or/and earlier strata during the rising of basaltic magma. Their age peaks closely respond to the complex multi-phase magma and tectonic events in the late Early Cretaceous or earlier time of the Altyn Tagh Fault. In addition, part of the age peaks coincident with the age of Paleozoic granite in the southern Altyn Tagh Terrane suggests that the Altyn Tagh Terrane was once connected to the Qilian Block.

Petrogenesis and Geological Significance of the Wenjiaping Granite in Jianglang Dome, Southern Rim of Songpan-Garze Orogenic Belt

ZHU Yudi, DAI Yanpei, WANG Lili, LI Tongzhu, ZHANG Huihua, SHEN Zhanwu

2018, 32(01): 16-27. DOI: 10.19657/j.geoscience.1000-8527.2018.01.02

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The petrogenesis and emplacement age of the Wenjiaping granite in the Jianglang dome remains unknown. Our petrological and geochemical data show that Wenjiaping granite is biotite granite, which is mainly composed of quartz (ca.40%), K-feldspar (ca. 35%), biotite (ca.15%) and plagioclase (<10%), with high SiO₂ (67.70%-70.09%), Na₂O+K₂O (7.43%-7.84%) and Zr+Nb+Ce+Y contents (363×10^-6-476×10^-6), high Mg^# (35.9-38.7) and 10,000×Ga/Al (2.58-2.84) values. They display enrichment of LREE and large ion lithophile elements (LILE) and depletion of high field strength elements (HFSE). Zircon U-Pb dating and Hf isotopic tracing indicate that the granite was crystallized at (164.6±0.9) Ma (n=21, MSWD=3.2) with ε_Hf(t) values of -13.0 to+1.4. Based on comprehensive studies, we proposed that the Wenjiaping granite belonged to a post-orogenic A2-type granite formed in lithospheric extension. The magma was chiefly originated from the Mesoproterozoic Liwu Group in the core of the Jianglang dome, with minor mantle-derived components. Combined with other geological evidence, we advocated that the doming of the Jianglang dome took place between the Early and Middle Jurassic, and the regional Cu and W mineralization was most likely associated with ca.165 Ma granitic magmatic activity.

Characteristics of Chronology and Geochemistry for the Cenozoic Alkali-rich Porphyry in Lijiang Area, Western Yunnan and Their Significance

HUANG Yonggao, LUO Gai, ZHANG Tong, XIONG Changli, JIA Xiaochuan, YANG Xuejun

2018, 32(01): 28-44. DOI: 10.19657/j.geoscience.1000-8527.2018.01.03

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The Cenozoic alkali-rich porphyry in Lijiang region of Western Yunnan is located in the connection part between Sanjiang fold orogenic belt and southwest of Yangtze plate, including alkali rock and alkali-granite. Alkali rock includes orthophyre, syenite and trachyte-prophyry, while alkali granite includes granite-prophyry, monzonitic granite-prophyry and masanophyre. The zircon U-Pb dating indicates that the ages of those porphyry are between 34.6 and 37.1 Ma, which is consistent with the ages of Cenozoic alkali-rich porphyry in Western Yunnan. Geochemical results showed that alkali rock belongs shoshonite series, with SiO₂ content of 54.54%-67.70%, K₂O>Na₂O. Alkali-granite belongs high-K calc-alkalic series, with SiO₂ content of 67.16%-70.66%, K₂O<Na₂O. They are both enriched in alkali (Na₂O+K₂O=7.03%-11.70%), showing metaluminous and weak peraluminous (A/CNK=0.64-1.15) characteristics. The porphyry shows alkali and adakitic geochemical characteristics, with enrichment of LREE and LILE(Sr, Ba, K, Pb, and so on), deficit of HREE and HFSE(Nb, Ta, Ti, and so on), with high Sr content and ratio of Sr/Y, La/Yb, low Y and Yb contents, and low values of Mg^# (<0.5). The comprehensive study shows that the porphyry is associated with partial melting of the base of thickened lower crust caused by decompression melting and underplating of mantle-derived magmas, formed from the structure transition phase of late-collisional between Indian and Asian continents, and was the magmatic event response to syn-collisional processes in the structural transform zone of southeast of the Tibetan orogen. It is considered that there is great gold-polymetallic prospective reserves of porphyry-hydrothermal deposits. This paper provides important constraints for understanding deeply the tectonic-magmatic-metallogenic processes of the Lijiang porphyry metallogenetic belt.

Geochemistry, Zircon U-Pb Geochronology and Hf-Sr-Nd Isotopic Characteristics of the Rhyolite Porphyry at Heyuanbei in Xiangshan Uranium Ore-field, Jiangxi Province

SI Zhifa, LI Ziying, NIE Jiangtao, LIU Jungang, WANG Jian, TIAN Mingming

2018, 32(01): 45-55. DOI: 10.19657/j.geoscience.1000-8527.2018.01.04

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A suite of rhyolite porphyry was found at Heyuanbei in Xiangshan uranium ore-field of Jiangxi Province, which intruded into the rhyodacite, tuff, argillaceous siltstone. LA-ICP-MS U-Pb isotopic dating on zircons from the rhyolite porphyry yields magmatic crystallization age of (131.8±0.7) Ma (MSWD=0.41). The rhyolite porphyry is characterized by high in SiO₂, K₂O, Al₂O₃ and relatively low in MnO and P₂O₅. It is enriched in Rb, Th, U, La, Ce, Nd and light rare earth elements, depleted in Ba, Nb, Sr, P and Ti, and shown slightly negative Eu anomalies (δEu=0.21-0.25). The zircon ε_Hf(t) values range from -6.77 to -10.38, with Hf depleted mantle model ages (T_DMC) between 1 619 and 1 846 Ma. The I_Sr values range from 0.710 92 to 0.712 01. And the ε_Nd(t) values range from -8.18 to -9.19. The experimental results indicate that the rock was generated by partial melting of crustal rocks during extension in Lower Cretaceous. And a sub-volcanic conduit may exist in the west of Xiangshan.

Sulfur and Lead Isotopic Compositions of the Pusangguo Cu-Pb-Zn Polymetallic Deposit in Tibet: Implications for the Source of Ore-forming Material

LI Zhuang, WANG Liqiang, LI Haifeng, DANZHEN Wangxiu, SHI Shuo

2018, 32(01): 56-65. DOI: 10.19657/j.geoscience.1000-8527.2018.01.05

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The Pusangguo Cu-Pb-Zn polymetallic deposit is located in the southern Gangdese volcanic magma arc, Tibet. The east to west trending skarn orebodies are bedded or lenticular, which mainly occurred in the skarnized marble of Cretaceous Takena Formation. On the basis of previous data and geological investigation, this study systematically analyses the characteristics of sulfur and lead isotopic compositions of sulfides including sphalerite, galena, chalcopyrite, and pyrite to discuss the source of ore-forming materials.The results show that the δ³⁴S values of sulfides range from -2.4‰ to 1.0‰, averaging -0.40‰,with the tower distribution features, indicating that the sources of sulfur have magma-derived sulfur features and is related to the dioritic porphyrite. ²⁰⁶Pb/²⁰⁴Pb ratios of sulfides vary from 18.344 to 18.625, averaging 18.555; ²⁰⁷Pb/²⁰⁴Pb ratios range from 15.549 to 15.794, averaging 15.716; ²⁰⁸Pb/²⁰⁴Pb ratios are between 38.12 and 39.34,averaging 39.044. The lead isotopic compositions are stable and belong to the normal lead. Combining the μ values with the tectonic evolution diagram of lead isotope, it can be concluded that the lead is primarily sourced from the upper crust with minor involvement of mantle-derived materials.

Thermoelectricity and Trace Element Characteristics of Pyrites from Tiyier Gold Deposit in West Junggar, Xinjiang and Their Geological Significance

YU Wenlin, GE Wensheng, LIAO Hua, HU Weixing, LU Shudong, LIU Xu, LI Lei, WANG Quanle

2018, 32(01): 66-76. DOI: 10.19657/j.geoscience.1000-8527.2018.01.06

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Pyrite is the main gold-bearing mineral in Tiyier gold deposit, the typomorphic characteristics of which is of great significance to deep prospecting. In this paper, the thermoelectricity and trace element characteristics of pyrite were systematically studied from the perspective of mineralogy and mineral geochemistry. The results show that the conductivity type of pyrite is mainly P-N hybrid type, and the occurrence rate of P-type pyrite gradually increases from the shallow to the deep part. Combining the vertical change of gold grade of different drilling, it is well known that the occurrence rate of P-type pyrite is positively correlated with the high gold grade. Moreover, the occurrence rate of P-type pyrite is consistent with the direction of lateral volts of orebody, which indicates that the ore body has some extension to the deep part. The ore-forming temperatures range from 100 to 330 ℃, which belong to epithermal deposit. The vertical projection contours of trace elements (As+Sb+Se+Te, Cu+Pb+Zn and Ti+Ni+Co+Cr) from pyrite show that the great prospecting potential existed under -250 m elevation between exploration line 1 and line 2 to northwest. Given the above, the typomorphic characteristics of the pyrite are significant for deep gold prospecting in the Tiyier gold deposit.

Genesis of Euhedral Pyrites in the Upper Cretaceous Mengyejing Formation in Simao Basin, Yunnan and Its Geological Significance

DONG Haowei, WANG Licheng, LIU Chenglin, WEI Yushuai, WANG Yanlu, BO Ying

2018, 32(01): 77-85. DOI: 10.19657/j.geoscience.1000-8527.2018.01.07

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The Simao Basin is located in the southeastern part of the Tethyan metallogenic belt. The Mengyejing Formation containing evaporite successions in the Upper Cretaceous is widely distributed in this region. The Mengyejing Formation is currently the only pre-Quaternary solid potash deposit in China. Samples of gypsum and pyrite were collected from the Mengyejing Formation in Jiangcheng County in Simao Basin, and the analysis of major and trace elements and sulfur isotopes of these samples were performed by electron probe micro-analyzer (EPMA) and mass spectrometer. The results show that the S/Fe value of pyrite is 2.02, showing that it belongs to a sulfur-concentration type pyrite. The Co/Ni values range from 3.01 to 10.74, and the varying range is larger.The δ³⁴S_V-CDTvalues of pyrite are in the range of -8.36‰ to -3.36‰ with an average of -6.33‰, while the δ³⁴S_V-CDTvalues of gypsum are in the range of 6.6‰ to 10.7‰ with an average of 9.48‰. The values of S/Fe, Co/Ni and sulfur isotope of pyrites and the values of sulfur isotope of gypsums suggest that the pyrite in the Mengyejing Formation in Jiangcheng County is formed in hydrothermal processes. The hydrothermal alteration causes the gypsum to be reduced to form S^2-. S^2- formed the granulated pyrite combined with Fe from the hydrothermal fluid. Through this study of the genetic mechanism of pyrite and gypsum of the Mengyejing Formation,it comes to the conclusion that the primary evaporites of the Mengyejing Formation in the Upper Cretaceous might be experienced obvious alterations by deep hydrothermal fluids accompanied by several kinds of metals, which is controlled by the Indian and Asian collision,and the hydrothermal activities in Simao Basin recrystallized the potash minerals of the Mengyejing Formation, but might have favorable contribution to the metal deposition.

Distribution,Source Identification and Risk Assessment of Heavy Metals in Topsoil of Huairou District in Beijing

LI Ping, HUANG Yong, LIN Yun, HUA Peixue, YUAN Guoli

2018, 32(01): 86-94. DOI: 10.19657/j.geoscience.1000-8527.2018.01.08

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At the agricultural area in the southeast of Huairou District in Beijing, 977 topsoil samples were collected, and 8 heavy metals in samples were analyzed, including Cr, V, Ni, As, Pb, Zn, Hg and Cd. The spatial distribution characteristics of these heavy metals were clearly illustrated by geochemical mapping. By applying the methods of multivariate statistics analysis, the concentration distributions of these heavy metals were dedi-cated, and the sources of them were determined, and risk assessment for them was also performed. The results show that the elements of Cr, V, Ni and As are mainly originated from soils parent materials. On the other hand, the elements of Pb, Zn and Hg are greatly influenced by the human activities, such as traffic and atmospheric deposition. Differently, Cd is mainly affected by inorganic fertilizer. The environmental risk of 8 heavy metals is assessed by Hakanson method, and all above heavy metals except Cd show a relatively low pollution risk. So, our study provides a significant reference for the risk assessment of agricultural soils and the future land-using plan at the area of Huairou District.

Geochemical Characteristics and Risk Assessment of Heavy Metals in Agricultural Soils in Miyun District of Beijing

DUAN Xuchuan, LI Ping, HUANG Yong, LIN Yun, YUAN Guoli, LUO Xianrong

2018, 32(01): 95-104. DOI: 10.19657/j.geoscience.1000-8527.2018.01.09

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One thousand and sixty-five surface soil samples were systematically collected at the agricultural area in the southwest of Miyun District of Beijing,and the concentration of 8 heavy metals in the samples were analyzed, such as Ni,V,Cr,As, Cd, Pb, Zn and Hg. By the methods of multivariate statistical analysis and spatial analysis, the geochemical distributions of 8 heavy metals were stated and the main sources for them were also determined. The results show that 8 heavy metals can be classified into three groups. The first group includes Ni, V, Cr and As.The mean concentration of them was found being lower than the background values in Beijing, and the spatial distribution of them was determined being dominantly influenced by the soil parent materials. The second group includes Cd, Pb and Zn. The mean concentration of them generally exceeded the background value in Beijing, and highest values were observed in the residential area. Besides of the origination from the soil parent materials, the spatial distribution of them was determined being greatly influenced by the human activities, in which Cd underwent greater influence than Pb and Zn. The third group only includes Hg,and atmospheric deposition was proposed to be the main influence factor for its distribution. Ecological risks of 8 heavy metals were mainly assessed by Hakanson method, and the indexes of the potential ecological risk for them are relatively low in the study area.

The Influencing Factors of Selenium in Soils and Classifying the Selenium-rich Soil Resources in the Typical Area of Enshi, Hubei

ZENG Qingliang, YU Tao, WANG Rui

2018, 32(01): 105-112. DOI: 10.19657/j.geoscience.1000-8527.2018.01.10

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Selenium is an essential element for mammals. In order to study the distribution characteristics, the important influencing factors of selenium distribution in soils and to classify selenium-rich soil resources, this study systematically collected and analyzed 199 top-soil samples and 60 crop samples in Shadi township of Enshi City. The correlation of the geochemical parameters, such as the selenium concentrations of corn seeds and top soils, was analyzed, and as a result an absorption model of selenium in corn seeds was established. Results of the analysis show that concentrations of total selenium in the top-soils ranged from 0.19 mg·kg^-1 to 15.57 mg·kg^-1, and averaged 1.88 mg·kg^-1, which is clearly higher than the average concentrations in Hubei Pro-vince and China as a whole. The area with selenium-sufficient soil and selenium-rich soil accounts for 84.43% of the study area. The distribution of selenium is mainly influenced by geology. There is a significant difference in selenium content distribution in top-soils formed in proximity to different geologies. The selenium content in the outcropping area of Permian Maokou Formation is higher than that of other stratigraphic regions. The results also indicate that soil TOC and altitude were important influencing factors on selenium content. The selenium concentrations in crops had a large range. Se-enriched crops have the largest proportions, accounting for 43.22%. The selenium-rich land and potentially selenium-rich land accounted for 65.33% and 23.12% of the study area, respectively.

Impacts and Mechanisms of Natural Organic Matter and pH on the Transport of Nanobiochar

YANG Meihong, LI Zhixiong, LIU Yuyan, MA Shaoqiang, CHEN Jiawei

2018, 32(01): 113-120. DOI: 10.19657/j.geoscience.1000-8527.2018.01.11

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Biochar, a kind of typical black carbon, has attracted attention for its application development in recent years. Since biochar is applied into the soils, some would gradually become fragmented into micro or nano sized biochar particles under the long term supergene geochemical process. It is very important to investigate the transport of biochar, specially, more reactive nanobiochar. Whereas, such research is few up to now. Hence, the column experiments were conducted on the transport of nanobiochar in quartz sand column to explore the breakthrough curve and retention curve. The aim of the present study is to elucidate the mechanism of the effects of natural organic matter (NOM) and different pH values (pH=4,7,10) on nanobiochar transport behavior. The results showed that humic acid (HA, a model NOM) enhanced the mobility of nanobiochar, and neutral or alkaline aqueous medium favored nanobiochar transport. One reason is that the dispersibility of nanobiochar was improved. The other is due to net negative charge of biochar and quartz particles increased in the presence of HA and alkaline environment. So, the Zeta potential of particles increased and electrostatic repulsion force strengthened, which was beneficial to the transport of nanobiochar. This work is of importance to understand the geochemical transport behavior of nanobiochar and the potential risk of contaminant adsorption onto nanobiochar transported in the environment.

Deep-water Sedimentary Structures of Yanchang Formation in Southern Ordos Basin and the Geological Significance

WANG Zhen, ZHANG Yuanfu, ZHANG Na, GAO Yong, JIAO Chaowei, BAI Yiming, ZHANG Bowen, WEI Kangqiang

2018, 32(01): 121-132. DOI: 10.19657/j.geoscience.1000-8527.2018.01.12

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The Chang7 member of Yanchang Formation in the southern margin of Ordos Basin develops typical gravity flow deposits. It is found that the gravity flow deposits develop various sedimentary structures in the field investigation on field outcrops, mainly including bottom layer structures, soft-sediment deformation structures. These deep-water sedimentary structure combinations can well reveal that deep-water gravity flow deposits are widely developed under the background of slope breaks in the study area. Slip-slump deposits, sandy debris flow deposits and turbidite deposits are the most widely developed types of deep-water gravity flow deposits in the study area. Slip-slump structures and soft-sediment deformation structures are the sedimentary response of triggering mechanism, while bottom layer structures are the sedimentary response of sandy debris flow deposits and turbidite deposits. After the comprehensive analysis of characteristics of a large number of tuff interlayers, plant debris developed in deep-water mudstone, a large number of light yellow mud gravel developed in deep-water sandstone and other sedimentary characteristics of the formation in the study area, it is inferred that the earthquake, volcanic eruption and seasonal floods are the most advantageous triggering factors of deep-water gravity flow deposits in the study area.

Geochemical Characteristics and Genetic Interpretation of Laminated Shales of the Third Member of Hetaoyuan Formation in the Biyang Depression of Nanxiang Basin

GUO Laiyuan, LIU Zhengjun, XIE Xinong

2018, 32(01): 133-144. DOI: 10.19657/j.geoscience.1000-8527.2018.01.13

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The occurence of black and white stripes of laminated shales is a very important and common phenomenon in sedimentary rocks. The X-ray fluorescence core scanner has been used for testing laminated shale samples from the fifth layer in the Biyang Depression. The analysis results show that some chemical elements of the lacustrine lamina, such as Sr, CaO, K₂O, SiO₂, TiO₂, Fe₂O₃, Al₂O₃ and Cu, show obvious regular changes in the black and white laminae. That is, the Sr and CaO contents in the white laminae are significantly higher than those in the black laminae, and the contents of K₂O, SiO₂, TiO₂, Fe₂O₃, Al₂O₃ and Cu in the black laminae are significantly higher than those in the white laminae. The formation machanism of laminae is analyzed combined with the boron element and paleoredox proxies and paleoclimate proxies, and the result suggests that these laminated shales would have mainly developed in the brackish-saline and semiarid-arid stratified water. Microscopic investigation also reveals that the black stripes are mainly composed of a high proportion of organic matters and argillaceous sediments, while white stripes are mainly composed of the calcite, gypsum, quartz, dolomite and other minerals. The black and white laminated material components are closely related with a terrigenous supply and authigenic minerals formed in a saline enviroment. The occurence of different elements between the black and the white reveals the different mineral compositions as well as seasonal rhythm changes in the continental lake basin. Therefore, core scanning provides a new effective method to evaluate geochemical characteristics of the laminated shale and its formation mechanism.

Analysis on Gravel Fabric Characteristics of the Yellow River’s Terraces in Gonghe Basin and the Environmental Signification

HU Mengjun, FENG Shuqin, LI Xiangfeng, PAN Ninghui

2018, 32(01): 145-153. DOI: 10.19657/j.geoscience.1000-8527.2018.01.14

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Based on the mathematical statistics of gravel fabric characteristics of the 12 terraces along Yellow River in the Gonghe Basin,the particle size, shape and orientation of each gravel layer were calculated, and the characteristics of gravel fabrics were analyzed to explore the environmental significance. The studies showed the following aspects: (1)the components of gravels were complex, mainly including sandstone and quartzite; (2)the flat sphere was the main shape of gravels, and the roundness of gravel layers was medium and the degree of weathering was low; (3)the intensities of the flowing water were listed in descending order as T8>T7>T5>T4>T10>T2>T9>T1>T3>T6>T11>T12 when the gravel layers were formed, and the gravel layers of T1, T3, T4, T7, T8 and T11 were caused by the stable river, and T2, T5, T6, T9, T10 and T12 were formed in alluvial water environments;(4)the direction of each gravel layer was consistent with that of field observation, and the directions of gravel sources and ancient water flows in T1, T2, T5, T6 and T10 were complex, while those of T3, T4, T7, T8, T9, T11 and T12 were simple. The environmental significance of this study is relatively simple, but it can be further used to reveal the characteristics of climatic environment and the condition of ground uplifted combined with chronological data of the terrace.

Subnormal Pressure Characteristics and Genesis Analysis of the Central Uplift Belt in Huimin Sag

LIU Yuanqing, ZHOU Le, ZENG Jianhui, LI Wei, ZHOU Junliang, HE Jin, WANG Xinfeng, LÜ Lin, DENG Qijun

2018, 32(01): 154-161. DOI: 10.19657/j.geoscience.1000-8527.2018.01.15

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There commonly developed subnormal pressure in Huimin Sag, which mainly located in the second and third members of Shahejie Formation vertically and around the Central Uplift Belt horizontally. The previous studies on genesis of subnormal pressure has still remained un-quantitative. Based on the measured data of 295 boreholes, the vertical and horizontal distribution characteristics of the strata pressure in Huimin Sag were discussed. Furthermore, the decrease of pressure caused by the influence of the strata denudation, temperature decrease, water consumption of mineral alteration and volume change of minerals was analyzed quantitatively, which was respectively 0.516 MPa, 2.02 to 3.73 MPa, 8.64 MPa and 4.36 MPa. Hydrocarbon filling led the pressure increased less than 32 MPa. All the above factors together made that the pressure evolution of Central Uplift Belt presented the cycle of depressurization-pressurization-depressurization, and finally formed the current distribution characteristics of pressure.

Sedimentary Facies and Sandbody Depiction of the Huagang Formation of H Structural Group and Its Adjacent Areas in Xihu Depression

HE Miao, HOU Guowei, QIN Lanzhi, LU Yan, XIE Jingjing

2018, 32(01): 162-172. DOI: 10.19657/j.geoscience.1000-8527.2018.01.16

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H structural group and its adjacent areas of Xihu Depression were formed under the background of huge extrusion and reversion, which located near the rich depression and proved to have potential oil and gas. In order to find the beneficial areas and the rich sand strata, this paper combines the characteristics of seismic reflection, FMI logging data, lithology data and paleontology data to do research on sedimentary background, considering that the Huagang Formation deposits under moderate hydrodynamic force and is affected by multidirection fluid. The pollen and other paleontological association suggest that Huagang Formation is under fresh water environment. According to logging and coring data, it is proved that the Huagang Formation develops anastomosing river deposits, and anastomosing channels, cross bar and vertical bar are well-developed among those microfacies. Furthermore, combining the well-to-well correlation and seismic profiles together, the vertical overlap and planar distribution characteristics of sandbodies are analyzed, indicating that the single-jointed, multilateral-jointed and incomplete folded sandboies are mainly deposited, and the planar sandbodies are mainly stripe, cross-linking stripe and net shaped. It is proved that the deep-deposited sandbodies have a great potential.

Architecture Characteristics of Low Sinuosity Distributary Channel Reservoir and Its Controlling Factors on Residual Oil Distribution: A Case Study of Xingbei Oilfield, China

LI Weiqiang, YIN Taiju, ZHAO Lun, LI Feng, XIE Pengfei, YANG Cheng, YAN Shaohuai

2018, 32(01): 173-182. DOI: 10.19657/j.geoscience.1000-8527.2018.01.17

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Low-sinuosity distributary channel reservoir is an important reservoir type of Xingbei oilfield and it is of great significance to further study its reservoir architecture characteristics for the adjustment and potential tapping. Based on the data of cores, wire-line logs and production performance from close well-spacing block, the reservoir architecture of low sinuosity distributary channel in Xingbei oilfield was finely analyzed by using “hierarchy analysis and depositional pattern guidance” with two primary hierarchies which were the determination of amalgamated channels and overbank sandstone bodies and the contact relationships among solitary channels. The 3-D reservoir architecture model was then established. Based on the static data of sealed coring wells and water-cut well-logging interpretation results and the production performance data, the waterflooding features of different periods and distribution of remaining oil were analyzed. Subsequently, the distribution of remaining oil was verified by numerical reservoir simulation based on 3-D reservoir architecture model. Finally, the distribution of remaining oil controlled by the reservoir architecture was summarized and demonstrated as follows: within the channel, the remaining oil volumes are enriched in the top and edge of the channel, the lower areas controlled by mud or calcareous interbeds between individual channels and undeveloped areas just connecting with low-permeability overbank sands. Outside the channel, they are mainly in low-permeability overbank sands, end of the overbank sands and the isolated sandstone bodies with imperfect injection-production systems.

Research on Oil-bearing Control Factors of the Chang 9 Tight Sandstone of Yanchang Formation in the Ordos Basin

WEN Fenggang, ZHU Yushuang, REN Zhanli, GAO Pengpeng, NI Jun, WANG Xianxian, XU Weiwu, MA Bin, GAO Mingxing, HONG Qianli

2018, 32(01): 183-190. DOI: 10.19657/j.geoscience.1000-8527.2018.01.18

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The oil-bearing control factors of the Chang 9 tight sandstone was studied in this paper based on the analysis of reservoir physical property, the core pictures and fluorescent image. The results are as followings: (1)The higher content of high plastic rock debris is, the worse sandstone physical property is, and the worse oil-bearing is;(2)The higher content of carbonate cement correlates negatively with oil-bearing; (3)The physical property correlates positively with the better oil-bearing; (4)Heterogeneity had a huge impact on oil-bearing led to petroleum partition in vertical and horizontal lines;(5)The lithology of sand bodies in underwater distributary channel mainly are gray mud gravel medium sandstone or middle-fine sandstone with good oil-bearing but that in interdistributary bay is dark grey mudstone, silty mudstone or argillaceous siltstone;(6)Fractures play a good role in improving the reservoir property. The simulated results also indicated the migration path of Chang 9 reservoir and the favorable exploration areas was selected that areas of Xinghe region to eastern Liandaowan, Xihekou-Ansai-Xiaping, Yanhekou-north of Fengzhuang.

Influence of Correction of Interfacial Tension and Wetting Angle to the Pore Size Distribution of Shale by Means of High Pressure Mercury Porosity:A Case Study of Qingshankou Formation in Songliao Basin

JIN Jiyang, XUE Haitao, TIAN Shansi, WU Cunzheng, LI Ying, ZHOU Bin, ZHAO Rixin

2018, 32(01): 191-197. DOI: 10.19657/j.geoscience.1000-8527.2018.01.19

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It is very important to study the pore structure of shale reservoirs for the exploration and development of shale oil and gas. The high pressure mercury intrusion method is widely used in the study of shale pore structure and pore size distribution. Some scholars have studied the wettability of mercury in graphene materials. It has been found that the interfacial tension γ and wetting angle θ of liquid mercury in the pores are a function of pore radius r. According to this understanding, the traditional data processing method, which regards the interfacial tension γ and wetting angle θ as determinants in the Washburn equation, shows obvious irrationality. So it is necessary to correct the parameters of Washburn equation. In this paper, the high-pressure mercury intrusion test was carried out in the Qingshankou Formation of the Songliao Basin. The data of the mercury intrusion corrected by the Washburn equation before and after the correction were analyzed. It was found that the volume fraction of the micropores (<2 nm) obtained after the calibration was increased by 118%, mesoporous (2 to 50 nm) volume proportion decreased by 7%, macroporous (>50 nm) volume ratio of the basic unchanged. The pore size distributions of the shales can be more accurately characterized by the pore size distributions obtained after the calibration.

Reasonable Water-injecting Development Methods of Multiple-fracturing Horizontal Well in Ultra-Low Permeability Glutenite Reservoir

CUI Chuanzhi, CHEN Honglin, GUO Yingchun, WANG Qian, ZHANG Shufan

2018, 32(01): 198-204. DOI: 10.19657/j.geoscience.1000-8527.2018.01.20

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At the ultra-low permeability glutenite reservoir conditions, when elastic development is used for the long well section fractured horizontal well, the productivity reduces rapidly as the formation energy reducing and the cost of development can’t withdraw. Using the multiphase seepage theory and reservoir numerical simulation method, and taking the example of the Yan 227 block in ultra-low permeability glutenite reservoir of Yanjia area, the reservoir numeric model is built up according to the actual data. The paper makes a feasibility research on water injection development in glutenite reservoir of Yanjia area. In the meanwhile, based on flowing mechanism and production law, the paper studies on the reasonability of normal water injection development,advanced water injection development and water injection & production development. Then the effective development methods is presented about the horizontal well in ultra-low permeability reservoir. The result shows that: the water rate of water injection & production is 25% lower than normal water-injection development and advanced water injection can improve about 30% production more than normal elastic development at the early period. So these two new development ways are useful to controlling the water logging problem and improving the recovery degree.

Experimental Study on Carbon Isotopic Composition Changes During the Formation of Gas Hydrates

CHEN Min, DENG Xingbo, LIU Changling, REN Hongbo, YIN Xijie, LI Jiaxuan, QI Hongshuai, ZHANG Aimei

2018, 32(01): 205-212. DOI: 10.19657/j.geoscience.1000-8527.2018.01.21

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Gas hydrates are a new type of clean energy, and they often appear in the deep sea or in the polar continent. Isotopic fractionation occurs in the gas hydrate formation. In this paper, experiments of methane-seawater hydrates, carbon dioxide-seawater hydrates, and methane-seawater hydrates formed repeatedly in sediments were carried out. Changes of carbon isotopic composition during the formation of gas hydrates were researched. The results prove that the carbon isotope fractionation exists during the gas hydrate formation, and the change of carbon isotope composition is significantly smaller than that of oxygen and hydrogen. The fractionation factor of carbon isotope is 1.000,3 to 1.000,9 in methane-seawater gas hydrate. Carbon and oxygen isotopic composition lightened in gas phase after carbon dioxide hydrate formation, and heavy isotopes tend to enter hydrates. The fractionation factor of carbon isotope is 1.000,7 to 1.001,2 in carbon dioxide-seawater gas hydrates. CO₂ gas dissolved in seawater will be captured in hydrate cage during methane hydrate formation and as a result,δ¹³C_DIC value becomes small and heavy carbon isotope tend to enter hydrates, and lighter carbon isotope is left in the seawater. Because the dissolved CO₂ gas content is limited in seawater, the variation of δ¹³C_DIC value would be smaller with time in the process of methane-seawater hydrates forming repeatedly in sediments.

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