Geoscience

Magmatism and Mineralization of Epithermalporphyry Deposit from BangonghuNujiang Metallogenic Belt: Taking Dongwodong Copper Deposit from Gerze County for Example

WEI Shaogang, TANG Juxing, SONG Yang，LIU Zhibo， WANG Qin，LIN Bin，HOU Lin

2016, 30(6): 1179-1196.

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The Dongwodong copper deposit, located in the east of the Duolong oreconcentrated district, is a newlydiscovered porphyry copper deposit in the BangonghuNujiang metallogenic belt in Gerze County, Tibet. Zircon UPb dating results show that the granodioriteporphyries intruded at (1210±12) Ma and the graniteporphyries intruded at (1215±10) Ma, which are similar to those of the orebearing porphyries from Duolong oreconcentrated area. These porphyries are systematically more enriched in largeion lithophile elements and LREE, relatively depleted in high strength elements and HREE, and have middle negative Eu anomalies, high Al and Sr, low Mg, Ti, Y and Yb, which are consistent with those of arctype magmas worldwide. These porphyries have similar ages and geochemical features to those of ore bearing porphyries from Duolong oreconcentrated area, suggesting that they were formed in a common magma chamber. The orebearing intrusions are characterized by high TZr ranging from 7796 to 8445 ℃. Additionally, they have varying εHf(t) values ranging from +34 to +111, T2DMC values ranging from 467 to 963 Ma. According to the obtained data, we proposed that the studied porphyries were generated by partial melting of juvenile crust under the background of BangonghuNujiang Tethys oceanic crust subducting northward to Qiangtang massif and the BangonghuNujiang oceanic basin was significant sizes during the Early Cretaceous. Besides, based on field geological surveys, we suggest that this deposit show typical porphyry copper deposit alteration characteristics. Its rock composition, mineralization and alteration, ages of diagenesis and mineralization, and tectonic environment and material source are consistent with those of the deposits in Duolong oreconcentrated area. Comprehensive analysis indicates that Dongwodong copper deposit shares a great potential to discover superlarge epithermalporphyry Cu (Au, Ag) concealed ore body.

Metallogenic Characteristics of the Belt and Prospecting Areas in Yunkai Region,Guangxi

AN Guoying，LEI Yingping，XIAO Rongge，FEI Hongcai

2016, 30(6): 1197-1208.

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As one of the important areas of goldsilverlead and zinc polymetallic metallogenetic province in Guangxi,Yunkai region has been being the focus and object of geological work region for a long time. Based on the synthetic analyses of geological background and metallogenic characteristics as well as geological metallogenic regularity, this paper discusses the prospecting potential and suggests the most targets for exploration in the near future through the analysis of enrichment characteristics of elements, typical characteristics of deposits and the newlydiscovered ore deposit. The result reveals that this region has complex structure, intense magmatism, deep basement metamorphism and active mineralization, forming an important orefield with lead and zinc as dominant minerals, gold silver as important mineral, together with copper, tungsten, tin and molybdenum as good resource prospects of minerals. Considering with environmental factors and the distribution of known ore deposits, nine concentration areas have been selected as exploration targets in the near future.

Thermoelectric Characteristics and Metallogenic Regularity of Pyrite in Yuku Molybdenum Deposit, Luanchuan,Henan

JIA Wenjuan，WANG Gongwen，HAN Jiangwei，YAN Changhai，SONG Yaowu，

2016, 30(6): 1209-1218.

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Luanchuan Yuku molybdenum deposit is located in the southern margin of the North China Craton, whose Yanshanian magmaskarn type mineralization is related to the large concealed Mo polymetallic deposit discovered in recent years. The samples from deep drilling mining (>1,000 m) were used to analyze thermoelectric characteristics of pyrite and the aim was to provide an important scientific basis for the exploration of deep prospecting in this area. The research contents and methods are as followed:the thermoelectric properties of pyrites are mainly of the N type with a total content of 96%.The thermoelectric parameters characteristics reflect the orebody denudation to the middle and lower position, but the statistical data shows the depth potential extension. According to the pyroelectricity of pyrite ore in the study area to calculate the forming temperature of fan between 270-332 ℃, the deposit belongs to shallow medium temperature hydrothermal mineralization. On the basis of geological statistics, ArcGIS Geostatistical Analyst modular was used to analyze the trend of metallogenic temperature, and the oreforming regularity and potential targets were discussed.

The Early Silurian Arc Magmatic Rocks of East Junggar, Xinjiang: Evidences from Geochemistry, Zircon UPb Age and Hf Isotopes of the Jianggeerkuduke Quartz Monzobiorite

HUANG Gang, NIU Guangzhi, WANG Xinlu, GUO Jun, YU Feng

2016, 30(6): 1219-1233.

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Abstract:There is few highprecision geochronological data of the Jianggeerkuduke quartz monzobiorite covered in angular unconformity by the Lower Devonian Zhuomubasitao Formation, East Junggar. The LAICPMS zircon UPb dating of the quartz monzobiorite is (4328±12) Ma, indicating that magmas emplaced during the Early Silurian. Geochemical analyses suggest that the quartz monzobiorite has low SiO2 (5564%-5868%), TiO2 (054%-071%) and high Al2O3 (1699%-1805%) contents. The quartz monzobiorite samples have characteristics of enrichment of LILE(K, Rb, Ba, Sr) and depletion of HFSE(Nb, Ta, Zr, Hf). These geochemical features imply a similar origin with subductionrelated tectonic setting. The rocks have positive εHf(t) (+108-+136) and TDM2 ages of 726-560 Ma slightly older than their formation ages, which prove that they were products derived by the partial melting of juvenile island arc materials formed from the Late Neoproterozoic to the early stage of Early Paleozoic. Combining with the regional geological background, we propose that the Jianggeerkuduke quartz monzobiorite was formed by the partial melting of the Late Neoproterozoic to the early stage of Early Paleozoic juvenile island arc materials of the mantle wedge by hydrous fluid originated from subducted oceanic crust and sediments, which was the product of the continental marginal arc magmatic formed by the southward subduction of the PaleoAsian oceanic crust in the Early Silurian.

The Diagenesis and Metallogenesis Age of the Intrusive Rock in Jiama Deposit in Tibet

LI Bo, HU Daogong, LIN Guangqi, XU Congcong,ZHANG Ruipeng, ZHANG Yifei

2016, 30(6): 1234-1243.

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Abstract: The Jiama coppermultimetal deposit in Tibet lies in the eastern part of the Gangdisi metallogenic belt. It belongs to superlarge porphyryskarn type deposit and has great potential for mineralization. The mineralization in the mining area is controlled by the NS normal fault, which offer the space for metallic element enrichment and magmatic hydrothermal rise. In this paper, LAICPMS zircon UPb dating was used to study the porphyry and skarn age. The dating results show that the diagenesis and mineralization age of the mining area is 14-16 Ma, and the ESR dating results show that the quartz veins age is 139-164 Ma, the calcite veins age is 5-7 Ma. The dating results show that the diagenesis and the metallogenesis are both in the Miocene period, in the later period, there are still weak metallogenesis in Jiama deposit influenced by tectonic movement.

Characteristics and Geological Implications of the Late Paleozoic Postorogenic Granite in Taxi Area of Heilongjiang

YANG Wenpeng,ZHAO Chao,YIN Guoliang,ZHANG Shengxu,SUN Jiangjun

2016, 30(6): 1244-1253.

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Abstract:The granites in Taxi area, located in the east of the Xingmeng orogenic belt,are mainly composed of syengranite and monzogranite.The zircon UPb( LAICPMS) age analyses from the granites is from 295 to 285 Ma,suggesting that it is the production of Late Paleozoic.According to macroscropical evidences it shows that the studied granite is weakly peraluminous,with middle to high K and the high K calcalkaline series,and that the result of the samples are enriched in light rare earth elements and depleted in heavy rare earth elements with weakly to moderate pronounced Eu anomalies. Evidences of the trace elements show that it is enriched in Rb,La and depleted in Ba,Sr of the LILE and enriched in Ce,Zr,Hf,Th and depleted in Nb,Ta of the HFSE. It is indicated that granitic magma crust and mantle contamination had occurred, with the participation of more crust source material, displaying the characteristics of postorogenic I type granite. We concluded that the granites formed in extruded to stretch conversion postorogenic environment,and that it is the product of postorogenic evolution after the collision of Xingan Block and Songnen Block.

Metamorphism of Metasedimentary Rocks in Madao Area, South Qinling Accretionary Complex Belt

WANG Dongsheng, WANG Zongqi, ZHANG Yingli, GONG Jianghua, WANG Tao,

2016, 30(6): 1254-1266.

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1 MLR Key Loboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing100037, China; 2 Institute of Geology, Chinese Academy of Geological Sciences, Beijing100037, China; 3 School of Earth Sciences and Resources, China University of Geosciences, Beijing100083, China

Geochemical Characteristics of Ionadsorption Type Rare Earth Elements Deposit in Huidong,Guangdong

YUAN Hongqing1,2,3，LI Shehong3，MIAO Bingkui3，YAN Song3，SU Yangyang3

2016, 30(6): 1267-1275.

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Abstract: Based on geochemical research, we analysis the weathering crust of ionadsorption type REE deposit in Huidong area, Guangdong. The data show that the content of CaO,Na2O and K2O are decreased with the increase of weathering, Al2O3 is opposite. The trace elements such as Ba,Sr,U and REE are enriched in the semiweathered layer and weathered layer. The characteristics of distribution and content of the elements in weathering crust profile reflect the nature of parent granite. The index of WIG is more effectively to describe the weathering degree of the profile than CIA. The degree of weathering and enrichment of REE decrease with the increase of WIG. It can be concluded that LREE are abundant in upper of weathering layer ,while HREE are abundant in semiweathered layer and in lower part of the weathered layer. Eu and Ce are significantly loss in area where enrichment of the REE.

Geochemical Characteristics of Stream Sediments and Prospecting Direction in the Tanshanzi-Huangcaoquan Area of Beishan, Gansu Province

WANG Lei, YANG Jianguo, WANG Xiaohong, QI Qi, ZHANG Zhouyuan, ZHANG Le

2016, 30(6): 1276-1284.

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Abstract:Based on the 1∶50,000 stream sediment survey in Tanshanzi-Huangcaoquan area of Gansu Province, the geochemical parameters of oreforming elements were calculated, and the distribution, correlation, and anomaly assemblages of these elements were analyzed accordingly. It is indicated that the main elemental geochemical anomalies are controlled by faults (Dashantou and Miaomiaojing fracture zone), stratigraphy (Jixian system, Cambrian system, and Ordovician system), and magmatite (Dashantou and Sangejing maficultramafic magma and Variscan granite). According to the characteristics of structures, lithologies, and geochemical anomalies in this area, the authors delineated four polymetallogenic prospective areas, namely Dashantou and Sangejing CuNi metallogenetic prospective areas, Miaomiaojing AuCuWMo polymetallogenic prospective area, Huangcaoquandong AuAg polymetallogenic prospective area. This work is expected to provide some insights for the future exploration.

Research of 1∶50,000 Land Quality Geochemical Survey Technique at A Hillybasin Area in Zhejiang Province

HE Ling, SUN Binbin, ZHOU Guohua, ZENG Daoming, LIU Zhanyuan

2016, 30(6): 1285-1293.

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Abstract: A research on the technique of 1∶50,000 land quality geochemical survey at a hillybasin area in central Zhejiang Province was carried out at 2014. The experimental procedure was as follows：(1)using the upper limit of sampling density of 1∶50,000 land quality geochemical survey, the average sampling density is 164 samples per km2, Kriging interpolation method is used for the patch assignment (hereinafter referred to as interpolation);(2)to reach the target of precise land management, use the land plots as sampling units. The average sampling density is 1795 samples per km2.Then use the measuring results in the patch assignment (hereinafter referred to as measured). Several parameters, including element content, geochemical grade of soil environment, geochemical grade of soil nutrient and geochemical comprehensive grade of soil quality were compared respectively in 16 samples per km2 and 180 samples per km2. The study showed that: (1) by studying the relative deviation (RD) between interpolation and measured value of 15 elements which are crucial in the land quality assessment, we found that the RD qualified rate pass 90%, 80% to 90%, under 80% were separately 9,4 and 2; (2) the difference between interpolation and measured value in single geochemical grade of soil environment and comprehensive geochemical grade of soil environment are quite small, while it was more distinct in geochemical grade of soil nutrient; (3) the proportions of number and area change between interpolation and measured value for the first and second grade patches are 118% and 74%.The comprehensive geochemical grade of soil quality has changed in about 40% of the patches. In the experiment plot, the RD between interpolation and measured value were mainly caused by the spatial difference of N, P, K. The research shows that, the results of 1∶50,000 land quality geochemical survey, in a word, according to the land quality geochemical assessment requirements, can provide the scientific reference for land utilization and fertilization. But not well enough for precise land management.

Study on Spatialtemporal Variation of Heavy Metal Elements Contents in Soil from the Farming Area in Panjin City，Liaoning

LI Yuchao，YU Tao，YANG Zhongfang，YU Chengguang，WANG Chengyu

2016, 30(6): 1294-1302.

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Abstract:Based on twice geochemical survey data about land quality in Panjin City of Liaoning, the characteristics of spatialtemporal variation of heavy metal elements in this area were studied by applying scientific statistical method (ie. mathematical statistics, multivariate statistical analysis, spatial analysis) to eliminate errors in sampling and analyzing, and the reasons for accumulation of heavy metal elements in soil were discussed combining present situation of land use. The results showed that the element contents of cadmium (Cd) in soil have been markedly increased from 2004 to 2009, with an average cumulative rate of 3128%, which mainly contributed by agricultural and human activity. Meanwhile, human activity also caused accumulation of some other heavy metal elements, eg arsenic (As), zinc(Zn). On the contrary, copper (Cu) and mercury (Hg) presented apparent depleted trend. Lead (Pb) showed double characteristics of either enrichment or depletion, while the contents of chromium(Cr) and nickel(Ni) had no significant changes as well as the pH value.

Sedimentotectonic Evolution and Petroleum Exploration Domains of Lower CongoCongo Fan Basin

SUN Ziming

2016, 30(6): 1303-1310.

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Abstract: Lower CongoCongo Fan Basin, located in the western coast of Africa, is one of the world's oil and gas exploration priorities and hot spots in recent years. Being rich in oil and gas and having the giant remnant resource potential, it has long been drawn the great concern from many researchers, and a series of exploration and research work were made from the different aspects such as tectonic evolution, petroleum geology, hydrocarbon migration and accumulation, and resource potential, etc. However, the exploration density is not uniform as the basin covers onshore and offshore which includes shallow water, deep to ultradeepwater areas from east to west. Therefore, how to fully evaluate the oil and gas remnant resource potential of the basin will be a key factor to guide next exploration deployment in the basin. By the integrated analysis of tectonostratigraphic framework and basin evolution, it is pointed out that Lower CongoCongo Fan Basin is a composite petroliferous salt basin superimposed of the Congo Fan Basin on Lower Congo Basin. Taking petroleum geological elements, and features of hydrocarbon migration and accumulation into consideration, three petroleum exploration domains are identified from Lower Cretaceous to Cenozoic, which are the Cenozoic exploration domain related to structurallithologic traps, the postsalt Cretaceous exploration domain related to structural traps, and the presalt Cretaceous exploration domain related to the Early Cretaceous rift, respectively. The subdivision of the three exploration domains lays a sound foundation for systematically evaluating hydrocarbon potential according to the exploratory objectives. By integrated analysis of the petroleum exploration domains, it is pointed out that onshore to shallow water area in the eastern basin is favorable for the postsalt and the presalt Cretaceous exploration domains, and deep to ultradeep water area in the western basin is favorable for the Cenozoic structurallithologic traps exploration domain.

Presalt Structure Characteristics and Its Control on Hydrocarbon Accumulation in the Lower Congo Basin

LIU Yalei

2016, 30(6): 1311-1317.

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Abstract:Based on the seismic interpretation of different structural profiles, the presalt structure characteristics of the Lower Congo Basin is studied and summarized, which can be divided into two sub basins by a central uplift,ie the inner and the outer riftbasins, while the Atlantic hinge line is the boundary fault between the central uplift and the outer riftbasin. In both outer and inner riftbasins, the structure characteristics can be described as two humps developed in three sags. The structure framework controls the type and distribution of the source rocks, reservoir rocks and the cap rocks, as well as the sourcereservoircap combination and accumulation model. Based on the abovementioned research, this paper points out that the uplift controlled by faults is the clear goal for the next exploration of the presalt layer in the Lower Congo Basin.

Quantitative Evaluation of Control of Faults on Hydrocarbon Accumulation and Play Fairway Prediction in Zhu I Depression of Pearl River Mouth Basin

PENG Huijie, PANG Xiongqi, LI Hongbo, WANG Zhuochao, YU Qiuhua, WANG We

2016, 30(6): 1318-1328.

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Abstract:The hydrocarbon in shallow groups including Zhuhai Formation,Zhujiang Formation,Hanjiang Formation in Zhu I Depression of Pearl River Mouth Basin mainly come from deeply buried source rock. The fault is oil source passage and plays an essential role in the formation and distribution of oil and gas reservoirs. In order to understand the control of faults on hydrocarbon accumulation in the Zhuhai Formation to Hanjiang Formation in Zhu I Depression of Pearl River Mouth Basin, fault distribution and anatomy of fault zone are studied. On the base of fault activity period and layer position broken by fault, different faults can be divided into five categories: early activity which cut deep, advanced activity which cut the shallow stratum, late activity which cut through deep and shallow strata, succession activity which cut through deep and shallow strata, bable type of fault. Based on the anatomy of the fault zone south of Enping, it is found fault controlling factors mainly include fault type, fault event rate, the size of the fault,and distance from the traps to fault. For the regions found reservoirs, the above factors are analyzed. The results show that: the fault that cut through deep and shallow strata controls hydrocarbon accumulation significantly. As the rate of fault activity is moderate, it is most favorable for hydrocarbon accumulation, which reach a maximum at 15 m/Ma; the larger the size of the fault is, the more favorable for hydrocarbon accumulation is; the closer the trap to the fault is, the better for reservoir hydrocarbon potential is. According to activity rate, fault scale and relative distance between trap and fault, an quantitative characterization of Tibetan formula is found out. It is found 978% of the current found oil and gas reservoirs are located in the probability of fracture controlled Tibetan region of 05. Southeastern Huidong low uplift and the north halfgraben, Enping in the northeastern part of the halfgraben are favorable areas of fracturecontrolled zone.

Carbon and Oxygen Isotopic Compositions and Their Evolution Records of the Xixiangchi Group in Sedimentary Sequences of Centralsouthern Sichuan Basin and Their Geological Implications

JIA Peng,LI Wei,LU Yuanzheng, FAN Ru,LI Xin, LI Ming,ZENG Yiyang,LIU Xin

2016, 30(6): 1329-1338.

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Abstract:The carbon and oxygen isotopes of the Xixiangchi Group in the Cambrian carbonate rocks of centralsouthern Sichuan basin are less modified by postdepositional diagenesis, and thus provide helpful insights into the original ocean. Based on the carbon and oxygen isotope data collected in this area, the carbon and oxygen isotopic compositions, evolution and geological significance of the Middle and Upper Cambrian sedimentary cycles are studied and discussed. Research suggests that the C and O isotopic profile has obvious cyclicity evolution in stratigraphic sequence. δ13C shows a shift from -56‰ to 3247‰ with a mean value of -0979‰ and most of the samples are in the range of -2‰ to 2‰. δ18O shows arrange from -111‰ to -52‰ averaging at -6934‰ and most of the samples are in the range of -9‰ to -6‰. Through the analysis of carbon and oxygen isotope data of sedimentary cycle in different scale, variation of sea level is the main controlling factor of cyclic sequence. The meterscale cyclic sequence is formed under mixing effect of highlyfrequent sealevel change, paleostructures and paleoclimate. Carbon and oxygen isotope analysis shows that the boundary between the Third Series and the Furongian Series is defined, which provides strong evidence for the division and correlation of the strata. The δ13C shows Xixiangchi Group underwent a slow regression after a rapid transgression in the early and middle stages and in the late stage entered a rapid regression after a slow transgression. Sea level changes suggested by carbon isotope distribution are consistent with the evolution of sedimentary facies.

Reservoir Diagenetic Facies and Favorable Reservoir Prediction of the Member 1 and 2 of Palaeogene Shahejie Formation in BZ34 Area of Huanghekou Depression

YAO Jia, WANG Xin, WANG Qingbin, LI Huan

2016, 30(6): 1339-1347.

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Abstract: To study the diagenesis, diagenetic facies (point, line, plane) and favorable reservoirs of of Es1-2, casting thin sections, scanning electron microscope(SEM), electron backscatter differaction(EBSD), cathode luminescence(CL), physical properties data and sedimentary microfacies analysis have been applied to the sampled drilling wells. The result indicates that: influenced by synsedimentary volcanic eruption and hydrolysis, diagenesis in alkaline condition took place in Es1-2 reservoir, forming ctenoid dolomite, potassium feldspar albitization and quartz dissolution. Meanwhile the layered igneous rock protected the underlying stratum by weakening the compaction. Besides, diagenesis in acid condition followed, such as dissolving feldspar and debris. Dissolved pore accounts for 567% percentage(average value) in Es1-2 reservoir. Adopting composite naming way as the diagenetic facies of casting thin section, single well and planar region are named following the “(microfacies) sandstone position+main diagenesis phenomenon+ pore types”, and classified into three types: the underwater distributary channel sand body flankfinesilt sandsiderite cementationlow porosity facies, the delta frontmediumfine sandundercompactiondolomite involucrumdissolved pore facies and the distal volcanic lavatufaceous mediumfine sandtufaceous cementationtight facies. The identification of oil reservoir and oilwater reservoir by well logging interpretation matched the undercompactiondolomite involucrumdissolved pore facies. In this research, the most prospected reservoir favors the delta frontmediumfine sandundercompactiondolomite involucrumdissolved pore facies.

Diagenesis of Tight Sandstones and Formation Mechanism of the Reservoir in the Xujiahe Formation, the Eastern Margin of Longnvsi

JIANG Wei，TAN Xianfeng，WANG Jia，FU Mingqing，CHEN Qing，WU Kangjun

2016, 30(6): 1348-1360.

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Abstract:Tight sandstones as an important carrier of unconventional oil and gas is great significance to study its densifying cause and formation of the reservoir.Through using drilling core, thin section observation, cathode luminescence and fluid inclusion, this article has researched diagenesis and the reservoirs formation mechanism of tight sandstones in the Xujiahe Formation, the eastern margin of Longnvsi, Sichuan. The results show that the Xujiahe Formation of the eastern margin of Longnvsi suffered mechanical compaction, pressure solution, cementation, replacement, dissolution and fracture. Mechanical compaction and cementation are the main factors that lead to densification of sandstones. Dissolution and fracture are the main factors that lead to formation of the reservoir. At present,the Xujiahe Formation is in the middle diagenetic stage AB. Main experienced fluid activities are early calcite cementation and chlorite film of surface water precipitation in syndiagenetic stage. Pressolution controls the formation of secondary quartz increase and pore fluid dissolution of clay minerals,feldspars,easily dissolved cuttings etc. in the early diagenetic stage B. A large number of oil and gas injecting promote secondary increase of quartz and dissolute a small amount of calcites in the middle diagenetic stage A. The formation of the Yanshan and Himalayan movement promote the formation of the reservoir in the middle diagenetic stage B. The formation mechanism of the reservoir is mainly covered by the preservation of the residual primary hole and the formation of the secondary pores. Formation of the reservoir is jointly controlled by favorable sedimentary environment, dissolution, abnormal high pressure and tectonic rupture. Favorable sedimentary environment, dissolution and abnormal high pressure are mainly to protect the primary hole and to form secondary pores. A large number of micro cracks are produced by tectonic disruption, not only improving seepage ability of the reservoir, also providing the conditions for forming the dissolution pores.

Feasibility Analysis of Water Flooding with Multifractured Horizontal Wells in Ultralow Permeability Reservoirs

WANG Mingxian, FAN Zifei, LUO Wanjing, DING Jie, TIAN Qing, YAO Min，BU Xia

2016, 30(6): 1361-1369.

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Abstract:For the feasibility of water flooding with multifractured horizontal wells in ultralow permeability reservoirs, using the streamline simulation, this paper studied the production dynamic behavior of the system including one injector and one producer with multifractured horizontal wells and then discussed the controlling factors affecting the systems water flooding. Simulation results show that without fracture channeling, horizontal wells can increase the injection volume and enhance the production rate and recovery. Its conducive for water flooding when the fracture distribution is not symmetric and the fracture penetration ratio is between 02 and 04. However, fracture channeling will increase the risk of water flooding with multifractured horizontal wells. Fracture channeling at the wellbores edge or multifracture channeling will accelerate the water breakthrough, thus fractured horizontal wells will lose their advantage. When the geological environment is stable and the fracture scale can be controlled, the experiment of water flooding with multifractured horizontal wells can be done. Results from this study can provide theoretical support for water flooding with multifractured horizontal wells in ultralow permeability reservoirs.

Application of Soil Free Hydrocarbon to Distinguish Properties and Preservation Conditions of Oil and Gas

ZHOU Yalong，SUN Zhongjun，YANG Zhibin，ZHANG Fugui， ZHANG Shunyao

2016, 30(6): 1370-1375.

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Abstract: Soil free hydrocarbon technique by directly detecting free light hydrocarbon anomalies affected by the landscape medium of little influence is introduced to obtain underground oil information in this paper. The known petroleum reservoir has a good show of free hydrocarbon geochemical anomalies in the test area in Tarim Basin, the aridity coefficient between 840 and 1989 of which indicates that free hydrocarbon geochemical anomalies is related to the thermal evolution of deep oil and gas. The underground oil and gas reservoir properties predicted and judged by the balance coefficient, soil humidity coefficient and characteristic coefficient of free hydrocarbon component are consistent with the actual geological results. The average of CH4/C3H8 index of nearsurface free hydrocarbon from north to south is between 25 and 116,which illustrates that the depth of oil and gas reservoir increases in turn. The feature of the butane heterogeneous ration and pentane heterogeneous ration shows that Yakela petroleum region has the highest maturity of organic matter. The result indicates that the component and the content variation of free hydrocarbon can forecast and judge the location, character, maturity of organic matter and preservation condition of underground oil and gas reservoir.

Analysis of Key Geological Parameters of Zhengzhuang Coalbed Methane Reservoir and Forecast of Sweet Spots: Investigated by Multiple Seismic Attributes

YANG Yinhui,YAO Yanbin, WANG Hui, CHEN Longwei

2016, 30(6): 1390-1398.

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Abstract:Seismic attribute is related to several geological factors, and thus any one attribute is hard to represent the complex and comprehensive geological characteristics of coalbed methane (CBM) reservoir. The key for selecting the sweet spot of CBM exploration by using seismic attributes is to find an accurate explanation of the seismic attribute characteristics, and to decide the main geological parameters of CBM reservoir. In the study area, the coal thickness, gas content, and permeability have high correlations with seismic attributes of amplitudes, frequencies and curvatures, respectively. Based on these correlations and a transformation of multiseismic attributes, this paper provides a forecast model for the main geological parameters of CBM reservoir. Then, a dynamic weight coefficient median method is used to determine the weightings of the key geological parameters that are related to the highest frequency of median evaluation value. Finally, the sweet spots of CBM production are forecasted by using the equations of evaluation values. The evaluation results of Zhengzhuang field show that the most favorable spot is located in the 59-60-57-55 well block in the northern part, and the secondary favorable spot is around the 53-62-49-45 well block in the northeastern part.

Diapir Conduit Fluid Mechanism and Its Relationship with Gas Hydrate Accumulations

LIU Jie, SUN Meijing, YANG Rui, SU Ming, YAN Heng

2016, 30(6): 1399-1407.

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Abstract:This paper describes fluid migration patterns about mud diapir with different origins, then discusses the relationship between natural gas hydrate accumulation and the evolution of mud diapir migration system, and analyzes the effect of mud diapir migration system on gas hydrate accumulation in Shenhu area.The fluid migration systems for diapir consist of external associated fault and fracture, the internal overpressured fluid fracture and structural fracture in the margin of diapir. Depending on migration conduit and migration dynamics, two kinds of fluid migration patterns have been proposed: overpressureconducting fracturing fluid migration type and marginal fracture migration type. In addition, the mud diapir (mud volcano) has different effects on formation and stability of the hydrate in the different evolution stages. The migration channel may not extend to the hydrate stability zone in the early stages of mud diapiric formation, which results in insufficient supply of CH4. It is conducive to the formation of natural gas hydrates in the middle stage, because of good matching in hydrate metallogenic conditions; the abnormal heat in the hydrate stability zone, caused by high temperature gasbearing fluid from mud volcano eruption, may lead to the decomposition of hydrates in the late stage. Until the quiet period of mud volcano activity, hydrates can be reserved again. According to morphological characteristics of diapirs in Shenhu Area, mud diapirs could be classified into two types: corolliform and domeform diapirs. The fluid migration pattern of corolliform diapirs belongs to overpressureconducting fracturing fluid migration type; the fluid migration pattern of domeform diapirs belongs to marginal fracture migration type. Different diapiric migration patterns may be one of main factors of nonhomogeneous distribution of gas hydrate in Shenhu area.

Geochemical Characteristics of Jurassic Source Rocks in the Muli Coal Field, Qilian Mountain Permafrost

CHENG Qingsong, GONG Jianming, ZHANG Min, ZHAO Qingfang， WANG Weichao

2016, 30(6): 1408-1416.

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Abstract:In order to find out the gas source of gas hydrates in Muli coal field of Qilian Mountain permafrost, fortyfour Jurassic samples were collected from drilling holes of QH1,QH2 and QH3 for geochemical analysis. On the basis of GCMS experiment and microscopical maceral identification of organic matters, the results show that the ranges of TOC and Ro of samples are 14%-166% and 071%~079%, respectively; mudstones TI is greater than 40, and coals TI is less than 0;the peak of normal alkanes appears in the first and the main peak of carbon distribution is C17-C19,while Pr/ Ph is generally greater than 11; tricyclic terpenes has the main peak with C19TT-C20TT, and C24Te has absolute advantage to C26TT; the distribution of C27-C28-C29 sterane series shows as a reverse “L”; C31 homohopane is an important component in hopane series and the content of C34-C35 homohopane is low, and G/C30H is low and mostly less than 02. The results reveal that the Jurassic source rocks stay in a mature stage;organic matters mainly belong to Ⅱ2-Ⅲ type, which are mainly from higher plants;the sedimentary environment belongs to swamp facies; the organic matter abundance is relatively high, indicating to be mediumgood source rocks.It can be drawn a conclusion that Jurassic source rocks in the study area are keeping in an oilgenerating stage and not the main gas source rocks.

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