10 May 2019, Volume 30 Issue 5

    

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  Main controlling factors on normal pressure shale gas enrichmentsin Wufeng-Longmaxi Formations in synclines,southeastern Sichuan Basin

  Hu Dong-feng

  Natural Gas Geoscience. 2019, 30(5): 605-615. https://doi.org/10.11764/j.issn.1672-1926.2019.01.013

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  The synclines develop well in transferring belt from wide spaced synclines to anticlines at the edge of southeastern Sichuan Basin and in the belt of wide spaced synclines outside Sichuan Basin.Due to the uplifting for long time,serious structural movements and great amount of erosion,the regional preservation condition is complex,there exists great differences in gas contents in Wufeng-Longmaxi Formations in various anticlines.On the basis of studies on the features of shales from Wufeng-Longmaxi Formations,preservation conditions and gas contents in anticlines,the article analyzes the main controlling factors on shale gas enrichments in anticlines and makes a conclusion on structural patterns favorable for shale gas preservation and enrichments.The studies show that quality shales are the bases for shale gas,and the quality shales either at the edge of Sichuan Basin or out of Sichuan Basin have similar hydrocarbon rock conditions;preservation condition is the key for gas contents in shales,great depth of shale layers,small dip angle of strata,great distance away from eroded areas and developed over-thrusting faults are favorable for the preservation of shale gas.All in all,the preservation conditions of synclines in transferring belt from wide spaced synclines at the edge of Sichuan Basin are better than that of the belt of wide spaced synclines out of Sichuan Basin.Three kind of structural patterns as uplifts develop in synclines in transferring belt from wide spaced synclines to anticlines,the central part of wide gentle synclines and the synclines covered by over-thrusting faults are favorable for shale gas enrichments.
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  The characteristics of carbonate minerals in the Longmaxi Formationgas shale and its impact on the reservoir performance in the Sichuan Basin

  Guo Qi-heng, Jin Zhen-kui, Geng Yi-kai, Zhao Jian-hua, Chang Rui, Cui Xue-min, Wang Jin-yi

  Natural Gas Geoscience. 2019, 30(5): 616-625. https://doi.org/10.11764/j.issn.1672-1926.2018.12.002

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  In order to investigate the characteristics of carbonate minerals in gas shale and its effect on the reservoir performance,the Longmaxi Formation in the Sichuan Basin is selected for this study.Based on the analyses of X-ray diffraction,scanning electron microscope,porosity analyses of high-pressure mercury injection and nitrogen adsorption experiments,combined with data of thin sections and well logging,different types and some characteristics of carbonate minerals present in the Longmaxi Formation gas shale have been discussed and its influence on reservoir performance was revealed.Carbonate mineral types are mainly calcite,dolomite and ankerite.Six different types of microscopic occurrence have been identified,and pore types associated with carbonate minerals are mainly intragranular dissolution pores and inter-partical pores.TOC and carbonate mineral contents have positive correlation,which indicates high carbonate minerals content may favour the enrichment of organic matter in this gas shale.It's found that when the carbonate mineral content in the Longmaxi Formation is less than 10%,the carbonate mineral content has no correlation with shale porosity.When the carbonate mineral in the shale increases to higher than 10%,the shale porosity decreases with increasing carbonate mineral content.The pore volume and specific area of micropore and carbonate mineral content have negative correlations for both the mesopore and macropore,especially for the pore volume of the mesopores.In conclusion,the carbonate mineral particles act similarly to quartz particles supporting reservoir skeleton,however,the increase of carbonate mineral contents has an adverse effect on shale reservoirs by reducing its porosity.
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  Rock mechanics study and fracability evaluation forLongmaxi Formation of Baojing block in Hunan Province

  Cui Chun-lan, Dong Zhen-guo, Wu De-shan

  Natural Gas Geoscience. 2019, 30(5): 626-634. https://doi.org/10.11764/j.issn.1672-1926.2018.12.021

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  In order to evaluate the shale gas potential and productivity of the Longmaxi Formation in Baojing block,we need to evaluate the fracability of the Longmaxi Formation shale reservoir after completion,which can provide a reference for the future fracturing transformation and well test.Based on the analysis and processing of wireline logging,mud logging and core test data in the study area,we study the characteristics of the Longmaxi Formation shale reservoir in Baojing block and the key factors affecting the fracability of rock,obtaining the positive correlation index and the negative correlation index which have impact on fracability.A mathematical model for quantitative evaluation of the shale reservoir fracability in the study area is established based on the correlation analysis method and the analytic hierarchy process.The results show that the Longmaxi Formation shale reservoir has many characteristics,such as rich in organic matter,low porosity,low permeability,high brittle mineral content,high Young’s modulus,medium Poisson’s ratio,and small difference coefficient of ground stress,with certain shale gas exploration potential and fracturing conditions.Using the fracture index,the shale fracability of the area is divided into three levels,that is,the fracability is poor (the fracture index is 0.1-0.4),the fracability is medium (the fracture index is 0.4-0.6),and the fracability is good (fracture index > 0.6).Reservoir with a fracture index greater than 0.4 should be selected for hydraulic fracturing.The fracture index model is used to calculate the fracability of the shale reservoir in the study area.With high fracture index,the Well Baoye 3 is an ideal fracture candidate well for study area.While Well Baoye 1 fracture index is lower and the fracturing transformation is more difficult.The evaluation results are matched with the post-fracturing effect.The research results can provide reference for the quantitative evaluation and fracturing construction of shale gas and coalbed methane in the future.
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  Sedimentary characteristics of Ordovician Wufeng Formation-Silurian Longmaxi Formation in southwestern Hubei Province

  Wang Xiu-ping, Mou Chuan-long, Xiao Zhao-hui, Zheng Bin-song, Chen Yao, Wang Qi-yu

  Natural Gas Geoscience. 2019, 30(5): 635-651. https://doi.org/10.11764/j.issn.1672-1926.2018.12.012

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  According to the previous research,there was a highland/underwater uplift developed in western Hubei and Hunan area,because of the absence of shell layer of Ordovician Guanyinqiao section or at least two graptolitic biozones between Ordovician Wufeng Formation and Silurian Longmaxi Formation.Based on the detailed study of sedimentary characteristics and the evolution of sedimentary environment,it can be figured out that there was nondepositional hiatus between Ordovician Wufeng Formation and Silurian Longmaxi Formation,and the existence of Hrinantian deposition.In the depositional process of Wufeng-Longmaxi Formations,the depth of sedimentary water was from gradually deep to shallow,and the paleoclimate experienced the significant cooling period.It was shallow shelf facies of Hrinantian under the background of global ice age,which was deposited on the Wufeng deep shelf facies,most as carbonaceous pelitic siltstone with the minerals of highest content of quartz,fewest of clay minerals,and higher of organic carbon content,and with the elemental constituent of the highest SiO2 and the least Al2O3.The shallow shelf facies was the most developed of Wufeng-Longmaxi Formations in southwestern Hubei,with rapid changes in lithology.Compared to others in Middle-Upper Yangtze area,the shallower sedimentary water was not conducive to the shale gas enrichment.
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  Characteristics of calcite cements in deep Xiagou Formationsandstones of Ying’er Depression，Jiuquan Basin

  Tang Hai-zhong, Wei Jun, Zhou Zai-hua, Xiao Wen-hua, Yu Hai-Dong, Wei Hao-yuan

  Natural Gas Geoscience. 2019, 30(5): 652-661. https://doi.org/10.11764/j.issn.1672-1926.2019.03.013

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  Authigenetic calcites are the biggest volume cement in the anomalously high porosity zones of the deep Xiagou Formation sandstones in Ying’er Depression,Jiuquan Basin.By casting slice,scanning electron microscope and electron microprobe analyses,the occurrences of these calcite cements were observed in detail and their geochemical compositions were probed,in order to investigate their genetic mechanisms and their relationship with the anomalously high porosity zones.The result shows that the calcite cements have three occurrences including disseminated,blocked and starlike structutes in the deep sandstones.The disseminated calcite cement is deposited from the compressed released water that is from the nearby muddy sediments during the early diagenetic stage A.The blocked and starlike calcite cements are the product of the dissolution-precipitation reactions of the disseminated calcite cement by 5-stage acid fluids with the multiple resources and diversified ways,which makes the ferrocalcite transmuted into the calcite and the tight sandstones with the disseminated calcite cement turned into the anomalously high porosity zones with the blocked and starlike calcite cements.The superimposition areas of 5-stage dissolutions of these calcite cements are the preferred targets of the hydrocarbon exploration and development.In view of this,aimed at the anomalously high porosity zones in the deep calcite-rich continental sandstones,the petrological characteristics should be the foundation for the study of the genetic mechanisms of the calcite cements and the confirmation of the anomalously high porosity zones,and the other information must obey this foundation.
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  Detrital zircon dating of LA-ICP-MS in the Upper Jurassic and indicative significance of the Qaidam Basin

  Zeng Xu, Lin Tong, Wang Wei, Yan Zhan-dong, Hao Cui-guo, Bian Ying-ying, Wang Jun

  Natural Gas Geoscience. 2019, 30(5): 662-672. https://doi.org/10.11764/j.issn.1672-1926.2019.01.004

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  At present,zircon dating technology is widely used in basin evolution and reconstruction.On the research of the stratigraphic sequence,sedimentary environment and source analysis of the Upper Jurassic that is the critical deformation period of the northern margin of Qaidam Basin,the spatial and temporal evolution pattern of the north margin of Qaidam Basin in late Yanshan-early Xishan period was discussed.Several evidences show that during the Middle and Late Jurassic,the Qilian Mountains began to uplift,and the whole north margin of the Qilian mountains was in a weak compression environment.The tectonic properties were reversed.The Lvcaogou and the Tuanyu mountains field outcrops show that the Upper Jurassic is a series of sedimentary sequences of braided river and shallow lake system in arid environment,which is quite different from the Middle Jurassic strata.In seismic section and field outcrop,the Upper Jurassic was in angular unconformity or parallel unconformity contact with the upper and lower strata.The zircon U-Pb chronological analysis of the Upper Jurassic coarse sandstone in Lvcaogou and Tuanyu  Mountains shows that the Upper Jurassic has similar age spectrum characteristics. The zircon age is between 2 800 and 222Ma.The age distribution of detrital zircons in Tuanyushan one of tue Upper Jurassic samples is 242-226Ma with main peak of 242Ma,414-255Ma with main peak of 383Ma,964-559Ma with main peak of 559Ma,1 515-1 125Ma with main peak of 1 130Ma,2 437-1 746Ma with main peak of 1 960Ma.Compared with the age spectrum of the peripheral provenance area,the main provenance area of the Upper Jurassic is the South Qilian area.Compared with the Middle Jurassic age,the detrital zircon age of the Upper Jurassic is characterized by reverse sequence denudation.The unconformity between the Middle and Upper Jurassic formed in the weak compressional environment is an efficient channel for oil and gas migration,and the lithologic trap of the Upper Jurassic is a main direction for oil and gas exploration in the next step.

  
  

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  The classification,characteristics and development model and couplingrelation with different accommodation space of platform margin reef:Case study of L2 member of Lianglitage Formation in the eastern Tazhong area,Tarim Basin

  Shi Ping-zhou, Wang Zhen-yu, Dong Yu, Fan Kun-Yu

  Natural Gas Geoscience. 2019, 30(5): 673-685. https://doi.org/10.11764/j.issn.1672-1926.2018.12.016

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  The platform margin reef was developed in the Late Ordovician Lianglitage Formation in the eastern Tazhong area of Tarim Basin.According to the thin section observation under single-well microscopy and the relative ratio profile of reefs,2-4 reef growth cycles were developed vertically,with the thickness of single cycle at 30-80m and good lateral contrast.According to the relationship between the variation of the accommodation space and the growth of reefs,reefs are divided into three types:(1) The vertical capacity increases,that is,when the relative sea level rises faster than the growth rate of reefs,retrogradation reefs are formed;(2) The vertical capacity decreases,that is,when the relative sea level rise speed is lower than the growth rate of reef,progradational reef is formed;(3) The vertical capacitance space remains unchanged,that is,the dynamic equilibrium exists between the growth of the reef and the sea level,aggradational reef is formed.The identification marks of three kinds of reefs and their coupling relationship with soluble space and their genetic models are established respectively:(1) Retrogradational reef.The logging curve of natural gamma ray (GR) is low,and the deep dual laterolog is nearly flat.The reef-forming organisms with,block,dendritic,and plate corals and sea moss is given priority to,more development in the early high water deposition,platform on the landward migration period.The reef-building organisms are mainly composed of solenopora,corals with blocky,dendritic and tabular form,and bryworm.Most of them are developed in the early stage of high water level deposition and stage of platform migration to land.(2) Progradational reef.The logging curve shows medium to low value of natural gamma (GR),and the deep dual-lateral logging shows low value.The reef-building organisms mainly include sea lilies,pelagic plankton and cryptophyta,mostly developed in the late stage of high-water level deposition.When the sea level drops or keeps still,the platform edge moves towards the basin,and the reef level gradually rises.(3) Aggradational reef.Low natural gamma (GR) value is shown in logging curves,and medium and high value is shown in the deep and shallow dual laterolog logs.The reef-building organisms mainly include gastropods,echinodermata and algae,and the reefs mostly develop in the middle of high-water deposition.
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  Diagenesis of sandstone and its implications for reservoir quality evaluationin the deep Xishanyao Formation in the central Junggar Basin

  Zhang Zhen-yu, Zhang Li-kuan, Luo Xiao-rong, Cao Bin-feng, Lin Hui-xi, Zeng Zhi-ping, Qin Feng, He Wen-jun, Li Chao, Lei Yu-hong

  Natural Gas Geoscience. 2019, 30(5): 686-700. https://doi.org/10.11764/j.issn.1672-1926.2019.04.002

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  Petrology and diagenetic features of the Middle Jurassic Xishanyao Formation sandstones in the Yongjin area of the central Junggar Basin are studied,based on an integrated method of thin section,scanning electron microscopy,electron probe and X-ray diffraction.The effects of diagenesis on the deep reservoir quality and the formation of high-quality reservoir rocks are investigated.The Xishanyao Formation sandstones are deposited in delta front facies,and are mainly very fine- to medium- grained litharenites and minor feldspathic litharenites.Authigenic minerals are dominated by combinations of calcite,Fe-calcite,ankerite,clay minerals,quartz,with minor amounts of zeolites and pyrite;Specific diagenetic factors that exert control on reservoir quality include mechanical compaction,carbonate and clay cementation and dissolution.Mechanical compaction is the primary cause of intergranular porosity loss through deformation of ductile grains.Carbonates fill residual intergranular pores and this causes the important diagenetic damages resulting in porosity reduction and enhancing reservoir heterogeneity.Chlorite coats may preserve porosity through the inhibition of pore-filling quartz cementation.The selective dissolution of unstable grains enhances porosity.The diagenetic patterns are mainly governed by detrital grain size and composition.Fairly moderate mechanical compaction,limited cementation,extensive chlorite precipitation and dissolution mainly occur in relatively coarser-grained sandstones in the middle-lower part of a distributary channel that contains less abundant ductile grains.Thus these coarser-grained sandstones constitute high-quality reservoir rocks in the Xishanyao Formation.This study shows that diagenetic pattern in deep sandstones is determined by original depositional environment,and reservoir quality distribution is fundamentally related to depositional facies and internal architectural structure of a reservoir.Therefore,unravelling the relationship between initial depositional conditions and diagenetic processes can provide insight into reservoir quality prediction for deep sandstones.
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  The channel stacking pattern under the control of sequence stratigraphicof Enping Formation in Lufeng area,Pearl River Mouth Basin

  Rui Zhi-feng, Deng Hong-wen, Yang Xiao-jiang, Li Xiao, Guo Jia

  Natural Gas Geoscience. 2019, 30(5): 701-711. https://doi.org/10.11764/j.issn.1672-1926.2019.01.011

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  Based on the integrated utilization of cores,logging and seismic data,and according to the fluvial sequence stratigraphic theory,the channel stacking patterns of Enping Formation were analyzed.Enping Formation was divided into three 3rd-order sequences which were controlled by the variation of accommodation.The three channel stacking patterns were summarized:Thick-stacked delta plain braided distributary channels under low accommodation,thick-stacked or isolated delta front branch channels under middle accommodation,thin-isolated branch channels-sheet sand under high accommodation.Different channel stacking patterns have different reservoir characteristics.The thick-stacked delta plain braided distributary channels under low accommodation mainly formed structural reservoirs,and the thin-isolated branch channels-sheet sand under high accommodation mainly formed lithologic reservoirs.This analysis method has some reference significance for other similar areas.
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  Effects of large-foraminiferal shells on sandstone reservoir space and physical properties:Case study of the 1^st member of Sanya Formation,Songnan Sag,Qiongdongnan Basin

  Ma Zun-qing, Chen Guo-jun, Yang Hai-zhang, Li Chao, Zhao Yi-lin,

  Natural Gas Geoscience. 2019, 30(5): 712-720. https://doi.org/10.11764/j.issn.1672-1926.2019.01.007

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  Casting thin-sections,SEM and statistical methods were used to study on the effects of large- foraminiferal fossils on the reservoir space and physical properties of the 1st member of Sanya Formation fine-medium sandstone,2 565.00-2 576.23m in the Well S34,Songnan Sag,Qiongdongnan Basin.The analysis shows that the fine-medium sandstone in this section has the physical characteristics of medium-low porosity,low permeability and ultra-low permeability.Large foraminiferal shells have a special effect on the reservoir space and physical properties of sandstone.Their compaction resistance can reduce the damage of compaction to the pore of coelom cavity and the pore between shell lattices,and conserve 1%-4% of the pore of coelomic cavity in sandstone.However,the foraminiferal shell is large and its hardness is smaller than siliceous debris particles,compaction can make many debris particles around the shell embedded in the foraminiferal shell wall.Foraminiferal shell can seal the debris intergranular pore around the shell and affect its permeability.The stable carbon and oxygen isotope test results of carbonate cements show that the values of δ¹³C ranged from -2.050‰ to 0.243‰,the values of δ¹⁸O ranged from -9.700‰ to -7.624‰,and the values of Z(paleosalinity) ranged from 118.93 to 123.67,with an average value of 121.42.The formation temperature of carbonate cements ranged from 56.5℃ to 64.8℃,with an average of 62.2℃.The carbonate cements are characterized by marine diagenetic environment and early diagenetic stage.Considering the positive correlation of the content between the foraminifera and carbonate cements in thin slices and the distribution of carbonate cements near foraminiferal shells,the large foraminiferal shells provide abundant material sources for the formation of carbonate cements,and the strong cementation caused by them is an important reason for the poor physical properties of sandstones.
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  Influence of volcanic activity on geochemical characteristics of hydrocarbonsource rocks in the Quse Formation in the South Qiangtang Basin

  Tang You-jun, Yang Yi-zhuo, Meng Xian-xin, Wang Ting, He Da-xiang, Li Meng-ru, Ji Chang-jun, Sun Peng, Cai Yi-lan

  Natural Gas Geoscience. 2019, 30(5): 721-728. https://doi.org/10.11764/j.issn.1672-1926.2019.02.004

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  The Qiangtang Basin in Tibet is a Mesozoic marine residual basin with huge potential for oil and gas resources in China.Volcanic eruption was frequent,especially in the Mesozoic.The source rocks in Quse Formation are deposited in marine environment,which are composed of oil shale,shale and limestone.The source rocks of Quse Formation in the study area near the Bijiang fault in the southern Qiangtang Basin are interbedded with volcanic rock.The source rocks and their surrounding basalts are different products in the same period.The source rocks were formed in the Early Jurassic,and volcanic rocks formed in the Early Jurassic.The hydrocarbon generated potential and biomarker composition of source rocks in Quse Formation are investigated using the conventional geochemical methods to discuss the sedimentary environment,the organic matter source and the influence of the volcanic activity on the source rock.The result shows that the organic matter abundance of source rocks is high,and the organic matter is mainly Type II.The bake effect of volcanic magma activity on the source rock is not obvious,the thermal evolution stage of organic matter is in the mature stage.The source rocks are deposited in reduced environment with the contributions of aquatic organisms.The comprehensive investigation indicates that the source rocks in the study area have good hydrocarbon generating potential.
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  Geochemical characteristics of lacustrine organic-rich fine-grainedsedimentary rocks and its effects on the accumulation of tight oil:Case study of Chang 7 member of Triassic Yanchang Formation in Longdong area,Ordos Basin

  Gao Yong-liang, Wen Zhi-gang, Li Wei

  Natural Gas Geoscience. 2019, 30(5): 729-739. https://doi.org/10.11764/j.issn.1672-1926.2019.03.010

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  In order to clarify the distribution characteristics of lacustrine organic-rich fine-grained sedimentary rocks and its effects on tight oil accumulation,the Chang 7 member of Triassic Yanchang Formation in Longdong area of Ordos Basin was taken as an example to study the geological and geochemical characteristics by rock pyrolysis,isotopic determination,maceral analysis,gas chromatography(GC),gas chromatography-mass spectrometry (GC-MS),core description and log interpretation.Lacustrine organic-rich fine-grained sedimentary rocks were divided into organic-rich shale and organic-rich mudstone according to their lithology and texture.The results show that organic-rich shale deposited in the quiet and anoxic deep lake environment,the stratification of water was obvious,the abundance of organic matter is high,and the organic matter mainly came from plankton and benthic algae (type Ⅰ-Ⅱ1).Organic-rich mudstone mainly deposited in the semi-deep lake environment,where the water was relatively shallow,the salinity of water was relatively low,and the abundance of organic matter was low,and the organic matter was derived from the mixed source of plankton and terrestrial clastic (type Ⅱ1-Ⅱ2).The organic-rich fine-grained sedimentary rock in the area of Bazhu-Maling-Qingcheng-Huachi is the thickest in Longdong area.The organic-rich shale is mainly developed in Chang 7₃ sub-member,while the organic-rich mudstone is developed in each sub-member of Chang 7 member.In Longdong area,tight oil is widely distributed in the Chang 7 turbidite sand bodies,and it was mainly derived from the Chang 7₃ organic-rich shale.The distribution of reservoir is controlled by the development of organic-rich fine-grained sedimentary rocks.
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  Elemental geochemical characteristics and limit on sedimentary environmentin the Late Ordovician Wufengian period in the Wuxi area,NE Chongqing

  Liu Tian, Feng Ming-you, Wang Xing-zhi, Chen Bo, Zhang Liang-hua, Liu Xiao-hong, Wang Jue-bo

  Natural Gas Geoscience. 2019, 30(5): 740-750. https://doi.org/10.11764/j.issn.1672-1926.2019.01.012渝东北巫溪地区晚奥陶世五峰期元素地球化学特征及其对沉积环境的限制

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  The deep-water rocks are confused to reflect fluctuation of sea level by the fine-grained sediments and occurrence of a thin succession.Upper Ordovician black siliceous rocks and siliceous shales (Wufeng Formation) from Wuxi (Northeastern Chongqing,Southwest China) are studied using integrated petrographic,and geochemical methods (major,trace elements and REE) and pyrite framboid in order to decipher depositional conditions during the sedimentation of siliceous rocks.Al₂O₃/(Al₂O₃+Fe₂O₃),SiO₂/Al₂O₃ and Al-Fe-Mn values indicate that the sediments of Wufeng Formation are deposited in a continental margin and influenced by detrital input.U_EF-Mo_EF and V/Cr-U/Th cross plots suggest the Wufeng Formation was formed in dysoxic to anoxic conditions.In addition,redox proxies such as U/Th and V/Cr suggest that the lower part of Wufeng Formation was deposited in an anoxic environment,while the upper part was deposited in a dysoxic environment.Furthermore,the gradual increase of the average size of pyrite framboids (from 3.46μm to 4.21μm) shows that the oxidizability increased.During the Wufengian period deposition,sea level fluctuations can be divided into a third-order cycles and subdivided into five fourth-order cycles.U/Th,Ni/Co,V/Cr,and the size of pyrite framboid decrease gradually,which indicates that oxidizability (from anoix to dysoxic) and depth of the water gradually increased.The sedimentary environment was transformed from outside shelf to inner shelf.
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  Strategy consideration of China’s natural gas exploration situation

  She Yuan-qi, Gao Yang, Yang Gui-ru, Li Jian, Li Jun, Li Ming-peng

  Natural Gas Geoscience. 2019, 30(5): 751-760. https://doi.org/10.11764/j.issn.1672-1926.2018.12.008

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  China’s natural gas exploration has entered the third stage of rapid development and faced new challenges. Through the analysis of China’s large gas field exploration progress,achievements of theoretical and technical,profound changes in natural gas exploration philosophy,source types and prospect,it revealed five major problems in China’s present natural gas exploration process:(1)Uncertainty of deep natural gas resources;(2)Insufficient understanding of accumulation mechanism in large gas fields leads to the lack of exploration targets;(3)The potential and economic prospects of unconventional gas has great uncertainty;(4)Complex gas reservoir still faces a series of technical bottlenecks;(5)Resources are getting worse and the ever-growing of costs leads to the decrease of exploration benefits. The analysis shows that the upstream of domestic natural gas should fully predict the impact of international industrial shock,combine the situation of domestic natural gas production and supply preservation,increase the strength and policy support of unconventional natural gas exploration,promote technological innovation and integration,and realize the complex benefit development. Under the new situation,exploration and deployment should be evaluated comprehensively by key indexes such as resource potential,reserves potential and comprehensive cost of exploration and development on the basis of domain classification,and different exploration deployment strategies should be carried out in combination with the development situation and characteristics of different exploration areas.
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  Source rock  TOC content prediction based on the support vector machine model:An application in Ordos Basin

  Zhang Cheng-long, Tao Shi-zhen, Bai Bin, Wang Qian-ru

  Natural Gas Geoscience. 2019, 30(5): 761-768. https://doi.org/10.11764/j.issn.1672-1926.2019.01.014

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  Calculating TOC content using Logging data is a relatively easy and inexpensive way to evaluate source rocks.The traditional ΔLogR method for calculation is widely used now.In order to adapt to the TOC calculation under complex geological conditions,a representative model well is selected under the sedimentary background.For the purpose of uniting logging data and TOC data,linear filter is used to preprocess the data.The Pearson matrix can help screening logging characteristics for training.Final feature and measured TOC values are used as inputs to build the support vector machine models,and cross-validation is used to select regional optimal models for the final prediction.The application of this support vector machine method in the Ordos Basin shows that it has high accuracy and generalization ability,and is superior to the ΔLogR method when TOC is relatively high or low.The result can effectively reflect the heterogeneity of organic matter abundance in the Chang 7 high quality source rock in Ordos Basin.
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  Specification of abstract writing

  Natural Gas Geoscience. 2019, 30(5): 769-770.

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  Natural Gas geoscience 2019-5 covers and titles

  Natural Gas Geoscience. 2019, 30(5): 9051-9052.

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