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Table of Content

    28 October 2018, Volume 39 Issue 5
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    Tectonic evolution stages and features of the Junggar Basin
    He Dengfa, Zhang Lei, Wu Songtao, Li Di, Zhen Yu
    2018, 39(5):  845-861.  doi:10.11743/ogg20180501
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    The analysis of tectonic evolutionary stages serves as the basis for addressing the basin formation and evolution,also as the important foundation for delineation of the spatial-temporal framework for oil and gas accumulation,and as a key reference for establishing the tectonic movement chronology for continents.Based on the information from deep boreholes and the high resolution reflection seismic data within the Junggar Basin,we delineated the tectonic evolution stages of the basin and explored the characteristics of every stage,through analyzing the tectonic subsidence and the tectono-stratigraphic sequence,and the tectonic events in the periphery of the basin.The results show that the basin has undergone six evolutionary stages,including the Carboniferous fault depression-depression,the Permian fault depression,the Middle Permian and Triassic foreland basin,the Jurassic extensional fault depression-compresso-shear basin,the Cretaceous-Paleogene intra-continental depression,and the Neogene-Quaternary intra-continental foreland basin,which can be grouped into four non-isochronous extension-compression cycles,namely the Carboniferous,Early Permian-Triassic,Jurassic,and Cretaceous-Quaternary cycles.The extension tends to be weaker,but the compression gets stronger north-southwardly,with time passing by.On the whole,the basin exhibits the character of "thrusting on its periphery and shrinking in scope",with the west-eastward shortening rate being 35.8%,almost three times of the 12.2% on the north-south direction.The compression from the west took place mainly during the Middle Permian-Early Triassic,while besides that,the compression from the east was still strong in the Late Triassic,early Middle Jurassic,and Late Jurassic-Early Cretaceous.The compression from the south took place strongly in the Middle and Late Permian,the Middle and Late Jurassic,and the Pliocene-Quaternary; while the extensive thrusting on the northern margin occurred in the Late Cretaceous.The pronounced spatial-temporal differences of the above extension and compression have given rise to the complex superimposed composite basin architecture,thus different tectonic units show strong differential evolution and unique features of oil and gas accumulation.
    Nanhua-Sinian tectono-sedimentary framework of Tarim Basin,NW China
    Shi Kaibo, Liu Bo, Jiang Weimin, Luo Qingqing, Gao Xiaoqiao
    2018, 39(5):  862-877.  doi:10.11743/ogg20180502
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    The systematic study on the Nanhua-Sinian tectono-sedimentary framework in Tarim Basin is the key to understanding its tectonic attributes,formation and evolution of continental rifts,and sedimentary filling processes.Based on the comprehensive analysis of outcrops in the periphery of Tarim Basin,drilling and seismic data,and previous studies relevant,we discussed the Nanhua-Sinian tectono-sedimentary framework of Tarim Basin.Research shows that there were two individual massifs of the north and south of Tarim in the Pre-Nanhua.The convergence of the north and south massifs led to the final formation of the unified Tarim plate during the Late Pre-Nanhua.During the Nanhua to Sinian,the Tarim Basin was in an extensional tectonic setting as a result of breakup of the Rodinia supercontinent,and underwent the formation and evolution of continental rifts.The evolution of the basin may be divided into three stages:(1) the rifting stage during the Early Nanhua (760-700 Ma), (2) the rifting to depression transitional stage during the Late Nanhua-Early Sinian (660-600 Ma), and (3) the post-rift depression evolution stage during the Late Sinian (580-540 Ma).During the rifting stage,the Awati rift in the west,north and south Manjiar rifts in the east and the NW-and SE-trending rifts in Maigaiti area in the south of the Tarim Basin formed.The tectonic framework of the basin controlled the paleogeographic characteristics and sedimentary assemblages.In the Nanhua,rifting predominated,resulting in clastic-volcanic rock assemblage under intensive extension.In the Sinian,depression predominated in Tarim Basin which showed the paleogeographic characteristics of uplift in the south and depression in the north,resulting in three types of sedimentary assem-blages,i.e.clastic rock,mixed clastic-carbonate,and carbonate assemblages.
    Characteristics of differential activities in major strike-slip fault zones and their control on hydrocarbon enrichment in Shunbei area and its surroundings,Tarim Basin
    Deng Shang, Li Huili, Zhang Zhongpei, Wu Xian, Zhang Jibiao
    2018, 39(5):  878-888.  doi:10.11743/ogg20180503
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    The faulting characters and evolution history of the Tuopu 39 fault system,and the Shunbei 1,Shunbei 5 fault zones,distributed in Shunbei area and its surroundings,Tarim Basin,were investigated in detail.Based on the analysis of fault evolution on mechanics and large amount of single-well production performance,we fully discussed the control of strike-slip faults on hydrocarbon enrichment.The integrated analyses reveal fundamental differences between the Tuopu 39 fault system and the Shunbei 1,Shunbei 5 fault zones in terms of geometries,kinematics,and structural evolution.The NNE-trending Tuopu 39 fault system experienced sinistral movement in conjugate strike-slipping state at the early stage,but turned to dextral strike-slipping at the late stage due to the change of the orientation of maximum principal stress.In comparison,the NNW-trending secondary faults inside the system were almost inactive.Shunbei 5 fault zone(NNW-NS-trending) formed ahead of the NE-trending Shunbei 1 fault zone and experienced different stress regimes and changes of the maximum principal stress orientation.The faulting movements of Tuopu 39 fault system in the late stage occur in Himalayan period,the same as hydrocarbon accumulation,thus control the hydrocarbon enrichment,particularly in the pull-apart areas along the fault zone.The analysis on multiple production wells on Shunbei 1 fault zone suggests that the underlying strike-slip fault segments and the juxtaposed pull-apart intervals corresponding to the en echelon normal faults of relative bigger intensity are more enriched in hydrocarbons.
    Sedimentary constraints on the tectonic evolution of Mianyang-Changning trough in the Sichuan Basin
    Li Shuangjian, Gao Ping, Huang Boyu, Wang Haijun, Wo Yujin
    2018, 39(5):  889-898.  doi:10.11743/ogg20180504
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    Mianyang-Changning trough is developed during the transitional period from the Sinian to Early Cambrian in Sichuan Basin.We systematically collected the outcrop samples and drilling data both inside and outside the trough and analyzed its tectonic evolution according to stratigraphic unconformity,lithological variation,log correlation and geochemical data.The results show that there are pronounced onlaps on the Lower Cambiran sequences in the trough,keeping the erosional unconformity between the Lower Cambrian and Sinian Dengying Formation intact.In addition,evidences of early stage karstification occur in the residual Dengying Formation,indicating that the trough has experienced exposure and erosion before the Cambrian sedimentation.Meanwhile,the sedimentary cycle correlation demonstrates that there is an additional sedimentary cycle in the Maidiping Formation with normal proportion of black rocks in the trough.Moreover,elemental logging in Well Ziyang-1 inside the trough shows that there are 20 m-thick siliceous argillaceous dolomites deve-loped in the lower part of the black rocks.Thus,in combination with the stratigraphic division based on drilling data in the adjacent areas,we believed that the black rocks within the trough include not only the Cambrian Maidiping Formation,but also the 3rd and 4th members of the Sinian Dengying Formation.Besides,the hydrothermal origin of siliceous rocks in the 4th member of the Dengying Formation proves that strong regional extension exists during that time.According to the Middle Neoproterozoic-Cambrian magmatic activity records and the characters of the Nanhua sedimentary strata,we considered that the Mianyang-Changning trough inherited from the persistent negative landforms on the basis of Nanhua rift,and it was formed under the combined effect of intermittent extensional subsidence and denudation from exposure.Therefore,the trough is an extensional-erosional trough in tectonics.
    Brittle-ductile transition zone of shale and its implications in shale gas exploration
    Yuan Yusong, Liu Junxin, Zhou Yan
    2018, 39(5):  899-906.  doi:10.11743/ogg20180505
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    Shale brittleness and ductility always attract much attention in shale gas exploration and development.The determination of the depth interval of brittle-ductile transition of shale is key to the evaluation of shale gas preservation and hydraulic fracturing.Based on rock mechanics tests,we established a set of methods for determining the brittle-ductile transition zone of shale.The pre-consolidation pressure was determined through uniaxial strain test,and the threshold of over-consolidation ratio(OCR) and the critical confining pressure of brittle-ductile transition of shales were defined via triaxial compression test.And in turn,the bottom boundary of brittle zone was determined according to the maximum palaeo-depth combined with the OCR threshold,while the top boundary of ductile zone was determined by the critical confining pressure of brittle-ductile transition.The brittle-ductile transition zone is the depth interval between the bottom boundary of brittle zone and the top boundary of ductile zone.The shale brittle zone,ductile zone and brittle-ductile transition zone defined by the above methods can be used for evaluations of shale gas preservation conditions and hydraulic fracturing.The results show that(1) in the brittle zone,the shale gas is not well preserved as brittle fractures are easy to occur under tectonic events;(2) in the ductile zone,the hydraulic fracturing does not work well because the hydraulic fractures are easy to close; but(3) in the brittle-ductile transition zone,the shales are not only more favorable for shale gas preservation but also better in fracturability.Therefore,the brittle-ductile transition zone is the best interval for the exploration and development of marine shale gas in southern China.The exploration practice indicates that the burial depth of the shale gas play zones with high and stable yield in the Silurian Longmaxi Formation is just within the brittle-ductile transition zone determined by the methods proposed in this study.
    Structural evolution and hydrocarbon accumulation in the eastern Junggar Basin
    Zheng Menglin, Tian Aijun, Yang Tongyuan, He Wenjun, Chen Lei, Wu Haisheng, Ding Jing
    2018, 39(5):  907-917.  doi:10.11743/ogg20180506
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    Surface geology,seismic and drilling data in combination with the research progress of orogenic belt in the Junggar Basin and its periphery were used to comprehensively study the structural deformation and its superinposition in the eastern Junggar Basin.The results show that the structural deformation in the study area is characterized by N-S zonation,E-W partition and multi-stage superinposition.From the south to the north,there are three major tectonic deformation regions of the Bogda front,the eastern uplift of the basin and the Kolameili front.To go a step further,the eastern uplift can be subdivided into three major structural deformation zones along N-S direction:the northern zone consists of a set of NE-trending anticlines and synclines;the central part is the NWW-trending paleo-uplifts;and the southern part is a nearly SN-trending structure controlled by early structures,forming a combination of imbricate folds and faults.The area has undergone multi-stage tectonic deformation such as the Carboniferous extensional faulted depression and SN-trending compressional deformation,the Mesozoic compressional strike-slip and the Cenozoic SN-trending compression.It contains varying patterns of structural deformation,such as compression,strike-slip,thrust nappe and kink-band,and chronologically,can be divided into six major tectonic evolution stages.Through the research of discovered oil and gas reservoirs,we considered that the factors controlling the distribution of oil and gas are structural deformation differences,multi-stage superimposed paleo-bulges,unconformities and faults.
    Characteristics of seismic wave groups and tectono-stratigraphic sequences of the Carboniferous,eastern Luliang uplift,Junggar Basin
    Zhang Lei, He Dengfa, Li Di, Zheng Menglin, Wu Songtao, Liang Yusheng, Yang Sidi
    2018, 39(5):  918-931.  doi:10.11743/ogg20180507
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    We explored the characters of seismic wave groups of the Carboniferous in the eastern Luliang uplift of Junggar Basin under the guidance of the latest drilling and seismic data.Accordingly,the tectono-stratigraphic sequences were identified in the study area.Four main reflection interfaces,namely T0,T1,T2 and T3,were identified based on analysis and correlation of synthetic seismograms of 30 wells.Among them,the interface T0 and T2 are characterized by high amplitude,good continuity,and stable waveform of reflective waves,thus are the main regional unconformities and the critical key beds of comparison in the area.Based on that,the seismic wave group characters of each seismic stratum among the four interfaces were summarized.We thus knew that the seismic wave groups between T1 and T2 have low amplitude,medium-low frequency and moderate-poor continuity,and wedge-shaped reflection,thus can be used as the key beds of comparison in the eastern Luliang uplift.Then we traced the unconformities,analyzed the outcrop,paleontological and chronological data,and subsequently subdivided the Carboniferous herein into four tectonic layers.From the bottom to the top,they are the lower sedimentary tectonic layer C1-s(Dishuiquan Formation),lower volcanic tectonic layer C1-v(Songkaersu lower group),upper sedimentary tectonic layer C2-s(Songkaersu upper group) and upper volcanic tectonic layer C2-v(Bashan Formation).The results can be summarized as follows:(1)the distribution of tectonic layers in the Carboniferous is controlled by the basement,tectonic setting,location of development and later modification.Their thickness is relatively large in the intra-arc fault depression and fore-arc basin,while is relatively small on the island arc convex;(2) two tectonic compression activities developed at the end of the Early and Late Carboniferous respectively lead to the denudation of the strata between C1-v and C2-s and that on top of the C2-v,and the inversion of the fault depression in the Carboniferous.
    Tectono-stratigraphic sequence and basin evolution of the eastern Junggar Basin
    Yi Zejun, He Dengfa
    2018, 39(5):  932-942.  doi:10.11743/ogg20180508
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    The east of Junggar Basin has undergone multi-stage tectonic movements since the Carboniferous.Its sedimentary center migrated several times and the strata suffered multiple stage erosion.In order to reveal the relationship between stratigraphy and basin evolution,we described the distribution of unconformity based on the interpretation of seismic profile covering the whole basin,and analyzed the tectonic dynamic conditions during unconformity formation.The results show that there are five regional unconformities in the eastern Junggar Basin.They are respectively located on top of the Lower Carboniferous,and at the bottom of the Middle Permian,the bottom of the Cretaceous,the bottom of the Paleogene and the bottom of the Neogene.Accordingly,the Carboniferous-Quaternary of the eastern Junggar Basin can be subdivided into six tectonic layers,namely the Lower Carboniferous,Upper Carboniferous-Lower Permian,Middle Permian-Jurassic,Cretaceous,Paleogene,and Neogene-Quaternary structural layers.From the Late Carboniferous to the Quater-nary,the area experienced five evolutionary stages in total.In the Late Carboniferous,the intra-continental tectonic defor-mation cycles appeared in the area;in the Hercynian,the continental basin formed initially,and in the Mesozoic-Cenozoic, superimposition of the Indosinian,Yanshan and Himalayan movements occurred in a row.The multi-phased and multi-section activities of Kelameili Mountain and Bogda Mountain,and the repeated reactivation of faults within the basin directly led to the tectonic layer superimposition and multistage evolution of Junggar Basin.
    Tectono-stratigraphic sequence and basin evolution of Shawan Sag in the Junggar Basin
    Liang Yusheng, He Dengfa, Zhen Yu, Zhang Lei, Tian Aijun
    2018, 39(5):  943-954.  doi:10.11743/ogg20180509
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    The study of tectono stratigraphic sequence and basin evolution in Shawan Sag,Junggar Basin,is of great signi-ficance both to the understanding of the basin structure and the petroleum exploration in this area,and to a certain extent to the understanding of the tectonic evolution of the Central Asian Orogenic Belt.Seismic and well data were integrated to perform fine tracing of seismic events,and to analyze the truncation,overlapping and pinch-out within each sequence deposited since the Carboniferous in combination of correlation on well-tie profiles,and finally six major tectonic sequences were recognized according to the corresponding tectonic regime transformation processes.Additionally,the fine interpretation of tectonics was based on the theory of fault-related folds,and the tectonic evolution of Shawan Sag since the Late Carboni-ferous was discussed mainly according to the fine interpretation and the balanced cross-section technique.The results show that the formation and evolution of the Shawan Sag can be divided into seven stages,namely the Late Carboniferous extensional fault depression,the Early Permian extensional depression,the Middle-Permian-to-Late-Triassic foreland basin,the Jurassic intracontinental depression and transpressional basin,the Cretaceous-to-Paleogene intracontinental depression,and the Neogene-to-Quaternary intracontinental foreland basin.The evolution is mainly controlled by multi-stage activities of the peripheral boundary fault zones.The strong transpression of the Hongche fault belt to the west boundary of the sag during the middle of Late Hercynian movement(P2),Late Indosinian movement(T3),and Middle-to-Late Yan-shanian movement(J2-E),is the most powerful factor affecting the tectonic evolution and associated stratigraphic development and distribution in the sag.
    Development pattern and prediction of induced fractures from strike-slip faults in Shunnan area,Tarim Basin
    Zhang Jibiao, Zhang Zhongpei, Wang Bifeng, Deng Shang
    2018, 39(5):  955-963,1055.  doi:10.11743/ogg20180510
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    Induced fracture from strike-slip faulting is an important type of reservoir space of carbonates,thus has been drawing more and more attention.However,its mechanism and scale are not clear now.In order to delineate fracture system controlled by strike-slip faults,we carried out quantitative evaluation by means of comprehensive application of core,image logging data and numerical simulation.After the identification and description of structural fractures in Shunnan area,the characters of fracture development controlled by strike-slip faults were summarized,and their main controlling factors were analyzed.Then through the construction of geological model,the induced local stress field and the deformation process of the strike-slip fault were simulated by using the finite element method.What's more,the influential factors and distribution of the induced fractures from strike-slip faults were discussed through analysis of stress-strain,and the pattern of fracture development in the 3D seismic acreage of Shunnan area was predicted further.The results show that(1) the structural fracture controlled by major strike-slip faults is the main type of fractures in Shunnan area,its strike is basically consistent with that of the faults,and it is dominated by high angle-nearly vertical shear fractures.Besides,fracture development is closely related to the segmentation and lithology of faults.(2) The extent of induced fractures from strike-slip faults is 1.25-6.5 times as many as the width of the core of fault zone,and the intensity and extent of fracturing in the pull-apart segments of faults are significantly larger than those in the strike-slip segments.(3) Along the lithologic interface,the scope of fracture development controlled by strike-slip faults expands obviously.The higher the competency of rocks is,the easier it is for the development of induced fractures,and the larger the extent of induced fractures becomes.(3) The Late Caledonian-Early Hercynian fractures are mainly distributed along the NE-trending strike-slip faults as a whole in the 3D seismic acreage in Shunnan area,and the fractures in the Yingshan Formation are better developed those that in the Yijiangfang Formation.
    NE-trending fault belts in Tanggubasi Depression of the Tarim Basin: Features,genetic mechanism,and petroleum geological significance
    Liu Shilin, Zhang Zhongpei, Yun Jinbiao, Li Huili, Gao Shanlin, Li Jianjiao
    2018, 39(5):  964-975.  doi:10.11743/ogg20180511
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    NE-trending faults are well developed in Tanggubasi Depression,Tarim Basin.Most of them can be divided into either southeastern basement-involved thrusting fault style or and a northwestern cover-decollement thrusting fault style,and present a huge arcuate faulting system bulging northwestward on map view.These NE-trending faults are mostly thrusting faults,but a few are characteristic of both thrust and strike-slip.Many faults show features of structural segmentation along strike,which are mainly displayed by the difference of main faults' thrusting directions and their related folds,and mainly located at the tail end of the arcuate structure.Meanwhile,most faults are characteristic of the layered superposition of multiple structural deformations vertically,and the major deformative layers concentrate in the Upper Cambrian-Ordovician sequences,and faults on the northwestern margin usually detach in the Middle Cambrian gypsolytes,while weak deformations are shown in other strata.The NE-trending fault system,a product of the collision between Tarim massif and North Kunlun-Altyn massif,is mainly developed during the late of Late Ordovician-earliest Silurian,and is an integral part of the Early Paleozoic foreland fold-thrust system of the Altyn-Cherchen faults on the southeastern margin of Tarim Basin.The formation of the NE-trending fault system is controlled by four factors,including the strike-slip and thrusting stress field of the major faults on the margin of Altyn-Cherchen,the distribution of the Cambrian gypsolyte weak layers,basement relief,and boundary fault strikes.The NE-trending fault belt locally controls the development of the Ordovician carbonate reservoirs of dissolution-fracture-cavity type and reef-shoal reservoirs at the platform margins.Favorable trap targets such as the fault zone wings can be selectively explored if the hydrocarbon source conditions are confirmed to be favorable.
    Geometrical and kinematic characteristics of Baliying fault in the eastern Tabei uplift,Tarim Basin
    Chen Jiajun, Wang Feng, Sun Fangyuan
    2018, 39(5):  976-983.  doi:10.11743/ogg20180512
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    Baliying fault serves as the boundary between the Caohu Sag and the Korla nose-shaped salient in the eastern Tabei uplift.The analysis of the fault geometry and kinematics plays a significant role in the study of the geological structure and tectonic evolution of the eastern Tabei paleo-uplift,Tarim Basin.Based on plenty of seismic reflection profiles crossing the Baliying fault,we used Petrel software to finely depict its geometry and realized 3-D visualization of the fault.In addition,the NS-trending geological structure profile crossing the study area was restored by means of balanced cross-section reconstruction.The results show that:(1) Baliying fault is in the shape of an arc horizontally and dips north-east.It is characteristic of the listric thrust fault with a high dip angle on top,which can reach 70°,but a gentler one at bottom;(2) Baliying fault can be divided into three segments.Two fault segments formed separately in the eastern and western parts in the early period,and then they got linked by a middle fault segment and developed into one fault.The fault experienced two major tectonic events during the Late Paleozoic(Late Caledonian-Hercynian) and Mesozoic(Indosinian-Yanshanian),and the intensity of the former is stronger than that of the latter;(3) Baliying fault formed and evolved rapidly with large fault slip during the Carboniferous-Permian.It finalized gradually during the Mesozoic,but minor movement continued throughout the Triassic and Early Cretaceous,influencing the Mesozoic sedimentation.Then the movement stopped in the Cenozoic.Bali-ying fault plays a significant role in controlling the Paleozoic and Mesozoic structure of its hanging wall;therefore,it is one of the main reasons causing the stratigraphic structural differences between Caohu Sag and Korla nose-shaped salient.
    Geometrical and kinematical characteristics of Haimiluosi fault zone in the Bachu uplift,Tarim Basin
    Zhang Yong, He Dengfa, Liu Changlei
    2018, 39(5):  984-1000.  doi:10.11743/ogg20180513
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    The tectonic style and evolution history of Haimiluosi fault zone,one of the boundary faults of Bachu uplift,can reflect the origin and process of the Bachu uplift formation,which will serve as a basis for exploring the intra-cratonic structural deformation mechanisms.Based on the fault-related fold theories,we analyzed the geometrical characteristics of several two-dimensional seismic profiles cutting through the Haimiluosi fault zone,and depicted the three-dimensional spatial distribution of the faults.Moreover,the tectonic activity of the fault zone was discussed according to the fault displacement and the amount of structural shortening on the profile.And the evolutionary features of faults on profiles were reconstructed using the balanced section technique.The results show that the Haimiluosi fault zone takes the shape of a broom on map,and is characterized by a three-layer structural deformation style on profile.Among them,the Cenozoic and Paleozoic faults take the Paleogene gyprock and Middle Cambrian saline rock as detachment surfaces respectively.The fault zone is located at the break along the strike of the southern boundary fault,accommodating the fault displacement at both ends of the southern fault,and features thrusting-strike-slipping on the whole.Besides,the zone formed through late inversion of the normal faults,that is,normal faults got inversed during the Middle and Late Ordovician due to the Caledonian movement,leading to the initiation of thrust fault and the mild uplifting of the deposited strata.At the end of Late Permian,the early faults reactivated and kept intensive activity for a long time.Subsequently,the Cenozoic boundary faults were formed mainly during the Eocene to Oligocene,and the fault zone reactivated and finalized gradually under the influence of Himalayan movement in the Quaternary.
    Analysis of regional structural cross section of the North and Central Tarim Basin and new insights into paleo-uplift origin
    Liu Changlei, Zhang Yiqiong, Zhang Yong, Sun Fangyuan, Chen Jiajun, He Dengfa
    2018, 39(5):  1001-1010.  doi:10.11743/ogg20180514
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    The Tabei uplift and Tazhong low salient are important strategic plays for oil and gas exploration in Tarim Basin.It will be of positive value for petroleum exploration and research ahead to study and compare their stratum systems,fault characteristics and geological structural differences.In order to reveal the geological structures and origins of the two paleo-uplifts,we selected a large NS-trending regional structural cross section in central Tarim Basin for a fine interpretation and description based on fault-related fold theories,combined with the latest drilling,logging,and seismic data.The results indicate that:the Tabei uplift and Tazhong low salient are the Paleozoic paleo-uplifts controlled by the large-scale basal fault bend folds.Stratum displacement caused by compressive stress from south to north is partly absorbed by Tazhong low salient,and then continues to pass to the northern Tarim area through the Manjar Depression,with the remaining displacement absorbed by Tabei uplift at last.The period from the Middle-to-Late Caledonian to the Early Hercynian is the main formation period of the two paleo-uplifts.However,Tabei uplift suffers damage due to the thrusting of the southern Tianshan fold belt at late stage,the Paleozoic and Mesozoic sequences suffer extensive denudation,while the Cenozoic gets thickened from north to south.Thus it is difficult to recognize the front wings of the fault bend folds.Tazhong low salient experiences intensive Paleozoic tectonic movement,but doesn't experience any large-scale faulting activities during the Mesozoic and Cenozoic,so it is stable in geometry.
    Early-Middle Cambrian paleogeography and depositional evolution of Tarim Basin
    Tian Lei, Cui Haifeng, Liu Jun, Zhang Nianchun, Shi Xiaoqian
    2018, 39(5):  1011-1021.  doi:10.11743/ogg20180515
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    Conforming to the guideline that tectonism controls sedimentation,the study investigated the Early and Middle Cambrian paleogeography and depositional evolution of Tarim Basin based on fine interpretation of 2D seismic profile and analysis of the latest drilling geological data.In the Early Cambrian,the tectonic paleogeography in Tarim Basin was characterized by the "framework with one uplift located between a southern and a northern depressions":a nearly EW-trending synsedimentary palaeohigh occurring in Bachu and eastern Tazhong uplift areas,and transiting to depressions in both the north and southwest directions.During the sedimentary period of the Yurtusi Formation in the Early Cambrian,Tarim Basin was a ramp with the deepwater shelf being dominant,and the tidal flat,slope,deepwater basin facies were successively developed along both the south and north sides of the central palaeohigh.But during the sedimentary period of the Xiaorbulak Formation in the Early Cambrian,Tarim Basin was a carbonate ramp of certain platform characters;the inner,middle and outer ramp facies and basin facies were developed along both the south and north sides of the central palaeohigh;and the outer ramp facies shows typical reflectance signatures of progradation on seismic sections.This study confirmed the existence of the central paleo-continent of the Early Cambrian in Tarim Basin,and preliminarily revealed the distribution of the paleo-continent and the relevant sedimentary facies belts of the Early Cambrian Yurtusi Formation and Xiaorbulak Formation.Through tectonic and sedimentary evolution analysis,we were sure,for the first time,that the Early Cambrian Tarim Basin was a ramp controlled by a north-south differential tectonic pattern instead of a carbonate platform in the real sense of the term.The platform in the western-central Tarim Basin came into being until the Middle Cambrian.
    Structural deformation mechanism and significance of the Zigui synclinorium,Sichuan Basin
    Deng Mingzhe, Zhang Weikang
    2018, 39(5):  1022-1036.  doi:10.11743/ogg20180516
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    The geological architecture and the deformation process of the southern and northern limbs of the Zigui synclinorium in Sichuan Basin were studied by analyzing data of the shallow layers and the newest deep seismic data,with a view to discuss the way of superimposition of the deformation fronts of the Dabashan structural zone with the West Hunan and Hubei fold zone.The study indicates that the activity of deep tectonic wedges is the main driving force for the deformation of the southern and northern limbs of the Zigui synclinorium.The tectonic wedge under the southern limb takes the south-dipping fault plane connecting the Silurian decollement layer with the basement decollement layer as the floor front-thrust fault,and takes the Silurian decollement layer and the north-dipping fault plane above it as the roof back-thrust fault,and the tectonic wedge composed of strata from the Silurian shales to the top of the Sinian as well as part of the deep basement material gets involved in deformation.The tectonic wedge under the nor-thern limb takes the basal decollement layer in the northern limb of the syncline as the roof back-thrust fault,takes the decollement layer in the deep as the floor front-thrust fault,and the tectonic wedge is consisted of basement materials as a whole.Further analysis shows that the formation of the southern limb of the Zigui synclinorium is controlled by the progressive deformation of the West Hunan and Hubei fold belt from the Late Jurassic to the earliest of the Early Jurassic,and the northern limb,as well as its inner secondary folds,is formed as a result of the southward compressive nappe of the South Dabashan thrust belt within the Dabashan structural belt from the middle to the late of Early Cretaceous.The overprint of the middle Early Cretaceous-Late Cretaceous deformation of the Dabashan structure on the Late Jurassic deformation of the West Hunan and Hubei fold belt is the basic pattern for the superposition deformation of the two structural belts.
    Geologic architecture and tectonic evolution of Xushui Sag,Bohai Bay Basin
    Shan Shuaiqiang, Zhang Yuying, Zhang Ruifeng
    2018, 39(5):  1037-1047.  doi:10.11743/ogg20180517
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    The Xushui Sag,located in the western Bohai Bay Basin,is separated from the Taihang Mountain uplift by the Taihang Mountain piedmont fault to its west.In order to improve the understanding of the formation of the sag and facilitate petroleum exploration in the region,we systematically studied the geologic architecture of Xushui Sag through the drilling and seismic data.Characteristics of the major faults in the study area were revealed based on fine interpretation of the seismic profiles within the sag.The post-Paleogene tectonic evolution process of Xushui Sag was reconstructed via the balanced cross-section technique.The results show that there are two regional unconformities in the Cenozoic in the Xu-shui Sag,one being at the base of the Paleogene and the other being at the base of the Neogene.According to these two unconformities,three tectonic layers,namely the basement,the Paleogene and the Neogene-Quaternary layers,are subdivided.The structural framework of the study area with faults occurring in its west and north and overlapping occurring in its east and south,is controlled by the NE-trending Taihang Mountain piedmont fault and the NWW-trending Laishui fault.This study demonstrates that the post-Cenozoic tectonic evolution of the study area can be divided into four stages:intense rifting stage,continuous rifting stage,transitional stage from rifting to depression and depression stage.Rifting in the Xushui Sag,characterized by episodic activities,began to grow in the Early Paleocene and proceeded until the Late Oligocene.
    Experimental study on dynamic and static elastic modulus conversion for shale under different temperatures and pressures
    Wang Fei, Bian Huiyuan, Zhang Yonghao, Duan Chaowei, Zhao Lun, Li Jianxin
    2018, 39(5):  1048-1055.  doi:10.11743/ogg20180518
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    There are differences between dynamic and static elastic parameters of shale.Thus when applied,they need to be converted.Most experiments carried out today by both domestic and foreign scholars in testing rock dynamic and static elastic modulus conversion are under normal temperature and pressure,without considering the influence of temperature and pressure on the results;consequently,the conversion results cannot fully display the mechanical properties of reservoirs.We studied the Wufeng-Longmaxi black shales of the Upper Ordovician and Lower Silurian in the Sichuan Basin,conducted mechanical experiments of rock dynamic and static elasticity under different temperatures and pressures,and analyzed the test results.The results show that:① when the temperature and pressure are constant,the dynamic Young's modulus test value is larger than that of the static Young's modulus test,and the two have a certain linear correlation.② The dynamic and static Young's moduli for shales are correlated with temperature and pressure.When the temperature keeps constant,the static and dynamic Young's moduli of shales increase with the increase of confining pressure.When the pressure is constant,the static and dynamic Young's moduli of shales decrease with the increasing temperature.Besides,the mechanism for the change of dynamic and static elastic mechanical parameters under different temperatures and pressures was analyzed.③ The conversion model for dynamic and static elastic parameters of shales under different temperatures and pressures was established.In applying the model,whatever the temperature and pressure,the dynamic elastic parameter obtained can be converted into the in-situ static one,and the results are reliable.This model can provide credible static moduli of elasticity for shale gas exploitation and hydraulic fracturing in the study area.All in all,the research is of certain practical significance.
    Joint control of the Cenozoic faults and magma on hydrocarbon accumulation in BZ34-9 oilfield in Huanghekou Sag,Bohai Bay Basin
    Yang Haifeng, Xu Changgui, Niu Chengmin, Yang Bo, Chen Lei, Guo Tao, Wu Jing, Su Wen
    2018, 39(5):  1056-1064.  doi:10.11743/ogg20180519
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    The study is based on integration of various data,such as regional geologic,3D seismic,well logging and geochemical data,as well as thin section and SEM observation.Its target is the key factors controlling hydrocarbon accumulation in the clastic rock reservoirs within the Cenozoic magma developing areas on the southern slope of the central low in Huanghekou Sag,Bohai Bay Basin.The result shows that the spatial and temporal coupling of fault activities and magma eruptions plays a pronounced role in controlling the hydrocarbon accumulation as follows:(1) the combination of fault and magma activities controls the formation of uplift zones on the slope and development of sizable traps; (2) the spatial and temporal coupling of faults and magma benefits the development of deeply buried Palaeogene clastic reservoirs of high quality;(3) the fault and magma jointly controls the differential hydrocarbon accumulation.Under the guidance of the cognition,a large and highly productive oilfield is discovered with reserves of nearly 80 million cubic meters and the highest single-well daily production in the oilfield is nearly 290 cubic meters.
    Strain distribution of tri-shear fault propagation folding
    Zhang Weikang, He Dengfa
    2018, 39(5):  1065-1072.  doi:10.11743/ogg20180520
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    The tri-shear fault propagation fold is an important type of structural pattern and trap of fold-thrust belts.Its genetic mechanism can be explored by studying the characteristics of structural deformation geometry and strain distribution patterns.Based on improved tri-shear velocity distribution model which meets the requirements of divergence-free velocity field and strain compatibility,the instantaneous strain rate within the tri-shear zone was worked out,and in turn its strain difference distribution was analyzed.The forward modeling of the tri-shear fault propagation folds was performed with MATLAB software to obtain the geometry and cumulative strain distribution of folds under the influence of various para-meters.Subsequently,the possible fault propagation modes were discussed according to the strain distribution.The results show that(1) the predicted strain concentrates directly in the region near the fault tip and serious deformation occurs in the adjacent areas of the fault tip,causing the forward propagation of the tip,so the strain attenuates sharply with increa-sing distance from the tip,and rocks fold accordingly;(2) The parameters affecting the strain distribution of tri-shear fault propagation folds are the apical angle of the tri-shear model and the ratio of P/S.The width of the fault propagation fold is directly controlled by the apical angle:with the decrease of the apical angle,the deformation zone becomes tighter and the strain grows stronger; while the P/S ratio affects the extent of strata involved in deformation and the cumulative strain time.When the ratio is high,the fault propagates fast and there is no significant internal deformation within the tri-shear zone,but when the ratio is low,beds have sufficient time to accumulate strain and deform before being cut by fault and result in pronounced synclines on the downthrown side of the fault and bed thickening.
    Distribution of submarine fans in the thrust fault zone of continental slope, Niger Delta Basin
    Lin Peng, Wu Shenghe, Zhang Jiajia, Hu Guangyi, Xia Qinyu, Fan Hongjun, Wang Nansu
    2018, 39(5):  1073-1086.  doi:10.11743/ogg20180521
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    The recent exploration for oil and gas in deep water has revealed that the distribution of submarine fans is complex in thrust fault zone on continental slope.While the influences of thrusting related topography on macroscopic distribution of submarine fans have been studied both at home and abroad,few researches have been carried out in terms of its distribution and evolution at different stages of thrusting.This paper studied the distribution pattern of submarine fans in the thrust fault zone on continental slope in a deep-water zone of the Niger Delta Basin,utilizing well-logging and seismic data.Results show that the Upper Miocene-Quaternary, the target in the study area,is divided into nine third-order sequences according to stratigraphic overlap and sea level variation,and three types of submarine fan depositional units(massive transport,channel and lobe deposits) are identified.Vertically,the submarine fans are mainly located in the re-trogressive system tracts(RST) of each third-order sequence,while laterally,they present complex evolution and distribution patterns due to the control of differential palaeogeomorphology at different stages of thrusting.In the study area,the submarine fans have evolved through four stages.The first one is equilibrium slope stage.As few thrust faults were active and the slope was relatively gentle in geomorphology at this stage,thrusting delivered little control to the submarine fans.And the submarine fan system was developed in the central part of the study area and was dominated by sinuous stripe-shaped channels.The second one is thrusting stage.The vigorous activity of thrust faults into the deep water triggered the formation of minibasins on the hanging walls of thrust faults;thus the transportation of gravity flow was prevented,and large composite lobes, linked with each other,occurred.The third one is mud diapire stage.The thrust fault activity slowed down and upward mud diapirism occurred in its core during this stage.Then the mud diapire anticline developed in the central part of the study area,while minibasins along the direction of continental slope grew on the east and west sides of the anticline.Plenty of gravity flow sediments bypassed these longitudinal minibasins,forming the submarine fan channel-lobe complexes that differentiated in east-west direction.The fourth one is sedimentation-dominant stage.As the thrusting in the study area almost stopped,the continental slope gradually turned to equilibrium and stripe-shaped channel deposits with low sinuosity were developed quite even in the whole area.