Oil & Gas Geology-2006, Volume 27 Issue 4

Fault systems and their tectonic evolution in the Eastern Tarim basin

Lu Huafu, Wang Shengli, Luo Juncheng, Shu Liangshu, Sang Hong, Zhu Wenbin, Li Yufeng, Jin Ying'ai

2006, 27(4): 433-441. doi:10.11743/ogg20060401

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Based on detailed interpretation of over 3000 km of seismic profiles,the fault systems in the Eastern Tarim basin have been established and three systems,the Kongquehe fault system,the Southeast fault system,and the extensional fault system,have been identified.The NW-trending Kongquehe fault system consists of the Kongquehe slope with the shape of tectonic wedge in the Paleozoic and the Early Triassic,the Yingjisu dextral transpressional fault series in the Late Jurassic and the Early Cretaceous,and the Kongquehe fault in the Cenozoic.It was related to collision between the Tarim massive colliding with the Central Kunlun terrane in the Silurian,and the Lasha/Qiangtang terrane collision and India/Tibet collision in the Mesozoic and the Cenozoic.The Southeast fault system includes the NE-trending northwestward thrusting Cheerchen fault in the Silurian,which reactivated in the Cretaceous,and the ENE-trending sinistral transpressional Altyn Tage fault in the Neogene and the Quaternary.The formation of Kongquehe fault was influenced by the collision between Tarim massive and Jungger massive in the Late Paleozoic,by the closing event of the Amur Sea Way in the Mesozoic,and by Indian-Tibet collision in the Cenozoic.The extensional fault systems are believed to be developed through the Cambrian,Ordovician,Early Silurian,Middle-Late Jurassic,and Paleogene.

Mineralogy and geochemical records of episodic reservoiring of hydrocarbon: example from the reservoirs in the northwest margin of Junggar basin

Hu Wenxuan, Jin Zhijun, Zhang Yijie, Yao Suping, Zhang Yunqian, Cao Jian

2006, 27(4): 442-450. doi:10.11743/ogg20060402

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Authigenic minerals,such as calcite and etc.with oil-bearing girdles that recorded the traces of episodic reservoiring event and their geochemical characteristics,are studied in this paper.The calcite(also called SiO₂ the fissure filler),consisting of various components and interweaving with a dozen or more oil-bearing girdles inside them,is likely to be found near the source faults of some reservoirs in the northwest margin of Junggar basin.Geochemical tracing analysis suggests that the hydrocarbon-bearing fluids were mainly sourced from the deep of the Permian and had carried with them such elements as Fe,Mn,and etc..Therefore,the oil-bearing calcite in close relation to hydrocarbon charging is rich in Fe and Mn and the contents of Fe,Mn,and Mg in the calcite girdle fluctuate remarkably.This phenomenon honestly recorded the periodic process of the episodic charging of hydrocarbon-bearing fluids.

Impact of geometry and kinematics of Lanliao fault on structural styles in Dongpu sag

Qi Jiafu, Wang Deren, Chen Shuping, Zhao Yanbing, Cheng Xiushen, Xie Chen, Xu Zhenqian

2006, 27(4): 451-459. doi:10.11743/ogg20060403

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Paleogene sediment in Dongpu sag had filled in a complex half-graben controlled by Lanliao fault.Except for an obvious change in its surface and detachment detpth along the axis of Dongpu sag,the Lanliao fault system can be generally described as having a listric surface.The northern segment of the fault system is a relative low-angle listric normal fault with detachment depth of 9-12 km.The middle segment is a relative high-angle listric fault with detachment depth of 14-16 km.The southern segment is a ramp-flat fault with detachment depth of 8 km in the upper part of the fault and of 11-13 km in the lower part of the fault.The kinematics of these segments also vary in different stages at Paleogene,causing the extension of the middle segment and its proportion to the total extension of Dongpu Sag relatively larger than the rest part of the sag.Under the impact of Lanliao fault geometry and its kinematics changes along the axis of Dongpu sag,the depression had developped quite different structural styles,deposit patterns and geological conditions for hydrocarbon accumulation.

Buried rift basins under the Thin-skinned Fold-Thrust Belts in the South Segment of the western Sichuan Foreland Basin and their Geological Significance

Chen Zhuxin, Jia Dong, Wei Guoqi, Li Benliang, Zeng Qing, Yang Guang

2006, 27(4): 460-466,474. doi:10.11743/ogg20060404

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Seismic interpretation reveals the rift basin in the south segment of the western Sichuan foreland basin,which had been developed before Permian,might be filled up with thousands of meters of Silurian-Carbo-(niferous) strata.The late stage of the area had gone through a tectonic compression in the Cenozoic,and as a result,the foreland basin exhibits a double-layer structure characterized by shallow fold-thrust structures and deep rift basins.The shallow structures consist of some flat-and ramp-related thrust faults and the associated fault bend folds,while the deep structures occur as graben-type basins and half-graben-type basins,which had experienced local positive inversion,resulting in the synchronous folding of the Permian,Mesozoic,and Cenozoic.The deep rift structures,to some extent,controlled the development of the shallow ones.It is suggested that the deep rift basins in the Paleozoic and the inverted anticlines in the Paleozoic and Mesozoic in the south segment in western Sichuan foreland basin may have large hydrocarbon potentials,thus are frontiers for exploration.

Characteristics and formation mechanism of the faults in Mesozoic-Cenozoic in Jiyang Depression

Zhang Peng, Wang Liangshu, Ding Zengyong, Zhong Kai

2006, 27(4): 467-474. doi:10.11743/ogg20060405

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Dominated by NW-trending faulting during the Mesozoic and jointly controlled by NW-and NE-trending faults in the Early Cenozoic,Jiyang depression was then governed by NE-trending faulting after the deposition of 4th Member in the Shahejie Formation.The faulting in Jiyang depression in Mesozoic-Cenozoic was jointly controlled by back-arc spreading resulted from the oblique subduction of the Pacific plate towards the Eurasia plate and the strike-slip movement of the Tanlu fault zone. A series of NW-trending normal faults were formed as a response to a sinistral strike slip of the Tanlu fault belt during the Early Cretaceous.In the Early Cenozoic,faulting in the eastern Jiyang depression was controlled by the sinistral strike slip of the Tanlu fault belt,while in the western part of the depression,it was mainly affected cy the back-arc spreading process.After about 43Ma when the convergence direction of the Pacific plate changed,the faulting in Jiyang depression was mainly controlled by the NW-SE trending regional spreading process.

Growth strata and their application in timing deformation of foreland thrust-fold belts in the north margin of Tianshan

Guo Zhaojie, Fang Shihu, Zhang Rui, Zhang Zhicheng, Wu Chaodong

2006, 27(4): 475-481. doi:10.11743/ogg20060406

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Three foreland thrust-fold belts,the Piedmont,the Huoerguosi-ManasiTugulu,and the Dushanzi-Anjihai,formed since the Cenozoic are recognized from south to north in the north margin of Tianshan.The sequences of growth strata developed in each belt have been established based on field observation and seismic interpretations.The fission-track dating evidences and available magnetostratigraphic data are also used in the timing of the Late Cenozoic tectonic deformation: the Piedmont formed since about 10 Ma;the Huoerguosi-Manasi-Tugulu formed from 7 to 2.58 Ma;and the Dushanzi-Anjihai formed after about 0.73 Ma.

Right-lateral strike-slip thrust system and its dynamics along the northern margin of Qaidam basin

Xiao Ancheng, Yang Shufeng, Chen Xiaogan, Dang Yuqi, Chen Xinling, Chen Yuanzhong, Wang Liang

2006, 27(4): 482-487,494. doi:10.11743/ogg20060407

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Interpretation of geophysical data and analysis of fault systems confirm that structures in the northern margin of Qaidam basin were formed after the Pliocene and occur as a series of right-lateral strike-slip thrusts.The faults within the strike-slip thrust belts occur as structure in sectional view,thus direct correlation of strata between the hanging wall and footwall is impossible. The formation of the right-lateral oblique thrust belts were controlled by the N-S oblique thrusting of South Qilian Orogeny and the main terrestrial stress came from the S-N intracontinental subduction of the north margin of Qaidam massive.To interpret the right-lateral strike-slip thrusting,a kinematics model is also provided.

Deformation characteristics and time of Cenozoic thrust belt in southern margin of Jiuquan basin

Chen Hanlin, Yang Shufeng, Xiao Ancheng, Pan Zhengzhong, Cheng Xiaogan, Chen Jianjun, Fan Mingtao, Tian Duowen

2006, 27(4): 488-494. doi:10.11743/ogg20060408

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The multi-layer thrust belt in the southern margin of Jiuquan basin consists of a long distance shallow thrust system,a short distance middle thrust system,and a deep in-situ thrust system.The long distance thrust system is composed of Ordovician and Silurian and some part of it shows as a klippe.The short distance thrust system that hides under the long distance thrust system and locally crops out as a structural window is composed of Paleozoic and Mesozoic and has the deformation style of imbricate structure.The in-situ thrust system,with duplex or stacking structure in its south,a simpler deformation of propagation fold and fault-bend fold in its northeast,and a pop-up in its front,is under the short distance thrust system and the Quaternary.The thrust belt in the southern margin of Jiuquan basin occurs as a thin-skinned thrust system with a large structural shortening of 52.7 km and a shortening rate of 55.1% on the Hanxia section.Deformation of the thrust belt started at about 9 Ma and extended northward progressively,with faulting beginning at 8.3 Ma in the front of thrust belt.

Paleogene extensional fault-bend folding in north depression of southern Yellow Sea basin

Wang Shengli, Lu Huafu, Li Gang, Chen Jianwen, Chen Guowei

2006, 27(4): 495-503. doi:10.11743/ogg20060409

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The north depression in the southern Yellow Sea basin is one of the Cenozoic rift basins in the east margin of the Eurasian continent.The northeast sag in the north depression was formed by fault-bend folding of the hanging wall of the north dipping listric Weihai normal fault caused by the northward movement of the hanging wall.In the process of extensional fault-bend folding,the sediments deposited simultaneously and the growth strata were formed in the north sag and recorded the growing process of the northeast sag.Analysis of geometry of the growth strata shows that the northeast sag totally extends 10012 m with an average extension rate of 0.225 mm/a,quite similar to those of single sags in the Paleogene rift basins in east margin of Eurasia,such as the Bohai bay basin,the Subei basin,and the East China Sea basin.

Detachment systems in deep of Jiaolai basin and their regional tectonic significance

Zhang Yueqiao, Li Jinliang, Liu Zongquan, Ren Fenglou, Yuan Jiayin

2006, 27(4): 504-511. doi:10.11743/ogg20060410

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Seismic interpretations reveal two low angle detachment systems in the Jiaolai basin: one,developed 8～10 km beneath the Zhucheng depression in the southern part of the basin,has a detachment surface gently dipping to the south; the other,developed in the north Gaomi and Laiyang depressions,consists of a series of N-dipping listric normal faults and has a major detachment surface gently dipping to the north or NNE.Based on the sed-imentary records analysis,profile retro-deformation,and estimated stretch properties of the above-mentioned depressions,in combination with the fault slip data analyses at the surface,the southern detachment system is considered to be formed during the early Cretaceous Laiyang stage when the Zhucheng depression had a N-S stretching rate of 36%～41% and a possible NW-SE maximum stretching.This detachment system inherited an early deep decollement zone in the Jiaonan(or Su-Lu) orogenic belt;its late reactivation dominated the asymmetric extension pattern and controlled the development of the narrow,elongate sedimentary depression in the Jiaolai basin in Laiyang stage.The northern detachment system had taken shape during the stretching stage in the late Cretaceous.It is possible that the stretching process continued until the Paleocene and controlled the deposition of the Wangshi Formations.The N-S extension across the Laiyang and Gaomi depressions during the stage is estimated to be at 20%～25%,the maximum stretching direction being nearly N-S.This detachment system accommodated the N-S pull-apart stretching of Jiaolai basin and its formation was related to the right-lateral shear along the NNE-trending boundary fault zones on the eastern and western sides of the basin.The spatial and temporal superimposition of these two detachment systems resulted in the complex extensional structural styles in the Jiaolai basin.The identification of these two deep detachment systems not only provides structural constraints on the mechanisms and dynamic setting of the basin formation,but also is of great significance for petroleum exploration in the basin.

An analysis of structural framework and formation mechanism of Zhongjiannan basin in the west of South China Sea

Gao Hongfang, Chen Lin

2006, 27(4): 512-516. doi:10.11743/ogg20060411

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Zhongjiannan basin,located in the west of South China Sea,has well developed faults and volcanic rocks,thus the geological conditions are very complex.The influence of the Cenozoic tectonic movement upon the formation and evolution of the basin was huge and is well reflected by its four superposed structural layers with different characteristics in profile,its NNE-NW trending,and its lozenge shape on plane.Both geometrical characteristics of strike-slip basin and geological characteristics of tensional basin can be found in the basin.Centered with a major depression and two secondary depressions,the basin has a structural framework with alternative depressions and upheavals.Extensional structures and strike-slipping structures had been developed in the basin.Different slipping directions brought about completely different effects on the evolution of the basin: sinistral strike caused extrusion while dextral strike slip resulted in extension and subsidence in the basin.The combination of tensile stress and shear stress shaped the area into a strike slip-extensional composite basin after several uplifting and subsidence cycles.

Fractal characteristics and reservoir distribution of fault system in the northwest margin of Jungar basin

Chen Xin, Lu huafu, Pu Shizhao, Chen Zhongmin, Li Shihong

2006, 27(4): 517-521. doi:10.11743/ogg20060412

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Study of fault system with the fractal theory reveals that the plane distribution of the faults has fractal characteristics in the northwest margin of Jungaar basin.Fault systems with larger fractal dimension consist of better developed and less evenly distributed faults.Based on this understanding,the relationship between the nature and trend of the faults and the fractal dimensions has been explored.The normal faults in the region are dominated by NW-trending faults,with strong self-similarity and larger fractal dimension(0.5623) than that of NE trending normal faults(0.5611).While the reverse faults are dominated by NE-trending faults,with strong self-similarity and larger fractal dimension(1.1356) than that of NW-trending reverse faults(0.9880).Reservoirs with well developed faults have larger fractal dimension(1.9640) than those without faults(1.7630),and reservoirs with reverse faults have a fractal dimension(1.9540) much larger than those with normal faults(1.1460).

A study on characteristics of the Late Cretaceous-Paleocene structures in Jiuquan Basin

Cheng Xiaogan, Zheng Dewen, Yang Shufeng, Xiao Ancheng, Chen Hanlin

2006, 27(4): 522-527. doi:10.11743/ogg20060413

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The unconformity between the Eocene and the Lower Cretaceous is common in Jiuquan basin.Based on analyses of the seismic profiles and remnant thickness of the Lower Cretaceous Zhonggou Formation,it is suggested that a strong structural deformation had happened during the Late Cretaceous-Paleocene,resulting in generally NW-trending structural lines in the basin.The deformation resulted in the separation of Jiuquan Basin from Minle Basin that were previous connected in the Early Cretaceous and Huahai depression from Shida depression in Jiuquan basin.It also controlled the hydrocarbon accumulation and the later sedimentation in the basin.

Tectonic setting and geological evolution of Mohe basin in Northeast China

Wu Genyao, Feng Zhiqiang, Yang Jianguo, Wang Zaijun, Zhang Liguo, Guo Qingxia

2006, 27(4): 528-535. doi:10.11743/ogg20060414

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Based on the sedimentary features and facies change of the Upper Jurassic in Mohe basin and supported by many other evidences,it is proposed for the first time that the late Jurassic Mohe basin is a molasse basin controlled by the Yanshanian intracontinental orogeny,which was caused by the activation of the fossil suture zones related to subduction of the Mongolia-Ochotsk ocean.Three stages of the development of the basin have been established and the northward migration feature of its dynamic evolution has been identified.At the end of Jurassic the basin closed and was reformed by the W-E trending thrusts(the main deformation episode) along with continent-continent collision.From the Cretaceous to the Eogene,two phases of reformation happened in the basin and their structure features are nearly NNE trending transtentional faults,with at least three deformation episodes recognized and W-E trending normal faults.In terms of oil and gas exploration potential,the central,eastern,and southern part of the basin are more promising than the rest parts of the basin.

A study on oil & gas prediction technology in carbonate rocks in south Tahe

Li Mingjuan, Zhang Yonggui, Wu Xingwei, Zheng Herong

2006, 27(4): 536-541. doi:10.11743/ogg20060415

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Three carbonate reservoir intervals are found in the Ordovician in south Tahe: the Lower-Middle Ordovician Yingshan Formation,the Middle Ordovician Yijianfang Formation,and the Upper Ordovician Lianglitage Formation.The Yijianfang Formation is the main pay zone in the reservoir in south Tahe,and the Yingshan Formation is mainly aqueous layer,while the Lianglitage Formation is seldom tested due to its unfavorable physical properties.The spectral analysis based on wavelet transform mainly reflects various frequency parameters and energy parameters of frequency domain in relation to formation liquid.In view of the depositional characteristics of reservoirs in the study area,different oil and gas prediction technologies are studied.The oil-gas-water distribution characteristics of the Yijianfang and Yingshan formations can be well described by using the attenuation gradient attribute of high frequency absorption-attenuation, while oil & gas distribution of the Lianglitage Formation can be well predicted by using the frequency attribution parameter that relates to 85% of high frequency energy.The attenuation gradient attribute technology is employed to detect oil and gas in over 70 wells.The prediction results show that it can effectively recognize dry layer and differentiate hydrocarbon layers from water layers with coincidence rate as high as 70%.

An analysis of the status of China's large oilfields and their changes during recent 20 years

Zhang Kang

2006, 27(4): 542-548,556. doi:10.11743/ogg20060416

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A statistical analysis of China's large oilfields(OIP>1?10⁸ t) is made in respect of the scales,locations,abundance,and crude quality of the geologic and recoverable reserves as well as the production,and reserve-production ratio of these oilfields in 2004.A comparison with the corresponding statistics in 1984 shows that the geologic and recoverable oil reserves of the large and giant oilfields in east china increased by 2.1 and 1.6 times respectively,while those in west China increased by 4.8 and 3.6 times respectively.Six offshore oilfields reached the lower limit of large fields.In 2004,the reserves and production rate of the large and giant oilfields in east China still remained the highest among all the oilfields in the country.Light and medium crude oil accounted for 68.2% of the recoverable oil reserves of these oilfields,while heavy oil dominated the large and giant offshore oilfields.Past experiences indicate that more large and giant oilfields will be discovered and developed in each oil region of China,but the crude quality will be on the downgrade.

Petrology and genesis of Mesozoic volcanic rocks in Tuo32 well block of Liaohe oilfield

Zhao Hailin, Li Xiaoguang, Chen Zhenyan, Di Yongjun, Liu Jie, Hong Shuxin, Zhao Guanghui

2006, 27(4): 549-556. doi:10.11743/ogg20060417

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The types of volcanic rocks in Tuo32 well block of Liaohe oilfiled include rhyolite,trachyandesite,andesite,rhyolitic breccia,rhyolitic eruptive tuff,andestic breccia,and andestic eruptive tuff.The volcano erupted five times in two phases in about(97.37?1.41)Ma and(79.52?1.25)Ma,with the first phase in the late Early Cretaceous and the second phase in the middle Late Cretaceous. The 'reverse' phenomenon in volcanic eruptions is explained as the result of a zonal lava chamber based on the theory of lava hydrokinetics.Models of the zonal lava chamber and the surface distribution of the volcanic rocks are built.

Researches on secondary hydrocarbon generation in Southwest of Jianghan Basin and its effects on hydrocarbon accumulations

Chenbo, Han Dingkun, Luo Mingxia, Yanliang

2006, 27(4): 557-562,570. doi:10.11743/ogg20060418

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Hydrocarbon enrichment varies dramatically in such structural belts as Xie Fengqiao,Fu Xingchang,and Caixue in the southwestern margin of Jianghan basin.The extent of hydrocarbon enrichment is found to be related to the uplift and erosion processes in the Late Eogene and the potentiality of secondary hydrocarbon generation.Evidences,such as the late mature of source rocks,crude with the same source but different maturities,and the fluid-inclusion anaysis,all suggest a possibility of secondary hydrocarbon generation in the study area.The oil reservoirs that were formed before the rise of basin were partly or entirely destroyed with the rise of the basin,structures that could capture the secondary hydrocarbon generation have relatively high hydrocarbon enrichment.Xie Fengqiao structure had captured and preserved the primary and secondary hydrocarbons, thus its enrichment level is the highest.Caixue and Fu Xingchang belts suffered from great loss of their primary hydrocarbons in the process of rise of the basin.However,Caixue belt has a higher enrichment of hydrocarbons for having received a supply of second hydrocarbon generation,while Fu Xingchang,without the process of secondary hydrocarbon generation,has a lower oil saturation and poor enrichment of hydrocarbons.

Sequence stratigraphic framework and its control on accumulation of various energy resources in the Mesozoic continental basins in Ordos

Yang Minghui, Liu Chiyang

2006, 27(4): 563-570. doi:10.11743/ogg20060419

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The types of sequences developed in the Upper Triassic and Lower-Middle Jurassic in Ordos basin include fluvial sequence,lacustrine sequence,and lake delta sequence,and they constitute two serial sequences namely the fluvial-lacustrine-lake-delta sequences in the Upper Triassic and the fluvial-lake-delta-fluvial-lacustrine sequences in the Lower-Middle Jurassic.The episodes and cyclicity of tectonic subsidence controlled the cyclicity of the sequence and the stage of sequence development;paleoclimate controlled the formation and preservation of the source rocks and coalbeds;sediment supply influenced the accommodation space of the basin;and the change of lake level was caused by the combined forces of tectonics,source and paleoclimate.These are the main factors leading to the formation of sequences in continental basins.The accumulation of various energy resources maight be related with the sequence stratigraphic framework.The well-developed reservoirs in lowstand system tract formed stratigraphic-lithological traps in the delta sand bodies in the Yanchang Formation and the channel sand bodies in the Yanan Formation.The condensed intervals of transgressive system tract are good source rocks and caps.The Yanan Formation coalbed was developed on the abandoned delta plain in the late transgressive system tract. In addition to the highstand system tract,the incised valley and braided channel sand bodies developed in the lowstand system tract of the Zhiluo Formation are also important potential target horizons for uranium deposits of interlayer oxidation zone and of sandstone-type.

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