石油实验地质

BASIN-MOUNTAIN SYSTEM AND OIL AND GAS POOL FORMING PROCESS

Shen Chuanbo, Mei Lianfu

2007, 29(6): 535-540. doi: 10.11781/sysydz200706535

Abstract(616) PDF-CN(383)

Abstract:
Integrating study the relationship between basin-mountain system and oil and gas pool forming process is one of the frontier research fields in the study of continental geodynamics,and also is a key problem of petroleum exploration in China.Based on the system thoughts,this paper analyzed the form of basin-mountain system and oil and gas pool forming process and its research methodology firstly.Se-condly,the paper also discussed the response relationship of basin-mountain system architecture,evolution,and tectonic function and petroleum reservoir forming process.Finally,the paper gave a case study about Sichuan composite basin-mountain system and oil and gas pool forming process.The research results indicate that studying basin-mountain system and oil and gas pool forming process should keep to thoughts and methods of system science.The prerequisite of oil and gas pool forming process research are studying basin-mountain system architecture,evolution and dynamics mechanisms.Different basin-mountain system architecture has different source rock attribute,trap type and hydrocarbon accumulation model.Multistage tectonic activities control the source rock evolution,hydrocarbon charging histories,conductor system change,hydrocarbon accumulation and its later adjustment and reconstruction.Basin-mountain tectonic actions have constructed and rebuild two effects on oil and gas pool forming process.

THE MESO-CENOZOIC BASINAL EVOLUTION AND HYDROCARBON ACCUMULATION IN THE MIDDLE AND SOUTHERN PART OF SOUTHERN NORTH CHINA

Xu Hongjie, Huang Zeguang

2007, 29(6): 541-544. doi: 10.11781/sysydz200706541

Abstract(657) PDF-CN(405)

Abstract:
The formation and evolution of the Meso-Cenozoic basins in the middle and southern part of southern North China was mainly controlled by the Tanlu fault system and the Dabie orogenic belt.Based on study of influence of above memtioned tectonic units on southern North China block,and what with mapping of basin prototypes,it was indicated that the Meso-Cenozoic basins underwent multiple juxtaposition and superimposition of basin prototypes with compression,tenso-shear,expanding and weak compression.All of these played a very important parts in hydrocarbon accumulation.

CONTROL OF THE TERTIARY SYNDEPOSITIONAL STRUCTURES ON SAND AND OIL IN THE DONGYING SAG,THE BOHAI BAY BASIN

Zhu Guilin

2007, 29(6): 545-548. doi: 10.11781/sysydz200706545

Abstract(641) PDF-CN(482)

Abstract:
The control of the Tertiary syndepositional structures on the deposition,the accumulation of oil and gas in the Dongying Sag,the Bohai Bay Basin has been discussed systematically through the analysis of the relationship between structure,deposition and reservoir forming.The results show that the syndepositional structures provided the basic favorable conditions for the generation,the migration,the accumulation and the preservation of oil and gas.It is pointed out that in order to improve the exploration effect after the large to middle scale oil-gas pools have been discovered,the sequence stratigraphy theory,the petroleum system theory,and the reservoir dynamic forming theory should be fully used in the Dongying Sag in studying the control of the development and evolution process of the syndepositional structures on the process of deposition,trapping and reservoir forming,as well as their relationship with time-space matching.The research on the syndepositional structures is developing from qualitative to time-fixing and quantitative direction,with not only the kinetic mechanism being increasingly attached importance,the simulation of quantitative process also being improved step by step.

PETROLEUM SYSTEM ANALYSIS OF THE NORTHERN SAG, THE SOUTHERN YELLOW SEA BASIN

Zhu Ping

2007, 29(6): 549-553. doi: 10.11781/sysydz549

Abstract(770) PDF-CN(424)

Abstract:
There is a graben-like sag with fault in the north and overlap in the south caused by severe block faulting effect from Mesozoic to Palaeogene in the north of the Northern Depression of the Southern Yellow Sea Basin.Lacustrine facies dark mudstone deposited during Taizhou and Funing periods is the main hydrocarbon source rock in the sag.CyClic movements such as Yizheng and Wupu movements result in superposition of reservoir and source rock,forming multiple sets of source,reservoir and cap formation.Traps as antiCline,fault nose and fault block are generated.Oil and gas in Taizhou Formation migrates through weathered zone in fault and unconformity and sandstone carrier bed to the up,the south and the slope,forming types of accumulations as lithologic,antiCline and fault nose.The sag is an independent petroleum system.Petroleum bearing traps distribute like a string of beads along the Qianliyan Fault Belt and the Slope Pivot Belt,which are the most favorable regions for exploration in the Southern Yellow Sea Basin.

THE ANALYSIS OF HYDROCARBON ACCUMULATION CONDITION OF UPPER PALAEOZOIC OF THE SOUTHWEST ORDOS BASIN

Chen Quanhong, Li Wenhou, Jiang Peihai, Hu Xiaolin, Qiang Fangqing, Cui Junping, Gao Yongxiang

2007, 29(6): 554-559. doi: 10.11781/sysydz200706554

Abstract(687) PDF-CN(445)

Abstract:
The source rocks in the Southwest Ordos Basin are mainly the coalbed and melanomudstone of Taiyuan Fm and Shanxi Fm,and the content of organic carbon is 0.2%～7.95%,its kerogen is Ⅱ-Ⅲ type and the mean value of R_o is 2.34%,and the rocks are generally of hige-or-super maturation.The reservoir are mostly the distributary channel sand of delta plain and subaquatic distributary channel sand,belonging to the Ⅱ-Ⅲ type.The caprocks are primarily the mud of littoral and shallow lake facies with good continuity and is well Closed.The gas continuously migrates to Qingyang area by means of diffusion through crevice and collects in litho-stratigraphic traps formed in Permian.The Hydrocarbon migration is generally controled by reservoir bed and regional tectonic.To the east of Huianbao-Shajingzi Fault is the Tianhuan SynCline in whose east slope there is comparatively developed regional tectonic of synCline and antiCline,and with the fairly good reservoir condition,it has the primary enrichment of gas.The main preffered exploration areas are the Jingchuan-Ningxian's mild slope and the top point of the tectonic of the good reservoir in the Huanxian-Zhenyuan synCline.

FRACTURE CHARACTERISTICS AND BASIN EVOLUTION OF THE TAIXINAN BASIN IN CENOZOIC

Yi Hai, Zhong Guangjian, Ma Jinfeng

2007, 29(6): 560-564. doi: 10.11781/sysydz200706560

Abstract(1061) PDF-CN(1047)

Abstract:
Based on fault development characteristics and basin structure analyses,there are 3 evolution stages of the Taixinan Basin in Cenozoic.From Late Paleocene to Early Oligocene,rift-depression basin on continental margin is formed during the first stage.Grabens are controlled by border fractures.From Late Oligocene to Middle Miocene,marginal sea basin is formed during the second stage.The southern depression of the Taixinan Basin subsides quickly influenced by the South China Sea movement and becomes the subsidence and sedimentary center of the basin.However,the northern depression of the Taixinan Basin is an up-lift at the same time.From Late Miocene to Holocene,extension fractures generate along continental margin.As the oceanic crust of South China Sea dives below the Luzon Island arc along the Manila trench,new extension movement takes place along slope of the southern depre-ssion.The southern depression subsides quickly again and becomes deep sea basin at last.At the same time,the Philippines plate dives northwest,resulting in compressive tectonic movement from east to west in the east of the northern depression.The northern depression has become the sedimentary center of the Taixinan Basin.

DIAGENESIS AND POROSITY EVOLUTION OF SHAXIMIAO FORMATION IN LUODAI GAS FIELD OF THE WEST SICHUAN

Li Jianlin, Xu Guosheng, Zhu Ping, Zhou Li

2007, 29(6): 565-571. doi: 10.11781/sysydz200706565

Abstract(769) PDF-CN(513)

Abstract:
From the analysis of thin section,it shows widely growing primary porosity and complicate secondary porosity in Shaximiao Fm of Middle Jurassic,Luodai Gas Field of the West Sichuan.Diagenesis and interstitial matter have great influence on porosity.Based on the X ray diffraction of Clay mineral and the scanning electron microscopic,the diagenetic stages here are Classified as earlier diagenetic A,B and middle diagenetic A,B.In the earlier diagenetic A,the primary porosity decreased rapidly to 10%～15% because of compaction and quarts growth Ⅰ.And in the earlier diagenetic B,the porosity is evaluated to hit 10% because of arise of carbonate and muriacite cementations.Then quarts growth Ⅱ occurred in heavy acidulous water and authigenic kaolinite deposited in the middle diagenetic A.Until the middle diagenetic B,the porosity were improved by the enhancement of denudation.During the whole middle digenetic stage,the porosity descented to 4%～9% after constant decrease and increase.After a series of diagenetic stages,the reservoirs were densified to low porosity and low permeability ones.

PETROLEUM SYSTEM IN THE SUFYAN DEPRESSION OF MUGLAD BASIN IN SUDAN

Zhang Yamin

2007, 29(6): 572-576. doi: 10.11781/sysydz200706572

Abstract(919) PDF-CN(382)

Abstract:
The Muglad Basin in Sudan is located the eastern boundary of Central Africa Strike-slip Fault Zone,is a large Mesozoic petroliferous rift basin.The Sufyan Depression is located most north end in this basin.Lower Cretaceous Abu Gabra Formation is an effective hydrocarbon source rock.Favorable reservoir in this area is the Abu Gabra Formation channel sandbody in delta or fan delta.Upper Cretaceou Darfur Group is the region cap rock.The hydrocarbon trap types have fault antiCline,fault nose and fault block etc.The Sufyan Depression has two petroleum subsystems vertically,among which Abu Gabra Fm subsystem has favorable assemblage with self generating,collecting and sealing.While the other petroleum subsystem is composed of Abu Gabra Fm source rock,Bentiu Fm channel sandstone reservoir and Darfur Group shale seal.Both they are favorable for exploration.The Central structure belt of the Sufyan Depression is most favorable for exploration.

GEOCHEMICAL CHARACTERISTICS AND GENESIS OF THE NATURAL GAS IN THE TAZHONG UPLIFT, THE TARIM BASIN

Guo Jianjun, Chen Jianfa, Zhu Lei, Ye Zhixu, Shi Shengbao, Liu Yinghui

2007, 29(6): 577-582. doi: 10.11781/sysydz200706577

Abstract(694) PDF-CN(440)

Abstract:
The genesis of the natural gas in the Tazhong Uplift is very complicated and there have been existing a variety of opinions for a along period.Based on the systematic research results of the composition and carbon isotope characteristics of the natural gas in the Tazhong Uplift,the natural gas in the Tazhong Uplift is mainly composed of hydrocarbon gases,but the composition and the carbon isotope in the west and east parts of the uplift differ apparently form each other.The natural gases in the eastern Tazhong Uplift and the No.1 structural belt have higher values of dry coefficients,higher nitrogen contents and heavier carbon isotopic ratios.It is regarded that these differences are mainly determined by the different thermal evolution degrees of the organic matter,in addition to the organic matter type and the secondary alteration.The maturity of the Lower Paleozoic organic matter in the east part was fina-lized earlier,and the organic matter distributed immediately near the Cambrian source rock layer of the Manjiaer Sag.Therefore,the gas accumulated in the eastern Tazhong Uplift mainly came from the high to over matured Cambrian source rocks.As a contrast,the maturity of the Middle-Upper Ordovician organic matter in the west part was finalized later,and the gas accumulated in the western Tazhong Uplift mainly came from the middle matured Middle-Upper Ordovician source rocks.These results suggest that the natural gas in the Tazhong Uplift is mainly generated from the kerogens of various thermal evolution degrees,and the amount of the oil-pyrolysis gas is not significant.

CARBON ISOTOPIC FRACTIONATION EFFECT CAUSED BY MATURITY DURING THE GENERATION OF COAL-PYROLYSIS HYROCARBONS

Liao Yuhong, Geng Ansong, Liu Dehan, Lu Jialan

2007, 29(6): 583-588. doi: 10.11781/sysydz200706583

Abstract(648) PDF-CN(460)

Abstract:
The carbon isotopic fractionation effect of 3 types of coal under different pyrolysis temperatures has been studied through the hydrocarbon generation-expulsion pyrolysis simulation experiment in a semiClosed system.The results indicate that the carbon isotopic fractionation effect caused by the maturity differences changes with the different organic types of the coal.The fractionation effect of the pyrolysis hydrocarbons from the humous coal is significant,whereas the carbon isotope of the coal itself changes little with maturity.The possibility of the secondary cracking of the pyrolysis hydrocarbons increases greatly under a higher maturity level,resulting in the significant increase of the carbon isotopic compositions of the individual n-alkanes,especially the residual hydrocarbons.The isotopic distribution curves of the individual n-alkanes from the same source rock under different temperatures are very similar,indicating that,alike the value,the curve shape of the isotope may also provide a very important basis for oil-source correlation.

FRACTURE-CAVE SYSTEM AND PETROLEUM DISTRIBUTION IN ORDOVICIAN IN MAIN REGION OF TAHE OIL FIELD

Rao Dan, Ma Xujie, Jia Cunshan, Jiang Xiaoqiong

2007, 29(6): 589-592. doi: 10.11781/sysydz200706589

Abstract(611) PDF-CN(450)

Abstract:
Macroscopic tectonic evolution and microscopic fluid geochemistry studies have proved that,petroleum distribution in the Tahe Oil Field is controlled by tectonic framework formed by combination of early and late Hercynian movements.Superposition of ancient structures controls generation of palaeo-geomorphology and fracture.Generation of palaeo-geomorphology and fracture controls ancestral rive orientation and erosion depth.They are the main controlling factors of karst effect.Especially in the superposition of ancient structure formed during late Hercynian and axle of the Akekule Uplift,karst and fracture generate in large scale.Commonly-found large angle fractures connect caves into large reserve,resulting in horizontal division of large fracture-cave system in main region of the field.Based on fluid heterogeneity and macroscopic tectonic evolution analysis in Ordovician in main region of the Tahe Oil Field,2 large and 1 middle-small fracture-cave systems are divided.

RELATIONSHIP OF FORMATION FLUID AND HYDROCARBON IN TAZHONG LOW UPLIFT OF THE TARIM BASIN

Xue Hui, Zhang Jinchuan, Wang Yi, Bian Changrong, Wang Min

2007, 29(6): 593-597. doi: 10.11781/sysydz200706593

Abstract(588) PDF-CN(442)

Abstract:
The Tazhong low uplift is considered to be in good preservation condition through analyses of salinity,water types and geochemistry exponents of formation water.The centers of high salinity,positive and negative geochemistry exponents match with hydrocarbon distribution very well in Carboniferous and Ordovician layers except Silurian.Carboniferous layer in the southeastern Tazhong and Ordovician layer in structural belt I in the northern slope of Tazhong are both favorable for preservation.Hydrocarbon migratory directions in both formations are related to hydrodynamic force.The former is from northwest to southeast affected by gravity flow while the latter is from northeast to southwest due to compaction flow.The relationship between salinity,geochemistry exponents and hydrocarbon accumulation is tight for the Tazhong low uplift.Beneficial geochemistry exponents of formation water inClude:1) salinity(35 g/L);2) r_Cl^-/r_Mg²⁺-r_Na⁺/r_Mg²⁺(0);3) r_Ca²⁺/r_Mg²⁺(1);4) r_Na+/r_Cl^-(0.9);5) r_SO2-₄×100/(r_Cl^-+_SO2-₄)(3);6)(r_HCO^-₃+r_CO^2-₃)/r_Ca²⁺(0.2).

GEOCHEMICAL CHARACTERISTICS OF THE CRUDE OIL IN THE LUXI SAG, THE KAILU BASIN

Zhou Shuqing, Huang Haiping, Liu Yuming

2007, 29(6): 598-603. doi: 10.11781/sysydz200706598

Abstract(609) PDF-CN(373)

Abstract:
The Luxi Sag is the area which has the highest exploration degree and the most oil and gas discoveries among the peripheral basins of Liaohe Basin.The crude oil maturity,the organic matter input and the depositional environment of Bao 1 Block and Bao 14 Block in the Luxi Sag have been studied based on the precise geochemical analysises of the crude oil samples.Many similar geochemical characteristics between the crude oils from Bao 1 Block and Bao 14 Block have been found,in Cluding:the Pr/Ph ratio is less than 0.6;the regular sterane distribution is dominated by C₂₉-steranes;the tricy Clic/pentacy Clic terpane ratio is less than 0.15,with the content of tricy Clic terpane being obviously less than pentacy Clic terpane;the base peak of the tricy Clic terpane is C₂₃ and that of the pentacy Clic terpanes is C₃₀,with the Ts/Tm ratio ranging from 0.7 to 1.0 and certain amount of gamacerene.But some differences between the two blocks also exist.Bao 14 Block has a slightly higher maturity,the base peak of n-alkanes in Bao 1 Block is mostly characterized by C₂₀,and that in Bao 14 Block is mostly characterized by C₂₁;the ratio of C_15-21/C_22-28 in Bao 1 Block is higher than that in Bao 14 Block;and Bao 1 Block has higher gamacerene index,indicating that Bao 1 Block was deposited under a higher salinity environment.The hopane/sterane ratio in Bao 1 Block is lower,suggesting that the algae were rather developed and the higher salinity environment may suppress the bateria.

THE ORIGIN OF JURASSIC OIL-SOAKED SANDSTONE IN THE PIEDMONT ZONE OF NORTH LONGMENSHAN, THE SICHUAN BASIN

Dai Hongming, Liu Wenlong, Yang Yueming, Li Yuegang, Duan Yong

2007, 29(6): 604-608. doi: 10.11781/sysydz200706604

Abstract(779) PDF-CN(484)

Abstract:
The piedmont zone of the North Longmenshan is located at the fault front structural zone of buried faults of the nappe structural belt.Zhongba and Hewangchang Gasfeilds and more hydrocarbon show are discovered.The Jurassic oil-soaked sandstone is discovered to be wide distribution by field survey and well drilling.It believes that the crude oil of oil-soaked sandstone is the product which generates in the oil generation peak of Cambrian muddy source rock.It is the production by more time charging,movement and redistribution,which is after the varying degrees biodegradation and long distance movement,and under the polytectonic movement.The main criterions are following.First,the normal alkane and branched paraffin of oil-soaked sandstone disappear by strong biodegradation.Second,the carbon isotope of aromatic hydrocarbon is Closed.It is-34.41‰～-35.03‰.Light hydrocarbon normal alkane in the hydrolytic product is predominantly to compare with hydrocarbon branched paraffin.It belongs to the product of marine Ⅰ-Ⅱ₁ type kerogen.Third,the pattern of biomarker is similar to Cambrian dark Claystone.At last,the maturity which is converted by methylphenanthrene index is 0.82%～1.25%.

INVESTIGATION OF THE SOLID BITUMEN BY CHEMICAL DEGRADATION METHOD——A CASE STUDY OF THE SOLID BITUMEN FROM THE NORTHEASTERN SICHUAN BASIN

Wang Yongquan, Xiong Yongqiang, Li Yun

2007, 29(6): 609-611. doi: 10.11781/sysydz200706609

Abstract(680) PDF-CN(476)

Abstract:
An investigation on the parent material and the genesis of the solid bitumen from the northeas-tern Sichuan Basin has been carried out by using the selective chemical degradation method combined with various organic geochemical analysis and measurement techniques.Compared with the soluble organic matter extracted from the solid bitumen sample,the biomarker obtained by the chemical degradation method has relatively lower thermal maturity,and can reflect the characteristics of the parent materials of the early evolution stage.The data of the biomarker parameters and the bitumen reflectivity indicate that the solid bitumen has experienced a relatively high thermal evolution,and possibly has under-gone a certain degree of biodegradation.Based on the biomarker distribution of the solid bitumen in the sample,it can be inferred that the precursor of the solid bitumen dominantly derives from the low-level aquatic biota such as the bacteria and the algae,which were deposited under a brackish or relatively deep water environment.

SIMULATION EXPERIMENT OF THE GEOCHROMATOGRAPHIC EFFECT OF AROMATIC HYDROCARBONS DURING HYDROCARBON EXPULSION

Chen Zhonghong, Zha Ming

2007, 29(6): 612-616. doi: 10.11781/sysydz200706612

Abstract(604) PDF-CN(336)

Abstract:
A simulation experiment has been conducted at a low temperature(150℃) and pressurized condition in order to study the geochromatographic effect of the aromatic compounds in the course of the hydrocarbon expulsion from the black mudstone strata and the calcilutyte strata.The samples used in the experiment are source rock samples with or without oil mixed,which were collected respectively from the mudstone strata at 3 160 m in the lower part of the 3rd Member of Shahejie Formation,Well Tuo-73 and the calcilutyte strata at 2 432 m in the upper part of the 4th Member of Shahejie Formation,Well Liangxie-61 in the Dongying Sag,the Bohai Bay Basin.The organic carbon content of the two samples are 3.08% and 4.0%,and the vitrinite reflectance(_Ro) are 0.42% and 0.45% respectively.The results show that the geochromatographic effect is directly related to the molecular weight,since the high-weight molecular hydrocarbon is more difficult to migrate and the geochromatographic effect is thus more insignificant.The hydrocarbon expulsion causes the ion flow content of the light-weight hydrocarbon series,such as naphthalene,increase and the ion flow content of the high-weight hydrocarbon series,such as triaromtic sterane,decrease in the whole.While within the hydrocarbon series,the rearranged 1,3,6-TMN(trimethylnaphthalene) can migrate more easily than the 1,2,5-TMN,whereas the dethylphenanthrene migrates more difficultly than the mother phenenthrene;the relative contents of the compounds in dibenzofurans,dibenzothiophenes,and biphenyl series change greatly compared with the other series,and the related ratios of the compounds within the above hydrocarbon series are regarded as potential indicators of hydrocarbon migration.

IMPROVEMENT EXPERIMENT OF NONSANDSTONE RESERVOIRS OF QIANJIANG FORMATION IN THE QIANJIANG SAG, THE JIANGHAN BASIN

Hou Xianhua, Zhang Yongsheng, Yang Yuqing, Zhang Haiqing

2007, 29(6): 617-622. doi: 10.11781/sysydz200706617

Abstract(755) PDF-CN(368)

Abstract:
Nonsandstone reservoirs between salt beds of Qianjiang Formation in the Qianjiang Sag of the Jianghan Basin are mainly composed of dolomicrite,glauberite rock,mudstone and their peperite.Porosity and permeability are commonly poor.In the experiment,sample No.4 of Member 2 of Qianjiang Formation in Well Wangyun 10-6(glauberite-bearing dolomicrite) and sample No.8 of Member 3 of Qianjiang Formation in Well Wangping 1(dolomite-bearing fine-medium crystalline glauberite) are processed with 3 different solutions:saturated saline water,mixture of saturated saline water and acetic acid,and mixture of saturated saline water,acetic acid and hydrochloric acid.Capillary pressure curves indicate that,expulsion pressures of the processed samples No.4 and No.8 decrease by 62% and 88% respectively.Maximum pore-throat radiuses increase by 187% and 743% respectively.There is obvious improvement in sorting coefficient of pore-throat too.In addition,porosities of both samples increase by over 100%.The experiment shows that,skeleton of the processed samples maintains intact,while porosity and permeability are improved effectively.

FLUID POTENTIAL ANALYSIS AND APPLICATION IN LITHO-STRATIGRAPHIC RESERVOIR EXPLORATION

Yang Zhanlong, Chen Qilin, Guo Jingyi, Huang Yunfeng, Sha Xuemei

2007, 29(6): 623-627. doi: 10.11781/sysydz200706623

Abstract(887) PDF-CN(444)

Abstract:
With the boundary of paleo-structural map of sedimentary sequence in fluid migration period,systematically taking into consideration the coefficients(such as reservoir thickness,porosity,perme-ability and pressure,etc.) pertained to fluid migration within sedimentary sequence,based on the division of migration-accumulation units,abiding the regularity that fluid migrates from higher potential area to the lower one,using the modeling software of Petro Charge to model the trace of fluid migration,the fluid-containing ability of lithologic traps on slopes in oil-and-gas bearing basins is finally evaluated.The applications in the Qianjiang Sag of the Jianghan Basin and the Shengbei Sag of the Tuha Basin show that,fluid potential analysis is an effective ancillary approach in oil-and-gas bearing evaluation of litho-logic traps.

DISCUSSION ON THE APPLICATION OF THE ROCK MAGNETIC FABRIC METHOD IN RESUMING PALEOTECTONIC STRESS FIELD IN SEDIMENTARY BASIN

Zeng Lianbo, Qi Jiafu

2007, 29(6): 628-632. doi: 10.11781/sysydz200706628

Abstract(866) PDF-CN(406)

Abstract:
The quantitative resumption of the paleotectonic stress field in the sedimentary basin has long been a difficult problem due to the shortage of the stress symbols.In order to probe the feasibility of using rock magnetic anisotropy to resume the direction of the maximum principle stress of the paleotectonic stress field in sedimentary basin,an experiment has been made at first to investigate the change of the magnetic anisotropy before and after the rock is slowly pressurized and deformed.After the rock is pressurized,the magnetic anisotropy parameters of H,P and q increase accordingly,the maximum and the minimum principal axes of the magnetic susceptibility also change significantly,indicating that the tectonic deformation process in the shallow formation may exert obvious influences on the rock magnetic anisotropy.A comparison analysis between the direction of the maximum principal compression stress determined by the minimum principal axis of magnetic susceptibility and that determined by the tectonic deformation analysis were then carried out in the northern Tarim Basin.The results show that the two is roughly consistent,suggesting that,in the area with strongly deformed structures,it is feasible to use the direction of the minimum principle axis of magnetic susceptibility in determing the direction of the maximum principal compression stress of the magnetic susceptibility of the paleotectonic stress field in the sedimentary basins.At last,some related issues such as the applicable scope of this method and the stage division of the tectonic stress field have been discussed.

FAST DETERMINATION OF BASIN'S PALEO-TECTONIC STRESS DIRECTION BY BALANCED CROSS SECTION——A NEW METHOD TO ANALYZE PALEO -TECTONIC STRESS DIRECTION

Tong Yanming, Zhong Qiaoxia

2007, 29(6): 633-636. doi: 10.11781/sysydz200706633

Abstract(768) PDF-CN(440)

Abstract:
To determine the direction of paleo-tectonic stress is a very important matter for basin's paleo-tectonic stress field research.A new method has been brought forward to analyze paleo-tectonic stress direction.Firstly,the balanced cross section technique is applied to obtain basin's deformation rates in different directions during each geological stage.Then,the strain rosette method is employed to calculate principal stress direction in mechanics of materials.Further,basin's deformation rates in 3 different directions are equated with strain rosette's linear strains.At last,basin's paleo-tectonic stress directions are figured out using the relevant formulae from mechanics of materials.The directions of the 1st extensional principal stress during Laiyang,Qingshan and Wangshi stages in the Jiaolai Basin have been obtained by this method,approximately NE-SW,NW-SE and S-N respectively.These results accord with those from other traditional geological methods,illustrating the feasibility of the new method.Besides,the changing trend of deformation rates in sections with different directions can reflect basin's mechanical property,so this method is also helpful for analyzing basin type and basin-forming mechanism.Obviously,this new method is convenient and can fast produce results,and is not restricted by strata outcrop condition.

2007 Vol. 29, No. 6

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