地质力学学报

TEMPERATURE DIFFERENCE BETWEEN THE QINGHAI-TIBET PLATEAU AND ITS CONTIGUOUS AREAS

JIANG Fu-chu, WANG Shu-bin, FU Jian-li, WANG Yan, YIN Wei-de

2006, 12(4): 399-405.

Abstract (228) PDF (384KB)(7)

Abstract:
This paper briefly discusses the difference of temperatures between the western and eastern parts south of the Kunlun-Qinling mountains of China.Comparison between the measured temperatures at weather stations and the temperatures obtained by conversion of the measured temperatures at sea level shows that the sea-level temperatures in the western,middle and eastern geomorphologic steps of China decrease gradually at 0.5℃/100 m from west to east.The annual average arithmetic temperatures in the plateau region of western China are higher than those in low,level region of eastern China,mainly because the climate of the Qinghai-Tibet Plateau of western China and the Southern Asian subcontinent has been controlled by the southwestern monsoons,while the climate in eastern China has been mainly influenced by the southeastern Asian monsoons and winter monsoons from high latitudes.Therefore,the global change and regional-scale monsoon climate are the primary cause responsible for the difference of arithmetic temperatures between eastern and western China,so we cannot broadly ascribe the temperature difference to the warming effect of the plateau and the effect of "cold troughs" in the east.

REDEFINITION OF THE EARLY PLEISTOCENE QANGZÊ FORMATION AND SEQUENCE STRATIGRAPHIC DIVISION IN THE ZANDA BASIN, NGARI, TIBET

ZHU Da-gang, MENG Xian-gang, SHAO Zhao-gang, YANG Chao-bin, HAN Jian-en, YU Jia, MENG Qing-wei, LÜ Rong-ping

2006, 12(4): 406-415.

Abstract (184) PDF (508KB)(9)

Abstract:
Based on the contact relationships,sedimentary cycles,sedimentary systems and lithofacies and lithologic characteristics of the stratigraphic section,the fluvio-lacustrine sediments of the early Pleistocene Qangzê Formation in the Zanda basin are divided into 2 sedimentary facies and 3 lithologic members.The first and second members of the Qangzê Formation consist of a sequence of coarse clastic rocks of conglomerate with sandstone,belonging to typical alluvial(diluvial) fan deposits.The third member consists of alternating beds of sandstone and conglomerate,belonging to glaciofluvial and paraglacial deposits.ESR and paleomagnetic dating indicates that the age of the fluvio-lacustrine sediments of the Qangzê Formation in the Zanda basin is earliest Pleistocene(2.681.36 Ma).The Zanda basin was a syngenetic downfaulted basin,which only experienced the alluvial systems tract and transgressive systems tract in the process of its reactivation in the late stage.The alluvial systems tract was formed in the early and middle stages of development of the reactivated stratigraphic sequence in the early part of the early Pleistocene,while the transgressive systems tract was formed in the late stage of development of the reactivated stratigraphic sequence in the early part of the early Pleistocene.

MAGNETOSTRATIGRAPHIC STUDY OF LAKE SEDIMENTS IN JIAOCHANG, MAOXIAN COUNTY, SICHUAN

WANG Shu-bing, LI Yi, XIA Xiong-gang, FAN Zhen-fei, FU Jian-li, WANG Yan, JIANG Fu-chu

2006, 12(4): 416-422.

Abstract (204) PDF (325KB)(6)

Abstract:
The Jiaochang section in Maoxian County,Sichuan Province,is 101.1 m thick,in which lacustrine sediments are 98.0 m thick,consisting of light yellow-gray silt,clayey silt and silty clay.Paleomagnetic measurements indicate that all the samples show normal polarity except two samples that have negative magnetic declination.The magnetic polarity belongs to Brunhes normal polarity and the B/M boundary is absent.According to the lithology,lithofacies and landform location,the strata can be correlated with the Longjie Formation in the Jinsha River valley,Yunnan.So it is inferred that the sediments began deposition at 100-120 ka BP.In addition,the optically stimulated luminescence(OSL) age is 16.7±1.2 ka BP at 4.0 m below the surface of the sediments,so it is inferred that the deposition ended at 10 ka BP according to calculation.The deposition of the lake sediments lasted for(100,000) years.The section is one of the exposed thickest sections since the last glaciation(deglaciation) in the Minjiang River valley.

MICROSTRUCTURES AND AGES OF ACTIVITY OF THE REVERSE FAULTS ALONG THE SOUTHERN MARGIN OF THE JUNGGAR BASIN

HAN Shu-qin, BING Ying, HU Ling

2006, 12(4): 423-428.

Abstract (329) PDF (730KB)(12)

Abstract:
The microstructures of fault gouge and tectonite in the Huo'erguosi-Manas-Tugulu reverse fault zones along the southern margin of the Junggar basin are studied and twelve samples of gypsum,fault gouge and quartz veins were collected and dated by using the electronic spin resonance(ESR) method.The results show that the gouges underwent at least three deformation stages.Many stick-slip microstructural marks such as slickenside striations and steps appear in gouges and on quartz grains.In addition,many creep deformation marks such as shear slip and oriented arrangement of clay minerals are also found.The results show that the Huo'erguosi-Manas-Tugulu reverse fault zones formed about 1.5 Ma ago and were readjusted at 0.4-1.0 and 0.08-0.12 Ma respectively.The time of faulting is consistent with the time of uplift of the Qinghai-Tibet Plateau,suggesting that the formation of the Huo'erguosi-Manas-Tugulu reverse fault zones on the southern margin of the Junggar basin is closely related to the uplift process of the Qinghai-Tibet Plateau.

NUMERICAL SIMULATION AND DYNAMIC ANALYSIS OF THE STRESS FIELD OF THE INDO-AUSTRALIAN PLATE

FENG Xiang-dong, LIU Wei-hu, WEI Dong-ping

2006, 12(4): 429-440.

Abstract (311) PDF (558KB)(11)

Abstract:
The types and nature of the Indo-Australian plate are very complex.A 3D lithosphere model of the Indo-Australian plate is constructed and numerical simulation of the tectonic stress field of the Indo-Australian plate is performed by using the pseudo-3D finite element method and adopting the WSM2000 observed stress data and stress state as constraints,and then the influence of the boundary forces applied at the Indo-Australian plate on the intraplate stress field is discussed.The results show that the intraplate tectonic stress field of the IndoAustralian plate is mainly controlled by two factors:(1) the asthenospheric static push;and(2) the resistance coming from collision zones,including Himalaya,Papua New Guinea,New Zealand and the northwestern boundary between the Indo-Australian plate and Eurasian plate.However,the effect of the extensional forces from the subduction zone on the intraplate stress field is relatively small.

CONTROLS OF NON-SYNDEPOSITIONAL FAULTS ON THE CHANGE IN THICKNESS OF STRATA ADJACENT TO FAULTS

YI Shun-hua, ZHU Zhang-xian, JIN Jun, DAN Wei

2006, 12(4): 441-444,440.

Abstract (186) PDF (318KB)(9)

Abstract:
This paper discusses the changes in thickness of strata adjacent to faults induced by non-syndepositional faulting according to outcrop-scale structural phenomena,geophysical maps,model experiments and domestic and foreign data. These changes are manifested by the following features:under the action of normal faulting the hanging wall thickens while the footwall thins,but under the action of reverse faulting the reverse is the case;in the case of a strike-slip fault,the thickening and thinning phenomena appear at the "slip-forward end" and "slip-apart end" respectively.This view has practical guidance significance for the petroleum,engineering and mineral prospecting sectors and also deepens the understanding in the theoretical study of structural geology.

A QUANTITATIVE MODEL OF HEAT PRODUCTION BY FAULTING AND ITS EFFECT ON THERMAL EVOLUTION OF HYDROCARBON SOURCE ROCKS

TONG Heng-mao, ZHANG Sheng-gen, HU Yuan-qing

2006, 12(4): 445-453.

Abstract (242) PDF (455KB)(9)

Abstract:
A quantitative heat-producing model of faulting was constructed proceeding from the basin stress state analysis and from the viewpoint of frictional heat production.On the basis of the model,the quantitative relationships between the heat quantity produced by fault plane friction and the fault nature,depth,tectonic stress and fluid pressure were established,and the effects of heat produced by fault plane friction on the thermal evolution of hydrocarbon source rocks were analyzed quantitatively under earthquake conditions.The results show that:the fault depth,tectonic stress,fluid pressure,fault displacement,friction coefficient on fault planes are decisive factors of heat quantity produced by faulting;the rate of fault movement has nothing to do with the cumulative heat quantity produced by fault friction,but it is a key factor of the temperatures on the fault plane;under the conditions of a high rate of fault movement(e.g.earthquake type),very high temperatures may be produced by fault friction,which can cause partial melting of rocks near fault planes but the scope and lasting time of its influence on the thermal evolution of rocks are very limited.

SEDIMENTARY DIFFERENCE AND LOW-PERMEABILITY RESPONSE OF THE UPPER TRIASSIC YANCHANG FORMATION IN THE LONGDONG AREA, GANSU-EXAMPLES FROM THE CHANG 6 RESERVOIR IN HESHUI AND CHANG 8 RESERVOIR IN BAIMA

SHI Cheng-en, LUO Xiao-rong, WAN Xiao-long, LI Liang

2006, 12(4): 454-461.

Abstract (129) PDF (632KB)(5)

Abstract:
The Chang 8 reservoir at Baima in the Longdong area consists of delta-front underwater distributary channel deposits formed in the process of lake basin expansion,while the Heshui Chang 6 reservoir was mainly delta-front turbidity sand.They are low-and very low-permeability reservoirs respectively,both belonging to the southwest provenance sedimentary system of the Ordos basin,and the very low-permeability reservoir formed in the area due to different hydrodynamic conditions,transport distances,depositional topographic conditions and depositional water depths,as well as the influence of the moderate compaction strength.The fine grain size,lacking of chlorite and high contents of carbonate cements are the main controlling factors that make the physical properties of the Heshui Chang 6₃ reservoir poorer than those of the Baima Chang 8₁ reservoir.

CHARACTERISTICS OF INTER-SALT NON-SANDSTONE RESERVOIRS AND GENESIS OF FRACTURES IN THE JIANGHAN OIL FIELD

XIANG Shu-an, LING Qing-zhen, TU Shui-jiang, WANG Feng

2006, 12(4): 462-468,453.

Abstract (273) PDF (515KB)(5)

Abstract:
Salt rhythms are well developed in the Qianjiang subbasin,Jianghan basin,and some rhythms contain oil accumulations of commercial value.The rocks consist predominantly of mudstone,evaporite,gypseous mudstone and glauberite dolostone.The reservoir spaces mainly include pores,cavities and fractures,with fractures predominating.There are several types of reservoir spaces in one reservoir.In such reservoirs,permeability does not completely depend upon porosity but is related to the size,shape and degree of connection of pore throats,as well as the development of fractures and degree of filling.The reservoir belongs to a medium-porosity,low-to very low-permeability one.Based on core observations,thin-section analysis,well tests and study of the shape,attitudes,density and distribution scope of the fractures,the authors consider that the fractures mainly formed under the integrative effects of high abnormal pressures,differential compaction,diagenesis and tectonism,of which diagenesis was the main factor for the formation of horizontal interlayer fractures and tectonism is the main factor for the formation of swelling and shear fractures.

GEOCHEMICAL CHARACTERISTICS OF HYDROCARBON SOURCE ROCKS IN THE NO. 2 STRUCTURAL BELT OF THE NANPU SUBBASIN, EASTERN HEBEI OIL FIELD, AND SOURCE ROCK CORRELATION

JIA Qi-shan, LI Sheng-li, MA Qian, XU Wen-shi

2006, 12(4): 469-475.

Abstract (193) PDF (350KB)(4)

Abstract:
The main oil-bearing horizons of the No.2 structural belt of the Nanpu subbasin are sandstone of the First Member of the Paleogene Dongying Formation and Ordovician limestone.Analysis of several items of organic geochemical markers of source rocks and crude oil samples from well LPN1 indicates that:the sedimentary environment of principal source rocks in the study area was a continental shallow-lake,weakly reduced environment;the source rocks of the First and Second members of the Dongying Formation are immature;and the source rocks of the Third Member of the Dongying Formation and the Shahejie Formation are mature,with a depth threshold of petroleum generation of 3100 m and a principal petroleum generation threshold below 3700 m,belonging to the Shahejie Formation.The integrated correlation of gas chromatogram and mass spectrum parameters of saturated hydrocarbons in oil and source rocks suggests that petroleum of the First Member of the Dongying Formation mainly came from source rocks of the First Member of the Shahejie Formation and formed an petroleum accumulation characterized by "generation below and accumulation above",while Ordovician petroleum was mainly derived from source rocks of the Third Member of the Shahejie Formation,forming a petroleum accumulation characterized by "generation in younger strata and accumulation in an older reservoir".

QUANTITATIVE PREDICTION OF DISTRIBUTION OF TECTONIC FRACTURES IN THE YANCHANG FORMATION IN THE ZHENYUAN-JINGCHUAN AREA, ORDOS BASIN

ZHANG Lin-yan, FAN Kun, LIU Jin-dong, ZHOU Xin-gui, WANG Chun-yu, YUAN Yang-sen

2006, 12(4): 476-484.

Abstract (211) PDF (538KB)(7)

Abstract:
Detailed observations and statistics of tectonic fractures in outcrops,drilling cores and thin sections have been made and the basic characteristics, mechanics and origin of tectonic fractures in reservoirs of the Triassic Yanchang Formation in the Zhenyuan-Jingchuan area have been analyzed.According to the actual conditions of tectonic fractures in the target strata in the Zhenyuan-Jingchuan area and on the basis of finite element simulation,the authors have quantitatively predicted and evaluated the distribution and development degree of the tectonic fractures by using the rock breaking method,which may be used as a reference for evaluation of a favorable target area in petroleum exploration in the Zhenyuan-Jingchuan area.

FACTORS INFLUENCING THE EFFECTS OF HYDROFRACTURING IN A LOW-PERMEABILITY OILFIELD AND POTENTIAL EVALUATION USING ARTIFICIAL NEURAL NETWORK

SUN Dong-sheng, WANG Hong-cai, HOU Mo, ZHAO Wei-hua, SONG Qing-xin, LIU Zhen-hua, NIU Shu-fang

2006, 12(4): 485-491.

Abstract (224) PDF (313KB)(9)

Abstract:
Hydrofracturing is one of the main technical means for improving the recovery efficiency in low-permeability oil/gas fields.However,there are many factors that influence the hydrofracturing effects,including geological characteristics,physical properties of reservoirs and energy of strata.In order to obtain ideal hydrofracturing results,it is necessary to give a comprehensive consideration of the relationships between various influence factors and find out the main factors that influence the hydrofracturing effects.The authors constructed a mathematic evaluation model by using the artificial neural network method and performed net training and method check and verification of a wealth of available production data.The results prove that the constructed potential evaluation model using hydrofracturing wells has good stability and a high precision of prediction.It has certain guiding significance for choosing wells and evaluating layers for hydrofracturing and forecasting of the production capacity.

2006 Vol. 12, No. 4

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