2011 Vol. 17, No. 4

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THEORETICAL MODEL ABOUT FRACTURE POROSITY, PERMEABILITY AND STRESS FIELD IN THE LOW-PERMEABILITY SANDSTONE
FENG Jian-wei, DAI Jun-sheng, LIU Mei-li
2011, 17(4): 303-311.
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Aiming at low-permeability sandstone, based on the principles of geological mechanics, using relationship between fracture parameters and stress field as a bridge, on the premise of reasonable preference of fracture criteria, through methods of tests and theoretical derivation, this paper establishes mechanical model between stress-strain and fracture parameters(porosity and permeability)to develop a set of quantitative methods. Results show that combining energy method with fracture criteria is effective approach to confirm the relationship between stress field and fracture parameters, after inner stress state reaching or exceeding failure conditions the fracture aperture, density will increase with strain energy density. At the same time, it is found that fractures in rock commonly formed under palaeostress field and their aperture and density were much larger than the present. Consequently, we can understand that current stress field goes against producing fractures and fracture aperture can be figured out through positive stress and shear stress acting on fracture face. Finally, Great success has been achieved in middle reservoirs of the third Shahejie Formation of Block Shishen100 in Shinan Oilfield by applying the program.
THEORETICAL DEVELOPMENT OF MAXIMUM EFFECTIVE MOMENT CRITERION
TONG Heng-mao, WANG Ming-yang, HAO Hua-wu, ZHAO Dan
2011, 17(4): 312-321.
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Theoretical analysis shows that the Maximum Effective Moment, which cause preexisting cleavage or bedding to rotate, is related to the direction of pre-existing cleavage or bedding, and the Maximum Effective Moment Criterion (Meff=0.5(σ1-σ3) Lsin2αsinα, simplified as MEMC) proposed by Zheng et al is theoretically expanded to General Criterion of Maximum Effective Moment (MG-eff=0.5(σ1-σ3) Lsin2αsin (α-θ), simplified as GCMEM), which can be used to determine the Maximum Effective Moment with any direction of cleavage in this paper.MEMC is a special case of GCMEM when cleavage is parallel to maximum principal compressive stress (σ1).Theoretical analysis of GCMEM shows that:① when cleavage is parallel to σ1, there occur two values of Maximum Effective Moment symmetrically on either side of σ1 in the direction of ± 54.7°, and two conjugate deformation zone are predicted to appear with obtuse angle (109.4°) facing σ1 direction.② When cleavage is oblique to σ1, one Maximum Effective Moment, along which one deformation zone will appear, is predicted to occur on other side of σ1, and the angle between deformation zone and σ1 will decrease (from 54.7 ° when θ=0° reduced to 35.3° when θ=90°), while the angle between pre-existing cleavage and deformation zone will increase (from 54.7° when θ=0° increased to 125.3° when θ=90°) with pre-existing cleavage deviating from the σ1 direction.③ when cleavage is perpendicular to σ1, there also occur two values of Maximum Effective Moment symmetrically on either side of σ1 in the direction of ± 35.3°, but two conjugate deformation zone with acute angle (70.6°) facing σ1 direction.When the directions of pre-existing cleavage and deformation zone on principal strain surface and shear direction (sinistral or dextral) are known, the direction of maximum principal stress can be determined.GCMEM overcomes the incompatibility of MEMC with Slip Line Theory, and can be used to explain most of the kink zone development and other non-conjugate phenomena.It is expected to have wide application prospects in ductile deformation field.
CHARACTERISTICS OF TANCHENG-LUJIANG FAULT AND ITS ROLE ON BASIN CONTROLLING
LIN Zong-man
2011, 17(4): 322-337.
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Tancheng-Lujiang Fault is a large scale fault belt in the east of China which has a long history of study and many achievements have been obtained.Based on the studies of predecessors, this paper advanced some new opinions as such:large scale strike-slip displacement of the fault may not exit; it formed in late stage of Early Cretaceous; it played a remarkable role on basin controlling.
SEDIMENTARY CHARACTERISTICS, BASIN TYPE AND DYNAMIC MECHANISMS DURING LATE TRIASSICJURASSIC IN SOUTHEASTERN HUNAN PROVINCE
BAI Dao-yuan, ZHONG Xiang, JIA Peng-yuan, LIU Yao-rong, HUANG Wen-yi
2011, 17(4): 338-349.
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There are different standpoints such as para-foreland basin and down-faulted basin about the Late Triassic-Jurassic basin in southeastern Hunan.Distribution of the sediments and lithofacies character show information as follows:there existed marine and marine-terrigenous sedimentary environment during Late Triassic-early Early Jurassic in southeastern Hunan, while continental sedimentary environment during late Early Jurassic-early Middle Jurassic; the Late Triassic basin was a NNE-SN trending narrow and long bay along the east side of Chaling-Chenzhou fault, and the basin expanded to east and west since Early Jurassic; the Late Triassic-Jurassic sediments covered crosswise on older layers.All the above indicated that the Late Triassic-Jurassic basin in southeastern Hunan wasn't a para-foreland depressive basin controlled by NS-compression.Combined with regional tectonic setting, the authors bring forward recognition as follows:the forming of the basin was mainly related with the EW-extention of NNE-trending faults under regional SN-compressional stress field, which confirmed that the lineament trend of Indosinian Movement in southeast Hunan was NNE; above evolution from marine to continental suggested that a EW-trending uplift formed to south of the study area since late Early Jurassic under regional S-N-compression, and that the study area was in a regional depressive tectonic setting when the basin extended in late development stage.These render the complex extensional or compressional space-time variation of tectonic regime when the Late Triassic-Jurassic basins developed in south China.
DIAGENETIC SEALING CHARACTERISTICS OF FAULTING ZONE AND ITS APPLICATION
WU Kong-you, LI Ji-yan, CUI Shi-ling, YANG Hai-bo, LIU Zhen-yu
2011, 17(4): 350-360.
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The diagenetic types which influence the fault sealing properties mainly include packing action, compaction, and cementation.The more shale contents of filler, the lower porosity and permeability of faulting zone, and the less possibility to seal.Packing action plays a vital role in control of the compactness of filler and the sealing strength of faulting zone when it is dormant.The faulting zone's sealing effect is directly proportional to the strength of packing action.After entering the shattered fault zone, hydrothermal minerals precipitated and crystallized with the decrease of temperature and pressure, and then they cemented fractures and breccias gradually.The main cementing minerals in faulting zone are calcite and quartz, and temperature and pressure play critical roles in cementation.The Well Xia-503 Faulting Zone occurs compact argillaceous fillers with one meter thickness approximately for being deeply buried and strongly cement.The observed result of scanning electron microscope shows that there are precipitating crystallization minerals in the fractures and pores of rock, and the sphere of cementation is 3 meters around the fault zone.Combined with packing action, compaction and cementation, Well Xia-503 Fault seals strongly, that is critical factor in hydrocarbon accumulation of Jiangjiadian Oilfield.
CHANGE OF THE PALEOCLIMATE AND EVOLUTION OF THE LAKE DURING PLIOCENE-EARLY PLEISTOCENE IN ZANDA BASIN, TIBET
HAN Jian-en, YU Jia, ZHU Da-gang, MENG Xian-gang, SHAO Zhao-gang, YANG Chao-bin
2011, 17(4): 361-372.
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According to the pollen combination analysis, paleomagnetic chronology, electron spin resonance (ESR) age of fluviolacustrine facies deposition and lithology characteristics, this paper discussed the relationship between paleoclimate and the evolution of Zanda paleolake during Pliocene-early Pleistocene in anda basin, Tibet. Study shows that the Zanda paleolake has went through three phases: early marsh period, the medium-term developing period and late dying out of lake period. The Zanda paleolake began to take shape in early period(5.41~4.40 Ma). The paleoclimate of Zanda basin firstly was woodland and grassland vegetation in arid climate with less warm, then into a warm and slightly wet climate of the forest-steppe vegetation, and finally into a warm and humid subtropical mixed forest climate. The Zanda paleolake was developing in the medium-term (4.40~2.57 Ma).The paleoclimate was into the cold period, reflected by the paleovegetation firstly from warm temperate zone of coniferous-broad leaf forests to mountain cool temperature zone of dark coniferous boreal forest, and then from mountain warm temperate zone of coniferous-broad leaf forests alternating process. The Zanda paleolake was disappearing in late period (2.57 ~ 1.36 Ma). Paleoclimate and paleoenvironment was into the cold period, with the paleovegetation alternating change from mountain dark coniferous forest and mountain dark coniferous forest to the low-shrub steppe and dry and cold grassland. Evolution of the Zanda paleolake has good relationship with the change of the paleovegetation and paleoclimate. Uplift of the plateau has controlled the paleoclimate and paleoenvironment changes, thereby affected the quantity of the lake changes.
ALOS INSAR COSEISMIC DEFORMATION OF YUTIAN EARTHQUAKE AND INITIAL ANALYSIS FOR GEOLOGY
XU Dan, YAO Xin, CHEN Qi, SUN Yue, LIU Yuan, LIU Feng-min
2011, 17(4): 373-380.
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A Ms 7.3 scale earthquake occurred in Yutian area, Xinjiang Uygur Autonomous Region, China, on March 21, 2008 is the biggest earthquake after the Ms 8.1 scale earthquake happened in Kunlun Mountain, November, 2001.Earthquake is concentrated reflection of tectonic activity, it can be accompanied by a large surface deformation and apparent fracture events, it can zoom the normal activities way of construct.Coseismic deformation is the effect directly reflected in the surface, it is very important for understanding of the nature of earthquake faulting and researching adjacent tectonic activity.In the harsh natural environment of northwestern margin of the Tibetan Plateau, the conventional methods can not carry out timely and effective for the field earthquake coseismic deformation measurement, so the advantages of InSAR technique have be highlighted.This article describes the InSAR observation principle, then gotten Yutian earthquake Co-seismic InSAR deformation field by ALOS PALSAR radar data, and presents geological results: Yutian Ms 7.3 earthquake macroscopic epicenter is located in the two north-south branches of Kangxiwar Fault southeast(Large Tamarisk Fault and Mousse Hill Fault) and the three branches of the triangle intersection which in Altyn Tagh Fault southwest; Yutian earthquake triggered a coseismic surface rupture which in Altyn Tagh Fault NS-trending branch, and the length of the rupture is 25.6 km; It is speculation that Yutian fault focal mechanism solutions is the normal fault under the deformed image of the interference radar, faults incline to west, the maximum range of motion on the plate over 200 cm; The tectonic stress around the two big faults intersection where Yutian earthquake occurred is mainly press in north and south direction.
NUMERICAL STUDY ON THE HAZARD EFFECT OF A BUILDING NEAR THE FAULT PRODUCED BY THE WENCHUAN EARTHQUAKE
SU Sheng-rui, ZHANG Yong-shuang, HAO Li-li, LI Song
2011, 17(4): 381-387, 409.
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Particular destroy phenomena occurred in the main building of Shuimo Silicon Company near the fault produced by the 2008 Wenchuan earthquake. On the basis of site investigation, two-dimensioanl finite element model is set up, and the hazard effect of a building caused by the faulting is simulated. The simulation result may be used to explain the mechanism for the formarion of the particular destroy phenomena of the building during the earthquake. It is thought that the formation of fault altered the local stress field and acceleration, thus led to the differential destroy of the building at the hanging wall of the fault which is characetrized by the stronger destroy near the fault. The destroy of the main beam is caused by the co-action of axial stress and shear stress.
RISK ASSESSMENT OF GEOHAZARDS BY USING GIS IN GANGU COUNTY, GANSU PROVINCE
WANG Lei, ZHANG Chun-shan, YANG Wei-min, SUN Wei-feng, QIU Zhan-lin, WANG Tao
2011, 17(4): 388-401.
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Based on detailed investigation of geo-hazards in Gangu County, the authors made evaluation zoning of geo-hazards risk assessment in Gangu County by using the combined qualitative analysis and quantitative evaluation on the GIS platform. On the basis of comprehensive analysis of the present landslides and geological environment in Gangu County, the authors analyzed the main factors controlling the formation of landslides. These factors involve such aspects as ①geo-hazards historical intensity, ②topography and geomorphic, ③engineering geological layer combination, ④tectonic setting and faults effects, ⑤the degree of vegetation coverage, ⑥the effects of water, ⑦human activities, and ⑧rainfall conditions. With the selected indices quantified according to experts' experience, the index system of geo-hazards risk assessment was formulated. The study area was finally divided into 4 levels of the high-grade area, the medium-grade area, low-grade area, and the very low-grade area. According to the results of landslide hazard zonation, the high-grade area covers 393.19 km2, accounting for 25.01% of the total study area; the medium-grade area is 544.04 km2, accounting for 34.61%;the low-grade area is 324.69 km2, accounting for 20.65%;and the very low-grade covers 310.08 km2, accounting for 19.73% of the whole county.
DEFORMATION MONITORING AND STABILITY ANALYSIS OF AN UNSTABLE SLOPE IN CHONGQING CITY
CHEN Xiao-yang, ZHANG Hong-yang, JI Dong, MAO Shi-long
2011, 17(4): 402-409.
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The unstable slope is located in the cantonal of Chongqing City, where large foundation excavation will be carried out in the influenced scope. Analysis on stability must be taken for construction safety. On the basis of previous studies, combined with field investigation, the geological environment of this study area is summarized. By analyzing the measured monitoring data, the displacement characteristics of the monitoring point is studied. To know the deformation of unstable slopes, FLAC-3D numerical simulation is adopted to obtain soil parameters by the comparison of monitoring curves and numerical results. Finally, based on limit equilibrium theory and strength reduction method, the evaluation results of stability are studied for natural state of unstable slopes and excavation.