2014 Vol. 20, No. 4

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CHARACTERISTICS, ACHIEVEMENTS AND PROBLEMS ON GEOMECHANICS
LIU Xue-qing
2014, 20(4): 331-338.
Abstract (263) HTML (231) PDF (927KB)(19)
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Geomechanics, which is a separate geological discipline, established by our China. Its background, characteristics, achievements are briefly introduced and some problems are proposed as well in this paper. Based on the influence of Geology Three Great Debates, especially for Continental Drift Theory, geomechanics is newly developed four basic characteristics include three theoretical foundations, nine basic concepts, seven research steps, and four basic viewpoints (essential, relevant, developmental, practical viewpoints).The paper discusses some outstanding achievements on the geomechanics, such as ten theoretical aspects, five technique methods, and five practice applications. Finally, some obvious problems are pointed out, for example, the geomechanics falls into "fixed theory" constraints; it refuses to go further because of not adopting new ideas; it overemphasizes the orogenic zone's long-termed succession activities to cause some great mistakes in identification of ancient tectonic periods; it imperfectly resolve some problems of deep geology and global oceanic geology. In a word, the geomechanics only emancipates the mind, advances with the times and faces to the globe could develop further.
NUMERICAL SIMULATION OF TECTONIC STRESS FIELD AND PREDICTION OF OIL-FAVORED AREAS: A CASE STUDY OF THE THIRD MEMBER OF QINGSHANKOU FORMATION IN GUIZIJING REGION OF QIAN'AN AREA, SONGLIAO BASIN
WU Lin-qiang, LIU Cheng-lin, LI Bing, WANG Zi-ling
2014, 20(4): 339-351.
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Tectonic stress is very important for oil-gas migration and accumulation. Petroleum accumulation for Gaotaizi reservoir in Songliao Basin mainly occurred in the end of Mingshui period. During this period, the peak of hydrocarbon generation and expulsion matches well with large scale hydrocarbon migration and accumulation periods and the formation of accumulations. In this paper, ANSYS is used to primarily simulate the tectonic stress field in the end of Mingshui period in Guizijing region of Qian'an area in South Songliao Basin. According to oil and gas migration mechanics driven by the crustal stress, migration potential field is also simulated. The results show that the first maximum principal stress is mainly controlled by lithology while the minimum principal stress is buried depth. Therefore, the well testing data shows that most wells with a show of oil and gas locate in low stress zone or low potential zone. Based on the distribution of crustal stress, migration potential fields and geologic structure features, the oil-favored areas predicted in this study will provide scientific guide for oil exploration and development.
CHARACTERISTICS AND REGULARITY OF LONGITUDINAL GEOSTRESS DISTRIBUTION IN SAND-MUDSTONE STRATA
ZHANG Dong-tao, TONG Heng-mao, ZHAO Hai-tao, LI Xue, ZHANG Hao
2014, 20(4): 352-362.
Abstract (197) HTML (74) PDF (6473KB)(29)
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Based on the analysis of basin geomechanics and mechanical properties of rocks, the characteristics and regularity of geostress distribution in the sand-mudstone strata are studied with numerical modeling by using the conceptual model of sand-mudstone strata abstracted from actual sedimentary strata. The results showed that horizontal principal stress mutates at the interface of sand-mudstone strata, and the change degree is mainly related to the difference of mechanical property of rock on both sides, then the regional tectonic stress. The effect of Young Modulus on the horizontal maximum principal stress is greater than that on the horizontal minimum principal stress; while the effect of Poisson Ratio on the horizontal minimum principal stress is higher than that on the horizontal maximum principal stress. The effect of Young Modulus and Possion Ratio on the horizontal maximum principal stress is different in different stress state. In extensional strike-slip and compressional stress state, Possion Ratio has greater roughly equivalent and samller effect on the horizontal maximum principal stress respectively. While, the effect of Possion Ratio on the horizontal minimum principal stress is always greater than that of Young Modulus in different stress state. The way of lithology changes in strata (mutations or gradient) has remarkable influence on the stress difference of horizontal principal stress, while the thicknesses no effect. The above understanding is valuable for effective reservoir hydraulic fracturing and reformation.
NUMERICAL SIMULATION OF PRESENT GEO-STRESS FIELD AND ITS EFFECT ON HYDRAULIC FRACTURING OF FUYU RESERVOIR IN GAOTAIZI OILFIELD
WU Ya, DAI Jun-sheng, GU Yu-chao, SHANG Lin, LIU Qiang
2014, 20(4): 363-371.
Abstract (186) HTML (97) PDF (8082KB)(18)
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In the research of present geo-stress of Fuyu reservoir in Gaotaizi oilfield, the micro seismic data and the experimental data of rock velocity anisotropy are used to get the directions of present geo-stress of wells. On the other hand, hydraulic fracturing data and rock dynamic experiment including paleomagnetic experiment, differential deformation experiment and acoustic emission experiment are employed to determine the value of present geo-stress of wells. Triaxial rock mechanical test is conducted to get rock mechanics parameters of Fuyu reservoir. On these basis, we have built up the three-dimensional finite element model by ANSYS software, which utilized the present geo-stress parameter of wells as constraint condition to proceed the numerical simulation of present geo-stress of Fuyu reservoir and to analyze the impact on artificial fractures in the fracturing operation created by the activity of natural fracture and present geo-stress. The results prove that the value of maximum horizontal principal stress stays in 34 MPa and its direction is NEE-SWW and the value of Minimum horizontal principal stress varies from 26 MPa to 30 MPa and its direction is NNW-SSE. The stress value in fault zone and anticlinal flanks in the northwest is much higher. However the gentle anticlinal core in the eastern and the southern part are low value zones. The anticlinal flanks and fault zone in the west are the active zones of natural fracture. The direction of artificial fractures are mainly affected by the natural fractures; in the eastern anticlinal core, the activity of natural fracture is lower.
INFLUENCE OF ROCK MECHANICS PARAMETERS ON DEVELOPMENT OF FRACTURE
YUE Xi-wei, DAI Jun-sheng, WANG Ke
2014, 20(4): 372-378.
Abstract (208) HTML (76) PDF (2597KB)(24)
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Elasticity Modulus, Poisson Ratio and density are key mechanical parameters of rocks. They have effect on development of fracture with other conditions unchanged. The study area of this paper is a gasfield in Tarim Basin. Based on the analysis of palaeo-stess field, we calculate the porosity of reservoir fracture through numerical simulation technique. Then we use the fracture porosity as index, and analyze the rock mechanics parameters influence on fracture development. The results show that with the elasticity modulus increasing, the fracture porosity increase, the lager the elasticity modulus the easier for rocks to rupture under the same stress; and when the Poisson Ratio is less than 0.2, with the Poisson Ratio increasing, the fracture porosity decrease; the Poisson Ratio is larger than 0.2, with the Poisson Ratio increasing, the fracture porosity increase. In addition, fracture porosity is not affected by rock density and can be ignored.
MULTI-SCALE LANDSLIDE HAZARD ASSESSMENT FOR KEY SECTION OF CHENGDU-LANZHOU RAILWAY, WENCHUAN SEISMIC REGION
WANG Tao, HU Qiu-yun, ZHANG Yong-shuang, WU Shu-ren, XIN Peng
2014, 20(4): 379-391.
Abstract (139) HTML (52) PDF (39604KB)(12)
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Taking Longmenshan key section of Chengdu-Lanzhou railway in Wenchuan seismic region as an example, we explore a sort of multi-scale landslide hazard assessing method for major project site in strong earthquake afflicted area. The spatial distribution characteristics of coseismic landslides induced by Wenchuan Ms 8.0 earthquake are inverted assessed with information value model. On this basis, landslide hazard assessments in regional and local scale are carried out. In regional railway corridor scale, the temporal and spatial distribution of daily maximum precipitation of 10% exceedance probability is predicted by Probable Maximum Precipitation method. Due to such probable precipitation, the landslide hazard is assessed with information value model. Also, combining seismic hazard zoning result, the landslide hazard is assessed due to basic earthquake ground motion of 10% exceedance probability in 50 years. In local railway station scale, with Rockfall Analyst software based on rolling stone kinematics simulation, runout characteristics and hazard of rockfall around Shiziyuan bridge site are simulated and assessed. All of the landslide and rockfall hazard assessment results above provide geological safety references in different scales for railway plan and line selection, site landslide defense design respectively.
GEOLOGICAL EVOLUTION AND HYDROCARBON RESOURCES POTENTIAL IN NORTH SLOPE, ALASKA
ZHANG Chun-yu, ZHAO Yue, WANG Luo
2014, 20(4): 392-403.
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Based on the collected data and materials, we analyze the evolution of tectonic and stratigraphy in the North Slope of Alaska and conclude the history of exploration, geological features and the hydrocarbon resources. Four major sequences are described here which are Franklinian sequence (older than Mississippian), Ellesmerian sequence (Mississippian to Triassic), Beaufortian sequence (Jurassic to Lower Cretaceous) and Brookian sequence (Lower Cretaceous to Quaternary) respectively. The North Slope of Alaska has gone complicated history of evolution where The North Slope basin evolved here. The basin has experienced three major evolutions which are Ellesmerian orogeny, rift and foreland basin tectonic stage. The North Slope has a large petroleum potential and has gone through a long exploration history. Petroleum prospective rocks in the province, are mostly Mississippian and younger, recording a sequential geological evolution through passive margin, rift and foreland basin tectonic stage. The main mean of undiscovered resources include 24.3 billion barrels of oil, 102.6 trillion cubic feet of gas, 0.94 billion barrels of shale oil and 42 trillion cubic feet of shale gas.
HYDROCARBON ACCUMULATION MODEL AND FUTURE EXPLORATION IN NORTHWEST SABAH BASIN
MA Liang-tao, LI Shi-xiong
2014, 20(4): 404-412.
Abstract (126) HTML (68) PDF (13147KB)(13)
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Guided by hydrocarbon geological theory, through typical reservoir dissecting, it identifies the features of Northwest Sabah Basin reservoir. The result shows that three different hydrocarbon accumulation patterns can be built based on the research for characteristic of structure, sedimentary formation and petroleum geology. They are lithologic, stratigraphic and rollover anticline type, respectively. The basin tectonic evolution involved rift, compression and inverse stage, depression stages and it developed four Cenozoic formations: Stage Ⅰ, StageⅡ, StageⅢ, StageⅣ. Mudstones and shales in the StageⅣ are the main source rocks. The pretty reservoir is provided by the Stage ⅠVA Lower Sandstone Unit, Stage ⅣC, ⅣD and ⅣE Upper Sandstone Unit and Stage ⅣC/ⅣD slump turbidite fan. Three reservoir-seal combinations, called lower, upper, deep-water turbidite fan combinations, are identified in basin. It builds three hydrocarbon accumulation models, named Updip sandstone pinchout, Unconformity and Rolling anticline type which distribute in different tectonic area in this basin. The fundamental conditions of hydrocarbon accumulation are analyzed. It shows that hydrocarbon source rocks and reservoir contacting each other in the plane and superimposing in the space provides favorable conditions for hydrocarbon migration and accumulation. Based on the above analysis, it suggests that stratigraphic reservoir in Inboard belt and lithologic reservoir in Outboard belt will be the future exploration targets for basin.
THE DEVELOPMENT MODEL OF STRUCTURAL FRACTURES IN ORDOVICIAN RESERVOIR IN YUBEI AREA, TARIM BASIN
ZHANG Ji-biao, YUN Jin-biao, ZHANG Zhong-pei, LIU Shi-lin, HUANG Wei
2014, 20(4): 413-423.
Abstract (109) HTML (54) PDF (14556KB)(9)
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Based on the identifying of fractures by the use of FMI, cores and slides data, the development law of structural fractures were summarized. The stages of structural fractures were classified according to the cross relation, the characteristics of cathodeluminescence and inclusions, and then the finite element method was applied to simulating the tectonic stress field mathematically in each fracture developing periods, also the genetic mechanism of structural fractures controlled by fault-fold in different periods were analyzed combining with the mechanical mechanism. The results showed that the structural fractures mainly developed along the high-steep zone in Yubei area, and their development degree and occurrence were controlled by fault and fold. Four stages of structural fractures recognized in this area: the fractures developed in Ⅰ and Ⅲ activities of the Middle Caledonian were mainly controlled by fault, the fractures developed in the Late Caledonian-Early Hercynian were controlled by fault and fold, and the fractures were mainly controlled by fold in the Late Hercynian. The fractures with high angle and parallel with the fault gave more contributions to reservoir development, and the fractures which developed both in the Late Caledonian-Early Hercynian and the Late Hercynian gave more conducive atmosphere to oil-gas accumulation.
FAULT ACTIVITY FEATURES OF TONGCHENG FAULT ZONE IN JINHU SAG
ZHANG Xiang-cheng, DAI Jun-sheng, ZOU Juan, WANG Xin-xin, YUE Xi-wei, WU Ya
2014, 20(4): 424-433.
Abstract (154) HTML (86) PDF (21364KB)(18)
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According to the interpretation of information of seismology and geology, structural features of Tongcheng fault zone is analyzed; the features and the stages of tectonic evolution are discussed. The research shows that the Tongcheng fault zone mainly develops NE-SW strike faults. Most faults are formed in the Funing period and Sanduo period. Tilt rotation of the blocks is obvious. The structures of fault block and fault nose are developed. Cenozoic tectonic activity shows alternating strong and weak characteristics, and fault activity is complex. The intensity of fault activity in Funing phase is gradually strengthened, and become relatively weak in Dainan period, In the Sanduo phase fault activity enhances, then fault activity largely discontinues. The differential fluctuation in Tongcheng fault is obvious on both sides of strata. Tectonic evolution of Tongcheng fault zone can be divided into four period: fault block development stage (Funing period), differential fluctuation stage (Dainan and Sanduo period), overthrust folded stage (Late Sanduo period), structure stable stage (Neogene and Quaternary). With the superposition of Wubao movement, Sanduo movement and early influence of basement faults, Tongcheng fault zone causes the development of fault nose structure, complex fault block structure and arc fault trap, which provides good places for oil-gas accumulation.
ROCK GEOCHEMICAL CHARACTERISTICS AND ORE-PROSPECTING PROGNOSIS IN THE BAIMIANSHAN METALLOGENIC FORECASTING AREA, NORTHERN GUANGDONG
QUAN Li-cheng, WEI Chang-shan, LUO Shuai, CAI Jin-hui
2014, 20(4): 434-445.
Abstract (110) HTML (41) PDF (13203KB)(14)
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According to the Baimianshan metallogenic forecasting area geological investigation to the west of Dabaoshan Mo deposit, we know that this area highly developed fault structures, mainly for the NW, NE and nearly NW three groups, among them, the NW fracture formed in the earliest time while NE the last. Along the NW and NE fault structures, we can see lots of suffer basic rock vein intruded. Following our investigation, we also find that along the fault zone of the surface existing multiple rock alteration and antimony lead-zinc pyrite mineralization points. Based on the test analysis in this area of surrounding rock and magmatic rock samples (ICP-MS), and from mineralization and geochemical characteristics of trace and rare earth elements reflecting the region is likely to have good metallogenic environment, combination of various metallogenic geological conditions and the predecessor's research of geochemical exploration work, we can conclude that there has ore-forming geological body which is not far from underground, and provided sufficient material sources for this region mineralization. Through the metallogenic information in this paper, we predict that between 500~800 meters underground in the mid-west of Baimianshan may be a considerable scale deposit of low temperature skarn type and zinc silver multi-metal.
THE EFFECT OF SALT-GYPSUM DEHYDRATION ON THE DEVELOPMENT OF SALT DIAPIR: A CASE STUDY OF DONGYING SAG
SUN Xiang-fei, CHEN Yong, WANG Cheng-jun, WANG Xin-tao
2014, 20(4): 446-454.
Abstract (168) HTML (65) PDF (19057KB)(9)
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There is a series of achievements about salt tectonics both at home and abroad. This paper points out that fluid in the tectonics development of the important role of salt, which is based on previous studies and the developmental characteristics of salt tectonics in Dongying sag. It contains a lot of salt-gypsum and salt-gypsum formations. This paper analyzes the characteristic of the salt tectonics according to the core, logging and seismic data. Abnormal high pressure created by salt-gypsum dehydration in stratum, high pressure can be used as a dynamic force fluid flow upward and this contributes to hydraulic fracturing in the overlying strata and can drive the salts material in the process of fluid upwelling upward movement. This paper proposes that salt-gypsum dehydration has an important influence on the formation of the salt tectonics. Based on the effect of salt-gypsum dehydration and overpressure fluid, the history of model of member 4 of Shahejie Formation salt diapir in Dongying sag is established according to seismic cross-section and logging data. Salt tectonics is analyzed during the migration of fluids in the process of development, salt-gypsum dehydration effect in early and mid-salt tectonic development important role.
SUPERPOSED FOLD: AN OVERVIEW
CHEN Long, SHI Wei
2014, 20(4): 455-468.
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Superposed fold, representing one of the most significant structures, is predominately derived from multistage crustal shortening, documenting a multiphase tectonic evolution history in a certain region. In order to deepen the understanding of the superposed fold, this paper gives an overview of the previous studies for superposed fold, and mainly focused on the structural style and formation mechanism. Here we suggest a superposed fold is dominantly originated from buckling folding, bending folding or shear folding, as reveled by an amount of field observation, physical and numerical simulation; then we give two case studies on the superposed fold. Additionally this paper summarizes a number of issues and probable methods on superposed fold analyzing.
CHARACTERISTICS OF GEOLOGICAL HERITAGE RESOURCES IN SHENGZHOU AND ITS PROTECTION
CAI Yao, ZHANG Zhong, TANG Xiao-ming, YOU Sheng-yi, YU Shu-jiao, FENG Hang-jian
2014, 20(4): 469-474.
Abstract (226) HTML (88) PDF (4937KB)(13)
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Shengzhou has abundant geological heritage resources, especially for the landscape, paleontology and water landscape. Based on its characteristic and genesis, we classify the Shengzhou resources into seven types, with revealing the typical characteristic. The advice of protection and exploitation has been proposed according to the situation of geological heritage protection at present.