2005 Vol. 11, No. 3

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QUANTITATIVE CHARACTERIZATION OF MECHANICAL PROPERTIES OF DEFORMATIONAL ZONES
ZHENG Ya-dong
2005, 11(3): 197-203.
Abstract (195) PDF (333KB)(14)
Abstract:
The determination of mechanical properties of a deformation zone is the first step in the geomechanical study.Some new concepts and methods have been proposed and can be used for quantitative characterization of mechanical properties of deformation zones.Natural deformational zones are commonly the result of general shear,a combination of pure shear(coaxial contraction or extension) and simple shear.In order to describe quantitatively their relative contributions,the kinematic vorticity number(Wk) is introduced and simply defined as cos υ,where υ is the angle between two eigenvectors containing the shear directions in the principal deformation plane(XZ-plane or ac-plane).For pure shear,υ=90° and Wk=0,and for simple shear,υ=0° and Wk=1.General shear is a combination of the above two,whose υ ranges between 0° and 90° and Wk from 0 to 1.The kinematic vorticity numbers may be signed as positive or negative.The positive and negative signs represent thinning and thickening of deformation zones respectively.The angle υ between the eigenvectors is available in several ways by means of polar-Mohr constructions.
Wk can be given by the orientation of the maximum principal stress(σ1):Wk=sin 2ξ,where ξ is the angle between σ1 and the normal to the deformation zone.Therefore,the related Wk and the mechanical properties of the deformation zone can be determined. Based on the maximum effective moment criterion,Meff=0.5(σ1-σ3)Lsin2 αsinα,where the angle α between a ductile deformation zone and the maximum principal compressional stress axis is 55°.The relationship can be used to infer the stress-orientation and,potentially,the value of the differential stress when the deformation zone formed.
SIMULATION STUDY OF THE LITHOSPHERIC THINNING IN EASTERN CHINA AND DYNAMIC MECHANISM OF SYNCHRONOUS BASIN-MOUNTAIN COUPLING
WU Hong-ling, YIN Xiu-lan
2005, 11(3): 204-214.
Abstract (154) PDF (532KB)(10)
Abstract:
A geomechanical model for the evolutionary process of lithospheric thinning in eastern China is constructed in light of the geological fact that significant changes took place in Cenozoic tectonics and geomorphology on the continent of China.Assuming that the various layers of the lithosphere are made of creep materials,the deep-level dynamic mechanism of synchronous basin-mountain coupling is quantitatively studied by using the numerical simulation method.A dynamic model of basin-mountain extension proposed by some geologists is theoretically discussed and verified.Study shows that lithospheric thickening or thinning is closely related to the thermal activity or thermal convection beneath the lithosphere and is one of the important factors affecting the formation of the synchronous basin-mountain coupling system.For the dynamic boundary condition of thermal convection of the basin-mountain system,only when both the upward buoyant force and the horizontal shear drag force caused by the thermal convection act on the bottom of the lithosphere,can the stress and strain conditions that accord with the actual tectonics and geomorphology be formed.Study of the creep features of the lithosphere shows that when the lasting forces act on the boundary,the stress and strain of various layers of the lithosphere vary with time.They increase rapidly in the initial stage and decrease steadily after reaching the peak value.The phenomenon of stress relaxation has great significance for the study of some common geological phenomena in tectonic activities.
QUANTITATIVE PREDICTION OF THE DISTRIBUTION OF TECTONIC FRACTURES RELATED TO FLEXURAL DEFORMATION IN UPPER PALEOZOIC TIGHT SAND RESERVOIRS IN THE TABAMIAO AREA, NORTHERN ORDOS BASIN
ZHOU Xin-gui, ZHANG Lin-yan
2005, 11(3): 215-225.
Abstract (156) PDF (777KB)(7)
Abstract:
The Tabamiao area is located in the Yishaan slope tectonic belt in the north of the Ordos basin.The structure is gentle and it is commonly thought that there are no conditions for fracture growth.However,many regional tectonic fractures in upper Paleozoic reservoirs and local tectonic fractures related to localized flexural deformation of strata have been found in the study area through core observations,thin-section analysis,measurements of physical properties and well tests and logging.This paper mainly introduces the method of estimating tectonic fractures related to low-amplitude flexural deformation of strata and the sites and degrees of development of fractures and their attitudes in the target horizons.The research results show that flexural deformation mainly occurred in the Yanshanian and Himalayan periods and modified the strata to some extent.Tectonic fractures are of little significance for the accumulation performance of tight reservoirs but they apparently improve the permeability of the tight reservoirs.
PREDICTION OF GAS POTENTIALS OF SAND RESERVOIRS OF THE LOWER SHIHEZI FORMATION IN THE TABAMIAO AREA, ORDOS BASIN
WU Li, SHI Wei, DONG Ning, ZHOU Xiao-ying, YU Wen-qin, MA Dian-ren, WEI Wei
2005, 11(3): 226-234.
Abstract (196) PDF (944KB)(8)
Abstract:
A set of techniques of prediction of 3D sand reservoirs suitable to the geological characteristics of the Lower Shihezi Formation in the Tabamiao area,Ordos basin,has been preliminarily established according to the key and difficult points of prediction in the area,combined with its geological and geophysical characteristics,and based on the seismic attribute extraction technique,seismic and well logging inversion technique and 3D visual interpretation technique.By using this set of techniques,the authors have ascertained the spatial distribution characteristics of the sand reservoirs of the target zone of the Lower Shihezi Formation and predicted the gas-bearing features of the target zone.On that basis,the study area is evaluated and the favorable reservoir zone and gas accumulation zone are determined.This study may guide gas exploration and exploitation in the area.
A METHOD FOR EVALUATING THE PRODUCTION POTENTIAL OF RESERVOIRS IN THE SHILONGCHANG-BAIYA OILFIELD IN NORTHERN SICHUAN AND ITS APPLICATION
YAN Bin, SHU Neng-yi, YANG Lei, XU Jing
2005, 11(3): 235-244.
Abstract (215) PDF (392KB)(9)
Abstract:
The Silongchang-Baiya oilfield,located in the northern Sichuan basin,is an oilfield that was put into production earliest by Southwest Subsidiary Company of SINOPEC.Geological conditions of the oilfield are so complicated that exploration and exploitation are very risky.Up to now,31 wells have been drilled and 185 zones with hydrocarbon shows have been recorded.However,the techniques and equipment for stimulating hydrocarbon zones were previously backward as compared with those nowadays;therefore some of the hydrocarbon show zones did not have good performances.On account of the above-mentioned problems,the authors have gathered almost all the data of the hydrocarbon show zones encountered by drill holes and conducted a comprehensive study to establish the correlation between different levels of shows and potential productive capacities of the reservoirs.The paper presents a new term,"potential factor"("PF" for short),to describe the production potential of reservoirs quantitatively.Case study shows that the method of evaluating the production potential presented by this paper can indicate the potential productive capacity of the evaluated reservoirs.The Dayi section in well SL11 is a hydrocarbon zone with the greatest potential in the field found by evaluation.Its potential factor is 0.86.Two different measures for stimulating its production were taken in September 1998 and December 2001 respectively.Both measures have successfully enhanced productivity remarkably and good benefits have been gained.
SEDIMENTARY SYSTEM OF “FOUR FANS AND ONE CHANNEL” IN THE BOHAI GULF BASIN AND ITS SIGNIFICANCE FOR PETROLEUM EXPLORATION
ZHAO Guo-lian, ZHA Chen-lin, YE Lian-jun
2005, 11(3): 245-258.
Abstract (166) PDF (917KB)(10)
Abstract:
This paper discusses the characteristics and distribution of sedimentary facies favorable for petroleum accumulation in Paleogene strata in the Bohai Gulf and its surroundings and their control on petroleum distribution.The sedimentary facies are obviously affected by structure.The understanding of the distribution of the sedimentary bodies is conducive to predicting petroleum distribution and can guide petroleum exploration.The classification of sedimentary systems should be based on a clear concept and various types of facies allow no overlapping.The sedimentary bodies in the Bohai Golf consist of fluvial fan facies,lacustrine delta facies,fan-delta facies,sublacustrine fan facies,non-fan channel turbidite facies,lakeshore-shallow lake beach-bar facies and semi-deep lake-deep lake facies(subfacies).The authors have studied the characteristics of various sedimentary systems and the characteristics of reservoirs of various systems in terms of source-reservoir-sealing.
STRUCTURAL SYSTEM AND HYDROCARBON DISTRIBUTION IN THE BOHAI GULF BASIN
XU Shou-yu, YAN Ke
2005, 11(3): 259-265.
Abstract (316) PDF (480KB)(14)
Abstract:
The Bohai Gulf basin is an important hydrocarbon base of China.In the basin many types of structural systems such as en-echelon and brush structural systems are developed and show a complex spatial distribution.The hydrocarbon accumulation and occurrence in the basin are controlled by different orders of the structural systems.Five hydrocarbon provinces,namely,the Jiyang and Huanghua brush hydrocarbon provinces,Lower Liaohe-Bohai arcuate hydrocarbon province and Jizhong and Dongpu en-echelon hydrocarbon provinces,may be distinguished in the Bohai Gulf basin.There are appreciable differences in hydrocarbon amounts and distribution characteristics between the five hydrocarbon provinces.Among these hydrocarbon provinces,the Jiyang brush hydrocarbon province contains the most abundant hydrocarbon resources and the Dongpu en-echelon hydrocarbon province has the smallest reserves.The Paleogene was the most important stage of structural evolution in the Bohai Gulf basin and is most closely related to hydrocarbon generation and accumulation formation.In the stage,the development of source rocks reached the culmination and many types of petroleum accumulation and several source-reservoir-seal combinations occurred.The Neogene witnessed the development of secondary petroleum accumulations dominated by drape anticline accumulations and good regional cap rocks in the basin.The complicated structural evolution of the Bohai Gulf basin brought about the formation of multiple source-reservoir-seal combinations.So the basin possesses basic geological conditions for the formation of large hydrocarbon regions.
ANALYSIS OF KINEMATIC FEATURES OF THE GANJIANG FAULT ZONE BASED ON THE TECTONIC EVOLUTION OF THE NANCHANG SUBBASIN
ZHOU Song-yuan, ZHANG Jie-hui, XU Ke-ding, JIANG Wei-shan, PEN Jun, LIU Jia-duo
2005, 11(3): 266-272.
Abstract (282) PDF (571KB)(8)
Abstract:
On the basis of an analysis of geological and geophysical data obtained by petroleum exploration in the South Poyang depression in recent years,the authors propose that the basining and tectonic evolution of the South Poyang depression were controlled by the activities of the Ganjiang fault zone under the constraint of the Yanshanian tectonic framework.The main tectonic activities were strike-slip movement and extension.The model of the tectonic evolution of the Nanchang subbasin is as follows:in the Lengshuiwuan(K1l),the subbasin was a strike-slip-pull-apart basin;in the Zhoujiadianian(K2z) to early Nanxiongian(K2n1) it was a sinistral strike-slip basin;at the end of the early Nanxiongian a tectonic turn took place;in the mid-late Nanxiongian(K2n2+3) it changed to a dextral strike-slip-extensional basin;in the Qingjiangian(E1q) it became a new downfaulted basin.According to the features of the basining and tectonic evolution of the Nanchang subbasin,the authors suggest that the large-scale sinistral strike-slip movement of the Ganjiang fault zone occurred in the early-mid Late Cretaceous and the turning point from the sinistral strike slip movement to dextral strike-slip movement occurred at the end of the Late Cretaceous early Nanxiongian(K2n1).
NUMERICAL MODEL OF FULLY COUPLED FLUID-SOLID SEEPAGE IN A DEFORMABLE POROUS MEDIUM AND ITS APPLICATIONS
DONG Ping-chuan
2005, 11(3): 273-277.
Abstract (186) PDF (217KB)(9)
Abstract:
The effective stress in the rock matrix of a reservoir increases as a result of the decline in pore fluid pressure with the continuous withdrawal of subsurface fluids.Under such conditions,more load is transferred to the rock matrix,and thus the rock is compacted or deformed,which can sometimes produce ground subsidence.The soil consolidation can be simulated by using a finite element numerical model of fluid-solid coupling of fluid seepage in a deformable porous medium.In addition,the production process of oil wells is also simulated.
APPLICATION OF THE ULTRASONIC FLAWLESS DETECTOR IN THE PRESERVATION OF UNEARTHED STONY CULTURAL RELICS
ZHANG Zhi-guo, PENG Hua, MA Yin-sheng, BAI Jia-qi, MA Xiu-min
2005, 11(3): 278-285,244.
Abstract (143) PDF (744KB)(8)
Abstract:
Taking for example the flawless detection of the imperial tablet of the reign of Emperor Qian Long of the Qing Dynasty unearthed recently for its protection and restoration,the paper introduces a new method of detecting quantitatively fractures and weathering degrees inside stony cultural relics with the ultrasonic detector.This method can not only detect the trend and development degrees of the fractures inside stony cultural relics(e.g.stone Buddha carvings,tablets and pillars) of different ages,but also judge their weathering degrees and intensities according to the ultrasonic characters.In a word,the detector can furnish reliable data for the preservation and recovery of cultural relics.
STUDY OF DEFORMATION AND FAILURE OF ROCK BASED ON PROPERTIES OF COHESION AND FRICTION
YOU Ming-qing
2005, 11(3): 286-292,258.
Abstract (220) PDF (558KB)(11)
Abstract:
In terms of microscopic textures,mineral particles are either cohesive or separated,and the cohesive force and internal frictional force of the Coulomb criterion cannot exit together locally.Cracks are produced and increase gradually with deformation,and the cohesion between particles in material loses with the deformation.The new cracks will produce friction and the shear stress of the material is supported by friction.If the loss of cohesive forces reduces the supporting capacity,then yield and failure will occur in localized fracture surfaces of a specimen and show the brittle character,otherwise the yield and failure will be distributed and show the ductile character.With increasing confining pressures,the frictional force of fissures will exceed the cohesive force of rock material.Then when the axial stress increases to the value of the cohesive force,shear yield will occur in material,producing plastic deformation.The frictional force will not increase to its maximum but keep the value of cohesive forces and the fissures will not slide either.Knowledge of the concept of friction is the key to understanding the deformation,strength and failure of various kinds of rock with changes in confining pressure.

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