Table of Content

25 June 1998, Volume 19 Issue 2

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HETEROGENEITY OF POROSITY AND PERMEABILITY IN CLASTIC ROCK RESERVOIRS

Jiao Yangquan, Li Sitian, Li Zhen, Wen Xianduan

1998, 19(2):  89-92,98.  doi:10.11743/ogg19980201

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The heterogeneity of porosity and permeability of reservoirs are closely related to the architectures of depositional systems,and can be studied by scale.(1)On the scale of depositional system,different depositional systems are different in porosity and permeability.Porosity and permeability of different genetic facies in the same depositional system may have great differences.This depends mainly on the paleo current energy and environment in which the genetic facies were formed.(2)On the scale of genetic facies, porosity and permeability of the same fluid flow unit and between different fluid flow units are on the whole different.This is related to lithology of reservoirs constituting the fluid flow units.The superimposition of nonhomogenous diagenesis could decrease greatly the porosity and permeability of fluid flow units.(3)On the scale of core,porous media show anisotropic characteristics.

APPLICATION OF ESR DATING TO PETROLEUM GEOLOGY

Zheng Rongcai

1998, 19(2):  93-98.  doi:10.11743/ogg19980202

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The basis of ESR dating is the ratio of total nuclear radiation amount absorbed by quartz to per year radiation amount that was calculated according to K,Th and U contents in surrounding substances.The ESR age of different genetic quartz may have different geological significance,so it is necessary to pay attention to the occurrence and genesis of the quartz during sampling.In practical,the ESR age of quartz is mainly used to distinguish different fissure and solution stages and ages;to distinguish tectonic periods and ages.Combined with the configuration and colour of the quartz crystal,the inclusions and the associated minerals,ESR dating could also be used to distinguish the geological features during hydrocarbon migration,to study the development and evolution rule of the fissur and solution.

GEOMETRIC ARCHITECTURE OF SEDIMENTARY SEQUENCE IN JIRGALONGTU DEPRESSION

Fan Tailiang, Zhu Ling

1998, 19(2):  99-105.  doi:10.11743/ogg19980203

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The geometric architectures of depositional sequences in fault-depressions play an important role in the analysis of sequence stratigraphy.According to its geometric architectures,the Sahantala Formation of the Jurassic Cretaceous in Jirgalangtu Depression,Erlian Basin could be classified into ten seismic sequences of third grade,which in turn constitute three supersequences.The shapes of the sequences are box-like,wedge shape and sheet drape in ascending order.The sequence boundaries varied from bilateral fault^→ monoclinal fault overlap^→ marginal overlap types,correspounding respectively to the fracture subsidence,depression and filling stages of the basin.The Jirgalangtu Depression is composed of low level,water inflow and high level configurations and contains abrupt slope subaqueous fan system,prograding fan delta-turbidite fan system and marginal minor fan delta system.The combination of the three sequences includes retrograding,prograding and aggrading types.It is proposed in this paper that the geometric architectures of sequences could reveal the process of sequence dynamics,the deposition property and evolution process of the basin.

AN APPROACH OF SPILL POINT CONSTRAINED VELOCITY FIELD:A METHOD FOR IMPROVING IMAGE ACCURICY OF LOW CLOSURE STRUCTURES

Pu Renhai, Ye Liusheng, He Faqi, Song Shanlin

1998, 19(2):  106-109.  doi:10.11743/ogg19980204

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Though there are many factors offecting the image accuricy of low closure structures,the building up of a real and reasonable variable speed velocity field is the most important one ofter eliminating mis-tie and calibrating and tracing exactly the horizon.A t₀ value can be found at the spill point in iso t₀ map,and the spill point depth can be obtained from base level corrected oil or gas wells.Then the spill point constrained average velocity can be derived.When well control point are rare or distributed unevenly,the seismic stacking derived average velocity should be constraint corrected with spill point average velocity and well point average velocity,then a reasonable varying speed velocity field could be obtained.Structural maps made in this way will have more accurate trap configuration and closure,and could provide more reliable basis for reserve calculation and development well allocation.

JURASSIC SEDIMENTARY SYSTEM OF FAULT DEPRESSION IN SOUTHEAST TARIM AND ITS HYDROCARBON SIGNIFICANCE

Li Wenhou

1998, 19(2):  110-115.  doi:10.11743/ogg19980205

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Fan,braided stream,fan delta and braided delta sysem constitute the primary Jurassic coarse clastic sedimentary system.The system is characterised mainly by short axial directional transportation deposition in the fault depression of the Southeast Tarim Basin.The asymmetrical bilateral fractures within the graben resulted in the drift of subsidence center and depocenter towards the main fracture.Fan fan delta system developed on the abrupt of the fault depression,and braided stream braided delta sysem developed on the gentle slope.Dark mudstone of semi deep lake facises is good hydrocarbon source rock.The major petroleum source in the Jurassic oil bearing sandstone should be attributed to shallow marine source rocks derived from underlying Paleozoic.The stream channel bar,the underwater distributary channel of fan delta front and braid delta front are major reservoir sandtone bodies.

NATURAL HYDRAULIC FRACTURE IN COMPACTED BASIN AND ITS KINETICS

Zhang Xiaoli, Feng Qiao, Li Wenhou

1998, 19(2):  116-123.  doi:10.11743/ogg19980206

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In a compacted basin,natural hydraulic fracturing is one of the key factors of the pore fluid expulsion of uncompacted belt.An uncompacted belt can be described as an abnormal pore fluid pressure belt surrounded by “shell”.The kinetics of the natural fracturing of the “shell” in continous sedimentation(loading)is different from that in succesive erosion(unloading).In loading condition,the shear fracturing of the bottom shell of the uncompacted belt would appear earlier than that of the top.In unloading condition,the “shell” would crack only when the load pressure decrease resulted from erosion is greater than the minimal load pressure required in vertical tensile crack of the “shell”,and the crack usually happens on the top shell.In this view,the expulsion of the pore fluid of the uncompacted belt can be described as a intermittent change process of expelling up and down.

HABITATS OF HERCYNIANINDOSINIAN RADIOLARIANS IN SOUTH CHIAN

Zhang Ning, Xia Wenchen, Zhang Suxin

1998, 19(2):  124-131.  doi:10.11743/ogg19980207

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Based on the study of radiolarian abundance,fossil differentiation,genus and species assemblage and bioecologic texture,the main indicators for recognizing the radiolarian bioecologic environment were discussed.The radiolarian habitats of South China during Hercynian Indosinian could be classified into 5 types:(1)shallow sea habitat type of 50-200 m water depth,(2)sime deep sea habitat type of 200-1 000 m water depth,(3)deep sea environment with more than 1 000 m water depth,(4)restrict rift sea habitat type of 50-200 m water depth,and(5)connected rifted sea habitat type of more than 200 m water depth. The radiolarian could be divided into three succession cycles according to the evolution of radiolarian assemblages in every stratigraphic unit.The radiolarian succession cycle of Middle Devonian-Early Carboniferous reflects a respreading process of the relict ocean trough.The Middle Permian radiolarian succession shows a open rifted oceanic environment.The radiolarian succession cycle of Late Permian-Middle Triassic indicates a development process of restricted rift trough^→connected rift trough^→open deep ocean .

DETERMINATION OF THRESHOLD OF ARGILLACEOUS ROCK SEALED HYDROCARBON

Fu Guang, Wang Pengyan, Chen Xin, Wang Yachun

1998, 19(2):  132-135.  doi:10.11743/ogg19980209

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The pore diameters of argillaceous caprock decreases as its buried depth increased.Only when the pore diameters are as small as or even smaller than the diameters of oil and gas moleculars,the argillaceous caprock could seal completely every states of hydrocarbon,and reach the sealing critical point.According to this rule,the sealing threshold depths of argillaceous caprock for both oil and gas could be calculated.Then the corresponding threshold time value could be calculated based on bed thickness and the rate of deposition.According to Φ_m=54.74 exp(-0.000 935 4z),K=0.136(Φ_e)^4.4/S_WB)² and r=√8K/Φ,the critical threshold depth for sealing oil in Sanzhao Region,Songliao Basin should be 2 500-3 000 m,and the critical threshold depth for sealing gas should be 5 000-5 200 m.This does not inclode the sealings of capillary pressure,abnormal pore fluid pressure and dense oil and gas.

SEDIMENTARY AND RESERVOIR CHARACTERS OF PERMOCARBONIFEROUS IN ORDOS BASIN

Wei Honghong, Peng Huiqun, Li Jingqun, Xie Zhengwen

1998, 19(2):  136-141.  doi:10.11743/ogg19980210

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The Carboniferous-Permian System in Ordos Basin was formed in marginal barrier sea^→delta^→river^→limnetic environment,and constitute a sedimentary sequence of silicarenite^→detrital silicarenite^→clastic sandstone in ascending order.The Benxi,Taiyuan,Shanxi Formations of the System are composed respectively of three subsequences.River channel sandbodies and deltaic front sandbodies are favourable reservoirs for natural gas;the reservoir spaces of the reservoirs could be classfied into four types such as big pore coarse throat type(I),big pore fine throat type(Ⅱ),small pore fine throat type(Ⅲ)and fine proe minimal throat ytpe(Ⅳ).Among them,type I occupies 11.19%,type Ⅱ occupies 50.53%,type Ⅲ occupies 28.06% and type Ⅳ occupies 9.5%.Commercial gas flows are usually preserved in the first three types.

KEY TECHNIQUES OF RESERVOIR DESCRIPTION BEFORE TERTIARY OIL RECOVERY

Chen Liang, Niu Yanping, Xiong Qihua

1998, 19(2):  142-145,151.  doi:10.11743/ogg19980211

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In order to provide a more accurate reservoir geological model for reservoir performance prediction,it is necessory to adopt the method of multidisciplinary association and static and dynamic information combination,to build an accurate interpretation model of waterflooding reservoir operating parameter,a textural model and a heterogeneity model before tertiary oil recovery.Therefor,11 key techniques such as computer information storage,reservoir parameter log interpretation should be used to predict or reveal the distribution regularity of remaining oil.These techmiques are usually related to reservoir origin and to the property of the flows within the reservoir.

RELATION BETWEEN SEQUENCE STRATIGRAPHIC-FRAMEWORK AND GAS POOL-FORMING OF XUJIAHE FORMATION,SICHUAN

Li Shaohu, Wu Chonglong, Wang Hua, Han Zhijun

1998, 19(2):  146-151.  doi:10.11743/ogg19980212

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The formation of the gas pools in Xujiahe Formation was controlled by its sequence stratigraphic framework.Ⅲ-1 sequence is constituted by lowstand system tract formed of clastic rocks,transgressive system tract formed of sandstone,arenaceous rock and highstand system tract formed of arenaceous rock and coal beds;Ⅲ-2 sequence contains respectively lowstand system tract formed of lacustrine facies and transgressive delta sediments,transgressive system tract formed of argillaceous rocks;Ⅲ-3 sequence is composed of lowstand system tract with huge thickness of fan deposits in the internal part of the basin,the transgressive system tract with lacustrine and regressive delta sediments,the highstand system tract formed of terrigenous debris.Both Ⅲ-2 and Ⅲ-3 sequences show the framework of progradation from periphery to the interior part.It is suggested that the transgressive system tract contains thick mudstone and abundant organic matter,and it should be the main source rock and regional caprock;the lowstand and highstand tracts contain sandstones with favourable porosity and permeability,and should be considered as reservoir rocks.

FLUID INCLUSIONS AND OIL- GAS MIGRATION PERIOD OF XIEJIAWAN STRUCTURE

Wang, Zhenyun

1998, 19(2):  152-156.  doi:10.11743/ogg19980213

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The fluid inclusions in the fracture filling minerals in the Lower Triassic,Xiejiawan Trap,Dangyang synclinorium,can be classfied into 5 kinds and 4 types of association.In each association type,the homogenization temperatures of the inclusions varied from low to high,then to low and finally to lower temperature again,suggesting the bury depth of the 5th Member of the Jialingjiang Formation changed from shallow^→deep^→shallow^→shallower again.According to the analysis of inclusion composition,the migration of liquid hydrocarbons of the study area should happen before Early Yenshan Period,but the migration of gaseous hydrocarbons started in Late Yenshan-Himalayan Period.

RESERVOIRING PROPERTY OF RIVER CHANNEL SANDBODIES IN ZHAOSHIYAO AREA

Zhang Yundong, Li Zhen, Wen Xianduan

1998, 19(2):  157-161,168.  doi:10.11743/ogg19980214

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The river channel sandbodies in Zhaoshiyao area are characterized by low compositional maturation and low textural maturation,high debris and feldspar contents.The filling materials of the sandbodies are mainly argillaceous,siliceous,iron substance and carbonatite.The sandbodies underwent three diagenetic periods such as syngenetic,burial and epidiagenetic periods.Their porosity and permeability are closely related to their granularity.The porosity of the sandbodies could be classfied into 8 pore types and 4 kind of pore textures.The pore textures are related to the granularity and the filling materials.It has been proved by study that the mid and lower parts of the meandering river point bars usually have the best porosity and permeability,the bottom part is secondary and the top and marginal parts ane the worst.

GENETIC TYPE OF NATURAL GAS IN TURPAN-HAMI BASIN

Zeng Fangang, Wu Chaodong, Su Chuanguo

1998, 19(2):  162-164.  doi:10.11743/ogg19980215

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The natural gases in Turpan-Hami Basin can be divided into 4 genetic types:oil-type gas,coal-formed gas,mixture source gas and biological remaking gas.Oil-type gas is mainly distributed in Tuokexun and Hami Sags,and characterized by high δ¹³C₃-δ¹³C₂,high maturity,δ¹³C₂<-2.88%;coal formed gas is enriched in Taibei Sag,and characterized by low δ¹³C₁,high δ¹³C₂,δ¹³C₃ ratios,δ¹³C₂>-2.88% et. al.;mixture source gas is distributed in Taibei Sag,Shanshan Oilfields and eastern Qiuling Oilfields,characterized by δ¹³C₁<δ¹³C₂<δ¹³C₃>δ¹³C₄“reverse”carbon isotopic;biological remaking gas is distributed only in Baha Oilfields and Ling 4 well area in Qiuling Oilfields in Taibei Sag,and characterized by low density,big dry coefficient,high ratios of iC₄/nC₄,C₂/C₃ and ³He/⁴He of,δ¹³C₂>δ¹³C₃ et. al..

CO₂:AN IMPORTANT RESOURCE IN MESO-CENOZOIC BASINS OF EASTERN CHINA

Luo Kaiping, Xia Zunyi, Xu Yangang Zheng Lunju, Gao Shanghai

1998, 19(2):  165-168.  doi:10.11743/ogg19980216

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The main part of China’s CO₂ resources—mantle magmatogenic CO₂ is concentrated in the Meso-Cenozoic stretching basins in Eastern China.The basic conditions for the formation of this kind of CO₂ pools or gas-fields are the faults cut deep in CO₂ gas source and mantle magmatic activities.The CO₂ gas pools could be divided into mantle magmatogenic origin and thermolysis origin.All the CO₂ gas pools and fields discovered are almost fault complex type.

A HYPOTHESIS:SCIENTIFIC METHOD IN RESEARCHES

He Ziai

1998, 19(2):  169-172.  doi:10.11743/ogg19980217

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The scientific history of finding a clue to the mystery of dinosaur extinct has further proved that hypothesis is a very efficient method in scientific reseaches.It is a “bridge” for establishing new theory and new thinking.It is not an easy job to establish a complete scientific hypothesis system.There are a lot of things for us to learn,including the process,the feature and the mode of thinking.Facing the incompleteness of geological research object and the single mode of geological researches,it is necessary to adopt supposition or inference as precursor.This method could be expressed as:document image/analogythinking in images→supposition(inference)deductive inferenceabstract thinking→question observationtest/simulation→collecting evidence inductive inferenceabstract thinking→new condition thinking in imagesabstract thinking new supposition(inference).This method places emphasis on:(1)adopting the precursor of supposition(inference),paying attention to the effect of hypothesis(inference)in every thinking process;(2)deriving related question from hypothesis is the most important process.The aim of this is emphasizing the directionality,selectivily and result determinant of thinking;(3)only combining thinking in imagine with abstract thinking can the hypothesis become scientific contribution.