Table of Content

25 December 1998, Volume 19 Issue 4

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SEQUENCE STRATIGRAPHY AND SOURCE RESERVOIR-CAP ROCK ASSEMBLAGES OF UPPER JURASSIC IN LUDONG SAG

Deng Hongwen, Xu Changgui, Wang Hongliang

1998, 19(4):  275-279,284.  doi:10.11743/ogg19980402

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Seven intermediate term stratigraphic base level circles and the corresponding seven stratigraphic sequences could be distingushed in Upper Jurassic in Ludong Sag,Kailu Basin.The intermediate term stratigraphic circles could be divided into two long-term circles correesponding to the basin's subsiding and fault-depressing stages.The high-resolution stratigraphic correlation framework of the sag could be established based on the principle of the stratigraphic circle correlation.It is suggested that the base level circles bear close relation to source-reservior-cap rock assemblage.The huge thick mudstone section deposited at the turning position from uprising to subsiding of the base-level is the main hydrocarbon source rock and favourable reginal cap rock.The sandbodies formed during the uprising and subsiding periods are the main reservoir bodies.What's more,the assemblages formed during uprising period are usually of the type with source rock in the up part and reservoirs below,or self-generation and self-reservoiring type;that formed during subsiding period usually belong to the type of source rock below reservoirs.It is proposed that the first kind of assemblages are more favourable.

A THEORETICAL STUDY ON MEASUREMENT OF ROCK COMPACTING FACTORS

Li Chuanliang

1998, 19(4):  280-284.  doi:10.11743/ogg19980403

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The measurement of rock compacting is theoretically based on Terzaghi Equation,which takes incorrectly the difference of P_o and P_i as net confining pressure.A new equation P_o = P_eff + ΦP_i is proposed in this paper to calculate the net confing pressure correctly,and an improving measurement procedure is presented.The compacting factors obtained in lab must be converted into the value which is applicable to reservoir engineering when practical calculatoins are being operated.The conversion formula is established in this paper.

RELATIONS BETWEEN SEDIMENTARY MICROFACIES AND OIL WATER DISTRIBUTION OF SHA-I POOL IN ZHUANG-52 BLOCK

Sun Wei, Pu Renhai, Cheng Shunyou, Luo Jinglan, Zhang Qingguo, Chen Zhenxin, Liu Zejun, Ma Yingjun

1998, 19(4):  285-290,295.  doi:10.11743/ogg19980404

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Reservoir-I in the lower part of the third member of the Shahejie Formation is attributed to midfan external fan facies zone of nearshore turbidite fan in Zhang-52 block fault,Zhanhua Sag.According to the division of single well base level cycle and the correlation of key horizon on 3-D seismic progile,oil reservoirs exist in the progradation retrogradation bodies extending from south to north based on isochronous principle,the isochrosnous relation of the top and base boundaries of the reservoirs of adjacent wells were made out,so the seguences of sedimentary cycles of each well.Then the nearshore turbidite bodies in the study area were divided into 20 imbricate prograding bodies.In vertical,single well may drill four subbeds.The south edges of the turbidites are near the onlap boundaries of the turbidites and the reservoir grain grade appears positive rhythmic property while that of the north edges shows negative rhythmic property,the central part of the subbeds are massive homogeneous deposits.The physical properties and petroleum bearing property of the subbeds get better from south to north and the best ones are in the central and north parts of the study area.

POOL-FORMING HISTORY OF OIL AND GAS IN SOUTH MARGINE OF JUNGGAR BASIN

Wang Yutao, Gu Bin, Wang Lihong

1998, 19(4):  291-295.  doi:10.11743/ogg19980405

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Three anticline zones developed on the south margine of Junggar Basin.The first anticline zone formed Triassic oil resorvoirs in Indosinian period and formed Jurassic reservoirs in Himalayan period.The first zone uplifted and was destroyed due to the Himalayan movement,the natural gas generated in Jurassic source rock migrated into the second and third anticline zones,thus forming coal related gas reservoirs;the gas generated in Permian source rock could not enter the overlying strata due to their great thickness.The discovery of Hutubi gasfields indicated that the deep strata in the study area may have significant hydrocarbon prospects.

POLYPHASE PULLS AND APARTS OF ACTIVE RIFT IN NANPU DEPRESSION AND THEIR RELATIONSHIP WITH OIL AND GAS

Cong Liangzi, Zhou Haimin

1998, 19(4):  296-301.  doi:10.11743/ogg19980406

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Nanpu depression,located in the north of the Bohai Gulf Basin,is a small Mesozoic Cenozoic superimposed sag with abundent hydrocarbon resources.It is characterized by the geodynamic regime of active rifting with polyphases of extension.During the Indo-Chinese epoch,Nanpu Depression experienced a prerifting and erosion stage with the maxim erosion thickness of 2 km.Since the Early Jurassic,Nanpu Depression has experienced an evolution of four phases of rifting and a period of tectonic reactivation.The four phases of rifting took place in Early Mesozoic,Late Mesozoic,Eocene to Mid-Oligocene and Mid-Oligocene to Miocene respectively.Different stages of tectonic evolution played different roles in the hydrocarbon generation and occurence of the depression.

FORMATION CONDITION OF SYNCLINAL HYDROSEALED GAS POOLS IN QINSHUI BASIN

Chen Gang

1998, 19(4):  302-306.  doi:10.11743/ogg19980407

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Qinshui Basin is considered to have the basic condition of forming of hydrodynamic sealed Paleozoic sycnlinal gas pools.The formation of hydrosealed gas pools is the result of the synthetic interaction of 4 essential geological factors:1,a synclinorium structure of the basin;2,abundant gas resources(3458.6?10⁸m³)in the synclinal center matched well with the structural conditions in time space of the basin;3,low porosity low permeability tight reservoir rock in downdip structural location;4,updip water block and fine regional caprocks.It is prodicted that the occurrence of the Paleozoic natural gas in Qinshui Basin is in two gas systems,i e the natural gas system of the Lower Paleozoic and the natural gas system of the Upper Paleozoic.

RESTORATION ON GENERATING HYDROCARBON POTENTIALITY OF SOURCE ROCKS:A CASE OF LOWER ORDOVICIAN CARBONATES IN ORDOIS BASIN

Xia Xinyu, Hong Feng, Zhao Lin

1998, 19(4):  307-312.  doi:10.11743/ogg19980408

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Different restoring methods of hydrocarbon generation potential of source rock,including simulation method,element balance method,degradation ratio method and dynamic method are discussed.These methods are all restricted to the realm of hydrcarbon generation,theory of kerogen degradation.The accuracy of restoration results depend sensitively on the initial organic matter type,mean hydrogen/carbon ratio of hydrocarbon products and oil expulsion efficency from high mature source rock.The restoration coefficients of total organic carbon in different condition all have maximum values.Restoration results show that Lower Ordovician carbonate in the Ordos Basin is poor source rock.

A STUDY ON HIATUS SURFACE OF NEOGENE EOGENE IN JIYANG DEPRESSION

Wu Zhiping, Shi Buqing, Zhou Yaoqi, Li Jianming

1998, 19(4):  313-317.  doi:10.11743/ogg19980409

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The hiatus surface of Neogene-Eogene in Jiyang Depression is situated between underlying erosion and overlap strata.Under the boundary,there were sediments formed in faulted depression and were eroded due to tectonic uplift.The stratigraphic ages of the sediments gradually changed from Archeozoic on uplifts to Mesozoic and Cenozoic in sags; the stratigaphic connection changed from nonconformity to parallel unconformity;the erosion amounts changed from 6 000-8 000 m on uplifts to less than 100 m in sags.On the the boundary,there were sediments formed in depression.The lower part of Guantao Formation is filled in deposit,the upper part is drape deposit covering all uplifts and sags.These properties indicate that the depression underwent the evolution process of fault subsiding→sloping→uplifting→eroding→subsiding.

RELATIONS BETWEEN BIOTURBATION STRUCTURES AND PETROPHYSICAL PROPERTIES OF DONGHE SANDSTONE RESERVOIRS IN CENTRAL TARIM

Qi Yong

1998, 19(4):  318-320.  doi:10.11743/ogg19980410

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Abundant trace fossil including Thalassinoides and its bioturbation structures were discovered in Donghe sandstone reservoirs of Upper Devonian in central Tarim.Based on the features of bioturbation and analysis of sandstone diagenesis and porosity structures,the bioturbation structures and the reservoir petrophysical properties appear to be negative correlation.It means that the more intensely the bioturbation,the worse the petrophysical properties of the reservoirs.The primary porosity was preserved to the greatest extent in the place of unbioturbation or weak bioturbation,thus forming high porosity and high permeability reservoirs.

RESERVOIR CHARACTERISTICS OF COAL FORMATIONS IN QINSHUI BASIN

Shan Xiuqin

1998, 19(4):  321-325.  doi:10.11743/ogg19980411

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Coal formation pores such as cleats and intergranular pores could be divided into five types in this area.The adsorption and desorption curves are mainly closed;the coalbed capillary pressure curves are principally fissure-pore type;large pores are widely distributed;the pore volume and specific area are both large;and the adsorption property is in middle-class.Therefore,the performance of coalbed reservoirs is good and coalbed methane could be easily developed in this area.

POOL-FORMING DYNAMIC PROPERTY OF LITHOLOGICAL OIL-GAS RESERVOIRS IN DONGYING SAG

Zeng Jianhui, Zheng Herong, Wang Ning

1998, 19(4):  326-329.  doi:10.11743/ogg19980412

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The lithological oil-gas pools mainly consist of lens shaped sandrock and up-tilted pinching sandrock oil reservoirs in Dongying Sag.The reservoirs show different dynamic characteristics due to the influence of the formation pressure.In normal pressure,the major drive force for oil-gas migration is buoyancy.Oil and gas migrate upward in separate phase along fault,uncomformity and reservoir rock and accumulate in the lithological traps.In abnormal high pressure system,the drive fore is predominantly the formation pressure difference between compaction and uncompaction and that drives oil and gas to migrate and accumulate in the lithological traps.The migrating phase is mainly mixed phase of oil,gas and water or separarte phase.

RESERVOIR PORE STRUCTURES AND ITS APPLICATION TO OIL POOLS ESSESSMENT IN SHIWU FAULTED DEPRESSION,SOUTH SONGLIAO

Zhu Luzhong, Zhao Xiumei, Wang Guangyun, Liu Jian

1998, 19(4):  330-336,345.  doi:10.11743/ogg19980413

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The pore structures of reservoirs in Shiwu faulted depression,south Songliao Basin could de divided into five types according to capillary pressure curves.Different facies zones may have different pore strutures.The pore stucture of fine sandstone in river channel,flood plain,shallow lake and sand bar facies zones are the best and belong to type I and type Ⅱ ;those of deep fan delta,subaqueous fan sandrocks are better and belong to I Ⅲ types.In oil pool essessment,the poorer the pore structures are,the higher the critical oil column and the thicker the oil water transitional zone would be.Under the same oil column,Xiaowujiazi structure is more favourable for oil and gas accumulation,and the Denglouku Formation in Aijiawobu,Xidingjia Pijiawobu is more favourable for searching gas.

DISCUSSION ON STRATIGRAPHIC AGE OF DRILL HOLE 5005 IN GONGPOQUAN BASIN,BEISHAN,GANSU

Wu Hongfeng, Zhao Chengling, Shi Jianmin

1998, 19(4):  337-339.  doi:10.11743/ogg19980414

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Based on the analysis of the samples from drill hole 5005,we discovred an sporo-pollen assemblege of Aratrisporites,Alisporites and Colpectopollis.Similar assemblege of fern and pollen can be found in corresponding group,such as Huangshanjie Group in Junggar Basin,Tuha Basin and Shantanghu Basin,Yanchang Group in Ordos Basin,Yangcaogou Group in Liaoxi.These members could often be found in Triassic System.It is suggested that the formation should belong to Upper Triassic.

RESERVOIR PROTECTION OF LOW PERMEABLE FRACTURED SANDSTONES FROM XIANGXI GROUP OF SOUTHERN SICHUAN

Chen Zhong, Tang Hongming, Shen Mingdao, Li Tao, Li Qirong, Yang Maokang

1998, 19(4):  340-345.  doi:10.11743/ogg19980415

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The fourth member of Xiangxi Group in southern Sichuan is tight packed and low permeable sandstone reservoir.Its porosity is less than 3.95%,its permeability is lower than 0.25×10^-3 μm².Microfractures are the main passages for gas migration.Formation water minerality is high.Further research proves that formation micronites and drilling fluid precipitates resulted from mud percolate and formation water may plug passages and decrease productivity.The tests of velosity sensitivity and alkali sensitivity suggest that the critical velosity of formation water is better to be 1.0 ml/min;the critical pH value of operating fluid is better to be 10.The long term static analysis of reservoir rock and mud percolate shows that none of new substance appeares.

LAYING A FOUNDATION FOR SHAXIMIAO GAS POOLS IN XINCHANG GASFIELD BY PALEOSTRUCTURES

Li Bangrong, Li Congjun, Xu Binggao

1998, 19(4):  346-350.  doi:10.11743/ogg19980416

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Gas producing wells in Shaximiao gas pools,Xinchang Gasfields are all located in the extent of paleostructures,which indicates that the paleostructures laid a foundation for the distribution and the boundary of the gas pools.From lower to higher positions,the contents of methane,heavy HC,CO₂ and H₂S,the dry index,ΔR₃ value of natural gas all change regularly.This shows that the paleostructures have controlled over the migration of gas.Recent structures may have considerable destructiveness,but thay cannot change the distribution pattern.Their control over gas pools is restricted in the superposed positions of the paleostructures with recent structures.

BEACH AND BAR SANDBODIES OF SHAHEJIE FORMATION IN BANQIAO DEPRESSION

Zhou Liqing, Shao Deyan, Fang Shiyu, Li Zhaoze, Zhang Jianguo

1998, 19(4):  351-355.  doi:10.11743/ogg19980417

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Beaches and sand-bars developed well in the Shahejie Formation,Banqiao Depression.They are mainly high matured medium or fine grained sandbodies with good degree of sorting and good psephicity,platy-wedged shaped and parallel cross-bedding,formed in transgression or regression process.The beaches usually occur normal cyclic sequence and the bars are in reversal cyclic sequence.Their porosity and permeability are high,and lithophysical property is better than other sediments.So they are good oil and gas reservoirs.

THE SYSTEMATOLOGY OF PETROLEUM EXPLORATION

He Zhiliang, Zhu Hong

1998, 19(4):  356-360.  doi:10.11743/ogg19980418

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In petroleum exploration of present time,there is hardly tranditional opportunity.New challenge needes new thinking.In order to get the biggest economic benefit,the oil- and gas-bearing system with optimun disposed varions natural factors,the exploration system with rational structure and complete function,accurate and effective managing and decision making system must be compatible.