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Table of Content

    25 October 2004, Volume 25 Issue 5
    Re-discussion on exploration potential of Paleozoic in Tarim basin: 20th anniversary of significant discovery in Shacan 2 well
    Kang Yuzhu
    2004, 25(5):  479-483.  doi:10.11743/ogg20040501
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    In 1984,a high-rate oil flow has been tested from the Paleozoic marine carbonates in Shacan 2 well,northern Tarim basin, which means a new prospect has been opened up in the Paleozoic petroleum exploration in the basin.Through a 20-year sustained efforts,18 fields,including the large Tahe oilfield and Hetianhe gasfield,have been discovered in the Paleozoic.It shows that the Paleozoic in Tarim basin has abundant oil and gas resources,favorable reservoiring conditions,and suitable geologic conditions for the formation of large-giant oil and gas fields,thus its exploration potential is very large.

    Progress in continental sequence stratigraphy and its application in petroleum exploration and development
    Gu Jiayu, Zhang Xingyang
    2004, 25(5):  484-490.  doi:10.11743/ogg20040502
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    Sedimentation in continental basins has been controlled by many factors and the main control factors in basins of different types are not the same.All these would lead to various sedimentation types,frequent facies changes,poor lateral continuity and large variation of sequence thickness.Frequent alternating of lake transgression and regression results in frequent change of cyclothems.The formation,structure and model of continental sequence stratigraphy would,therefore,be more complex and more difficult to study.According to the boundary characteristics of both continental basins and system tracts,initial and maximum flooding surfaces and existence of slope-break zone,Chinese geologists have established sequence stratigraphic frameworks and models of depression basin and faulted basin,which tally with the reality of basin fills in China.Development of continental stratigraphic sequence has mainly been controlled by lake level fluctuation,tectonic movement,climate,base-level change and provenance supply,especially tectonic movement and climate are quite important,because they directly control the fluctuation of lake level.Methodologies for studying sequence stratigraphy in continental basins include outcrop sequence study,experimental observation and analysis,logging and seismic sequence stratigraphic analyses,and numerical simulation of sequence stratigraphy.Sequence stratigraphy can play an irreplaceable role in play exploration stage,prospect exploration stage and development stage.

    Self-similarity of constitution of sequence stratigraphy and distribution of sandbodies and lithologic reservoirs:taking delta-turbidite fan system as an example
    Deng Hongwen, Wang Hongliang, Wang Jufeng, Xie Xiaojun, Su Zongfu, Shang Erjie
    2004, 25(5):  491-495.  doi:10.11743/ogg20040503
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    Strata in sedimentary basins are characterized by remarkable multistage cyclicity,due to the control of multistage base-level cycles.Sedimentary cycles in different stages have certain self-similarities.Sequence stratigraphic analysis of large delta-turbidite systems in terrestrial basins indicates that self-similarity of sedimentary cycles would result in the self-similarity of sedimentary facies and reservoir distribution of sequences in different stages.Low-level fan of turbidity genesis,formed in the lowstand system tract and associated with large-scale progradation of delta,are generally adjacent to the lower boundary of long-term base-level cycle (third-order sequence).Within the long-term cycle,turbidite fans of certain scale also occur during the early rising of medium-term base-level cycle,and are distributed along the lower boundary of medium-term cycle (fourth-order sequence).The self-similarity of sequence stratigraphy leads to the self-similarity of distribution of turbidity sand bodies and lithologic reservoirs that are associated with large scale delta sedimentary systems.

    Gas potential of Jurassic in southern Junggar depression
    Wang Jinqi
    2004, 25(5):  496-500,512.  doi:10.11743/ogg20040504
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    The multilayer source rocks in southern Junggar depression are characterized by their extremely high abundance of hydrocarbon generation.The Permian and Trassic have been buried very deeply in the depression,so they would not have any exploration significance anymore except transporting hydrocarbons upward along faults to shallow reservoirs.Although the Jurassic is a good source of hydrocarbons,conventional accumulations would not be formed in later stage,because it has been deeply buried,as deep as 10000m in the center of the depression,and has become tight and ultra-tight strata.The Jurassic had experienced early formation of deep basin gas and later destruction,modification and adjustment of deep basin gas.Gas accumulations may exist in the following areas. (1) Some deep basin gas reservoirs might have been preserved in Beidapo (Northern Big Slope) area; (2) The 3 rows of structures formed in foothill belt by compressive and shear tectonic movement.Hydrocarbons might have migrated along faults to the shallow structures,resulting in formation of secondary gas reservoirs; (3) Although the Jurassic has very large burial depth,it might become prolific gas reservoir with large reserves again,as a result of the fractures formed in Later stage,thus it would still have large exploration potential; (4) In the deep basin gas area,large attention should be paid to the gas potential in the "sweet points",such as thick and large sandbodies and ancient traps in the favorable facies zone.

    Characteristics of gas distribution and reservoiring in Upper Triassic Xujiahe Formation in Western Sichuan depression
    Yang Keming, Ye Jun, Lu Zhengxiang
    2004, 25(5):  501-505.  doi:10.11743/ogg20040505
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    Since Late Triassic,Western Sichuan depression has experienced Indosinian,Yanshanian and Himalayan movements,leading to the multi-stage changes of poroperm characteristics,structural features,fluid properties and geopressure fields,as well as reservoiring through repeated migration and accumulation of hydrocarbons.Gas in Upper Triassic Xujiahe Formation in Western Sichuan depression has been accumulated around the Pengguan hydrocarbon-generating sag,and distributed in the eastern,western and northern slopes of the sag.Distinct fracture systems have acted as the key pathways of natural seeping of gas.Gas has mainly accumulated in various composite traps formed on the basis of early structures.Comprehensive analysis of hydrocarbon generation and expulsion stages,reservoir compaction stage,fluid charging stage and trap forming stage shows that the original gas reservoirs in the Upper Triassic in Western Sichuan depression have been formed in middle-late Indosinian to middle-late Yanshanian. Since Late Cretaceous,the whole reservoirs have been compacted,peak of hydrocarbon generation and expulsion has finished,and hydrocarbons have been "sealed up" as a result of the compaction.This area has been strongly deformed by Himalayan movement and the hydrocarbons "sealed up" during the earlier compaction have been reactivated by the fractures.Therefore,the reservoiring of gas in Upper Triassic Xujiahe Formation of in Western Sichuan depression are characterized by the early "palaeo-structures" to be the basis of gas accumulation,intermediate "compaction seal-up" to be the condition of gas preservation,and the late "fracture activation" to be the key to gas enrichment.

    Sequence stratigraphic study and exploration target appraisal of AG Formation in northeastern Muglad basin,Sudan
    Xue Liangqing, Fan Tailiang, Xu Dafeng, Liu Guoqiang, Huang Wei, Cheng Yan
    2004, 25(5):  506-512.  doi:10.11743/ogg20040506
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    AG Formation in northeastern Muglad Basin of Sudan can be divided into lower,middle,and upper sequences.The lower sequence, formed in the early chasmic stage of the basin,mainly consists of rapidly accumulated coarse sediments.The middle sequence,deposited in the spreading period of the basin,is an important interval with well developed source and reservoir rocks in Muglad basin.The upper sequence is mainly composed of fluvial formations, deposited in the shrinking stage of the basin.Comprehensive evaluation shows that the middle sequence with favorable combination of source,reservoir and cap rocks is an important series of strata for exploration in AG Formation in Muglad basin.The middle sequence in the eastern gentle slope zone is the most favorable play,where the prospect I is a relatively mature exploration target.

    High accuracy sequence stratigraphy of Lower Tertiary in Zhanhua depression, Bohai bay basin
    Wei Kuisheng, Shi Shuling, Li Daliang, Luo Yan, Lu Songtao, Qiu Yigang, Zong Guohong, Zheng Herong, Hao Yunqing, Song Guoqi
    2004, 25(5):  513-518,538.  doi:10.11743/ogg20040507
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    Based on 3-D seismic,drilling data and other data,and by using the theories and methods of high-accuracy sequence stratigraphy,sequence stratigraphic framework has been established in Zhanhua depression,which consists of 1 first-order sequence,4 second-order sequences,17 third-order sequences,51 system tracts,70 parasequence sets and 109 parasequences.Critical surfaces,such as sequence boundary,initial flooding surface and maximum flooding surface,have been defined on seismic profiles,according to the termination patterns of reflection configuration,transformation of stacking patterns of parasequence sets and lithologic profile.Sedimentary systems are categorized and restored based on the stacking pattern of parasequence sets and seismic phases.In the sequence stratigraphic framework,lowstand system tract (LST) consists of many types of sedimentary systems,which are characterized by alluvial fan-fan delta (delta)-lowstand wedge-lowstand fan under control of the third-order slope break.The sedimentary systems in transgression system tract and high stand system tract have inheritance.Combinations of sedimentary systems in each system tract have genetic continuity.Areas where sedimentary systems developed during strong fault subsidence and allocated with unconformities and fault planes are the favorable exploration play.

    Genesis and evolution of accommodation transformation systems in 2nd member of Upper Triassic Xujiahe Formation,Chuanxi foreland basin
    Xing Huanqing, Jiang Zaixing, Wang Yaqing, Wang Jiao
    2004, 25(5):  519-523,569.  doi:10.11743/ogg20040508
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    During deposition of the 2nd member of Upper Triassic Xujiahe Formation in Chuanxi foreland basin, the variation of accommodations in different locations within the basin are not unitary, due to the tectonic movement.According to the differential subsidence of basement and relative changes of lake level, it is believed that the water depth within the foreland basin can be divided into an increasing zone, a decreasing zone, as well as an invariant zone.The uneven changes of accommodations in the same period in a foreland basin are characterized as accommodation transformation system. Accommodation transformation system can be subdivided into several internal structural units,such as transformation body and transformation plane. During the deposition of the middle and lower 2nd member of Xujiahe Formation, the accommodations in Chuanxi basin appear to be elongated in NE direction along Longmenshan structural belt,and can be divided successively into 7 accommodation transformation zones basinward, including primary accommodation transformation zone (Ⅰ),primary accommodation increasing zone(Ⅱ),primary accommodation transformation zone(Ⅲ),primary accommodation decreasing zone(Ⅳ),secondary accommodation transformation zone(Ⅴ),secondary accommodation increasing zone(Ⅵ),and secondary accommodation decreasing zone(Ⅶ).These accommodation transformation systems have mainly been caused by the tectonic stress fields that lead to the alternating occurrence of compressional subsidence and nappe uplifting. Presently, the primary accommodation transformation zones are the most prolific gas areas where the largest number of gas reservoirs have been discovered, and they are also the practical exploration target areas at current technical conditions.

    Features and control factors of wave impedance of fluvial strata
    Lin Huixi
    2004, 25(5):  524-527.  doi:10.11743/ogg20040509
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    Based on the sedimentologic theory and acoustic transit mechanism and by using logging data of wells drilled with oil-based and water-based mud,this paper systematically analyzes features and control factors of various acoustic impedances and actual wave impedances met in sandstone-mudstone section while logging.Logging acoustic impedances of fluvial strata are largely influenced by drilling mud.Under the condition of using water-base mud,alteration of argillaceous strata and borehole collapse can often lead to mismatch or pseudomorph in inversion of logging acoustic impedance.In contrast,stratigraphic actual wave impedance is mainly controlled by shale contents,and it reaches its maximum value when the shale contents is equal to the stratigraphic maximum effective porosity.Generally,values of wave impedance in argillaceous sandstone and sandy mudstone are relatively large,while that in mudstone is relatively small,and that in sandstone is situated between the two.

    Reservoir characteristics and genesis of turbidite fans in the 3rd member of Shahejie Formation in central Dongying depression
    Wang Jufeng, Zheng Herong, Su Faqing
    2004, 25(5):  528-532.  doi:10.11743/ogg20040510
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    Turbidite fans in the 3rd member of Shahejie Formation in central Dongying depression,mainly distributed in the deepest sag of the depression,can be divided genetically into three types:slump turbidite fan,slope-sliding turbidite fan and sublacustrine fan.Their formation was closely related to the fluctuation of base level.Slump turbidite fans were formed during the short-term falling of base level,as a result of redeposition of the slumped frontal sediments of the prograding delta.Slope-sliding turbidite fans were formed during the short-term rising of base level,as a result of redeposition of sediments sliding from marginal slope of the lake basin to deep lake area,due to erosion and washing of delta front and plain by dynamic force of lake-and flood-water.Sublacustrine fans were formed during the medium-term rising of base level and located in the sequence stratigraphy corresponding to the lowstand fans in the lowstand system tract in classical sequence stratigraphy.Of these three types of turbidite fans,the sublacustrine fans and slope-sliding fans,with large thickness,good poroperm characteristics and petroliferous properties,are the main reservoirs in this area,while slump turbidite fans are characterized by smaller sizes and relatively poor poroperm characteristics.

    Integration of seismic processing and interpretation for fine reservoir characterization:taking Moxizhuang area in Junggar Basin as an example
    Xie Xiaojun, Deng Hongwen, Wang Jufeng
    2004, 25(5):  533-538.  doi:10.11743/ogg20040511
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    Based on high resolution interpretation of sequence stratigraphy,3-D velocity field processed with AVO is used to perform AVO attribute inversion,spectrum analysis,attribute attraction and wave form analysis to get reservoir information.Through combining the reservoir information with interpretation results of seismic and sedimentary facies of the reservoir,integrated seismic processing and interpretation in profile-plane-space is carried out to assign correct geologic meaning to seismic attribute information,so as to realize accurate prediction of reservoir distribution.This method has been used to study the first member of Badaowan Formation in Moxizhuang area,central of Junggar basin.The results show that the plane reservoir distribution achieved through AVO attribute inversion and wave form analysis has good coincidence with that achieved by using theory of high resolution sequence stratigraphy.

    Reservoir heterogeneity and distribution of remaining oil in upper Guantao Formation in 7th block west,Gudong oilfield
    Chen Depo, Wang Yanzhong, Liu Shicheng, Yang Renjin
    2004, 25(5):  539-543,581.  doi:10.11743/ogg20040512
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    Reservoir heterogeneity is one of the main factors that impact distribution of remaining oil.Intralayer,interlayer and plane-layer heterogeneities exist in the upper Guantao Formation in the 7th block west of Gudong oilfield.Plane-layer heterogeneity is mainly controlled by sedimentary facies zones and distribution of sandbodies.Interlayer heterogeneity is mainly affected by the thickness of single sandbody and sand-shale ratio.Intralayer heterogeneity is mainly associated with intraformational beds and intracyclothems.Remaining oil is relatively rich in sandbodies with relatively poor poroperm characteristics,such as in the lower part of interbeds and on the top of positive cyclothems.In addition,sandbodies with limited distribution on the periphery of channel sands and in abandoned channels are also rich in remaining oil.

    Quantitative evaluation of Tertiary petroleum accumulation systems in Huanghua depression
    Chen Shanyong, Jin Zhijun, Liu Xiaoping
    2004, 25(5):  544-547,602.  doi:10.11743/ogg20040513
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    According to the concept of petroleum accumulation systems and the basic principles of analytical hierarchy process,the Tertiary in Huanghua depression can be divided into four petroleum accumulation systems and sixteen subsystems.Quantitative evaluation method of petroleum accumulation system has preliminarily been established.22 geological factors in respect of source rocks,carrier rocks and traps have been selected,including organic carbon content,type of organic matter,maturity,thickness of source rock,areal coefficient of hydrocarbon delivery and intensity of hydrocarbon generation,fault,reservoir,unconformity,as well as their spacial combination.Quantitative evaluations of the elements and maturity of petroleum accumulation systems and subsystems in Huanghua depression show that the three elements,i.e.source rocks,carrier rocks and traps of the 4 systems are remarkably different,of which the Qibei system in the central part of the depression has the best development conditions,followed by the Qinan system in the same area,while the system in the south is relatively poor and the system in the north is the poorest.The maturities of the Qibei and Qinan systems in the central part of the depression are high,while those in the south and in the north are low.

    Carboniferous non-structural traps in Tazhong area and prediction of favorable exploration targets
    Su Zongfu, Deng Hongwen, Fan Tailiang
    2004, 25(5):  548-553.  doi:10.11743/ogg20040514
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    The Carboniferous non-structural traps in Tazhong area can be divided into stratigraphic traps,lithologic traps and combination traps according to their genesis and shapes.Formations of these traps are closely related with unconformities,paleotopography and depositional settings.Non-structural traps are characterized by their lateral zonation and vertical layering due to the control of their geneses.Based on the developmental features and spatial distribution characteristics of Carboniferous non-structural traps in the study area,it is believed that the overlap traps of Donghe Formation sandstone,lithologic traps of sandstones filling the eroded ravines and valleys in the central uplift and the combination traps in northern Arwati are relatively favorable exploration targets,of which the former two are the most favorable,thus priority should be given to them in exploration.

    Developmental characteristics of Cambrian subsalt structures in central Bachu area,Tarim basin
    Wang Hongyu, Fan Tailiang, Wei Fujun, Wu Yan, Xu Yaning
    2004, 25(5):  554-558.  doi:10.11743/ogg20040515
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    Development of the Cambrian subsalt structures in central Bachu area has mainly been controlled by fault movements.The present structural traps have been modified by multiphase tectonic movements.Kabei,Gudongshan and Karasay structures have reached their optimal trap shapes in Late Hercynian and Early Mesozoic,respectively.The structural traps have then been modified and destroyed by later structural movements,as a result,Kabei structure has been transformed from anticline into faulted anticline,while Karasay structure from anticline into faulted anticline and faulted nose.The closures of both structures have been reduced to some extent.In contrast,Gudongshan structure has lost the condition of forming relatively large local traps,because later faults have broken the original structural traps into strips,and the Himalayan tectonic movement has unevenly uplifted the structural belt and become low in the south and high in the north.Kangtakumu structural trap has been formed in a relatively short time,i.e.it has been formed in Middle Himalayan and strengthened in Later Himalayan stage,and the closure has also been enlarged.

    Reservoiring mechanism and finalization period of Dina 2 gasfield in Kuqa basin
    Sun Dongsheng, Jin Zhijun, Lu Xiuxiang, Zhou Xinyuan, Yang Minghui
    2004, 25(5):  559-564,591.  doi:10.11743/ogg20040516
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    There are two overpressure systems,lower and upper overpressure systems,in Kuqa foreland basin.The former was closely related with rapid and large gas generation,and thus the gas generated from Mesozoic source rocks mainly took the form of water-soluble gas.The upper overpressure system has the characteristics of reservoiring at normal pressure.When gas in the lower overpressure system migrated upward along faults in the form of miscible fluids into the upper normal pressure environment,degasification would occur and then accumulated in reservoirs.At a later stage,the upper overpressure system was formed under further compression of tectonic movement.Dina 2 gasfield is the final results of gas accumulation in the upper overpressure system.Based on analysis of trap development history and hydrocarbon generation history,in combination with fluid inclusion in the reservoir and K/Ar dating of authigenic illite,it is believed that Dina 2 gasfield had been charged in three different stages.In the first stage,liquid hydrocarbons were charged at the end of Paleogene and destroyed later.In the second stage,mixed liquid and gaseous hydrocarbons were charged in early-middle Kuqa stage.In the third stage,natural gas was charged in late Kuqa and early Xiyu stages,which was the key reservoiring stage of the field.

    Study leakage of fault with geochemical techniques
    Hou Dujie, Zhu Junzhang, Tang Youjun, Xiao Zhongyao, Wang Qinghua
    2004, 25(5):  565-569.  doi:10.11743/ogg20040517
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    It is one of the new advances in reservoir geochemistry to study leakage of fault with geochemical techniques.According to the distribution of n-alkane and the characteristics of biomarkers,there exist 5 types of crude in Kokyar oil reservoir,including original-state oil,residual oil from fractionation through migration,condensate and light oils from evaporation and retrograde condensation,residual crude from gas washing,and crude with wax crystallization.The second type of crude is mainly distributed on the top of the structure,indicating that leakage occurred along small faults and the top of the structure,leading to the obvious difference between ancient and present OWC.Moreover,molecular geochemical analysis of the crude verifies that crude on the top of the structure have relatively higher maturity and higher contents of heavy components and those uneasily to be migrated.

    Formation, evaluation and exploration of water-bearing oil reservoirs: search after a possible new reservoir type
    Zhang Ruifeng, Dang Zhenrong, Wang Jian, Yuan Yijun, Wang Xiu, Kang Hongquan
    2004, 25(5):  570-576.  doi:10.11743/ogg20040518
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    Water-bearing oil reservoirs generally occur in medium-low porosity and low-ultra low permeability clastic rocks and have the prominent characteristics of strong heterogeneity. Microscopically, clastic rocks have dual-pore structures, i.e. artesian pore throat system with the occurrence of liquid hydrocarbons and stagnant pore throat system saturated with original formation water. The artesian pore throat system contains artesian water, while the stagnant pore throat system mainly contains fine pore water, micropore water, stagnant pore water and molecular bound water. Stagnant pore throat system, accounting for a large proportion of pore volumes, would not only constrain production of oil and water, but also lead to the oil saturation of most water-bearing reservoirs to be below 50%. The geological conditions of formation of water-bearing reservoirs are related mainly to the structure of clastic rocks, extremely low compositional maturity and the poroperm characteristics drastically become poor due to compaction in the Mesozoic rift basin groups in Erlian. In the present economic and technical conditions, water-bearing oil reservoirs are still on the margin of commercial recovery, thus dynamic identification and evaluation of water-bearing oil reservoirs should be performed as early as possible according to oil-bearing condition of cores, water dropping test of cores, mud logging, thin-section analysis, poroperm analysis, mercury injection test, NMR and reservoir testing, so as to avoid ineffective investment.

    A discussion on geologic features and genesis of low-efficiency gas reservoirs
    Gu Li, Yu Xinghe, Li Shengli, Xu Anna, Zhu Yixiang, Tian Changbing
    2004, 25(5):  577-581.  doi:10.11743/ogg20040519
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    Low-efficiency gas reservoirs refer in particular to those with low abundance of reserves and low well productivity.The reserves of such reservoirs in China account for about 70% of our total gas reserves.In China, reservoir rocks of such gas reservoirs are commonly of fluvial and delta facies with relatively large burial depth,which are characterized by poor continuity,low porosity and permeability,as well as strong heterogeneity.As a result,exploration and development of these reservoirs are quite difficult.For the sake of effectively utilizing these gas resources,the characteristics of low-efficiency gas reservoirs in continental clastic rocks have been analyzed,based on systematic correlating the geological features of low-efficiency gas reservoirs both in China and abroad.It is believed that the types of sedimentary facies and diagenesis are two major geologic factors leading to low efficiency of reservoirs.Sedimentary facies control the poroperm characteristics and continuity of reservoirs,while compaction and cementation are the main factors that destroy primary pores and lead to the formation of tight sandstones.

    A study of paleo-fluid potential from inclusions in the 2nd member of Xujiahe Formation in northwestern Sichuan
    Xu Hao, Tang Dazhen, Wei Guoqi, Wu Shixiang, Zhang Junfeng
    2004, 25(5):  582-585.  doi:10.11743/ogg20040520
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    Comparative analyses of petrology,thermodynamic characteristics and components of inclusions in the 2nd member of Xujiahe Formation in northwestern Sichuan show that the inclusions had been formed in 4 different stages,i.e.in Late Triassic to Shaximiao age,middle-late Late Jurassic to early Early Cretaceous,Early Cretaceous to pre-Himalayan, and post-Himalayan, respectively,which represent 4 hydrocarbon charging processes.Analysis of the fluid inclusions can reveal paleo-elevation-density and-pressure when the inclusions were entrapped.These data can be used to calculate the fossil fluid potential.This method has been used to calculate the fossil fluid field of the 2 ndmember of Xujiahe Formation in northwestern Sichuan.The results show that regional fluid field obviously has gone through an evolution process of variation adjustment revariation-readjustment.

    Development technique of MQ volcanic oil reservoir in Jiangsu oilfield
    Zhang Renling
    2004, 25(5):  586-591.  doi:10.11743/ogg20040521
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    Volcanic oil reservoir is a special type oil reservoir, which is completely different from those in sedimentary rocks.Its reservoiring and permeating mechanism is more complex than sedimentary reservoir.It has,therefore,particular production feature and development technique.According to the study of development technique of MQ volcanic oil reservoir in Jiangsu oilfield,effective location of oil well is the key factor affecting development index and economic benefit.In the early stage of development,wide spacing (well spacing of 900m) should be adopted to control the structural high and the zone where pores,fissures and vugs are well developed;and in the middle and later stage,well spacing can be adjusted to 500m.Reasonable injection pattern is that water should be injected in the lower position or edge of reservoir.The optimum injection pressure coefficient is 0.45-0.65.The perforated interval in the well is better to be placed 30m above the oil-water contact.Water injection well should avoid to perforate the sedimentary intercalated bed,and the injection pressure should be lower than the critical pressure of water entering the intercalated bed.
    A discussion on economic evaluation of medium-long term exploration & production plan
    Jing Keyao, Xiao Xizhen, Zhao Hongyu
    2004, 25(5):  592-595.  doi:10.11743/ogg20040522
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    There are two basic principles of economic evaluation of medium-long term exploration & development plan.One is to obey relevant rules and policies and to be in accordance with national macro-economic polices,and another is to give priority to benefits and to be favorable for sustainable development of enterprises.Economic evaluation includes specifically collecting basic data correlated with the plan and estimating investment,calculating various economic indicators in the exploration and development,calculating various dynamic and static indicators and analyzing the profitability of the project,as well as making risk analysis aimed at the characteristics of petroleum industry.Special attentions should be given to selection and optimization of some key parameters such as planned reserves,planned production and costs of oil and gas.Static medium-long term plan should be changed into dynamic and progressive plan through combining with annual plan.In the economic evaluation,limits of various technical and economic indicators should be defined rationally and dimension of investment should be controlled appropriately according to the existing technical conditions.

    Progress in computer modeling of sequence stratigraphy
    Yan Weipeng, Deng Hongwen, Wang Hongliang
    2004, 25(5):  596-602.  doi:10.11743/ogg20040523
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    Computer modeling of the filling process of a sedimentary basin has been relatively thoroughly studied in the 1960s.Computer modeling of sequence stratigraphy is a newly developed basin modeling technique along with the appearance of sequence stratigraphy.It is of the category of filling process modeling of a sedimentary basin.Presently,forward modeling is widely applied,while inverse modeling is still in research and several inverse modeling systems have been developed.1-D and 2-D modeling are relatively mature,and 3-D modeling represents the trend of development.Internationally,this technique has been advancing more rapidly and is more mature,while it is mainly used to model continental sequence stratigraphy in China.Mathematical models that are applied in sequence stratigraphy modeling include sedimentation model,structural subsidence model,loading subsidence model,compaction model and erosion model.Along with the deepening of research,sequence stratigraphy modeling technique will make a rapid progress in respects of modeling method,design of models, degree of integration,simulation dimensions and its application in continental basins.