Table of Content

25 June 2009, Volume 30 Issue 3

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Fission track records of tectonic uplift during the Cenozoic and Mesozoic in the periphery of the Jianghan Basin

Wang Shaohua, Luo Kaiping, Liu Guangxiang

2009, 30(3):  255-259.  doi:10.11743/ogg20090301

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Thermal history modeling of fission track can be used to reconstruct time-temperature histories of a sample and reflect subsidence-uplifting process resulted from tectnonic activity and sedimentation in a basin.On the basis of apatite fission track thermal history modeling results of intrusive rock samples from Yichang and Tongshan in the periphery of Jianghan Basin,we think that the samples have come through four stages of cooling with different cooling rates since Mesozoic,indicating the constant uplifting since the Indosinian period in the periphery of Jianghan Basin.Two rapid cooling stages respectively correspond to two quick uplifting in the Yanshan and Late-Himalayan Periods in the periphery of Jianghan Basin.This kind of process is coupled with the tectonic setting,tectonism-sedimentation and tectonic deformation since the Indosinian period in Jianghan Basin.

Genetic types and pooling of nature gas in the Yitong Basin

Guo Xiaowen, He Sheng

2009, 30(3):  260-267.  doi:10.11743/ogg20090302

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Based on the appraisal of source rocks in the Yitong Basin,we studied the geochemical characteristics and origin of natural gas in that basin.Using the Basinflow software,and simulated the directions of gas migration to recognize the favorable accumulation zones.The results show that there are three sets of source rocks in the Yitong Basin,including the Shuangyang,Sheling and Yongji formations,among which the Shuangyang Formation source rocks are the highest in the organic matter abundance.The types of organic matter are mainly TypeⅡ₁ and Ⅱ₂,partly Type Ⅲ andⅠ.The natural gas,with its maturity below 1.3%,is mainly composed of wet gas and is classified as associated gas.The gases in the Yitong Basin are mostly of oil-type and partly of mixed origins.The kerogens of the source rocks are mainly of TypeⅡ₁ and Ⅱ₂.The simulation results of gas migration and accumulation show that,the Wanchang structural belt and the hanging wall of No.2 fault in the Wuxing structu-ral belt of the Yitong Basin are the most favorable areas for gas accumulation and are characterized by contribution from two sources.

Hydrochemical characteristics and hydrocarbon accumulation in the Chengbei fault terrace zone of Dagang oilfield

Zhang Zongfeng, Zha Ming, Gao Changhai

2009, 30(3):  268-274.  doi:10.11743/ogg20090303

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The groundwater in the Tertiary Chengbei fault terrace zone in the Dagang oilfield is considered to be mildly saline water.The contents of positive ions are characterized by Na⁺+K⁺>Ca²⁺>Mg²⁺,and the contents of negative ions feature in Cl^->HCO₃^->SO₄^2->CO₃^2-.The Cl^-controls the total ion content.The salinity of groundwater shows obvious vertical zonations.The high salinity NaHCO₃ water is the main type and distributes widely in the study area.According to the vertical change of salinity and chemical compositions of the groundwater,three types of hydrochemical profiles could be recognized,including positive type,reversed type and multi-directional type.The reversed and multi-directional type profiles reflect that the vertical connectivity is fine,ma-king it good for hydrocarbon migration.Based on the vertical distribution of parameters such as salinity,ion content,Na⁺-Cl^-ratio and coefficient of desulfurization,we have divided the hydrochemical dynamical zones into three types:the formation water exchange smooth zone,the exchange retardation zone and the exchange dilatoriness zone.Usually under the fluid compartment and with relatively high salinity,the exchange dilatoriness zone is considered rich in oil and gas.Therefore,we have predicted that the Shahejie Formations in the Zhangdong and eastern Zhangdong areas are favorable exploration targets.

Research on hydrocarbon pooling and distribution patterns in the Zhu-3 Depression,the Pearl River Mouth Basin

Jiang Hua, Wang hua, Li Junliang, Chen Shaoping, Lin Zhengliang, Fang Xinxin, Cai Jia

2009, 30(3):  275-281,286.  doi:10.11743/ogg20090304

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The Zhu-3 depression in Pearl River Mouth Basin is a typical dustpan-shaped basin faulted in its south and overlapping to the north.It belongs to a marginal sea basin abundant in oil and gas resources.Three petroleum systems,namely the Wenchang A,Wenchang B,and Wenchang C,can be recognized in accordance with the strong controlling effect of the major faults.Different types of reservoirs had been developed in different structural zones:buried-hill or buried hill drape anticline hydrocarbon reservoirs and local stratigraphic overlap reservoirs in the gentle slope zone and its peripheral uplift zone,lithological-structural reservoir near the major faults,slump subtle reservoirs of fan delta front in the steep slope zone,and lenticular distal turbidite fan reservoirs in central basin.It is suggested that the unconformity-lithological reservoirs in the gentle slope zone and lenticular reservoirs in the central basin be favorable near-term exploration targets.

Stratigraphic characteristics and sedimentary models of near-surface formations in the estuary area of the Yellow River Delta

Fan Dehua

2009, 30(3):  282-286,281.  doi:10.11743/ogg20090305

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This paper focused on the estuary area of the Yellow River Delta,applied the methods of lithology coring and cone penetration testing and analyzed the sedimentary characteristics of the shallow strata of the delta.The sedimentary facies tracts mainly include river channel,crevasse splay,floodplain and tide flat.There are mainly two vertical sequence types:the estuary sand sheet-lateral margin of delta and the estuary sand sheet-lateral margin of delta-sand sheet,of which the former is predominant in the northern part of the estuary area,while the latter is predominant in the northwestern part.Based on these facts,we have proposed the sedimentary model for the development of the Yellow River Delta.This model not only offers quantitative surface geophysical parameters for high-density seismic acquisition,but also provides an example for the study of sequence stratigraphy.

Distribution characteristics of evaporates and formation pressure of the fourth member of the Shahejie Formation in the Dongying Sag,the Bohai Bay Basin

Liu Hui, Cao Yingchang, Jiang Zaixing, Wang Shenglan, Wang Yanzhong, Xu Lei

2009, 30(3):  287-293.  doi:10.11743/ogg20090306

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Three sets of gypsolyte-salt rocks occur vertically in Es⁴(the fourth member of the Shahejie Formation) of the Dongying Sag,the Bohai Bay Basin.The gypsolyte-salt rhythmic units show apparent depositional sequence of evaporation in genesis.On plane view,the gypsolyte-salt rocks are in ring-like distribution,and salt rock,gypsolyte,argillaceous gypsolyte,carbonate,marl,and clastic rock occur successively from the center to the border of the basin.Studies based on formation pressure coefficient calculation through interval transit times and statistics of the measured pressures show that the Paleogene presents vertically a "double layer structure" with normal pressure at the upper part and abnormal high pressure at the lower part.On plane view,the distribution of the abnormal pressure matches well with that of the gypsolyt-salt-rocks.It is suggested that the gypsolyte-salt-double seal mechanism of pressure seal and physical property seal is one of the key elements controlling the formation of the abnormal pressure in Es⁴ in Dongying depression.

Seismic properties of reservoir sandstones and their implication to rock texture in the Dongying Sag,the Bohai Bay Basin

Deng Jixin, Wang Shangxu, Wu Xiangyang

2009, 30(3):  294-299,309.  doi:10.11743/ogg20090307

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A total of 250 sandstone samples were selected from various sections of the Paleogene(dominated by the Shahejie Formation) in the Dongying Sag of the Bohai Bay Basin to measure their compressional-and shear-wave velocities by pulse transmission techniques under simulated reservoir conditions.Statistic petrophysical models under reservoir conditions,such as velocity versus porosity and velocity versus density,were built based on the measured data.On the cross plot of P-wave velocity vs.Possion's ratio,the samples show two major trends,which reflect the effects of shale content and calcareous cement content on the elastic properties of sandstone samples respectively.For each trend,the rock texture changes gradually from grain-supporting to matrix-supporting with the increase of shale content and calcareous cement content,and thus the propagation of elastic wave also changes from via grain-to-grain contacts to via rock matrix.These are the main reasons for the two entirely different trends of the sandstone samples.The results provide a basis for extracting information about rock texture,sedimentary and diagenetic features by using the petrophysical properties of reservoir sandstones.

Determination of hydrocarbon charging events and timing of accumulation in the Triassic of Tahe area,the Tarim Basin

Lü Haitao, Chen Honghan, Tang Daqing, Ma Li

2009, 30(3):  300-309,299.  doi:10.11743/ogg20090308

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Controlled by regional "seesaw" tectonic movements and the fault carrier system,the Triassic of the Tahe area experienced a very complicated hydrocarbon accumulation process.In this study,we systematically analyzed 291 fluid inclusion samples.The hydrocarbon charging events and timing of accumulation in the Triassic were determined according to the fluorescent colors of oil inclusions and through projecting the homogenization temperature on burial history.The results show that,each of the upper,middle and lower oil layers in the Triassic were charged in three stages.The reservoirs in the northern Yuqi area were charged in the earlier(40-7.5 Ma) three discontinuous stages,while the reservoirs in the central-south area were charged in the later(11-0.9 Ma) three continuous stages.Based on these understandings,we have proposed that the peri-salt and supra-salt structural zones and lithological updip pinchout zones are the favorable targets for further exploration.

Genetic mechanisms and controlling factors of terrestrial biogenetic gas in the Quaternary of the Qaidam Basin

Wei Shuijian, Wang Jingpeng, Guan Zhiqiang, Xu Ziyuan, Jiang Guifeng

2009, 30(3):  310-315,323.  doi:10.11743/ogg20090309

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The Quaternary in the Qaidam Basin is an ideal site to study biogenetic gas.Based on the analysis of the forming environment of biogenetic gas and in combination with the results of modeling experiments of biogenetic gas generation,we have concluded that the generation of terrestrial biogenetic gas is under the control of various factors including temperature,bacterial group types,groundwater properties and sedimentary rates,etc.The survival temperature of bacterium which produces methane is 0-80℃,and the most favorable temperature to produce methane is 30-55℃.The peak of gas generation occurs at 35℃,which corresponds to a burial depth of 500m.The groundwater in the Quaternary of the Qaidam Basin has the characteristics of high salinity.Its salinity decreases with the increasing of depth.In addition,there are sulfate reduction zone in the shallow strata.These factors restrain the activity of methane bacteria in the shallow and surface areas,making it favorable to generate gas in the deeper strata.The rapid sedimentation buries organic matters quickly,which provide abundant organic sources for later microbial activities.

Control of faults at different evolution stages on hydrocarbon accumulation in Tazhong area,the Tarim Basin

Zhang Zhongpei, Wang Yi, Yun Jinbiao, Zhou Bo, Zhao Zhehui, Zheng Menglin

2009, 30(3):  316-323,315.  doi:10.11743/ogg20090310

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An analysis of how faulting activities in different evolution stages control the hydrocarbon distribution and accumulation is carried out based on a summarization of the basic features of different faulted zones in the Tazhong area,Tarim Basin.The result shows that faults in the Tazhong area were most active during the Mid-Late Caledonian,softened during the Hercynian,and weak during the late Himalaya.It also indicates that the major fault zones are significantly different in the time and stages of activity,control on the formation and deformation of sedimentary formations and stratigraphic contact relationships between the upper and lower layers.The diffe-rences in hydrocarbon accumulation among different oil/gas-bearing faulted zones are closely related with the evolutionary stages of the faults,as being embodied in the differential control of faults at four evolutionary stages on hydrocarbon accumulation,namely syn-sedimentary fault,post-sedimentary fault,peak-hydrocarbon-generation-stage fault and post-hydrocarbon-accumulation fault.

A discussion on the geochemical characteristics and migration and accumulation of natural gas in the eastern Tarim Basin

Lan Xiaodong, Zhu Yanming, Ran Qigui, Cheng Honggang

2009, 30(3):  324-329.  doi:10.11743/ogg20090311

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There are two sets of source rocks in eastern Tarim Basin.Comprehensive analysis of components,isotopes of carbon and hydrogen,and light hydrocarbon constituents of the samples from the basin indicates that natural gas there is marine organic oil-prone gas derived from the Cambrian and Ordovician source rocks.The gas was formed at a very high temperature and therefore can be classified as cracked gas.Study on gas accumulation and migration patterns based on character of carbon isotope and gas migration index(ΔR₃) shows that the direction of gas migration is generally from structural low to high.Data of the well Yingnan-2 show that the reser-voirs there had experienced at least two times of hydrocarbon charges.

Accumulation mechanism of low-abundance oil reservoirs in the Yanchang Formation of Shuguang oilfield,the Ordos Basin

Zhou Wen, Su Fuyi, Dai Jianwen

2009, 30(3):  330-336,349.  doi:10.11743/ogg20090312

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The mechanism of oil-gas migration of the exceptionally low-abundance oil reservoirs in the Yanchang Formation of the Shuguang oilfield,Ordos basin,is analyzed in this paper by applying the theory of secondary hydrocarbon migration.The results show that the major source rocks of the Chang-7 member(the 7th member of the Yanchang Formation) had generated and expelled large amount of hydrocarbons during the mid-late Yenshanian(Cretaceous),and the Chang-6 and Chang-8 sandbodies acted as carriers beds for hydrocarbon migration.During the migration process,small amount of hydrocarbon was 'left behind' because of local barriers formed by physical property contrast and lithology changes,and formed the so-called low-abundance oil reservoirs inside the migration-discharge zone.This kind of reservoir is one of the most important reservoirs that deserve much more attention not only in Ordos Basin but also in other large basins in China.It shall be regarded as an important target for future hydrocarbon exploration.

Features of organic matter and formation environment of marine carbonate rocks

Zhou Xinke, Xu Huazhen

2009, 30(3):  337-342,349.  doi:10.11743/ogg20090313

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Marine carbonate rocks are usually formed on neritic continental shelf where sea water evaporates fu-riously,living organism flourishes,and Eh and pH values change easily.Turbulent sea water with its high oxygen content destroys the soft parts of dead organism and forms carbonate rocks with low-abundance and low grade organic matters.Worldwide,carbonate rocks with TOC less than 0.2% and kerogen type of Ⅲ or Ⅱ₂ are common.It is therefore concluded that pure carbonates can not serve as effective source rocks.The TOC of carbonate rocks increases as the shale content becomes bigger,and only a small amount of marls with TOC larger than 0.5% may be effective source rocks.

Geochemical characters of carbonates and indicative significance of sedimentary environment——an example from the Gaoyuzhuang Formation of the Changcheng System in the northern Hebei Depression

Wang Kaiming, Luo Shunshe

2009, 30(3):  343-349,336,342.  doi:10.11743/ogg20090314

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The Gaoyuzhuang Formation of the Changcheng System in northern Hebei Depression is dominated by carbonates and can be roughly divided into shallow water platform and deep water platform-basin facies zones and further divided into five different facies tracts.Based on the correlation analysis of carbonate rock sample testing results,the authors of the paper discuss the enrichment mechanisms of their elements and components and environmental significance.The analysis shows that geochemical characters are closely related to the initial sedimentary environment in the study area:the Ca/Mg ratio is the lowest in supralittoral zone where dolomite is predominant,gradually increases from intertidal zone to slope zone,and reaches its highest value in deep water basin where calcite dolomite is predominant.The average Na content is the highest in supralittoral zone where it is be-neficial to dolomitization and preservation of Na.The contents of Mn and Fe are the highest in intertidal zone but relatively low in the platform-basin.The contents of trace elements as Al,K,V,P and Ti tend to increase from shallow to deep water sedimentary environment,thus could be used to indicate relatively changes of ancient water depth and sea level.Sr is mainly hosted in calcite.The average Sr content and 1000 Sr/Ca ratio tend to increase from shallow water platform to deep water platform-basin.The blue green microalgae rich in Sr is the main rock-forming organism for stromatolite dolomite,and the stromatolite dolomite is more highly developed in the supralittoral zone and intertidal zone than in subtidal zone.Thus the average Sr content and 1000 Sr/Ca ratio are relatively high in the supralittoral zone and intertidal zone.All of these indicate that geochemical characters of carbonates can be regarded as an effective indicator of sedimentary facies.

Characteristics of karst reservoirs in the Middle Ordovician Majiagou Formation of gas fields in the central Ordos Basin

He Jiang, Fang Shaoxian, Hou Fanghao, Yang Xiyan

2009, 30(3):  350-356. 

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The accumulative proved geologic reserves of the gas fields in central Ordos Basin is about 337.73 billion cubic meters,of which more than 80% comes from carbonate reservoirs(mostly the karst reservoirs) in the Majiagou Formation of the Middle Ordovician.On the basis of a systematic and detailed description and study of the key core samples as well as the microscopic observation of cast thin sections,the authors of the paper put forward the formation environment,genetic types,mechanisms of the Ordovician karstification and the karstic re-servoir characteristics.They also suggest that coarse medium crystalline dolomite with intercrystalline pores and the nodular dolomite with anhydrite deposited in particular environment are the material bases of reservoir deve-lopment,while the development and preservation of the secondary pores,the fractures and the vugs formed by the karstification in the epidiagenetic stages and burial diagenesis stages are crucial for the formation of a good reservoir.The karstification in the burial diagenesis stages and structural fissures mainly overprinted on the pore system formed in the epidiagenetic stage.The reservoirs can be further classified into the fracture-dissolved pore(vug) type,the fracture-pore-dissolved pore type and the pore type,among which the fracture-dissolved pore(vug) type is predominant.Quality reservoirs are mainly distributed vertically in the M₁³ and M₁² sub-members with well-developed anhydrite nodular medium crystalline dolomite and horizontally in the central basin-marginal flat facies belt with anhydrite nodules.

Application of multiwave joint inversion to the prediction of relatively high-quality reservoirs——an example from the prediction of deep tight clastic sandstone reservoirs in the western Sichuan Basin

Ye Tairan, Fu Shun, Lü Qibiao, Lai Weirong

2009, 30(3):  357-362,369.  doi:10.11743/ogg20090315

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Clastic sandstones of delta facies were developed in the fourth member of the Tertiary Xujiahe formation(T₃x⁴) in the western Sichuan Basin and they are tight with low porosity and low permeability.The sandbodies are large in thickness,but their gas-bearing reservoirs are thin.The wave impedance of these reservoirs is similar to the surrounding rocks—tight sandstone and mudstone.It is very difficult to accurately predict the distribution of these reservoirs using conventional seismic methods.Taking advantages of 3D3C exploration,we have carried out a joint inversion of P-wave and converted shear wave.Based on the analysis of petrophysical parameter sensitivity,we have proposed the idea of "recognize quality sandstone in sandstone".The multiwave attribute data volume such as Poisson's ratio and P-wave impedance are selected for multi-volumes crossplot interpretation to recognize mudstone and tight sandstone.In this way the relatively high-quality reservoirs within tight sandstones can be accurately identified.

Experiment and application of NMR in carbonate reservoir analysis:an example from Tahe oilfield

Lang Dongjiang, Shang Genhua, LüChengyuan, Ding Shaoqing, Sun Aijun, Shang Xulan

2009, 30(3):  363-369,362.  doi:10.11743/ogg20090317

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Carbonate reservoirs in the Tahe oilfield feature in fractures and vuggies.Nuclear magnetic resonance(NMR) was therefore employed to analyze these formations.The paper expounds on the working principles of NMR imaging as well as T₂ spectrum in rock property testing.By using these technologies,the authors established the spatial structures for cores and classified the carbonate reservoir space types.They also carried out oil and water detection,and studied conditions for fluid moving inside the cores and methods for appraisal of reservoir development effect.The results show that NMR can directly detect fluid and its distribution inside the cores,and that no connection exists between testing results and the shape and size of the samples.The carbonate reservoirs in the Tahe oilfield can be classified into four main types:pore(matrix),dissolution pore,fracture,and pore-vug-fracture,each has unique NMR imaging and T₂ spectrum characteristics and therefore can be easily recognized.The T₂ cutoff value(an important physical parameter for evaluating the development potential of carbonate reservoirs) of the carbonate reservoirs in the Tahe oilfield is 86.25 ms.Application of the methods in different blocks with carbonate reservoirs in the Tahe oilfield indicates that the prediction of reservoir development accord with the actual results,thus verifies the feasibility of the method in the evaluation of carbonate reservoir development.

An integrated seismic-geological approach to the study of complex traps in the Biyang Depression

Sun Yaohua, Wang Hua, Lu Yongchao, Li Sitian

2009, 30(3):  370-378,383.  doi:10.11743/ogg20090318

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The theories on high-resolution sequence stratigraphy were applied to the systematical recognization and correlation of the sequence stratigraphic units of different orders for the Upper Cretaceous to Paleogene in the Biyang Depression and to the establishment of correlation frameworks for sequence stratigraphic units of each order.We identified several favorable hydrocarbon reservoir types,including the complex fault block reservoirs of the high-stand prograde delta in the northern slope zone,the fault-lithologic reservoirs in the low-stand fan of the hinge zone in the northern slope,the lenticular reservoirs in the slump turbidite and sublacustrine fan in the deeply-sagged area,and the lithologic reservoirs in the southern steep slope zone.Based on these discoveries,we studied the various trap types developed in the northern slope zone,deeply-sagged area and the southern steep slope zone and carried out research on their seismic recognition and prediction.Many subtle reservoirs were identified through seismic prediction and proved through drilling.

Methods for determining the petrophysical property cutoffs of extra-low porosity and permeability sandstone reservoirs——an example from the Xishanyao Formation reservoirs in Yongjin oilfield

Jiao Cuihua, Xia Dongdong, Wang Jun, Liu Lei, Sheng Wenbo, Cheng Peitao

2009, 30(3):  379-383,378.  doi:10.11743/ogg20090319

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With the porosity range of 4% to 6% and the permeability range of 0.01?10^-3 μm²-0.30?10^-3 μm²,the Xishanyao Formation reservoirs in the Yongjin oilfield of the Junggar Basin are typical extra-low porosity and extra-low permeability reservoirs.According to the static and dynamic data and petrophysical experiments,we have determined the effective porosity and permeability cutoffs of these reservoirs through methods of empirical statistics,oil-bearing occurrence test,physical property test,nuclear magnetic resonance,minimal pore throat radius and displacement pressure.The results show that the lower limit of porosity is 6% and the lower limit of permeability is 0.08?10^-3 μm²,providing basis for determining effective thickness and estimate reserves.

New application of the forecast model of oil/gas output

Liu Chuanxi, Wang Shuping, Liu Yanqing

2009, 30(3):  384-387.  doi:10.11743/ogg20090320

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Weibull,HCZ and Logistic models are widely used to forecast output of oil/gas fields.They are only suitable for oil/gas fields in middle or late stage of development and in declining.However,they are not applicable to fields in early development stage due to the shortage of production data.In this paper,the calculation methods of parameters are improved for obtaining the parameters of these models with the limited data in the early stage of development.In this way the range of application of these production forecast models can be extended for use in the early stage of development.In addition,methods of model optimization are also presented to provide a basis for choosing the proper model for production forecast of different oil/gas fields.

An analysis on influential parameters for modeling permeability profile during underbalanced drilling in horizontal wells

Lu Hongyou, Chen Xiaohong, Huang Handong

2009, 30(3):  388-392.  doi:10.11743/ogg20090321

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Underbalanced drilling can reduce or even eliminate formation damage from drilling fluid invasion,and therefore,it is getting more and more popular.To ensure that the bottom hole pressure is lower than the re-servoir pressure,it is essential to adjust the gas fraction of the drilling fluid and to accurate inflow calculations.The permeability profile is an important parameter to calculate inflow.We have derived a model for calculating permeability profile and proved it by applying numerical simulator.Parameters such as formation heterogeneity,formation pressure and drilling rate were studied in this paper.The results show that the model is applicable in certain areas.