Table of Content

24 February 2008, Volume 29 Issue 1

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Tight sandstone gas reservoirs:their origin and discussion

Zhang Shaonan

2008, 29(1):  1-10,18.  doi:10.11743/ogg20080101

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Tight gas reservoir sandstones are generally defined as gas-bearing and-yielding sandstones with porosity of less than 10% and permeability to gas less than 0.1md.Tight gas reservoir sandstones are characterized by high capillary entry pressures,high irreducible water saturations and predominance of secondary pores.This paper suggests that tight reservoir sandstones be classified into four types in terms of the origin:1)tight sand formed by sedimentation of large amount of authigenic clay minerals;2)tight sand resulted from crystallization and precipitation of cements altering primary pores;3)tight sand caused by compaction of large amount of ductile clasts;4)tight sand formed by filling of intergranular pores by detrital clay matrix.To explain the origin of se-condary pores in these sandstones,researchers have developed many theories.However,none of the theories are capable of clearing all the doubts due to the complexity of this kind of reservoirs.As a result,the issue is still in debate.Despite their complex burial history of tight reservoir sandstones and diagenesis being determinant in tightening of sandstones,original depositional environment is still a basic factor controlling the formation of tight sandstone reservoir.Deeper understanding of their depositional environment and the diagenetic history is critical to the prediction and evaluation of tight reservoir sandstones.

Geological features and significance of base-surge deposits

Liu Zhaojun, Miao Qiaoyin, Liu Xiang, Liu Rong

2008, 29(1):  11-18.  doi:10.11743/ogg20080102

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Base-surge deposits,commonly considered as a special kind of pyroclastics,are aqueous pyroclastics that are produced by explosive magma-water interaction.Volcanic explosion provides rich material resources for base-surge.Base-surge deposits are characterized by accretionary lapilli and large-scale dunelike structures,therefore they can be easily differentiated from other volcanoclastic rocks.The clastic texture of base-surge deposits is dominated by volcanic pisolite and gravel mostly in half-round shape,followed by round shape,and some in subangular shape.Since base-surge deposits have some characters of pyroclastic debrits and sedimentary rocks,they serve as excellent oil and gas reservoirs.In addition,study on its genesis is helpful for preventing and forecasting disaster.

Control of transfer zone on sandbodies in the extensional structure system——a new approach to reservoir prediction

Wang Jiahao, Wang Hua, Xiao Dunqing, Wei Ajuan, Liao Yuantao

2008, 29(1):  19-25.  doi:10.11743/ogg20080103

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Two typical transfer zones,the lateral uplift and the strike slope,are common in rifted-basins.Large-scale sandbodies of fan delta or turbidite fan are generally developed in the corresponding down throw blocks.The controlling mechanism of these transfer zones on sandbodies is the differential palaeotopography caused by syndepositional faulting,especially the convergence and guidance of drainage systems by the palaeotopographic low on the down throw blocks in the transfer zone.Apart from that,the antithetic parallel transfer zone,developed at the large lengthways uplift belt in the central of rifted-basins,usually forms fault-troughs serving as axial channels for sediment transportation.

Sedimentation simulation tests on formation and distribution of flood turbidity sandbodies

Liu Zhongbao, Gong Wenping, Wang Xinhai, Zhang Chunsheng, Luo Shunshe, Jiang Shan

2008, 29(1):  26-30,37.  doi:10.11743/ogg20080104

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An experimental program for sedimentary simulation of flood turbidity current is described in this article.It is designed by using the sedimentation simulation test technology,collecting information concerning prototypes of flood turbidity sandbody,and integrating the forming environment and conditions for flood turbidity currents.The article also discusses the forming processes of flood turbidity current under different conditions,such as slope length and gradient,the initial velocity,mud-sand ratio and sand content,and etc;analyzes its deposition pattern;reveals the distribution and sedimentary characteristics of sand and muddy in flood turbidity current;dissects the controlling effect of lake-floor topography on flood turbidity sandbody and reveals the hydrodynamic mechanism for the formation and development of flood turbidity sandbody.The experimental results show that the flood turbidite deposition is influenced by various parameters,such as the slope gradient and elevation difference,the landform of the lake floor,the lake water level and the flow velocity,and that the contents of sand and mud in flood turbidity current determine its flow behaviour and sedimentary structure.

Application of the variable scale fractal technique in fracture prediction and reservoir evaluation

Liu Lili, Zhao Zhongping, Li Liang, Chen Wenlong, He You'an

2008, 29(1):  31-37.  doi:10.11743/ogg20080105

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By using the acoustic travel time(AC) data,other test data and variable scale fractal techniques,the distribution of natural fractures in Chang 4+5₂^1-2 reservoirs of Yuan 48 wellblock in Tiebiancheng oilfield was predicted,and the relationship between the fracture development degree and initial deliverability of oil wells was also discussed.Based on the distribution characteristics of zones with relatively well-developed fractures and their formation conductivity,Chang 4+5₂^1-2 reservoirs are comprehensively classified and evaluated,and the results are in accord with the actual production data.The research results can be used for reference in the fracturedescription in low-permeability reservoirs.

Stratigraphic division and correlation in areas with complicated sedimentary environment——a case study of Daniudi gas field in the Ordos Basin

Luo Dongming, Tan Xuequn, You Yuchun, Liu Jiandang, Feng Qiong, Liu Zhongqun

2008, 29(1):  38-44.  doi:10.11743/ogg20080106

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The main gas-bearing horizons in Daniudi gas field of Ordos basin is the Upper Carboniferous Taiyuan,Lower Permian Shanxim and Xiashihezi Formations.Stratigraphic division and correlation are difficult because of rapid change of fluvial facies,sparse well pattern,and large project area in the field.Single stratigraphic division and correlation method failed to work effectively.At the very beginning of the study,there were several schemes as for how to solve the problems.As a result,a composite method of stratigraphic classification and correlation suitable for complicated sedimentary environment are developed by integrating the marker bed method(introducing coal seams as markers and supplementary horizon markers),the isopach method(the same layer having similar thickness) in adjacent wells,the sequence stratigraphy method,and the dense well pattern analysis method(i.e.,applying knowledge obtained from analysis of dense well pattern to sparse well pattern).By doing that,this paper presents a new scheme of stratigraphic division and correlation,which have been used successfully in real practice and achieved a unified understanding of the formations in the study area.

A discussion on gas and oil exploration activities and discovery patterns in the Tarim Basin

Jin Xiaohui, Yan Xiangbin, Li Tiejun, Zou Yuanrong

2008, 29(1):  45-52,60.  doi:10.11743/ogg20080107

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The history of oil and gas exploration in Tarim basin can be divided into three periods and six stages.Works in the first period were mainly focused on the piedmont structural belt of the basin.Guided by the structural trap theory and following the oil seepage as the clue,the first breakthrough in oil and gas exploration was achieved at the place.While during the second period,the northern Tarim basin was the focus of exploration.Guided by lithologic trap theory and carbonate source rocks theory,oil and gas exploration of marine facies began in China,with the cratonic paleo-uplift and paleo-slope as the main targets.The third period can be described as all-round exploration,which was carried out by taking the hydrocarbon accumulation theory of superimposed basin as the guidance and the cratonic paleo-uplift and paleo-slope as well as the foreland thrust fold belts as the exploration targets.During the process,a comprehensive appraisal system for the basin had been developed.The exploration practice in the basin shows that for oil and gas discovery,new theories and deeper understandings are the foundation;flexibility is the critical catalyst,enlightenment of the nearby analog prospecting region is the shortcut,advancement in engineering technology is the bridge,and the scientific decision-making for exploration is the key of speeding up.At present,oil and gas output from Tarim basin has already surpassed 20 000 000 tons of oil equivalent,symbolizing that oil and gas exploration in Tarim basin will soon enter the fast discovery stage and lying down the foundation for the realization of China's strategic replacement of oil and gas resources.

Identification and evaluation of the Triassic non-structural traps in Tahe oilfield

Shi Yu, Li Zongjie

2008, 29(1):  53-60.  doi:10.11743/ogg20080108

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Exploration and development activities in Tahe oilfield indicate that the Triassic targets are characte-rized by great burial depth and low amplitude of local structures.Its traps are mainly of subtle types,including low amplitude structure,lithologic structures,and lithologic-structural combination traps.This paper puts forward ways of identification and evaluation of non-structural traps based on the experiences of exploration in the Triassic strata.Favorable oil an gas plays are firstly located through an all-round,dynamic,and comprehensive regio-nal study;then,seismic identification and evaluation techniques of non-structural traps with amplitude extraction as the core are developed based on study of sequence stratigraphy to locate and identify favorable non-structural traps in Tahe oilfield;and finally,trap evaluation is performed by using the technology of seismic hydrocarbon detection.A rational combination of the above-mentioned methods may be a effective way to reduce exploration risks and improve success rate.

Log interpretation and evaluation of the Ordovician carbonate rock reservoirs in Tahe oilfield

Fan Zhenjun, Liu Jianhua, Zhang Weifeng

2008, 29(1):  61-65.  doi:10.11743/ogg20080109

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The Ordovician oil pools in Tahe oilfield are of karst fractured-vuggy carbonate reservoirs formed by multiphase tectonic movements and karstificaion.The main reservoir space,composed of pores,cavities,and fractures,is featured by low-porosity and strong anisotropy and heterogeneity.The log interpretation and evaluation of these reservoirs differs greatly from that of sandstone reservoirs.This paper summarizes the main reservoir types that can be identified by FMI logging based on core calibration.It also studies conventional log response characteristics of all types of reservoirs and identification methods of reservoir through log interpretation,and analyzes factors that might affect the identification of reservoirs and methods for differentiating these factors.Based on ca-libration of core and FMI logging data,the paper presents integrated probability model for fracture and dual porosity model,and realizes quantitative assessment of fractured-vuggy carbonate reservoirs with conventional log data.Positive results have been gained by using them in quantitative log assessment of the fractured-vuggy carbonate reservoirs of the Ordovician in Tahe oilfield.

A discussion on the genesis of light and heavy oil distribution of inverted sequences in the Chepaizi Uplift,the Junggar Basin

Shen Yang, Li Maorong

2008, 29(1):  66-71.  doi:10.11743/ogg20080110

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It is generally believed that light oil is often found at the lower part or the central of an oil pool while heavy oil is more often located at the upper part or the periphery.However,the oil density distribution in the Chepaizi Uplift of Junggar basin proves otherwise:light oil is on top of heavy oil.Oil-source correlation and research on the regional structures,source rock evolution and preservation conditions indicate that multiple types of the Permian and Jurassic source rocks have generated and expulsed hydrocarbon sin several stages in the study area.Multiphase structural activities and sedimentation formed cap rocks of different sealing capacities.It is multiphase reservoiring and different sealing conditions in each reservoirng phase that caused the inverted sequence of light and heavy oil in the Chepaizi uplift.And later injection and certain preservation conditions are consi-dered necessary for forming light oil pool in the Neogene Shawan Formation of the uplift.It is suggested that exploration of the area shall take the possibility of "light oil on top of heavy oil" into consideration.

Study on formation water in Mosuowan area of the Jungger Basin

Jiang Lin, Song Yan, Zha Ming, Qu Jiangxiu, Bo Dongmei

2008, 29(1):  72-77.  doi:10.11743/ogg20080111

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Mosuowan area has developed a rather complicated formation water including Na₂SO₄,NaHCO₃,MgCl₂ and CaCl₂ four types.There are two pressure systems in the vertical direction,of which the lower high-pressure system shows reverse hydrochemical depositional sequence,while the upper part with normal pressure system has a little different hydrochemical depositional sequences in different areas.Study on regional structure features of the area and analysis of formation water types and salinities show that formation water in Mosuowan area is within hydrogeologic system of NaHCO₃ type.The CaCl₂-type formation water is sourced from the deep strata and migrates into the reservoir through faults,while the Na₂SO₄-and MgCl₂-type formation waters are mixtures of CaCl₂-type water of high salinity and NaHCO₃-type water of low salinity.The difference between the geological conditions in Peng-5 well-block and Pengcan-2 wellblock is the main cause of the different hydrochemical depositional sequences of the strata with normal pressure in these two wellblocks.Diagenesis and hydrocarbon generation are the reasons behind the reverse hydrochemical depositional sequences of the strata with high pressure.

Structural-paleogeomorphologic features of Chepaizi area and mechanism of their control on sandbodies

Xing Fengcun, Lu Yongchao, Liu Chuanhu, Xiang Kui

2008, 29(1):  78-83,106.  doi:10.11743/ogg20080112

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Seismic,log,and test data as well as the backstripping technique and trend analysis method of erosion restoration,were employed in the synsedimentary palaeogeomorphology reconstruction of basal boundaries of the lowstand system tracts(LST) of the Lower Cretaceous Tugulu Group sequence,the LST of the Paleogene sequence and the lacustrine expanding system tract of the Miocene Shawan Formation sequence in the Chepaizi area,Junggar basin.The paleogeomorphologic features of these three stages and their control on glutenite in incised valley,fan deltaic glutenite and longshore sandbody were analyzed.Based on the results of these studies,this paper summarizes the controlling patterns of the geomorphology on sandbody distributions during these three stages.The LST of the Tugulu Group sequence is characterized by sand supply from the uplift,diversion of the low uplift and "ridge",transportation along the valley,and accumulation in the sag.The LST of the Paleogene sequence shares the similar features with the Tugulu Group sequence except for the insignificant feature of transportation along the valley,while the lacustrine expanding system tract of the Miocene Shawan Formation features in control of slope-break zone and low uplift zone on transportation and deposition of sand.

Application of pressure-drop method to Sebei-1 gas field

Luo Wanjing, Tang Hailong, Wang Xiaodong, Fan Xinwen

2008, 29(1):  84-87.  doi:10.11743/ogg20080113

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Pressure testing data collected in Sebei-1 gas field are considered sufficient enough for calculating dynamic reserves of constant-volume gas reservoirs with pressure-drop method.By using the P/Z and G_p data acquired in different development stages in Sebei-1 gas field,three types of pressure-drop curves were mapped,including linear curve,late upward broken curve and late downward broken curve.The first type of curve indicates that reservoir poroperm characteristics are homogenous in the swept region and production is stable.While reperforation may generate the second type of curve and boundary effects and inter-well interference may induce the third type of curve.Accordingly,dynamic reserves can be calculated through extrapolating the straight pressure line until P/Z equals to 0,while for the later two types of curves,the calculation may be performed by selecting the late section of straight line and extrapolating it.

Pattern and potential of petroleum reserves growth in the Bohai Bay Basin

Zhai Zhongxi, Bai Zhenrui

2008, 29(1):  88-94.  doi:10.11743/ogg20080114

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Bohai Bay is currently a large-scale peroliferous basin with the largest petroleum reserves discovered so far in China.It harbors three large hydrocarbon-enriched zones: the Jizhong depression in the west,the Huanghua-Linqing depression in the central,and the Jiyang-Bozhong-Liaohe depression in the east.Based on studies of numerous exploration cases and reserves growth pattern and analysis of relationship between these plays and their geological features,this paper estimates the potential of reserves in Bohai Bay basin and presents corresponding exploration strategies.The offshore part of the basin has a ration of proved reserves to OOIP as low as 29.7%,therefore shall be regarded as the important future target for reserve growth;while for the onshore part,exploration shall aim at subtle structural-lithological combination reservoirs with different strategies for different series of strata.In the shallow part,new 3-D seismic acquisition and reprocessing of old seismic data are to be performed to discover new plays;in the middle part,review of old wells and progressive exploration and deve-lopment will be carried out to define new targets;while in the deep part,detailed reservoir study will be performed to look for carbonate reservoirs.By doing this,it is certain that the Bohai Bay basin will see a new run of reserves growth in the near future.

Control of the structure of the Paleogene Dongying Formation upon fan-delta deposition in the Nanpu Depression,Jidong oilfield

Liu Yanli, Qiu Chunguang, Deng Hongwen, Li Ming

2008, 29(1):  95-101.  doi:10.11743/ogg20080115

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Boundary fault features and deposition characteristics of the Dongying Formation support a division of the Nanpu depression into three structural units,namely the steep slope zone,the depressed zone,and the gentle slope zone.The analysis of drilling,log and seismic data points out that fan-deltaic depositional systems are mainly developed in the steep slope zone and are controlled by different paleo-structures and paleogeomorphology,thus showing clear disparity in grain size of reservoir rock and development scales.Based on these observations,the paper sums up three fan deltaic genetic models,including fault-platform,fault-terrace,and fault-scarp.They differ tremendously in reservoir capacity.The delta plain subfacies and fan delta front subfacies developed in the fault-platform setting and the fan delta front subfacies developed in fault-terrace setting are considered as the favourable facies belt for forming high quality reservoirs.

Strike-slip faulting activities in the Tanlu fault zone and their relationship with hydrocarbon accumulation——an example from Jinxian area

Deng Jinhui, Zhou Xinhuai, Wei Gang, Sun Shubin, Wang Gang

2008, 29(1):  102-106.  doi:10.11743/ogg20080116

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Tanlu strike-slip fault zone had experienced several phases of movement,exerting strong influence and control upon the hydrocarbon pooling within the zone.Located inside the strike-slip fault zone and also the north part of a hydrocarbon kitchen(Liaozhong depression),Jinxian area,one of the major discoveries in Bohai offshore in recent years,possesses favorable hydrocarbon pooling conditions with its extensive well-developed delta and fan delta sandbodies sourced from Jiaoliao,a uplift to its east side.Faults are relatively well developed along the zone and can be divided into 3 different fault sets according to their strikes,among which the NNE-trending strike-slip fault and near NE-trending strike-slip accommodation fault are the main hydrocarbon migration pathways for the east and west fault walls in Jinxian area,and control the migration horizons and pooling depth of the Paleogene hydrocarbon.

Crustal extension and fault activity during the Mesozoic-Cenozoic in the Jiyang Depression and the Luxi Uplift,East China

Ding Zengyong, Wang Liangshu, Zhang Peng, Zhong Kai, Liu Shaowen

2008, 29(1):  107-112,140.  doi:10.11743/ogg20080117

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Jiyang depression and Luxi uplift share the same type of crystalline basement.Three typical deep seismic reflection profiles acquired in these two regions during recent years were used to reconstruct the depositional burial history of the basin.By repeatedly matching the tectonic features of the basin,kinematic parameters during each main tectonic evolution stage were quantitatively calculated and the extensional process of the basement was analyzed in detail.The results show that both basement extension and fault activity are in temporal and spatial non-equilibrium in Jiyang depression and Luxi uplift,and the intensity of extensional deformation during Paleogene is much stronger than that during the Mesozoic for both of the regions.For Jiyang depression,both the ratio and rate of the Paleogene extension in N-S direction are two times bigger than those in E-W direction.This article provides an important basis for the further study of the tectonic evolution and crustal extensional deformation of the Great North China in Eastern China during the Meso-Cenozoic.

Exploration practices and directions for deep natural gas in the Songliao Basin

Xie Xiao'an, Zhou Zhuoming

2008, 29(1):  113-119.  doi:10.11743/ogg20080118

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Oil and gas exploration in Songliao basin has gone through three stages,i.e.,structural,non-structural,and current deep reservoir exploration.During the practices if deep gas reservoir exploration,discoveries have been achieved in well Xushen-1,Changshen-1 and Yaoshen-1,and a gas industry base begun to take shape in the basin.Exploration activities in the basin prove that for obtaining breakthrough in deep gas exploration,deeper geologic understanding and creative exploration idea are the basis,application of the advanced engineering technique is the key,and consistency and cooperation in exploration and enforcement in management are the guarantee.Generally speaking,Songliao basin remains largely unexplored and there are plenty of opportunities for further exploration activities.Three direction of explorations are volcanic rocks,clastic rocks,and the Carboniferous-Permian marine facies.It is safe to say that more discoveries of larger scale will be achieved through strengthening exploration in these three directions.

Structural characteristics and gas accumulation in the deep of the Changling Fault Depression,the South Songliao Basin

Zhang Wei, Li Hongge, Li Mingjie

2008, 29(1):  120-127.  doi:10.11743/ogg20080119

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Large 2D seismic sections,3D seismic data,and drillinglog data,combined with high-accuracy gravity,magnetic and electric survey data,were used in a systematical analysis of the regional geological structure in Changling fault depression.It is suggested that the Changling fault depression is not a simple single fault depression but a complicated fault depression cluster,which is composed of many primary and secondary fault depressions and connected with the northern part of Gulong fault depression.Structural units and plays in the area are identified based on integrated industrial mapping.Geometric and kinematic analyses of the main faults are also carried out and based on that,the structural evolution of the fault depressions is studied and divided into the following three periods: basement formation,fault depression development,and modification.With analyses of petroleum geological conditions,the accumulation characteristics of different gas reservoirs are studies and potential exploration targets are defined.

Research on techniques of reservoir geologic modeling constrained by seismic data at high water-cut stage

Hu Shuiqing, Han Dakuang, Xia Jizhuang

2008, 29(1):  128-134.  doi:10.11743/ogg20080120

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At high water-cut stage of development,it is necessary to build high precision reservoir geologic mo-dels by giving full play to the high lateral sampling density of seismic data and the high vertical sampling density of well data.In this paper,a new approach is proposed to build such a model constrained by results of highly accurate geophysical reservoir predictions.Case study shows that the seismic-constrained reservoir modeling approach can bring the advantage of geostatistics(i.e.,multidiscipline integration) into full play,effectively integrate sesmic,well log,and geologic data,and reduce the uncertainty of reservoir geologic models.The approach is proved to be effective in improving the precision of geologic models and have great application potentials.

Experimental investigation into Biot's coefficient and rock elastic moduli

Ma Zhonggao

2008, 29(1):  135-140.  doi:10.11743/ogg20080121

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The effects of effective pressure and lithology on Biot's coefficient and rock elastic moduli were analyzed through experimental testing at simulated in-situ conditions(including temperature,and confining pressure) upon 87 samples of sandstone from the Palaeogene formation in Jiyang Sag and by combining with the core thin-section analysis results.It is concluded that Biot's coefficient decreases as effective pressure and calcite cement content grow and increases with the increase of rock porosity,while rock elastic moduli become bigger as the effective pressure gets stronger.A Biot's coefficient model and a relational model between rock elastic moduli and porosity are built.The upper limits of bulk modulus or compressional velocity calculated through the mo-dels are closer to the measurements of samples,proving that the model may yield more logical parameters for oil field development.

Application of spectrum imaging technique to the reservoir prediction of the Caixue Structure

Sheng Qiuhong, Xiao Lanxiong

2008, 29(1):  141-145.  doi:10.11743/ogg20080122

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According to the tuning principle of reflection of thin layer,seismic reflection coming from each thin layer has a corresponding special frequency component in frequency domain,which reveals the thickness of the thin layer.The frequency spectrum imaging technique transforms seismic data into frequency domain by using the time-frequency analysis method of wavelet transform.Amplitude spectrum describes the changes of layer thickness,while phase spectrum shows the lateral continuity of geological body.In reservoirs prediction,attenuation gradient of high frequency energy can be extracted and measured to predict oil-bearing properties of reservoirs.The braided channel sandbodies in the Cretaceous Yuyang Formation are the main oil-bearing stratum in Caixue structure at the south-western edge of Jianghan basin and their optimum response of frequency spectrum is between 25 Hz and 45 Hz.The prediction with spectrum imaging technology shows that favorable oil-bearing zone is located at the east of Caixue structure and is distributed in a NNE direction.Drilling has discovered industrial oil flow,showing a high consistency with the prediction results.

Application of cabazoles,phenols and dibenzothiophenes indexes in hydrocarbon migration research

Zhou Shuqing, Huang Haiping, Xu Xuhui, Zhu Jianhui, Liu Yuming

2008, 29(1):  146-150,156.  doi:10.11743/ogg20080123

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Chemicals,such as Cabazoles,phenols and dibenzothiophenes,in oils and source rocks may serve as ideal tools for hydrocarbon migration researches.Alkylated carbazoles concentration and shield and semi-shield isomersexposed isomers ratios and benzocarbazole [a]/([a]+[c]) ratios are considered perfect indexes for migration.However,the distribution of these chemicals may be affected by input of organic matters,depositional environment,thermal maturity,primary and secondary migration,and biodegradation.For example,different environments may lead to different distribution of carbazoles,and carbazole migration parameters may increase with maturity increasing at low maturity environment but decrease in a highly matured environment,reducing the reliability of these parameters as the indexes of hydrocarbon migration.Alkylated phenols concentration may serve as migration index but it also affected by many other factors such as sedimentary facies,environments,maturity,and biodegradation.The parameters of alkyldibenzothiophenes of cogenetic oil such as 4-/1-MDBT,2,4-/1,4-DMDBT and 4,6-1,4-DMDBT can fit as migration indexes for oils with different maturity,biodegraded oils,and mixed cogenetic oils of two separated charges,thus can serve as excellent tools for migration direction assessment.It is also suggested that many other factors shall be taken into consideration when molecular geochemistry parameters of crude oils and source rocks are used to trace hydrocarbon migration since these parameters are easily affected by changes in maturity,facies and depositional environment in rifted-basins.

Derivation of methods for estimating OGIP and recoverable reserves and recovery ratio of saturated coal-seam gas reservoirs

Chen Yuanqian, Hu Jianguo

2008, 29(1):  151-156.  doi:10.11743/ogg20080124

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Reservoir space in unconventional coal-seam gas reservoirs,also known as coalbed methane reservoirs,consists of the primary matrix porosity system(micropores) and the secondary fracture porosity system(macropores).Some of coal-seam gas are stored in the matrix system in an adsorbed state and the rest are in the fracture system as free gas.For saturated coal-seam gas reservoirs whose initial reservoir pressure equals to the critical desorption pressure,King proposed a material balance equation by using the balance fundamental of gas mole numbers in the process of gas recovery.However,the equation was failed to be put into real practice due to its inherent limitations.Based on King's research,Ahmed proposed a linear relationship formula which may be used to determine the gas-bearing area of constant-volume saturated coal-seam gas reservoirs and has already been employed in practice.By combining the studies of King and Ahmed with the basic fundamental of gas reservoir engineering,the article presents a new linear relationship formula that may be to used to determine adsorption gas in-place and free gas in-place simultaneously.In addition,methods for determination of recoverable reserves and recovery ratio are also proposed.The practicability and effectiveness of these methods have been testified during their application.