Table of Content

25 February 2007, Volume 28 Issue 1

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Innovation of petroleum geology in China

Li Desheng

2007, 28(1):  1-11.  doi:10.11743/ogg20070101

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Since the foundation of People's Republic of China in 1949,several generations of petroleum man have generously exerted their efforts on the development of Chinese petroleum industry and have successfully re-sharpened China into one of the major oil producing countries in the world.Despite the fact that new issues have never stopped showing up during the exploration of oil and gas in China,the petroleum theories have been renewed and enriched through addressing these challenges.The theories are mainly concerning: 1) formation and accumulation pattern of continental oil and gas reservoirs;2)distribution pattern of composite hydrocarbon accumulation belts(zones);3)exploration and development of low and ultra-low permeability reservoirs;4)buried hill hydrocarbon reservoirs;5)research and exploration of coal-drived hydrocarbon;6)exploration of the Palaeozoic marine reservoir;and 7)thrust belt exploration of foreland basins.Under the current circumstance of unstable energy supply and sharply increasing demand,Chinese petroleum geoscientists will continue playing important role in the discovery of onshore and offshore oil/gas fields,especially the large and giant ones,and contri-bute more to a sustainable development of Chinese petroleum industry and innovation of petroleum geological theories.

Geochemical characteristics and genesis of nitrogen in natural gas from Tarim Basin

Liu Quanyou, Dai Jinxing, Liu Wenhui, Qin Shengfei, Zhang Dianwei

2007, 28(1):  12-17.  doi:10.11743/ogg20070102

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Statistical measurements of 103 gas samples from the Tarim Basin indicate that the oil-type gas and the coal-derived gas dominate the basin and that the former contains much more nitrogen than that of the latter.The gas with abnormal high concentration of nitrogen(more than 20%) occurs in the Paleozoic gas reservoirs of Tazhong,Donghetang,and Hade regions,and the Mesozoic gas reservoirs of Lunnan region(in the Paleozoic craton area).The gas with the lowest N₂ content(N₂<5%) are mainly coal-derived and are distributed in the Cenozoic strata of the basin and the Mesozoic strata of southwestern Tarim and Kuqa depressions.In the Tabei area,the N2 contents in natural gas are considerably varied.Gases with low nitrogen concentration are mostly coal-derived;while those with high nitrogen concentration are often oil-type gas,in which the origins and contents of nitrogen are changed with the different thermal stages of sapropelic source rocks.The nitrogen molecular in Yakela gas may be explained by the mixture of organic nitrogen formed by sapropel-type kerogen during over-mature stages and a little amount of inorganic nitrogen derived from deep crust.

Analysis on reservoir characteristics of Qaidam Basin and its significance to petroleum exploration

Li Weilian, Liu Zhen, Xu Zhangyou, Wu Xinsong

2007, 28(1):  18-24,34.  doi:10.11743/ogg20070103

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Six features of the reservoirs in Qaidam Basin is summarized through a detailed analysis of its 19 oil/gas pools: ① oil layers are thin and oil/gas-bearing area is relatively small;② reservoir petrophysical properties are rather poor;③ Tertiary oil maturity is relatively low as a whole;④ pool types can involve structural,stratigraphic or lithological ones or a combination of them;⑤ the distribution of oil and gas pools is controlled by faults and fault reservoirs are dominant;and ⑥ late destruction of oil/gas pools is more severe.By systematic study of all these characteristics,the writers further point out that ① small and middle-sized oil fields is scattered in the basin,but larger ones are rarely found;② hydrocarbon accumulations are mainly distributed in the palaeo-structural traps near oil-generating center(source rocks);③ while continuously strengthening the exploration of structural oil and gas pools,the searching for stratigraphic and lithological oil and gas pools should also be stressed,and ④ the role of faults in the formation and distribution of oil and gas pools should be further stu-died.

Comparative study of free hydrocarbons in pores with inclusion hydrocarbons and oil-source rock correlation for Silurian sandstone in Tazhong area

Zhu Dongya, Jin Zhijun, Hu Wenxuan, Zhang Xuefeng, Yao Suping

2007, 28(1):  25-34.  doi:10.11743/ogg20070104

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Pore free hydrocarbons and inclusion hydrocarbons in 6 Silurian bituminous sandstone samples from the Tazhong area of Tarim basin are separated and analyzed with GC and GC-MS.The analysis results show that pore free hydrocarbons and inclusion hydrocarbons have different characteristics.The pore free hydrocarbons are represented by light hydrocarbons of pre-peak distribution and peak carbon number at nC₁₆ or nC₂₀,without odd carbon number predominance,which are usually associatee with significant biodegradation.The inclusion hydrocarbons are represented by heavy hydrocarbons of bimodal distribution and peak carbon number at nC₂₅ or nC₂₉,with odd carbon number predominance.In respect of biomarker,the pore free hydrocarbons have a relatively high concentration of tricyclic terpanes and pregnane,with the C₂₇,C₂₈ and C₂₉ steranes of asymmetrical "V" distribution;whereas the inclusion hydrocarbons have a relatively low concentrations of tricyclic terpanes and pregnane,with the C₂₇,C₂₈ and C₂₉ steranes of oblique-ascending distribution.Oil-source correlation indicates that the hydrocarbons entrapped in the inclusions of bituminous sandstone might be sourced from the Middle-Lower Cambrian source rocks,while the pore free hydrocarbons might be generated by the Middle-Upper Ordovician source rocks.

Tectonic evolution of Subei-South Nanhuanghai superimposed basin from the Late Mesozoic to the Cenozoic and marine petroleum potential

Ma Liqiao, Chen Hanlin, Dong Yong, Xia Jiufeng, Sun Fengxia, Yang Lanying

2007, 28(1):  35-42.  doi:10.11743/ogg20070105

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Based on comprehensive study on tectonic stress field,structural feature,and sedimentary formation,the tectonic evolution of Subei-South Nanhuanghai(North Jiangsu-Southern South Yellow Sea) superimposed basin since the late Triassic plate collision between the Huanan plate and Huabei plate can be divided into the following four stages: ① the foreland basin development stage under the influence of the late Triassic to Middle Jurassic paleo-Tethyan closing;② the thrust nappe development stage controlled by the Late Jurassic-Early Cretaceous oblique subduction of Izanagi oceanic plate;③ the basin extension development stage under the in-fluence of the late Cretaceous-Paleogene subduction of the Pacific plate,including the late Cretaceous depression development stage and Paleogene fault depression basin development stage;④ the depression development stage under the influence of Neogene Himalaya orogenesis.In relation to the development of the Paleogene half-graben-like fault depression,this paper focuses on the controlling effects of the left-lateral strike-slip and pul-lingapart movement along with the NWW basement faults and of the NE thrust nappe over the development of the basin and half graben-like fault depression,and points out the exploration prospect of marine petroleum system from the aspect of sedimentation,reworking,and preservation.

Analysis on main formation mechanisms of abnormal fluid pressure in the Upper Triassic,West Sichuan area

Wang Zhenliang, Li Yaohua, Zhang Jian

2007, 28(1):  43-50.  doi:10.11743/ogg20070106

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The overpressured gas reservoirs are common in the Upper Triassic strata,Western Sichuan basin.On the basis of the distribution of measured reservoir pressures in the Western Sichuan basin,the effects of uncompaction,hydrocarbon generation, and tectonic compression on the formation of abnormal pressure are analyzed.The analysis indicates that the Upper Triassic sedimentation and lithologic association are conductive to the formation of compaction.The evidence from compaction curves also indicates that the undercompaction since the end of Jurassic has caused a highly abnormal pressure and its effect still exists in the Upper Triassic strata.Owing to the low permeability in the Xujiahe Formation,the rapid buildup of reservoir pressure is most likely interpreted to be caused by hydrocarbon generation,especially the generation of larger amount of gas.The actual pressure increment depends on such factors as the duration of pressure increase caused by undercompaction and the closing degree of fluid system.In the areas with rapid tectonic stress relief,the tectonic compression is unlikely to induce fluid pressure buildup.In the areas with slow tectonic stress relief,the fluid within the closed system bears most of overburden load;the abnormal pressure caused by tectonic compression accounts for 80～100% of measured pressure data.The pressure increase by tectonic compression occurred mainly during the period of Himalaya orogeny.

Seismic facies of the Cretaceous Abu Gabra Formation in Fula Depression,Muglad Basin,Sudan

Li Dejiang, Zhu Xiaomin, Yang Junsheng

2007, 28(1):  51-58.  doi:10.11743/ogg20070107

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The Cretaceous Gabra Formation in the Fula Depression,Muglad basin,Sudan,can be classified into seven three-order sequences.Based on the seismic reflection parameters,internal reflection configuration and external shape,five types of seismic facies are identified on the seismic reflection profiles of the Abu Gabra Formation.They are chaotic facies,paralleling and sub-paralleling sheet facies,foreset wedge facies,foreset(wedge)-filling faceis,and onlap-filling faceis.These facies may be further subdivided into nine classes in terms of their amplitudes and continuities,i.e.(1)parallel sheet facies with strong amplitude and high continuity,(2)parallel sheet facies with medium-strong amplitude and moderate-high continuity(3)sub-parallel sheet facies with me-dium amplitude and moderate-poor continuity,(4)sub-parallel sheet facies with medium amplitude and moderate-high continuity,(5)wedge-filling facies with medium-strong amplitude and moderate continuity,(6)wedge-fil-ling facies with medium amplitude and moderate-poor continuity,(7)onlap-filling facies with medium amplitude and moderate-poor continuity,(8)foreset-wedge facies with medium amplitude and moderate continuity,and(9)chaotic facies with medium amplitude and poor continuity.These seismic facies distinguish from one another ho-rizontally but show hereditability and differentiation over vertical sections.The spacial distribution of the seismic facies corresponds well with the structure and tectonic evolution of Fula depression.

Parasequence of fluvial deposit:a case study of the Xujiahe Formation in Central Sichuan

Gao Zhiyong, Han Guomeng, Zhang Lihua

2007, 28(1):  59-68.  doi:10.11743/ogg20070108

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Based on a detailed analysis of the dynamics characteristics of meandering stream and braided river deposits,3 parasequence models of fluvial deposit are preliminarily recognized in the Xujiahe Formation in central Sichuan basin.Two parasequences,i.e.the graded fining-upward parasequence and the graded coarsening-upward parasequence,occur in meandering river deposits.The graded fining-upward parasequence represents a water shallowing-upward facies sequence combination of subaqueous fluvial channel(lag deposits),marginal bank,natural levee and flood plain deposits.Whereas the graded coarsening-upward parasequences represents a facies sequence combination of alternative flood plain-crevasse-splay deposits.The braided river parasequence mostly appear as a graded fining-upward and water shallowing-upward parasequence of facies sequence combination of subaqueous fluvial channel(lag deposits),channel bar and overbank deposits,while the graded coarsening-upward braided river parasequences are not developed.The fluvial parasequence boundary is the erosional surface at the bottom of channel sandbodies and also is the onshore equivalent interface of the lake water or sea water flooding surface on the parasequence boundaries in lake/marine basins.However,it is more similar with the parasequence boundary of transgressive lag deposits rather than dark mudstone.In the graded coarsening-upward flood plain,crevasse splay or channel deposits,the parasequence boundary is the interface between exposed mudstone and upper dark flood mudstone.Based on the proposed fluvial parasequence models,the vertical supe-rimposition pattern of fluvial parasequence and its time-space evolution are analyzed,and the heterogeneity of fluvial parasequence are studied for the Upper Triassic Xujiahe Formation in central Sichuan basin.

Sequence boundary types and logging identification of Donghe sandstone in HD4 oilfield,Tarim Basin

Jiao Cuihua, Wang Haigeng, Niu Yujie, Chang Lunjie, Xu Huaimin, Liu Taixun, Liu Xiaobing

2007, 28(1):  69-76.  doi:10.11743/ogg20070109

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Five types of sequence boundaries within the third-order sequence of Donghe sandstone in Tarim Basin are recognized through the detailed analysis of outcrop and core data:the third-order sequence boundary,parasequence group boundary,parasequence boundary,stratum group boundary,and stratum boundary.Based on the response characters of conventional logging and dip logging through sequence boundaries,the standards and methods of sequence boundary identification using logging data are proposed,including the identification model of conventional logging data,the identification model of dip data with long window-length processing,the identification model of original dip-logging conductivity curves,the identification model of precise dip-processing data,etc.By applying the above-mentioned models to the multi-sequence boundary identification and correlation in all wells of the oilfield,five orders of sequence boundaries are identified,and one third-order sequence,one parasequence group(sandbody group),twelve stratum groups(substratum zone) and fifty stratum(single sandbody) are recognized.As a result,the high-resolution sequence stratigraphic framework of Donghe sandstone is established.

Logging curve changing characteristics of different reservoir development phases——a case study of Shaer 1～2 layer in Shenger block,Shengtuo oilfield

Zhao Hongbing

2007, 28(1):  77-82.  doi:10.11743/ogg20070110

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The Shaer 1² reservoir in Shenger block,Shengtuo oilfield,has experienced fourty-two years of high-efficient waterflooding development,resulting in a relevant variation of well log that reflects and records the reservoir characteristics.A study based on couplet-well theory is carried out by superimposing correlation techniques of reservoir parameters from new and old wells and by core calibrating logging method.The result indicates that,after a long time of production in the Shaer 1² reservoir,the resistivity logging curves represent two variation patterns with water injection:1) continuously decreasing or 2)decreasing first and increasing afterwards.The acoustic time log has a tendency of sustained increase;the SP curve shows wandering base line and narrow amplitude difference in different development stages,and the micro-electric log displays relatively small amplitude and amplitude differences.

Characteristics and development experiences of Fula N structural-hydrodynamic oil pool in Muglad Basin,Sudan

Wang Wangquan, Fan Tailiang, Cheng Zhongliang, Li Guocheng, Nie Changmou

2007, 28(1):  83-87.  doi:10.11743/ogg20070111

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Located in the south of central transitional zone of the Fula sub-basin,northeastern Muglad Basin,Sudan,the Fula N is a structural-hydrodynamic heavy oil pool with shallow burial depth,loosely cemented reservoir,high porosity and permeability,and active bottom water.These features make the CHOPS(cold heavy oil production with sand) a suitable technology for the development of the pool.Matching technologies,such as completion with bigger size casing and long sand pocket and protection of interbedded shale in thick oil layer during perforation,are adopted,achieving an average daily production of more than 100 m³ from single well.In wells with severe sand problem,the production technology known as "limited sand control" is used to reduce the ope-ration cycle and cost,and enhance the economic returns.

Gas single-phase percolation characteristics of overpressured gas reservoir in Penglaizhen Formation,Xinchang gas field

Zheng Xiangke, He Shunli, Wang Xibin, Li Yuanqin

2007, 28(1):  88-91.  doi:10.11743/ogg20070112

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Based on the conventional core experiments and pressure-sensitive features of gas reservoirs,it is suggested that the "slip flow of gas" and "threshold pressure" may be caused by pressure sensitivity of gas reservoir.This paper takes the overpressured tight gas reservoir in the shallow Upper Jurassic Penglaizhen Formation,Xinchang gas field,Sichuan province,as a research object,analyses the data collected from gas single-phase percolation experiments on its rock samples,and discusses the causes of the sophisticated percolation process with the coexistence of "slip flow of gas" phenomena and "threshold pressure" features.It proposes that the percolation process be induced by pressure sensitivity rather than by traditional Klinkenberg effect or low rate non-Darcy mechanism.The experiments also indicate that the Penglaizhen gas reservoirs in Xinchang gas field shows strong pressure sensitivity,and its fitting factor ranging between 0.3 to 1.9 and permeability reduction magnitude varying from 10% to 80%.

Integrated 2D seismic interpretation and trap evaluation on the western block of Mahuang Mountain

Tan Junmin, Liu Lifeng, Xu Yunshu, Yu Wenqin, Guo Qingpeng

2007, 28(1):  92-99.  doi:10.11743/ogg20070113

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By using the Ricker wavelet of positive and negative frequencies in 2D seismic data,the calibration of accurate composite seismic traces and structural interpretation are conducted on three marker beds at the bottom of Jurassic Zhiluo Formation(T₄)in 14 wells.The results show that reverse faults are developed in the western fractural area of the block;four main faults that extend from north to south are sheared by two E-W adjusting faults in the middle;the trap types are mainly faulted anticline,faulted nose,and faulted block.In its eastern part,strata are gentle and faults are not developed;trap type are mainly low-amplitude anticlines.Through the establishment and analyses of the accurate velocity field under the complicated surface conditions,the precision of structural maps of T₄,T₅,and T₆,is greatly enhanced.The proposals concerning the exploration strategy in the block are also put forward based on comprehensive evaluation.

3D coherence technique in fault system interpretation and reservoir prediction

She Deping, Cao Hui, Guo Quanshi

2007, 28(1):  100-105.  doi:10.11743/ogg20070114

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3D coherence technique can be used to determine the horizontal heterogeneity of strata and lithology by capturing the signal coherency of adjacent seismic channels among the data volume of 3D seismics.The technique has the following features: ① it is based on tectonic characteristics of acquisition areas and can automatically detect the fault systems,thus yielding more objective interpretations by avoiding the dependence on workers' experiences of conventional structural interpretation;② numbers of coherent track,size of time window,and selection of delay parameters,are of vital importance for the interpretation quality of the technique;③ it can be used in the description of horizontal heterogeneity of reservoirs and determination of the boundary of special geologic anomalous bodies,such as karst topography,channel sand,sand bank,and etc.;④ by utilizing the rapid processing speed of computers,it enhances the interpretation efficiency and reduces the exploration cycle.

Prediction of reservoir permeability with improved artificial neural network principle:taking the Southwest Weizhou Depression in Beibuwan Basin as an example

Shan Jingfu, Ji Youliang, Liu Chengzhi

2007, 28(1):  106-109,115.  doi:10.11743/ogg20070115

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Computational method of artificial neural network is a non-linear processing system,which predicts reservoir physical property with logging data.In previous calculation of permeability with genetic algorithm,only single data points were used and no data of the neighboring horizons were involved in the training,thus the accuracy and reliability of the prediction model were limited.In order to solve this problem,the data points of several neighboring horizons are used for training and a prediction model of reservoir permeability is built.Based on the normalization of core test data and relevant logging data,reservoir permeability is calculated point-by-point with the improved windowing technique and feedback neural network method.Its application to petroleum exploration in Southwest Weizhou depression of Beibuwan basin shows that the predicted and measured permeability coincides well.

Pore structure study of low porosity and permeability reservoirs in MHM oilfield of Ordos Basin with fractal theory

Zhang Chenkai, Shen Jinsong, Fan Zhen

2007, 28(1):  110-115.  doi:10.11743/ogg20070116

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Fractal features of pore structure are studied by using analytic data of capillary pressure of core samples.The fitting relationship between the volume percentage(S)of pores with pore diameter smaller than a given value(r)and the pore diameter(r)is used to calculate the fractal dimension of pore structure of the low porosity and permeability reservoirs in the Triassic Yanchang Formation and Jurassic Yan'an Formation of MHM oilfield,Ordos basin.The capillary pressure curves of both formations have a scale interval,in which pore structure shows fractal features.The macropore and micropore intervals of same core sample show multi-fractal features.For the 10th member of Yan'an Formation(Yan 10 reservoir),the fractal dimension of pore structure in macropore interval is larger than that in micropore interval,while for the 6th member of Yanchang Formation(Chang 6 reservoir),the distribution of fractal dimension is just the opposite.In macropore interval,the fractal dimension of Yan 10 reservoirs is smaller than that in Chang 6 reservoirs,indicating that the pore structure of the latter is more complex than that of the former.Fractal dimension of pore structure,in conjunction with the other pore characteristic parameters,can well reflect the complexity of microscopic pore structure.It provides a convenient and effective method for study on the microscopic heterogeneity of reservoir pore structure,and a solid basis for further reservoir evaluation.

Prediction of gas distribution with frequency attenuation attribute in TNB area

Bi Yanbin, Long Shengxiang, Guo Tonglou, Bao Zhidong, Liu Bin, Ma Dianren

2007, 28(1):  116-120.  doi:10.11743/ogg20070117

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The 2^nd member of the Lower Triassic Jialingjiang Formation and the 3^rd member of the Lower Triassic Feixianguan Formation are the main gas-producing zones in TNB area,with the characteristics of deeper burial depth and thinner reservoir thickness.Although the major discoveries have been made in this area,the prediction of gas distribution remains the key factor for better exploration achievements.The spectral analysis based on wavelet transform,however,can be used effectively in gas distribution prediction.In connection with the reservoir characteristics of target area,the feasibility of gas distribution forecasting by frequency attenuation attribute is addressed by the comparison of gas logging data(total hydrocarbon detection) with frequency attenuation attribute,the reservoir forward modeling,and the interwell section examination of gas distribution.Their results indicate that different gas-bearing characteristics are exhibited horizontally and vertically in the 2^nd member of Jialingjiang Formation and the 3^rd member of Feixianguan Formation. The T₁j² gas reservoir(sand beach reservoir)is characterized by single gas reservoir with a larger pool area,while the T₁j³ Formation(oolitic beach re-servoir) is the multiple and vertically superimposed gas reservoirs with a relatively smaller pool area.

Residual basin of passive continental margin—a neglected basin type

Zhao Xikui, Yong Ziquan, Li Guorong, Zhang Xiaobing, Deng Guangjun, Li Kun

2007, 28(1):  121-128.  doi:10.11743/ogg20070118

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One type of basin known as "residual basin of passive continental margin" has been overlooked in all basin classifications.It is usually formed in mid-oceanic ridge and was subducted under active continental margin with plate convergence.However,its basic features of passive continental margin remain unchanged except that normal faulting is rather intensive due to surface tension caused by flexing of the subducted plates.The "Qinfang trough" and "Shiwandashan basin" in Guangxi province was not a unified ancient continent block with the Cathaysia in Eopaleozoic.Therefore,when Wuyi and Mintai mini-blocks attached to South China ancient plate,the "Qinfang trough" was in the evolution stage of the "residual basin of passive continental margin".Later,it evolved successively into a remnant ocean basin in Early Devonian,a Tethyan passive continental margin basin in Neopaleozoic,a foreland basin in early Late Permian,a foreland basin in Mesozoic,and a strike-slip fault basin in Cenozoic.