Table of Content

25 February 2009, Volume 30 Issue 1

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Status,problems and proposals of the quantitative modeling techniques for hydrocarbon migration and accumulation

Shi Guangren

2009, 30(1):  1-10.  doi:10.11743/ogg20090101

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After a brief discussion of the development and application of quantitative modeling techniques for primary migration(hydrocarbon expulsion),and this paper focuses on the study of modeling techniques in se-condary migration(hydrocarbon migration-accumulation).For primary migration,it is proposed to adopt simplified but less-debated methods for hydrocarbon expulsion calculation and verify their validity through comparing modeling results of secondary migration with real exploration data.As for secondary migration,at present there are four quantitative modeling techniques available:multi-phase Darcy flow,flowpath,hybrid method(multi-phase Darcy flow+flowpath),and invasion percolation.Though great improvements have been made in these four techniques in the past 10 years,their particular disadvantages have not been by and large overcome.Their disadvantages include(1) though the multi-phase Darcy flow has excellent ability to model various times,it cannot generally be effectively applied due to limited computer resources;(2) both flowpath and invasion percolation are basically unable to model different geologic times,i.e.,usually the modeled object is only the present-day(0 Ma) geologic body,while the modeling of other geologic times(≠0 Ma) is still under research;(3) since the practical value of the hybrid method results mostly from the flowpath method,strictly speaking the hybrid method also basically has no ability to model different geologic times.Herein summarizes the background,method and application of each technique,expounds the advantages,disadvantages,and applicability of each method,and proposes a plan for their future modification and development.The paper recommends a comprehensive scheme utilizing quantitative modeling techniques with the ability to model various geologic times.It uses single-phase(water) Darcy flow for calculating overpressure in full space-time.The flowpath modeling is adop-ted when the data is sparse and invasion percolation is employed when the data is dense.

Two pooling patterns of superimposed reservoirs in Sebei-1 gas field,the eastern Qaidam Basin

Cheng Fuqi, Jin Qiang, Zhou Tingquan, Zhang Shuichang, Ma Fengliang

2009, 30(1):  11-16,25.  doi:10.11743/ogg20090102

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The Sebei-1 field consists of seven vertically superimposed gas reservoirs with various biogas enrichments.These reservoirs are divided into high-enrichment reservoirs(HER) and low-enrichment reservoirs(LER) based on such data as reserves per unit volume,abundance of gas reserves,and flow rate tested.The pooling conditions for these two types of reservoirs are compared and analyzed.The results are used to define the controlling factors for the biogas enrichment in the field.The lower four deeper reservoirs with burial depth greater than 950 meters are the HER type,while the upper three shallow ones belong to the LER type.The former ones are favorable for gas pooling and enrichment as they are located in the central of a gas-generation zone with biogas charging both from the local area and central depression,and apart from that,they also have favorable re-servoir-seal assemblage,trapping and preservation conditions.In contrast,the later ones are unfavorable for gas pooling and enrichment as the source rocks have not reached peak gas generation,the biogas are mainly sourced from the lower gas reservoirs through diffusion,and the preservation conditions are relatively poor.Based on the analysis of pooling conditions,the paper suggests that the pooling patterns for the HER and LER reservoirs be described as source-charged and dispersion-charged respectively.

Reconstruction of the paleo-fluid potential field of Es³ in the Dongying Sag of the Jiyang Depression with systematic fluid inclusion analysis

Cai Limei, Chen Honghan, Li Chunquan, Li Zhaoqi, Liu Huimin, Hao Xuefeng

2009, 30(1):  17-25.  doi:10.11743/ogg20090103

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Based on the analyses of 376 samples of fluid inclusions from the middle Es³ in the Dongying sag,hydrocarbon charging in the study area was divided into three different stages with exact time.The evolution of paleo-formation pressure during these three charging stages was obtained through PVT thermodynamic modeling of the fluid inclusions.The results in combination with the plane and sectional views of current pressure distribution reveal that the hydrocarbon reservoirs in Es³ belong to the same pressure system.The evolution of paleo-fluid potential fields in Es³ during these three stages were reconstructed with the parameters obtained from fluid inclusion analysis and their distribution features were analyzed.The favorable areas for hydrocarbon accumulation during these three periods of hydrocarbon charging were discussed.It is believed that the reservoir distribution in the Dongying sag was closely related to the evolution of paleo-fluid potential,and the thresholds of paleo-fluid potential controlling hydrocarbon accumulation in these three charging periods were 7 kJ/kg,10.5 kJ/kg and 22 kJ/kg respectively.The northern slope of the Lijin subsag and the southern slope of the Niuzhuang subsag were the favorable areas for hydrocarbon accumulation during the first period of hydrocarbon charging;the surrounding areas of the Lijin and the Niuzhuang subsags(high oil potential centrers) were the favorable areas during the second period of hydrocarbon charging;while the surrounding areas of the Minfeng and the Boxing subsags were the favorable areas during the third period of hydrocarbon charging.

Oblique compressional structures and hydrocarbon distribution patterns in the northwestern margin of the Junggar Basin

Yang Geng, Wang Xiaobo, Li Benliang, Shi Xin, Li Xuan, Guan Shuiwei

2009, 30(1):  26-32.  doi:10.11743/ogg20090104

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Data gathered from field survey,geological interpretation of satellite remote sensing images,and the reinterpretation of crustal magnetotelluric measurement data and comprehensive analysis of seismic data of the northwestern margin of Junggar Basin,indicate that the oblique compressional structuress in the study area is consisted of the Dalabute sinistral strike-slip fault,overthrust nappe in the northwestern margin,and NW-trending dextral transverse strike-slip faults.The sinistral strike-slipping of the Dalabute boundary fault controlled the development of the latter two structures,and the area between the two structures is considered to be the key zone for oil and gas accumulations in the northwestern margin of Junggar Basin.

Sedimentary features of the Dongying Formation in Chengdao area and their geological significance

Wu Guanghua, Wang Hongliang, Lin Huixi, Wang Shenghao, Gao Xiaopeng

2009, 30(1):  33-40.  doi:10.11743/ogg20090105

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The exploration focus in the Dongying Formation of Chengdao area,the Bohai Bay Basin is stratigraphic-lithologic reservoirs,to which the key is a correct understanding of deposition characteristics of reservoir sandbody.A comprehensive analysis of core,drilling/logging,and seismic data of the area,confirms the existence of sedimentary systems such as deeper lake-turbidite fan,fan delta-slump turbidite fan,braided delta,low-sinuosity stream-flood plain,and etc,and provides insights into the composition and features of these sedimentary facies.The results indicate that palaeogeomorphic characteristics before the deposition of the Dongying Formation show a strong controlling effect upon the deposition of the lower Dongying Formation.Based on sedimentary facies analysis within the sequence stratigraphic framework,the paper discusses the spatial distribution of these sedimentary facies and the petroleum geologic significances of the study on sedimentary features in such aspects as the types and distribution of reservoir sandbody,favorable strata,characteristics of spatial distribution,and so on.

Control effects of carrier systems on hydrocarbon pooling in the He-31 block of Xianhezhuang oilfield,the Dongying Sag of the Bohai Bay Basin

Liu Hua, Ren Jinglun, Jiang Youlu

2009, 30(1):  41-46.  doi:10.11743/ogg20090106

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The characteristics of carrier system and its relationship with the distribution of middle-shallow hydrocarbon pools in the He-31 block of the Xianhe oilfield in the Dongying Sag show that faults and sandbodies dominate the hydrocarbon carrier system in the block.The distribution of sandbodies and faults is not the only factor that control hydrocarbon enrichment in the study area.The spatial and temporal configurations of faults and sandbodies also control the effectiveness of carrier system,thus determine the formation and occurrence of the oil reservoirs in the middle-shallow layers(especially the Es¹).The second-order faults and later induced faults are important to hydrocarbon migration.At the same time,the sandbodies well connected with these faults are the main destination of hydrocarbon migration.

Micropores from devitrification in volcanic rocks and their contribution to reservoirs

Zhao Hailing, Huang Wei, Wang Cheng, Di Yongjun, Qi Jingshun, Xiao Yong, Liu Jie

2009, 30(1):  47-52,58.  doi:10.11743/ogg20090107

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Petrography studies show that devitrification in volcanic rocks can produce a considerable number of micropores.The micropores observed in volcanic rocks are a complex of micropores from devitrification and that from interaction of minerals with fluids.In pyromerides and ignimbrites,micropores from devitrification are the second largest pore type after the vesicle,accounting for 20%and 30%of the total of all pore types in pyromerides and ignimbrites respectively.While in tuff,they are the predominant pore type and account for about 70%of the total pore spaces.The principles and methods of mass balance and the physical processes of devitrification can be used to estimate the micropores generated by devitrification of glass in pyromeride,ignimbrite and tuff.Calculation with the thermodynamical theories and methods of fluid-rock interaction shows that feldspar dissolution at least can produce pores of 20 cm³/mol.

Pore-preserving mechanism of chlorite rims in tight sandstone—an example from the T₃x Formation of Baojie area in the transitional zone from the central to southern Sichuan Basin

Liu Jinku, Peng Jun, Liu Jianjun, Wang Yan, Liu Jianfeng

2009, 30(1):  53-58.  doi:10.11743/ogg20090108

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The occurrence,forming conditions,and pore-preserving mechanism of chlorite rims in the Upper Triassic Xuejiahe Formation of Baojie area from central to southern Sichuan basin were studied in detail by means of thin section analysis and SEM analysis.The result shows that chlorite rims grew vertically on the grain surface and took the shape of isopachous grain-coating.This kind of cement was formed during the early diagenetic stage and was controlled mainly by depositional environment and provenance conditions.The presence of chlorite rims enhanced the compaction resistance of rock,inhibited quartz overgrowth on detrital-quartz grains,accelerated dissolution and formed excellent pore-throat configuration.Therefore,the chlorite rims played an important role in the preservation of residual primary pores in the tight sandstone reservoirs in the study area.

Relation between the evolution of temperature field of intrusions and the development of carbonate reservoirs in Tazhong-Bachu area,the Tarim Basin

Nie Baofeng, Yu Bingsong, Liu Yongshun, Xu Zheping, Yang Xiaofa, Yang Yongheng

2009, 30(1):  59-67,73.  doi:10.11743/ogg20090109

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Through microscopic identification,geochemical analysis and numerical simulation of the intrusions penetrated in the Tazhong-Bachu area,the paper discusses their thermal effect and influences upon the development of carbonate reservoirs.The study indicates that the layered intrusions in the carbonate reservoirs in the area are mainly of hypersthene gabbro and dolerite.The former has labradorite and hyperite as the host minerals and apatite as the accessory mineral,while the later has a host mineral assemblage consisting mainly of clinopyroxene and basic plagioclase.Geochemical analysis shows that the gabbro from Well He-3 and He-4 belongs to alkaline series,with w(SiO₂)of 44.58%-45.39%,w(K₂O+Na₂O) of 3.91%-4.67%,and w(Na₂O)/w(K₂O) of 2.16%-4.23%.Its partitioning pattern of REE is of LREE enrichment type,with LaN/YbN ranging from 5.010 to 5.980,and δEu from 0.910 to 1.002,with very weak or even no negative Eu anomaly.The equation of heat conduction was used to calculate temperature profiles adjacent to the thin layered intrusions during the cooling processes.The result points out that these intrusions have limited range of thermal effect,which is closely related to the thickness of intrusions:the thicker,the bigger.

Geochemical behaviors of gases from inclusions in high-CO₂ reservoirs,the Songliao Basin

Mi Jingkui, Zhang Shuichang, Wang Xiaomei, Tao Shizhen

2009, 30(1):  68-73.  doi:10.11743/ogg20090110

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Study on inclusions and geochemical behaviors of gases from these inclusions in high-CO₂ reservoirs in the Songliao Basin shows that CO₂ inclusions are underdeveloped in the reservoirs and the geochemical behaviors of CO₂ from inclusions differ greatly with that from the reservoirs.The CO₂ from inclusions is of organic origin,while that from the reservoirs is of inorganic origin.However,the isotopic characteristics of hydrocarbon gases from gas pools and inclusions show certain consistency.The reasons behind all these include that the mantle-derived CO₂ charged too quickly to allow the growth of inclusions and that the reservoir rock was saturated by hydrocarbon gases before CO₂ charging,forming geological settings unfavorable for inclusion growth due to lack of water needed.Based on the geological settings of the Songliao Basin,it is suggested that CO₂ charging happened later than hydrocarbon gas charging.

Sedimentary organic facies of the Triassic Yanchang Formation in the Ordos Basin

Yao Suping, Zhang Ke, Hu Wenxuan, Fang Hongfeng, Jiao Kun

2009, 30(1):  74-84,89.  doi:10.11743/ogg20090111

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Coal and hydrocarbon source rocks in the Triassic Yanchang Formation in the Ordos Basin were stu-died to identify their sedimentary organic facies by combining the basic organic rock compositions of sedimentary organic facies with the sedimentary faices and the organic geochemical characteristics of enriched or dispersed organic matters in the Yanchang Formation.The result indicates that there are six types of organic facies:the terrestrial forest(bog) organic facies(A),the swamp forest(bog) organic facies(B),the swamp-marsh forest(bog) organic facies(C),the marsh(bog) organic facies(D),the allochthonous residual(float bog) organic facies(E),and the open lake algae organic faces(F).Among them,A and B generate coal,F generates hydrocarbons,while C,D and E generate both hydrocarbon and coal.The hydrocarbon generating potential of each organic facies was analyzed through Rock-Eval experiments.It is suggested that the study on sedimentary organic facies is a useful method in evaluating the paragenesis of various types of combustible organic minerals,including coal,oil,gas,and oil shale.A comprehensive evaluation of the hydrocarbon-generation trends and convertion ability of the coal and hydrocarbon source rocks in the Yanchang Formation was also carried out by adopting knowledge concerning the organic sedimentary facies

Origin of natural gas in Mingfeng area,the Jiyang Depression

Hu Xiaoqing, Jin Qiang, Wang Xiuhong, Lin Lamei, Wang Li, Wang Juan, Wang Tingting

2009, 30(1):  85-89.  doi:10.11743/ogg20090112

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It is controversial about the origin of the natural gas in Minfeng area.A set of indexes for differentiating kerogen-pyrolysis gas and oil-cracked gas is presented based on geologic analysis and thermal simulation experiments on source rocks and crude oil samples from the Es⁴.In mature phase,the kerogen-pyrolysis gas features in rapid generation of methane and low contents of cyclane and benzene.While in high mature phase,both kerogen-pyrogenic gas and oil-cracked gas are characterized by high contents of cyclane and benzene.The condensate oil and natural gas in Mingfeng area show a larger scope of ln(C₁/C₂) ranging from 2 to 6 than that of ln(C₂/C₃) varing from 1 to 1.5 and have relatively high contents of cyclane,isoalkane and aromatic hydrocarbon,revealing the characteristics of kerogen-pyrolysis gas in high mature phase.Therefore,it is believed that the natural gas in Minfeng area is of kerogen-pyrolysis gas.

A study on genetic types and source discrimination of natural gas in the north margin of the Qaidam Basin

Song Chengpeng, Zhang Xiaobao, Wang Liqun, Xu Ziyuan, Ma Lixie

2009, 30(1):  90-96.  doi:10.11743/ogg20090113

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Based on the analyses of chemical components and carbon isotopic composition of 35 natural gas samples from the Tertiary and Cretaceous reservoirs in 9 fields or trap structures in the northern edge of Qaidam Basin,we defined indexes for identifing genetic types of gas,determined the thermal evolutionary stages,and identified the sources of natural gases.The result shows that the natural gases in the north margin of Qaidam Basin can be divided into three genetic types:coal-type,oil-type,and hybrid-type.Some of the gas samples from Yikeyawuru,Nanbaxian,Lenghu-5,Eboliang and Mabei are of coal-type gas;several gas samples from Mabei and Lenghu-3,Lenghu-4 and Lenghu-5 are of oil-type,and some gas samples from Hulushan and Mabei are of hybrid-type.Samples of coal-type from Yikeyawuru,Nanbaxian,Lenghu-5,and Eboliang,are mostly at high maturation stage;those of oil-type from Lenghu-3 and Lenghu-4 are mostly at maturation stage,those from Hulushan are at over-mature stage,while samples from Mabei have highly-varying maturities.Gases in Lenghu-3,-4,and-5,Eboliang,and Hulushan,were mainly sourced from the Kunteyi depression,among which gas in Lenghu-3 was generated by sapropel organic matter and those from Lenghu-4 and-5,Eboliang,and Hulushan,were sourced from humic organic material.Gases in Nanbaxian were derived from humic organic material in the Yibei depression;and those in Mabei was originated from such depressions like Yibei,Saishiteng,Yuqia,and Gaxi.

Origin and distribution patterns of carbon dioxide in the Songliao Basin

Lu Xuesong, Wang Zhaohong, Wei Lichun, Liu Shaobo, Hong Feng

2009, 30(1):  97-101,107.  doi:10.11743/ogg20090114

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Various indexes such as CO₂ carbon isotope,³He/⁴He and CO₂/³He ratios show that CO₂ with high content in the Songliao Basin is mantle-derived gas.Distribution of CO₂ in the Songliao Basin is highly uneven.The content of CO₂ in the Songliao Basin shows a kind of "two-end member" distribution.Vertically,CO₂ are mainly concentrated in the Yingcheng Formation and the fourth member of the Quantou Formation and their distribution is under the control of regional caprock and reservoir characteristics.While laterally,they are locally distributed in several patchy or narrow-and-long zonal areas,and their distribution is obviously under the control of deep major faults and has relatively close genetic relations with the basement faults and volcanic rock bodies.Conventional hydrocarbon gas and mantle-derived CO₂ occur in hybrid,as both of them are controlled by the major basement faults and sharing some trap and reservoir elements.It was pointed out that,to a great extent,the combination type of pathways for mantle-derived CO₂ migration and accumulation determined the relative content of CO₂ and hydrocarbon gas in volcanic reservoirs and accumulating horizons of CO₂-bearing natural gas.

Pattern of fracture occurrence and its influence on waterflooding in the Es³ reservoirs of Wendong oilfield

Zhao Liangjin, Huang Xinwen, Wang Jun

2009, 30(1):  102-107.  doi:10.11743/ogg20090115

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By analyzing cores,thin section and pressure build-up tests,this paper discusses the occurrence of natural fractures in the reservoirs.The earth stress characteristics are identified through research on Kayser effect,seismic anisotropy,paleomagnetic and borehole cave-in.The direction of maximum horizontal major stress is perpendicular or near perpendicular to the direction of the major faults and natural fractures,while is in parallel with the direction of artificial fractures.The direction,length and strength of natural fractures are quantitatively predicted through the methodology of main curvature.The natural fractures are predominantly of tectonic origin and were mainly formed during the deposition of the Tertiary Dongying Formation.During different stages of development,natural and artificial fractures have different degrees of influences on waterflooding.Given the natural fractures being basically closed,attentions should be focused on the artificial fractures when designing injection-production pattern.

Potential and technologies of refined exploration in mature oil and gas regions

Hou Lianhua, Zou Caineng, Kuang Lichun, Wang Jinghong

2009, 30(1):  108-115.  doi:10.11743/ogg20090116

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In order to further strengthen exploration in China's mature oil and gas regions,researchers studied the distribution of oil and gas reservoirs and residual oil and gas resources in petroliferous depressions and proposed that the key formations as well as those underlying and overlying them in the potential zones of these depressions be the future targets of refined exploration.Based on the analysis of exploration experiences in mature oil and gas regions,they put forward a new idea of refined exploration and established a set of approaches and technologies(including identification and protection of oil and gas layer,prediction of oil and gas reservoirs,oil and gas production enhancement,and etc.) aiming at different kinds of reservoirs and pools.Their wide application has resulted in large reserve growth.Compared with exploration in offshore and frontier areas,refined exploration in mature oil and gas regions has lower cost,shorter period of capital recovery,and higher economic returns.

Prediction of dolomite reservoirs for the Cambrian buried hills in the Yaha fault structural belt,the Tarim Basin

Cui Haifeng, Zhang Nianchun, Zheng Duoming, Teng Tuanyu

2009, 30(1):  116-121.  doi:10.11743/ogg20090117

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Severely eroded Cambrian buried hill in the Yaha fault structural belt of Tarim Basin consists of the Upper,the Middle,and the Lower Cambrian dolomites.The Cambrian buried hill reservoirs are mainly distributed in the weathering crust and have a thickness of less than 100 m.They as a whole belong to fractured-vuggy reservoirs,with the characteristics of relatively small pores,fractures and vuggies,undistinguished seismic responses and strong lateral heterogeneity.The results of model-based reservoir inversion can not reveal the real lateral distribution of buried hill reservoirs,but that of seismic attribute-based reservoir prediction with amplitude-preserved 3D seismic pure wave data are more reliable.According to the analysis of seismic attribute coherence,RMS amplitude,reflection strength slope and arc length attributes were selected to perform a multi-seismic cluster analysis.The results show that the dolomite reservoirs in the Cambrian buried hills mainly occur in the structural high and nor-thern slope area and are in patchy distribution.These predictions are consistent with the drilling results.

A binomial deliverability equation for horizontal gas wells in formations with nonlinear seepage flow features

Yuan Yingzhong, Zhang Liehui, Wang Jian, Pu Yanwei

2009, 30(1):  122-126.  doi:10.11743/ogg20090118

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A horizontal well is one of the most effective methods for developing low-permeability gas reservoirs which are characterized by the effects of start-up pressure gradient and turbulent flow under high-speed non-Darcy flow.A seepage flow model was established and solved for horizontal gas wells.It involves well-bore structure parameters,turbulent gas flow under high-speed non-Darcy flow in near-wellbore area and start-up pressure gradient.A binomial deliverability equation for horizontal gas wells was derived.Based on strict theoretical derivation and calculation,deliverability of horizontal and vertical wells was compared to understand the influences of start-up pressure gradient and non-Darcy flow on the deliverability of horizontal gas wells.The results indicate that the start-up pressure gradient is in negative linear relationship with the deliverability,the non-Darcy flow decreases the deliverability of horizontal gas wells and its influence on horizontal gas wells is smaller than that on vertical gas wells.