Table of Content

28 August 2013, Volume 34 Issue 4

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Oil-gas shows from destruction oil/gas reservoirs in the petroliferous basins of China and their geological significance

Huo Zhipeng, Pang Xiongqi, Du Yijing, Shen Weibing, Jiang Tao, Guo Fengtao

2013, 34(4):  421-430.  doi:10.11743/ogg20130401

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Oil-gas shows can provide much important information to explore the related residual or secondary reservoirs.Based on field survey,geological analysis and literature investigation,this paper systematically studied the distribution of oil-gas shows in different basins/regions in China,discussed their genetic mechanisms and analyzed their petroleum geological significance.According to the degree of destruction of reservoirs,oil-gas shows can be classified into three types:partial destruction,strong destruction,and complete destruction.All these three types of oil-gas shows are widely distributed in each basin/region in China.The partial-destruction type of oil-gas shows,including oil seepage,gas seepage and mud volcano,is mainly distributed in the western and southern China.The strong-destruction type of oil-gas shows such as heavy oil is mainly distributed in the western and eastern China.The complete-destruction type of oil-gas shows,such as natural bitumen,tar sand and mineral wax,mainly occurs in the western and southern China.On the other hand,in terms of the times and extent of destruction of reservoirs,the genetic mechanism of oil-gas shows can be categorized into two types:primary-destruction and secondary-destruction.The former type of oil-gas shows include surface oil seepage,gas seepage and volcano and their formation are influenced by the intense tectonic movements,frequent earthquakes and rapid deposition.It can be further divided into four kinds according to their ways of out-flowing the surface of earth:surface-cutting fault,uplifting-denudation,diapir penetrating,unconformity outcropping.The secondary-destruction type of oil-gas shows include heavy oil,natural bitumen,tar sand and mineral wax on the surface and underground,and features in water washing oxidation and biodegradation after destroyed directly and they are usually paragenic and transitional.In the early stage of petroleum exploration,the oil-gas shows of partial-destruction type or that on thrust belt and diaper structure have greater guiding significance to discover underground reservoirs.On the one hand,although all kinds of destructive effects can destroy reservoirs to form oil-gas shows,they could also have positive influences on the redistribution and preservation of hydrocarbons.Therefore,preservation condition is the key factor to find reservoirs in areas with oil-gas shows.

A comparison of hydrocarbon accumulation characteristics of the Paleozoic marine carbonates in Tarim Basin and Williston Basin

Tao Chongzhi, Bai Guoping, Wang Dapeng, Zhang Minghui, Niu Xinjie, Zheng Yan, Bai Jianpu

2013, 34(4):  431-440.  doi:10.11743/ogg20130402

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The Paleozoic marine carbonates are the main exploration targets in both Tarim and Williston basins.Based on a comparative analysis of both tectonic-depositional setting and conditions for the formation of hydrocarbon accumulations,this paper discusses the similarities and differences of hydrocarbon accumulation in the Paleozoic marine carbonates of the two basins.Williston Basin locates within the large North America Plate with relatively stable tectonic setting.The sedimentation within the basin was mainly controlled by eustasy.In contrast,Tarim Basin locates in the much smaller Tarim Plate and experienced frequent and intensive structural deformations.As a result,the sedimentation within the basin was mainly controlled by the tectonic movements.Williston Basin has high-TOC effective source rocks,good porous-type reservoirs and evaporite cap rocks,while Tarim Basin has high-mature to overmature source rocks,karst and dolomite reservoirs,and mudstone and evaporite cap rocks.Different kinds of traps are developed on the paleo-highs in both basins,which constitute the main carbonate play fairways.Williston Basin has multiple evaporite sequences,which makes it possible to effectively apply the petroleum system concept to the basin.In comparison,the hydrocarbon accumulation system concept can provide effective guidance for the hydrocarbon exploration in basins such as Tarim Basin featuring in multiple source rocks,multiple kitchens and multiple episodes of hydrocarbon charging.The favorable reservoir-seal assemblage in Williston Basin is dolomite reservoir and evaporite seal.The comparative analyses indicate that the favorable carbonate play fairways are the areas with the assemblage of the Lower-Middle Cambrian dolomite reservoirs and the Middle Cambrian evaporite seals in the Bachu and Tazhong areas.

Possibility of formation of deep basin gas reservoirs in the Denglouku Formation of Gulong-Changjiaweizi region, northern Songliao Basin

Zhang Lei, Zhang Xuejuan, Lu Shuangfang, Yang Zhiru

2013, 34(4):  441-449.  doi:10.11743/ogg20130403

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The Denglouku Formation in Gulong-Changjiaweizi region is still immature in petroleum exploration,especially for tight sand gas.Based on a systematic analysis of gas accumulation conditions in respects of source rock,reservoir and preservation and a comparison with the basic accumulation conditions of deep basin gas reservoir,we discussed the f possibility of formation of deep basin gas reservoir in the Denglouku Formation of Gulong-Changjiaweizi region.The results show that the 2^nd member of Dengkouku Fm (K₁d²) and its conterminous layers in Gulong-Changjiaweizi region have favorable geological conditions for the accumulation of deep basin gas,including tight sandstone reservoirs with low porosity and low permeability,abundant and continuous gas charging,stable and gentle structural background as well as close superimposition of source rocks and reservoirs.Therefore,the Gulong-Changjiaweizi region could be favorable for accumulation of deep basin gas in the northern Songliao Basin.The K₁d² and its conterminous layers within the effective gas generation area of K₁d² source rock and its periphery may be the major target for future deep basin gas exploration.

Geological features of the Lower Jurassic shale gas play in Fuling area, the southeastern Sichuan Basin

Zhou Dehua, Jiao Fangzheng, Guo Xusheng, Guo Tonglou, Wei Zhihong

2013, 34(4):  450-454.  doi:10.11743/ogg20130404

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Based on integration of drilling,core,outcrop and logging data,this paper comprehensively studied the geological characteristics of the Lower Jurassic Da'anzhai shale gas play in Fuling,southeastern Sichuan Basin in such aspects as spatial distribution of organic-rich shales,geochemical characteristics,mineral components,shale porosity and permeability conditions,and geomechanical properties.We quantitatively evaluated such characteristics as TOC content,R_o,gas content,porosity,brittleness,mineral composition and rock mechanical parameters.We believe that the shale gas play is analogy basically to Bakken shale in North America.The Da'anzhai mudstone-shale features in frequent interbedding with limestone and sandstone,and the deep to semi-deep lacustrine shales are organic-rich exploration targets.The limestone in the upper Da'anzhai is 10-30 m thick and has low porosity and extra-low permeability.The lower Da'anzhai shale with interbedded thin limestone and sandstone has well-developed micro-fractures and high porosity.The shale gas play has an average TOC content of 1.33%,average clay content of 51.7%-56.1%,average quartz content of 33% and on-site measured average gas content of 1.66 cubic metre per ton,and is at high thermal maturity stage of generating gas condensate to wet gas.The Young modulus is 29GPa and Poisson ratio is 0.30,being favorable for the creation of fracture networks through hydraulic fracturing.The middle Da'anzhai shale of shallow lacustrine facies is more favorable for fracture development,thus is the favorable target.A play fairway with an area of 820 km² is identified.

Shale oil accumulation conditions and exploration potential of faulted basins in the east of China

Wu Xiaoling, Gao Bo, Ye Xin, Bian Ruikang, Nie Haikuan, Lu Fuchang

2013, 34(4):  455-462.  doi:10.11743/ogg20130405

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Shale oil is one of the important unconventional petroleum resources,and its exploration and development has greatly expanded the traditional domain of the industry.The lacustrine shale in the faulted basins of East China has been considered as having great potential for shale oil based on the facts that it has large coverage,high organic matter content,and considerable thickness matched well with shallow buried depth,and that most of it is still within the oil-generating peak stage.Based on comparison with the typical shale oil producing plays in the US,the paper analyzes geological conditions of shale oil in these basins in accordance with their sedimentary facies belt,lithology combination,reservoir space types,hydrocarbon source condition of the organic-rich mudstone and shale.Based on the results,the paper explores characteristics of these reservoirs and classifies three main types of shale oil reservoirs,i.e.pure shale reservoir in deep depression,shale reservoirs within salt layers,and shale reservoirs with thin brittle interbed such as thin sandstone,limestone and dolomite.A preliminary analysis of the exploration potential for shale oil in these basins is also carried out and favorable zones for its exploration are identified.

Characteristics and patterns of shale gas accumulation in typical North American cratonic basins and their enlightenments

Yang Zhenheng, Han Zhiyan, Li Zhiming, Nie Haikuan

2013, 34(4):  463-470.  doi:10.11743/ogg20130406

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Michigan Basin,Delaware Basin and Illinois Basin are the typical cratonic basins with shale gas plays in North America.This paper analyzed shale gas reservoir lithology,organic matter type,hydrocarbon generation,burial depth,thermal maturity,adsorbed gas content and the role of fracture in shale gas accumulation.We summarized two shale gas accumulation patterns:the Antrim shale gas accumulation pattern in Michigan Basin (A-pattern) and the Barnett shale gas accumulation pattern in Delaware Basin (B-pattern).The primary features of A-pattern is that,from the shallow periphery to the deep basin,biogenic gas,mixed gas and thermogenic gas occcur in sequence.The main characteristics of B-pattern are that the shale gas is of thermogenic origin and is indigenously generated and accumulated,Shale gas of different genetic types occur in areas with different thermal maturities.We suggested that the Barnett shale gas accumulation pattern(B-pattern)of Delaware Basin is of greater significance for shale gas exploration in China,and Antrim shale gas accumulation pattern in Michigan Basin (A-pattern) also cannot be ignored for shale gas exploration.

Material balance equation with revised rock compressibility for shale gas reserve calculation

Liu Botao, Yin Hu, Wang Xinhai, Li Qingquan

2013, 34(4):  471-474.  doi:10.11743/ogg20130407

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As shale gas reservoirs have different change pattern of porosity with conventional gas reservoirs and their effective stress tending to lower porosity and matrix shrinkage tending to enlarge porosity have coupling effect,these two factors must be considered comprehensively when establishing the material balance equation for shale gas reservoir.Based on the material balance principle,Bangham solid deformation theory and Langmuir isotherm adsorption model are used to establish shale gas reservoir material balance equation with correction rock compressibility.The equation is linearized to a straight line equation only containing original free gas and absorbed gas.Actual production data are substituted in the equation to obtain the data points of the linear equation.These data points are fitted to obtain a fitting equation,the slop of which is the content of free gas and theintercept is original absorption content of gas.The sum of these two is original geological reserves of shale gas reservoir.Case analysis shows that considering the matrix shrinkage effect makes compressibility factor decrease at the beginning and stablize at the later.The lowering of shale gas reservoir porosity caused by the change of compressibility factor is slower than that of conventional gas reservoir.The correction of the rock compressibility of shale gas reservoirs and linear fitting the actual production data lead to the increase of the calculated amount of absorbed gas and the decrease of estimated content of free gas,so the estimated geological reserves increase and are more close to actual reserves.

Features and evaluation of the Palaeozoic tight sandstone reservoirs of the Rub Al Khali Basin in the Middle East

Zheng Lei, Jin Zhijun, Zhang Shaonan

2013, 34(4):  475-482.  doi:10.11743/ogg20130408

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Tight sandstone reservoirs occur in the Palaeozoic Unayzah and Sarah Formations in Rub Al Khali Basin in the Middle East.Thin section analysis reveals that quartz sandstone is the main rock type,with some lithic sandstone,lithic arkose,lithic quartz sandstone and feldspathic quartz sandstone.The main pore type is residual intergranular pore.The cement types and their development degree are closely related with the depositional environment.Measurement of reservoir pore structure through mercury intrusion and SEM indicates that pore throat size distribution is large and the proportion of samples with small pores and narrow throats is large.The capillary pressure cures show that most samples have the poroperm characteristics of reservoir rocks.The testing data indicates that the Unayzah and Sarah formations have good re-servoir quality.On this basis,we determined the lower limits of the reservoir parameters and proposed the evaluation criteria for reservoir classification.The comprehensive evaluation indicates that the Unayzah Formation is moderate-good reservoir,with typeⅠand typeⅡ reservoirs widely developed vertically,whereas the Sarah Formation is moderate-poor reservoir,with typeⅡ and type Ⅲ reservoirs being predominate.

Reservoir controlling factors and geological prediction models of the 4^th member of the Xujiahe Formation in Xiaoquan-Xinchang area,the western Sichuan Basin

Meng Wanbin, Lü Zhengxiang, Liu Jiaduo, Tian Jingchun, Feng Mingshi, Li Min

2013, 34(4):  483-490.  doi:10.11743/ogg20130409

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A study is carried out on the controlling factors and geological prediction models in the 4^th member of the Xujiahe Formation in Xiaoquan-Xinchang area,western Sichuan Basin.Technical methods or tools such as thin section observation,SEM and cathodoluminescence spectroscope had been employed and data like reservoir physical parameters,sedimentary facies and so on had been utilized.The results show that the reservoirs in the formation are mainly sandstones with high lithic content,such as lithiarenite,sublitharenite and calcarenaceous sandstone.These sandstones have high compositional maturity and medium textural maturity.Reservoir space is mainly intergranular dissolved pore,intragranular dissolved pore and moldic pore.The reservoir are mainly of porous type and fractured-porous type with poor reservoir quality,and are typical tight sandstone reservoirs.Compaction and cementation caused densification of the sandstone while dissolution and fracturing played key roles in the formation of reservoirs with relatively good quality.Factor as depositional microfacies,the position of sandstone in the Paleostructures during early burial process and dissolution period,and fracture growth (mainly at the lower section) are considered to control the formation of reservoirs with relatively good quality in the 4^thmember of the Xujiahe Formation.Hence,two geological prediction models are established for the upper and lower section of the 4^th member respectively:they are delta front distributary channel microfacies and/or mouth bar microfacies plus paleostructural high during early burial process,sandy braided distributary channel microfacies and/or mouth bar microfacies plus paleostructural high during dissolution period plus fracture zone.

Depositional patterns of the 2^nd member of the Shahejie Formation in Q oilfield of the Shijiutuo Uplift, Bohai Sea

Ni Jun'e, Sun Lichun, Gu Li, He Juan, Zhao Weiping, Liu Xinguang, Guo Lina, Wu Mengyang

2013, 34(4):  491-498.  doi:10.11743/ogg20130410

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One of the most important Palaeogene reservoirs in Bohai Bay Basin is of the hybrid lacustrine carbonates and clastics,with frequent facies changes and strong heterogeneities.In order to gain a good insight into the distribution of such reservoirs,Q oilfield in Shijiutuo uplift,Bozhong depression,had been analyzed as an example.Based on core,logging and geophysical data,combined with the analysis on the regional tectonic setting,sediment supply,paleogeomorphological and paleoclimatic data,we studied the petrologic characteristics,sedimentary facies as well as the depositional models of the 2^nd member of Shahejie Formation in Q oilfield.According to this study,the bulk of the 2^nd member of Shahejie Fm of Q oilfield was developed in a depositional setting favorable for the accumulation of hybrid lacustrine carbonate-clastic deposits.Two depositional models,namely the hybrid-deposit model and the skirt-rim model,were proposed.Uncertainty and risk of reservoir connectivity exist in both models,thus corresponding measures should be taken to lower risk during oilfield development.Hybrid-deposition played a positive role in improving the quality of the middle-deep clasitic reservoir.

Deposition and sequence stratigraphy of the Silurian Shiniulan Formation in southeastern Sichuan-northern Guizhou province

Wang Zhenghe, Tan Qinyin, He Li, Cheng Jinxiang, Wang Ruihua

2013, 34(4):  499-507.  doi:10.11743/ogg20130411

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Based on the integrated analysis of seismic,drilling and outcrop data,this paper studied the deposition and sequence stratigraphy characteristics of Shiniulan & Xiaoheba formations in southeastern Sichuan-northern Guizhou pro-vinces.The following results were obtained.The Shiniulan Fm and its underlying Longmaxi Formation compose a separate third-order sequence,and the Shiniulan Formation is part of a high-stand system tract.There are two sub-eustatic sea le-vel cycles in the Shiniulan Formation,so this formation can be further divided into an upper and a lower fourth-order sequence.There are one to two development phases of platform margin reef & bank facies in the high-stand system tract of each fourth-order sequence,but the best platform reef & bank facies lies in the upper one.The bioherms developed during the deposition of the Shiniulan Formation are generally small and in scattered or beaded distribution due to the non-exis-tence of obvious slope break between platform margin and slope as well as the dilution of terrigenous inputs.In the study area,the dolomitization of the Shiniulan Fm is very weak as a whole.It is assumed that the salinity was low in this stage mainly due to factors.The first is the input of fresh water from the central Guizhou Uplift in the south and Xuefeng Uplift in the east.The second is the low amplitude of uplift of platform margin reef & bank.The sedimentary environment of the Xiaoheba Formation in Nanchuan area should be a shallow water constructive delta with low river energy,non-well deve-loped provenance and predominant suspension transport.

Characteristics and hydrocarbon accumulation patterns of volcanic rocks in the Yixin Formation Zhangqiang depression, southern Songliao Basin

Zhang Bin

2013, 34(4):  508-515.  doi:10.11743/ogg20130412

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Mafic-intermediate volcanic rocks are widely developed in the Cretaceous Yixian Formation (K_1y) in the periphery of Liaohe oilfield in southern Songliao Basin,and commercial oil flow has been tested in these volcanic rocks in Zhangqiang depression.Based on core observation and slice analysis,14 different rock types have been recognized in the Yixian Fm vocanic rocks.Among them,andesitic lava and andesitic volcanoclastic rocks have the greatest thickness and most extensive distribution.The volcanic lithofacies can be divided into 3 lithofacies and 7 subfacies,of which effusive lithofacies accounts for about 84%.The volcanic reservoirs have 6 main types of primary and secondary reservoir spaces and 4 kinds of pore associations.The plane and vertical distribution of reservoirs are jointly controlled by lithology,lithofacies and faults.The reservoir space types,reservoir capacity,permeability and connectivity are determined by diagenesis and tectonism.According to analyses of physical property and reservoir data,the most favorable reservoir facies belts include the pyroclastic lava,vesicular mandelstone lava,volcanic conduit facies (volcanic neck lithofacies or concealed explosion breccia lithofacies) and the upper effusive lithofacies.It is highly possible for the hydrocarbons to accumulate in the vent and proximal vent lithofacies,as well as the upper and top of volcanic eruption cycle/stage in areas adjacent to hydrocarbon kitchen and/or the structural high of deep large faults.

Palaeogeomorphology and karst distribution of Tongwan unconformity in Sichuan Basin

Li Qigui, Li Kesheng, Zhou Zhuozhu, Yan Jihong, Tang Huanyang

2013, 34(4):  516-521.  doi:10.11743/ogg20130413

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The distribution of weathering crust karst reservoirs of the Sinian Dengying Formation in Sichuan Basin is mainly controlled by palaeo-highlands and palaeo-slopes of unconformity produced by the Tongwan Movement.Based on the interpretation of the cross-basin seismic profile and drilling data,this paper restored the palaeogeomorphology of Tongwan unconformity by using printing method.The palaeogeomorphology features in a framework consisting of the northwes-tern high,central slope and southeastern sag.Outcrop,drilling and seismic data were integrated to study the development characteristics of the solution cavities and pores and predict favorable karst reservoirs in the Dengying Formation.It is concluded that solution cavities and pores are well developed in the karst weathering crust with three widely distributed karst belts.The karst is thick in the west and thin in the west.The favorable and fair karst belts occur on the palaeo-karst slopes,such as Zigong-Guangan-Daxian-Tongjiang.And the local karst belts occur on the palaeo-karst high and in the palaeo-karst sag,such as Chengdu-Ziyang,Mingyang-Guangyuan as well as the south-eastern part of Sichuan Basin.

Deformation and tectonic evolution of the Selibuya fault zone in Tarim Basin

Yao Wenqian, Tang Liangjie, Xie Daqing, Yang Yong, Jiang Huashan, Zhang Yuhang, Yu Tengxiao, Cao Zicheng

2013, 34(4):  522-527.  doi:10.11743/ogg20130414

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The Selibuya fault zone separates the Maigaiti Slop and the Bach Uplift in the Tarim Basin,and its structural styles and tectonic evolution Fault zoneis related to some extent with the evolution of Bachu and Keping.Referring to the latest data of drilling,logging and 2D-seismic interpretation,we proposed that the previous defined Selibuya Fault zone be divided into two fault zones including Selibuya and Yasongdi.On sectional view,the former mainly features in basement-involved high-angle thrust extrusion and consists,together with the early Piqiang fault on Keping uplift,Piqiang-Selibuya fault zone,while the later is a superimposed thrust fault resulted from the superimposition of the SW-dipping shallow thrust fault of cap rock slipping type and the NE-dipping deep basement-involved thrust fault.On plane view,the Selibuya fault zone recognized in this paper can be divided into a north segment and a south segment.The whole Selibuya fault zone are characterized by high-angle deep thrust and positive flower structures.The south segment of this fault zone cuts upward into the Neogene and Quaternary,leading to the weak folding of the Neogene and Quaternary and the associated local decollement along the Paleogene cap rock.Combined with the evolution of Selibuya and the regional evolution of Bachu and Keping,it is believed that Selibuya fault zone went through mainly four main stages:the Late Caledonian,the Late Hercynian,the Early-Middle Hymalayan,and Late Hymalayan.

Discovery of diapir structure and its significances for exploration in Doshan area, South Turgai Basin

Dai Hansong, Hong Liang, Zhang Mingjun, Zhang Jing, Zhang Yajun, Wang Xin

2013, 34(4):  528-532.  doi:10.11743/ogg20130415

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The diapir structure newly defined in Doshan area,South Turgai Basin is a typical duplex structure.The lower carbonate diapir superimposes on the deeper one,and maintains the consistency of structural configuration with that of the latter at the same time.These small-scale diapir structures are generally on NW-SE trend.They are recognized as deep-source diapirs based on their regional stress background,plastic deformation,and pyrolysis gas show.Their development is mainly controlled by the upswelling of deep materials along small-scale faults due to the revitalization of deep base paleo-faults during the Late Cretaceous large-scale strike-slipping and uplifting deformation in southern Turgai Basin.The discovery of this kind of structures not only provides a new mode of tectonic research,but also a new domain of petroleum exploration in southern Turgai Basin.Diapir structures located in slope-burial hill belt have favorable accumulation conditions,and are favorable targets for discovering structural and/or lithologic hydrocarbon reservoirs.

Distribution and rheological characteristics of evaporates in Tongnanba area

Li Xinzi, Liu Bin, Wu Xiaoling, Liu Guoping, Feng Qiong, Fu Xiaoyue

2013, 34(4):  533-539.  doi:10.11743/ogg20130416

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The vertical distribution and geometry of evaporates in Tongnanba area are generally steady and continuous.However,when the overlying and underlying competent dolomite are deformed by folds and faults,they occur in special shapes like moundy,wedge and spindle set.The evaporates are characterized by multilayers (57-110),a large gross thickness (273-415m),and close relationship with the shapes and structures of competent beds.The initial dominant wavelengths of the dolomite layers are larger than the thickness of evaporates,the evaporates and the surrounding multiple competent beds interact with each other,and the contact strain zones have relatively large influences on the evaporates,therefore,the evaporates are apt to form disharmonious folds.The evaporates are easy to form creep fractures due to the influences of stress,temperature,fluid and other factors,and abnormally-shaped evaporate bodies are developed due to faulting of the competent beds.It was proved that sealing capability of multilayer evaporates was weaker than that of single evaporates with large thickness.The thickness of evaporate body enlarges significantly when they get abnormally-shaped,thus the surrounding areas are favorable targets for hydrocarbon exploration.

Control of faults on hydrocarbon migration and accumulation in the Nanpu Sag

Sun Yonghe, Zhao Bo, Dong Yuexia, Zheng Xiaofeng, Hu Ming

2013, 34(4):  540-549.  doi:10.11743/ogg20130417

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This paper systematically studies the control of faults on hydrocarbon migration and accumulation in Nanpu sag and predicts favorable exploration targets through establishing fault transporting models.Research shows that positive local structures such as horst/half horst,negative flower structure combinations of anticline,fault terrace belt of anticline and so on are the favorable for hydrocarbon accumulation.When the juxtaposition thickness of faults in Ed² cap rock is less than 90-95 m,hydrocarbons can penetrate the cap rock and accumulate in the middle-shallow layer.The greater the fault density is,the shallower the hydrocarbon accumulation is.Type Ⅴ and Ⅵ faults are source rock-rooted faults and two or more intersected faults are the preponderant pathways of vertical hydrocarbon migration,and some hydrocarbons may migrate along reservoirs with a net-to-gross ratio of over 20%.The hydrocarbons charging into the fault traps can accumulate and be preserved in large scale only when both the palaeo and current sealing ability of faults are strong enough.Favorable deep exploration targets include the local positive structures related with type Ⅰ,Ⅱ and Ⅳ faults and reservoirs with high net-to-gross ratio as well as local positive structures related with type Ⅴ and Ⅵ faults and reservoirs having a juxtaposition thickness of Ed₂ cap rock over 90-95 m and high net-to-gross ratio.While the shallow-to-moderate favorable exploration targets include positive local structures related with type Ⅴ and Ⅵ faults and reservoirs having a juxtaposition thickness of Ed² cap rock less than 90-95 m and high net-to-gross ratio as well as that with good lateral fault sealing ability.

A new method for apatite fission track dating—the Laser-ICPMS method

Li Tianyi, Zhou Yan, Fang Shi, He Sheng, He Zhiliang, Fan Dehua

2013, 34(4):  550-557.  doi:10.11743/ogg20130418

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In this paper,a new method for apatite fission track dating using Laser-ICPMS is introduced in detail.The fission track ages of three international standard samples determined by using the new method and the conventional external detector method are basically in consistency.The test results of four clastic rock core samples,including apparent fission track ages,single grain ages and U contents are also basically the same for the new and conventional methods.The two group of ages may reflect the same tectonic uplift cooling event.As it eliminates several steps such as thermal neutron irradiation,mica ablation and induce fission rack accounting,the new method is more rapid and convenient than the traditional method,can shorten the cycle of testing,reduce the influence of human factors,and improve accuracy and reproducibility of the analysis results.However,the new method still has some uncertainties such as the influence of ablation on ²³⁸U content,depth of laser ablation,the influence of uneven U content and the selection of standard samples with similar property with apatite.

Rock type-constrained geological modeling of carbonate reservoirs：a case study of carbonate reservoir A in the Zagros Basin

Tan Xuequn, Lian Peiqing, Qiu Maojun, Li Yanhua, Dong Guangwei

2013, 34(4):  558-563.  doi:10.11743/ogg20130419

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For carbonate reservoirs which undergo significant overprint of diagenesis,sedimentary facies-constrained reservoir modeling method is no longer applicable.This paper puts forward a rock type-constrained geological modeling method for this kind of reservoirs.By taking advantage of the available core data such as porosity,permeability and capillary pressure,we used Winland R₃₅ method to identify the rock types of carbonate reservoirs,and to derive porosity-permeability relationships for different rock types.The relationships between rock types and log responses were then established for the cored wells,and were utilized to predict rock types in uncored wells.A porosity model was finally built based on the coordinated constraint of rock type and seismic acoustic impedance volume,and a permeability model was built by using the porosity-permeability relationships for different rock types.The reliability of geological model was checked by the method of decreasing wells.This method is particularly applicable to carbonate reservoirs with strong diagenesis and deep burial depth.

Application of comprehensive prediction error filter analysis to stratigraphic division and isochronous correlation

Liu Luofu, Xu Jingling, Gao Peng, Zou Changchun, Wang Yuanzheng, Xu Xinyu

2013, 34(4):  564-572.  doi:10.11743/ogg20130420

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Aiming at solving the problems such as difficulty in stratigraphic division,subjectivity and ambiguity of stratigraphic correlation,this paper studied the superimposition sequence and cycle structures of strata and established corresponding geological models based on the analysis of the sedimentary sequences on outcrops and cores.We converted the structures of sedimentary cycles into signals of numerical simulation via the geological model.According to the features of the signals,we proposed the comprehensive prediction error filter method and presented its principle,steps and functions.Frequency trend lines that can reflect the stratigraphic superimposition and structures of sedimentary cycles were extracted through processing of the simulation signals,and were linked indirectly with the changes of the sedimentary environment and base level.Therefore,we can find the inflection points and trends that reflect the same isochronous stratigraphic surfaces.According to the inflection points and trends,we can perform isochronous stratigraphic comparison,providing a solid basis for precise stratigraphic division and isochronous comparison.Processing of real logging data shows that this method is valid.