Table of Content

28 August 2012, Volume 33 Issue 4

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New advances in petroleum geology and exploration techniques of clastic reservoirs in the four large-sized basins in central-western China

Zheng Herong

2012, 33(4):  497-505.  doi:10.11743/ogg20120401

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Since Late Paleozoic,the four large-sized petroliferous basins (i.e.Ordos,Sichuan,Junggar and Tarim) in central-western China have experienced similar evolution processes during different geologic time,and have two kinds of petroleum exploration plays in clastic strata,i.e.self-source and self-reservoir type and marine-source continental-reservoir type.The clastic sequences deposited in compressional environments have "dual system tract structure",which determines the high quality of the exploration plays.Three types(inner-sourcing,out-sourcing and hybrid-sourcing)and six subtypes of petroleum accumulation systems can be identified in the clastic sequences.The differences in tectonic deformation among these four basins result in the differences in their petroleum accumulation system distributions.A technique series consisting of 3D 3C seismic acquisition,processing and interpretation has been developed for fractured reservoir prediction.Seismic acquisition and processing techniques for loess tableland are developed to identify tight reservoirs and subtle traps.Fracturing techniques are developed for stimulation of the fractured tight reservoirs in western Sichuan depression.Compensation fracturing techniques are developed for stimulation of the tight sands in southern Ordos Basin.The advances in petroleum geologic theories and exploration techniques have promoted the discovery of the large- to medium-sized oil and gas fields (such as gas reservoirs in the 2^nd member of Upper Triassic Xujiahe Formation,the classtic oil reservoirs in Tahe area,the Zhenjing oil field in southern Ordos Basin).

Characteristics and their controlling factors of Cretaceous Kezilesu Group sandstone reservoirs in Akmomu gas field, northwestern Tarim Basin

Shi Shi, Chang Zhiqiang, Xu Yanmei, Yang Jianping, Chu Guangzhen

2012, 33(4):  506-510,535.  doi:10.11743/ogg20120402

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Characteristics of Kezilesu Group sandstone reservoirs and factors controlling their development are investigated based on the analysis of routine thin-sections,cast thin-sections,physical property and grain sizes.The results show that the reservoir rocks are dominanted by feldspathic litharenite and lithic sandstones with low porosity and permeability,and the pore types are mainly secondary pores including intragranular dissolved pores,intergranular dissolved pores and micropores.The mercury intrusion curve has high displacement pressure,indicating that the sorting of pore throats is poor and the pore structure feature in small pores and fine throats.The development of Kezilesu Group sandstone reservoirs in Akemomu gas field has strong correlation with grain sizes,debris content and diagenetic compaction,cementation and dissolution.For reservoir rocks were deposited under the control of braided rivers,their quality improves with grain size enlarging,debris content increasing and enhancing of dissolution.On the contrary,compaction and cementation of carbonate,clay and siliceous mineral formed during the post-diagenesis have adverse effects on reservoir rocks.

Current status and problems of volcanic reservoir study: an example from the Lower Permian volcanic rocks in Ke-Xia area of Junggar Basin

Dong Guodong, Zhang Qin, Zhu Xiaomin, Xian Benzhong, Zhu Shifa, Niu Huapeng, Chen Qingyun

2012, 33(4):  511-519.  doi:10.11743/ogg20120403

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Taking the Lower Permian volcanic rocks of Ke-Xia area in Junggar Basin as an example,this paper discussed the problems of volcanic reservoir research.As there is still no commonly accepted classification scheme of volcanic rocks,different classification criteria were adopted in exploration and development of volcanic reservoirs.Thus it is urgent to find a suitable classification scheme of volcanics for exploration and development of volcanic reservoirs in China.There are many big challenges in the study on the volcanic eruption patterns and facies distribution due to strong volcanic facies heterogeneity,variable eruption types,complex volcanic facies and facies sequence,common overlapping of volcanic rocks of different origins,as well as limited drilling data of volcanic reservoirs.The characteristics and genesis of fractures especially micro-fractures in volcanic reservoirs are still poorly understood.To solve these problems,more attentions should be paid to surface diagenesis of volcniac rocks and advanced logging techniques should be applied to research on volcanic reservoirs.

Volcanic reservoir prediction of Yingcheng Formation in Fengle area, Xujiaweizi fault depression,northern Songliao Basin

Cao Jianhua, Jiang Chuanjin, Zhao Fuhai, Li Naigao, Cao Hongming

2012, 33(4):  520-525.  doi:10.11743/ogg20120404

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Distribution of volcanic reservoirs is controlled by various factors such as volcanic edifice,lithology and lithofacies and is difficult to be precisely predicted because of their complexity and heterogeneity.Volcanic reservoirs of crater-near crater sedimentary microfacies are the most favorable reservoirs and their seismic responses are characterized by chaotic high-frequency,discontinuous and irregular reflection configuration,rapid facies change and dome reflections.It is difficult to precisely characterize the volcanic reservoirs through seismic interpretation due to the limitation of seismic data quality.In the paper,we present a new seismic interpretation workflow based on the technique of three-dimensional seismic voxel and imaging analysis.First,structurally-oriented noise filter technique is used to improve the signal/noise ratio of post-stack amplitude data.Then,volumetric seismic attributes including chaos and structurally-oriented discontinuity are used to identify volcanic reservoirs.Finally,three-dimensional imaging techniques with high resolution including attribute classfication automatic geobody detection and 3D visualization are applied to predict the spatial distribution of the volcanic reservoirs.This workflow is applied in Yingcheng Formation volcanic reservoir characterization in Fengle area,Xujiaweizi fault depression,northern Songliao basin.The reservoirs are clearly imaged and mapped,providing instructive constraints for further physical properties prediction of the volcanic reservoirs.

Characteristics,timing and controlling factors of structural fractures in tight sandstones of the 2^nd member of Xujiahe Formation in Jiulong Mountain structure, Sichuan Basin

Bai Bin, Zou Caineng, Zhu Rukai, Zhang Jian, Zhang Benjian, Bi Lina

2012, 33(4):  526-535.  doi:10.11743/ogg20120405

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Physical properties of tight sands in the 2^nd member of Xujiahe Formation in northwestern Sichuan Basin are controlled by structural fractures(SF)formed at different stages.The study on characteristics,timing and controlling factors of the structural fractures can provide useful information for reservoir evaluation and prediction.Identification of cutting relations of the SF on the basis of fracture observation on outcrops,cores and thin sections reveals that the SF can be grouped into NW-SE-trending,NE-trending,NNW-trending,near EW-trending and SEE-trending,of them NW-SE-trending is predominant.At least four stages of SF were identified based on the analysis of the fluid inclusion homogenization temperature of fillings in fractures with different cutting relation and ESR,as well as palaeo-stress data.The first stage is the Late Indosinian,and the SF formed at this stage feature in calcite filling and fluid inclusion homogenization temperature(FIHT)of 84-120℃.The second stage is the Late Yanshanian,and the SF formed at this stage are characterized by quartz filling and FIHT of 72-137℃.The third stage is the Early-middle Himalayan Period and the SF formed at this stage feature in quartz filling,cutting relations with the SF of previous two stags,and FIHT of 153-179℃.The fourth stage is the Late Himalayan Period,and the SF formed in this stage are characterized by coarser calcite fillings with some dolomites and FIHT of 165-190℃.Because of the active tectonic movement during the Indosinian and Himalayan Period,the SF are well developed.The formation and distribution of SF are jointly controlled by tectonic stress and the mechanical property of rocks.Lithic sandstone with high porosity,fine particle and thin layer are favorable for SF development.

Application of seismic waveform classification technique in thin sandstones reservoir prediction in northern Ordos Basin

She Gang, Zhou Xiaoying, Dai Mingang, Liu Weidong

2012, 33(4):  536-540.  doi:10.11743/ogg20120406

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During the deposition of fluvial sand body,various lithological assemblages can be formed due to different spatial distribution and thickness of sandstones and mudstones,and their corresponding seismic reflections have different waveform patterns.The technique of the neural network waveform classification can be used to analyze and summarize their seismic waveforms,and then predict regional distribution of sandstone sedimentary facies.Considering the low resolution of the seismic data and the thin thickness of sand layers,it is necessary to do a band spread processing with fidelity.However,this processing should be based on higher correlations between wells and seismic data and stable lateral amplitude trends.According to the sedimentary characteristics of the 3rd member of the Permian Xiashihezi Formation in Daniudi gas field in the Ordos Basin,we performed correlation and classification of seismic waveforms which reflect different lithological assemblages by using the neural network waveform classification technique,and predicted the distribution of several sandstone sedimentary models.Comparison with well data-based sandbody distribution map shows that they are consistent.The technique is quick and effective for sandbody prediction and has a better resolution for thin sand bodies.

Definition and application of tight oil and shale oil terms

Zhou Qingfan, Yang Guofeng

2012, 33(4):  541-544,570.  doi:10.11743/ogg20120407

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Based on a thorough literature investigation and a detailed analysis of the meanings and applications of the tight oil and shale oil terms,this paper compares their similarities and differences,and presents suggestions for a better understanding and application of the two terms.Though shale oil also refers to the crude generated through processing kerogen from shale rocks,both terms bear broad and narrow senses when used to indicate the oil from shale or shale-like formations.The current usage of the two terms can be summarized and described in the following three scenarios:(1)They refer to different kinds of unconventional resources,therefore are regarded as totally different from each other;(2)They are thought to be identical and are used alternatively;(3)They are different but also inherently connected.It is suggested that when using the terms,we shall follow the rule of "showing respect to customs and facilitating communications" and try to understand fully their connotations and extensions instead of only reading the lines.To tackle problems encountered during using or understanding the terms,we also shall adapt the policy of "continuous perfecting and timely modification" so as to achieve a more objective definition of the terms.Meanwhile,their international applicability shall also be taken into consideration.

Dynamic evolution simulation of the Upper Triassic source rocks in central part of western Sichuan Depression

Jiang Xingge, Zeng Huasheng, Zhu Jianhui, Cao Qian

2012, 33(4):  545-551.  doi:10.11743/ogg20120408

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The Upper Triassic source rocks in the central of western Sichuan Depression got mature during the deposition of the 3^rd member of Xujiahe Formation,over-mature stag in the late of Early Jurassic and post-mature in the Late Jurassic.The EW-dipping tectonic framework in western Sichuan depression determines that the source rocks in the west got mature earlier and have higher maturity than that in the east.Area with high maturity was near the piedmont of Longmen Mountain at the end of deposition of the 3^rd member of Xujiahe Formation,and it extended eastwards with the highest maturity migrating near to Longshen-1 well at the end of deposition of the 5^th member of Xujiahe Formation.Later it migrated eastwards as a whole at the end of the Jurassic.The area with high maturity has centered in Mianyang-Deyang-Pengzhou-Dayu from the Creataceous to present,with the highest maturity occurring at Mashen-1 well and Dayu North.The whole amount of gas generated from source rocks in the Xujiahe Formation in western Sichuan depression is 167.812 5 tcm.The gas generated during the deposition of the Maantang Formation-3^rd member of Xujiahe Formation accounts for 2.53% of the total,that during the deposition of 4^th and 5^th members of Xujiahe Formation accounts for 10.84%,that in the Early and Middle Jurassic 22.97%,that in the Later Jurassic 22.86% and that in the Early Cretaceous 40.97%.

Coalbed methane accumulation conditions and production characteristics

Zhao Qingbo, Kong Xiangwen, Zhao Qi

2012, 33(4):  552-560.  doi:10.11743/ogg20120409

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Based on the occurrence status of coalbed methane and structure setting of coal beds,the accumulation models of coalbed methane are divided into three types:self-source and self-reservoir adsorbed gas,self-source and self-reservoir free gas,and inside-source outside-reservoir gas.Coalbed methane enrichment and production mechanisms vary with various accumulation models.According to methane content and δ¹³C₁ distribution in different coalbed methane accumulation in Qinshui Basin,eastern margin of Ordos Basin,Fuxin Basin and Tiefa Basin,three coalbed methane accumulation stages are indicated as early accumulation stage,late structural-reworking accumulation stage and secondary accumulation stage during production.The secondary accumulation is induced by inter-zone and inner-zone flow during production.Micro-cycles within thick coal beds are analyzed based on sedimentary facies and the coal bed intervals with high coalbed methane content are identified.Furthermore,the types of coal-forming parent materials and their control on coalbed methane enrichment and productivity are studied based on analysis of sedimentary facies.This paper also discusses tectonic stress field and hydrodynamic force influencing coalbed methane accumulation.Finally,this paper summarizes the production characteristics of coalbed methane.The production of methane well can be divided into three stages including blocked,unblocked,and unsaturated stages.The unsaturated stage is subdivided into several step-like declining stages.Structural positions and inner-layer heterogeneity result in three types of self-supporting,exporting and importing production characteristics.

Petroleum accumulation systems of clastic strata and their distribution in the four large-sized basins in central-western China

Hu Zongquan, Yin Wei, Wu Xinhe, Gao Jinhui, Li Song, Liu Chunyan, Chen Chunfang

2012, 33(4):  561-570.  doi:10.11743/ogg20120410

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Since the Late Paleozoic,the four large-sized basins(i.e.Ordos,Sichuan,Junggar and Tarim)in central-western China have experienced a similar evolution process from cratonic depression to intra-continental depression and finally to foreland(pseudo-foreland)basin,and their deposition features in thick clastic rocks.Hydrocarbon source rocks were widely developed in the intra-continental depressions,while thick high-quality source rocks were deposited in the pseudo-foreland basins,providing favorable basis for hydrocarbon accumulation in the clastic strata in the four basins.There are three types(inner-sourcing,out-sourcing and hybrid-sourcing)and six subtypes of petroleum accumulation systems.The inner-sourcing petroleum accumulation system is the major target for large- and medium-sized oil/gas reservoirs.For the inner-sourcing systems in the four basins,their oil and gas distribution has features of oil in upper part and gas in lower part as well as more gas to the south,their hydrocarbon accumulation were developed early in the north and late in the south.The temporal and spatial combination of source rock and reservoir is the major factor controlling hydrocarbon accumulation and enrichment.Slope zone and piedmont thrust belt are play fairways for these inner-sourcing systems.The distribution of the out-sourcing and inner-sourcing system are significantly complimentary,so greatly broadening the area and horizons for petroleum exploration in the clastic strata.The out-sourcing systems are distributed mainly in the south parts in the four basins.Hydrocarbon resource condition of marine strata and vertical migration pathways are major factors controlling hydrocarbon accumulation and enrichment in the out-sourcing systems.The paleo-uplift zones of marine strata and the Meso-Cenozoic faults zones are the play fairways for petroleum exploration in the out-sourcing system.

Differential tectonic evolution and hydrocarbon distribution in clastic strata of petroliferous basins in central-western China

Fang Chengming, Huang Zeguang, Duan Tiejun, Hu Zongquan, Yang Fan

2012, 33(4):  571-577.  doi:10.11743/ogg20120411

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The relationship between tectonic evolution and hydrocarbon distribution is complex in major petroli- ferous basins such as Sichuan,Ordos,Junggar and Tarim in central-western China.Analysis of the tectonic evolution and late differential tectonic modification of these basins shows that the four basins had the similar process and different geologic timing of tectonic evolution and basin formation,i.e.they all have a similar basin-forming process featuring in transformation from extensional to compressional or transpressional basin.The late tectonic modification of the clastic strata is characterized by lateral aligning and vertical superimposition of three basic structural styles including foreland thrust,differential uplifts and titled structure.Tectonic activity,basin formation and late modification jointly control hydrocarbon accumulation types,sizesand distribution.Simple basin-forming process but diversified tectonic transformation determines that the four basins have similar play types but differential distribution patterns.The basic modification style of the four basins determines their hydrocarbon accumulation types,while the superposition features control the timing and sizes of hydrocarbon accumulation.Based on the understanding of the similarities and differences of tectonic controlling factors on hydrocarbon accumulation among these basins,we put forward a play classification scheme.According to this scheme,we identified 4 play types including palaeo-uplift,slope,foreland folded-thrust and large fault.

Fractal theory-based calculation method of relative permeability curves——a case study from the Hetaoyuan Formation in Shuanghe oilfield,Nanxiang Basin

Chen Tianyong, Mao Xin, Liu Shiyin, Yuan Ke, Peng Xiaodong, Wu Wanglin

2012, 33(4):  578-581,590.  doi:10.11743/ogg20120412

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Relative permeability curve is of great importance in reservoir engineering research,and traditionally obtained through polynomial curve fitting of core data.However,the relative permeability curves obtained using the traditional method cannot reflect the whole picture of oil reservoirs due to reservoir heterogeneity,experimental error and limited core numbers.Based on the Fractal theory,a new method of calculating relative oil-water permeability was derived by using the production data from Shuanghe oilfield,Nanxiang Basin.It was applied in the pay Ⅵ in the Hetaoyuan Formation of Shuanghe oilfield and the calculation results were verified with water cut.The relative permeability curves calculated using the new mothod are more reliable and representative than the results measured in laboratory and can reflect well the real reservoir performance.The new method can improve the reliability of relative permeability from core test and can be applied in reservoir engineering.

Identification and distribution of the Mesozoic plays in Ordos Basin

Su Fuyi, Zhou Wen, Jin Wenhui, Deng Hucheng, Liu Yan

2012, 33(4):  582-590.  doi:10.11743/ogg20120413

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This paper systematically identifies plays in the Triassic Yanchang Formation of the Mesozoic in Ordos Basin.The play division is mainly based on the play definition and the following characteristics of target beds:(1)distributions of source rocks and sandstone reservoirs;(2)distributions of structures and paleo-structures,main faults and carrier systems;(3)distributions of main source rocks for each play;(4)distribution of seals especially regional seals for each play.In addition,the distribution of known structural traps and other possible structural traps as well as the preservation of petroleum system are also considered to identify play.Six plays were identified in the Triassic Yanchang Formation in Ordos Basin:MemberⅩto Member Ⅶ play,Member Ⅶ to Member Ⅴ play,Member Ⅶ to Member Ⅳ+Ⅴplay,upper of Member Ⅳ+Ⅴ to Member Ⅲ play, Member Ⅳ+Ⅴ to Member Ⅱ play and Member Ⅳ to MemberⅠ play.According to the analysis of source rocks,reservoirs and cap rocks in different plays,the Mesozoic plays are mainly distributed in the northwest and southeast and southwest parts of Yishan slope and the south part of Tianhuan depression.

Mesozoic petroleum accumulation systems and play fairways in southern Ordos Basin

Yin Wei, Zheng Herong, Hu Zongquan, Liu Chunyan, Wu Xinhe, Li Song, Chen Chunfang, Gao Jinhui

2012, 33(4):  591-598.  doi:10.11743/ogg20120414

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According to the concept of "petroleum accumulation system",in combination with source rocks,source-reservoir relationship,reservoir characteristics and accumulation mechanism,we recognized two Mesozoic petroleum accumulation systems in the southern Ordos Basin,i.e.near-source system and far-source system.The near-source accumulation system is dominated by lithologic traps,and features in short migration distance,abnormal pressure as major driving force of migration,and implicit carrier system.Hydrocarbon accumulation in the near-source system is mainly controlled by high-quality source rocks and reservoirs as well as favorable structural setting,and the pattern of hydrocarbon accumulation can be described as "near-source and facies-control".The far-source system is dominated structural traps and structural-lithologic traps,and is characterized by long migration distance,buoyancy as the major driving force of migration and source rock-rooted faults containing the major carrier system.Hydrocarbon accumulation in the far-source system is mainly controlled by source rock-rooted faults,local structures and high-quality sandstone reservoirs,and the pattern of oil accumulation can be described as "far-source and fault-control".The source rock-reservoir relationship in the near-source system has a "sandwich-like" structure.The synchronism of peak hydrocarbon generation with hydrocarbon accumulation provides favorable conditions for widespread and large-scale hydrocarbon charging and accumulation near source rocks.The near-source systems are the priority of future exploration,and the top-ranking play fairways in the CH₉-CH₈-CH₇ near-source systems are the important exploration targets for large- and medium-sized oil and gas fields.

Late diagenetic dissolution of dolomites in the Feixianguan Formation, northeastern Sichuan Basin

Zhang Jun, Cai Liulu, Xiang Lei, Cai Chunfang

2012, 33(4):  599-606.  doi:10.11743/ogg20120415

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Comprehensive analyses were performed on thin-section,carbon,oxygen and strontium isotopes and fluid inclusions of reservoirs in the Feixianguan Formation of northeastern Sichuan Basin.In the northeastern part of Kaijiang-Liangping shelf,intercrystalline pores resulting from dolomitization of calcite are absent in the high-quality reservoirs.In contrast,dolomite intergranular dissolution pores or intergranular enlarged dissolution pores are well developed in these reservoirs.Both two kinds of dissolution pores may coexist closely with calcites of light carbon isotope and occur in space between solid bitumen and dolomite crystals,thus they should have been produced by dolomite dissolution after solid bitumen precipitation.In the southern part of Kaijiang-Liangping shelf,dolostones are absent,thus pores of similar origin are also not developed.Under acidic conditions,dolomite may react with anhydrite or celestite,to produce MgSO₄ in the northeastern part of Kaijiang-Liangping shelf.As the MgSO₄ can be easily reduced by hydrocarbons to produce H₂S, further promoting the dissolution of dolomite,anhydrite and celestite,the precipitation of giant crystal/poikilitic calcite,and the enlarging of secondary pores in local areas.This genetic mechanism can clearly explain the differences of reservoir physical properties between the northeastern and northwestern areas.The MgSO₄ is likely to be the primary intermediate reactants of TSR.

Formation fluid characteristics and hydrocarbon migration and accumulation in Junggar Basin

Li Mei, Jin Aimin, Lou Zhanghua, Fa Huan, Zhu Rong

2012, 33(4):  607-615.  doi:10.11743/ogg20120416

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Junggar Basin is a large transpressional superimposed basin experienced multi-stage tectonic movements.Its hydrocarbon accumulation process and reservoirs distribution are complex.By using the new theories and methods of fluid history analysis of petroliferous basins,we comprehensively studied the evolution characte- ristics of chemistry pressure and hydrodynamic fields as well as their effects on petroleum accumulation and distribution in Junggar Basin,revealed the control of hydrodynamics on hydrocarbon generation,migration and accumulation as well as oil-gas-water contact,and identified favorable areas for hydrocarbon exploration.The sealing conditions are poor nearby the northwestern margin of Junggar Basin where desalination occurs due to meteoric water percolate in a downwards direction.Small oil/gas pools may exist in local litholgoic traps or stratigraphic traps in Mahu sag and Pen-1 west sag where desalination occurs due to water discharging from shale compaction.Large oil/gas fields may exist in the northwestern fault-terrace belt, Luliang uplift,Mosuowan-Mobei uplift,Dabasong uplift and Cheguai area where drainage occurs through leakage and leakage-evaporation.

Differences of oil accumulation conditions and patterns in Putaohua play, Sanzhao depression, Songliao Basin

Liu Yunyan

2012, 33(4):  616-623.  doi:10.11743/ogg20120417

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Analysis of typical oil reservoirs and hydrocarbon accumulation conditions indicate that there are four major differences of hydrocarbon accumulation and distribution between Putaohua play inside and outside hydrocarbon kitchen in Sanzhao depression.①Oil sources are different.Oil of Putaohua play inside the kitchen is directly sourced from the source rocks in the underlying 1^st member of Qingshankou Formation(MQF),while that outside the kitchen is directly sourced from the underlying Fuyang play.②Hydrocarbon migration conditions are different.Oil migration to Putaohua play inside the kitchen are driven by both buoyancy and overpressure and features in short distance and small amount of loss.In contrast,that outside the kitchen is solely driven by buo- yancy,and is characterized by long distance and large amount of loss.③Hydrocarbon accumulation process and patterns are different.For Putaohua play inside the kitchen,oil generated by MQF source rocks migrates to the overlying Putaohua play along the source rock-rooted faults under the driving of overpressure and buoyancy,and accumulates in fault blocks or fault-lithologic traps near the faults.In contrast,for Putaohua play outside the kitchen,oil from Fuyang play migrates to the overlying Putaohua play along the source rock-rooted faults under the driving of buoyancy and accumulates in fault blocks or fault-lithologic traps near the faults.④Controlling factors of hydrocarbon accumulation and distribution are different.Hydrocarbon accumulation and distribution of Putaohua play inside the kitchen is mainly controlled by the distribution of the source rock-rooted faults,while that outside the kitchen is jointly controlled by the distribution of Fuyang play and source rock-rooted faults.

Hydrocarbon sources and accumulation in Puffin oilfield, Vulcan sub-basin, Australia

Shi Lei, Yin Jinyin, Tian Naxin, Jiang Xiangqiang, Lu Hongmei

2012, 33(4):  624-632.  doi:10.11743/ogg20120418

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Hydrocarbon sources,distribution of the major source rocks and timing of hydrocarbon generation and expulsion are poorly understood in Puffin oilfield,constraining future exploration.Two-dimension hydrocarbon generation modeling and biomarker fingerprinting reveal that the Lower Vulcan marine shale is the most important source rocks in the study area and its peak hydrocarbon generation and expulsion occurred from Cretaceous to Miocene.In contrast,the Plover source rocks got over matured during the Late Jurassic,and contributed limited hydrocarbons due to its low capability of hydrocarbon generation.The events chart shows that the traps on the Puffin horst were mainly formed in the Jurassic-Cretaceous period.Before the Miocene,the hydrocarbon generated from the Vulcan source rocks mainly accumulated in the Jurassic traps in the graben as faults were undeveloped in strata above the Jurassic.At the end of Miocene,lots of vertical faults were created or reactivated by the regional tectonic compression,causing that hydrocarbons in the early pools vertically migrated to and accumulated in the shallow Cretaceous reservoirs.So oil in the discovered Cretaceous reservoirs is mostly secondary.

Progress of geochemical research on dibenzofuran and its chemical mechanism as molecular tracer for oil charging pathways

Zhang Liwen, Li Meijun, Yang Fulin

2012, 33(4):  633-639.  doi:10.11743/ogg20120419

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Dibenzofuran and its alky homologues(DBFs)possess the same structure and characteristics as dibenzothiophenes and carbazoles,and their relative and total abundances are constrained by thermal-maturation and migration fractionation.Based on the hydrogen bond mechanism and the polarity caused by dipoles,dibenzofuran can also produce migration fractionation effect similar to that of carbazoles during oil migration.This paper states the chemical mechanism of the migration fractionation caused by dibenzofurans during its migration process and calculates the relative abundances of dibenzofurans by using deuterium substituted dibenzofuran as internal standard.Taking oil samples from the Tahe oilfield as typical marine oil example and those from the Fu- shan depression of Beibuwan Basin as non-marine oil example,this paper studies the depositional environment and organic matter thermal maturity by using DBFs-related geochemical parameters.By comparing with the total content of carbazoles,it is concluded that the total content of DBFs can also be used as effective geochemical parameters for tracing of oil charging pathways.

ANSYS-based simulation of fracturing pressure reducing mechanism

Su Jianzheng, Huang Zhiwen, Long Qiulian, Liu Changyin

2012, 33(4):  640-645.  doi:10.11743/ogg20120420

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According to characteristics of various fracturing pressure reducing techniques for fracturing operation in deep wells,this paper established stress calculation models for open hole completion and casing-perforated completion using the ANSYS software,and calculated the rock stress near the wellbore during fracturing.We also analyzed the effects of various factors on fracturing pressure,such as reservoir burial depth,reservoir rock physical property,deep penetration perforation and acidification pretreatment.The results show that the Yang’s modulus of reservoir rock has great influence on the fracturing pressure.Fracturing pressure of rocks increases with the increasing Yang’s modulus.In contrast,Poisson’s ratio has less influence on the fracturing pressure.Acidification pretreatment may reduce the Yang’s modulus.The effect of perforating depth on reducing fracturing pressure decreases as the perforating depth increases.In field operation,the perforating depth needs to be optimized based on the well condition.

Impacts of oil prices and operation costs on proved reserves reporting

Xu Jinjin, Ren Yulin, Fan Zheyuan, Zhang Yaxiong, Wei Ping, Zhang Ling, Guo Mingli

2012, 33(4):  646-649,654.  doi:10.11743/ogg20120421

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Several Chinese oil companies are listed on the U.S. stock market,their petroleum reserve disclosure by SEC proposed rules is indispensable,and the proved reserves is the most concerned.We face great challenges for SEC reserves disclosure because of crude price changing,operation costs rising and other factors,it is necessary to determine the impacts of oil price and operation costs on proved reserves reporting.Taking the A oilfield in China as an example,we obtained various combinations of oil price and operation costs by increasing price and cost at a rate of 10%.Based on calculation with ORGE software,we analyzed the impacts of changes of oil price and the cost on proved reserves reporting.The results show that proved reserves might increase as oil prices rise,but the increasing rate tends to decline gradually.The proved reserves might reduce as operating costs increase,but the decreasing rate also tends to decline progressively.The impacts of oil price and cost on proved reserves is nonlinear,and can be divided into three stages,including dramatic impact,moderate impact and weak impact stages.

Prediction method of critical liquid-carrying flow rate for directional gas wells

Li Li, Zhang Lei, Yang Bo, Yin Yin, Li Dengwei

2012, 33(4):  650-654.  doi:10.11743/ogg20120422

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Current popular models for calculating critical liquid-carrying flow rate for directional gas wells are established based on vertical wells without considering the influences of deviation angle on liquid-carrying.Now more and more directional wells and horizontal wells are deployed in coal-bed methane recovery,but the current vertical well-based models cannot accurately predict the critical liquid-carrying flow rate of these wells.To solve this problem,we performed study based on Turner calculation model with impacts of deviation angle integrated.Analysis of the force balance of spherical droplets reveals that the liquid drops do not always rise up along the central line but fall off slowly on the tubing wall and finally glide up along the tubing.According to Newton’s friction law,we calculated the friction force between the tubing wall and liquid drop,and rebuild a new model to predict critical liquid-carrying flow rate for directional gas wells.Finally,on the basis of the Turner model,we derived correction factors which are related to the friction coefficients and the deviation angles.The practical application shows that this calculation method has higher precision.

Development scheme and EOR technique of fracture-vug reservoirs in Tahe oilfield

Zhan Junyang, Ma Xujie, He Changjiang

2012, 33(4):  655-660.  doi:10.11743/ogg20120423

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The fracture-vug carbonate reservoir of A area in Tahe oilfield is a complex oil reservoir consisting of various spatially superimposed and connected fracture-vug units with multiple pressure systems and complex water-oil contacts.These fracture-vug units differ greatly in driving mechanism and production characteristics.The type-Ⅰ unit is dominated by water drive,the type-Ⅱ unit features in alternating water drive and elastic drive,while the type-Ⅲ unit is predominantly of elastic drive is for.According to the geological features of the reservoirs,this paper proposes a development scheme,i.e.taking the fracture-vug unit as the basic development blocks and implementing differential development,and presents an EOR method that is single well water injection to drive oil and multi-wells unite water injection for development.An additional recovery efficiency of 3.7% is obtained after field application of this method.