Table of Content

08 February 2014, Volume 35 Issue 1

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Major breakthrough of gas exploration in Yangchang blocks and its significance

Wang Xiangzeng

2014, 35(1):  1-9.  doi:10.11743/ogg20140101

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The natural gas exploration blocks of Yanchang Petroleum Group(Yanchang exploration blocks)are located in the southeast of Yishan slope of Ordos Basin.The basin has long been believed to be rich in oil in its south part and abundant in gas in its north-a mindset that resulted in pessimistic evaluation data of gas potential in the Upper Paleozoic exploration blocks of the Group.The first real exploratory well for gas was drilled in the area in 2003.Geological data gathered since then have revealed that the blocks sit in the eastern part of the northern Shanbei slope,which is rich in both oil and gas.The reservoirs are dominated by underwater distributary channels and barrier islands,source rocks are widely distributed,and mudstone seals are thick and stable.The gas resource was estimated to be over 750 bcm.Theoretical and technological innovation obtained during exploration in the blocks by the Group had led to the following achievements:(1)A new understanding of gas accumulation is proposed,i.e.gas accumulations are controlled by combination of reservoirs with paleo-fluid migration and accumulation space;(2)A new foam fracturing system(VES-CO₂) was deve-loped and tested for the Upper Paleozoic tight gas reservoirs.A proven gas in place of more than 300 bcm and annual gas production capacity of 720 million cm³ were obtained. What's more,the Carboniferous Benxi Formation in the basin was found to be able to produce gas at an absolute open flow of over million cubic meters.

Conditions for the formation of large marine gas fields and gas field clusters in Sichuan Basin

Han Keyou, Sun Wei

2014, 35(1):  10-18.  doi:10.11743/ogg20140102

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This paper discussed the forming conditions of large marine gas fields and gas field clusters in Sichuan Basin.Based on comprehensive analyses of structure and lithofacies,we discussed the control of the Indosinian and Caledonian paleouplifts on the marine petroleum accumulation.There are significant changes in exploitation targets in the Sichuan Basin,from anticlinal gas fields in the early stage to large gas fields correlated with porous reservoirs of bank facies,and to composite large gas fields related with peleouplifts now.In the first stage of exploration,small gas field clusters were found in Luzhou peleouplift.In the second stage,the Carboniferous porous gas reservoirs were discovered in eastern Sichuan Basin.In the third stage,the Wubaiti large gas field and gas field cluster were discovered in the Kaijiang paleouplift.In the fourth stage,medium-to-large gas field clusters represented by Puguang gas field were found in the Permian and Triassic reservoirs of reef-shoal facies.Recently,several highly-productive wells have been successfully completed in the Sinian Dengying Formation and the Lower Cambrain Longwangmiao Formation in the Leshan-Longnvsi paleouplift.The favorable superimposition of reservoirs,paleostructures and modern structures makes it possible to form giant gas field in this area.

Characteristics and distribution patterns of deep petroleum accumulations in the world

Bai Guoping, Cao Binfeng

2014, 35(1):  19-25.  doi:10.11743/ogg20140103

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Exploration for deep petroleum accumulations(DPAs)is of great significance to reserve growth and production stabilization of established petroleum provinces(fields).With an update database for the worldwide DPAs,this study attempts to document their distribution characteristics.Among the 349 petroliferous basins in the world(excluding US Lower 48 States),87 basins have discovered DPAs.Clastic rocks and carbonates host 63.3% and 35.0% of the total proved plus probable(2P)deep petroleum reserves in the world,respectively.The remaining 1.7% are in igneous and metamorphic rocks.In terms of trap type,73.7% of the total are entrapped in structural traps.Passive margin and foreland basins contain the bulk of the total 2P deep petroleum reserves,with the former accounting for 47.7% of the total and the latter 46.4%.Stratigraphically,the 2P deep petroleum reserves are largely stored in five reservoir intervals:the Paleogene(hosting 22.3% of the total),Upper Paleozoic(22.2%),Cretaceous(18.3%),Neogene(12.8%) and Jurassic(12.8%).Such a stratigraphic distribution is similar to that of shallow-intermediate reservoirs.As salts have a cooling effect for the subsalt sediments,the maturation of sub-salt source rocks or the conversion of trapped oil to gas can be retarded or delayed.Salt-bearing deep basins deserve special attention for deep petroleum exploration.This study suggests that deep petroleum exploration should target the play fairways where major discoveries have been made in the shallow-intermediate reservoirs,particularly those fairways with salts of certain scale.

Characteristics and main controlling factors of hydrocarbon accumulation in Ordovician Yingshan Formation in Yubei area, Tarim Basin

Tan Guanghui, Qiu Huabiao, Yu Tengxiao, Liu Shaojie, Hao Jianlong

2014, 35(1):  26-32.  doi:10.11743/ogg20140104

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Poor understanding of the main factors controlling hydrocarbon accumulation is the major constraint of petroleum exploration in Yubei area of Tarim Basin at present.The characteristics of hydrocarbon accumulation in Yubei 1 fault belt were studied.Oil reservoirs in the Ordovician Yingshan Formation in Yubei-1 wellblock are of karst-fractured vuggy type controlled by unconformity and related with paleo-karst of carbonate rocks.The reservoir spaces of the Yingshan Formation carbonates consist of pores,vugs and fractures,and the reservoirs can be divided into 3 types,namely fractured-vuggy type,fractured type and vuggy type,of which the fractured-vuggy type is the most significant in this area.The reservoir distribution is mainly controlled by the karst of carbonate rocks.The reservoirs are characterized by strong heterogeneity,vertical superimposition and lateral connection in large area,as well as uneven oil-bearing property.The Yingshan Formation reservoirs experienced multiple phases of hydrocarbon accumulation,of which the Late Hercynian was the major one.Hydrocarbon accumulation in the study area was jointly controlled by oil sources,reservoir,carrier system and cap rock.The oil sources were the foundation of hydrocarbon accumulation.The three-dimensional carrier network consisting of faults and unconformities provided high quality pathway for hydrocarbon migration.The reservoir distribution controlled the formation of the pools and their scales.Mudstone intervals in the Lower and Middle Bachu Formation provided regional seals for the preservation of oil and gas.Based on the analysis of reservoir characteristics and controlling factors of hydrocarbon accumulation,we established a hydrocarbon accumulation pattern for the Yingshan Formation reservoirs in Yubei area.

Genesis of calcite vein and its implication to petroleum preservation in Jingshan region, Mid-Yangtze

Gao Jian, He Sheng, He Zhiliang, Zhou Yan, Zhao Mingliang

2014, 35(1):  33-41.  doi:10.11743/ogg20140105

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Field observation shows that multiple phases of calcite veins occur along fractures in the Ordovician,Permian and Triassic of overthrust belts and fold-thrust belts in Jingshan region,Mid-Yangtze.Using rare earth elements(REE),electron microprobe,oxygen isotope,fluid inclusions and basin modeling,this paper analyzed the genesis of these calcite veins.The REE of calcite veins in the Ordovician and Triassic are characterized by enrichment of LREE,loss of HREE and obvious positive Eu anomaly,indicating that their vein-froming fluids were affected by hydrothermal fluids.Calcite veins in the Permian feature in low REE,only slight enrichment of LREE,flat HREE patterns,and the presence of a moderate negative Ce anomaly,implying that their vein-froming fluids originated from meteoric water infiltration.Analysis of Fe and Mn through electron microprobe indicates that some calcite veins in the Ordovician were derived from the dissolution of surrounding carbonate rocks,the calcite veins in the Permian were derived from leaching and dissolution of carbonates by meteoric water,and those in the Triassic were related to the dissolution of carbonate derived from other horizons.Combined with burial and thermal history modeling of pseudo-wells,analysis of oxygen isotope temperatures and homogenized temperature of fluid inclusions show that the calcite vines filling fractures in these 3 sequences were formed at 150~60 Ma ago at burial depth in the range from 2 000 m to 2 500 m.Based on a comprehensive analysis of geochemical behaviors of the calcite veins,it is believed that hydrothermal fluids,vein-froming fluids and meteoric water infiltration associated with tectonic compression and uplifting during Yanshan Orogeny may have damaged petroleum preservation conditions in Jingshan region to some extent.

Hydrocarbon generation kinetics of type-Ⅰ organic matters in the Cretaceous lacustrine sequences, Songliao Basin

He Kun, Zhang Shuichang, Wang Xiaomei, Mi Jingkui, Mao Rong

2014, 35(1):  42-49.  doi:10.11743/ogg20140106

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A pyrolysis experiment with gold-tube modeling apparatus was carried out to study the features and kinetics of hydrocarbon generation from the type-Ⅰ organic matters in the Cretaceous lacustrine sequences,Songliao Basin.Quantitative analysis of the liquid and gas products from the simulation experiment of type-Ⅰ organic matters indicates that oil is the dominant product and gas yield is limited with the maximum value from the primary cracking at 100 mg per gram of organic matter.The chromatograms of light oils and the activation energy distribution of hydrocarbon gas genereation collectively demonstrate that the hydrocarbon gas in confined system are generated from multiple reaction processes,wherein the secondary cracking of liquid hydrocarbons initially generated have a greater contribution.Meanwhile,kinetics calculation shows that the reaction kinetic parameters of different liquid hydrocarbons differ from one another;the activation energy of light components is obviously higher than that of the heavier ones;the average activation energy of secondary cracking of residual oil in source rocks was 57.3 kcal/mol,being lower than that in normal reservoirs;and the generation of primary cracked gas from the type-Ⅰ organic matters lasted from the initial stage of oil generation to the early cracking stage of residual oil within source rocks.

Hydrogeochemical behaviors of oilfield water in the Tertiary in western Qaidam Basin

Li Jiansen, Li Tingwei, Peng Ximing, Han Yuanhong, Li Zhongping, Ma Haizhou

2014, 35(1):  50-55.  doi:10.11743/ogg20140107

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The elements and hydrogen and oxygen isotope geochemistry analysis of oilfield water in the Tertiary in western Qaidam basin shows high salinity and abundant ions of potassium,boron and lithium of industrial mining grade.The analysis also reveals a hydrogen isotope value distribution of 75.61‰ to 13.35‰ and an oxygen isotope value distribution between -7.68‰ and 10.58‰.Combining these results with chemical analysis of the water,we concluded that the water was of typical terrestrial origin and was sourced from meteoric water,which seeped down along deep faults and was in-fluenced by deep-sourced magmatic fluids during its "deep circulation".The high salinity of the water may be caused by dissolution of saline minerals and their concentration through evaporation.Potassium,boron and lithium are mostly controlled by deep-sourced fluids and ions like Ca²⁺ and HCO₃^- are mainly sourced from dissolution of carbonate minerals.High concentration of calcium ion and low concentration of bicarbonate radical are thought to be linked to replacement of calcite by dolomite and dissolution of calcite.The formation of CaCl₂ type water is therefore inferred as the result of an adequate water-rock reaction and the participation of deep-sourced fluids.It is preliminarily inferred that the Tertiary in Nanyishan area of the basin may be a potential target for exploration of potassium.

Sedimentary characteristics of bioherm in the Lower Silurian Shiniulan Fm, southeastern Chongqing

Tan Xianfeng, Li Zhijun, Jiang Yanxia, Li Jie, Li Hang

2014, 35(1):  56-64.  doi:10.11743/ogg20140108

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A certain amount of bioherm are developed in the Lower Silurian Shiniulan Formation in southeastern Chongqing.Taking the Jiqiangtai outcrop in Wansheng of Chongqing and Houtan outcrop in Xishui of Guizhou as the main study targets,we studied in detail the bioherm in the Lower Silurian Shiniulan Formation through field observation,ordinary thin section observation and carbon/oxygen isotope measurement.The bioherms mainly occur in the Upper and Middle Shiniulan in the study area and have a certain scale.Rock structure and carbon/oxygen isotopes reveal a change of sea level from slow rising to sharp declining.Depositional environment developed from shallow mixed continental shelf in the early stage to biological reef-shoal in the middle stage and finally to reef-front slope in the late stage.The aquatic environment was suitable for the coral bioherms and biological communities to thrive.The development of bioherm in the Lower Silurian Shiniulan in southeastern Chongqing was mainly affected by sea-level changes and terrigenous clastics input.Slow change of sea level was the basic condition for bioherm growth and the amount of terrigenous clastics input controlled the process of bioherm development.

Pore types and controlling factors on porosity and permeability of Upper Triassic Xujiahe tight sandstone reservoir in Southern Sichuan Basin

Zhu Haihua, Zhong Dakang, Zhang Yaxiong, Sun Haitao, Du Benqiang, Meng hao, Zhang Chunwei, Yang Zhe

2014, 35(1):  65-76.  doi:10.11743/ogg20140109

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Based on thin sections,scanning electron microscopy(SEM),core porosity and permeability data,and mercury injection data,this paper summarized the pore types,physical property of tight sandstone of the Xujiahe Formation and discussed the controlling factors on pore types,poroperm relationship and spatial change of physical property.The result shows that the rapid compaction process and minor dissolution resulted in the relative abundant of primary pore followed by dissolution pore and intergrannular micropore.As the porosity increases,the permeability change shows a three-stage pattern,namely rapid increasing first,then getting stabilized and increasing again.This distribution pattern is mainly controlled by pore throat filling authigenic chlorite and illite which offset the increases in permeability due to the increase of porosity.The poor connectivity of dissolution pore and micropore also influence the permeability of sandstone.The spatial change of physical property of sandstone is controlled by sedimentary condition.The relative short transport distance or low energy environment resulted in low compositional and textural maturity and poor physical property.Only the sandstone with long transport distance and high energy environment are abundant in porosity.The physical quality in middle and lower part of single fluvial sandstone is better than that of the upper and bottom parts.The major reason is that the decreases of energy during fluvial sandstone deposition result in higher compositional and textural maturity of the middle part and lead to the diagenetic heterogeneity within a single sandstone.

Alteration of volcanics and its controlling factors in the Lower Permian reservoirs at northwestern margin of Junggar Basin

Zhu Shifa, Zhu Xiaomin, Wu Dong, Liu Yinghui, Li Panpan, Jiang Shuxian, Liu Xuechao

2014, 35(1):  77-85.  doi:10.11743/ogg20140110

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Based on observations of available cores,thin-sections and SEM and analysis of rock geochemistry,we studied low-temperature-burial metamorphism(alteration)of volcanics in the Lower Permian at northwestern margin of Junggar Basin.These volcanics include volcanic glass,volcanic clasts,feldspar,and mafic minerals such as pyroxene and hornblende,etc.,which originate from lavas,pyroclastic rocks,and volcaniclastic sandstones or conglomerates.In oil/gas reservoirs containing volcanics,the authigenic minerals that are common but important to pore spaces include chlorite,zeolites(like analcime,heulandite,and laumontite),calcite,albite,and authigenic quartz.Based on the paragenetic relationship of minerals and the composition and migration of elements,we analyzed the microscopic characteristics and origins of authigenic minerals,and established diagenetic evolution models during volcanic alteration.The alteration can be summarized as follows:①volcanic glasses hydrolysis-montmorillization-zeolitization-albitization;②chloritization related to mafic minerals and smectites;③transformation of feldspar to chlorite,calcite,and finally to albite.The alteration of volcanics and the formation of authigenic minerals in the study area were controlled by various factors such as the precipitation of authigenic minerals,composition of neutral-basic host rocks,temperature and pressure,and the chemical behaviors of pore water.The study on alteration process,alteration products,and control factors is helpful to understand the mechanisms that cause the differences of volcanics-bearing reservoir qualities,so as to provide a scientific geological foundation for the predication of high-quality reservoirs.

Oil-controlling models of caprock-fault combination and prediction of favorable horizons for hydrocarbon accumulation in middle-shallow sequences of Nanpu sag

Lü Yanfang, Xu Chenlu, Fu Guang, Liu Naiyu, Cui Shoukai, Pang Lei

2014, 35(1):  86-97.  doi:10.11743/ogg20140111

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There are 3 caprocks that control the vertical distribution of oil and gas in the middle-shallow sequences of Nanpu sag,namely the mudstone caprock of the Lower Minghuazhen Formation(Nm),the volcanic caprock of the third member of Guantao Formation(Ng³)and the mudstone caprock of the second member of Dongying Formation(Ed²).The sealing abilities of the caprocks were destroyed in different degrees due to faulting.Based on analysis of the thresholds of juxtaposition thickness of faults in these caprocks and in combination the vertical positions of fault cutting cross the caprocks,areal fault distribution and faulting history,we built 3 oil-controlling models of caprock-fault combinations.①Full sealing at the bottom.This model is favorable for oil accumulation under the mudstone caprock of the 2nd members of Dongying Formation;②Open at the bottom but sealing in the middle.This model is favorable for oil accumulation under the volcanic caprock of Ng³;③Limited sealing at the bottom and middle.This model is favorable for oil accumulation all the reservoirs under the mudstone caprock of Ed² in Nanpu sag.According to these 3 models and the characteristics of caprock and faults in Nanpu 1-5 block,we predicted the horizons favorable for oil accumulation in the study area.Area under the control of fault f1-3 and f2-12 is the second model,and favorable horizons for oil accumulation are the 4th member of Guantao Formation,the 1st member and the reservoirs below the 2nd member of Dongying Formation.Area under control of fault f4-48 is the first model,and the favorable horizons for oil accumulation are reservoirs below the caprock of the second member of Dongying Formation.Area under control of fault f13-1 is the third model,and all reservoirs under the caprock of the Lower Minghuazhen Formation are favorable for oil accumulation.These models have effectively guided the prediction of potential exploration targets.

Analysis on the fault system of Yubei region, Tarim Basin

Huang Taizhu

2014, 35(1):  98-106.  doi:10.11743/ogg20140112

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Based on accurate 3-D seismic interpretation,comprehensive analysis of the drilling and geological data,it is indicated that the fault systems of the Yubei region in Tarim Basin are dominated by thrust faults.These thrust faults occur in two horizons.One is the basement where the thrusts consist basement fault zone(or basement weak zones).The other is the Cambrian-Ordovician carbonates where a thrust zone occurs.The Yubei fault system consists of a series of NEE-trending thrust zones including Yubei No.7,Yubei No.1,Yudong No.1,Yu-dong No.2,Yudong No.3 and Yudong No.4.Each single thrust belt is often composed of one main thrust and a set of associated secondary thrust faults.The fault plane of the main fault dips steeply at the upper part and flattens towards the deeper part,and detaches in the Mid-Lower Cambrian salt la-yers.The main thrust and its associated secondary back-thrusts commonly form pop-up fault assemblage showing "fault-horse" geometry on profile.These fault zones in the Cambrian-Ordovician carbonate rocks were mainly formed in the mid-Caledonian,experiencing movement of the early-epoch(the Early Ordovician Penglaiba stage),Ⅰ-epoch(the Mid-Early-Ordovician Yingshan stage),and Ⅲ-epoch(the Late-Ordovician)of the mid-Caledonian.The fault movement was very weak in the Hercynian.The fault zones are characterized by significant segmented deformation.The fault system and major unconformities jointly control the vertical structural layering.

Hydrocarbon accumulation pattern jointly controlled by strike-slip faults and cap rocks：a case from Yingshan Formation in ZG-51 wellblock of eastern Tazhong area, Tarim Basin

Lan Xiaodong, Lü Xiuxiang, Zhu Yanming, Li Shiyin, Xie En

2014, 35(1):  107-115.  doi:10.11743/ogg20140113

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Oil/gas/water distribution is complex in the marine carbonate reservoirs of the Yingshan Formation in ZG-51 wellblock of eastern Tazhong area.Based on analysis of the existing oil and gas exploration results,fault characteristics and reservoir-seal assemblage,we studied the oil/gas distribution and accumulation characteristics of the Yingshan Formation by using various data such as routine logging,image logging,seismic data and geochemical data.The reservoirs of Yingshan Formation in this wellblock are predominantly of vuggy type and fractured-vuggy type,and show quasi-layer distribution along unconformities.The strike-slip faults significantly controlled hydrocarbon accumulation.The distance between oil/gas wells and major strike-slip faults ranges from 0.5 to 4.0 km.The daily oil and gas output decreases away from the strike-slip faults.The geochemical behaviors of oil and gas also changes regularly with the distance to the strike-slip faults.In plane view,the gas reservoirs are near the faults,while oil reservoirs are far from these faults.The 3^rd to 5^th members of Lianglitag Formation as well as the high resistive intervals of the Yingshan Formation act as barriers.Vertically,multiple reservoir-seal combinations superimpose each other,resulting in oil/gas accumulation in multiple layers.The early oil pools were influenced by gas invasion in later stage,resulting in the vertical distribution characteristics of "upper oil and lower gas".Hydrocarbons accumulated in favorable structural traps and lithologic traps under the jointly control of cap rocks and strike-slip faults.

Structural characteristics and active ages of the Gudongshan fault belt in Bachu uplift, Tarim Basin

Yang Yong, Tang Liangjie, Yue Shujuan, Huang Taizhu, Yun Lu, Xie Daqing

2014, 35(1):  116-123.  doi:10.11743/ogg20140114

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2-D seismic data interpretation combined with structural analysis was used to build a geometry model and determine active ages of the Gudongshan fault belt.The formation and evolution of this fault belt with complicated tectonic deformation may be closely related to the evolution of oceanic basins and orogenic belts around Tarim Basin.Faulting activities were the most obvious in key tectonic periods of Tarim Basin,namely the Middle Caledonian,Early Hercynian,Middle Hercynian,Early Himalayan and Later Himalayan.Faults No.1 and No.2 in the Gudongshan fault belt control the thickness of the Palaeozoic strata on both sides of the belt and also show signs of multiple-stage activities.Fault No.1 was active during phase Ⅰ and Ⅲ of the Middle Caledonian and shows feature of progress intensification of its activity.Fault No.2 was developed in the Early Hercynian and successively experienced negative inversion in the Carboniferous and positive inversion at the end of Paleogene.Fault No.3 was formed in the Early Himalayan and controlled the tectonic framework of the Precambrian basement which is higher in southwest and lower in northeast.Faults No.4 and No.5 were developed in the Later Himalayan.The former has a thrust displacement up to 20 km and a denudation-caused monocline at the hanging wall.

Analysis and application of components and isotopic compositions of fluid inclusions in volcanic reservoirs of the Xujiaweizi fault depression

Li Jijun, Cao Xicheng, Wang Weiming, Shi Lei, Li Jingkun, Huo Qiuli

2014, 35(1):  124-130.  doi:10.11743/ogg20140115

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A comparative analysis of components and isotopic compositions of gas inclusion in volcanic reservoirs of the Xujiaweizi fault depression before and after thermal decrepitation was performed by using the vacuum mechanical crushing method.The origin of natural gas was further discussed in combination with the corresponding characteristics of natural gas produced from wells and the results of thermal simulating test.The hydrocarbon content of gas from magma degassing is high,indicating that some hydrocarbon gases may be of inorganic origin,thus it is necessary to further research on the differences between gas from volcanic action and that from magmatic action.The main cause of reversal carbon isotopic sequence of hydrocarbon gas in the study area is the mixing of natural gases generated in different times or from different sources,rather than the component and isotopic fractionation during dissipation of natural gas through the caprock.Therefore,the reversal phenomenon can not be used individually to confirm the genesis of natural gas.In comparison with organic gas,inorganic gas(including CH₄,C₂H₆,CO₂)often has a heavier carbon isotopic value.It is applicable to some extent to use the the δ¹³C₁ value over -20‰ as the criteria for determining inorganic gas,but this criteria is over strict.The CO₂ in Xujiaweizi fault depression is mainly sourced from magma degassing.The inorganic CO₂ did not experience primary migration and had no chance to contact with formation water,being favorable for their accumulation.These understandings are helpful to determine the origin of natural gas in Xujiaweizi fault depression.

A review of numerical simulation of shale gas reservoirs

Yu Rongze, Bian Yanan, Qi Yadong, Zhang Xiaowei, Li Yang, Yan Jun, Wang Meizhu

2014, 35(1):  131-137.  doi:10.11743/ogg20140116

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This article expounds on the recent advancement of the technology all around the world through the following three aspects:shale gas occurrence and flow mechanism,gas reservoir modeling,as well as theoretical study and application of numerical simulation.It suggests that four issues remain to be improved and further probed:①Improving reservoir modeling to take the effect of organic matte into consideration;②Expounding more on flow mechanism and main controlling factors of single-phase gas desorption,diffusion and percolation,and establishing mathematical model and numerical model for two-phase(gas/water)flow;③Understanding the importance of accurate modeling of natural and induced fractures to shale gas reservoir numerical simulation,and combining related results of other detecting techniques in practical application;④Establishing corresponding standards and norms for shale gas reservoir numerical simulation.

Rate transient analysis of multistage fractured wells with horizontal fractures in tight oil reservoirs

Liu Botao, Li Qingquan, Zhang Fuxiang, Wang Xinhai, Li Guoliang, Lu Chong, Yue Hailing, Wang Zhao

2014, 35(1):  138-142.  doi:10.11743/ogg20140117

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Permian Lucaogou Formation(P₂l)in Jimusaer(JMSE)sag of Karamay oilfield is a typical representative of tight oil reservoirs in Junggar Basin.Staged fracturing technology is commonly used to improve the productivity of single well.While previous researches were more concentrated on the cases of vertical fractures,the vertical fracture model could not explain the actual data in the blocks.At the same time,the theoretical and experimental studies show that horizontal cracks are easy to form during the process of fracturing according to the matching relationship between natural fracture azimuth and geostress.Therefore there is a lack of theoretical guidance in study area.Based on the law of conservation of mass and considerations of starting pressure gradient,pressure sensitivity and finite conductivity fractures,a dimensionless mathematical model has been set up to study the flow in the multistage horizontal fracturing fractured well in dual porosity and single permeability reservoir in this paper.And numerical solutions of the model are obtained by using implicit diffe-rence method and conjugate gradient algorithms.The effects on unsteady productivity of starting pressure gradient,formation heterogeneity coefficient,interporosity flow coefficient,pressure sensitive coefficient,conductivity and the number of cracks are studied through numerical simulation in turn.Research results show that the fracture parameters and formation parameters affect the productivity curves.So it is necessary to consider both fracture parameters and the pressure decline reasonably,as choosing an appropriate fracturing scheme to obtain maximum productivity.

Application of geological modeling technology in secondary development of old and complex fault block oilfields

Zou Tuo, Zuo Yi, Meng Lixin, Liu Yunli, Xing Xiangrong, Feng Jinyi

2014, 35(1):  143-147.  doi:10.11743/ogg20140118

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Re-understanding of underground geologic system is one of the key technologies for secondary development of old oilfields,while geological modeling is the only way to quantitatively re-understand geologic system of reservoirs.Old and complex fault block oilfields are characterized by long history of exploitation,complex structures,large lateral variation of reservoirs,and local enrichment of remaining oil.In viewing of these features,we proposed corresponding strategies and methods of geologic modeling.According to the characteristics that many faults crosscut each other,the idea of stepwise simulation-key horizon controlling-overall structural modeling was adopted to accurately and efficiently build fine structure models.In order to approximate the "real" microfacies simulation,multiple iterations microfacies modeling technology under dual vertical and lateral geological trend constraints is adopt to ensure the maximum approximation of subsequent attribute models with the 'real' geological parameters distribution of reservoirs.Meanwhile,for the key potential oil-bearing sandbodies,configuration fine modeling technology that use different stochastic simulation methods in a nested way and performs simulation step by step was used to rapidly build geologic models.This new geological modeling technology was successfully applied to the secondary development of Gangdong oilfield.

Stereology-based simulation of 3D fracture network with 2D data

Ni Chunzhong, Liu Chunxue, Zhang Shitao, Li Aimin, Li Yujian, Cang Baohai, Liu Lei

2014, 35(1):  148-152.  doi:10.11743/ogg20140119

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Various attribute information of fissures such as length,width and density can be extracted from CT scanning images of oriented rock samples that are systematically collected through field work.These information can play a important role in defining spatial distribution of fissure networks within rocks.Both trace distribution and fissure network distribution follow the power-law distribution,thus statistical analysis can be performed on the field-collected trace data.The extension length and interlink of fissures on 2D images can be inversed to 3D space by applying stereological techniques,so as to deduce 3D fissure length and density distribution and realize conversion of rock fissure attributes from 2D to 3D.This approach was applied in Gaosong ore field.Based on analysis of the traces on the CT scanning images,we obtained the maximum trace length of 64.1 mm,the minimum of 2.2 mm,a mean of 16.69 mm and a variance of 12.33 mm.The fissures were divided into 9 groups,and the probability distribution of diameters of each group was obtained.Simulation was performed on the extracted trace data when the fractal dimension(α)is 1.5 and 2.5 respectively.The mean of fissure diameter was 27.60 mm,and fracture network density was 0.30/cm³.This approach can be popularized to other mines to obtain attributes of 3D fissure network when only 2D data are available.

Evaluation criteria and classification of shale gas reservoirs

Tu Yi, Zou Haiyan, Meng Haiping, Xia Zhiyuan, Li Nan

2014, 35(1):  153-158.  doi:10.11743/ogg20140120

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Establishment of shale gas evaluation criteria and reservoir classification methods is important for shale gas exploration and development.Based on investigation and survey of geological features,gas generating capacities,gas storage capacity and recoverability of typical shale gas plays in the world,10 parameters for shale gas reservoir evaluation were selected in combination with the specific geological conditions of Sichuan Basin and their scores for shale gas reservoir classification were also determined.Grey relational analysis method was used to define the relationship between these factors and to calculate the weights of the principle and secondary factors and the comprehensive evaluation factors of shale gas reservoir quality.Shale gas reservoir classification was further performed on the calculation results.Shale gas reservoirs in Sichuan Basin are similar with that in the 5 major shale gas basins in the America.The comprehensive evaluation factors of shale gas reservoirs in the Longmaxi Formation and Qiongzhusi Formation are 0.48 and 0.45 respectively,which are very close to that of New Albany shale gas basin.Case study shows that the reservoir classification results accord well with the practical production situation.This evaluation method can be applied to shale gas reservoir evaluation and selection in China.

Geochemical behaviors of shallow soil in Muli permafrost and their significance as gas hydrate indicators

Xing Xuewen, Liu Song, Zhou Hongying, Zou Liqun, Li Guangzhi, Gao Wei

2014, 35(1):  159-166.  doi:10.11743/ogg20140121

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Muli,the only gas hydrate hosting area in China proved by core sampling,is located in Qilian Mountain permafrost area.Petroleum geochemical exploration was carried out with three hydrocarbon detection techniques(HS,acidolysis hydrocarbon and altered carbonate survey methods)in the area.The results show that the former two methods are more effective than the latter one.Analysis of free hydrocarbons extracted through HS and absorbed hydrocarbons from acidolysis indicates that the components of hydrocarbon gas in soil of areas containing gas hydrate in Muli are complex.In addition to the major component of methane,there are also small amount of ethane,propane,butane and pentane.There are both hydrocarbon gas of pyrolytic origin and that of microbiogenic genesis.The hydrocarbon gas can be classified as oil-prone gas,coal-drived gas and biogas.Methane contrast diagram in combination with the geologic background and core samples in wells discovering gas hydrate reveal that its eastern-central part with well-developed faults and high methane anomaly may be a favorable target for gas hydrate exploration.