Table of Content

08 October 2014, Volume 35 Issue 5

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Evolution of paleo-hydrodynamics and hydrocarbon migration and accumulation in southern Dongpu Sag, Bohai Bay Basin

Jiao Daqing, Li Mei, Mu Xiaoshui, Xu Tianwu

2014, 35(5):  585-594.  doi:10.11743/ogg20140501

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Hydrocarbon migration and accumulation are closed related with hydrodynamic field.In this paper,the hydrocarbon migration and accumulation mechanism of southern Dongpu Sag was analyzed in respect of the paleo-hydrodynamic evolution.Forming time of hydrocarbon reservoir was determined by analyzing the homogenization temperature of fluid inclusions,and then hydrocarbon charging process was restored.The results show that there are three hydrodynamic units in southern Dongpu Sag:centrifugal flow of mudstone compaction-released water developed in the east and west sub-sags,centripetal flow of meteoric water occurred in the Lanliao fault belt,and cross-formational flow and discharge area in the central uplifted belt.The later is the most favorable place for hydrocarbon accumulation.The sedimentary period of Dongying Formation(Ed)was the primary stage for hydrocarbon migrating to and accumulating in the bottom of down-thrown blocks of faults.The stage of Dongying tectonic uplifting was the main period of hydrocarbon adjustment.Hydrocarbons from the deep reservoirs formed in early stage remigrated to and accumulated in the shallow layers on structural high,forming the secondary oil reservoirs.The Guantao and Minghuazhen were the main periods for gas accumulation.Natural gas mainly accumulated in the deep strata of structural limbs,owing to the increasing sealing ability of faults,resulting in the "upper oil lower gas,top oil marginal gas" hydrocarbon distribution pattern.

Main controlling factors and models of hydrocarbon accumulation in weak structural belts of oil-rich sags, the Jizhong Depression

Gao Changhai, Zha Ming, Ge Shengquan, Chen Li, Zhao Xianzheng, Jin Fengming

2014, 35(5):  595-600,608.  doi:10.11743/ogg20140502

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Weak structural belts in this paper refer to Wenan and Lixian slope zones of the oil-rich sags in Jizhong Depression，where the exploration maturity is low but resource potentials are large and exploration prospects are good.Based on the integrated analysis of geological elements and in combination with physical simulation experiments,the paper illustrates the main controlling factors of hydrocarbon accumulation,reveals hydrocarbon accumulation patterns and establishes hydrocarbon accumulation models,so as to provide theoretical guidance for further oil and gas exploration of the weak structural belt.The result shows that the main controlling factors of hydrocarbon accumulation in weak structural belt are source rock,carrier system and nose structure.Among them,the source rock controlled the distribution range and the enrichment degree of hydrocarbons,the carrier system controlled the horizons of hydrocarbon accumulation and the reservoir types,and the nose structure controlled the hydrocarbon migration direction.Two hydrocarbon accumulation models were established for the weak structural belt based on the configuration relationships between the source rock and the carrier system.One is distal stepwise accumulation model on wide-gentle slope zone,featuring in joint driving of overpressure and buo-yancy,stepwise migration dominated by lateral transportation through sandbody and adjusted vertically by faults,accumulation in multi-layers far from the source rocks.The other is proximal Z-style accumulation model on gentle slope belt,featuring in driving of buoyancy,Z-style migration through vertical adjustment of faults and lateral transportation of sandbo-dies,the accumulation in multiple layers near the source rocks.

Tectonic-sedimentary characteristics and their influences on the forming of lithologic hydrocarbon reservoirs in the Shichang Subsag of the Nanpu Sag

Liu Junrong, Wang Xiaowen, Zhao Zhongxin, Zhang Lei, Li Jie, Lu Pengfei

2014, 35(5):  601-608.  doi:10.11743/ogg20140503

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Shichang Subsag of Nanpu Sag is an old exploration and development area of Jidong Oilfield,the its main structural reservoir has been proven,and put into development.The next is to find new areas torelay.In this paper,the lithologic reservoir accumulation mode is established through research and analysis of tectonic evolution,sedimentary system and their controlling role on lithologic traps.That provides a theoretical basis for future exploration.In the early Shahejie Formation(Es)period,the provenance was mainly from the bulge on the upthrown side of Baigezhuang fault in the east of subsag.There existed multiple fan-delta systems along the Baigezhuang downthrown side and they prograded far towards the subsag center.Meanwhile,small fan-delta,shallow lake and semi-deep lake sediments distributed along the downthrown side of Xinanzhuang faults in the west.In the late Es,the activity of Baigezhuang fault leaded to the inversion of early strata attitute.And the early downlap sandbody pinched on the slope, forming a updip pinchout type deposition mode.These sand bodies and sub-sag cooperated with west uplift tectonic introversion to form the updip pinchout trap,which formed the most important lithologic reservoirs in Shichang Subsag.These reservoirs have the characteristics of multi-strata-enrichment,large-scale and multi-oil-water systems.

Fluid inclusion characteristics and hydrocarbon accumulation process of deep reservoirs in Changling rift, Songliao Basin

Jin Xiaohui, Yan Xiangbin, Sun Dongsheng, Li Lina, Chen Xia, Sun Yipu, Li Shujun

2014, 35(5):  609-613.  doi:10.11743/ogg20140504

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Research on hydrocarbon accumulation process is the basis for studying hydrocarbon enrichment patterns and identifying favorable areas for petroleum exploration.Based on the microscopic description of fluid inclusion and analysis of homogenization temperature,hydrocarbon inclusions mainly occur in the secondary quartz overgrowth,microfractures crossing these overgrowth and calcite cement.The dominant frequency of homogeneous temperature was 130-150 ℃.The diagenetic history and burial history show that high maturity natural gas migrated upward with maturing of hydrocarbon source rock and displaced the oil accumulated in the lower traps into the higher traps,resulting in the formation of Well SN189 and Well SN183 accumulations.Residual asphalt in the Yingcheng Formation in Well SN115,which is near the hydrocarbon generation center,was the product of crude oil pyrolysis in this period.Natural gas generated during later period migrated upward along the fault and formed Well SN182 natural gas pool where the inclusions are mainly of natural gas.As a result,along the fault up-dip direction,the number of liquid hydrocarbon inclusions gradually decreases,while the number of natural gas inclusions gradually increases.Oil accumulated in the higher position,and gas accumulated in the lower parts.The oil and gas share the same hydrocarbon source.Up-dip pinchout sandstone and sandstone lens in the depression and slope area of Changling rift are the main targets for natural gas exploration.

Oil accumulation patterns and key controlling factors of Fuyu oil layer in the western slope of the northern Xingshugang oilfield, Songliao Basin

Wang Yachun, Chen Chongguang, Wang Lu, Zhu Lin, Jiang Zheng, Xi Guoxing

2014, 35(5):  614-621.  doi:10.11743/ogg20140505

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A slope zone is an important region for hydrocarbon migration and accumulation,thus has relatively high exploration potential.Through integration of seismic,well logging and oilfield production data,this paper studied the oil reservoir characteristics and important exploration targets in the Fuyu oil layer in the western slope zone of the northern Xingshugang oilfield,Songliao Basin.The results show that oil reservoirs in this area are developed under the joint control of fault and lithology,and the major oil reservoir types include fault-screened,fault block,fault-nose,fault anticline,updip lithologic pinch-out,and fault-lithologic reservoirs.These oil reservoirs are characterized by 'upper oil and lower water without unified oil-water contact’.Two hydrocarbon accumulation patterns are identified in the Fuyu oil layer,namely downward migration and accumulation within the source kitchen and lateral migration and accumulation beyond the source kitchen.The former refers to that,driven by the paleo-overpressure of the Qingshankou Formation,the oil sourced from the 1^st Member of Qingshankou Formation(K₂qn¹),migrated downward along the faults connecting the K₂qn¹ source rock and the underlying sand bodies and traps of the Fuyu oil layer,forming oil reservoirs.The latter means that the oil sourced from the K₂qn¹ source rock in the Qijia-Gulong depression first migrated downward to the Fuyu oil layer,and then migrated laterally into the northern Xingshugang region along pathways such as sand bodies and faults connecting the Qijia-Gulong depression and the northern Xingshugang region,forming oil reservoirs.The distribution of oil reservoirs are mainly controlled by available oil sources,match of faults and sand-bodies,and antithetic normal faults.The overpressure of the Qingshankou Formation is the key to ‘downward migration’ of oil,while abundant oil sources form the material basis and match of faults and sand-bodies provides pathways for ‘downward migration’ of oil.At last,it is suggested that the hanging walls of antithetic normal faults in good match with sandbodies are important targets for oil exploration.

Salt-related structure and its control on hydrocarbon of the Cambrian in Sichuan Basin

Li Shuangjian, Sun Dongsheng, Zheng Menglin, Meng Xianwu

2014, 35(5):  622-631,638.  doi:10.11743/ogg20140506

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Gypsolyte-salt layers of the Middle-Lower Cambrian are widely developed in the southern and eastern Sichuan Basin,resulting in a variety of salt-related structures.Analyses of outcrop,drilling and seismic data reveal that the gypsolyte-salt layers of the Cambrian in Sichuan Basin formed on restricted intra-craton platform and has the characteristics of old age,deep burial depth,uneven thickness,more gypsolyte and less salt,and various associated rock types.The gypsolyte-salt related structures show obvious layering due to the differential gypsolyte and salt mobility,tectonic compression,basement faults,and detachment,.The post-salt structures are mainly anticlines,thrust nappes and faulted-anticlines.The structures within the salt layers are mainly salt pillows,tail structures and plastic flow structures.The presalt structures mainly include imbricate thrusts and pop-up structures controlled by the complex basement faults.The gypsolyte-salt layers of the Cambrian provide good sealing conditions for hydrocarbon accumulation in the Lower Sinian-Lo-wer Cambrian.Meanwhile,they also can improve reservoir quality through TSR and supergene dissolution that they are involved.Even more important,as a region detachment layer,the gypsolyte-salt rock plays an important role in the structural deformation of the post-salt and pre-salt Sinian-Lower Paleozoic,resulting in a series of hydrocarbon traps.According to the characteristics of gypsolyte-salt related structures,the pre-salt faulted anticlines in western Hubei-eastern Chongqing and post-salt faulted anticlines in southeast Sichuan are the favorable exploration targets.

Differential deformation of strike slip faults in the Liaodongwan Depression, offshore Bohai Bay Basin

Yu Yixin, Zhou Xinhuai, Xu Changgui, Wu Kui, Liu Yubo, Yang Keji, Zhou Xin

2014, 35(5):  632-638.  doi:10.11743/ogg20140507

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As an important fault type in the Liaodongwan Depression,strike slip faults are components of the Tan-Lu fault zone,and they have exerted major influences on the structural framework and hydrocarbon accumulation in the depression.Based on detailed 3D seismic interpretation,this paper reveals the spatial distribution and segmented differential deformation characteristics of the strike slip faults in the Liaodongwan Depression.The strike slip faults mainly occur in the eastern and central Liaodongwan Depression,trend northeast as a whole,and have good continuity.They appear as flower structures on sectional view,while appear as strike slip duplex and imbricated structures on plane view.Comparison of deformation features of strike slip faults in different areas shows that the strike slip fault zone features in obvious segmented differential deformation.The strike slip faults can be divided into two segments,namely transpressional segment in the south and uplifting segment in the north.The uplifting segment can be subdivided into complex-uplifting,buried-uplifting and single-uplifting segments according to the shapes of the uplift.The development of the Liaodong uplift was mainly controlled by the transpressional movement of the strike slip faults,but the Liaoxi uplift with earlier initiation of uplifting was influenced by extensional stresses resulted from mantle uplifting.

Sealing ability of faults in northeastern Chepaizi Uplift at western margin of Junggar Basin

Dong Dawei, Li Li, Liu Jian, Zhao Li, Liu Haijian

2014, 35(5):  639-645.  doi:10.11743/ogg20140508

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Faults are the main oil-gas migration pathways in Chepaizi area and can also form associated hydrocarbon re-servoirs,thus research on fault sealing ability is of great significance for confirming spatial distribution of reservoirs in the study area.Through qualitative analysis of fault characteristics and the timing between faulting and hydrocarbon generation and expulsion,and quantitative evaluation of factors controlling sealing ability such as juxtaposition of lithology,shale smear,and normal stress on fault surface,we studied the sealing ability of two major faults(F1 and F2)in northeastern Chepaizi Uplift,and performed comprehensive judgment by using fuzzy evaluation method.The results show that the sea-ling abilities of F1 and F2 feature in ‘vertical periods and lateral segmentation’.Vertically,the fault sealing ability can be divided into periods,including Cretaceous(K),the first member of Neogene Shawan Fm (N₁s¹),2^nd member of Neogene Shawan Fm(N₁s²),and 3^rd member of Neogene Shawan Fm(N₁s³).The sealing ability of faults in Cretaceous is good as a whole except for the southern segment of F2.For N₁s¹,sealing ability of F1 is good in the northern segment,poor in the middle segment,and good to poor in the southern segment,while that of F2 is poor to fair as a whole.For N₁s²,fault sealing abilities are good as a whole.For N₁s³,fault sealing abilities are poor as a whole,except for the middle segment of F2 whose sealing ability is good.

Genesis of low permeability reservoirs of nearshore subaqueous fan in Shahejie Formation in Dongying Sag, Bohai Bay Basin

Zhu Xiaomin, Wu Dong, Zhang Xin, Wang Xingxing, Han Xuefang, Zhang Shoupeng

2014, 35(5):  646-653.  doi:10.11743/ogg20140509

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In order to demonstrate the genesis of low permeability reservoir of nearshore subaqueous fan in northern steep slope of Dongying sag,abundant cores and reservoir analysis data were utilized to conduct the research on lithological characters of reservoir,diagensis,diagenetic sequence and porosity evolution as well as their controlling factors.The sandbodies of nearshore subaqueous fan of the Shahejie Formation consist of arkose and feldspathic lithic sandstone and the reservoirs have experienced strong compaction,carbonate cementation,dissolution of calcite and feldspar in the burial diagenetic evolution.The reservoirs are at the middle diagenetic stage now,have a burial depth in the range of 1 700-3 500 m and mid-low porosity(mean porosity 11.3%)and low permeability(mean permeability 23.12×10^-3 μm²).The strong compaction and carbonate cementation reduced the porosity and permeability of the reservois,while dissolution contributed to the improvement of reservoir quality.The intergranular pores and intragranular pores resulted from dissolution of calcite and feldspar at the depth of 2 900-3 200 m are constructive to reservoir quality(porosity up to 25% and permeability up to 1 000×10^-3 μm²).Obviously,identification of dissolution and intervals with well-developed secondary pores is extremely important for predicting favorable reservoir.

Characteristics of calcarenaceous sandstone reservoirs and gas accumulation control factors of the 3^rd Member of Xujiahe Formation in Yuanba area, Northeast Sichuan Basin

Xiao Kaihua, Li Hongtao, Jia Shuang

2014, 35(5):  654-660.  doi:10.11743/ogg20140510

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The 3^rd Member of Xujiahe Formation(T₃x³)has great petroleum exploration potential and its predicted gas resource volume is a hundred billion cubic meters in Yuanba area,Northeast Sichuan Basin.However,the characteristics and gas accumulation control factors are not clear.Based on cores,thin sections and physical properties,the characteristics and gas accumulation control factors of T₃x³ were studied through correlation between well and seismic data.The results indicate that the dominant sedimentary facies are braided river delta plain and delta front.The calcarenaceous sandstones are characterized by high carbonate debris content and low quartz content,and low natural gamma value and high resistance.The calcarenaceous sandstones are of low porosity and extra-low permeability.The reservoirs have a variety of pore types,which are dominated by dissolution pores and authigenic mineral intercrystal pores,followed by micro-fractures.The dissolution pores mainly occur in between calcarenaceous grains and have good connectivity.They are the main pore paces of high-quality reservoirs.The prior factors of gas accumulation and high production are the existence of conglomeratic calcarenaceous sandstones,calcarenaceous sandstones and glutenites in distributary channels of delta plain and delta front.The horizontal and low-angle interlayer fractures and the dissolution pores along the fractures are the determinant factors for the gas accumulation.In addition,structures and faults are also important factors.

Multiple diagenetic environments and evolutionary patterns of the Eocene red beds in the eastern Dongying Sag

Niu Shuanwen, Li Jiyan

2014, 35(5):  661-669.  doi:10.11743/ogg20140511

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In order to investigate the control of diagenetic environment on diagenetic evolution of red-beds reservoir,we studied the diagenetic environments of the Eocene red-beds in the eastern Dongying Sag Bohai Bay Basin through burial history reconstruction,thin section analysis,scanning electron microscopic observation,routine core analyses.On this basis,we described intensity of diagenesis and established evolutionary patterns of red-bed reservoirs under the control of diagenetic environment.The diagenetic environment of the Eocene red-beds in the eastern Dongying Sag is divided into two types according to the differences of control factor,range of influence and property types,namely original alkaline environment and burial acidic environment,which correspond to penecontemporaneous period-early diagentic stage A,early diagentic stage B-middle diagenetic stage A respectively.The diversity in diagenetic products and intensity is sharp due to the differences of diagentic environment.A diagenetic modification model of the Eocene red-beds reservoir was established based on quantitative description of diagenetic intensity,namely "early strong cementation and weak dissolution-middle and late moderate dissolution and weak compaction" under the control of diagenetic environment with alkality to weak acidity-moderate-strong acidity.Red bed reservoirs under the control of this model feature in a pore evolutionary pattern of "rapid-decreasing of primary porosity,slow-growing of secondary porosity in early stage;slow-decreasing of primary porosity,rapid-growing of secondary porosity in middle and later stages".

Comparison between shelf-margin delta of 21 Ma and 13.8 Ma in Pearl River Mouth Basin

Yi Xuefei, Zhang Changmin, Li Shaohua, Du Jiayuan, Luo Ming, Li Xiangyang

2014, 35(5):  670-678.  doi:10.11743/ogg20140512

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Shelf-margin delta,an important type in the dynamic classification of delta,has become the focus of science researches and hot spot in oil & gas exploration.According to the driving factors,shelf-margin delta can be categorized into two types,namely sediment supply-driving delta and accommodation-driving delta.The Pearl River Mouth Basin had favorable geological condition for shelf-margin delta development at 21 Ma and 13.8 Ma.Shelf-margin deltas(21 Ma and 13.8 Ma)are analyzed in respects of topography,relative sea-level change and sediment supply through integration of well logging,logging curves and seismic data.The forming condition analysis shows that the delta at 21 Ma is of sediment supply-dri-ving type,while the delta at 13.8 Ma is of accommodation-driving type.Although SQ2 and SQ9 are obviously different in respects of topography,relative sea-level change and sediment supply,they both are type I sequences,and have well-developed lowstand fans,shelf-margin delta and delta-front slumping deposits,which belonging to stable shelf-margin deltas.

Characteristics and genesis of the bleached Pisha sandstone in Ordos Basin

Song Tushun, Liu Li, Wang Yujie, Liu Na, Yu Miao

2014, 35(5):  679-684.  doi:10.11743/ogg20140513

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Bleached Pisha sandstones are widely distributed in Ordos Basin and mainly occur in Yan'an Formation of the Mesozoic,In Dongsheng area，the bleached Pisha sandstone overlying on the coal seam is an important evidence of the existence and migration of hydrocarbons.In this paper,the samples collected during field geological investigation were analyzed by using polarization microscope,scanning electron microscopy(SEM),X-ray diffraction and X-ray fluorescence spectrum and inductively coupled plasma mass spectrum.The results show that the main mineral composition of the bleached Pisha sandstone are quartz and alkali feldspar,followed by illite,kaolinite and a small amount of illite/smectite mixed layer.The content of SiO₂ is 72.76%-74.96%,that of Al₂O₃ is 16.17%-16.17%,K₂O 1.93%-1.93%,CaO 0.08%-0.08% and Fe₂O₃ 0.01%-0.69%.Hf,Zr,Ss,Ba and U are relatively enriched.The ∑REE and LREE/HREE was are in the ranges of 67-296 μg/g and 7.36-13.67,respectively.REE distribution pattern features in light REE enrichment,but heavy REE deficient,with significantly negative anomaly of Eu and weak deficient of Ce(the content of Ceanom being in the range of -0.07--0.17,averaging at -0.12),suggesting an anoxic reducing environment.The studies show that the bleached Pisha sandstone is the result of sulfate and natural gas reduction,and thus can provide a geologic basis for the formation and dissipation of oil and gas in the study area.

Tectonic-sedimentary constrains for hydrocarbon generating organism assemblage in the Lower Cambrian argillaceous source rocks, Tarim Basin

Hu Guang, Liu Wenhui, Tengger, Cheng Qianglu, Xie Xiaomin, Wang Jie, Lu Longfei, Shen Baojian

2014, 35(5):  685-695.  doi:10.11743/ogg20140514

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Hydrocarbon generating organism is an important object for the source rock research.The studies,so far,were focused on their hydrocarbon-generation potential via simulation experiments,and less attention was paid to the geological settings that affect development and distribution of hydrocarbon generating organisms.However,the development and distribution of hydrocarbon generating organisms is very important for predicting source rocks and guiding petroleum exploration.In this study,the Lower Cambrian Xishanbulake and Yuertus formations were selected from the Southern Yaerdangshan and Dongergou sections in Kuluketage and Keping districts,respectively.Researches on two formations demonstrate that the hydrocarbon generating organisms in the Xishanbulake Formation are dominated by benthic algae,and include some planktonic algae;whereas hydrocarbon generating organisms in the Yuertusi Formation are benthic algae.Anomaly of elements Ce and Eu and REE patterns of cherts in the two formations imply that the two sections were affected by hydrothermal fluid,and that the influence in the Southern Yaerdangshan section was stronger than that in the Dongergou section.Major and trace elements analyses of mudstones indicate that the Xishanbulake Formation have less reduction water,and more active volcano in the Kuluketage district which might be resulted in more undulating terrain than that in the Keping district during the Early Cambrian.Correlated with distribution of extant algae,it could be concluded that the difference in tectonic activity,water depth,and paleo-terrian may be the major cause for the difference in hydrocarbon generating organism assemblages between the Xishanbulake Formation in the Southern Yaerdangshan section and the Yuertus Formation the Dongergou section.

Comparison and enlightenment of coalbed methane geology at home and abroad

Long Shengxiang, Li Xinzi, Ye Liqin, Chen Chunfang

2014, 35(5):  696-703.  doi:10.11743/ogg20140515

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America,Australia and China all have many coal bearing basins with greatly different geological conditions of coalbed methane.Among these basins,most are poor in geological conditions of coalbed methane,excerpt for a few which have rich coalbed methane resources,excellent reservoir characteristics,structural and hydrological conditions,thus are successful in exploration and development.Even in well developed basins，such as San Juan Basin and Qinshui Basin,the geology conditions are also greatly different in different regions.According to CBM geological conditions,accumulation models and development conditions,these basins can be divided into mid-high-rank coal basins and low-rank coal basins.A CBM classification and correlation method system was established to perform comparative analysis among the mid-rank coal in San Juan Basin and low-rank coal in Powder River Basin of America,complex rank coal in Bowen/Surat Basin of Australia,high rank coal in Qinshui Basin and complex rank coal in Ordos Basin of China,as well as the main zones(areas)in these basins.It was found that the most prospective Ordos Basin and Qinshui Basin in China are greatly different with San Juan Basin,Bowen/Surat Basin.Fanzhuang,Hancheng,south Yanchuan,Zhijin and other blocks are only similar to the Zone-3 in San Juan Basin’s.It is therefore concluded that the coalbed methane geological conditions and recoverability are relatively poor in the coal basins in China,and effective exploration and development targets are different to find in the near and medium terms.So from a strategic perspective,the long-term development goals should not be set too high.And from a tactical perspective,attentions should be paid to analyzing difference,forecasting resources sweet spot,picking the favorable target,arranging targeted deployment on exploration and development,and controlling development speed.

Shale organic heterogeneity evaluation method and its application to shale oil resource evaluation—a case study from Qingshankou Formation, southern Songliao Basin

Huang Wenbiao, Deng Shouwei, Lu Shuangfang, Yu Ling, Hu Shuo, Zhang Ju

2014, 35(5):  704-711.  doi:10.11743/ogg20140516

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It is well known that shale has strong organic heterogeneity.As the amount of measured geochemical data is imited by the available samples,it is hard to describe the spatial distribution of shale oil and gas precisely.Through evaluation of organic abundance and retained hydrocarbon content by using the improved ΔlgR model,the spatial distributions of enriched,low-efficiency and inefficient shale oil resources are well mapped respectively with reference to the shale oil resources grading evaluation standards.The heavy hydrocarbon and light hydrocarbon compensate coefficients for S₁ are determined through correcting the experiments and component hydrocarbon generation thermal simulation experiment with pyrolysis chromatography parameters.Volume method is used to quantitatively evaluate different grade shale oil resources,and recognize favorable exploration areas.Research shows that the improved ΔlgR model enhances the accuracy and operability of evaluating geochemistry parameters with logging data.Application results show that the shale oil resources of the Qingshankou Formation in southern Songliao Basin occur in the lower-middle part of its first member.And the play fairways are distributed in Fuxin Uplift,Honggang terrace and northern Changling Sag,where the estimated shale oil resources is 4.808 billion tons，accounting for a third of the total resources.The method of evaluating distribution of shale oil/gas by describing organic heterogeneity not only can reveal the spatial distribution features of shale oil,but also can save the cost of laboratory test,and more important,it can provide substantial guidance for future exploration and development of shale oil.

Accumulation conditions of the Lower Cambrian shale gas in southern Anhui province

Lu Bingxiong, Zheng Rongcai, Wen Huaguo, Xu Wenli

2014, 35(5):  712-719.  doi:10.11743/ogg20140517

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Based on outcrop investigation,thin-section observation and SEM analysis,a detail division scheme of sedimentary facies was proposed for the Lower Cambrian in southern Anhui combining with geology and wellbore data.The most favorable facie belt for shale gas accumulation is deep-water deduction environment in the basin,while the carbonate ramp is unfavorable for shale gas exploration.Fractures make the greatest contribution to the storage of shale gas reservoir,followed by the secondary dissolution micro-pores.In contrast,intercrystalline pores contribute the least due to their relatively poor development.This paper comprehensively studied the geological characteristics of the Lower Cambrian shale gas play in southern Anhui in such aspects as spatial distribution of organic-rich shale,geochemical behaviors and preservation conditions.The study was focused on quantitative evaluation of shale thickness,TOC content,R_o and brittleness.The Lower Cambrian shale in southern Anhui is more than 50 meters on average,with the maximum thickness in the range from 200 to 600 meters occurring in Shitai and Nanling counties.The shale gas play has an average TOC content of 2.37%.The average Ro is more than 2%,indicating that the shale is at mature-high mature stage.The average brittle mineral content is 46.89%,being favorable for the creation of fracture networks through hydraulic fracturing.Based on comparison with the geochemical parameters of the main large shale gas plays in America,it is indicated that the Lower Cambrian shale in southern Anhui has favorable accumulation conditions for shale gas,thus can be selected as one of the play fairways in China.

Evaluation, optimization and decision system for prospects to drill

Cai Lixue, Yan Xiangbin, Li Na, Li Jun, Yang Shuang, Ma Xiaojuan

2014, 35(5):  720-728.  doi:10.11743/ogg20140518

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Evaluation and selection of prospects to drill is one of the main tasks for the decision-makers of oil companies.Based on the principles of risk analysis and portfolio management, in combination with the Chinese technical criteria of prospect evaluation, a system of evaluation, optimization and decision has been built for prospects to drill.1)A management system of prospects with graphs, images, numbers, forms and texts integrated is established to perform basic data management, outcomes data management, graphics management and document management.2)Considering the geological process of petroleum accumulation and trapping, the discovery probability of hydrocarbon is defined.The general guidelines of evaluation are used to assign probability to each individual geological factor involved with respect to database reliability.At the same time, the distributions of resource amount of a prospect and a group of prospects are simulated and predicted by Monte Carlo, and three methods of reality checks have been provided to help evaluate those predictions.And then the economic characteristics of the resources of the prospects are valued by the conventional discounted cash-flow based on the whole process of petroleum exploration and production.3)'Risk analysis vs.economic value’ method is proposed for selection of the favorable prospects to drill, including prospect screening, wildcat well selecting, prospect ranking by expected return and risked value, and portfolio optimization.4) A post-drill assessment system is set up to monitor the wildcat drilling projects and improve the predictive performance, which consists of four parts: comparison between pre-and post-drill estimates of resource/reserve, comparison between predictive and actual results of key geological factors, calibration of hydrocarbon probability and analysis of the causes for the failure.This system has been successfully applied to decision-making of wildcat drilling programs in different geologic provinces.

Chronology and its significance of the Lower Jurassic tuff in Ordos Basin and its periphery

Li Zhenhong, Feng Shengbin, Yuan Xiaoqi, Qu Hongjie

2014, 35(5):  729-741.  doi:10.11743/ogg20140519

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Tuff in stratigraphic sequences of sedimentary basins is a direct product of the orogenic activity of the source region,and is closely related to orogenic activity.The successive discovery of the Lower Jurassic tuff in Ordos Basin and its periphery is very important for constraining the key timing of tectonic evolution and tectonic background.In this paper,we determined the critical time of tuff eruption for the Lower Jurassic using zircon U-Pb geochronology.In conjunction with the tuff geochemistry in the key areas,we discussed the tectonic background for tuff eruption.The following results were obtained.The distribution of the Lower Jurassic tuff show obvious regional differences.They mainly occur in the Pingliang and Ankou counties in the southwestern Ordos Basin and in the Ningwu-Jingle Basin and Guangling Basin of the northeastern Ordos Basin,and are closely related to the evolution of the North Qinling Orogenic belt and the Yanshan Orogenic belt.The eruption of tuff is not completely synchronous in different regions.The tuff on Cedi section and Ankou section of the southwestern Ordos Basin are dated at 175.2 Ma±2.4 Ma and 168.4 Ma±1.3 Ma respectively,the volcaniclastic rocks on the Chenjiabangou section of Ningwu-Jingle Basin at 179.2 Ma±0.79 Ma,and the tuff on the Bantasi section of Hunyuan-Guangling Basin at 171.0 Ma±1.0 Ma.Overall,the eruption of tuff is date at the late Early Jurassic to early Middle Jurassic.On the Th/Hf-Ta/Hf diagrams,all the points fall into the continental rift zones or the initial rift zones,which indicates the extensional tectonic setting from the Early Jurassic to early Middle Jurassic in Ordos Basin and its periphery.The timing of tuff eruption may provide a direct chronological evidence for study of the Mesozoic thermal evolution of the Ordos Basin.

Zircon U-Pb age and formation model of volcanic rocks from Nanpu Sag of Bohai Bay Basin

Du Jingxia, Shi Wenwu, Zhou He, Wang Quanli, Xia Qiujun, Liu Junrong

2014, 35(5):  742-748.  doi:10.11743/ogg20140520

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Nanpu Sag underwent two magmatic cycles and four episodic eruptions.Zircons of volcanic rocks from Nanpu Sag are dated by U-Pb SHRIMP,LA-ICPMS and Lu-Hf isotope method.The results indicate that more than 95% of zircons in the early magmatic cycle are formed by metamorphic recrystallization,with a big range of U-Pb age.It is explained that they are formed by collision granite crust in 1 800 Ma,which is caused by remelt and recycling process induced by collision between new crust of Middle and Neo-Archean(2 900～2 600 Ma)with palaeo-oceanic crust.In the middle to late magmatic cycle,zircons are formed by crystallization of mantle-derived magma overflow,and they contain magmatic zircon and rich captive crystal,which are helpful for chronology and isotope studies.Through those zircon ages,a vertical sequence of correspondent tectono-thermal events of the North China craton and Nanpu Sag is established.Moreover,the absolute ages of mantle-derived magma overflow and the related strata are calibrated accurately.The result shows that Guantao Formation belongs to Miocene,Dongying Formation belongs to the Oligocene and Shahejie Formation crosses Paleocene and Eocene.