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Table of Content

    28 December 2018, Volume 39 Issue 6
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    Paleogeographic evolution of the Late Ordovician-Early Silurian in Upper and Middle Yangtze regions and depositional model of shale
    Sun Shasha, Rui Yun, Dong Dazhong, Shi Zhensheng, Bai Wenhua, Ma Chao, Zhang Leifu, Wu Jin, Chang Yan
    2018, 39(6):  1087-1106.  doi:10.11743/ogg20180601
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    We studied the shale deposited during the Late Ordovician-Early Silurian in Upper and Middle Yangtze regions to investigate the link between paleogeographic evolution and marine shale deposition in southern China.The graptolite-bearing shales from 24 shale gas wells that can be used to stratigraphic division are the focus of the study.Combined with the outcrop data from the GBDB database and previous data, we proposed the classification scheme in the facies-sub-fa- cies-micro-facies sequence,that is three sedimentary facies(continental shelf,tidal-flat and delta),including eight sub-facies and several micro-facies,according to the characteristics of sediments,sedimentary setting,geo-chemical parameters and logging data.It’s made certain that during the Late Ordovician-Early Silurian,the Upper and Middle Yangtze regions were in a restricted low-energy epicontinental shallow sea environment surrounded by paleo-uplifts,and the favorable se-dimentary facies zones for shale reservoirs therein were the restricted deep shelf facies.The lithofacies paleogeographic framework of the Katian,Hirnantian,Rhuddanian,Aeronian stages in a row for the study area was reconstructed by taking the sedimentary facies profile/wells covering the whole region as controlling points,employing the “favorable facies” approach and taking chronostratigraphic “stage” as the research unit,and thus the boundaries of paleo-uplifts during va- rious stages can be predicted effectively.The thicknesses of graptolite-bearing shale intervals were accurately measured by taking the “stage” as the ruler,and the temporal-spatial distribution of sedimentary systems and shale distribution pattern in each stage were summarized.The results suggest that the distribution of black shales is controlled by global sea-level rise,regional tectonic movement and plaeogeographic framework,while the thickness of black shales is apparently controlled by the pattern of alternating uplifts and depressions.The depositional model is a type of “one depression entrapped by two uplifts”,with the shale gas enrichment area located within the depression restricted by two uplifts on both sides.Graptolite-bearing shale intervals are absent to various extents at the regions near the uplifts.Such regions as well as uplifts should therefore be undesirable in terms of shale gas exploration and development.
    Qualitative description and full-pore-size quantitative evaluation of pores in lacustrine shale reservoir of Shahejie Formation,Jiyang Depression
    Wang Min, Guan Ying, Li Chuanming, Liu Yang, Liu Wei, Xu Jianpeng, Li Zheng, Lu Shuangfang
    2018, 39(6):  1107-1119.  doi:10.11743/ogg20180602
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    The organic matter lamina,mineral composition,and pore geometry of the lamellar shale from the Shahejie Formation,Jiyang Depression,were qualitatively analyzed and the size and distribution of pores were quantitatively studied,through combined experimental methods,such as the large-area visual field splicing scanning electron microscope(SEM) technology,low temperature N2/CO2 adsorption experiment,and high pressure mercury intrusion experiment.Meanwhile,the characteristics of pore distribution before and after core cleaning were compared,and the possible spaces for shale oil enrichment were analyzed.The organic matter and calcite in the samples studied are distributed in both banded and dispersed forms,and the distribution of clay minerals and quartz is complex.Although the shale samples studied are in the stage of low maturity-oil generation,organic pores are still well developed in them,which may be ascribed to the efflux or escape of some hydrocarbons(especially the light oil and gas).In addition,large number of intergranular pores,intragranular pores and micro-cracks are also developed.Low-temperature N2 adsorption experiment(used to describe pores with diameter being less than 100 nm)and high-pressure mercury intrusion experiment(used to describe pores with diameter ranging from 100 nm to a dozen μm)and large-area visual field splicing SEM scanning can effectively reflect the full size of lacustrine shale reservoir space.Interconnected reservoir space of shale is composed of pores of nano-scale(with pore diameter being less than 300 nm)and micro-fractures(with the width of 0.5 to a dozen of μm)in micrometer scale.While shale oil mainly accumulates in pores less than about 100 nm and micro-cracks larger than about 1 μm.The analytical methods and conclusions presented in this study can be of referential value to the related studies on shale during its oil generation stage.
    Oil-water distribution and its major controlling factors of Putaohua reservoir of the Cretaceous Yaojia Formation in syncline area of Sanzhao Sag,Songliao Basin
    Sun Yu, Yu Limin, Yan Baiquan, Liu Yunyan, Cong Lin, Ma Shizhong
    2018, 39(6):  1120-1131.  doi:10.11743/ogg20180603
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    The volume of oil and gas in the syncline area of Sanzhao Sag,Songliao Basin,is sizable.It’s hard,however,to make clear the complicated oil-water distribution in Putaohua reservoir,and so far its controlling factors are rarely known.Reservoir types discovered and their distribution patterns were investigated,controlling factors of hydrocarbon accumulation were analyzed,and the main controlling factors of oil-water distribution in the syncline area of the prolific sag were discussed,by using the abundant static data and performance data of the mature development blocks of the oilfield.The results show that (1) oil-water distribution of Putaohua reservoir in the syncline area is controlled by a single trap composed of local structure and single sand body,the oil-water interface of a single trap is unified,but the oil-water distribution patterns vary for different single traps adjacent. (2) In a single trap, the oil-water distribution in the syncline area is controlled by the patterns of hydrocarbon accumulation and superimposition:complex spatial superimposition of single traps with and without hydrocarbons ultimately results in the complexity of hydrocarbon accumulation and oil-water distribution in the syncline area,Sanzhao Sag. (3) The superimposition of traps that are composed of vertically multi-layered and laterally multi-branched single sand bodies and complicated local structures with non-traps is the main controlling factor of oil-water distribution in the syncline area.Therefore, reservoir prediction in the syncline area should begin with the analysis of elements of irregular geologic body controlling hydrocarbon accumulation,that is,the evaluation of faults,single sand bodies and their spatial assemblage.
    Central uplift of Tarim Basin being the Neoproterozoic basement structure zone of orogeny origin:Evidences from clastic samples of deep holes
    Li Xiaojian, Wang Yi, Li Huili, Gao Shanlin, Zhang Zhongpei, Yue Yong, Yan Quanren, Jiang Wen
    2018, 39(6):  1131-1145.  doi:10.11743/ogg20180604
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    Three deep holes(Well TX1,XH1 and BT5)encountered clastic sedimentary rocks underlying the Cambrian carbonates in the Bachu uplift of the Tarim Basin.After detailed study of these clastic rocks through petrographic observations,clastic composition statistics and geo-chemical analyses,their provenances and the tectonic setting for their formation were discussed in depth.The clastic compositions of conglomerates and sandstones together with the geochemical characteristics of mudstones indicate that the provenances of the clastic sedimentary rocks underlying the Cambrian carbonates in the three wells include sedimentary rocks,igneous rocks,metamorphic rocks,among which the intermediate-acidic volcanic rocks and intrusive rocks are predominant.The angular-to-sub-rounded appearance of the clastic particles in the conglomerates and sandstones,the presence of erodible compositions in gravels(such as carbonates,schists)and the lower Th/U ratio of mudstones collectively show that these clastic rocks are near-source deposits with low maturity.By comparing the clastic composition,geochemical characteristics,and age structure of detrital zircons,we could determine that the detrital components of these clastic rocks are mainly derived from the underlying basement.The detrital models of conglomerates and sandstones,geochemical characteristics of mudstones and in-situ trace element characteristics of detrital zircons suggest that the source area,that is the underlying basement,was located in an arc-related tectonic setting on the active continental margin in the Neoproterozoic(peak: 790-730 Ma).The newly obtained evidences of clastic rocks are well consistent with the previous studies on the age and tectonic setting of the andesites and dacites at the bottom of Well Tong-1 and the granodiorites and diorites at the bottom of Well Tashen-1 in the Katake uplift,demonstrating that the central uplift zone(Bachu uplift-Katake uplift-Guchengxu uplift)across the central Tarim Basin is a Neoproterozoic continental marginal arc,while the basement of the Tarim Basin is the result of amalgamation caused by Neoproterozoic orogeny.
    Types and evaluation of the source-reservoir configuration of lacustrine shale gas in the Sichuan Basin
    Zhu Tong, Hu Zongquan, Liu Zhongbao, Feng Dongjun
    2018, 39(6):  1146-1153.  doi:10.11743/ogg20180605
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    Exploration of the lacustrine shale gas in Sichuan Basin has discovered strong gas shows and/or commercial gas flow in the Middle and Lower Jurassic of Jiannan,Fuling,and Yuanba areas,east of Sichuan,which are prospective areas for petroleum exploration.Compared with organic-rich marine shale,the lacustrine shale is characterized by fast change of sedimentary facies,diversity of lithofacies(interbed and alternating beds),low abundance of organic matters,strong reservoir heterogeneity and complex source-reservoir configuration.According to the types of lithofacies,the lacustrine shale can be divided into two types of source-reservoir configuration,namely the type of “reservoir interbedded within source rocks” configuration and the type of “source-reservoir alternating” configuration,which can be further subdivided into four subtypes.Through such methods as organic geochemistry,microscopic storage and permeability experiments and nano CT,we stu-died the characteristics of hydrocarbon generation,storage capacity and fracturability for each type of source-reservoir configurations,and established the evaluation model for source-reservoir coefficients conformable to the characteristics of the lacustrine source-reservoir configurations of various types,with each type as an independent “source-reservoir” unit.The evaluation results show that the source-reservoir configuration of the alternating shale and shell limestone deposited in a carbonate lake has favorable conditions for hydrocarbon generation,shale gas storage,permeability and fracturability,beneficial to the formation and stimulation of shale gas reservoirs,thus functions as the most favorable type of source-reservoir configuration of the lacustrine facies.In comparison,the source-reservoir configuration with shell limestone interbedded within shale has favorable hydrocarbon generation and reservoir conditions,but poor permeability and fracturability,thus is fair in quality.The above two types can be taken as the preferred layer for the development of lacustrine shale gas.
    Quantitative evaluation of provenance supply capacity for sandy conglomerates: A case study of Guojuzi subsag in Chezhen Sag
    Wang Yanzhang, Lin Hongmei, Feng Jianwei, Li Baojuan, Cao Xiaoli, Cai Hongxing, Hu Qiuyuan
    2018, 39(6):  1154-1163.  doi:10.11743/ogg20180606
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    Sandy conglomerates in steep slopes are characterized as various fan types,abundance of provenances,and high deposition rate,and the provenance supply capacity is one of the main factors controlling sandy conglomerate scale and its sedimentary system.However,the quantitative study of provenance supply is always a weak point which constrains the study of sedimentary system.In order to address the problem,we worked out the provenance supply index with weighted average of parameters which have positive and inverse relation with provenance supply rates.The calculation was based on the study of conglomerate content,ratio of sand and formation,lithologic index,development degree of interbed(frequency,thickness,percentage),mineral content,granularity distribution.And the results show that (1) the areas with high provenance supply indexes are mainly distributed in the north,close to the downthrown side of Chengnan fault,along large faults in the form of apron; (2) the provenance supply capacity determines the development scale of sandy conglome-rates:the distribution patterns and scales of sandy conglomerates beside plate-,shovel-,ladder- and slope-shaped boundary faults vary with the varying provenance supply capacities.In addition,a combination of the provenance supply capacity and depth of water controls the types of sedimentary facies.With the change of these two factors,the studied area has developed such sedimentary facies as fluvial facies,alluvial fan,carbonate rock,delta,fan delta,turbidite fan,sublacustrine fan,coastal subsea apron and so on.
    Distribution characteristics and superimposition pattern of the Late Jurassic shallow water deltic sand body in the foreland basin of Western Sichuan Depression
    Liu Junlong, Sun Dongsheng, Ji Youliang, Zhu Hongquan, Yu Haiyue, Wang Tianyun
    2018, 39(6):  1164-1178.  doi:10.11743/ogg20180607
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    This study analyzed the sedimentary characteristics of shallow water deltic sand bodies grown with frequent changes of lake level,summarized their vertical superimposition relationship and areal distribution, and finally established their superimposition pattern,based on the theory of high resolution sequence stratigraphy,combined with a dataset consisting of seismic,logging,core and experiment data.Through analysis,we found that: ① distributary channels (CHs) and mouth bar-beach bar complexes are the main sand body types of the shallow water deltas in the Penglaizhen Formation.In the plan view,the distributary channels are mainly branch-shaped,distributing along the source direction,and MBCs are strip-shaped,parallel to the bank line;while vertically,sand bodies of different genetic types are superimposed into various types of composite sand bodies. ② As relief reduces gradually from the tectonically active margin to the basin, the stream energy decreases linearly with the gradient descent of the river system.Accordingly,the width and depth of the distributary channels of the shallow water delta decrease downwards.The low frequency lake level fluctuation controls the progradation and retrogradation of shallow water delta,whereas the change of high frequency lake levels determines the distribution and superimposition patterns of sand bodies of different genetic types. ③ The sedimentation evolution model of the Late Jurassic shallow water deltas in the foreland basin of Western Sichuan Depression was established,and four types of superimposition patterns for sand bodies there were classified,including superimposed low-accommodation channels, rivers over bar,superimposed high-accommodation channels and superimposed mouth bars.
    Genesis of formation water in the 6th member of the Upper Triassic Yanchang Formation in southern Ordos Basin and its petroleum significance
    Liu Futian, Li Rongxi, Zuo Zhifeng, Liu Xuefeng, Zhao Bangsheng, Wu Xiaoli, Li Delu
    2018, 39(6):  1179-1189.  doi:10.11743/ogg20180608
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    Chemical analysis of formation water in the 6th member of Yanchang Formation(Chang 6 member)in the sou-thern Ordos Basin reveals that the formation water is high in total salinity;Cl-,(Na++K+)and Ca2+ are dominant,and thus the water is of CaCl2 type.Vertically,the total salinity,mainly controlled by ions of Cl- and(Na++K+),tends to increase with increasing depth,demonstrating the ever-condensing feature of formation water with depth and the ever-growing sealing conditions subsurface.Laterally,the distribution of the total salinity is relatively consistent with the sand body thickness,and is controlled by sedimentary facies.Given that the formation water in Chang 6 member is characte- rized by low sodium-chloride ratio,magnesium-calcium ratio,coefficient of desulfurization and exchange coefficient of cations,and high metamorphism coefficient in chemistry,we are sure that the formation water therein is located in alternating stagnant zones,a closed anoxic and reducing environment,which is conducive for hydrocarbon accumulation and preservation.Besides,the formation water therein belongs to the enclosed deep water isolated from the surface water,and both its total salinity and Ca2+ concentration have a certain positive correlation with porosity of Chang 6 member.Accor-dingly we may conclude that the origin of formation water in the area is closely related with the diagenesis and thermal evolution of organic matters,based on the regional thermal evolution history.What’s more,it is original sedimentary water,having undergone strong condensation and metamorphism and been affected by organic fluids such as oil and gas.All in all,the formation water associated with oil and gas in the 6th member of Yanchang Formation in the southern Ordos Basin manifests that the hydrocarbon reservoirs in the southern part of the basin is in a stable and closed environment,and the prospects for its oil-gas exploration are brighter.
    Main factors controlling the tight oil enrichment in the 7th oil layer group of the Triassic Yanchang Formation in Fuxian-Ganquan area, Ordos Basin
    Ge Yunjin, Ren Laiyi, He Yonghong, Ma Fangxia, Wang Quan, Du Kefeng, Li Hongjin
    2018, 39(6):  1190-1200.  doi:10.11743/ogg20180609
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    The major factors controlling the enrichment of tight oil in the 7th oil layer group of the Triassic Yanchang Formation(Chang 7 oil layer group)in Fuxian-Ganquan area,Ordos Basin,were investigated from multiple perspectives of outcrop,core,logging and laboratory testing,combined with such dynamic data as production tests.The results show that the high-quality source rocks of Chang 7 oil layer group are developed well and widely and are characterized by large thickness,high organic richness,favorable type of kerogen and moderate maturity,thus provide an abundant oil source for tight oil enrichment and control the oil-water contact of the Chang 7 tight oil reservoirs.The Chang 71 and Chang 72 sub-layer groups in the Chang 7 oil layer group together with the underlying source rocks make up a source-reservoir assemblage characteristic of closeness between the underlying source rock and overlying reservoir.The analysis of diagenetic facies shows that quality diagenetic facies of reservoir controls the zones of tight oil enrichment.There is multi-phase oil charging in the tight oil reservoirs.During the early charging stages,the wettability of the reservoir rock was turned from water wet to mixed wettability with oil charging,leading to the formation of preferential channels for oil migration and accumulation,which determines the pathway and scope of oil migration and accumulation in the major pool-forming period,and to a certain extent constrains the distribution of the Chang 7 tight oil reservoirs.Baffles and barriers of various sizes compartmentalize the reservoirs into a network structure with intense heterogeneity,leading to differential fluid flow and complex oil-water contact in the sandstone.Meanwhile,the shelter of tight layers can also play a role in controlling the accumulation of Chang 7 tight oil.All the factors mentioned above collectively determine the limited distribution of tight oil,the complexity of water-oil contact and the coexistence of oil wells and water wells.
    Mixed carbonate-siliciclastic sequences of deep-water contour current overflow origin of Kelimoli Formation in Zhuozishan area,western margin of Ordos Basin
    Li Xiangdong, Que Yi, Huan Yaqi, Chen Haiyan
    2018, 39(6):  1201-1212.  doi:10.11743/ogg20180610
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    The deep-water contourites are widely developed in the Middle Ordovician Kelimoli Formation in Zhuozishan area,western margin of Ordos Basin.The Shixiagu outcrop thereto is generally regarded as an ideal section for studying the contourites of the Darriwilian stage for its complete stratum and obvious lithological variations.Here we focus on the mechanism of limestone associations alternating with shale in the middle Kelimoli Formation based on outcrop observations,study of thin sections in labs,data from relevant geochemical tests and previous works.The results show that: ① the middle part of Kelimoli Formation consists of ten limestone associations which could be grouped into three cycles; ② the single limestone layer pinches out in shale with different forms and patterns of lens; ③ a succession of parallel layer-homogeneous layer-parallel layer and streaky structures in the shape of gentle ripples are developed in the limestone,displaying alternating zones of lime mud and very fine crystalline under microscope.In combination of previous research,we may conclude that the mixed sequences consisting of limestone and shale in the middle Kelimoli Formation can be divided into two types,one is the mixed sequence of terrigenous clastics with carbonate,and the other is the mixed sequence of carbonate(terrigenous clastics)with diamictite,and their genetic mechanism could be attributed to the periodic overflow of contour current controlled by astronomical cycles in deep-water slope environment.The discovery of mixed sequences caused by deep-water contour currents can be of great significance for the Ordovician shale gas exploration at the western margin of Ordos Basin.
    Main factors controlling formation of dolomite reservoir underlying gypsum-salt layer in the 5th member of Ordovician Majiagou Formation,Ordos Basin
    Yu Zhou, Ding Zhenchun, Wang Lihua, Zhang Daofeng, Luo Chao, Wei Yuan, Guo Wei, Wei liubin
    2018, 39(6):  1213-1224.  doi:10.11743/ogg20180611
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    The dolomite underlying gypsum-salt layer in the 5th member of Ordovician Majiagou Formation in the eastern Ordos Basin proves to be of great gas potential by latest exploration practice.Thus we conducted systematic study on its petrological features,reservoir space,porosity and permeability by core observation,thin section identification,physical property analysis and geochemical analysis.The results show that the reservoirs underlying the gypsum-salt layer in the Ordovician are of porous dolomite type in the Ordos Basin,and they occur vertically in O1m65,O1m75 and O1m95.The litho- logies of the O1m65 reservoirs are mainly granular dolomite and porphyritic dolomite with very fine-crystalline,while the lithologies of O71m5 and O1m95 reservoirs are dominated by granular dolomite and dolomite with very fine-to fine-crystalline.The reservoir spaces for the three reservoir intervals are primarily dissolved pores or cavities,with residual intergranular pores,intercrystalline dissolved pores,intercrystalline pores and micro cracks ranked second.The average porosity for each is 5.84%,6.81% and 7.03%.Sedimentary paleo-geomorphology,sea level eustacy and penecontemporaneous meteoric water dissolution collectively control the development and distribution of the dolomite reservoir underlying gypsum-salt layer.It is concluded that the central paleo-uplift belt and Yulin-Hengshan uplift belt,located outside the boundary of the gypsum-salt layer,are relatively higher in topography,and the deposits of grain shoal facies are relatively thicker,so they are prone to undergo meteoric water dissolution during penecontemporaneous and shallow burial stages.Its internal pores are not easily subject to filling of gypsum salt.All in all,they are the favorable areas for the growth of dolomite reservoirs underlying the gypsum-salt layers inside the basin.
    Reservoir lithology and space characteristics of the Archaeozoic basement rock in Ciyutuo buried hill,Liaohe Depression
    Zhu Yixiu, Wang Huan, Shan Junfeng, Yang Chengyu
    2018, 39(6):  1225-1236.  doi:10.11743/ogg20180612
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    Understanding of the interior of the Archaeozoic metamorphic basement rocks in Ciyutuo buried hill,Liaohe Depression,is relative poor.The comprehensive research that involves logging,seismic,core and experimental data could be of great help to detect the lithology and distribution of the basement rock,types and characters of reservoir space as well as the impact of lithology on the reservoir physical properties,to further explore and develop petroleum effectively,and to perfect the new theory of petroleum accumulation in the interior of basement rock reservoirs.The Archaeozoic basement rock litho- logy in the study area is quite complicated,and can be classified into 11 categories and 18 kinds.The lithologies of the me-tamorphic reservoir include migmatitic granite,biotite granite-gneiss,migmatitic-gneiss,cataclasite and murbruk rock.The basement rocks feature vertical segmentation and lateral zonation of lithology:migmatitic granite with cataclasite interlayer occurring the lower part,migmatitic-gneiss and migmatitic granite with cataclasite interlayer in the middle-lower part,and gneiss in the upper part.The reservoir space of the metamorphic buried hill is cracks and dissolved pores and fractures starting from the cracks,with the structural fractures being dominant.The fractures are developed to various degrees in different lithologies,have strong heterogeneity,and are characterized by zonation.Reservoir zones with highly developed fractures are the main target of the exploration.The basement rock reservoir in Ciyutuo buried hill is controlled by petrology and mineralogy.Fragmented migmatitic granite and fragmented granite-gneiss could be quality reservoirs.Statistics show that the cataclasite-migmatitic granite with a ferromagnesian content of less than 10% and the cataclasite granite-gneiss with a ferromagnesian content of less than 12% are favorable for the formation of quality reservoir rocks.
    A method to determine preferential pathways for hydrocarbon migration in “lower source rock and upper reservoir” combination and its application
    Wang Haoran, Fu Guang, Su Bilin, Sun Tongwen, Tang Wenhao
    2018, 39(6):  1237-1245.  doi:10.11743/ogg20180613
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    The study is based on the analysis of characters of hydrocarbon migration within a lower source rock-upper reservoir combination,and 3D seismic and logging data.We worked out a method to determine the preferential pathways for hydrocarbon migration through combining fault activity ratio with hydrocarbon potential energy on fault plane and combining net-to-gross ratio with fluid potential on top of sand bodies.It can be used to define the scope of preferential hydrocarbon accumulation in this mode.Its application in the 1st member of Nantun Formation (K1n1) within a local structure of Bei’er Sag,Hailar Basin,reveals that hydrocarbon migration in the reservoir could be divided into two modes:the mode of vertical migration and the mode of vertical migration followed by lateral migration.There are 17 preferential migration pathways for the former and 11 for the latter.Correspondingly,their scopes of preferential hydrocarbon accumulation are within 2.3 km and 1km respectively,just coinciding with the practical hydrocarbon distribution.It demonstrates that this method is feasible for determining preferential pathways in hydrocarbon migration within a lower source rock-upper reservoir combination,and conducive to delineating the scope of petroliferous region in the reservoir.In conclusion,it is of importance to guide future petroleum exploration.
    Nature of “reverse prograding deposits” at the southeast margin of Pre-Caspian Basin
    Dai Hansong, Chen Bintao, Hao Jinjin, Liu Xiongzhi, Hong Liang, Zhao Xu, Deng Guoxin
    2018, 39(6):  1246-1255.  doi:10.11743/ogg20180614
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    Progradating deposits,a result of the progressive accumulation and superimposition of sediments transported from provenance to unloading areas,is a normal sedimentary configuration in petro-exploration, dipping to the unloading areas.The interior MKT Formation mudstone of the middle block at the southeast margin of Pre-Caspian Basin is composed of a series of “reverse prograding deposits” dipping west (i.e.towards the early uplifted provenances).As the origin of the sedimentary configuration has triggered many controversies,there is no consensus as to the sedimentation and evolution of the Carboniferous,which has constrained follow-up exploration.Through the analysis of regional setting,dril-ling and seismic data,we made a comparative analysis of such elements as depositional mode,lithology,paleo-geographic location,geometry and scale,discussed the genetic mechanism of the “reverse prograding deposits”,and proposed that the MKT Formation is deep water tractive current deposits,instead of a retrogradation wedge of transgression origin.Therefore,the “reverse prograding deposits” is a peculiar sedimentary configuration resulted from landward migration of sediments along with the deep water tractive current.In the end,we analyzed the evolution of the MKT Formation and divided it into four stages,namely initiation,peak,recession and late adjustment.The discovery of deep water tractive current deposits not only improves our understanding of the sedimentary evolution rules at the southeast margin of the Carboniferous Pre-Caspian Basin,paves the way for further exploration,and enriches the category of basin sedimentation,but also provides a precious case for global research on the Paleozoic deep water tractive current.
    Origin and controlling factors of Mesozoic-Cenozoic gas condensates with high wax content and high-gravity oil in Kuqa Depression
    Su Zhou, Zhang Huifang, Han Jianfa, Liu Yongfu, Sun Qi, Bai Yin, Duan Yunjiang, Qu Yang
    2018, 39(6):  1255-1269.  doi:10.11743/ogg20180615
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    The analysis of a large number of oil samples demonstrates that the Mesozoic-Cenozoic gas condensates and high-gravity oil in Kuqa Depression feature a high wax content.The study discusses the origin and controlling factors of gas condensates with high wax content and high gravity oil in Kuqa Depression based on previous research and available data.The results show that some exinite and sapropelinite of the organic macerals in source rocks are turned into oil with high wax content,whilst vitrinite of the organic macerals produces gas condensates and high-gravity oil.These organic macerals determine the production of gas condensates with a high wax content and high-gravity oil in Kuqa Depression.The wax content in crudes is mainly controlled by three factors: oil maturity,hydrocarbon reservoir type,gas washing and oil migration.Among them,the oil maturity is predominant.The oil in Kuqa Depression is generated by thermal evolution of source rocks during its mature stage,with oil maturity Ro ranging between 0.8%-1.05%,while the crudes as a whole are characterized by a high wax content,and the wax content in crudes decreases with increasing oil maturity.Besides,the hydrocarbon reservoir type plays a secondary role.The wax content of crudes is less than 5% in dry gas reservoirs,ranges between 5%-10% in condensate gas reservoirs with low gas condensates,while is more than 10% in condensate gas reservoirs with high content of gas condensates and oil reservoirs;the wax content of crudes increases with the decrease of lo-garithm of producing gas/oil ratio of hydrocarbon reservoirs.In addition,the effect of gas washing and oil migration ranks last.Under the same oil source conditions,the higher degree of gas washing the crudes undergo,the lower the wax content of crudes will be;meanwhile the farther the crudes migrate,the lower the wax content of crudes will be.
    Evaluation of the brittleness and fracturing characteristics for tight clastic reservoir
    Wang Sheng, Liu Bo, Fu Xiaofei, Zhao Wanchun
    2018, 39(6):  1270-1279.  doi:10.11743/ogg20180616
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    The way to evaluate the fracturing characters and brittleness of tight clastic reservoir is of significant value for optimizing hydraulic fracturing design of tight oil reservoir.We performed tri-axial compression experiments on rock samples of various lithologies taken from the tight clastic reservoir in the Shahejie Formation,Liaohe Basin,analyzed the macroscopic fracturing behaviours and the types of microscopic hydraulic fractures.After considering such brittleness evaluation methods as conventional elastic parameter method and mineral composition method,a new method to evaluate rock brittleness was proposed based on the conservation of energy during triaxial compression.The experimental results show that the fracturing characteristics of rocks are controlled by rock brittleness and its confining pressure.On the one hand,rocks with higher brittleness usually develop transgranular tension cracks,and as the brittleness declines,the number of cracks decreases and the cracks are mainly intragranular.On the other hand,the confining pressure greatly refrains the propagation of micro-fractures,since the transgranular tension cracks turn into intragranular cracks as the confining pressure increases.The brittleness obtained with conventional elastic parameter method is just opposite to that obtained through experiments (i.e.the brittleness is high,but the fracturing degree of rock is low),while the mineral composition method cannot be used to differentiate the degrees of rock brittleness under different confining pressures.The new method proposed in this study can describe the complete mechanical evolution process of rocks transforming from super brittleness to ductility.The brittle indexes are correlated not only with pre-peak Young’s modulus but also with post-peak stress gradient(softening modulus).All in all,the method can be used to describe the tight sandstone brittleness under different confining pressures,and the results coincide with the fracturing behaviours of rock obtained through experiments,verifying the feasibility of the method.
    Analysis of the “Source-to-Sink” system in the 2nd member of the Paleogene Dongying Formation in the eastern slope of Chengdao in Bozhong Say,Bohai Bay Basin
    YangKe, DongYanlei, Zhu Xiaomin, Pan Rong, Zhang Mengyu, Wu Wei, Wang Heng
    2018, 39(6):  1280-1292.  doi:10.11743/ogg20180617
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    “Source-to-Sink” system is a hot topic in recent sedimentology research.The eastern slope of Chengdao,which constitutes a complete “Source-to-Sink” system together with Chengbei low salient and its surrounding depositional areas,is a transitional slope zone from Chengbei low salient to Shanan and Bozhong Sags,and located in Bohai Bay Basin.Based on the core,logging and 3D seismic data,we defined the basement rock types of provenance,reconstructed the palaeogeomorphology of the 2nd member of Dongying Formation(Dong 2 member),made a quantitative analysis of elements in the “Source-to-Sink” system,finely mapped the sand bodies within the depositional area,and established the coupling model of the “Source-to-Sink” system in the eastern slope of Chengdao.The results show that the isolated flood sublacustrine fan deposits,being predominant in the Dong 2 member,are all sourced from Chengbei low salient,and their basement rocks are composed mainly of clastic and pyroclastic rocks.The distribution patterns and scales of sand bodies in depositional areas are mainly controlled by source type,relief,area of catchment,size of transportation pathways,slope break zone,palaeomorphology of depositional area and so on.Among them,the total volume of sediments imputing into the depositional area is closely related to the relief and the catchment area.The larger the relief(averaging at about 1 280 m)and catchment area(averaging at around 7 km2)are,the larger the scale of the fan system will be;on the contrary,the fan system contracts accordingly.In addition,the palaeogeomorphology in the depositional area and slope break zone also exert an important control on the size of fan system.Two types of slope break zones were recognized in this study,namely the topographic and fault slope break zones.The angles of the slope break zones range between 3.9° and 9.8°,and show a positive correlation with both the fan body thickness and area.Meanwhile,the size of transportation channels(width/depth ratio and cross-sectional area)also determines the distribution characteristics of sand bodies.In summary,the elements in the “Source-to-Sink” system in the study area are relatively stable during the deposition of the study interval.Finally,we proposed a multi-factor coupling model of source areas with multiple lithologies(provenances)-channels of paleo-ravines or fault troughs within provenance-transportation pathways of topographic/fault slope break zones(transportational area)- isolated flood sublacustrine fan(sinks).This model establishes the relationship between the size of sand bodies and their provenances,and provides potential implications for predicting favorable sand bodies in future oil and gas exploration.
    Technique for describing baffles and barriers in oil reservoir with horizontal well data integrated and its application
    Xia Zhu, Zhang Tingting, Zhang Sheng, Hu Shaohua, Wang Guizhong, Bie Jing, He Chuanhang, Li Kai
    2018, 39(6):  1293-1304.  doi:10.11743/ogg20180618
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    The prediction for the distribution of baffles and barriers is an indispensable part for the fine description of oil reservoirs in the middle-late stages of oilfield development,because the differential permeability caused by these layers has become an important factor affecting the distribution of remaining oil.As for complex and highly heterogeneous reservoirs,it is difficult to accurately and reasonably characterize their thin baffles and barriers simply by using the geological data of outcrop, limited vertical well data and geological experiences.As there are abundant horizontal well data available,we proposed a new idea and technical process to describe baffles and barriers by the combination of vertical and horizontal well data.The cross-plotting analysis technique of change amplitude parameter values of logging curves being sensitive to baffles and barriers was introduced into the technical process.The identification criteria of baffles and barriers and the method of predicting their occurrences with horizontal well logs under the constraint of seismic structural surfaces were used to establish the isochronous correlation framework and the relationship of logging responses of baffles and barriers between vertical wells(segments)and laterals,and to determine the types and quantitative interpretation standards of baffles and barriers in single laterals.Then the distribution of baffles and barriers along the trajectory of horizontal wells was discussed, and multiple data and geologic models were integrated to guide the correlation of baffles and barriers on profiles and the study of their planar distribution,and to verify and correct the previous interpretation results obtained based solely on vertical well data.Finally,the oil-water movement process and residual oil distribution and enrichment characteristics under the control of the baffles and barriers were comprehensively analyzed in combination with the dynamic development data.This study provides a powerful basis for the adjustment of subsequent oilfield development plans and the emplacement of new wells.
    Advances in numerical simulation technology of chemical flooding in high temperature and high salinity reservoir
    Hu Bo
    2018, 39(6):  1305-1310.  doi:10.11743/ogg20180619
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    For the high temperature and high salinity reservoir,Shengli oilfield has developed some new oil displacement systems in recent years,such as heterogeneous system and emulsion surfactant system.The oil displacement mechanisms of these new systems are obviously different from the traditional ones,and could not be described by the commercial numerical simulation software effectively;while the self-developed numerical simulation software is slow in calculation and not suitable for large-scale field application.Based on the SLCHEM,a proprietary chemical flooding numerical simulation software,we established a B-PPG throughput factor-based mathematical model of heterogeneous combination flooding and the mathematical model describing emulsification and viscosification by emulsion surfactant flooding,after the laboratory experiments and study of mechanisms.Through these models,we carried out in-lab fitting and put the models into application,verifying the rationality and accuracy of the mathematical models.In addition,the sequential implicit algorithm,the parallel algorithm and the alternating direction algorithm were applied to fast run the models of mega node scale.The efficiency test for the calculation was carried out through the conceptual model,and the results show that it needs 2.9 hours to run a model with 1 million grids,116 wells and 5 years’ production history.The laboratory test and field application show that,compared with the commercial software,the modified SLCHEM software can realize accurate fitting between the in-lab experimental results and field performance indexes of the new oil displacement systems,so it could provide effective technical support for plan optimization and performance analysis of chemical flooding.
    Advances in fine description of reservoir in high water-cut oilfield
    Chen Huanqing, Shi Chengfang, Hu Haiyan, Wu Hongbiao, Cao chen
    2018, 39(6):  1311-1322.  doi:10.11743/ogg20180620
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    Major oilfields in central-eastern China have entered into the high water-cut development stage during which about 40%-60% reserves need to be recovered.Fine description of reservoir is the most essential work for effective oilfield development; at the same time the fine description of high water-cut reservoir is of special significance for boosting production practice in oilfields and deepening understanding of production performance.Based on the detailed study on related documents both in Chinese and in foreign languages,in combination with practical experiences in typical oilfield production,we systematically introduced the status quo of the research on fine description of reservoir in high water-cut oilfield,and summarized the five main problems existing in the present research,including fine division and correlation of stratigraphy,reservoir heterogeneity,patterns of reservoir variation in the process of oilfield development,comprehensive remaining oil characterization with integration of various data,and tertiary oil recovery in high water-cut oilfields.Subsequently,several new techniques and methods with better application results now were pointed out.In addition,the focuses of present research were summarized as follows: ① fine interpretation of fracture system; ② fine characterization of reservoir architecture; ③ logging interpretation for water-flooded layers; ④ identification of preferential seepage channels; ⑤ multipoint geostatistical modeling.
    Method to assess recoverable tight oil based on multiple regression analysis
    Zhang Xinshun, Wang Hongjun, Ma Feng, Bian Congsheng, Wang Zhaoming
    2018, 39(6):  1323-1335.  doi:10.11743/ogg20180621
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    It is hard to reliablely estimate recoverable resources of tight oil by means of conventional resource evaluation methods due to the abnormal features of unconventional oil and gas accumulation.Through the study of the productive tight oil play in the B12 interval of Wolfcamp Formation in the Permian Basin of North America,we proposed a new me- thod for evaluating recoverable tight oil resources in the Permian Basin based on multiple regression analysis.In line with the correlation between the geological parameters of pay zones and the actual production of the tight oil play,a model for evaluating recoverable tight oil was established;then,the geological parameters and their corresponding influence coefficients were determined by correlation and multiple regression analyses,so as to get the calculation model for recoverable tight oil abundance in the study area.Finally,the volume of recoverable tight oil in the study area was worked out.After the detailed analysis of SJ area in the Permian Basin,the geological factors affecting the recovery of tight oil can be graded in terms of significance as follows: brittle mineral content,maturity,porosity and oil saturation,with the degree of significance decreasing from the beginning.Meanwhile,the correlation coefficient between the predicted yield by the model and the practical yield reaches 0.7885,signifying the reliability of the model,and the total volume of recoverable tight oil is 46.15 million tons.Since the tight oil evaluation model based on multiple regression corresponds directly with the production,after setting the constraints on production,we can also get to know that the recoverable volumes of Type Ⅰ,Ⅱ and Ⅲ tight oil are 0.44,24.83 and 18.69 million tons,respectively.In summary,the new model based on multiple regression analysis is more effective for assessing recoverable tight oil resources and thus its scope of application is broader.
    Experimental study of acid-fracturing-induced fracture permeability in shale in Fuling area,Sichuan Basin
    Fang Haoqing, Guo Tiankui, Wang Yang, Zhai Naicheng, Qu Zhanqing
    2018, 39(6):  1336-1342.  doi:10.11743/ogg20180622
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    Volume fracturing is a necessary technical means to realize commercial development of shale gas,but the effectiveness of its stimulation mechanism and various auxiliary production-enhancing measures still needs further exploration.The effects of carbonate content,acid type and concentration and proppant on the permeability of acid-etching shear fractures in shale reservoir were investigated through experiments testing the permeability of acid-etching fractures,and the changes of the microscopic pore throat structures before and after acid etching were studied by CT scanning.The results show that when the carbonate content of shale is about 2%,the best acid etching effect can be obtained by using the mud acid formula of about 11.25% HCl+6.75% HF,while for the shale with a carbonate content of 15%,the acid concentration should be about 7.5% HCl for the best acid-etching effect,and for the shale with a carbonate content of 25%,the acid concentration should be about 2.5% HCl.If natural fractures filled with calcium cements are well developed in shale reservoir,optimal acid concentration should be raised appropriately.Nevertheless,if open natural fractures or fractures filled with calcium cements are not well developed in the shale reservoir,even acid with high concentration cannot drive through the cores due to the extremely low matrix permeability in shale.The experimental results provide more valuable information for the design of effective hydraulic fracturing in shale reservoirs.