最新刊期
卷 43 ， 期 4 ， 2022
- 摘要：Upon previous researches， insights have been gained through detailed observation of 12 new outcrop sections and cores （mostly gathered after 2016） from 31 typical wells on the perihhery of Tarim Basin as well as fine interpretation of sedimentary facies in 82 wells together with the interpretation and seismic facies identification from 188 two-dimensional seismic lines and three-dimensional seismic data in five acreages focusing on the Ordovician in the Tarim Basin. Firstly， sedimentary facies types and features are determined by observing single outcrop sections and analyzing drilling data of single wells. Secondly， sedimentary facies changes are mapped through correlation between outcrop sections and well profiles. Thirdly， facies boundaries are delineated based on seismic facies types and their planar distribution determined through seismic interpretation and tracing. Finally， the lithofacies paleogeography during the deposition of each formation of the Ordovician are mapped to reveal their paleogeographic and sedimentary patterns. The results show that the sedimentary period of the Penglaiba-Yijianfang Formations in the early Ordovician is rather a pattern of "one platform with two edges and two basins" than a pattern of "a west platform coupled with an east basin" that as previously determined. The Ordovician carbonate platform is suggested to have evolved from a unified carbonate platform to multiple platforms after differentiation and to the final extinction. Based on these understandings， three sedimentary filling models are established for the evolution of the Ordovician， i.e.， the early single platform - coexisting gentle slope and steep slope edge - basin， the middle multiplatform - multiple edge - multiple basin and the late marine environment with terrigenous clastic input.关键词：sedimentary facies correlation;paleogeography mapping;lithofacies paleogeographic evolution;sedimentary model;Ordovician;Tarim Basin26|16|13更新时间：2022-07-19
- 摘要：Efficient oil and gas exploration and development in petroliferous continental rift basins relies heavily on a profound understanding of sequence stratigraphic architectures and sandbody distribution characteristics in different tectonic evolution stages. Based on a review of the development status of sequence stratigraphy and geological characteristics of continental rift basins， this study characterizes the sequence stratigraphic architectures and sandbody distribution according to a four-stage tectonic evolution of the basins： ① During the early syn-rift stage， faulting at basin boundaries starts with parasequences being vertically aggraded and superposed， and with near-source coarse-grained depositional systems including alluvial fan， distributary channel， and fan delta being developed. ② During the main syn-rift stage， faulting intensifies with parasequences showing a variety of overlapping styles in different structural belts and systems tracts， and basins fill mainly with fluvial， delta and gravity flow. ③ During the transition stage from rifting to depression， faulting starts to wean with parasequences being overlapped and dominated by progradation and aggradation， and depositional systems dominated by axial fluvial and deltaic depositional systems being developed. ④ During the post-rift depression and subsidence stage， faulting nearly ends with basins in an overcompens and with the fluvial-shallow-water deltas being developed. Current hot topics and future development of sequence stratigraphy in continental rift basins are also discussed based on the above analyses.关键词：sequence architecture;sandbody distribution;tectonic evolution stage;depositional system;sequence stratigraphy;continental rift basin17|10|29更新时间：2022-07-19
- 摘要：Both the sequence stratigraphy and source-to-sink system are modern geoscience disciplines with theories and methodologies being widely applied and employed. However， the connections and distinctions between the two have not been discussed thoroughly for a better discipline integration and synergy. The sequence stratigraphy is focused on establishing high-resolution isochronous stratigraphic frameworks for sinks and trying to reveal their sedimentary filling processes， temporal-spatial distribution patterns and genetic mechanisms. While the source-to-sink theory expands further to transport areas and provenances， tracing the dynamic responses of denudation， transport， and accumulation of sediments in multiple dimensions， and determining the driving mechanisms and prototype patterns of sediment partition from source to sink. The internal connections between the two disciplines are reflected mostly through the analysis of denudation-sedimentation response and quantitative prediction of sedimentary bodies in isochronous stratigraphic frameworks， while their distinctions are mainly illustrated during the description of different key elements and structures of inner sequence units. Judging by the current development trends， we could expect a rapid development of the methodology systems of the two disciplines in respects of standardization of their application， combination of ancient and modern data， and quantitative analyses and prediction through multi-disciplinary and multi-parameter integration.关键词：connection and distinction;structure of systems tract;topographic configuration;sediment body predication;sequence stratigraphy;source-to-sink system18|9|20更新时间：2022-07-19
- 摘要：In the Pearl River Mouth Basin， a majority of hydrocarbons were discovered in the Miocene-Oligocene reservoir rocks deposited during the depression stage， while only 8 % of the discovered hydrocarbons were found in the Eocene reservoir rocks formed during the rifting stage， and no commercial discoveries have been made in the Mesozoic buried hills. The main problems in exploration for the Paleogene reservoir rocks and Mesozoic buried hills include whether there are a quantity of hydrocarbons still preserved in the middle-to-deep downfaulted reservoir rocks of hydrocarbon-rich sags， whether the hydrocarbon migration pathways are effectively developed in the Paleogene reservoir rocks and Mesozoic buried hills， as well as whether the hydrocarbon accumulation dynamics， traps and reservoir-seal assemblages are well developed. In line with the assessment theory of “source-migration-accumulation”， the study discusses the static and dynamic elements of the hydrocarbon accumulation system in Huizhou 26 Sag， Pearl River Mouth Basin， including the hydrocarbon source in terms of types and quality of source rocks， thermal evolution and hydrocarbon generation-expulsion history， and types and scale of hydrocarbon resources， the hydrocarbon migration in terms of migration unit and direction， migration pathway， confluence intensity， as well as the hydrocarbon accumulation in terms of secondary structural belt and trap， reservoir-seal assemblage， charging intensity and preservation condition. In conclusion， the study reveals the characteristics of source-migration-accumulation for the Paleogene reservoir rocks and Mesozoic buried hills in Huizhou 26 Sag， sets up a dynamic accumulation model featuring “accelerated maturation of oil-prone source rocks at later stages， generation of oil at first followed by gas， joint control of fault and overpressure， strong hydrocarbon supply by source-reservoir juxtaposition， and 3D migration and accumulation”. Major breakthrough has been made thereby in the exploration for the Paleogene reservoirs and Mesozoic buried hills in Huizhou 26-6 structure.关键词：dynamic accumulation;source-migration-accumulation assessment;Mesozoic buried hill;Paleogene;Huizhou 26-6 oil/gas field;Huizhou 26 Sag;Pearl River Mouth Basin15|12|34更新时间：2022-07-19
- 摘要：The Neoproterozoic in the Longshan area， North China， is well exposed. With clastic rocks and carbonates developed successively from bottom to top， the strata serves as an ideal subject for the study of sequence stratigraphic framework and sedimentary facies evolution， which has been considered significant to the paleogeographic reconstruction of North China. Field and lab analyses of lithologic characteristics and sedimentary sequences of the strata are combined with the regional tectonic movement to establish the isochronous sequence stratigraphic framework， analyze the sedimentary facies evolution， and build up the sequence stratigraphic development model. The results show that according to the unconformities and lithologically abrupt interfaces， the Neoproterozoic Qingbaikouan System can be divided into three third-order sequences from bottom to top： the SQ1 （Xiamaling Formation）， SQ2 （Changlongshan Formation） and SQ3 （Jingeryu Formation）， each consisting of transgressive systems tract （TST） and highstand systems tract （HST）. The SQ1 and SQ2 sequences are mainly composed of clastic rocks indicating sufficient input of terrigenous clastics. The SQ3 sequence is dominated by mixed siliciclastic-carbonate rocks against a relatively clear water depositional setting. The lithological characteristics， sedimentary structures and superposing styles， all point to shallow sea shelf facies for the SQ1-TST， and subtidal sand flat and intertidal mixed sand-mud flat for the SQ1-HST. The SQ2-TST mainly develops subtidal sand flats and tidal channels， while SQ2-HST mainly develops intertidal mixed sand-mud flats and supratidal mud flat. The SQ3-TST develops subtidal sandy shoal and argillaceous limestone flat， while SQ3-HST mainly develops intertidal dolomitic limestone flat and supratidal calcareous and argillaceous dolomite flat. Based on the understanding， a sequence stratigraphic development model of mixed siliciclastic-carbonate rocks dominated by tidal flat-shallow sea shelf facies is established， indicating the possibility of an open epicontinental sea with gentle slopes.关键词：tidal flat facies;sequence stratigraphic framework;sequence stratigraphic development model;mixed siliciclastic-carbonate rock;Qingbaikouan System;Neoproterozoic;Longshan area;North China12|7|2更新时间：2022-07-19
- 摘要：A systematic analysis was carried out on a combination of field outcrop data with surface natural gamma ray measurement and element contents （Fe， Ca， Mg and B） as well as well data to characterize the sequence stratigraphy of the third member of Bashijiqike Formation in an outcrop section from the northern Kuqa Depression. The results show that the member has three distinct lithologic intervals， with the lower interval characterized by two sedimentary cycles （periods） of thick brownish-gray medium to fine sandstone and thick brown mudstone， the middle interval by a large set of thick brown and brown-gray siltstone， fine sandstone with thin reddish brown mudstone interbeds and the upper interval by alternating brown-gray siltstone， fine sandstone and reddish-brown mudstone. The surface natural gamma curves values range between 5 and 40 API and occur mostly as dented bell curves or flattened boxes with dents in between， which can be readily compared with well logs. The variation trends of Fe3+ and Fe2+， Ca/Mg ratio and B in the section show striking stratigraphic cycles， corresponding to the paleo-water variation in an order of shallow - deep - shallow - deep - shallow - deep - shallow for the Bashijiqike Formation. These long-period cycle interfaces in the third member of Bashijiqike Formation are contrastive and can be easily identified in outcrops. Observation of the lithology， color， bedding and other characteristics of the outcrop section reveals two types of short-term base-level cycle superposition patterns， i.e.， the “upward-deepening asymmetric” pattern and the “upward-deepening followed by upward-shallowing near-symmetric” pattern； and if combined with the characteristics of natural gamma curves and elemental analysis， medium-term cycles can also be identified. Based on this method， the third member of Bashijiqike Formation in the outcrop can be divided into three medium-term cycles （fourth-order sequences） and six short-term cycles （fifth-order sequences）， with one short-term cycle missing from parts of the outcrop. However， compared with data gathered from wells drilled closer to lake basin center， absence of one medium-term cycle and four short-term cycles are often observed in the outcrop. The medium-term cycles of MSC1， MSC2 and MSC3 in the outcrop correspond respectively to the medium-term cycles of MSC2， MSC3 and MSC4 in subsurface， and they share the similar alternating patterns of sand body with mudstone interlayers/barriers. The study may be used to guide gas exploration in the deep of northern Kuqa Depression.关键词：sedimentary cycle;high-resolution stratigraphy;Bashijiqike Formation;outcrop profile;deep gas;Cretaceous;Dabei Gasfield;Kuqa Depression;Tarim Basin18|10|7更新时间：2022-07-19
- 摘要：Lithologic traps formed by gravity flow deposits have gradually become the focus of hydrocarbon exploration and development. The eastern slope of Liaoxi uplift or the western slope of Liaozhong Sag is still at an early stage of exploration in the Liaodong Bay Depression， Bohai Bay Basin. A gravity flow fan of high-density turbidite nature was drilled recently in the gentle slope zone of the intra-basinal uplift and shows a potential target for future exploration of lithologic-stratigraphic reservoirs in the slope zone. In the study， a high-resolution sequence stratigraphic framework of the 3rd member of the Paleogene Dongying Formation in the study area is established at first， followed by a comprehensive study on the geomorphology and its controlling factors of gravity flow deposits within the systems tracts based on an integrated analysis of seismic， logging， and core data. The results show that four types of slope fans are mainly developed in the gentle slope zone to the east of Liaoxi uplift， namely the ligulate fan， petal-shaped fan， lobe-shaped fan and channel-shaped fan， the morphology of which is determined by slope gradient and sand richness of gravity flow sediment sources （the distally-sourced braided river delta front）. Among others， the more complex the slope break and the steeper the slope， the larger the aspect ratio of the sublacustrine fan is， displaying in a long ligulate shape， while the simpler the slope break type and the gentler the slope， the smaller the aspect ratio of the sublacustrine fan is， displaying in a lobe shape. On the other hand， the sand richness of sediment source determines the degree of channelization of sublacustrine fan and its stability. The higher the sand richness， the lower the channel stability is， while the higher the argillaceous sediment content， the higher the channel stability is. Therefore， the steep slope rich in sand is prone to form a ligulate fan， the gentle slope rich in sand is prone to form a lobe-shaped fan， and the gentle slope rich in argillaceous sediment is prone to form a channel-shaped fan； the petal-shaped fan is but of a transitional type.关键词：gravity flow;high-density turbidite;sedimentary morphology;sequence stratigraphy;gentle slope zone of intra-basinal uplift;Liaodong Bay Depression;Bohai Bay Basin12|12|12更新时间：2022-07-19
- 摘要：The reef-shoal gas reservoirs of Changxing Formation around the Kaijiang-Liangping trough in the Sichuan Basin are the major targets of natural gas exploration and development in eastern Sichuan Basin. However， few studies have been seen on the sedimentary architectures of reef-shoal around platform margin and their differences as of now. An integrated analysis of cores， thin sections， well logs， and seismic data， is applied to disclose the changes of slope angle at the front， lithologic composition of organic reef-shaol facies， reef cycle， external contour， vertical superimposition pattern， lateral migration， spatial distribution characteristics and differences around the trough， coupled with the seismic stratigraphic framework around the trough. The results are as follows. First， the Kaijiang-Liangping trough formed during the Late Permian rifting， when the NW-trending tensional basement-rooted faults were active， has nearly U-shaped platform marginal zones developed around. The palaeotectonic pattern of platform margin is characterized by “deep water in the steep northwest and shallow water in the wide and gentle southeast”. Second， the sedimentary architectures of platform margins around can be classified into four types， that is， the fault-controlled steep slope type with accretion rim， sedimentary steep slope type with accretion rim， gentle slope break type with retrograding strip， and extremely gentle slope type with discrete migration. These architectures are in alternative distribution around the trough， the western and northern platform margin dominated by fault-controlled or vertical superimposed steep slope type and the eastern and southern by extremely gentle slope type with discrete migration. Third， tectonic palaeogeomorphology and sea level eustacy jointly control the formation of sedimentary architectures of the platform margin in the study area and their differences. Among others， the former controls the pattern of the platform margin and accommodation of organic reef， and the latter controls the sedimentary architecture， migration and superposition of reef-shoal.关键词：organic reef-shoal facies;platform margin;sedimentary architecture;Changxing Formation;Late Permian;Kaijiang-Liangping trough;Sichuan Basin16|11|10更新时间：2022-07-19
- 摘要：To enhance the Mesozoic sequence stratigraphic division and sedimentary fill evolution reconstruction in the Tabei Uplift region of the Tarim Basin， an integral analysis of seismic， logging， core and outcrop data is carried out to redefine the sequence stratigraphic framework， identify the major sedimentary systems and reveal the sedimentary fill evolution features and their correspondence to the emergence and disappearance of the Tabei Uplift. Four second-order sequences （Ⅰ-Ⅳ） and eleven third-order sequences are divided with the recognition of four regional angular unconformities， one regional parallel unconformity and seven local unconformities in the study area. Analyses indicate that during the Late Triassic （Ⅰ-SQ3）， the EW-trending Tabei Uplift provided abundant sediments to its steep narrow north slope and gentle broad south slope where alluvial fan/fan deltas and braided deltas were formed respectively. During the Early Jurassic （Ⅱ-SQ1）， the uplift expanded and provided more sediments to the south slope where larger braided deltas were developed. By the end of deposition of the Lower Cretaceous Kapushaliang Group （Ⅲ-SQ4）， the uplift was mostly disappeared and sediments in the area were mainly sourced from a denuded zone in the southeast and deposited as deltas. By the end of the Lower Cretaceous Bashijiqike times （Ⅳ-SQ3）， the study area turned into a south-dipping slope with sediments mostly sourced from a denuded zone in the east and an orogenic belt in the north and deposited as a shallow-water braided delta. This study may help understand the depositional evolution of the Mesozoic continental lacustrine basin in the region and provide a reference for future exploration.关键词：sedimentary system;depositional fill evolution;sequence stratigraphy;Mesozoic;Tabei Uplift region;Tarim Basin12|10|9更新时间：2022-07-19
- 摘要：The 7th member of Yanchang Formation （Chang 7 Member） in Zhenjing area at the southwestern margin of Ordos Basin， features development of both high-quality source rocks and turbidite reservoirs. The Chang 7 Member is deposited in a period of maximum lake depth of the Ordos Basin， with its sedimentary system transitioning from deep-semi-deep lacustrine facies to deltaic facies. As the oil/gas exploration and development has been progressing in the study area， more and more attention has been paid to fine-grained deposits and shale oil/gas reservoirs， especially the sedimentary characteristics of turbidites therein. An integration of outcrop， core and logging data is applied to study sedimentary evolution and depositional patterns of the turbidites within a fourth-order sequence stratigraphic framework， in which sequence stratigraphy and sedimentology methods are adopted. The results show that the Chang 7 Member can be divided into three fourth-order sequences from bottom to top， namely MSC1， MSC2 and MSC3. The member in general is dominated by fine-grained deposits and exhibits signs of turbidite deposition in a pre-deltaic and lacustrine setting. Among others， the pre-deltaic subfacies is widely seen in MSC3 and MSC2； while the lacustrine facies predominates in MSC1 with underdeveloped deltas facies. The three fourth-order sequences feature diverse kinds of turbidite development. Three sedimentary evolution models are established for the turbidites： the lacustrine transgressive muddy type， early highstand mixed sandy and muddy type， and late highstand sandy type， with the last type being the major target for future exploration. In the process， the sedimentary evolution characteristics in the study area are considered； the relative position of lake level is taken as the proxy of the base level fluctuation （Va）， and the mean decompacted thickness serves to reflect the sediment supply rate （Vs）. Besides， the variation of the ratio of the increase rate in accommodation space （ΔVa） to the sediment supply rate （ΔVs） is also taken into account.关键词：accommodation space;sediment supply rate;fourth-order sequence;evolution model of turbidite deposits;sedimentary system;Chang 7 Member;Zhenjing area;Ordos Basin11|11|11更新时间：2022-07-19
- 摘要：The pay zone in the 6th member of the Upper Triassic Yanchang Formation （Chang 6 pay zone） is one of the tight oil-rich intervals in the Ordos Basin. The study on the characteristics and genesis of tight oil reservoir sand bodies is of guiding significance to further exploration and development of tight oil in the basin. Apart from multiple previous research results， we make a thorough analysis of cores from the Chang 6 pay zone in Huachi-Qingyang area to clarify the types and characteristics of the tight oil reservoir sand bodies therein， and discuss in detail the superimposing reservoir sand bodies of diverse types in the pay zone. The results show that the tight oil reservoir sand bodies of the Chang 6 pay zone can be mainly grouped into four types： delta front， seismite， debris-flow， and turbidite types. Four kinds of superimposing relationship are formed vertically， including seismite type superimposing with delta front type， seismite type superimposing with debris-flow type， debris-flow type superimposing with turbidite type， and seismite/debris-flow types superimposing with turbidite type. From the delta front to the center of the lacustrine basin， we can find sand bodies of diverse genesis in vertical superimposition due to changes of palaeogeomorphic settings and environmental conditions， which serve for constructing a genetic model of the tight oil reservoir sand bodies in the Chang 6 pay zone based on the regional depositional pattern.关键词：genetic model;reservoir sand body;tight oil;Chang 6 pay zone;Upper Triassic;Ordos Basin11|10|10更新时间：2022-07-19
- 摘要：The study focuses on the petrological characteristics， reservoir space characteristics and diagenesis of the Upper Permian marine tuffaceous deposits in Yuanba area， Sichuan Basin based on thin section observation， analysis of scanning electron microscope （SEM） and energy dispersive spectroscopy （EDS）， X-ray diffraction analysis， and mercury intrusion porosimetry （MIP） test. The research results indicate that the tuffaceous deposits interbedding with organic mudstones and carbonaceous mudstones are in laminae of 0.1-10.0 mm thick， and sandwiched within biogenetic limestones or marlstones， which can be classified into tuff， sedimentary tuff and tuffaceous sedimentary rocks. Under the joint effect of seawater and hydrotherm， the tuffaceous deposits have been altered by diagenetic effects such as recrystallization， cementation， metasomasis， dissolution and filling， resulting in a variety of secondary rock types. Acidic hydrotherm can dissolve tuffs and water-rock reaction serves to reproduce an alkaline environment resulting in filling or metasomasis of ferrodolomite/dolomite， gypsum， and a small amount of albite and barite. At the same time， the alkaline environment is also favorable for the formation and preservation of illite or mixed-layer illite/smectite， which in turn stimulates the formation of micrometer-scale dissolved pores in tuffs and nanometer-scale intercrystal pores in authigenic clay. In addition， the directionality of detrital and authigenetic clay minerals， and the existence of laminae in the tuffaceous deposits are conducive to the formation of bedding-parallel fractures， which have effectively improved the reservoir property of the rocks.关键词：petrological feature;diagenesis;reservoir space;tuffaceous deposit;Upper Permian;Yuanba area;Sichuan Basin12|9|4更新时间：2022-07-19
- 摘要：The Carboniferous Simen Formation located at the southern margin of Xuefeng Mountain in Guangxi Zhuang Autonomous Region of China is of good hydrocarbon accumulation conditions. It is of great significance to finding out the formation and development mechanism and controlling factors of Simen Formation reservoirs regarding the petroleum exploration therein. An integration of field outcrop observation and various data including drilling and core， scanning electron microscopy （SEM）， casting thin section， inclusions， as well as porosity and permeability， is applied to clarify the basic characteristics of the Carboniferous Simen Formation reservoir at the southern margin of Xuefeng Mountain； and meanwhile the factors controlling reservoir development， formation mode of high-quality reservoirs， and distribution of play fairways are discussed. The research results show that the reservoir rocks of Simen Formation mainly include fine-grained quartzite sandstone and detrital quartzite sandstone， which are dominated by reservoir spaces of primary intergranular pores， secondary dissolved pores and fractures. The reservoirs are of the pore-fracture type and pore type， characterized by low porosity and low permeability as a whole. On the other hand， sedimentation， diagenesis and tectonism jointly control the reservoir quality， that is， microfacies of coastal sand bar， sandy-argillaceous shore and mixed flat control the distribution of reservoir sand bodies in the Simen Formation. Strong compaction is the primary cause for tight reservoirs， which could result in a pore loss rate of about 85.2 %， while dissolution effectively improves the reservoir quality （with a porosity rise of about 2.3 %）， and structural fractures greatly promote the carrier system of the reservoirs with some areas still favorable for the development of high-quality reservoirs in terms of physical conditions. Finally， a model for the reservoir development is established， by which two favorable areas for reservoir distribution of Desheng and Luobu counties are mapped in the study area.关键词：reservoir characteristics;reservoir development model;play fairway distribution;tight sandstone;Simen Formation;Carboniferous;southern margin of Xuefeng Mountain13|10|2更新时间：2022-07-19
- 摘要：The fine analysis of deep-water gravity flow deposits in the Ordovician Lashenzhong Formation outcropping at the western margin of Ordos Basin， serves for revealing the evolutionary pattern and sedimentary model of deep-water gravity flow channel-lobe system， and then the reservoir distribution therein. The results show that the gravity flow depositional units in the study area include complex channels， migration channels， vertical aggradation channels with layered fill， distributary channels， as well as proximal and distal lobes， the evolution of which is closely related to the type and energy of gravity flow. At the initial stage， gravity flow is dominated by debris flows and turbidites， commonly leading to the development of complex channels. As the gravity flow gets waning in energy， turbidites become predominant， resulting in the formation of migration channels and vertical aggradation channels in succession through multi-stage erosion and sedimentation. Subsequently， distributary channels， proximal and distal lobes are generated in turn when the turbidites fade. In addition， the process of complex channel development could be divided into youthful， prime， and decline stages which are corresponding to the short-term gravity flow evolution processes. Complex channels in the prime stage， migration channels， and vertical aggradation channels are favorable reservoirs， with the storage capability declining in turn. The middle parts of channels are generally better compared with those at the flanks in terms of reservoir potential， and reservoirs of proximal lobes are superior to those of distributary channels.关键词：turbidite;debris flow;gravity flow;channel-lobe system;depositional model;Lashenzhong Formation;Ordovician;Ordos Basin8|8|16更新时间：2022-07-19
- 摘要：The deep coarse-grained siliciclastic rocks of the 4th member of the Paleogene Shahejie Formation （Es4） in Minfeng-Yanjia area of the eastern section of the steep slope zone to the north of Dongying Sag， Bohai Bay Basin， are taken to identify markers and time of deep hydrothermalism and make a preliminary discussion on its geological significance. A variety of data are applied in the study including the core， scanning electron microscopy （SEM）， thin section， fluid inclusion， X-ray diffraction （XRD） of clay minerals， vitrinite reflectance （Ro）， physical properties of core sample and hydrocarbon source Rock-Eval parameters； besides， the research results of tectonic evolution， magmatic activity， stratigraphic burial and hydrocarbon accumulation history are also taken into consideration. The results show that， there are explosive breccia， cubic pyrite and some mineral assemblages， such as mixed layer illite/montmorillonite-ankerite-apatite， mixed layer illite/montmorillonite-apatite-pyrite， chlorite-apatite-pyrite and apatite-pyrite， which just reflect the deep hydrothermalism in the Es4 coarse-grained siliciclastic rocks of the study area. The vertical evolution of clay minerals is characterized by an abnormal increase of illite/montmorillonite ratio and transient dramatic increase of kaolinite content. The contents of free hydrocarbon （S1） and pyrolysis hydrocarbon （S2） are abnormally high at a burial depth ranging from 3 400 m to 4 800 m， while they are relatively low at a burial depth of 5 500 m when the maximum pyrolysis temperature （Tmax） is abnormally high. At a burial depth of 4 269 m to 4 800 m， there are abnormally high-temperature inclusions in quartz fractures. The δ13 C
in the carbon stable isotopes of natural gas is greater than -8 ‰， indicating inorganic origin and formation water of NaHCO3 type as associated with the deep CO2-rich hydrothermalism. The characteristics mentioned above all indicate deep fluid activity of mantle-derived CO2-rich origin in the Es4 coarse-grained siliciclastic rocks in Minfeng-Yanjia area during the Guantao-Minghuazhen sedimentary period. The deep hydrothermal fluid has played a dual role in reforming the physical properties of the coarse-grained siliciclastic reservoir. On the one hand， it causes fractures and promotes dissolution to improve the reservoir physical properties； on the other hand， the authigenic minerals in precipitation clog pores thereby hinder fluid migration and damage the physical properties of the reservoir. In addition， deep hydrothermal fluid has got involved in the thermal evolution and hydrocarbon generation of source rocks in the lower section of the 4th member of Shahejie Formation （Es4L）， which has a potential impact on hydrocarbon expulsion and crude oil cracking of the source rocks. 关键词：identification marker;hydrocarbon generation;reservoir modification;deep hydrothermal fluid;deep coarse-grained siliciclastic rock;the 4th member of Shahejie Formation （Es4）;Dongying Sag;Bohai Bay Basin14|9|12更新时间：2022-07-19 - 摘要：The lower to middle carbonate-evaporite assemblages of the Ordovician Majiagou Formation in the Ordos Basin are potential exploration targets but questions have been raised concerning whether there are source rocks developed， how well they are developed and if they match well with reservoirs. Detailed observation of cores and analyses of high-frequency sedimentary cycles from wells Shan 473 and Tao 112 encountering the Majiagou Formation show that： ① Carbonate-evaporite assemblages consist two kinds/eight types of sedimentary cycles （recording gradually dry-up climate） of limestone （without dolomitization）， dolostone， thin dolomite-evaporite interbeds， and evaporites， of which the dolostone and thin dolomite-evaporite interbeds are further recognized to contain 10 types/111 high-frequency sedimentary cycles characterized with frequent cycles and thin single layers. ② Based on analysis of these high-frequency sedimentary cycles， two types of source rocks are identified： the high-quality source rocks consisting of black argillaceous dolostone in millimeter-scale lamina with high TOC （>2.50 %） and the medium-quality source rocks consisting of grey-black dolostone with low TOC （1.21 %）. The high-quality source rocks are facies and horizon conditioned and mostly distributed in the interbedded thin dolomite-evaporite sections around the evaporitic lake and with gas resource amounting up to 850.494 BCM. ③ Two types of facies-controlled dolostone reservoirs are recognized： the dolo-grainstone reservoir on the paleo-uplift and its periphery， and the microbial dolostone reservoir around the evaporite lake， both are favorably located with source rocks. The above understandings may be used as guidance to the future exploration in the lower and middle assemblages of Majiagou Formation， Ordos Basin.关键词：carbonate-evaporite assemblage;high-frequency sedimentary cycles;argillaceous dolostone source rock;microbial dolostone reservoir;Majiagou Formation;Ordovician;Ordos Basin9|9|24更新时间：2022-07-19
Petroleum Geology
- 摘要：Cyclostratigraphy is widely used in fields such as high-precision geological dating of sedimentary strata and high-resolution stratigraphic division and comparison due to its high timing accuracy. The study on cycle division of fine-grained sedimentary strata has been the focus in sequence stratigraphy， though the difficulty. The lacustrine shale from the upper interval of the upper sub-member of the 4th member of the Paleogene Shahejie Formation （Es4scs） in Well Fanye 1， Dongying Sag， Jiyang Depression， Bohai Bay Basin is taken to identify the Milankovitch cycles recorded in the interval. Both logging and geochemical data are selected as alternative indicators for cycle analysis. A combination of spectrum analysis， wavelet transform， power spectrum estimation， and filter analysis is applied to identify the Milankovitch cycles， and geochemical indicators are used to verify the feasibility of logging data-based cycle identification. Subsequently， a “floating” astronomical time scale is established to calculate the sedimentation rate. At the same time， the abundance of organic matter in sediments and paleo-redox proxies are in exploratory application to discuss the response characteristics of the orbital periodicities. The research results are shown as follows. First， it is obvious that the sedimentary cycles of lacustrine shale are significantly controlled by Milankovitch cycles， including 405.00-kyr long-eccentricity cycle （E1）， 124.22-kyr short-eccentricity cycle （E2）， 39.76-kyr obliquity cycle （O2） and 22.00-kyr precession cycle （P1）. Second， a total of 6 E1， 22 E2， 65 O2， and 110 P1 are identified in the studied interval. According to the “floating” astronomical time scale， the duration of deposition may be 2.73 Myr with an average sedimentation rate of 0.069 m/kyr. Third， the abundance of organic matter and variation of the paleo-redox conditions in the fine-grained lacustrine sedimentary strata are controlled by astronomical cycles. Fourth， when the amplitude of eccentricity is large and at its maximum， the earth as a whole is in the interglacial period， warm and humid， prone to generate anoxic organic-rich sedimentary strata， which are the most favorable targets for shale oil exploration. In all， the ideas and methods proposed in the study are of referential value to the division and comparison of cycles of the same type of fine-grained sedimentary strata， the establishment of “floating” astronomical time scales， the calculation of sedimentation rates， and the study of organic matter enrichment rules. In addition， the research results have been directly applied to the unconventional oil and gas exploration and development in the fine-grained sedimentary strata of Shahejie Formation in the Dongying Sag.关键词：Milankovitch cycle;astronomical time scale;sedimentation rate;orbital periodicity;environmental response;shale oil exploration;Shahejie Formation;Dongying Sag13|10|21更新时间：2022-07-19
- 摘要：With the increasing of exploration maturity， beach-bar deposit， as an important reservoir type in downfaulted lacustrine basins， has drawn more attention in search of subtle oil/gas reservoirs. The analysis of the core， lithology， and electrical properties serves to determine the type and combination of beach-bars in the 1st member of Shahejie Formation （Es1） in the Baxian Sag， Bohai Bay Basin. The spatial distribution of these beach-bars of diverse genetic types is then clarified by a comprehensive interpretation of 3D seismic data and based on the principle of seismic sedimentology. The results show that the lithologic types of the beach-bars in the study area mainly include （calcareous） fine-grained sandstone， siltstone， biolimestone， dolomite and argillaceous limestone. According to lithologic combinations， the beach-bars can be classified into four types， that is， clastic rock type， carbonate rock type， mixed carbonate-silisiclastic rock type and tempestite type， the depositional models of which are established respectively. Among others， the beach-bar of clastic rock type is a product of reformation and re-accumulation of delta-front sand bodies； the beach-bar of carbonate rock type is a product of primary deposition of carbonate rocks in the lacustrine basin under low provenance supply capacity； the beach-bar of mixed carbonate-silisiclastic rock type is a product of mixed deposition of terrigenous clastics and intrabasinal carbonate； and the beach-bar of tempestite type is developed under the destructive effect of waves on early formed beach-bars. The temporal and spatial distribution of beach bars show the feature of inheritance. Vertically， beach-bars of clastic rock type， of mixed carbonate-silisiclastic rock type， of carbonate rock type， of mixed carbonate-silisiclastic rock type and of clastic rock type are deposited and superimposed successively from lake transgressive systems tract to highstand systems tract. While in map view， beach-bars are mainly developed on the tilted fault walls and salients of paleo-lakebed form in the paleo-lake basin. Beach-bars of carbonate rock and mixed carbonate-silisiclastic rock type are seen in large scale in local uplifts caused by compression at the end of Maxi strike-slip fault. In all， the types and development characteristics of beach-bars serve to record the tectono-stratigraphic sequence evolution of the downfaulted lacustrine basin and as the material manifestation of paleogeographic pattern and its evolutionary process in the early stage of rifting. The fine description of beach-bars is conducive to restoring the early evolutionary process of the basin， so as to be of referential value to reservoir prediction and oil/gas exploration and development in the future.关键词：sedimentary model;seismic sedimentology;downfaulted lacustrine basin;beach-bar;the 1st member of Shahejie Formation （Es1）;Palaeogene;Baxian Sag;Bohai Bay Basin10|11|8更新时间：2022-07-19
- 摘要：The Xihu Sag is one of the petroliferous sags in the East China Sea Shelf Basin. Recent exploration has confirmed that the Oligocene Huagang Formation is the major gas pay zone in the sag. However， sequence division of the formation is still in dispute， seriously impeding the isochronous correlation of sand bodies and the fine exploration of oil and gas. Based on the sequence stratigraphy and astronomical cycle theory， the study mathematically analyzes natural gamma curves with wavelet transform and INPEFA（Integrated predication error filter analysis） technology to obtain signal curves， spectrums and INPEFA curves for the establishment of a geologic time scale and high-precision sequence boundary framework for the Huagang Formation. The GR curves are reconstructed through wavelet transformation into different wavelet signal curves and spectrums with the sequence interfaces and cycle information highlighted by abnormal vibration and energy group change trend. At the same time， the maximum entropy spectrum analysis technology is used to integrate the GR curves into the INPEFA curves with sequence boundaries and cycle information highlighted by inflection points as well as positive and negative trends. The Huagang Formation is divided into five third-order sequences （namely SQ1 to SQ5 from top to bottom）. Spectral characterization of strata superimposition and cycles within these sequences are combined with their wavelet signal curves to divide the Huaguang Formation into a total of 12 fourth-order sequences （namely H1 to H12 from bottom to top）. The multi-window spectrum analysis of GR curves shows 1 to 3 Ma development duration for the five third-order sequences. The multi-scale and multi-method integration of logging technology for the construction of multi-order isochronous stratigraphic frameworks in the areas lacking of cores and paleontological fossils is proved to have certain promotional value for the future oil and gas exploration in the Oligocene Huagang Formation of the Xihu Sag.关键词：wavelet transform;INPEFA;astronomical cycle;sequence stratigraphy;Huagang Formation;Oligocene;Xihu Sag;East China Sea Shelf Basin12|10|15更新时间：2022-07-19
- 摘要：Evaluation of “double sweet spot” in shale gas reservoirs， i.e. shale gas sweet spot that are both geologically and engineeringly feasible， is challenging due to insufficient accuracy of gas saturation calculation， limitations of fracability assessment methods （though quite a few）， and inadequate integration between the geological and engineering assessments. In view of these， a gas abundance curve representing the geological “sweet spot” is established to tackle the accuracy problem through a sequential reconstruction of the sensitivity relationship between logging curves and gas bearing property based on gas bearing principles. A comprehensive fracability index representing the engineering “sweet spot” is developed to enhance the usability of the fracability assessment methods based on the correlation of rock brittleness index， mechanic parameters and in-situ stress difference coefficients to fracturing. And a geology-engineering evaluation chart is also proposed to better integrate the two aspects based on the production data and productivity classification of layers tested. This study improves the accuracy of qualitative identification and fracability assessment of shale gas sweet spots. The chart has been proven to be effective in recognizing high- medium- and low-potential gas pay zones as well as dry layers. Practices show that the technology is applicable and reliable in assessing shallow/deep layers in the Sichuan Basin and its periphery.关键词：gas abundance;compressibility index;sweet spot;geology-engineering integration;shale gas;reservoir assessment;Sichuan Basin11|12|9更新时间：2022-07-19
Methods and Technologies
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