Method and Description of Sedimentary System Characterization Based on Sequence Stratigraphy

A Oilfield is the most representative mid to deep oil field in the Bohai Sea, with the main oil bearing intervals being the upper and middle Shahejie-3 sections of the Paleogene Shahejie Formation. By combining well seismic analysis, the middle section of Shahejie-3 is divided into high-level system tract and forced lake retreat system tract, corresponding to the II oil formation and I oil formation, respectively. Using sequence stratigraphy methods, based on seismic profiles and drilling lithological cycles, the high stand system tract is divided into 5 stages of delta progradation. The first and second stages are high angle S-type progradation with large sedimentary thickness, the third stage is oblique progradation, and the fourth and fifth stages are S-oblique composite progradation;By combining seismic data, we characterized the large-scale (8 small-scale) progradation bodies of 5 periods, clarified the distribution characteristics of reservoir planes, and laid the foundation for the later exploration of oilfield potential.

Holocene shelf-coastal sedimentary systems associated with the Changjiang River: An overview

The fate of the terrestrial sediment supplied by rivers is a critical issue for understanding the patterns of Holocene environmental change on continental shelves. The East China Sea is a typical broad continental shelf with abundant sediment supply from large rivers. Here, a variety of sedimentary records were formed during the Holocene period. The sedimentary systems associated with these records have unique charac- teristics in terms of spatial distribution, material composition, deposition rate and the timing of deposition, which are related to active sediment transport processes induced by tides and waves, shelf circulations and sediment gravity flows. The sedimentary records thus formed are high resolution slices, i.e., each record has a temporal resolution of up to 10^-10-1 a, but only covers a limited part of the Holocene time. In terms of the spatial distribution, these records are scattered over a large area on the shelf. Further studies of these systems are required to understand the underlying process-product relationships. In particular, the mid- Holocene coastal deposits on the Jiangsu coast, the early to middle Holocene sequences of the Hangzhou Bay, as well as the Holocene mud deposits off the Zhejiang-Fujian coasts, should be investigated in terms of the material supply （from both seabed reworking during the sea level rise event and river discharges）, transport-accumulation processes, the sediment sequences and the future evolution of the sedimentary systems. Advanced numerical modeling techniques should be developed to meet the needs of these studies.

A Cretaceous Desert-Playa Sedimentary System Controlled the Potash Formation in the Simao Basin

Objective The Simao Basin in Yunnan Province has developed Cretaceous evaporite-bearing clastic deposits, including the Mangang and Mengyejing Formations which were originally interpreted as fluvial and lacustrine deposits. The Mangang Fm. composed of well-rounded quartz sandstones, were commonly considered as the bottom part of the Mengyejing salt series. Dttring last decades,

Experimental Simulation Study of the Dominant Enrichment Area of Terrestrial Organic Matter in the Shallow-Delta Sedimentary System of the Yacheng Formation in the Qiongdongnan Basin

Shallow-delta sedimentary systems receive both terrestrial and marine organic matter. As oil and gas exploration activities determine that the source rocks of the deep-water area of the Qiongdongnan Basin, northern South China Sea, are generally rich in and even dominated by terrestrial organic matter, this has led many researchers to examine the rules governing terrestrial organic matter enrichment in shallow-delta sea sedimentary systems. However, the deep burial of source rocks in deep-water areas and the relatively small amount of drilling undertaken have greatly restricted the study of these rules. In this study, the ‘forward modeling' research method was used to observe and analyze the deposition and preservation of terrestrial organic matter through flume experiments, where the depositional results were carefully depicted and sampled. The total organic carbon content of selected samples was measured and when combined with qualitative observations and quantitative comparison results, the dominant enrichment areas of terrestrial organic matter were identified. The experimental results show that the overbank parts of the delta front, the dune countercurrent surface, the low-lying parts, the delta front slope area and the shallow-prodelta sea area are where terrestrial organic matter is predominantly enriched. This provides an important basis and guidance for the prediction of the development areas of marine source rocks with terrestrial input in the deep-water areas of the Qiongdongnan Basin.

The Sedimentary System and Evolution of the Early Tertiary in the Sunda Basin, Indonesia

The Sunda basin is located at the north of the Sunda Strait situated between Sumatra and Java islands, Indonesia. It is an early Tertiary typical half-graben basin, in which developed a series of terrigenous clastic sedimentation. Previous work suggested that the early Tertiary sediments were alluvial, fluvial, lacustrine and swamp deposits, of which the Banuwati formation was alluvial and lacustrine deposits, the Zelda member fluvial deposits, and Gita member fluvial and swamp deposits. In this paper, based on the integrated research on core lithology （including lithology succession and structure）, well log shape, and seismic reflection characteristics, a more detailed sedimentation system was set up as follows： l） In addition to the alluvial, lacustrine, fluvial and the swamp deposits presented in previous work, subaqeous fan, shore-shallow lacustrine, deep lacustrine and turbidite fan, fan delta and delta deposits also developed in this basin. 2） Alluvial fan, subaqeous fan and fan delta deposits occurred on the steep slope adjacent to the synrift boundary fault; while the deltaic depositional system usually distributed on the gentle slope of the basins. 3） The Zelda member that was interpreted as a fluvial deposit in previous work is now interpreted as a subaqueous fan, fan delta, delta and lacustrine deposit system. 4） From the point of view of sedimentology, the evolution of basin could be divided into four stages： the initial subsidence （matching the Banuwati formation）, the rapid subsidence （matching the low Zelda member of Talang Akar formation）, the steady subsidence or fluctuation （matching the middle Zelda member of Talang Akar formation）, and the uplifting （matching the upper Zelda member and the Gita member of Talang Akar formation）. At the initial subsidence stage, the alluvial fan, flood plain, braided stream deposits developed, and then subaqeous fan sedimentation; at the rapid subsidence stage, shore-shallow lacustrine and deep lacustrine deposits and turbidite fans occurred; at the steady subsidence stage, thick fan deltas and delta sandstones developed; and at the uplifting stage, came fluvial （including meandering fiver and the anastomosed stream） and swamp sediments. Sediment supply was mainly from the northwest, secondly from the east. From the beginning to the end of the terrigenous basin evolution, the area of sedimentation was gradually enlarged. The palaeo-topography became increasingly flat.

Sedimentary architecture of submarine channel-lobe systems under different seafloor topography:Insights from the Rovuma Basin offshore East Africa

Seafloor topography plays an important role in the evolution of submarine lobes.However,it is still not so clear how the shape of slope affects the three-dimensional(3-D)architecture of submarine lobes.In this study,we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa.We characterize the shape,size and growth pattern of different hierarchical lobe architectures using 3-D seismic data.We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes.When the topography is irregular and presents topographic lows,lobe complexes first infill these depressions.Single lobes are deposited preferentially at positions with higher longitudinal(i.e.across-slope)slope gradients.As the longitudinal slope becomes higher,the aspect ratio of the single lobes increases.Lateral(i.e.along-slope)topography does not seem to have a strong influence on the shape of single lobe,but it seems to affect the overlap of single lobes.When the lateral slope gradient is relatively high,the single lobes tend to have a larger overlap surface.Furthermore,as the average of lateral slope and longitudinal slope gets greater,the width/thickness ratio of the single lobe is smaller,i.e.sediments tend to accumulate vertically.The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments,which helps us better understand the development and evolution of the distal parts of turbidite systems.

Sedimentary elements,evolutions and controlling factors of the Miocene channel system:a case study of the deep-water Taranaki Basin in New Zealand

Deep-water channel systems are important petroleum reservoirs,and many have been discovered worldwide.Understanding deep-water channel sedimentary elements and evolution is helpful for deep-sea petroleum exploration and development.Based on high-resolution 3D seismic data,the Miocene channel system in the deep-water Taranaki Basin,New Zealand,was analyzed by using seismic interpretation techniques such as interlayer attribute extraction and strata slicing.The channel system was divided into five composite channels(CC-I to CC-V)according to four secondary level channel boundaries,and sedimentary elements such as channels,slump deposits,inner levees,mass transport deposits,and hemipelagic drape deposits were identified in the channel system.The morphological characteristics of several composite channels exhibited stark variances,and the overall morphology of the composite channels changed from relatively straight to highly sinuous to relatively straight.The evolution of the composite channels involved a gradual and repeated process of erosion and filling,and the composite channels could be divided into three evolutionary stages:initial erosion-filling,later erosion-filling(multistage),and channel abandonment.The middle Miocene channel system may have formed as a consequence of combined regional tectonic activity and global climatic change,and its intricate morphological alterations may have been influenced by the channel's ability to self-regulate and gravity flow properties.When studying the sedimentary evolution of a large-scale deep-water channel system in the Taranaki Basin during the Oligocene-Miocene,which transitioned from a passive margin to plate convergence,it can be understood how tectonic activity affected the channel and can also provide a theoretical reference for the evolution of the deepwater channels in areas with similar tectonic conversion environments around the world.

Sedimentary Environment and Mineralization of the Black Shale Polymetallic Layer in the Early Cambrian,SW China:Constraints from in situ LA-ICP-MS Analysis of Pyrite

A polymetallic layer is usually developed at the bottom of the early Cambrian black shale in Guizhou Province.The mineral that makes up the polymetallic layer is related to the sedimentary facies.To analyze the differentiation mechanism between polymetallic deposits(Ni-Mo and V),the Zhijin Gezhongwu profile located in the outer shelf and the Sansui Haishan V deposit located in the lower slope are selected to study the in situ sulfur isotopes and trace elements of pyrite.The results show that δ^(34)S values of pyrite vary widely from−7.8‰to 28‰in the Gezhongwu profile,while the δ^(34)S values are relatively uniform(from 27.8‰to 38.4‰)in the Haishan profile.The isotopic S composition is consistent with the transition that occurs in the sedimentary phase from the shelf to the deep sea on the transgressive Yangtze platform;this indicates that the δ^(34)SO_(4)^(2−)values in seawater must be differently distributed in depositional environments.The sulfur in the Ni-Mo layer is produced after the mixing of seawater and hydrothermal fluid,while the V layer mainly originates from seawater.Overall,the Ni-Mo and V deposits have been differentiated primarily on the basis of the combined effect of continental weathering and hydrothermal fluid.

Biogeochemistry of sedimentary organic matter in the Yongjiang River estuary in the southern part of Hangzhou Bay,China,since the Late Pleistocene

A sediment core(YJK19-02)collected from the southern outlet of Hangzhou Bay near the Yongjiang River estuary in East China was analyzed for grain size,lignin,bulk elemental composition,stable carbon isotope,and rare earth elements(REEs)to determine the sources and diagenesis of sedimentary organic matter(OM)of the estuary and adjacent areas since the Late Pleistocene.δ^(13)C values(-24.80‰–-23.60‰),total organic carbon/total nitrogen(TOC/TN)molar ratios(8.00–12.14),and light rare earth element/heavy rare earth element ratios(LREE/HREE=8.34–8.91)revealed the predominance of terrestrial sources of OM,mainly from the Changjiang(Yangtze)River.The lignin parameters of syringyl/vanillyl(S/V=0.20–0.73)and cinnamyl/vanillyl(C/V=0.03–0.19)ratios indicate the predominance of nonwoody angiosperms,and the vanillic acid/vanillin ratios[(Ad/Al)_(V)=0.32–1.57]indicate medium to high degrees of lignin degradation.An increasing trend ofΛ(total lignin in mg/100-mg OC)values from ca.14500 a BP to ca.11000 a BP reflected the increase in temperature during the Late Pleistocene.However,a time lag effect of temperature on vegetation abundance was also revealed.The relatively higher and stableΛvalues correspond to the higher temperature during the mid-Holocene from ca.8500 a BP to ca.4500 a BP.Λvalues decreased from ca.4000 a BP to the present,corresponding to historical temperature fluctuations during this time.Our results show that the vegetation abundance in the Yongjiang River Basin since the Late Pleistocene was related to the temperature fluctuation duo to climate change.

Assessment of Radiological Hazards of Sedimentary, Igneous and Sediments Natural Rocks

Gamma-ray spectroscopy based on a 100% efficiency hyper-pure germanium detector was used to evaluate the activity concentrations of 226Ra, 232Th, and 40K natural radionuclides in sedimentary, conglomerate, igneous and sedi-ments rock samples collected from four different locations in Eastern desert in Egypt. The obtained activity concentrations are used to evaluate the radi-ological hazards indices, absorbed dose rate, annual effective dose equivalent in air, radium equivalent, external and internal hazard index, radiation level index, annual gonadal dose equivalent, excess lifetime cancer risk and expo-sure rate. The results show that 1) the absorbed dose rate depends on the rock type, 2) the annual effective dose equivalent in air in 71% of sample below 20 mSvy-1 (permissible limit for workers), 3) the conglomerate rocks show low radioactivity level, 4) sedimentary rocks are rich in radium while igneous rocks are rich in thorium and the sediments rocks are rich in both radium and thorium.

Control of paleogeographic pattern on sedimentary differentiation of evaporite-carbonate symbiotic system:A case study of the sixth sub-member of Ordovician Majiagou Formation M5 Member in central-eastern Ordos Basin,NW China

The relationship between paleogeographic pattern and sedimentary differentiation of evaporite-carbonate symbiotic system is examined based on logging,core and thin section data,by taking the sixth sub-member of fifth member of Ordovician Majiagou Formation(M56)in the central-eastern Ordos Basin as an example.(1)Seven sub-geomorphic units(Taolimiao west low,Taolimiao underwater high,Taolimiao east low,Hengshan high,East salt low,North slope and Southwest slope)developed in the study area.(2)The“three lows”from west to east developed dolomitic restricted lagoon,evaporite evaporative lagoon and salt evaporative lagoon sedimentary facies respectively,the"two highs"developed high-energy grain beach and microbial mound,and the north and south slopes developed dolomitic flats around land.(3)The paleogeographic pattern caused natural differentiation of replenishment seawater from the northwest Qilian sea,leading to the eccentric sedimentary differentiation of dolomite,evaporite and salt rock symbiotic system from west to east,which is different from the classic“bull's eye”and“tear drop”distribution patterns.(4)As the Middle Qilian block subducted and collided into the North China Plate,the far-end compression stress transferred,giving rise to the alternate highland and lowland in near north to south direction during the sedimentary period of M56 sub-member.(5)Taolimiao underwater high and Hengshan high developed favorable zones of microbial mounds and grain shoals in south to north strike in M56 sub-member,making them favorable exploration areas with great exploration potential in the future.

Sedimentary characteristics of distributive fluvial system in arid area: A case study of the Shule River distributive fluvial system, NW China

Based on detailed investigation of the modern sedimentation of the distributive fluvial system of Shule River and the data of unmanned aerial vehicle(UAV)aerial photography and satellite remote sensing,the sedimentary characteristics and differences of distributive fluvial system in arid areas are analyzed.By comparing the changes in slope,river morphology and sedimentary characteristics in different sections from the apex to the toe,the distributive fluvial system of Shule River can be divided into three facies belts:"proximal","middle"and"distal".The proximal belt has the largest slope and strongest hydrodynamic condition,mainly appears as large-scale braided river deposits;the fluvial bars in this belt are mainly composed of gravels,the gravels have good roundness and certain directionality,and are medium-large boulders,with low sand content;the main microfacies in this belt are braided channel and flood plain.The middle belt with slope smaller than the proximal belt,is mainly composed of braided bifurcating river deposits.Due to branching and infiltration,this belt has weaker hydrodynamic conditions,so some of the distributive rivers dry up,appearing as ephemeral rivers.This belt has small lenticular sandbodies,fine to medium gravels,higher sand content,and mainly braided channel,flood plain and aeolian dune microfacies.The distal belt has the smallest slope and flat terrain,where the river begins to transform from braided river to meandering river,the sediment is mainly sand.Due to the influence of slope,this belt has weaker erosion toward source and stronger lateral erosion,and point bars developing around the edge of the active lobes.In this belt,the river is completely meandering,and the main microfacies are braided channel,meandering channel,flood plain,aeolian dune,lake and swamp.

Classifying the sedimentary environments of the Xincun Lagoon,Hainan Island,by system cluster and principal component analyses

An understanding of the sedimentary environment in relation to its controlling factors is of great importance in coastal geomorphology,ecology,tourism and aquaculture studies.We attempt to deal with this issue,using a case study from the Xincun Lagoon,Hainan Island in southern China.For the study,surficial sediment samples were collected,together with hydrodynamic and bathymetric surveys,during August 2013.Numerical simulation was carried out to obtain high-spatial resolution tidal current data.The sediment samples were analyzed to derive mean grain size,sorting coefficient,skewness and kurtosis,together with the sand,silt and clay contents.The modern sedimentary environments were classified using system cluster and principal component analyses.Grain size analysis reveals that the sediments are characterized by extremely slightly sandy silty mud（ESSSM） and slightly silty sand（SSS）,which are distributed in the central lagoon and near-shore shallow water areas,respectively.Mean grain size varies from 0 to 8.0Ф,with an average of 4.6Ф.The silt content is the highest,i.e.,52% on average,with the average contents of sand and clay being 43% and 5%,respectively.There exists a significant correlation between mean size and water depth,suggesting that the surficial sediments become finer with increasing water depth.Cluster analyses reveals two groups of samples.The first group is characterized by mean grain size of more than 5.5Ф,whilst the second group has mean grain size of below 3.5Ф.Further,these groups also have different correlations between mean grain size and the other grain size parameters.In terms of the tidal current,the average values of the root mean square velocity（RMSV） are 7.5 cm/s and 6.9 cm/s on springs and neaps,respectively.For the RMSVs that are higher than 4 cm/s,a significant positive correlation is found between the content of the 63–125 μm fraction and the RMSV,suggesting that the RMSV determines the variability of the very fine sand fraction.Based on system cluster and principal component analyses（PCA）,the modern sedimentary environments are classified into three types according to the grain size parameters,RMSVs and water depth data.The results suggest the importance of grain size parameters and high-spatial resolution hydrodynamic data in differentiating the coastal sedimentary environments.

Seismic Imaging of the Sedimentary System of the Upper Cretaceous Nenjiang Formation in the Northern Songliao Basin

This paper studied seismic imaging of the sedimentary system of the Nenjiang Formation in the Northern Songliao Basin based on seismic sedimentology. An accurate and detailed depiction and explanation is provided for underground geological bodies within a relative geological period using the stratal slice technology,based on three-order sequence correlations of well logging and seismic data for the purpose of obtaining high-resolution pictures of the sedimentary system. Research results have revealed that the sedimentary system of the Upper Cretaceous Nenjiang Formation in the Northern Songliao Basin includes meandering streams,anastomosing streams,lake deltas,and sediment gravity flow channels. Based on seismic imaging analysis,the genesis and seismic geomorphology of the sedimentary system of the Nenjiang Formation are explored in order to understand the spatial distribution of typical sedimentary bodies and the evolution of streams in the Nenjiang Formation. According to the research results,the sedimentation of the Nenjiang Formation was subject to the delta system in the east and northeast of the formation. The provenance in the northeastern part played a dominant role during the deposition of the Nenjiang Formation for some time;after the earlier maximum flooding in the second and third members of the Nenjiang Formation,the northeastern system began to decline and was gradually replaced by the eastern system. Stratal slices have revealed that a well-developed gravity flow channel system was developed in the first member of the Nenjiang Formation,and massive slip blocks occurred in the second and third members of the formation. The research results indicated that the large gravity flow channel system in the first member of the Nenjiang Formation was formed by streams that emptied directly into the lake;and the slip blocks in the second and third members were the results of gravity sliding of sediments along steep slopes at the delta front.

Classification and control factors of pore-throat systems in hybrid sedimentary rocks of Jimusar Sag, Junggar Basin, NW China

Aiming at the complicated problem of the genesis of high-quality hybrid sedimentary rocks,the pore-throat systems,controlling factors and fluid mobility of hybrid sedimentary rocks in the Permian Lucaogou Formation in Jimusar Sag were examined.The results show that the hybrid sedimentary rocks contain 5 types of pore-throat system,intergranular(Type A),mixed intergranular-dissolved-intercrystalline(Type B),dissolved(Type C),mixed dissolved-intercrystalline(Type D)and intercrystalline(Type E)ones.The pore-throat systems are controlled by 3 major factors,the component content and arrangement(CCA)of hybrid sedimentary rocks,sedimentary environment and diagenesis.CCA controls the matrix support mode of hybrid sedimentary rocks,and therefore controls the types and changes of pore-throat system.The sedimentary environment mainly controls the macroscopic distribution of pore-throat system,i.e.,hybrid sedimentary rocks deposited in the near source and high-energy environment are characterized by high content of coarse-grained component,granular/interbedded-support mode,and development of Type A and Type B pore-throat systems.Hybrid sedimentary rocks deposited in the medium-energy environment far from source are characterized by dolomitic/mud support mode and Type C and Type D pore-throat systems.Hybrid sedimentary rocks deposited in low-energy environment far from source have mainly Type E and Type D pore-throat systems.Diagenetic processes such as compaction and calcite cementation make the proportions of Type A and Type C pore-throat systems decrease further.In the hybrid sedimentary process of sandy-mud,pore-throat system types show a change of"A→B→C→D",in that of dolomite-sand,pore-throat system types show a change of"A→C→D→E"or"B→D→E",and in that of dolomite-mud,pore-throat system types show a change of"D→E",which are affected in details by the contents of coarse-grain component,feldspar and dolomite.The reservoir with Type A pore-throats has the best physical properties and fluid mobility,and the reservoirs with Type D and Type E pore-throats have the poorest.The movable fluid distribution is related to the matrix support mode,and the larger pores in hybrid sedimentary rocks of dolomite/mud support mode have no obvious advantage in fluid mobility.The findings of this study provide a geological basis for evaluating and building reasonable interpretation model of hybrid sedimentary rocks sweet spot.

Geochemical characteristics and sedimentary environment significance of carbonate rocks in Nanfen Formation of Qingbaikou System in Tonghua,Jilin Province

In order to reveal the sedimentary environment of carbonate rocks in Nanfen Formation of Qingbaikou System in Tonghua,Jilin Province,the mineral composition and petrochemistry of carbonate rocks in Nanfen Formation were analyzed.The mineral compositions of five carbonate rock samples in Nanfen Formation mainly consist of calcite,with minor clay minerals and quartz,and the rock type is siliceous marlite.The Mn/Sr va-lues range from 1.52 to 4.08,with an average of 2.64,indicating that the carbonate rocks experienced weak diagenesis;the Sr/Ba values range from 1.26 to 2.51,with an average of 1.93,indicating marine environment;the ratio of Mg/Al ranges from 35.33 to 86.34,with an average of 62.95,indicating the seawater environment,which is consistent with the result from Sr/Ba;the MgO/CaO values range from 0.01 to 0.04,with an average of 0.02,indicating humid environment;the values of V/(V+Ni)range from 0.63 to 0.73,with an average of 0.70,indicating anoxic environment.In summary,geochemical analyses show that the Nanfen Formation carbonate rocks are marine deposits,in a warm,humid,anoxic environment with poor flow of seawater,and subsequently underwent weak diagenetic alteration.

Controls of accommodation to sediment-supply ratio on sedimentary architecture of continental fluvial successions

The applicability of sequence stratigraphic models to continental fluvial successions has long been topic for debate. To improve our understanding of how fluvial architectures record responses to changes in the ratio between accommodation rate and sediment-supply rate (A/S), two case studies are analyzed, including a densely drilled subsurface fluvial reservoir imaged with a seismic cube, and an outcropping fluvial succession. The subsurface dataset provides a larger, three-dimensional perspective, whereas the outcrop dataset enables observation at higher resolution. On the basis of both datasets, channel-body density, channel-body stacking patterns and their formative river types are interpreted at different scales, and how these may reflect responses to A/S change (the rate of accommodation creation relative to the rate of sediment supply) are discussed. The results indicate that (i) channel-body stacking patterns undergo four evolutionary stages along with the A/S increase, i.e., multi-story, mixed multi- and two-story, two-story, and isolated patterns;(ii) channel-body density decreases along with the channel-body stacking patterns varying from multi-story to isolated;(iii) formative rivers types are interpreted as evolving from braided planforms to braided-meandering planforms and then to meandering ones, with the increase of A/S.

Sedimentary Processes and Depositional Characteristics of Coarse-grained Subaqueous Fans along Steep Slopes in a Lacustrine Rift Basin:A Case Study from the Dongying Depression,Bohai Bay Basin,China

Coarse-grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin,China.The insufficient understanding of their sedimentary processes,depositional patterns,and controlling factors restricts efficient exploration and development.Coarse-grained subaqueous fans in the Yong′an area,Dongying Depression,are investigated in this study.These fans include nearshore subaqueous fans,and sublacustrine fans,and their sedimentary processes,depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology.Nearshore subaqueous fans developed near the boundary fault during the early–middle deposition stage due to strong tectonic activity and large topographic subsidence.Early sublacustrine fans developed at the front of the nearshore subaqueous fans in the area where the topography changed from gentle to steep along the source direction.While the topography was gentle,sublacustrine fans did not develop.During the late weak tectonic activity stage,late sublacustrine fans developed with multiple stages superimposed.Frequent fault activity and related earthquakes steepened the basin margin,and the boundary fault slopes were 25.9°–34°.During the early–middle deposition stage,hyperpycnal flows triggered by outburst floods developed.During the late deposition stage,with weak tectonic activity,seasonal floods triggered hyperpycnal flows,and hybrid event beds developed distally.

Experimental Research on Supercritical Carbon Dioxide Fracturing of Sedimentary Rock:A Critical Review

Supercritical carbon dioxide(ScCO_(2))fracturing has great advantages and prospects in both shale gas exploitation and CO_(2)storage.This paper reviews current laboratory experimental methods and results for sedimentary rocks fractured by ScCO_(2).The breakdown pressure,fracture parameters,mineral composition,bedding plane angle and permeability are discussed.We also compare the differences between sedimentary rock and granite fractured by ScCO_(2),ultimately noting problems and suggesting solutions and strategies for the future.The analysis found that the breakdown pressure of ScCO_(2)was reduced 6.52%–52.31%compared with that of using water.ScCO_(2)tends to produce a complex fracture morphology with significantly higher permeability.When compared with water,the fracture aperture of ScCO_(2)was decreased by 4.10%–72.33%,the tortuosity of ScCO_(2)was increased by 5.41%–70.98%and the fractal dimension of ScCO_(2)was increased by 4.55%–8.41%.The breakdown pressure of sandstone is more sensitive to the nature of the fracturing fluid,but fracture aperture is less sensitive to fracturing fluid than for shale and coal.Compared with granite,the tortuosity of sedimentary rock is more sensitive to the fracturing fluid and the fracture fractal dimension is less sensitive to the fracturing fluid.Existing research shows that ScCO_(2)has the advantages of low breakdown pressure,good fracture creation and environmental protection.It is recommended that research be conducted in terms of sample terms,experimental conditions,effectiveness evaluation and theoretical derivation in order to promote the application of ScCO_(2)reformed reservoirs in the future.

Sedimentary evolution and control factors of the Rizhao Canyons in the Zhongjiannan Basin, western South China Sea

Submarine canyon is an important channel for long-distance sediment transport, and an important part of deepwater sedimentary system. The large-scale Rizhao Canyons have been discovered for the first time in 2015 in the continental slope area of the western South China Sea. Based on the interpretation and analysis of multi-beam bathymetry and two-dimensional multi-channel seismic data, the geology of the canyons has however not been studied yet. In this paper, the morphology and distribution characteristics of the canyon are carefully described,the sedimentary filling structure and its evolution process of the canyon are analyzed, and then its controlling factors are discussed. The results show that Rizhao Canyons group is a large slope restricted canyon group composed of one east-west west main and nine branch canyons extending to the south. The canyon was formed from the late Miocene to the Quaternary. The east-west main canyon is located in the transition zone between the northern terrace and the southern Zhongjiannan Slope, and it is mainly formed by the scouring and erosion of the material source from the west, approximately along the slope direction. Its development and evolution is mainly controlled by sediment supply and topographic conditions, the development of 9 branch canyons is mainly controlled by gravity flow and collapse from the east-west main canyon. This understanding result is a supplement to the study of “source-channel–sink” sedimentary system in the west of the South China Sea, and has important guiding significance for the study of marine geological hazards.