Lithologic Reservoirs

In recent years, large oil and gas fields with reserves of billions of tons have been discovered of Neogene in Bohai Bay Basin. A comprehensive study was conducted on the sedimentary characteristics and paleoen-vironment of the shallow water delta in the lower section of the Minghuazhen Formation of the Neogene in the Kenli 6-1 oilfield in the Bohai Bay Basin，utilizing geological，logging，and seismic data. The results show that：（1）The sedimentary period of Minghuazhen Formation in Kenli 6-1 Oilfield in Bohai Bay Basin was characterized by a temperate humid climate，gentle terrain，ancient terrain slope less than 1°，average water depth less than 6.5 m， and abundant supply of sediment from the northeast direction.（2）The reservoir lithology is mainly composed of lithic feldspar sandstone，followed by feldspar sandstone and feldspar lithic sandstone；the probability curve of grain size is mainly in a two-stage form，and various sedimentary structures reflecting strong hydrodynamics are developed；the logging curves are mainly bell shaped and box shaped, and low amplitude tile shaped progradation features can be seen on the seismic profile.（3）The V1 layer underwater distributary channel has a long extension distance and narrow width, and is distributed in northeast-southwest direction as a whole；the farthest extension distance can reach 20.10 km，and the average length is 10.06 km；the width of the underwater distributary channel sand body is between 64 m and 420 m，with an average width of 219.65 m；the average thickness of the underwater distributary channel sand body is about 9.42 m. Based on the comprehensive distribution of sedimentary microfacies，the shallow water sedimentary style of Minghuazhen Formation in Kenli 6-1 Oilfield in Bohai Bay Basin was summarized. The research results provide strong geological basis for new drilling in the later stage of the oilfield，and also provide comparative materials for the exploration and development of other shallow water delta sediments in the Bohai Bay Basin.

Sedimentary characteristics and genesis model of the Eocene shallow-water delta front in the Koulele Oilfield, Termit Basin, Niger

YIN Yanshu, HUANG Shengbin, HUANG Qizhi, XIE Pengfei, WANG Lixin, WU Wei

2025, Vol.37(2): 12–25 Abstract ( 52 ) PDF (9623 KB) ( 73 )

doi: https://doi.org/10.12108/yxyqc.20250202

The Koulele Oilfield in the Termit Basin of Niger is rich in oil and gas resources. Accurate prediction of the spatial distribution of sand bodies can provide a geological basis for subsequent reservoir exploration and development. By comprehensively utilizing core，well logging，and 3D seismic data，and based on the analysis of paleotopography and sediment supply conditions，combined with modern sedimentary comparisons，the depositional characteristics of the late Eocene shallow-water delta front in the study area were summarized and a depositional model was established. The results show that:（1）During the deposition period of the E1 oil formation in the late Eocene of the Koulele Oilfield in the Termit Basin of Niger，the terrain was flat with a gentle slope and abundant sediment supply. Mainly shallow-water delta front deposits and typical tractional current depositional structures developed，with lithologies dominated by siltstone to fine sandstone and mudstone. The well logging curves are mainly characterized by five types: box-shaped，bell-shaped，finger-shaped，funnel-shaped，and straight，with box-shaped and bell-shaped curves accounting for more than 70%. On seismic slices，the sand bodies appear as branch-like strips and contiguous lobe-shaped features. Lenticular reflection characteristics of channel fills can be observed on cross-sections，with no obvious progradational features. The sand body thickness map predicted by seismic intelligent fusion inversion exhibits single finger-like extensions，some of which are branchlike strips with bifurcating ends that develop into contiguous lobe-shaped features，similar to the morphology of modern finger-bar deltas.（2）The distribution and evolution characteristics of sedimentary microfacies vary at different times in the study area. In the early deposition stage of the E1 oil formation，river channels were mostly single-finger shaped with low curvature. Mouth bars developed in a lobe shape at the ends of river channels，with a relatively small scale，a width of less than 100 m，a thickness of 2 to 3 m，and a limited extension. In the middle deposition stage of the E1 oil formation，the scales of river channels and mouth bars increased，and branching phenomena occurred in the river channels. In the late deposition stage of the E1 oil formation，the scales of river channel and mouth bar sand bodies reached their maximum，with high curvature river channels distributed in a branching strip shape and bifurcating ends，and mouth bars distributed contiguously.（3）Overall，finger-like channel sand bodies are more developed in the inner delta front of the study area，while contiguous lobe-shaped mouth bar sand bodies are more developed in the outer delta front. Along the sediment source direction，the development scale of mouth bars gradually increases，while the development degree of river channels decreases. River channels undercut mouth bars，presenting a pattern of“rivers running over bars”. Vertically，the sand bodies are superimposed and developed.

Transition surfaces and the characteristics of large-scale traps occurrence in lacustrine basins

YANG Zhanlong, LI Xiangbo, SHA Xuemei, HAO Bin

2025, Vol.37(2): 26–37 Abstract ( 41 ) PDF (20864 KB) ( 80 )

doi: https://doi.org/10.12108/yxyqc.20250203

Based on the analysis of the controlling factors of lacustrine basin infilling，considering the infilling features in different stages and the evolution of a whole lake basin，the transition surfaces and the developmental relationship between occurrence of large-scale traps and various transition surfaces were discussed. The results show that：（1）With the jointly controlling of tectonic activity and climate change，lake basins can be divided into three types，such as overfilled，balanced-fill，underfilled according to the relative balance of potential accommodation change with sediment + water supply and each stage has typical source-reservoir-cap assemblages.（2）Tectonic transition surfaces，mainly dominated by unconformity due to the change in tectonic activity，sedimentary transition surface，mainly caused by lithology variation due to the changes in environment and sedimentary system，and biological and geochemical transition surfaces，totally affected by the difference of biological species and abundances and chemical stratification of water，are widely developed in lacustrine basins. There is a certain dependency relationship between different types of transition surfaces. The tectonic transition surface is necessarily a sedimentary，biological，and geochemical transition surface. The biological and geochemical transition surfaces often correspond to sedimentary transition surface in certain level and even to the tectonic transition surface，but the sedimentary transition surface is not necessarily the biological and geochemical transition surfaces.（3）Tectonic transition surface mainly reflects the occurrence of tectonic and stratigraphic large-scale traps in different infilling stages. The lithological，diagenesis and physical properties traps controlled by sedimentary transition surface mainly reflect the large-scale traps occurrence in a single infilling stage. Biological and geochemical transition surfaces mainly affect the occurrence of large-scale traps by controlling the background and characteristics of source rocks of a lake.（4）Sedimentary systems with large-scale traps，such as nearshore underwater fans，hyperpycnal flow and gravity flow etc. are favorable potential exploration domains of lacustrine basins.

Restoration of sedimentary paleogeography and its control on sedimentary system: A case study of the Triassic Baikouquan Formation in Shixi area of Junggar Basin

LI Xiang, FU Lei, WEI Pu, LI Junfei, XU Gang, CAO Qianqian, ZHONG Yang, WANG Zhenpeng

2025, Vol.37(2): 38–48 Abstract ( 66 ) PDF (6432 KB) ( 97 )

doi: https://doi.org/10.12108/yxyqc.20250204

Using 3D seismic data combined with logging and drilling data，the paleogeomorphology of the Triassic Baikouquan Formation in Shixi area of the Junggar Basin was reconstructed using sedimentary paleogeomorphology restoration techniques. Based on the clarified planar distribution characteristics of sedimentary facies，the relationship between paleogeomorphology and sedimentary facies was explored，and favorable areas for oil and gas exploration were identified. The research results show that：（1）The steps for restoring ancient landforms include calculating the thickness of the strata in the time domain，calculating the thickness of the strata in the depth domain，recovering denudation thickness of the strata，decompaction correction，and restoring the ancient water depth. During the deposition of the Baikouquan Formation，Shixi area exhibited a "northwest high，southeast low" structural pattern. The northwest was characterized by a large highland，while the central and eastern parts developed uplifts and six primary troughs，which interwove with each other. The southern part contained three depressions. The paleogeomorphology was primarily a combination of uplifts，troughs，and depressions.（2）In the northern and central parts of the study area，a braided river delta plain subfacies was predominantly developed，characterized mainly by distributary channel microfacies，segmented by interdistributary bay microfacies. In the southwestern and western regions，a braided river delta front subfacies dominated，including underwater distributary channel and interdistributary channel microfacies，with localized development of mouth bar and sheet sand microfacies.（3）The paleogeomorphology in the study area controlled the distribution of sedimentary facies. The shape and characteristics of the paleogeomorphology directly influenced sediment sources，transportation pathways，and depositional environments. Specifically，sediment from the northeastern source was transported through delta sand bodies to the southwestern lake basin center，with six paleotroughs serving as primary transportation channels and restricting frequent channel migrations. Strong hydrodynamics in the troughs resulted in thick，multi-period stacked distributary channel sand bodies. In uplift areas，river channels had minimal influence，allowing for the accumulation of thick mudstone，with interdistributary bay microfacies development. In depressions，where channels expanded，hydrodynamics weakened，resulting in fine sandy deposits and the development of extensive sheet sand microfacies.（4）The eastern trough area and southern depressions in the study area are favorable zones for reservoir development and key exploration targets.

Paleogeomorphological characteristics and reservoir control of the sedimentary period of Silurian Longmaxi Formation in Luzhou-Yuxi area

LIU Yong, LIU Yongyang, ZHAO Shengxian, YIN Meixuan, LI Bo, CHEN Lei, WU Shuaicai, XIE Shengyang

2025, Vol.37(2): 49–59 Abstract ( 39 ) PDF (32996 KB) ( 162 )

doi: https://doi.org/10.12108/yxyqc.20250205

The Silurian Longmaxi Formation shales in Luzhou-Yuxi area is one of the key blocks for unconventional oil and gas resource exploration in China. Based on whole rock X-ray diffraction analysis，rock mineral identification，seismic data interpretation and drilling data research，the sedimentary paleogeomorphology of the study area was reconstructed using the impression method，and its influence on the distribution of high-quality shale reservoirs was analyzed. The results show that：（1）During the deposition of Silurian Longmaxi Formation shale，the Luzhou-Yuxi area exhibited a paleogeomorphological pattern characterized by“one uplift，one depression，and two gentle slopes”.The sedimentary area can be subdivided into underwater uplift zones，underwater slope belts and underwater depression areas.（2）The mineral composition of shale is mainly composed of siliceous minerals，followed by clay minerals，carbonate minerals and pyrite. Ten types of shale lithofacies can be identified，mainly consisting of siliceous shale facies association（S）and mixed shale facies association（M）. With the siliceous shale facies association（S）being more prevalent and continuous in the underwater uplift zones，make it the high-quality lithofacies in the area.（3）Significant differences in the development of shale lithofacies and reservoir parameters（TOC，porosity and gas content）were observed across different geomorphic units. In the underwater uplift zones，the TOC value of the shale ranges from 3.03% to 5.06%，with an average of 4.25%；the porosity ranges from 4.81% to 6.30%，with an average of 5.46%；and gas content ranges from 1.70% to 7.62%，with an average of 5.05%. The shale reservoir quality in this zone is significantly superior to that of underwater slope belts and underwater depression areas. Horizontally，high-quality shales，characterized by high TOC，high porosity and high gas content，are distributed in a banded pattern across the underwater uplift zone and its periphery.

Genesis and geological significance of foam-spongy dolomite in the second member of Sinian Dengying Formation in Penglai-Gaomo area, central Sichuan

LI Ling, DENG Yu, ZHANG Xinyu, LUO Wenjun, ZHAO Dongfang, ZENG Jianjun, LIU Yun, TAN Xiucheng

2025, Vol.37(2): 60–69 Abstract ( 25 ) PDF (7602 KB) ( 60 )

doi: https://doi.org/10.12108/yxyqc.20250206

In order to clarify the genetic mechanism and e geological significance of the foam-spongy dolomite of the second member of Sinian Dengying Formation（Deng2 member）in the Penglai-Gaomo area of Sichuan Basin，the petrological characteristics，carbon and oxygen isotope characteristics，trace element characteristics and rare earth partition model are analyzed by using core and thin section data combined with geochemical methods. The results shows that：（1）The foam-spongy dolomite of Deng2 member in the study area has granular foam body，and its outer wall is ringed and cemented，which reveals that its original rock is granular dolomite.（2）The foam-spongy dolomites can be divided into honeycomb and trell-shaped according to their macroscopic distribution，both of which develop at the upper or top of the high-frequency cycle. Macro and micro characteristics and geochemical analysis show that the two types of foam-spongy dolomites are affected by different degrees of atmospheric fresh water，revealing that the development of foam-spongy dolomites is controlled by karst in the early diagenetic stage，and karst strength determines the development type. The strength of honeycomb karst is relatively small，and the strength of lattice karst is relatively large.（3）The foam-spongy dolomite has undergone the diagenetic evolution process of particle deposition，submarine cementation，early cloud-forming，early atmospheric freshwater karstification and late cementation and filling，while early atmospheric freshwater karstification is useful to form ingrain solution holes（casting mold holes），karst caves，solution fractures，solution gullies of reservoir space.（4）The formation mechanism of foam-spongy dolomite is the transformation of granular original rock by dissolution，which reveals that the sedimentary facies of Deng2 member in the study area are mainly granular rock and granular beach.

Characteristics and genetic mechanisms of anomalous high-porosity zones of the Paleogene Dongying Formation in western sub-sag of the Bozhong Sag

ZHU Wenqi, ZAN Chunjing, ZHANG Ying, WANG Tao, SHI Zhaowen, BA Lixia, CHEN Liang, JI Hancheng

2025, Vol.37(2): 70–80 Abstract ( 24 ) PDF (27421 KB) ( 57 )

doi: https://doi.org/10.12108/yxyqc.20250207

Based on the analysis of drilling and logging data，combined with core analysis and test data such as thin section identification，scanning electron microscopy and X-ray diffraction，the reservoir characteristics，distribution law and genesis mechanism of the Paleogene Dongying Formation in western sub-sag of the Bozhong Sag were analyzed. The results show that：（1）The lithology of the Paleogene Dongying Formation in western sub-sag of the Bozhong Sag is mainly feldspathic sandstone，lithic feldspathic feldspathic sandstone and feldspathic lithic sandstone，and the reservoir space is dominated by secondary karst pores，followed by primary intergranular pores.（2）The abnormally high porosity zone in the study area is mainly developed in the depth range of 2 400-3 400 m，and the pore types are mainly intergranular dissolution pores，particle dissolution pores and microcracks.（3）The physical properties of the reservoirs in the Dongying Formation in the study area are mainly controlled by the original sedimentary environment，and the subfacies reservoirs in the front edge of the braided river delta have good sortability，medium particle size，low cementation content，and excellent reservoir performance.（4）The Dongying Formation in the study area are in the mesodiagenetic stage A，which forms a large number of dissolved secondary pores due to the high degree of thermal evolution of organic matter（0.5% ≤ Ro ≤ 1.0%），the increase of organic acid content，and the dissolution of unstable components such as carbonate cement，feldspar and cuttings. Among them，the H2S generated by the thermal redox reaction（TSR reaction）of sulfate also caused the formation of a small number of secondary pores，and these factors improved the physical properties of the reservoir to varying degrees. Combined with diagenetic facies analysis，the TSR reaction zone and cementation-dissolution facies distribution area in the sedimentary microfacies at the inner front of the braided river delta and the inner front of the shallow water delta are favorable reservoir development areas in the study area.

Sedimentary evolution and favorable reservoir distribution of Permian Qixia Formation in the southern margin of Deyang-Mianyang Sag, Sichuan Basin

LI Ya, WANG Wei, ZHAO Like, LIU Ran, ZHANG Xihua, CHEN Yangui, HUANG Tianhai, XIAO Di

2025, Vol.37(2): 81–91 Abstract ( 40 ) PDF (27139 KB) ( 59 )

doi: https://doi.org/10.12108/yxyqc.20250208

Based on the comprehensive analysis of core samples，cuttings，well logging，and seismic data，this study investigates the sedimentary microfacies characteristics and evolutionary processes of the Permian Qixia Formation in the southern margin of the Deyang-Mianyang depression，Sichuan Basin. Furthermore，the research delineates favorable reservoir zones based on the aforementioned analysis. The results show that：（1）The southern margin of the Deyang-Mianyang depression in the middle Permian Qixia period is a set of carbonate ramp facies deposits，which are further subdivided into shallow Gentle Slope，deep Gentle Slope-basin subfacies and a variety of microfacies. The lithology is dominated by grained dolomite，sparry bioclastic limestone，micrite bioclastic limestone，bioclastic micrite limestone，micrite limestone and argillaceous limestone.（2）During the sedimentary period of Qi1 Member，the water is relatively deep and the overall development of the beach facies was low. It was only deposited in the Gaoshitai area with relatively high paleotopography. The lithology was dominated by micritic bioclastic limestone，and the sedimentary facies was greatly influenced by the paleotopography. During the lower of Qi2 sedimentary period，the water became shallower，and the shoal facies developed in Gaoshiti area in the upper part of the paleogeomorphology migrated laterally to Moxi area in the lower part of the paleogeomorphology due to the lack of space to accommodate it，the difference of sedimentary geomorphology decreased and reverse. During the upper of Qi2 sedimentary period，the shoal facies in the Moxi area not only experienced vertical accretion but also progressively migrated and expanded towards the Penglai region. Although the topographic relief of the depositional environment decreased during this phase，no significant inversion occurred.（3）The Qixia Formation is mainly composed of dolomite reservoirs，and its development is mainly controlled by factors such as lithology，karst，and fractures. The relatively high-energy particle beach， due to its relatively high sedimentary topography，is prone to exposure and early karstification，forming highquality reservoirs. The high porosity and permeability provide fluid channels for further stacking of dolomite. The high-energy beach is the most developed in the Moxi area，which is the most favorable reservoir zone in the study area，followed by the Penglai area in the north. The periphery of the“Deyang-Mianyang”depression is expected to become the next natural gas accumulation area with a certain scale of facies control.

The deposition characteristics and favorable reservoir prediction of Jurassic Shaximiao Formation in Dongguachang area, southwestern Sichuan Basin

WU Guanhua, LIU Hong, SONG Linke, ZENG Qi, YANG Tao

2025, Vol.37(2): 92–102 Abstract ( 31 ) PDF (30794 KB) ( 48 )

doi: https://doi.org/10.12108/yxyqc.20250209

In response to the unclear distribution patterns of channel sand bodies of Jurassic Shaximiao Formation in Dongguajing area of Sichuan Basin，this study utilized seismic sedimentology theory and integrated data from drilling，core samples，well logging，and seismic data. Various techniques，including seismic lithology analysis，stratigraphic slicing，and RGB attribute fusion，were employed to study the sedimentary system of the Shaximiao Formation in the research area. The results show that：（1）In the Dongguajing area，the Shaximiao Formation mainly consists of two third-order sequences（SQ1-SQ2）and five fourth-order sequences（ssq1-ssq5）. SQ1 belongs to the overall lake retreat system，while SQ2 belongs to the lake transgression system.（2） During the sedimentation period of the Shaximiao Formation，the dominant sedimentary facies in the study area were shallow-water delta deposits，which can be divided into two types：delta plain and delta front subfacies. Delta plain subfacies developed during ssq2 and ssq3，while delta front subfacies developed during ssq1，ssq4， and ssq5.（3）The development of channel sand bodies in the Shaximiao Formation is influenced by base-level cycles and sediment supply. The ssq1-ssq3 can accommodate lower space and have stronger sediment supply，resulting in larger channel sizes with overlapping and incised channel configurations. The ssq4-ssq5，on the other hand，have higher accommodation space and weaker sediment supply，leading to relatively independent and smaller channel development.（4）Large-scale connected channel sand bodies are mainly found in the channels of ssq1-ssq3，with the characteristics of good reservoir，and shoes are the favorable reservoir

Sedimentary characteristics of the middle member Pinghu Formation of Eocene in Kongqueting area, Xihu Sag, East China Sea Shelf Basin

CHEN Shenghua, WANG Jianwei, LIU Shu, YAN Shumei, HAN Jianhui, FU Heng, XIE Caizhu, SUN Li

2025, Vol.37(2): 103–114 Abstract ( 27 ) PDF (30028 KB) ( 49 )

doi: https://doi.org/10.12108/yxyqc.20250210

The middle member Pinghu Formation in the Eocene strata on the western slope of the Xihu Sag within the East China Sea Shelf Basin，specifically within the Kongqueting Block，is the primary oil and gas reservoir. However，systematic studies of the detailed sedimentary evolution and sand body distribution within the third-order sequence framework in this block remain lacking，limiting the effectiveness of oilfield development. By integrating lithology，well logs，and high-resolution 3D seismic data，the sedimentary system and sand body distribution of middle member Pinghu Formation in the Eocene strata on the western slope of the Xihu Sag within the East China Sea Shelf Basin were characterized using methods such as paleo-geomorphology restoration，seismic facies identification，and attribute integration through a stepwise regression model. The results show that：（1）In terms of sequence stratigraphy，a secondary sequence and five tertiary sequences can be identified within the Pinghu Formation. The ancient topography within this sequence framework was characterized by a northwestsoutheast gradient of stepped deepening，and sediments in the study area were derived from the northwestern continental margin uplift.（2）The middle member Pinghu Formation is located in the highstand systems tract（HST） of a third-order sequence，primarily developing a braided river delta-barrier coastal depositional system. This system can be further subdivided into four sub-facies—delta plain，delta front，prodelta，and tidal flat.（3）The macroscopic boundaries of sand body distribution，showing that sand bodies primarily develop within three microfacies：delta plain distributary channels，delta front subaqueous distributary channels，and mouth bars. The middle member Pinghu Formation primarily develops three sand layers，P8，P7，and P6，corresponding to three fourth-order cycles within the highstand systems tract（SQE2p3）of the middle Pinghu section. The development sequence begins with P8 at the maximum flooding surface，followed by P7 in the mid-highstand phase，and then P6 in the late highstand phase.

Sedimentary characteristics of the shallow-water braided river delta of Jurassic Qigu Formation in Yongjin area, Junggar Basin

HU Xin, ZHU Xiaomin, JIN Xuling, HUANG Cheng, ZHOU Yue, CHENG Changling, XIU Jinlei, REN Xincheng

2025, Vol.37(2): 115–126 Abstract ( 30 ) PDF (48936 KB) ( 53 )

doi: https://doi.org/10.12108/yxyqc.20250211

Based on seismic sedimentology theory，the core，logging and seismic data are comprehensively utilized to recover evolution history of Jurassic Qigu Formation in the Yongjin area of Junggar Basin，to quantitatively characterize the temporal and spatial distribution pattern of the thin-layered sands in the Qigu Formation，and construct sedimentary evolution models under different stratigraphic grids，by using the techniques of 90°phase-shift，attribute clustering，RGB attribute fusion，stratigraphic slicing，and waveform-indicating simulation. The results show that ：（1）Jurassic Qigu Formation in the Yongjin area of Junggar Basin developed shallow-water braided river delta front subfacies. During the lowstand tract system，the main channel of subaqueous diversion was developed at the front margin，the sand body of the river channel was wide and continuous，and the sedimentary sequence mostly showed intermittent positive rhythms without mudstone interlayers；during the lacustrine transgressive system tract，the secondary channel was developed at the front margin，the sand body of the river channel was narrow and intermittently distributed，and the sedimentary sequence mostly showed intermittent positive rhythms with mudstone interlayers.（2）The stratigraphy of the Qigu Formation in Yongjin area is spreading like a wedge from north to south，and the thickness of the sand body is between 32-48 m，with an average thickness of 35 m. During the period of the lowstand tract system，the sand body shows the development of composite sand body superposition，with a thick layer and good connectivity；during the period of the lacustrine transgressive system tract，the development of a single sand body is dominated，with a thin thickness and poor connectivity.（3）The planar spreading pattern of the river sand body in front of the shallow delta of the Qigu Formation in the Yongjin area is controlled by the paleomorphic pattern and the change of lake level rise and fall， to form two types of subaqueous diversionary river sand bodies，the front edge of the shallow braided river delta in the low level system domain is in the form of a branch，and in the lake intrusion system domain is in the form of a net spreading pattern.

Seismic response characteristics of strike-slip fault multi-core damage zones in Fuman Oilfield, Tarim Basin

LIANG Xinxin, ZHANG Yintao, CHEN Shi, XIE Zhou, ZHOU Jianxun, KANG Pengfei, CHEN Jiuzhou, PENG Zijun

2025, Vol.37(2): 127–138 Abstract ( 19 ) PDF (32774 KB) ( 53 )

doi: https://doi.org/10.12108/yxyqc.20250212

Comprehensively using of outcrop，seismic attributes，logging and production data，the internal structure of the strike-slip fault damage zone in the Fuman Oilfield of Tarim Basin was studied，and the reservoir control function of the damage zone was discussed. The results show that：（1）The Piqiang fault in Tarim Basin is a leftlateral tear strike-slip fault，and the damage zone structure can be divided into five types based on the degree of outcrop deformation：fault gouge，large joint development area，breccia，cataclasite，and fracture development zone. The Piqiang fault is a complex strike-slip fault zone composed of multiple secondary faults，with a multicore fault damage zone，and the fault core is composed of cataclasite and fault gouge.（2）The strike-slip fault of Fuman Oilfield follows the same outcrop development model，which is a multi-core fault damage zone model. The structure of the strike-slip fault damage zone under different stress mechanisms is significantly different： the width of the strike-slip segment damage zone is the smallest，with an average width of 368.50 m，and the damage zone mainly develops fractures；the width of the pull-apart segment damage zone is large，with an average width of 1 174.00 m，and fracturing mainly occurs within the boundary fault zone，characterized by fractures and karst caves；the width of the push-up segment damage zone is relatively large，with an average width of 951.25 m，and fracturing not only occurs within the fault zone but also has a certain impact on the surrounding area of the fault zone，with developed fractures and underdeveloped karst caves.（3）The activity intensity of strike-slip faults is positively correlated with the scale of the damage zone in the study area；the stronger the fault activity，the larger the scale of the damage zone，and the more developed the reservoir. The single well production capacity is not only controlled by the scale of the reservoir but also influenced by the stress environment of the fault. The production capacity and the scale of the reservoir in the pull-apart and strike-slip segments generally show a positive correlation，while there is no obvious correlation between the production capacity and the scale of the reservoir bodies in the push-up segment.

Meandering river sedimentary characteristics and its control on reservoir of Paleogene Dong 3 Member in Qingyuan area, Baoding Sag, Bohai Bay Basin

XUE Hui, YE Dashuai, GUO Yuemiao, CHEN Ketong, WU Jianping, XU Mengting, LI Yawen

2025, Vol.37(2): 139–152 Abstract ( 18 ) PDF (19505 KB) ( 50 )

doi: https://doi.org/10.12108/yxyqc.20250213

Based on the study of petrological characteristics of Paleogene Dong 3 Member in Qingyuan area，Baoding Sag，Bohai Bay Basin，three aspects such as lithofacies description，sedimentary facies identification and analysis of geophysical response characteristics were analyzed，in order to clarify the sedimentary distribution characteristics，sedimentary model and the control mechanisms of sedimentation on reservoir. Meanwhile，the favorable zones were predicted in this area. The results show that：（1）The mudstone color of Dong 3 Member in Qingyuan area were mainly oxidation color，the sandstones were dominated by lithic feldspathic sandstone and feldspathic lithic sandstone，the rock of Dong 3 Member have low-middle compositional maturity and textural maturity，and have obvious river traction flow characteristics. During the deposition of the Dong 3 Member，the climate was arid and semi-arid，which indicated a terrestrial freshwater and oxidizing environment.（2）Nine lithofacies types can be identified in the study area，including four kinds of sandstone lithofacies，three kinds of siltstone lithofacies，two kinds of mud stone lithofacies. The study area developed meandering river facies， which can be divided into six microfacies：river bed retention sediment，point bar，natural levees，oxbow lake， crevasse splay，flood plain，five well logging response characteristics can be identified，including middle-high amplitude box-shaped，middle-high amplitude bell-shaped，middle amplitude finger-shaped，middle-low amplitude funnel-shaped，low amplitude linear，and the reservoir have moderate-strong ampitude，high frequency，middle and bad continuity on seismic section. The sand bodies were deposited in southwest-northeast trending in the plane，the thickness and distribution of the sand body of meandering river decreases from lower to upper，single belt type and network continuous sedimentary model of meandering river were established.（3）The sedimentation determined the reservoir characteristics in study area，the reservoirs physical properties of river bed retention sediment and point bar were the best microfacies，strong and stable hydrodynamic conditions，low content of clay mineral and thick sandbody were the basis of the formation of high-quality hydrocarbon reservoirs，the Ⅰ reservoir have the best physical properties，which were mainly distributed in the Ⅱ and Ⅲ oil-bearing formations in the vertical direction，well area G77-70X and G77-30X were the favorable target areas.

Application of seismic sedimentology in predicting the Lower Cambrian sedimentary structure and reservoir rocks in Gucheng area, Tarim Basin

XU Zhaohui, ZENG Hongliu, HU Suyun, ZHANG Junlong, LIU Wei, ZHOU Hongying, MA Debo, FU Qilong

2025, Vol.37(2): 153–165 Abstract ( 28 ) PDF (91891 KB) ( 70 )

doi: https://doi.org/10.12108/yxyqc.20250214

Well Luntan-1 revealed huge hydrocarbon potential in Lower Cambrian deep dolostone reservoir in Tarim Basin. Gucheng area is located in the same platform margin with Well Luntan-1 during the Early Cambrian. Two branches of seismic sedimentology，i.e.，seismic geomorphology and seismic lithology were used to study the sedimentary characteristics of Lower Cambrian in Gucheng area. Techniques of phase rotation，frequency decomposition by wavelet，wheeler-domain transformation，stratal slicing，and RGB fusion were integrated into a seismic geomorphologic（model driven）workflow to qualitatively restore sedimentary facies. Techniques of phase rotation，frequency decomposition by wavelet，seismic attribute extraction，principal component analysis，and random fitting were combined into a seismic lithologic（data driven）workflow to quantitatively predict reservoir distribution. The results show that：（1）The inner ramp，middle ramp，and outer ramp to basin from west to east in Gucheng area consist of an integral series of sedimentary facies of Lower Cambrian in Gucheng area of Tarim Basin. Three sets（six periods）of reef-shoal systems were interpreted in the middle ramp. The second set was modified by later tidal-channels，resulting in a tidal-channel modified carbonate grainstone shoal. Strata are homogenous in the channels while heterogeneous in the inter-channel areas，which leads to higher seismic frequency.（2）Line-sourced slope fans in the proximal-end of outer ramp and point-sourced basinfloor fans in the distal-end of outer ramp to basin were recognized in the study area. Sediment materials sourced from the reef-shoal system in the middle ramp were transported to the slop fans and basin-floor fans through canyons related to synsedimentary strike-slip faults conducted.（3）Reservoirs are abundant in the middle ramp，minor in the outer ramp to basin，and rare in the inner ramp in this area. The reservoir rocks are thick at the slope fans and the basin-floor fans in the outer ramp to basin area，as well as at inter-channel karstified grainstone shoals and channel-mouth tidal delta in the middle ramp area.

Sequence stratigraphy division and petroleum geological significance in the middle submember of the third member of Shahejie Formation in Liangdong area, Dongying Sag

QU Xingyu

2025, Vol.37(2): 166–177 Abstract ( 21 ) PDF (39821 KB) ( 53 )

doi: https://doi.org/10.12108/yxyqc.20250215

Using three-dimension seismic and well-logging data，a study was conducted on the sequence stratigraphic characteristics of the middle sub-member of the third member of Paleogene Shahejie Formation in the Liangdong area of the Dongying Sag. The internal systems tracts，composition，structure，sedimentary characteristics，and spatial variation patterns of the sequences were analyzed. The results show that：（1）The middle submember of the third member of Shahejie Formation in the Liangdong area of the Dongying Sag can be divided into highstand systems tract（HST），falling stage systems tract（FSST），lowstand systems tract（LST），and transgressive systems tract（TST），reflecting a complete base-level change cycle. Due to the lateral variations in sediment supply and accommodation space，the main source area in the middle sub-member of Shahejie Formation developed a complete sequence. In contrast，on both sides of the main sedimentary area，the thickness of the systems tracts gradually thins，and shoreline migration characteristics are not obvious.（2）The FSST facies in the study area are dominated by delta front deposits，which can be further subdivided into microfacies such as underwater distributary channels and mouth bars，with some occurrences of gravity flow microfacies. The LST inherits the sedimentary characteristics of the FSST in its evolutionary sequence，mainly represented by a deltagravity flow system，but further extending towards the basin. The sedimentary center of the LST shifted westward compared to the FSST，indicating the long-distance progradation characteristic of the sedimentary system in the LST.（3）The strong activity of growth fault F1 in the study area controlled the distribution of sand bodies. The differential subsidence between the hanging wall and footwall of the fault caused changes in sediment supply and accommodation space，leading to variations in the geometric characteristics of the systems tracts and strati-graphic stacking patterns along the sediment source direction. In the hanging wall of the fault，where there is higher subsidence and greater accommodation space，the systems tracts are fully developed，and the sand-toshale ratio is the highest. In the footwall，with higher elevation，lower subsidence，and smaller accommodation space，the thickness of the HST and LST decreases significantly，and the sand-to-shale ratio is also relatively smaller.（4）The HST in the study area is composed of thick layers of dark mudstone and oil shale，which can serve as excellent source rocks. The deltaic and gravity flow sand bodies in the LST and FSST are the main reservoirs. The TST is characterized by widespread dark mudstone，which can act as a cap rock. The vertical arrangement of the systems tracts in the middle sub-member of the third member of Shahejie Formation forms a favorable source-reservoir-seal configuration.

Fluvial to lacustrine alternating sedimentary characteristics of the Oligocene Huagang Formation in Xihu Sag, East China Sea shelf Basin

QIN Lanzhi, LI Ning, XU Donghao, SUN Zhongheng, WANG Wei

2025, Vol.37(2): 178–188 Abstract ( 16 ) PDF (24950 KB) ( 46 )

doi: https://doi.org/10.12108/yxyqc.20250216

Based on drilling core，well logging，and 3D seismic data，combined with evolution sequence recon-struction and spatial distribution depiction of depositional systems，the fluvio-lacustrine interactive depositional characteristics and sand-controlling mechanisms of Oligocene Huagang Formation in the shallow lacustrine basin of the Huangyan area，central-southern Xihu Sag of East China Sea shelf Basin were studied. The results show that：（1）There are three major depositional systems，including river-floodplain，shallow delta，and lacustrine systems，primarily developed from north to south in the Huagang Formation of the Xihu Sag. Huangyan area in central-southern region characterized by three sedimentary facies types：fluvial，shallow delta，and lacustrine. （2）The fluvial-lacustrine interaction system of the Huagang Formation in the Huangyan area can be subdivided into three distinct sedimentary units：river-dominated main area，fluvial-lacustrine transitional zone，and lake-dominated main area. The main area of the river control zone is developed with thick layers of gravel sandstone，and the seismic facies exhibit low-frequency weak amplitude characteristics；The interaction zone between rivers and lakes is characterized by the development of thick sandstone layers and an increase in mudstone interlayers. The seismic facies show low to medium frequency and weak amplitude，mainly consisting of implicit progradation and imbricate progradation；The mudstone in the main area of the lake is relatively developed，and the seismic facies are characterized by medium to high frequency and moderate to strong amplitude.（3）During the deposition of the Huagang Formation in the Huangyan area，micro-geomorphology and episodic fluctuations in water levels played pivotal roles. Within the isochronous framework of third-order sequences，three sand-controlling models for shallow lacustrine basins were established：During flood periods， the lake-dominated zone reached its maximum extent，with the main delta body submerged underwater and isolated sandbars developed.During average water levels，the lake level declined，the fluvio-lacustrine interactive zone expanded，resulting in laterally continuous sheet-like sandbodies and vertically separated sandbodies. During dry periods，the river-dominated zone predominated，with rivers shrinking into a network distribution and fine-grained sandstone deposition becoming more pronounced within channels.（4）The Huangyan area has developed multiple inverted anticline structures，with their limbs exhibiting significant potential for the development of large-scale structural-lithologic traps. favorable sand bodies are enriched in laterally superimposed lobes during flood periods，abandoned channels during normal flow periods ，and within channels during dry periods.

Seismic sedimentology characteristics of the second member of Sinian Dengying Formation in Penglai area, north-central Sichuan Basin

ZHANG Kun, LIU Hong, TAN Lei, LIANG Feng, WANG Lien, MA Zike, LIU Bowen, YANG Mengxiang

2025, Vol.37(2): 189–200 Abstract ( 18 ) PDF (35839 KB) ( 45 )

doi: https://doi.org/10.12108/yxyqc.20250217

In order to clarify the temporal and spatial distribution of the mound-shoal complex of the second member of Dengying Formation（Deng 2 member for short）in Penglai area and explore the application of seismic sedimentology in carbonate rocks，the mound-shoal complex of Deng 2 member in Penglai area were identified and characterized by seismic sedimentology techniques such as paleogeomorphology restoration，forward modeling，waveform clustering and attribute fusion based on drilling，core，logging and 3D seismic data. The results show that：（1）During the sedimentary period of Deng 2 member，Penglai area is characterized by carbonate platform deposition，and can be subdivided into four sedimentary subfacies：mound-shoal complex，intershoal sea，platform flat and restricted lagoon.（2）Through fine seismic-lithologic calibration，a good correspondence between seismic facies and sedimentary facies is established. The high-energy mound-shoal complex face is characterized by low-amplitude mound-like shape，internal disorder or intermittent-weak intermittent reflection，and bright spot reflection in the inner core. PCA multi-attribute fusion technology based on seismic facies constraints can effectively improve the recognition accuracy of mound-shoal complex.（3）The distribution of mound-shoal complex in the Deng 2 member has the characteristics of differentiation zone. The mound-shoal complex in the SQ1 sedimentary period of the Moxi area are more developed than those in the Penglai area. Until SQ2 sedimentary period，the development scale of the mound-shoal in the Penglai area has become larger，and the moundshoal complex core microfacies have a wide range of development. The Moxi area is dominated by platform sediments，and the mound-shoal complex are only sporadically developed in local areas.