A large number of tidal deposits are developed in the Pinghu Formation in Xihu Sag of the East China Sea Shelf Basin, which has great potential for oil and gas exploration. In this paper, core and logging data are used to analyze the lithofacies and sedimentary microfacies of Pinghu Formation in W well block of Xihu Sag, and comparative sedimentology study is conducted through modern sedimentary investigation in Rudong-Dongtai coastal area in Southeast Jiangsu Province, then the tidal sedimentary characteristics and development law of Pinghu Formation in the study area are clarified, and the sedimentary model is established. The results show that a set of tidal-controlled delta tidal flat depositional systems are developed in the Pinghu Formation in the study area, and the sedimentary subfacies mainly include delta front, supra-tidal zone and intertidal zone. Nine types of sedimentary microfacies, including underwater distributary channel, interdistributary bay, estuary bar, sheet sand, swamp, mud flat, sand flat, mixed flat, and tidal channel are further identified. Based on the analysis of the sedimentary system, a tidal delta-tidal flat sedimentary model in the study area is established, which provides reference and guidance for tidal sand body prediction and oil and gas exploration of Pinghu Formation.

西湖凹陷西部斜坡带油气藏整体呈现“小、断、贫、散”的特征，综合利用录井、测井、地震、生产等多种资料，分析总结西部斜坡带已发现油气的分布规律，提出西部斜坡带具有“南北分区、上下分层、近源富集”的油气分布特点。通过西部斜坡带典型油气藏解剖和失利井地质原因分析，认为圈闭和运移是油气成藏的主控因素。构造样式决定圈闭的类型和有效性，进而控制了不同区域的油气藏类型和差异富集；不同油气运移模式和两期充注、蒸发分馏作用控制了研究区近源成藏和“上油下气”的特征。通过成藏条件分析，指出平湖斜坡潜山、天台斜坡北段和杭州斜坡迎翠轩断裂带具有较好的圈闭和运移条件，是西湖凹陷西部斜坡带的勘探新领域。

The western slope zone of Xihu Sag is characterized by "small, faulted, poor and scattered". A comprehensive utilization of various data such as geological logging, well logging, seismic and production has been conducted to summarize the distribution patterns of oil and gas discovered in the western slope zone. It is believed that the western slope zone has the characteristics of oil and gas distribution of "north-south zoning, upper-lower stratification, near source enrichment". By dissecting typical oil and gas reservoirs and analyzing the geological reasons of the failed wells in the western slope zone, it is believed that traps and migration are the main controlling factors for oil and gas accumulation. Structural styles determine the type and effectiveness of the trap, and control the types of oil-gas reservoir and differential enrichment in different zones. The different migration of oil and gas, as well as the two-stage filling and evaporation fractionation, control the characteristics of near source accumulation and upper oil and lower gas in the study area.By analysis of reservoir forming condition, it is pointed out that buried hill of Pinghu slope, north section of Tiantai slope and Yingcuixuan fault belt of Hangzhou slope have better trap and migration conditions, which are new exploration directions of the western slope zone in Xihu Sag.

Through the analysis of drilling, logging and three-dimensional seismic data, the sequence stratigraphic composition, source-to-sink system difference, sedimentary evolution, sand control mechanism and lithologic-stratigraphic trap model in hanging wall of Pinghu fault in PH slope overlap belt of Xihu Sag are comprehensively studied. The results indicate that: (1) The Pinghu Formation in the PH slope overlap belt is controlled by different genetic slope breaks such as erosion and flexural, and is divided into three third-order sequences (SQ1 to SQ3) from bottom to top. Among them, SQ1 is limited in distribution, and development of the lowstand system tract is controlled by the steep slope break of deflection, forming the fan delta system coupled with ancient valley and slope break, which is dominated by the nearby basement provenance of Mesozoic magmatic rock. SQ2 and SQ3 are widely distributed, and development of the transgression and highstand system tracts are controlled by gentle slope break of erosion, forming the delta system dominated by the distant basement provenance of Proterozoic metamorphic rock. (2) The slope break controls the sand body distribution, and the slope break trough under the flexural slope break is a restrictive landform, which controls the layer by layer accretion and overlap of fan delta sand body vertically overlaied in lowstand tract. The low-lying area under the erosion slope break is the place where the highstand tract delta sand bodies are distributed, and the sand bodies of delta front are superimposed and dsitributed contiguously on plane. (3) Under the control of system tract and slope break, three types of lithologic-stratigraphic trap models are developed. During the low stand stage, the fan delta front sand body overlaping stratigraphic traps blocked by the physical properties of bedrock and fan root are mainly developed under the flexural slope break. During the transgressive stage, the tidal sand bar and tidal channel lateral pinchout lithologic traps blocked by the mudstone in the flooding period are mainly developed. During the highstand stage, lithologic traps in distributary channels of delta plain controlled by erosion slope break, updip pinch out and lateral pinch out, are mainly developed.

The sediment sources of the Yangtze Shoal were traced by analysing surface and core sediment particle size, detrital and clay minerals, carbon and nitrogen isotopes, and radioisotope dating. In the estuary, the sediments are dominated by silty clay, high stable mineral, and extremely high illite/chlorite. Stable organic carbon isotopes (delta C-13-TOC) indicated a marine-dominated mixture. On the shoal, the sediments are mainly composed of fine sand, high unstable mineral. The delta C-13-TOC indicated predominantly marine sedimentation. The average TOC of core sediments was similar to 0.26%, and the average TN was similar to 0.05%. The TOC/TN was 5.4-7.8, the delta C-13-TOC was - 19.8 to - 22.1%, and the age of the sediments spanned the last similar to 10.8 ka (Holocene). The sediments and provenance of the Yangtze Shoal have been controlled by the East Asian monsoon, sea level change, riverine sediment flux and ocean circulation. The intervals 8.3-6.3 ka and 3.8-1.5 ka, are characterized by Yangtze River sources, whereas 6.3-3.8 ka and 1.5-0.8 ka, are characterized by a source mixture with Yellow River input. Tracing the multiple sources effectively confirms the hypothesis that the southern Yangtze Shoal was a delta formed by combined sedimentation from the Yangtze River and Yellow River during times of low sea level.

根据钻井岩心、测井、高精度三维地震等资料，利用古地貌恢复、地震相识别、数学逐步回归模型融合属性等方法，对东海陆架盆地西湖凹陷始新统平湖组中段沉积体系及砂体展布特征进行详细研究。研究结果表明：①西湖凹陷孔雀亭地区平湖组可识别出1个二级层序，5个三级层序，古地貌呈北西—南东向阶梯式加深格局，沉积物源来自西北部的海礁凸起；②研究区平湖组中段位于三级层序的高位体系域，主要发育辫状河三角洲—有障壁滨海沉积体系，可细分为三角洲平原、三角洲前缘、前三角洲及潮坪4个亚相；③研究区砂体主要发育于三角洲平原分流河道、三角洲前缘水下分流河道及河口坝3个微相中，平湖组中段主要发育P8，P7，P6共3个砂层组，对应于平湖组中段高位体系域内的3个四级旋回，从最大海泛面开始发育P8砂层组，高位体系域中期发育P7砂层组，高位体系域末期发育P6砂层组。

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（SQE₂<i>p</i>3）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.