东海丽水凹陷西次凹古新统明月峰组下段砂体成因分析

在井资料匮乏背景下,迫切需要借助地震沉积学手段精细刻画岩性圈闭。在层序地层划分基础上,结合地震沉积学沿层属性切片、储层反演及三维岩性体雕刻等地球物理技术,重点对研究区主力产层明月峰组下段地震沉积相特征进行精细研究,分析明月峰组下段砂体的形成与演化特征。研究认为,明月峰组下段包括下降、低位、海侵和高位4个体系域。在下降和低位体系域沉积期,断裂坡折之上发育2条下切河道,这些河道将砂体运送至陆架边缘形成三角洲前缘沉积,下降域由于物源供给更充足,形成了位于三角洲前缘的薄层浊流沉积;海侵及高位体系域均发育受波浪作用改造形成的滩坝障壁岛沉积,因沉积物供给缺乏,主要分布于构造坡折之上。研究成果可有效指导研究区明月峰组岩性圈闭的预测,并为下一步勘探部署提供决策依据。     

Mineral types and organic matters of the Ordovician-Silurian Wufeng and Longmaxi Shale in the Sichuan Basin,China: Implications for pore systems,diagenetic pathways,and reservoir quality in fine-grained sedimentary rocks

Mineral types (detrital and authigenic) and organic-matter components of the Ordovician-Silurian Wufeng and Longmaxi Shale (siliceous, silty, argillaceous, and calcareous/dolomitic shales) in the Sichuan Basin, China are used as a case study to understand the control of grain assemblages and organic matter on pores systems, diagenetic pathway, and reservoir quality in fine-grained sedimentary rocks. This study has been achieved using a combination of petrographic, geochemical, and mercury intrusion methods. The results reveal that siliceous shale comprises an abundant amount of diagenetic quartz (40–60% by volume), and authigenic microcrystalline quartz aggregates inhibit compaction and preserve internal primary pores as rigid framework for oil filling during oil window. Although silty shale contains a large number of detrital silt-size grains (30–50% by volume), which is beneficial to preserve interparticle pores, the volumetric contribution of interparticle pores (mainly macropores) is small. Argillaceous shale with abundant extrabasinal clay minerals (>50% by volume) undergoes mechanical and chemical compactions during burial, leading to a near-absence of primary interparticle pores, while pores preserved between clay platelets are dominant with more than 10 nm in pore size. Pore-filling calcite and dolomite precipitated during early diagenesis inhibit later compaction in calcareous/dolomitic shale, but the cementation significantly reduces the primary interparticle pores. Pore-throat size distributions of dolomitic shale show a similar trend with silty shale. Besides argillaceous shale, all of the other lithofacies are dominated by OM pores, which contribute more micropores and mesopores and is positively related to TOC and quartz contents. The relationship between pore-throat size and pore volume shows that most pore volumes are provided by pore throats with diameters <50 nm, with a proportion in the order of siliceous (80.3%) > calcareous/dolomitic (78.4%) > silty (74.9%) > argillaceous (61.3%) shales. In addition, development degree and pore size of OM pores in different diagenetic pathway with the same OM type and maturity show an obvious difference. Therefore, we suggest that the development of OM pores should take OM occurrence into account, which is related to physical interaction between OM and inorganic minerals during burial diagenesis. Migrated OM in siliceous shale with its large connected networks is beneficial for forming more and larger pores during gas window. The result of the present work implies that the study of mineral types (detrital and authigenic) and organic matter-pores are better understanding the reservoir quality in fine-grained sedimentary rocks.     

松辽盆地泉四段扶余油层地层层序新认识

松辽盆地泉四段扶余油层发育浅水湖泊三角洲相和浅水湖泊相，沉积构造环境属于闭塞浅水坳陷湖盆，其层序特征类似于稳定克拉通盆地层序，也类似于缓坡被动大陆边缘型盆地层序，气候是控制陆相坳陷盆地层序形成的主要因素，三级层序内总体应表现为水进体系域-高位体系域构成1个完整的层序，而低位体系域不发育。通过岩心、录井、地震等资料研究分析，认为泉四段扶余油层是1个三级层序，发育水进体系域和顶部薄层强制水退边缘体系域；泉四段与泉三段地层分界是其层序的底界；泉四段顶界地震反射层T2也是层序边界，是泉四段三级层序的顶界。精确识别和建立地层层序格架对石油勘探开发具有重要的指导意义。     

四川盆地焦石坝地区龙马溪组页岩层序及页岩气“甜点”地震预测

我国页岩气勘探开发在四川盆地焦石坝地区龙马溪组已经取得重大突破, 针对性的页岩气"甜点"地球物理技术亟待研究和探索。沉积相是进行页岩气甜点预测和描述的重要基础和依据。应用层序地层学理论, 建立了页岩层段的三级层序地层格架, 认清了深水陆棚页岩沉积相的展布规律, 目的层五峰组及龙马溪组富碳高硅和高碳高硅泥页岩主要分布在三级层序的海侵体系域。在此基础上, 探索了层序地层格架控制下的页岩气"甜点"的地球物理识别和预测方法。研究认为, 页岩气地球物理识别与预测技术在含气页岩有机碳含量(TOC)、裂缝和脆性等方面具有较大的优势, 能为页岩气水平井分段压裂工程和水平井轨迹设计提供有力的技术支持。     

Geological models of gas in place of the Longmaxi shale in Southeast Chongqing,South China

Gas-in-place (GIP) is one of the primary controlling factors in shale gas production, but studies examining GIP have been lacking for the Lower Silurian Longmaxi shale in South China. In the present study, a suite of Longmaxi shale samples was collected from an exploratory well in Southeast Chongqing, South China, and the adsorption parameters were fitted using a supercritical Dubinin-Radushkevich (SDR) model based on the high-pressure methane adsorption experiment data for the samples. The results show that the adsorbed phase density and the adsorbed gas capacity of the samples have a positive correlation with the content of total organic carbon (TOC) but a negative correlation with temperature. Combined with the geological characteristics of the Longmaxi shale in Southeast Chongqing, GIP models were constructed under three different fluid pressure conditions. The absolute adsorbed amount of the samples increases and later decreases with increasing depth with a maximum corresponding to depths between 800 and 1200 m. The fluid pressure coefficient has no obvious effect on the absolute adsorbed amount when burial depth is over 2000 m but controls the free gas content. Overpressure primarily increases the free gas content and thus increases the total gas content. The free gas content of the Longmaxi shale in the Pengshui Block is reduced to 47%–58% of that in the Fuling Block, which is the main reason for its low gas production. Further exploration of the Longmaxi Formation should be expanded to deeper burial shales in the eastern area of Southeast Chongqing.     

渤中凹陷西斜坡BZ3-8区块东营组东二下高分辨率井震层序及地震沉积学

渤海海域凹陷由于资料的限制,其沉积相研究多为宏观的区域性研究,制约了储层的精细解释。基于最新采集的高精度地震三维资料,结合地震地层学、层序地层学、地震沉积学等理论方法,开展渤中凹陷西斜坡BZ3-8区块东营组重点目的层,东二下层序高分辨率井震层序分析及其地震沉积学研究。结果表明,研究区南北两侧具有不同的物源体系和沉积相模式。低水位体系域(LST)和高水位体系域(HST)时期,研究区北部物源均形成扇形、朵形的地震多属性及振幅切片异常,对应于扇三角洲沉积;南部物源均形成NE向展布的条带状地震多属性及振幅切片异常,对应于辫状河三角洲沉积。海进体系域(TST)时期,湖平面快速上升导致扇体不发育,仅在研究区北部局部发育小规模的扇三角洲沉积。东二下层序LST(富砂)-TST(富泥)-HST(富砂)的岩相演化规律,充分反映了经典层序地层学理论层序格架中的地层岩相组合分布规律,对储层和烃源岩的预测具有指示意义。     

Sequence stratigraphic context and organic geochemistry of Palaeogene oil shales,Jordan

The potential oil shales of the Palaeogene Muwaqqar Chalk Marl and Umm Rijam Chert Limestone formations are investigated from a subsurface location in the west of Jordan. Detailed organic geochemistry data is placed in the context of a sequence stratigraphic framework derived from vertical foraminiferal biofacies and lithological changes and biostratigraphically calibrated using planktonic foraminiferal biozonation. This shows that the transgressive systems tract of a Selandian (P4, probably P4a) sequence has the best potential in the studied section to generate oil if subjected to induced pyrolysis. A Ypresian (no older than E2) transgressive sequence has some potential, whilst highstand systems tracts offer the least potential. Both the sequence model and oil shale potential compares well with equivalent age sediments in Egypt and highlights that whilst the Maastrichtian portion of the Muwaqqar Chalk Marl Formation is often regarded as the key interval for oil shale prospectivity, parts of the Paleocene succession also have some potential.     

辽东湾晚第四纪层序地层

通过对辽东湾高分辨率浅地层剖面声学地层与典型钻孔沉积地层的对比分析,揭示了研究区晚第四纪MIS5以来的地层层序。辽东湾高分辨率浅地层剖面自下而上划定的6个声学地层单元(SU₅、SU₄、SU₃、SU₂、SU₁²、SU₁¹)与钻孔岩芯划分的6个沉积地层单元(DU₅、DU₄、DU₃、DU₂、DU₁²、DU₁¹)具有良好的对应关系。分别与MIS4期、MIS2期低海面时期的沉积间断密切相关的两个层序界面R5、R3,将辽东湾识别出的地层单元自下而上划分为3个层序(SQ3、SQ2、SQ1)。其中SQ3仅识别出上部的海侵体系域与高水位体系域,对应MIS5期海平面相对较高时期的滨浅海相沉积(DU₅);SQ2自下而上由低水位体系域(MIS...     

神狐海域水合物钻探区第四纪米氏旋回高频层序地层划分

基于高分辨率2D地震资料,建立了珠江口盆地白云凹陷第四纪层序地层格架,将第四纪沉积充填序列划分为3个体系域,即低位体系域(LST)、海侵体系域(TST)、高位体系域(HST)。根据陆坡进积特征和地层叠加样式、垂向上侵蚀特征变化(其上见下切水道)、中频强振幅同相轴的空间可追踪性等地震反射特征,将高位体系域(HST)进一步划分为两个沉积旋回单元HST-I、HST-Ⅱ。在等时地层格架的约束下,以神狐海域水合物钻探区well-I钻井作为研究对象,选择自然伽马曲线(GR)通过频谱分析进行米兰科维奇旋回特征的研究,识别出偏心率周期(95 ka)、斜率周期(40 ka)和岁差周期(22、19ka)。研究区第四纪沉积充填序列主要受偏心率周期(95 ka)的控制,偏心率(95 ka)对应于旋回厚度11.494 m,以此周期和对应的旋回厚度计算出钻探区第四纪沉积速率为12.1 cm/ka。通过构建滤波器对测井曲线进行滤波处理,发现95 ka的偏心率控制的优势旋回个数在20个左右。对斜率周期(40 ka)识别出的高频旋回采用Fischer图解法求取其可容纳空间变化曲线,检验了高精度层序地层划分的正确性。     

Sequence stratigraphy,sedimentary facies and reservoir quality of Es4s,southern slope of Dongying Depression,Bohai Bay Basin,East China

Thin-bedded beach-bar sandstone reservoirs are common in the Eocene Shahejie Formation (Es4s) of Niuzhuang Sag, along the southern gentle slope of the Dongying Depression. Here we report on the link between sequence stratigraphy, sedimentary facies and diagenetic effects on reservoir quality. Seismic data, wireline logs, core observations and analyses are used to interpret depositional settings and sequence stratigraphic framework. Petrographic study based on microscopic observation of optical, cathodoluminescence (CL), confocal laser scanning (LSCM) and scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were used to describe the fabric, texture, allogenic and authigenic mineralogy of these highly heterogeneous sandstone reservoirs. The Es4s interval is interpreted as third-order sequence, composed of a lowstand systems tract (LST), a transgressive systems tract (TST) and a highstand systems tract (HST). On the fourth order, twenty-nine parasequences and seven parasequence sets have been identified. Sand bodies were deposited mainly in the shoreface shallow lake beach-bar (clastic beach-bar), semi-deep lake (carbonate beach-bar) and the fluvial channels. The depositional and diagenetic heterogeneities were mainly due to the following factors: (1) fine grain size, poor sorting, and continuous thin inter-bedded mud layers with siltstone/fine-sandstone having argillaceous layers in regular intervals, (2) immature sediment composition, and (3) even with the dissolution of grains and several fractures, destruction of porosity by cementation and compaction. Secondary pores from feldspar dissolution are better developed in sandstones with increased cementation. Grain coating smectite clays preserved the primary porosity at places while dominating pore filling authigenic illite and illite/smectite clays reduced permeability with little impact on porosity. Due to the high degree of heterogeneity in the Es4s beach-bar interval, it is recognized as middle to low permeable reservoir. The aforementioned study reflects significant insight into the understanding of the properties of the beach-bar sands and valuable for the comprehensive reservoir characterization and overall reservoir bed quality.     

下扬子皖南地区下寒武统荷塘组页岩地球化学特征及地质意义

中国南方下寒武统富有机质黑色页岩发育,具有分布面积广、沉积厚度大、有机碳含量高等有利条件,蕴藏着丰富的页岩气资源潜力,有望成为页岩气“增储上产”的重要区域。以下扬子地区下寒武统荷塘组页岩气首口参数井−XY1井为研究对象,利用岩芯资料和地球化学分析测试数据,探讨了研究区元素地球化学特征与古环境意义。研究结果表明：主量元素SiO2、K2O相对富集,其他元素均不同程度地相对亏损;微量元素Sr、Rb亏损,Ni、Co、Ba元素明显富集。荷塘组黑色页岩属大陆边缘沉积,硅质主要来源于硅质生物,为生物成因,沉积时期气候温暖潮湿,为咸水-高盐水体环境,有利于有机质的形成,沉积期具有较高的古生产力,水体环境以贫氧-厌氧为主,有利于有机质保存。     

溱潼凹陷阜一段层序地层格架及沉积体系研究

溱潼凹陷属走滑伸展型断陷,应用层序地层学原理和方法,建立了阜一段的层序地层格架,并在阜一段识别出湖泊三角洲和湖泊两大沉积体系。同时结合含砂率与地震属性研究,恢复了阜一段低位域、湖扩域和高位域的沉积体系,认为各体系域沉积体系在时空展布上具有一定的继承性和差异性。综合分析认为,研究区阜一段东部的殷庄—广山地区在低位域时发育大型三角洲沉积体系,主要以前缘河口坝及席状砂沉积为主,可作为良好储集层;西部斜坡带华港—北汉庄地区,低位域及高位域均发育三角洲沉积体系且规模较大,主要为平原河道及前缘河口坝沉积,也可作为很好的油气储层。     

南黄海盆地下三叠统层序地层格架

南黄海盆地是下扬子地块向海洋的延伸,中、古生界海相地层研究程度较低,仍未开展过系统的地层格架研究,制约了研究区的油气勘探进程。结合陆域下扬子的研究成果,利用研究区以及陆上苏北盆地的地质、钻井、测井、岩心等资料建立起下三叠统的三级层序地层格架。研究结果表明:三级层序边界为岩性转换界面或者不整合面;下三叠统可以划分为3个三级层序,其中每个三级层序又可以划分为海侵和高位体系域,低位体系域均不发育。以上研究为后期沉积相划分、储层预测等提供了可靠的地质依据。     

东海丽水凹陷始新统温州组浪控三角洲-浊积扇沉积特征及沉积模式

东海陆架盆地丽水凹陷是重要的油气勘探区。为了加快浅层始新统温州组岩性圈闭勘探,利用新采集的三维地震、地质资料,运用层序地层学理论方法,对温州组进行层序地层划分,将其划分为SQ1、SQ2、SQ3共3个三级层序,其中,SQ1发育典型的低位、海侵和高位体系域,SQ2仅发育海侵和高位体系域。各体系域地震反射终止关系和地震相差异明显。本次研究重点是对SQ1低位域沉积平面展布特征进行刻画。SQ1低位域发育浪控三角洲-浊积扇沉积体系,沉积微相以三角洲前缘滨岸砂坝和薄层灰岩浅滩为主,垂向叠置样式以进积为主。根据浪控三角洲和浊积扇的沉积特征,建立了温州组SQ1低位域浪控三角洲-浊积扇沉积模式。本次研究厘清了低位域三角洲-浊积扇沉积体系的展布特征和形成机制,以期为在始新统温州组寻找岩性圈闭提供参考。     

Seismic based characterization of total organic content from the marine Sembar shale,Lower Indus Basin,Pakistan

The exploration and production of unconventional resources has increased significantly over the past few years around the globe to fulfill growing energy demands. Hydrocarbon potential of these unconventional petroleum systems depends on the presence of significant organic matter; their thermal maturity and the quality of present hydrocarbons i.e. gas or oil shale. In this work, we present a workflow for estimating Total Organic Content (TOC) from seismic reflection data. To achieve the objective of this study, we have chosen a classic potential candidate for exploration of unconventional reserves, the shale of the Sembar Formation, Lower Indus Basin, Pakistan. Our method includes the estimation of TOC from the well data using the Passey’s ΔlogR and Schwarzkofp’s methods. From seismic data, maps of Relative Acoustic Impedance (RAI) are extracted at maximum and minimum TOC zones within the Sembar Formation. A geostatistical trend with good correlation coefficient (R²) for cross-plots between TOC and RAI at well locations is used for estimation of seismic based TOC at the reservoir scale. Our results suggest a good calibration of TOC values from seismic at well locations. The estimated TOC values range from 1 to 4% showing that the shale of the Sembar Formation lies in the range of good to excellent unconventional oil/gas play within the context of TOC. This methodology of source rock evaluation provides a spatial distribution of TOC at the reservoir scale as compared to the conventional distribution generated from samples collected over sparse wells. The approach presented in this work has wider applications for source rock evaluation in other similar petroliferous basins worldwide.     

Geomorphology and sedimentary sequence evolution during the buried stage of paleo-uplift in the Lower Cretaceous Qingshuihe Formation,Junggar Basin,northwestern China: Implications for reservoir lithofacies and hydrocarbon distribution

The evolution of large-scale paleo-uplifts within sedimentary basins controls the sedimentary provenance, depositional systems and hydrocarbon distributions. This study aims to unravel changes in paleo-geomorphology, interpret sedimentary sequence evolution, and investigate favourable reservoir types and the hydrocarbon distribution during the buried stage of a long-term eroded paleo-uplift, taking the Lower Cretaceous Qingshuihe Formation (K₁q) in the Junggar Basin as an example. These research topics have rarely been studied or are poorly understood. This study integrates current drilling production data with outcrop and core analyses, drilling well logs, 3D seismic data interpretations, grading data, physical property comparisons and identified hydrocarbon distributions.After more than 20 million years of differential river erosion and weathering in arid conditions, the large-scale Chemo paleo-uplift within the hinterland area of the basin formed a distinctive valley–monadnock paleo-geomorphology prior to the deposition of K₁q. Since the Early Cretaceous, tectonic subsidence and humid conditions have caused the base level (lake level) to rise, leading to backfilling of valleys and burial processes. Two systems tracts in the target strata of K₁q, consisting of distinctive depositional systems, can be identified: (1) a lowstand systems tract (LST), which is confined within incised valleys and is mainly composed of gravelly braided rivers and rarely occurring debris flows and (2) an extensive transgressive systems tract (TST), which developed into an almost flat landform and consists of braided river delta to lacustrine depositional systems. Overall, the physical properties of braided river reservoirs in the LST are better than those of the braided river delta reservoirs in the TST. However, the inhomogeneous distributions of carbonate cements cause differences in the physical properties of conglomerate reservoirs in the LST. However, for sandstones in both the LST and TST, coarser grain sizes and better sorting result in better physical properties. Altogether, four types of reservoir can be identified in the study area: Jurassic inner monadnock reservoirs, K₁q LST stratigraphic onlap reservoirs, LST structural reservoirs and TST structural reservoirs.     

桑沟湾周边海域晚更新世以来的层序地层

通过桑沟湾周边海域高分辨率浅地层剖面的地质解译,结合典型钻孔沉积地层的对比分析,揭示了研究区晚更新世以来的层序地层序列。研究表明,桑沟湾周边海域晚更新世以来的地层上覆于基岩之上,自下而上识别出了具有层序意义的3个声学地层单元（SU2、SU1-2、SU1-1）,与钻孔的3个沉积地层单元（DU2、DU1-2、DU1-1）对应性良好。桑沟湾周边海域晚更新世以来的层序序列,形成于末次冰盛期低海面时期及早—中全新世高海面以来,自下而上包括低水位体系域（河流-河道充填相沉积）、海侵体系域（潮流沙脊与滨海相沉积）、高水位体系域（浅海相沉积）。研究区低水位体系域受河流下切侵蚀作用,沉积厚度变化较大,介于0～15 m;海侵体系域的沉积厚度普遍介于4.5～5.5 m,分布广泛;高水位体系域由岸向海,自西南至东北沉积厚度逐渐增加,最厚处超过30 m。     

Diagenetic alterations related to marine transgression and regression in fluvial and shallow marine sandstones of the Triassic Buntsandstein and Keuper sequence,the Paris Basin,France

The distribution of diagenetic alterations in Triassic fluvio-deltaic, quartzarenitic to sublitharenitic, lowstand systems tract (LST) sandstones of the Grès á Voltzia Formation, anastomosing fluvial, quartzarenitic transgressive systems tract (TST) sandstones of the Grès á Roseaux Formation, and shallow marine, quartzarenitic to sublitharenitic, TST sandstones of the Grès Coquiller Formation, the Paris Basin (France), can be linked to transgression and regression events, and thus to the sequence stratigraphic context. Near-surface eogenetic alterations, which display a fairly systematic link to the depositional facies and sequence stratigraphic framework, include: (i) cementation by meteoric water calcite (δ¹⁸O=−8.9‰ and δ¹³C=−9.1‰) in the fluvio-deltaic, LST sandstones, (ii) cementation by mixed marine–meteoric calcite (δ¹⁸O=−5.3‰ to −2.6‰ and δ¹³C=−3.9‰ to −1.3‰) and dolomite (δ¹⁸O=−4.6‰ to −2.6‰ and δ¹³C=−2.9‰ to −2.3‰) in the foreshore, TST sandstones and below parasequence boundaries (PB), and transgressive surface (TS), and in the shoreface, TST sandstones below maximum flooding surfaces (MFS), being facilitated by the presence of carbonate bioclasts, (iii) dissolution of detrital silicates and precipitation of K-feldspar overgrowths and kaolinite, particularly in the fluvio-deltaic, LST sandstones owing to effective meteoric water circulation, and (vi) formation of autochthonous glauconite, which is increases in abundance towards the top of the fluvio-deltaic, LST sandstones, and along TS, and in the shoreface, TST sandstones, by alteration of micas owing to the flux of seawaters into the sandstones during transgression, whereas parautochthonous glauconite is restricted to the TS sandstones owing to marine reworking. Mesogenetic alterations, which include cementation by quartz overgrowths and illite, display fairly systematic link to fluvio-deltaic, LST sandstones. This study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution.     

下扬子烃源岩新层位——中下奥陶统

中下奥陶统通常主要作为储层看待,然而皖南地区的下奥陶统宁国组主要为一套富含笔石的灰黑色—黑色薄层硅质、碳质泥岩,属广海陆棚相至深海盆地相沉积;而中奥陶统胡乐组主要为一套同样富含笔石的深灰色薄层粉砂质泥岩和中厚层硅质泥岩,属深海陆棚相至盆地相沉积。二者分布范围相当,但宁国组厚度明显大于胡乐组。下奥陶统宁国组6个样品的岩石热解数据显示,恢复后的TOC均值为1.24%。根据上升流的识别标准,宁国组和胡乐组的岩性和岩相特征以及宁国组地球化学测试结果,推测皖南地区中下奥陶统可能是一套受上升流影响的中—好烃源岩。鉴于南黄海是下扬子的主体,建议加强南黄海中下奥陶统烃源岩的研究。     

High-resolution sequence stratigraphy,sedimentology and reservoir quality evaluation of the Yaojia Formation in the Longxi area of the Western Slope,Songliao Basin,China

Delta-front sand bodies with large remaining hydrocarbon reserves are widespread in the Upper Cretaceous Yaojia Formation in the Longxi area of the Western Slope, Songliao Basin, China. High-resolution sequence stratigraphy and sedimentology are performed based on core observations, well logs, and seismic profile interpretations. An evaluation of the reservoir quality of the Yaojia Formation is critical for further petroleum exploration and development. The Yaojia Formation is interpreted as a third-order sequence, comprising a transgressive systems tract (TST) and a regressive systems tract (RST), which spans 4.5 Myr during the Late Cretaceous. Within this third-order sequence, nine fourth-order sequences (FS9–FS1) are recognized. The average duration of a fourth-order sequence is approximately 0.5 Myr. The TST (FS9–FS5) mostly comprises subaqueous distributary channel fills, mouth bars, and distal bars, which pass upward into shallow-lake facies of the TST top (FS5). The RST (FS4–FS1) mainly contains subaqueous distributary-channel and interdistributary-bay deposits. Based on thin-sections, X-ray diffraction (XRD), scanning electron microscope (SEM) and high-pressure mercury-intrusion (HPMI) analyses, a petrographic study is conducted to explore the impact of the sedimentary cyclicity and facies changes on reservoir quality. The Yaojia sandstones are mainly composed of lithic arkoses and feldspathic litharenites. The sandstone cements mostly include calcite, illite, chlorite, and secondary quartz, occurring as grain coating or filling pores. The Yaojia sandstones have average core plug porosity of 18.55% and permeability of 100.77 × 10⁻³ μm², which results from abundant intergranular pores and dissolved pores with good connectivity. Due to the relatively coarser sediments and abundant dissolved pores in the feldspars, the FS4–FS1 sandstones have better reservoir quality than the FS9–FS5 sandstones, developing relatively higher porosity and permeability, especially the FS1 and FS2 sandstones. The source–reservoir–cap-rock assemblages were formed with the adjoining semi-deep lake mudstones that were developed in the Nenjiang and Qingshankou Formations. This study reveals the deposition and distribution of the delta-front sand bodies of the Yaojia Formation within a sequence stratigraphic framework as well as the factors controlling the Yaojia sandstones reservoir quality. The research is of great significance for the further exploration of the Yaojia Formation in the Longxi area, as well as in other similar lacustrine contexts.