Mechanism of carbonate cementation and its influence on reservoir in Pinghu Formation of Xihu Sag

Carbonate cements are the most abundant authigenic mineral and impact on physical properties greatly in sandstone reservoir.In this paper,Pinghu Formation of Xihu Sag was taken as a target.Characteristics,distribution and formation of carbonate cements were investigated via optical microscopy,cathodoluminescence(CL),electron probe and in-situ carbon-oxygen isotope.The results showed that carbonate cements varied in types and shapes.Calcite/dolomite mainly present as poikilotopic cements,while ferrocalcite/ferrodolomite/ankerite generally present as pore-filling cements.Carbon isotope(δ^(13)C)values of carbonate cements were ranging from–7.77‰to–2.67‰,with an average of–4.52‰,while oxygen isotope(δ^(18)O)values were ranging from–18.94‰to–12.04‰,with an average of–14.86‰.Theδ^(13)C/δ^(18)O indicated that the paleo-fluid of carbonate cement was mainly freshwater.Organic carbon mainly came from organic matter within mature source rocks,and inorganic carbon came from dissolution of carbonate debris and early carbonate cements.Distinctiveδ^(13)C/δ^(18)O values manifest that carbonate cements with different types formed in different periods,which make different contributions to the reservoir properties.Calcite/dolomite formed during eodiagenesis(70–90℃)and early mesodiagenesis stage(90–120℃),and were favorable to reservoir owing to their compacted resistance and selective dissolution.Ferrocalcite/ferrodolomite/ankerite formed during middle-late mesodiagenetic stage(above 120℃),and were unfavorable to reservoir due to cementing the residual intergranular pores.Hence,in order to evaluate the reservoir characteristics,it is of significantly important to distinguish different types of carbonate cements and explore their origins.

Application of seismic sedimentology in characterization of fluvial-deltaic reservoirs in Xihu sag, East China Sea shelf basin

The fluvial-deltaic reservoirs of the Oligocene Huagang Formation in the Xihu sag of the East China Sea shelf basin reflect rapid lateral change in sedimentary facies and poor morphology of conventional slice attributes,which bring difficulties to the reservoir prediction for subsequent exploration and development of lithologic reservoirs.The traditional seismic sedimentology technology is optimized by applying the characteristic technologies such as frequency-boosting interpretation,inversion-conventional–90°phase shift joint construction of seismic lithologic bodies,nonlinear slices,paleogeomorphology restoration,and multi-attribute fusion,to obtain typical slice attributes,which are conducive to geological form description and sedimentary interpretation.The Huagang Formation developed three types of sedimentary bodies:braided river,meandering river and shallow water delta,and the vertical sedimentary evolution was controlled by the mid-term base-level cycle and paleogeomorphology.In the early–middle stage of the mid-term base-level ascending cycle,braided channel deposits were dominant,and vertical superimposed sand bodies were developed.In the late stage of the ascending half-cycle and the early stage of the descending half-cycle,meandering river deposits were dominant,and isolated sand bodies were developed.In the middle–late stage of the descending half-cycle,shallow-water delta deposits were dominant,and migratory medium–thick sand bodies were developed.Restricted paleogeomorphology controlled the sand body distribution,while non-restricted paleogeomorphology had little effect on the sand body distribution.Based on reservoir characterization,the fault sealing type and reservoir updip pinch-out type structural lithological traps are proposed as the main directions for future exploration and development in the Xihu sag.

Defining stratigraphic oil and gas plays by modifying structural plays:A case study from the Xihu Sag,east China Sea Shelf Basin

The study focuses on an area of relatively mature oil and gas exploration located in the western slope of the Xihu Sag,East China Sea Shelf Basin.Three stratigraphic oil and gas plays are introduced to replenish the shrinking prospect inventory in the area.The reservoirs of these plays are traditional pay intervals of the Eocene Pinghu Formation and Baoshi Formation composed of tide-dominated delta front,tidal flat and delta front sand bar facies.By investigating conventional seismic data,seismic inversion volumes,and well log data,multiple tidal-influenced delta front channels,beach sand packages have been mapped out in different reservoir sand intervals of the Pinghu Formation and Baoshi Formation.We recognize four types of stratigraphic terminations:channel flank pinch-outs,axial pinch-outs of sand-fills,channel mouth sand bar pinch-outs,and onlap pinch-outs for the Baoshi Formation.Both the depositional facies and relatively low sand-shale ratio of the reservoir formations favor the occurrence of stratigraphic terminations.The closure mechanism of all these plays are similar to the traditional structure plays in the area:fault blocks or fault-bounded rollover anticlines,except that one or more closing faults are replaced by these stratigraphic terminations.Several small-sized closures should exist but the relatively large ones are centered around a major intra-slope rise,raising the exploration potential in this maturely explored area.The new exploration drilling campaign has so far tested the play of delta front channel facies,with three out of four wells commercially successful.These play concepts open up a novel approach to identify new traps in the study area and many other rift basins with similar settings in eastern China.

Fracture development and hydrocarbon accumulation in tight sandstone reservoirs of the Paleogene Huagang Formation in the central reversal tectonic belt of the Xihu Sag, East China Sea

By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement(12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement(9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging(9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day(0–3 Ma ago), the fractures are tectonic ones developing successively;matching with the second stage(0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.

Diagenetic fluids evolution of Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag, the East China Sea Shelf Basin： constraints from petrology, mineralogy,and isotope geochemistry

The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, scanning electron microscopy, and isotope geochemistry, the different diagenetic features were identified, the typical diagenetic parasequences were established, and the diagenetic fluids evolution history were reconstructed for the Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag. The Huagang Formation sandstone reservoir is now in Period B of the mesodiagenesis, which has undergone significant diagenetic alterations such as mechanical compaction, Pore-lining chlorite cement, feldspar dissolution, quartz cementation and dissolution, and carbonate cementation. Three types of carbonate cements（early siderite,medium ferrocalcite and late ankerite） were identified in the Huagang Formation sandstone reservoir. The carbon and oxygen isotopic compositions of carbonate cements show that the early calcite precipitate from alkaline lacustrine environment whereas the late carbonate cements were closely related to the organic acids. To the Huagang Formation sandstone reservoir, it has experienced two main episodes of dissolution during diagenesis.The early dissolution is that unstable components such as feldspar, lithic fragments, and carbonate cement were dissolved by acidic water. The second dissolution is that quartz and other silicate minerals were dissolved under the alkaline condition. Two main phases of hydrocarbon charging occurred in this study area. The first hydrocarbon emplacement was prior to the medium carbonate cementation but posterior to feldspar dissolution and the onset of quartz cementation at the end of the Miocene. The second hydrocarbon charging occurred in the Quaternary period after the late carbonate precipitation.

Studies on the Inversion Phenomenon of Physical Properties Observed in the Huagang Formation Reservoir in the Xihu Sag Based on the Water-Rock Reaction Experiments

In the Xihu Sag,the reservoirs of the Paleogene Huagang formation have entered the middle diagenetic stage A and the rock physical properties of the water layer are considerably more suitable for the gas migration and storage than those of the present gas layer,indicating the inversion of the physical properties.In this study,core samples were collected from the corresponding reservoir to conduct water-rock reaction experiments in acidic,alkaline,and neutral systems under the specific temperature and pressure.The reasons for the inversion of physical properties were investigated based on the experiment results in reservoir diagenetic environments.The inversion of physical properties can be attributed to the fact that the diagenetic environment around the gas-water interface controls the water-rock reaction effect.With different types of acidic substances,two different situations corresponding to inverted physical properties were analyzed along with the corresponding mechanisms.When the pore fluid is acidic,the physical properties make the overall water layer a better reservoir space than the gas layer,which can be referred to as the overall inversion of physical properties.When the fluid were generally neutral or weakly alkaline and the gas layer was rich in CO2,only the physical properties of the water layer adjacent to the gas-water interface were more favorable for the gas migration than those of the gas layer.This phenomenon can be referred to as the near-interface inversion of physical properties.

Factors controlling the development of tight sandstone reservoirs in the Huagang Formation of the central inverted structural belt in Xihu sag, East China Sea Basin

By means of thin section analysis, zircon U-Pb dating, scanning electron microscopy, electron probe, laser micro carbon and oxygen isotope analysis, the lithologic features, diagenetic environment evolution and controlling factors of the tight sandstone reservoirs in the Huagang Formation of Xihu sag, East China Sea Basin were comprehensively studied. The results show that: the sandstones of the Huagang Formation in the central inverted structural belt are poor in physical properties, dominated by feldspathic lithic quartz sandstone, high in quartz content, low in matrix, kaolinite and cement contents, and coarse in clastic grains;the acidic diagenetic environment formed by organic acids and meteoric water is vital for the formation of secondary pores in the reservoirs;and the development and distribution of the higher quality reservoirs in the tight sandstones of the Huagang Formation are controlled by sediment source, sedimentary facies belt, abnormal overpressure and diagenetic environment evolution. Sediment provenance and dominant sedimentary facies led to favorable initial physical properties of the sandstones in the Huagang Formation, which is the prerequisite for development of reservoirs with better quality later. Abnormal high pressure protected the primary pores, thus improving physical properties of the reservoirs in the Huagang Formation. Longitudinally, due to the difference in diagenetic environment evolution, the high-quality reservoirs in the Huagang Formation are concentrated in the sections formed in acidic diagenetic environment. Laterally, the high-quality reservoirs are concentrated in the lower section of the Huagang Formation with abnormal high pressure in the middle-northern part;but concentrated in the upper section of Huagang Formation shallower in burial depth in the middle-southern part.

西湖凹陷中南部花港组下段储层成岩孔隙演化

西湖凹陷中南部花港组下段储层具有丰富的致密气资源,是该区油气勘探开发的热点。基于岩石薄片、扫描电镜、物性测试和X衍射等资料,对西湖凹陷中南部花港组下段储层特征、成岩作用及孔隙演化等进行了研究。结果表明,储层孔隙度主要在7%∼10%,渗透率主要在0.10∼0.50 mD,裂缝不发育,属于致密储层。储层先后经历了早成岩A期、早成岩B期和中成岩A期,目前处于中成岩B期,压实作用、溶蚀作用和胶结作用较强。孔隙定量演化结果显示,压实作用使储层孔隙度降低了29.67%,是储层原生孔不发育的主要原因;溶蚀作用使储层孔隙度增加了15.14%,是深部储层发育的关键因素;胶结作用使储层孔隙度降低了13.55%,是储层孔隙结构变差的重要原因。综合孔隙演化结果和油气充注时间关系,该区花港组下段储层属于“先致密后成藏”的致密储层。

西湖凹陷平北地区武云亭凝析气田形成条件与成藏特征

基于对武云亭地区烃源岩、储层、圈闭等油气藏形成基本条件的总结,系统分析油气特征及来源、压力分布与断层封闭、油气充注历史及油气运聚成藏过程,建立武云亭凝析气田成藏模式。研究表明,武云亭洼广泛分布的煤系烃源岩和宁波27主洼烃源岩生烃能力强、断层和砂岩尖灭耦合形成大型构造-岩性复合圈闭、三角洲沉积优质储集体发育、有利的断-砂配置、盖层质量好等因素共同构成了武云亭凝析气田形成的基础。武云亭油气田平湖组中下部成藏组合具有“武云亭洼煤系源岩供烃、源内持续弱超压充注”成藏特征;中上部成藏组合具有“武云亭洼和宁波27洼双源供烃、侧向持续强充注”成藏特征,早期双向来源原油与晚期大规模侧向来源高熟气混合形成凝析气藏。武云亭油气田总体上具有“早期油晚期气,多期成藏,连续充注”的特征,建立“多源持续强充注-断砂联控”成藏模式。

西湖凹陷花港组浅水三角洲平原分流河道沉积构型

渐新统花港组上段是东海陆架盆地西湖凹陷中南部地区的主要产油气层位,但对其沉积体系的认识一直存在争议,砂体构型特征及控制因素的研究也相对匮乏。综合运用岩心、测井及地震等资料,研究渐新统花港组上段沉积环境、沉积微相类型、砂体沉积构型特征及其控制因素。结果表明:西湖凹陷中南部花港组上段以浅水三角洲平原沉积为主,分流河道是最主要的砂体类型。根据弯曲度差异,可将分流河道划分为辫流型(弯曲度1~1.05)、曲流型(弯曲度大于1.15)和辫-曲转换型(弯曲度1.05~1.15)3种类型,其中辫流型分流河道砂体“宽而厚”,平面组合呈交织宽条带状,心滩呈斑点状排列,砂体垂向叠置样式以切叠型为主;曲流型分流河道砂体“窄而薄”,平面样式为单一条带型或分叉-合并型,厚砂以点坝的形式分布在河道边缘,砂体垂向叠置样式以“孤立型”为主;辫-曲转换型分流河道是辫流型和曲流型的过渡类型,河道砂体规模中等,河道内心滩和点坝同时发育。3类分流河道的厚度与宽度呈对数正相关,宽厚比具有辫流型>辫-曲转换型>曲流型的特征。推测古地貌和基准面变化是影响浅水三角洲分流河道构型特征的主要因素,其中古地貌控制了分流河道的河型变化,较陡的地形有利于低弯度辫流型分流河道的形成,而长期基准面上升造成了分流河道规模逐渐下降,中期基准面的上升造成了分流河道砂体叠置样式发生切叠型→叠加型→孤立型的演变。研究成果完善了浅水三角洲的沉积构型知识库,对地下浅水三角洲分流河道储集层的预测及开发具有重要的指导意义。

西湖凹陷K气田宝石组“源-渠-汇”及沉积体系分析

西湖凹陷K气田宝石组的油气潜力可观,但其古地理环境尚不明确。该文应用"源-渠-汇"耦合的思想,利用地震及钻井资料对K气田宝石组进行沉积体系演化及展布研究,明确了宝石组沉积相类型及分布规律。结果表明,宝石组可以划分为宝上、宝下两段,物源主要来自西北部海礁凸起。K气田宝石组主要发育三角洲前缘亚相沉积,包括砂坝、分流主河道、分流次级河道、河道间沉积微相。研究区南、北两个次洼,是优势沉积汇聚区,其中宝上段的水下分流河道以及宝下段的砂坝为下一步勘探开发的有利目标。该研究可为K气田宝石组油气勘探提供参考。

西湖凹陷西次凹古近系花港组—平湖组深层油气成藏过程

西湖凹陷西次凹古近系花港组和平湖组深层油气资源丰富,是东海陆架盆地勘探开发新领域,受储层差异致密化影响,油气成藏机理复杂。为了厘清西次凹深层油气成藏过程,本文通过流体包裹体岩相学特征、显微测温、激光拉曼光谱、包裹体所含油气地球化学等实验分析,结合构造演化、地层埋藏史、热史等,开展了系统的储层特征、油气成藏期次、成藏过程研究。结果表明,花港组深层(>4000 m)和平湖组储层均已致密化,溶蚀孔隙是主要的储集孔隙类型;花港组和平湖组均发育两期油气包裹体,早期含油包裹体较多,晚期以天然气包裹体为主,成藏时间分别为龙井运动期和冲绳运动期,以晚期天然气成藏最为关键。包裹体中油气地球化学特征类似,反映生烃母质以高等植物生源为主,低等生物为辅,与平湖组煤系烃源岩特征一致。冲绳运动叠加平湖组生气增压是晚期天然气成藏的主要动力,此时H10段及以上储层未致密化。根据储层致密化与成藏时序匹配关系可将西次凹M构造深层油气藏类型划分为常规型、先成藏后致密型、先致密后成藏型和边成藏边致密型4种。本文成果可为研究区下一步致密砂岩气的勘探开发部署提供重要的理论依据。

东海盆地西湖凹陷南部火成岩发育区G构造油气成藏特征

G构造是一个大型挤压反转背斜,位于西湖凹陷西南角的天台斜坡带火成岩发育区。由于目前对该区火山活动规律及后期油气保存等成藏演化条件认识不清,严重限制了天台斜坡带的油气勘探进程。通过对研究区地震资料进行解释,研究了G构造区火成岩的岩石学、年代学和时空分布特征,重建了火山活动、圈闭形成与油气成藏过程的关系。结果表明,G构造范围内发育的火成岩为中新世中期的浅层侵入岩、溢流相喷出岩和通道相火成岩,该火成岩的发育使得平湖组和花港组的地层碎裂化,由于该背斜核部存在早期火山通道,后期挤压形成的圈闭有效性差。龙井运动(中新世末期,5.3 Ma)至上新世三潭组沉积期,该背斜转折端发育了一系列近EW向次级断层,进一步破坏了圈闭的完整性。由于背斜翼部未受火成岩影响,该处的构造-岩性圈闭应该是下一步勘探的重要方向。

西湖凹陷中央反转带花港组储层成岩演化南北差异及其影响因素分析

东海盆地西湖凹陷花港组砂岩储层作为西湖凹陷的重要勘探目的层,储层非均质性研究至关重要,笔者等基于储层成岩作用和成岩演化分析,明确中央反转带南北差异,进一步分析其差异成因。研究结果表明,北部地区具有更强的压实作用和溶蚀作用,纵向上以3500 m和4000 m为界划分为酸性、酸碱过渡和碱性3个成岩带,经历两期硅质胶结和三期钙质胶结;而南部地区埋深浅、地温低,仅具有两期钙质胶结,纵向上以4000 m为界划分为酸性和碱性两个成岩带;由于北部地区具有更多的岩浆岩母源贡献使得储层抗压实能力较差,遭受压实更强,但烃源岩较强的生烃强度使得储层遭受溶蚀作用更强,因此北部地区花港组储层具有低孔高渗的特征。该研究对优质储层发育研究和甜点预测具有重要意义。

西湖凹陷西部斜坡带原油来源

原油来源分析是确定油气勘探方向的重要依据。利用有机地球化学分析手段,分析了西湖凹陷西部斜坡带原油和烃源岩特征,通过生物标志物谱图和生物标志物参数的对比,结合原油与烃源岩分布特征,确定了西湖凹陷西斜坡不同区原油的来源。结果表明:(1)研究区原油总体上富含指示陆源高等植物输入的生物标志物,但平北地区原油碳同位素重,二萜类丰富,规则甾烷以C29甾烷为主;平湖地区原油碳同位素较轻,二萜类含量较高,且具有较低的伽马蜡烷;黄岩-天台地区原油碳同位素轻,二萜类含量低,规则甾烷以C29甾烷为主,同时C27甾烷的含量也较高。(2)研究区发育煤系烃源岩(包括煤和炭质泥岩)和暗色泥岩两类烃源岩。煤系烃源岩富含来源于裸子植物的异海松烷类和蕨类植物的16β(H)-扁枝烷,从平北到黄岩-天台地区的煤系烃源岩中16β(H)-扁枝烷含量增加;暗色泥岩二萜类含量低,16β(H)-扁枝烷相对于降异海松烷占优势,且从平北到黄岩-天台地区暗色泥岩中C27甾烷、16β(H)-扁枝烷增加。(3)平北地区原油主要为煤系烃源岩贡献,平湖地区原油为煤系烃源岩和暗色泥岩混合贡献,且煤系烃源岩的贡献较大,黄岩-天台地区原油主要为暗色泥岩贡献。研究成果对深化西湖凹陷油源认识及油气勘探部署有一定的指导作用。

西湖凹陷中北部花港组上段浅水辫状河三角洲发育特征

从分析岩芯资料和砂体平面展布着手,重新厘定了东海盆地西湖凹陷中北部花港组上段H4、H5砂组的沉积相,创新提出了研究区花上段发育浅水辫状河三角洲沉积,研究区中南部发育规模性砂体。研究认为:在研究区的西部及东部边缘为辫状河三角洲平原相主导区,以发育辫状河三角洲平原河道砂体为主,局部有少量的辫状河三角洲前缘相发育。在研究区的中部及中南部,为辫状河三角洲平原与辫状河三角洲前缘交互发育区,主要特征是在较短的沉积期内形成了三角洲平原相与三角洲前缘相交互沉积;在枯水期时,以发育三角洲平原沉积为主,南部边缘发育三角洲前缘相沉积;在丰水期时,主要发育三角洲前缘相沉积及少量浅湖相沉积。在浅水辫状河三角洲沉积模式指导下,在研究区中南部发现了众多三角洲水道砂体及朵叶状砂体,这些砂体被钻井证实为油气藏。研究区的中南部仍然是油气勘探的潜力区,这一认识已被最新探井所证实。

西湖凹陷保俶斜坡K构造异常高压分布特征及主要成因

西湖凹陷保俶斜坡带K构造中上始新统平湖组油气发现井中一半以上具有异常高压特征,异常高压与该地区油气成藏关系密切。通过铸体薄片、物性、镜质体反射率等分析化验资料及钻井、测井资料,对K构造的异常高压特征进行了分析,明确了中高带、中低带、低带异常高压的成因。K构造异常高压主要发育在平湖组中下段,异常高压顶界面的埋深从中高带到低带有逐渐增大的趋势,中高带泥岩预测的压力系数略大于砂岩实测压力系数,中低带两者相当,低带相反。研究区中高带异常高压的主要成因是不均衡压实,中低带是不均衡压实和流体膨胀复合成因,低带异常高压的主要成因是流体膨胀。生烃增压和黏土矿物脱水增压对中低带和低带的异常高压均有贡献。异常高压带是油气富集的有利区带。

西湖凹陷平湖斜坡北段平湖组薄煤层与泥岩的微观岩石学特征及其沉积学意义

西湖凹陷平湖斜坡北段平湖组受河流与潮汐作用共同影响,水动力条件复杂,分支流水道砂体与潮汐水道砂体的成因存在争议。通过煤层与泥岩的微观岩石学特征分析,探讨其岩石结构与矿物组成、泥岩中碎屑颗粒排列方式、水动力条件与水介质环境,进而划分岩性相类型,展开砂-泥岩一体化的微相划分与水动力分析。其中,薄煤层可分为封闭洼地含草莓状黄铁矿煤层、分支流间湾沼泽纯煤层与天然堤粉砂质纹层煤层;泥岩可分为封闭洼地水平纹层状菱铁矿、分支流间湾含结核状菱铁矿,以及砂岩中交错纹层状菱铁矿。泥岩中广泛发育的菱铁矿指示平湖组沉积时期,发育富铁的局限潟湖环境;泥岩中黏土矿物以高岭石与伊利石混合的黏土为主,指示淡水-海水混层的沉积水介质环境。泥岩中微古生物与煤的显微组分指示其互层的箱形、钟形砂体为三角洲背景下的水道沉积,砂体为多期水道叠置的复合体。薄煤层与碳质泥岩及相关砂岩的微观岩石学分析表明,平湖斜坡北部平湖组具有典型的缓坡局限浅水沉积背景,陆源有机质供给丰富,泥岩中普遍富含碳质,砂体以单向水流沉积作用为主。薄煤层与泥岩岩相分析为薄煤层与砂岩成因分析提供了新的沉积学信息,为砂体预测评价提供了新的依据。

东海盆地西湖凹陷平湖斜坡始新统平湖组成岩相类型及对储层的控制

为了在深埋藏、强非均质性背景下寻找相对优质储层,本文以东海盆地西湖凹陷平湖组为例,基于直观微区观测、间接压汞表征及孔渗分析相结合的方法,在储层沉积学分析的基础上,先划分成岩相类型,进而明确不同成岩相的差异储集能力特征,评价成岩相储集能力。结果表明:平湖组沉积于河流和潮汐双向水动力条件的三角洲-潮坪体系,砂体多发育于水下分流河道、河口坝、潮道、砂坪和混合坪中,以细粒和极细粒为主,主要为长石岩屑砂岩和岩屑长石砂岩;基于成岩作用类型的强度差异将成岩相划分为3类,包括长石溶蚀相、富塑性压实相和钙质胶结相;同一成岩相类型孔渗特征和孔隙结构特征均一,而不同成岩相之间物性差异显著;以孔隙度、渗透率、最大连通孔喉半径为标准对3类成岩相进行量化参数分级评价,长石溶蚀相孔隙度>15%,渗透率>10.0×10^(-3)μm^(2),最大连通孔喉半径>5.0μm,物性条件优于富塑性压实相和钙质胶结相,优选出长石溶蚀相为最有利的储层砂体类型。

西湖凹陷中部深层甜点气藏发育条件与分布预测

深层致密气藏特征及甜点分布预测是制约油气高效勘探与开发的关键问题。通过铸体薄片、扫描电镜、激光微区碳氧同位素、天然气碳同位素及含烃包裹体测温等实验分析,结合测井及地震资料,论述西湖凹陷中部深层甜点发育条件及分布规律。结果表明:①中部Y构造花港组发育厚层洁净粗粒砂岩,次生溶孔发育且孔喉半径集中,4200~4500 m发育大量特低孔低渗甜点;②心滩微相优质砂体、有机酸溶蚀改造及晚期高熟气强充注是Y构造深层规模成藏的关键,H3气藏为先致密后成藏气藏,断砂耦合控制了强溶蚀区的发育且利于晚期高熟气的充注,邻近断层处形成局部甜点;③地质-地球物理联合预测显示H3砂组高气饱甜点主要分布于F1断层上盘,平面预测结果与实钻结果吻合好。基于成藏模式形成的地质-地震甜点预测技术,能明显提高深层/超深层复杂地质条件下的甜点预测精度,对深层、少井区甜点预测具有推广借鉴意义。