Petroleum Systems of Chagan Depression,Yingen-Ejinaqi Basin, Northwest China

INTRODUCTIONYingen-Ejinaqi basinis locatedin the WulatehouBanner in the west of the Inner Mongolia Autono-mous Region of China ,and covers an area of approxi-mately 122 000 km2( Chen et al ., 2001) . As aMesozoic-Cenozoic depression in Yingen-Ejinaqi ba-sin,the Chagan depression lies in the northeast ofthis basin (Fig.1) .It is about 60 kmlong and 34 kmwide and covers an area of approxi mately 2 000 km2( Wang et al .,2002) .In terms of the basement ter-rain,forms of major structural…     

东海盆地西湖凹陷油岩地球化学特征及原油成因来源

东海盆地西湖凹陷具有大量的原油资源,但对于原油成因讨论较少.采集西湖凹陷多个油样和岩样,利用气相色谱和傅里叶红外光谱等手段,全面分析了该区烃源岩和原油的地球化学特征,综合讨论了原油来源以及凝析油和高蜡轻质油的成因.研究结果表明,平湖组煤系源岩均处于热演化的成熟阶段,其中碳质泥岩和煤岩以陆源生物为主要生源,其干酪根类型为Ⅲ型,暗色泥岩则具有陆源生物和水生生物双重生源贡献,其干酪根类型Ⅱ-Ⅲ型,同时碳质泥岩和煤的生油潜力远高于泥岩.原油主要为凝析油和轻质油,凝析油具有低密度、低蜡等“六低一高”的特点,轻质油具有高蜡特质,而且轻烃组分有明显差异.生标参数显示大部分原油为腐殖型,少部分原油表现出具有腐殖和腐泥母质的特点,同时该区原油均处于中等成熟阶段.油油对比和油岩对比表明大部分油来自平湖组碳质泥岩和煤岩,具有典型Ⅲ型腐殖油的特征;少部分油来自暗色泥岩,具有Ⅱ-Ⅲ型油的特征(总体上仍偏腐殖型).凝析油和轻质油的物性及轻烃组分的差异与源岩母质无关.凝析油是干酪根在成熟演化阶段生成的原油遭受蒸发分馏作用的结果,高蜡轻质油除了是“蒸发分馏作用”的残余油外,还有部分是“混合作用”的结果.      

西湖凹陷渐新世层序地层格架与沉积充填响应

东海陆架盆地是中国近海最大的沉积盆地,而西湖凹陷又是其中规模最大的富油气凹陷。多年的勘探实践证明渐新统花港组为西湖凹陷主力产气层段,但其层序地层划分长期存在较大争议。在分析了西湖凹陷盆地结构与构造格局的基础上,依据测井、岩芯以及地震反射特征,将西湖凹陷渐新统划分出5个三级层序与12个体系域,建立了其等时地层格架;并通过大量岩芯的写实性描述,结合沉积构造与遗迹化石鉴别以及地球化学资料分析对沉积环境进行了判识,分析结果认为西湖凹陷渐新统花港组沉积时期发生过两次较大的海侵事件,形成“南海北陆”的沉积格局,并发育了河流、三角洲、潮控河口湾以及无障壁海岸四种沉积体系,其沉积体系类型较多,从南到北变化巨大。西湖凹陷渐新世整体表现为“东西短轴三角洲”、“南部潮汐河口湾”、“东北缓岸滩坝”的沉积体系展布格局。系统分析了沉积相在各层序中的展布特征及其对海平面变化的响应、层序演化过程及其对海平面变化的响应,构建了东海陆架盆地西湖凹陷构造-沉积成因模式,明确了“断坳转换,海陆交替”的盆地构造背景与沉积充填的响应关系。     

东海陆架盆地西湖凹陷岩石圈热流变性质

为了探讨东海陆架盆地西湖凹陷岩石圈热流变性质,本文以实测地温数据为依据,模拟西湖凹陷岩石圈热结构,在此基础上,应用流变学原理模拟确定西湖凹陷岩石圈流变性质。结果表明,西湖凹陷岩石圈为一个冷地壳-热地幔、强地壳-弱地幔的"奶油蛋糕"型岩石圈。西湖凹陷平均地表热流密度为71 m W/m~2,地幔热流密度为40~65 m W/m~2,对地表热流密度的贡献度达73%~79%,地表热流受地幔热流控制,莫霍面温度在700℃左右,热岩石圈平均厚度为66 km。西湖凹陷岩石圈流变分层明显,上、中地壳基本为脆性层,下地壳和岩石圈上地幔为韧性层,岩石圈总流变强度平均约为2.65′10~(12) N/m,其中地壳流变强度为2.12′10~(12) N/m,地幔流变强度为5.29′10~(11) N/m,有效弹性厚度为11.7~14.5 km,地壳的流变性质控制了岩石圈的流变行为。此外,西湖凹陷岩石圈总强度较低,在构造应力作用下易于变形,且存在壳幔解耦现象。西湖凹陷岩石圈热状态及流变性质决定了西湖凹陷东部地区主要以浅部地壳的断层滑动和地层破裂来调节深部的构造应力。     

东海西湖凹陷新生界主要不整合面地层剥蚀厚度恢复

综合地质对比法、声波时差法以及不连续镜质体反射率法得到西湖凹陷新生界T2^0、T2^4、T3^0三个重要的不整合面上地层的剥蚀厚度。剥蚀量的宏观分布与主要构造带的走向基本一致，局部构造的剥蚀与其特定的构造位置有关。T2反射界面为斜坡-褶皱型地层剥蚀模式，剥蚀量主要分布在中央背斜构造带，沿龙井一井-东海一井-花港一井-玉泉二井-残雪一井一线附近的地层剥蚀量最大，可达2000m以上；西部斜坡区次之。T2^4反射界面地层剥蚀模式为过渡型剥蚀模式，地层剥蚀量在凹陷东部边缘较大，最大可达800m以上；中央背斜带的东海一井构造带、龙井一井构造带、花港一井构造带、玉泉一井构造带、玉泉二井构造带、残雪一井构造带、春晓构造带等有局部剥蚀，一般在400～600m以内。T3^0反射界面为断块-斜坡地层剥蚀模式，地层剥蚀量以西部斜坡最大，中央背斜局部构造有剥蚀。西部斜坡带剥蚀量一般在200～800m之间，中央构造带的龙井二井构造带、花港一井构造带、玉泉二井构造带、天外天一井构造带以及东缘构造带有较少剥蚀，一般在200～400m以下。     

东海陆架盆地西湖凹陷花港组原型盆地性质厘定

西湖凹陷是东海陆架盆地最主要的含油气构造单元,渐新世花港组是西湖凹陷重要的油气勘探目的层系,然而对于花港组沉积时期原型盆地的性质却一直存在争议且缺乏有说服力的证据.以最新的区域二维地震资料解释为基础,通过对关键不整合界面特征、盆地充填几何形态、盆地边界改造特征等方面的系统分析,提出西湖凹陷花港组原型盆地为一大型挤压挠曲坳陷型盆地,花港组底界面T30为盆地挤压背景下广泛发育的一个区域隆升侵蚀型不整合界面,是花港组原型盆地的成盆界面.花港组顶界面T20主要是受钓鱼岛隆褶带隆升活动控制的局部隆升侵蚀型不整合面,是花港组原型盆地的改造界面.在上述认识的基础上,进一步建立了花港组原型盆地的形成演化模式.      

Numerical modeling of Late Miocene tectonic inversion in the Xihu Sag,East China Sea Shelf Basin,China

The East China Sea Shelf Basin is an important oil- and gas-bearing basin in the West Pacific continental margin. This region was affected by subduction of the Pacific Plate and the Philippine Plate in Cenozoic and experienced multi-stage tectonic inversions. This paper presents results from a numerical simulation by finite element method to the Xihu Sag in the East China Sea Shelf Basin and neighboring areas in an attempt to evaluate the WNW-directed compression on the sag during Late Miocene. Based on comprehensive structural analysis of a large number of seismic profiles, we determine the structural geometry of the sag, including the basement of the basin, the sedimentary cover, and 29 major faults in the Xihu Sag. Simulation results show that under continuous WNW-directed compression, tectonic inversion occurred firstly in the Longjing and Yuquan tectonic zones in the sag. Based on quantitative analysis of vertical displacement field of the Xihu Sag and peripheral areas and its stress intensity evolution, we identify a compressional regime in the Longjing Anticline Zone with a gradually propagated uplifting from south to north; whereas the propagation of uplifting in the Yuquan Anticline Zone is from north to south. The inversion intensity decreases from north to south. The formation of the tectonic inversion zone in the Xihu Sag is not only correlated to the direction of compression and fault patterns in the basin, but also closely related to the spatial configuration of fault surfaces of the Xihu–Jilong Fault in the Xihu Sag.     

东海陆架盆地西湖凹陷超压成因机制

西湖凹陷超压普遍发育,成因机制复杂,目前研究未见深入.从产生超压的主要因素入手,采用定性分析与定量计算相结合的方法,基于超压层段的测井响应特征、速度与垂直有效应力、沉积速率与孔隙度演化史、压力演化史与生烃强度史耦合的初步判断,再通过定量的计算综合分析了西湖凹陷超压的成因机制.研究表明:不均衡压实作用和生烃作用是西湖凹陷超压形成的主要机制,但在不同的区带有一定的差异.其中保俶斜坡带以不均衡压实作用为主,经过估算生烃作用贡献率为23%～57%,平均达到41%;而在中央背斜带超压形成机制有两种模式,大部分是以生烃作用为主的增压模式,贡献率为51%～78%;个别井位研究显示以不均衡压实作用为主的增压模式.在三潭深凹超压的形成中,不均衡压实作用与生烃作用相当,生烃作用增压稍强于不均衡压实作用增压,生烃作用的平均贡献率为60%左右.      

东海西湖凹陷平湖斜坡带断裂系统特征及成因机制探讨

综合运用地震剖面解释结果和构造编图成果,对东海西湖凹陷平湖斜坡带断裂系统按发育规模和形成期次进行分类,分析了断裂系统的平、剖面展布特征,采用古落差法和活动速率法研究了断裂运动学特征,结合区域应力场特征探讨了其成因机制。结果表明,平湖斜坡带断裂系统可划分为4个断裂带,由北至南依次为孔雀亭同向断裂带、武云亭反向断裂带、平湖同向断裂带和平南堑式断裂带。平湖斜坡带以发育多米诺、地堑、梳妆、正牵引等伸展构造样式为主,局部(如平湖同向断裂带)见微弱反转构造。断裂运动学特征研究表明,断裂活动高峰期具有分带性,平湖同向断裂带断层活动性最强,孔雀亭同向断裂带和武云亭反向断裂带次之,平南堑式断裂带最弱。平湖斜坡带断裂系统的发生、发展是应力集中与断层间相互影响共同作用的结果,是对东海陆架盆地构造演化过程的局部响应。     

Dynamic Systems of Petroleum Accumulation in the Nanpu Depression,Bohai Bay Basin,China

<正>It is significant to distinguish the dynamic systems of petroleum accumulation(DSPA) for the understanding of petroleum accumulation and distribution.According to the formation pressure framework,genetic types of petroleum and characteristics of conduit systems,three dynamic systems of petroleum accumulation were identified in the vertical profile in the Nanpu depression,Bohai Bay basin.The deeper DSPA(including formations Es_3 to Es_2) is a sealed system with high-overpressure and high-mature self-sourced oil.Most of the crude oil in the system accumulated in the periods of late Oligocene(23.5 Ma) and late Pliocene(2.4 Ma).The middle DSPA(including formations Es_1 to Ed_1) is an overpressured half-sealed system with mature or lower-mature self-sourced oil.The accumulation of oil in the system also occurred in the late Oligocene(23.5 Ma) and late Pliocene(2.4 Ma).The shallower DSPA(including formations Ed_2 to Q) is a hydrostatic system with lower-mature aliensourced oil from the middle system.Oil within this system accumulated only in the late Pliocene period.The oil in the shallower system migrated vertically along the faults from the formerly accumulated oil in the middle system by lateral migration along the sandbodies,whereas petroleum accumulation in the deeper system was mainly derived from the system itself by lateral migration along the sandbodies and rarely migrated out of the system.In this case,it seems that the deeper system is a more potential exploration prospect in addition to the other two proved favorable systems.     

埕岛复式含油气系统研究及评价

针对渤海湾南部埕岛地区的油气成藏特征和较高勘探程度的特点，对埕岛复式含油气系统（composite petroleum system)，含油气系统，亚油气系统和子系统进行了四个不同勘探级次的划分，描述，以及各含油气系统之间相互关系的讨论，从油气的生成，运移，聚集，保存和破坏有机联系的四个方面18种要素，对不同级次的系统用多级模型综合评判的数学方法，进行了综合定量评价，并在此基础上优选出下一步的有利勘探目标。     

东海西湖凹陷花港组层序划分

大部分学者将东海西湖凹陷花港组划分为两个三级层序,但其层序界面与构造运动、古气候等重大地质事件之间在时间上不十分协调。本文以经典层序地层学、地震地层学为理论指导,在岩电特征、古生物特征、地震相分析等方面研究的基础上,结合全球性构造运动、海平面变化及古气候研究,重新厘定了东海西湖凹陷古近系花港组层序。在花港组识别出两个二级层序界面和两个三级层序界面,将花港组划分为3个三级层序。本研究对东海西湖凹陷层序地层的研究具有重要意义,同时对精细刻画层序格架内有利储层,指导生产具有积极意义。     

东海陆架盆地西湖凹陷渐新世海侵作用与潮控体系沉积特征*

西湖凹陷位于东海陆架盆地东部坳陷带,是该盆地规模最大的富油气凹陷。然而,西湖凹陷渐新世沉积环境与沉积体系类型一直存在较大争议。本文以井、震为基础,岩心为核心,结合地球化学指标,通过泥岩甾烷与自生海绿石的特征,明确了渐新世西湖凹陷南部整体处于海陆交互的过渡环境,且发生5次主要的海侵事件。西湖凹陷南部渐新统以厚层砂岩与薄层泥岩互层为特征,发育典型的双向交错层理、双黏土层、透镜状层理及泥质披覆,共识别出4种主要的岩相类型: 含泥砾块状中粗粒砂岩相、交错层理中细粒砂岩相、沙纹层理粉细砂岩相、纹层状泥岩相。渐新世,西湖凹陷南部主要发育潮控河口湾体系,其中包括潮汐水道、潮汐沙坝、沙质潮坪及泥质潮坪等多个沉积微相,其沉积地形在SW向逐渐变为开阔的展布特征,说明研究区河流供源来自东北部,而潮汐水流来自西南部。渐新世西湖凹陷南部与开阔海连通,受到海侵作用下潮汐水流的强烈改造,且由于地形坡度较缓,无大规模的河流携带碎屑物质注入,易形成潮汐作用为主的河口湾体系。     

东海盆地西湖凹陷构造样式及其演化

西湖凹陷是经历多期构造作用的白垩—第三纪盆地。多期裂陷和反转构造作用的叠加导致了相对复杂的构造格架样式和盆地地质结构。凹陷总体上具有东西分带,南北分块的构造格局。裂陷期的同沉积断裂组成了多种复合的构造样式：西部斜坡带主要发育断阶、地堑和地垒构造;中央洼陷带则以复合“Y”字型、羽状和似花状断裂组合为主;东缘断阶带主要发育“Y”字型、梳状和羽状组合。坳陷反转期,早期的同沉积断裂发生了不同程度的逆冲反转,形成了多种复合的构造样式,例如反冲叠瓦扇构造、后断叠瓦式逆冲构造等叠合构造样式。从盆地的构造样式出发,探讨了盆地的形成演化和构造- 沉积充填过程对有利圈闭带发育分布的控制作用,对富生烃凹陷油气预测具有重要指导意义。     

东海陆架盆地西湖凹陷新生代反转构造样式及其形成机制初探

通过对东海陆架盆地西湖凹陷十多条地震剖面的精细解释,发现西湖凹陷自晚白垩世以来,经历了早期的拉张和晚期的断续挤压两个构造演化阶段.晚期的断续挤压在凹陷内产生构造反转的样式复杂多样,可划分为上下均正型、下正上逆型、下凹上凸型、上下均凸型、下正上隆型和下隆上逆型等6种单个的反转构造样式及y形、帚状、"似花状"等7种反转构造组合样式.对反转断层生长指数（Gi）并结合平衡剖面的研究,表明西湖凹陷新生代经历了多期构造反转.通过计算反转率（Ri）,发现凹陷内反转程度存在明显的不均一性,具有中带强和东、西弱的特征.结合晚白垩世以来东亚大陆边缘的区域构造演化及新生代以来太平洋板块相对欧亚板块的俯冲速度讨论了西湖凹陷构造反转的机制,并探讨了它对油气勘探的意义.     

东海陆架盆地西湖凹陷东部边缘结构解释及地质意义

东海陆架盆地西湖凹陷东部过XH-1井的GH-1剖面,揭示了盆地边缘在新生代多次盆地原型迭代中的结构变化。在梳理前人关于盆地原型学术观点的基础上,通过T₂⁵、T₂⁴、T₂³上超点不断东扩的特征,确认了陆相盆地发展跨越式、旋回性的演化特点;根据T₂⁴、T₂⁰两期构造反转,确认了陆内迁移拗陷期渐新统、中新统（龙井组和玉泉组）分别为两个二级构造层序;结合柳浪组的成因机制,探讨了柳浪组在盆地发展史中的归属问题。通过玉泉运动、花港运动和龙井运动机制探讨及界面确认,深化了断陷期、拗陷期西湖凹陷东部边界的认识,明确了西湖凹陷经历了古新世-始新世走滑拉张断陷-转换边缘拗陷、渐新世-中新世陆内迁移拗陷、上新世-第四纪弧后陆架边缘拗陷的盆地原型迭代发展史。     

Sedimentary environment and facies of the Huagang Formation in the northern central Xihu Depression,East China Sea Basin,China

Abstract

The sedimentary facies of the Huagang Formation, the major petroleum exploration horizon in the Xihu Depression in the East China Sea Basin, have not been well constrained, owing to limited drilling and core recovery. Interpretations are vague and vary from beach bar, braided river and braided-river delta front sediments. In this paper, the paleosedimentary environments of the Huagang Formation are discussed based on detailed organic and inorganic geochemical analysis and proxies used to interpret the sedimentary facies. Kerogen, dominated by sapropelinite, is mainly of Type I and Type II, and n-Paraffins are dominated by short-chain and medium-chain, with no obvious odd-over-even advantages. The distribution of isoprenoid alkanes and steroids indicates that the organic matter in mudstones is mainly of lacustrine and mixed origins. Elemental ratios of Th/U (4–6), V/Cr (1–4), Ni/Co (3–11) and V/(V?+?Ni) (0.5–0.75) indicate that in the area studied, the Huagang Formation was deposited under anoxic to reduced conditions with some oxygen-enriched horizons. Both inorganic and organic geochemical signatures show that the Huagang Formation was mainly deposited in an aquatic environment but with some minor periods of subaerial exposure. The sequence of the Huagang Formation is characterised by interbedded grey-white thick sandstones and grey-black thin mudstones. Normally graded cycles are widely developed, with rare mudstone in the upper part and scoured surfaces at the base. The cumulative grainsize distribution curve is mainly a two-stage type. The sedimentary facies indicative markers are dominated by braided-river channel deposits and combined with the paleosedimentary environments it is inferred that the sedimentary system in the study area was typical of a braided-river delta front. The cores available were intensively analysed using a hand-held X-ray fluorescence spectrometer to probe the variations in the paleoclimate and show that the braided-river channels were controlled by paleoclimate. During arid climatic settings, the sediments within individual channels were thin, and grainsizes varied significantly; at the base of each channel, basal conglomerates were common. In contrast, under humid climatic settings, thin multi-stage channels were superimposed, and the bottom often developed erosion surface.

1. KEY POINTS

2. The paleosedimentary environments are discussed based on detailed organic and inorganic geochemical analysis.

3. The Huagang Formation was deposited in a freshwater lacustrine basin under warm and humid climatic settings.

4. The Huagang Formation is characterised by braided-river delta front facies.

5. The development of braided-river channels was controlled by paleoclimate.

     

层序地层学在东海陆架盆地的应用现状

本文从研究方法的角度,总结了近年来对东海陆架盆地层序地层研究的部分成果。(1)确定和完善了瓯江凹陷和西湖凹陷的层序格架。(2)分析了这两个凹陷中主要油气目的层段的体系域发育情况,即在瓯江凹陷中分析了盆地发育初期(T_6~0～T_5~0)两个层序的体系域发育情况,以及T_5~0～T_3~0中海相层序的体系域发育情况;在西湖凹陷中分析了海陆过渡相层序(T_3~1～T_3~0)和陆相层序(T_3~0～T_2~1)的体系域发育情况。(3)总结了体系域与油气之间存在的关系;指出了非构造圈闭可能存在的位置,为进一步的油勘探提供依据。     

东海西湖凹陷西斜坡和西次凹近致密-致密砂岩气藏的地质特征及发育前景

基于沉积构造背景和大量钻测资料,利用气样地球化学测试、铸体薄片、扫描电镜、激光扫描共聚焦显微镜和阴极发光等手段,揭示了东海西湖凹陷西斜坡和西次凹近致密-致密砂岩气藏的地质特征,并分析了发育前景。研究结果表明:2个靶区近致密-致密砂岩气藏均分布在中深层,且位于常规气藏之下,但发育层位不同,西斜坡在平湖组中下段,西次凹在花港组下段。2个靶区的近致密-致密砂岩气均为煤型气,来源于平湖组煤系源岩,西次凹致密气藏属于"下生上储"型,西斜坡属于"自生自储"型。西次凹属于典型的致密砂岩储层,西斜坡属于近致密砂岩储层。强压实作用和硅质、自生伊利石及碳酸盐胶结是储层致密化的重要因素。溶孔和原生粒间孔是致密砂岩储层主要储集空间;2个靶区的近致密-致密储层不同深度段发育"孔隙型"甜点,为酸性溶蚀成因,但西斜坡的溶蚀强度大于西次凹。另外,西次凹深层发育部分裂缝,形成该区"裂缝型"甜点。西次凹致密气藏具有弱超压特征,西斜坡具有超压-强超压特征。平湖组广覆式分布高有机质丰度的煤系源岩全天候持续供气是靶区发育大规模近致密-致密砂岩气藏的物质基础,大面积近致密-致密储层提供了良好的储集体,因此发育前景好,勘探潜力大。     

东海西湖凹陷春晓构造各井区含油气性特征

春晓构造是近年来东海油气勘探与开发的重点靶区之一，目前开发工作已准备就续。该区现有钻井5口，但测试结果各井差异较大。如何评价其含油气性特征？本文应用测井、地震和试油等资料进行了综合分析，并提出了春晓构造上的另一个有利于油气聚集和保存的区块－－春晓构造南高点断层上盘。