【作者】 蔡佳；

【导师】 王华；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2009， 博士

【摘要】 琼东南盆地是南海北部边缘盆地的一个重要含油气区，是我国大型近海富油气盆地之一，总面积4．5×10~4km~2。截至2008年，琼东南盆地油气资源量估算为3．5万亿m~3天然气，三级储量为0．22万亿m~3。已发现资源量占盆地总量的15．38%，未发现则为84．62%，勘探程度低，剩余资源量多，勘探潜力大，具备大型油气田发育的基本石油地质条件，正处于勘探突破准备期，显现出巨大的发展潜力。琼东南盆地处于欧亚板块、印支板块和太平洋板块的交汇处(欧亚板块东南边缘的南海北部大陆架)，属滨太平洋构造域。可进一步划分为北部坳陷带、北部隆起带、中央坳陷带和南部隆起带，盆地中有12个次级凹陷，整体具有南北分带、东西分块的特征。琼东南盆地经过五十二年的勘探工作，在崖城凸起等地区均发现了重要的油气藏(以气藏为主)。浅水区资源的探明程度不断增高，这意味着既有继续发展的余地又隐伏着颠峰过后的危机。从勘探上，深水区应该是重要突破口，但深水区复杂的地质条件，高温超压的恶劣环境，储层预测的困难是摆在勘探人员面前的三大艰巨任务。资源探明率的不断提高，发现大型整装油气田的难度不断加大，单纯的构造圈闭勘探已经不能满足油田工业生产的需要，急需加强本区层序地层学方面的研究，尤其是从层序地层学角度引入隐蔽油气藏勘探思路显得尤为重要，用隐蔽油气藏勘探思路来指导琼东南盆地的油气勘探工作。在当前能否在琼东南盆地获得重要突破的关键是技术上的突破与研究思路上的创新。从理论研究上来说，层序发育的控制因素一直是层序地层学研究中的重点和难点。古地貌和沉降史不同配置关系可以影响到层序的构成和沉积体系分布。在琼东南盆地这样一个重要的富油气凹陷开展层序地层、沉积体系以及控制因素方面的综合研究，对琼东南盆地隐蔽油气藏勘探有着重要的理论价值和实际意义。本文以地震、测井、岩芯等资料为基础，对琼东南盆地古近系系统的开展层序地层学研究，主要内容摘要如下：1．琼东南盆地古近系发育时期是琼东南盆地的断陷活动强烈期，盆地的隆凹格局由于构造活动的强烈影响发生了巨大的变化。根据凹陷内断裂展布特征和对构造区划的影响作用，琼东南盆地被分成四带十凹，分别是四带(北部坳陷带、北部隆起带、中央坳陷带和南部隆起带)、十凹(崖南凹陷、崖北凹陷、松西凹陷、松东凹陷、乐东凹陷、陵水凹陷、松南凹陷、宝岛凹陷、长昌凹陷、北礁凹陷)。2．琼东南盆地古近系层序界面的识别依据比较典型的削截、上超、下超和顶超等地震层序界面识别标志和测井曲线上的基值明显突变的特征，将琼东南盆地古近系划分为7个二级层序(SQEsx、SQEyc3、SQEyc2、SQEyc1、SQEls3、SQEls2、SQEls1)；体系域划分则依据地震反射可以识别出下切谷、低位扇体以及低位前积、湖扩退积、高位前积等结构特征。在重点层段的三级层序内相应划分出3个体系域：低位体系域(LST)、湖扩体系域(EST)和高位体系域(HST)。3．根据录井资料和岩芯观察的分析，同时结合地震资料的分析，在琼东南盆地古近系可识别出：冲积扇体系、扇三角洲体系、(湖泊)三角洲体系、海岸平原体系、滨海体系和(半封闭)浅海体系等沉积体系类型。地震相分析可以通过刻画地震剖面上地震反射同相轴的前积、上超和下超等反射波的终止特征来识别出扇三角洲体系、湖泊三角洲体系、滨海体系和(半封闭)浅海体系的砂质碎屑堆积体。4．琼东南盆地古近系在体系域级别上，沉积体系具有如下时空演化特征：(1)时间上，从始新统到陵水组总体为一大的海进过程，主体表现为盆缘和盆内古隆起区逐渐被淹没，低水位断坡带控制的深凹陷区(浅海深水区)分布范围明显扩大，水深加深，各凹陷的水体连通性变好。同时，随着主体海进作用的增强，由始新统的陆相、崖城组的海湾-局限海(崖三段)、局限海(崖二、崖一段)，逐渐过渡到滨海平原受潮汐影响(陵三段)的开阔海及潮控的开阔海(陵二、陵一段)，其碎屑体系的时空展布也受到此影响。(2)空间上，主物源(即盆缘主水系)在古近系具继承性，尤其是西北端崖13-1区注入于崖南凹陷的扇三角洲和东北端注入松东凹陷的三角洲或扇三角洲，及盆地的东南部从南向北注入到宝岛凹陷和沿同样方向注入到北礁凹陷的盆缘扇三角洲，在陵水组和崖城组各层序发育时，均具有相对的稳定性；而盆内孤立古隆起区向周缘凹陷注入的碎屑体则具多变性，碎屑沉积体位置和规模也随时、空变化而变化，尤其是低位扇体的随时、空的变化更为明显。5．琼东南盆地发育三种不同的典型层序构成样式：(1)琼东南盆地中各个单断式凹陷(崖南凹陷、松西凹陷、松东凹陷、北礁凹陷等)的斜坡部位是具缓坡坡折带的典型代表，发育缓坡坡折型层序样式。该类型层序样式与经典层序地层学Ⅰ型层序具有类似的结构特征。坡折带至向凹陷中心的平坦湖底区，低位体系域斜坡扇、盆底扇、低位楔发育，储层砂体在该部位的局部富集造就了岩性油藏的有利发育；坡折带以上的平台区发育少量的下切谷充填和较薄的湖扩体系域、高位体系域沉积。(2)5号断层、2号断层、3号断层等下降盘为断控陡坡背景，发育断控陡坡带型层序样式。低水位时期发育大型的扇三角洲、水下扇体系及其远端进一步向凹陷中心搬运沉积的盆底扇；高水位时期发育相对规模较小的扇三角洲、水下扇体系，局部不发育扇三角洲、水下扇，反映物源供给缺乏或未抵达凹陷区。总体上，整个层序构成前积一退积一前积的旋回性特征。(3)2号断裂带下降盘、长昌凹陷边缘的断层系下降盘等呈多级断阶背景，发育断阶带型层序样式。上部断层往往成为低位体系域分布的边界，向凹陷深处的断坪上发育低位扇、低位楔沉积是该背景下低位体系域的特点。高位体系域的分布不受断层控制，表现为向盆地边缘斜坡减薄、顶部削截。6．琼东南盆地古近系沉积时的古地貌特征体现出南北分带、东西分块的构造特征。沉积范围逐步扩大，地形逐步平缓，隆、凹的差异性逐渐减弱，由东西分块演化为南北分带，物源由南北及凹陷中的凸起提供演变为南北供源，凸起物源消失。琼东南盆地的沉降特征与古地貌的隆凹格局相对应。琼东南各沉积期沉降中心是不断变化和迁移的，沉降速率也随构造活动程度的变化而发生变化。中央凹陷带为沉降第一梯队，北部凹陷带为沉降的第二梯队，边缘有三大非沉降区。上述的沉降速率高值区和古地貌中的沟谷发育区在地理位置有很高的吻合度。7．古地貌和沉降速率二者的配置关系会形成不同的层序构成和沉积体系。对沉积体系展布的控制表现为：当断陷活动起主要控制作用时，盆地周围的三大物源和盆地凸起物源都是盆地内沉积砂体的主要营建力量。2号断裂带、长昌凹陷边界断阶带的多级断阶作用明显，形成了断阶式层序构成模式，低位体系域和高位体系域均发育三角洲体系或扇三角洲体系，断阶带上形成的多级输送渠道导致凹陷深处断坪上发育重力流扇体。与此同时，3号、5号、11号断裂等控制凹陷陡坡的沉积，这些地区发育断控陡坡带；各个凹陷的缓坡发育坡折带。此时断控陡坡带低位体系域都比较发育，是砂体主要集中部位，而缓坡砂体不太发育。由于凹陷边缘的古地貌影响，低位域内主要发育低位三角洲，其远端进一步向凹陷中心搬运沉积的盆底扇，砂体富集，是岩性圈闭勘探的重点区域。高位体系域发育高位三角洲。随着断陷活动的减弱，断层的控制作用逐步减弱，加上陵水组时期的海侵，使得凸起物源消失，盆地呈现出南北物源为主的局面，多级断阶的控砂作用开始减弱，断控陡坡带和坡折带的坡度也开始变缓。在琼东南盆地高速沉积充填期，盆内的古地貌和沉降速率是控制层序构成和沉积样式的主要控制因素。物源体系决定三级层序和沉积体系发育的位置，古地貌和沉降速率决定三级层序和沉积体系的展布特征，三者的结合决定层序样式和沉积类型。本论文的创新性主要体现在：1．在琼东南全区建立古近系的层序地层格架，首次在全区识别并闭合界面T71、T72，将崖城组划分为三个三级层序，对盆地重要烃源岩始新统和崖城组储层的分布有重要的意义。2．首次系统开展琼东南盆地古近系同沉积期古地貌、沉降特征以及层序和沉积响应关系的耦合分析，建立古地貌控制下的层序发育样式及沉积特征。更多还原

【Abstract】 Qiongdongnan Basin is an important hydrocarbon bearing area in the northern margin basinof the South Sea.It is one of the large nearshore hydrocarbon-rich basins in China,with a totalsquare of 4.5×10~4km~2.Up to 2008,the hydrocarbon estimation of Qiongdongnan Basin is about3.5 billion m~3 volume of natural gas,and 0.22 billion m~3 volume of third-order reserves.Thediscovered resources amount is up to 15.38% of the total in the basin,and the undiscovered isabout 84.62%.The basin is of low exploration degree,huge surplus resources,and largeexploration potential.It is provided with the basic petroleum geological conditions fordeveloping a large oil-gas field,which is in the phase of preparation for exploration breakthroughand shows a great development potential.Qiongdongnan Basin is located in the intersection place of Eurasian plate,Indochina plate,and Pacific plate (the northern continental shelf of the South Sea in the northeast margin ofEurasian plate),belongs to Pacific tectonic domain.It can be divided into northern depressionzone,northern uplift zone,central depression zone,and southern uplift zone.There are 12secondary sub-sags in the basin,with the characteristics of“zones distributed along north-southand blocks distributed along east-west”.During 52 years of exploration work in Qiongdongnan Basin,important reservoirs (mainlygas reservoirs) have been found in Yacheng uplift and et al.The proven degree of resources inshallow area has been increasing,which indicates a margin for development and also a crisis afterprosperity.In exploration,the deep area should be a key point to break through.But thecomplicated geological conditions in deep sea,high geothermal and overpressure,difficulties inreservoir prediction are the three hard problems that need to be solved.The proven rate ofresources is increasing;the difficulty of discovering large and intact reservoirs is getting bigger;the exploration of single tectonic trap can no more meet the needs of the industrial production ofthe oilfields.We are in dire need of strengthen the study on sequence stratigraphy in this area,especially bring in the thought of seeking subtle reservoirs from sequence stratigraphic point anduse it to guide the hydrocarbon exploration work in Qiongdongnan Basin.At present,the keyfactor that whether can get a breakthrough or not in Qiongdongnan Basin is the breakthrough intechnology and innovation in research thoughts. From the point of theoretical study,the control factors of sequence development havealways been the emphasis and the difficulty in sequence stratigraphy study.Different allocationrelations between paleo-morphology and subsidence history can affect the sequence architectureand distribution of sedimentary system.In an important hydrocarbon-rich basin such as Qiongdongnan Basin,to develop thecomprehensive study on sequence stratigraphy,sedimentary system,and controlling factors,it isof great theoretical value and practical meaning for the subtle reservoirs exploration inQiongdongnan Basin.Based on seismic,logging,borehole data,etc.,sequence stratigraphy of the paleogenesystem in Qiongdongnan Basin has been studied in this paper.Following are the Abstract:1、The fault depression activities more in the stage of Paleogene system in QiongdongnanBasin,and the uplift-sag pattern had a huge changes because of the enormous influence of thetectonic activities.Based on the faults distribution and influence on structure district,Qiongdongnan Basin can be divided into“four belts and ten sags”:North depression belt,Northuplift belt,Zhongyang depression belt,South uplift belt,Yanan sag,Yabei sag,Songxi sag,Songdong sag,Ledong sag,Lingshui sag,Songnan sag,Baodao sag,Changchang sag,andBeijiao sag.2、Seven third-order sequences (SQEsx、SQEyc3、SQEyc2、SQEyc1、SQEls3、SQEls2、SQElsl ) are identified in Paleogene system of Qiongdongnan Basin based on the typicaltruncation,onlap,downlap toplap and the features of well-logging.Based on the seismicreflection,the incised valleys,low-stand fans,low-stand progradation,lake expandingretrogradation and high-stand progradation can be identified.For each third-order sequence of thekey formations,it can be divided into three systems tracts:low-stand systems tracts (LST),lakeexpanding systems tracts (EST) and high-stand systems tracts (HST).3、According to the observation of rock core,analysis of mud well -logging,and associatedwith the analysis of seismic data,alluvial systems,fan delta depositional systems,(lacustrine)delta depositional systems,coastal plain systems,coastal systems and (semi enclosed) submarinesystems are identified in Paleogene system of Qiongdongnan Basin.The analysis of seismicfacies which is based on the reflection abeyance pattern (such as progradation,onlap anddownlap ) can identify the fan delta depositional systems,lacustrine delta depositional systems,coastal systems and (semi enclosed) submarine systems.4、The evolution characteristics of depositional systems of Paleocene of Qingdongnan basinas follows::(1) in temporal,there is a huge transgression process from Eocene to lingshuiformation,it presents the basin margin and ancient uplift of basin are submerged gradually.Meanwhile,with the enhance of mainly transgression effect,it gradually transition fromcontinental of Eocene,bay-restricted sea of Yacheng formation (Ya-3 section),restricted sea ofYacheng formation (Ya-2,Ya-1 section) to open sea of coastal plain which is effected by tide(ling-3 section) and tide-controlling open sea (ling-2,ling-1 section),the time area distribution ofclastic system is also influenced.(2) in spatial,the main source (main water system of basinmargin) have inheritance at Paleocene,especially fan delta injected Yanan depression from YA 13-1 Structure on the northwest,fandelta of basin margin inject Beijiao depression fromnortheast,fan delta of basin margin inject Baodao depression and Beijiao depression from southto north on the northeast of basin.They all have relative stability when every sequences ofLingshui formation and Yacheng formation developing.Isolated ancient uplift inject clastic toperiphery depression with changefulness.The location and scale changed with the change oftemporal,especially low-stand fan.5、Three typical tectonic backgrounds develop in Qiongdongnan basin.(1) Slope position ofevery mono-faulted depression in Qiongdongnan basin (Yanan depression,Songxi depression,Songdong depression,Beijiao depression etc.) is typical representative with gentle slope break,itdevelops gentle slope break sequence style.This style has similar structure characters with classsequence stratigraphy sequence I.Typical low-stand bodies like slope fan and low-stand wedgedevelop in this place,which is from slope break to the center of lake.This area also is thefavorable exploration area of lithological reservoir.The platform that is on the slope breakdevelops small incised valley,thin expansion system tract and high-stant system tract.(2) Thethrown side of No.5 fault,No.2 fault,No.3 fault is steep slope controlled by fault,developsequence architecture with steep slope controlled by fault.Large fan delta,underwater fan andbasin floor fan formed by transportion of distal underwater fan develop in low-stand systemstracts.Fan delta and underwater fan systems with a small extent develop in high-stand systemstracts,fan delta and underwater fan develop slightly in local area,which reflect the scarceprovenance or the provenance can’t reach the sag.In general,the sequence architecture is withthe cyclicity of progradation-retrogradation- progradation.(3) The thrown side of No.2 fault andthrown side of Changchang depression margin take on multi- fault-terrace,develop fault-terracebelts sequence architecture.The upper fault always be boundary of the low stand system tractdistributing.It develops low-stand fan and low stand wedge on flat of depths of depression.Thedistribution of high stand system tract does not controlled by fault,it represent slope thinning andtop truncation to basin margin.6.Before the Paleogene of Qiongdongnan Basin deposited,the palaeo-geomorphology tookon a structure characteristic which is north-south zoning distribution and west-east divisibleblock.The range of Deposition progressively expanded,terrain gradually gentled,and thedifference between uplift and depression gradually weakened.The evolution was from west-eastzoning distribution to north-south.It was that sediment source provided by the North and theSouth and uplift in the Depression evolved into provided by the the North and the South,and thesediment source of uplift disappeared.And the subsidence characteristic of Qiongdongnan Basin was matched with itspalaeo-geomorphology structure characteristic.the center of subsidence was changing andtransferring during each depositional stage,and the rate of settlement changed with the degree oftectonic activity.the central of the depression zone is the first echelon of settlement,and thenorthern part of the depression zone is the second echelon the settlement,and there are threenon-settlement areas on the edge.The above high-rates of subsidence areas are highly coincidedwith the areas where the gully developed in the geographical position. 7.The different configuration relationship of the palaeo-geomorphology and the rate ofsettlement would produce different patterns of sequence and different sedimentary systems.Thecontrol to the sedimentary systems’ distribution represents that:When fault depression exercisesthe primary control function,three big provenance around the basin and the bulge provenancebuild the great strength in the deposition of sand body in the basin.The many stages of the faultterrace effects of the second fault zone and the boundary fault terrace of the Changchangdepression are obvious,and form broken stage wise sequence structure model.Both of the lowstand system tract and the high stand system tract develop delta system and fan delta system.Themany stages transportation channels of the step-fault zone cause the development of the gravityflow fan body in the fault flat in the deep place of the depression.Meanwhile the third、the fifthand the eleven fault control the deposition of the steep slope of the depression.These areasdevelop break controlling steep slope zone.The gentle slopes of each depression develop slopebreak.The low stand system tract of break controlling steep slope zones is quite growth,which isthe main centralized spot of the sand body.But the gentle slope sand body is not well developed.Because of the influence of the ancient landform of the depression edge,the low stand systemtract mainly develop low stand delta,the distal of which form basin floor fan.The sand body isenrichment in the low stand system tract where is the mainly prospecting area.the high standsystem tract mainly develop high stand delta.As the fault activities decreased,the control effectof fault gradually decreased.With the transgression of Lingshui Group,the provenance of salientdisappeared.The basin presented that the north and south provenance dominated.The controleffect of fault terrace decreased.The slope of the break controlled steep slope and the slope breakbegin to slow.The palaeo-geomorphology and the rate of settlement were the main controlling factorswhich controlled the patterns of sequence and the pattern of sedimentation when the high-ratefilled activities happened in the QiongDongnan basin.Firstly,the provenance system controlledthe position of third-order sequences and sedimentary system,while the palaeo-geomorphologyand the rate of settlement controlled the distribution of third-order sequences and sedimentarysystem,and the interaction amont the three controlled the types of sequence and sedimentation.Innovations of the thesis are as follows:1.Build the sequence stratigraphic framework in the whole Qiongdongnan area.For the firsttime identify and close boundaries T71,T72,and divide Yacheng Formation into three third-ordersequence.2.For the first time,systematically analyze syn-depositional paleo-morphology,subsidencecharacteristics,response coupling relations between sequence and sedimentary of the paleogenein Qiongdongnan Basin,and build sequence developing architecture and sedimentarycharacteristics under the control ofpaleomorphology.更多还原