珠江口盆地白云凹陷裂陷期发育文昌组与恩平组2套烃源岩,湖盆沉积演化控制烃源岩的形成.通过三维地震资料及深部钻井分析,认为白云主洼裂陷期发育轴向辫状河三角洲体系、断控扇三角洲体系、北缘缓坡带辫状河三角洲体系以及盆内滨浅湖—中深湖体系.裂陷早期,发育多组NE向断阶且呈现多隆洼的地貌特征,物源主要从东西轴向进入凹陷内,形成多点供源水系,发育多洼成烃;裂陷中期,由于拆离断层的伸展作用,湖盆扩张,北部番禺低隆起被强烈抬升,形成缓坡大规模的三角洲体系及大型湖盆;裂陷晚期,湖盆以拗陷作用为主,受华南物源及由南往北的海侵影响,发育煤型及海侵烃源岩.通过沉积相、地球化学指标可将白云凹陷烃源岩划分为3种类型:文昌组中深湖相Ⅰ—Ⅱ1型烃源岩、文昌组浅湖相Ⅱ2型烃源岩以及恩平组浅湖相Ⅱ2—Ⅲ型烃源岩,不同类型烃源岩生烃潜力有差异,以文昌组中深湖相最优.元素地球化学指标揭示湖盆成烃环境整体表现为淡水—微咸水、还原—强还原的水体环境,而古生物揭示湖盆生油母质为湖相浮游藻类及陆源植物,优质烃源岩有机质来源以浮游藻类为主.总之,白云凹陷拆离断裂活动及沉积体系控制了烃源岩的发育厚度和规模,优质的水体环境控制了优质烃源岩的形成.因此,白云凹陷烃源岩具有厚度大、分布范围广的地质条件,具有大的资源和勘探潜力.

南海北部珠江口盆地恩平凹陷大面积三维地震资料揭示了新近系类型丰富的砂体,在古珠江三角洲演化及相带迁移的控制下形成了较好的岩性圈闭发育条件.近年来,凹陷内发现的多个构造-岩性圈闭均与河道砂体相关.但在已有的层序地层划分方案中,河道砂体的成因、分类和展布特征与体系域的耦合关系差,砂体发育规律不明,制约了岩性圈闭的勘探效果.基于沉积层序理论,利用大范围井震资料,系统厘定了恩平凹陷珠江组一段?韩江组六段的高精度层序地层框架,并在此基础上开展了精细的三维地震沉积学解剖.分析结果显示,目的层发育的大型辫状河道、小型曲流河道和中型曲流河道,分别与低位、海侵和高位等特定体系域具有密切的耦合发育关系,进而建立了层序格架对河道砂体的有效预测模式,系统指明了凹陷不同区域、不同体系域内岩性圈闭的发育潜力及有利区.本文相关认识对其他海相三角洲盆地岩性圈闭勘探具有启示作用.

在前人研究基础上,利用珠江口盆地恩平凹陷与惠州凹陷二维地震资料,结合断层活动速率分析方法,研究了凹陷内部断裂体系几何学与运动学差异性.依据断裂特征及其活动性差异,将珠江口盆地北部断裂体系发育演化重新划分为裂陷早期(E2w)、裂陷晚期(E2e)、拗陷期(E3z-N1z-N1h)和构造活化期(N1y-N2w-Q)4个构造期次.同时,依据断层展布规模、活动速率大小及活化时期等研究成果,推测惠州凹陷比恩平凹陷更有利于形成大中型油气田.建议将近EW向和NWW向断层作为后期构造研究的重点.

珠一坳陷古近纪陆相湖盆发育优质烃源岩,通过对文昌组、恩平组泥岩系统取样,进行常量、微量元素、同位素含量等分析,优选出对环境敏感的元素与元素比值,系统分析了珠一坳陷烃源岩形成时的古环境,包括古盐度、古水深、氧化还原条件、古气候及古水体的封闭性,并建立了有机碳与环境敏感元素比值的定量关系.开展优质烃源岩发育的水化学性质研究,明确研究区优质烃源岩形成演化所具有的古环境特征,最终探讨了文昌组优质烃源岩的发育模式.研究结果表明,珠一坳陷(除韩江凹陷无样本点)文昌期温暖略干气候条件下,湖盆水体主要为淡水—微咸水,发育中—深湖相,整体表现为开放—半封闭、还原—强还原的环境,极利于有机质的保存和优质烃源岩的发育,各凹陷古环境差异不大.烃源岩质量与咸度、水深、还原条件呈正相关,共同影响了优质烃源岩的发育.总之,温暖略干、微咸、深水及强还原、开放—半封闭环境共同控制了珠一坳陷优质烃源岩的发育.

Hundreds of millions of tons of oil and gas geological reserves have been discovered through exploration in the deep-water area of the northern continental margin of the South China Sea, and the distribution of large-scale effective reservoirs during the Paleogene rifting period is the key for continuous discovery in deep-water zone. Large braided fluvio-delta can be observed on seismic data from the Wenchang to Enping formations in the rifting period of the flexural gentle slope belt in the deep-water zone. Due to the absence of wells or few wells, for further understanding of the composition and evolution of large braided fluvio-deltaic sedimentary units in the process of tectonic subsidence in this region, a simulation experiment on the response of the deltaic sedimentation process in the flexural gentle slope zone to flume was carried out. Three phases of tectonic subsidence were designed for the simulation experiment, corresponding to the three phases of Paleogene regional tectonic-sedimentary evolution including balanced rifting period, detached rifting period, and faulted depression rifting period. The hydrodynamic mechanism of tractive flow was simulated by means of flood, flat water, and dry water. Simulation results showed that during the three stages of tectonic subsidence, the flexural gentle slope zone deve-loped distributary channels, natural dikes, floodplains, underwater distributary channels, estuaries, inter-tributary bays and other delta sedimentary microfacies units. The braided river delta was dominated by lateral proliferation, supplemented by vertical accretion, and the sedimentary center gradually migrated to the center of the depression, with almost no degeneration. The delta shape and sand body distribution in the flexural gentle slope zone during the rifting period were mainly controlled by factors such as structural geomorphology, river discharge amount into lake, lake level changes, and water depth.

珠江口盆地恩平凹陷中浅层近年来相继有商业油气发现,虽目前仍然以构造圈闭为主,但古珠江三角洲相关岩性目标的评价亟待展开.基于高品质井、震资料,本次研究以恩平凹陷中新统珠江组上段?韩江组下段(T50?T35)为主要目的层,以三级层序界面和最大海泛面为界,建立了恩平凹陷T50?T35间的四级层序格架.在高精度层序地层格架的约束下,进一步采用地震沉积学手段揭示了恩平凹陷以分流河道为主的沉积特征,并建立了不同海平面背景下的河道沉积模式:海侵早期和高位末期河道规模较大,延伸距离较远,平面上常连片发育;海侵晚期和高位早期的河道规模适中,平面上孤立性较强,且前缘常被波浪改造.研究发现,不同类型的河道砂体与特定的构造背景结合可发育"河道切割型"岩性圈闭,并且最大海泛面上下更适合于相关圈闭的发育.据此,研究锁定了恩平A油田西侧斜坡带、E油田东侧斜坡带和G油田西侧披覆构造带等3个岩性圈闭有利区及2个有利勘探目标,为盆地岩性油气藏勘探提供了新思路.

珠江口盆地西江凹陷南部包括两个相邻洼陷:西江36洼和番禺4洼,钻探结果却揭示了截然不同的油气勘探前景,其中,番禺4洼探明储量已过亿吨,而西江36洼却未有商业发现,导致勘探上对西江36洼烃源潜力有所顾虑.为了揭示这种差异油气地质条件产生的原因,亟待开展两个洼陷的对比研究.以主要烃源层系文昌组为切入点,通过开展精细的层序-沉积研究,进一步系统评估西江36洼烃源潜力.依据地震、钻井及分析化验等资料,在西江36洼与番禺4洼文昌组共识别了6个三级层序.西江36洼和番禺4洼文昌组发育扇三角洲、辫状河三角洲、湖底扇及湖泊沉积等沉积相类型,垂向上沉积相带具有旋回特征.伴随裂陷不同阶段和边界断层活动差异,陡坡带和缓坡带三角洲沉积体系规模呈现差异演化特征,而湖盆和半深湖-深湖相规模总体呈现出先增大后减小的规律.沉积相带在横向上也具有明显的迁移特征,表现为文六段时期先在西江36洼开始沉积,文五段开始再扩展到番禺4洼,同时文一段时期西江36洼湖盆已经消失,只在番禺4洼沉积充填.进一步对比两个洼陷各三级层序反映优质烃源岩条件的半深湖-深湖规模及物源供给量,结果显示在文六段至文四段时期两个洼陷烃源条件基本一致.鉴于该层段作为番禺4洼的主力源岩,其巨大的生烃潜力已经被勘探所证实,因此认为不能低估具有相似烃源条件的西江36洼生烃潜力.

为了弄清珠江口盆地西江主洼南部缓坡转换带文昌组和恩平组地层的沉积样式及其发育规律,通过钻井、测井、地震、岩芯和分析化验等资料,从岩性、层理构造、结构特征及地球物理特征等方面总结两种缓坡转换带沉积体系的特征,并剖析研究区断裂特征.研究认为,文昌期(T80-Tg)主要发育NE和NW向控洼大断裂,分布于盆地边缘,断裂组合形态以平行状、阶梯状及斜交状为主;恩平期(T70-T80)主要发育NE向、EW向和SE向断裂,分布于盆地中央,断裂组合形态以同向、反向及斜交状为主;虽然同属缓坡带,但文昌组地形较恩平组陡,湖盆较深,发育辫状河三角洲;恩平组地形宽缓,发育浅水三角洲,湖盆中央断裂的活动及季节性洪水的发生,使得浅水三角洲水下分支河道极为发育.两种不同类型的三角洲具有不同的岩性组合特征:文昌组辫状河三角洲砂岩粒度粗且厚,泥岩层薄,恩平组浅水三角洲砂岩粒度粗且薄,泥岩层厚,含煤,均为有利油气勘探区域.

壳幔拆离断裂活动与沉积体系响应为世界陆缘演变研究的热点,选取珠江口盆地白云凹陷壳幔拆离体系及其沉积响应开展系统性解剖.结合陆缘演变认识新进展、长电缆三维地震和钻井综合解释等揭示白云凹陷南部主控断裂带主要由4排NEE-NE向断至莫霍面的高角度铲式壳幔拆离断裂组成,裂陷期幕式活动使得白云凹陷经历了均一裂陷、拆离裂陷和断拗转换三阶段演化;均一裂陷期(下文昌组),控洼断裂未延伸至莫霍面,主要发育断裂转换带控制下的轴向陡坡辫状河三角洲/湖相沉积体系,缓坡物源体系不甚发育;拆离裂陷期(上文昌组),壳幔拆离断裂断至莫霍面,呈现强烈水平伸展和垂向落差,导致上盘远离断层一侧强烈旋转翘倾、抬升剥蚀成为最主要缓坡物源体系,靠近断层北侧沉降深陷成为深湖盆,上盘中段发育大型三角洲沉积;断拗转换期(恩平组),拆离作用减弱而沉降作用显著增强,控制了北部缓坡挠曲坡折和NW-SE向推进的大型三角洲/湖相沉积体系的发育.由此,主控断裂由均一伸展到壳幔拆离伸展的构造演变导致白云凹陷上文昌组至恩平组缓坡大型三角洲、下文昌组东西轴向转换带辫状河三角洲和洼陷周边陡坡带扇三角洲砂岩三类规模储集体与湖相泥岩满盆叠置的分布格局,使其成为深水勘探向中深层拓展的主要对象.

大型海相三角洲分布范围广,沉积动力复杂,其精细层序—沉积构型和演化规律是沉积学领域长期研究的热点.综合岩矿、测井和三维地震资料,充分结合高精度层序地层学和三维地震沉积学分析方法,对古珠江三角洲西侧的恩平地区中新世早-中期沉积特征进行了精细研究,识别出了辫状河道、曲流河道等河控三角洲的主要微相单元,同时也揭示出海岸砂脊等浪控三角洲中发育的典型微相类型.在高精度层序格架约束下,揭示出单一典型层序内古珠江三角洲的演化特征:低位体系域以河控三角洲为主,发育大型交切状辫状水道;海侵和高位体系域河道规模明显减小,以小规模曲流河道为主,且易于见到海岸砂脊等波浪作用的典型特征.此外,针对恩平地区中新世早-中期沉积相带的系统编图和演化分析,在大约6Ma时间内识别出6次河道大规模改道现象,推测恩平地区沉积演化明显受到自旋回沉积过程的影响.

Rift-related normal faults generally have various geometries, and cause the syn-rift stratigraphy in their hanging wall to be characterized by different infilling patterns. Our understanding of the tectonic control on the syn-rift stratigraphy mainly stems from the analysis of fault kinematics, stratigraphic styles and depositional facies. However, questions remain about how fault geometry, kinematics and slip rate influence the style of a rift-related half-graben and the syn-rift stratigraphy, and what enlightenment that relationship has for the hydrocarbon exploration in rifts. Using the 2D MOVE Software, this study attempts to simulate the development of a fault-bounded half-graben, with the aim of investigating the aforementioned questions. The modeling results show that, a planar, listric and ramp-flat-ramp border fault controls a tabular, wedged-shaped, and composite wedge-shaped growth package, respectively, but exceptionally, the planar fault bounds a wedge-shaped package if the fault rotates with movement. In addition, rollover structure forms when the border fault has a listric or ramp-flat-ramp shape, indicating that the fault geometry and kinematics dominate the syn-tectonic stratigraphic pattern. Besides, fault slip rate relative to sediment supply affects the scale, dip and infilling pattern of the syn-tectonic stratigraphy. In details, reduction of fault slip rate or increment of sediment supply results in: i) the extent of the syn-tectonic stratigraphy enlarging, ii) the dip angle of the syn-tectonic stratigraphy decreasing, and iii) the water depth in the related half-graben getting shallower. This study provides insights into understanding the origin of the variable styles of rift-related half-graben and syn-rift stratigraphy. Also, our modeling results have an important implication for evaluating source rock quality in rifts. Finally, we give a preliminary example of using the MOVE Software to investigate the geometry and evolution of fault-bounded basin, which is well worth being further explored.

During the Miocene, when the Zhujiang Formation was deposited, the eastern part of the Pearl River Mouth Basin, northern South China Sea, underwent intense mixed siliciclastic and carbonate sedimentation, particularly on the platform of the marginal ramp of the Dongsha Rise, northeastern margin of the South China Sea. Cores and well logs from industrial boreholes were collected and systematically investigated to reveal the sedimentary-petrographic characteristics of the mixed deposits and their formative processes. Four lithotypes were differentiated in the deposits, that is, (1) sandstone, (2) dolomitic sandstone and calcitic sandstone, (3) sandy dolomite and sandy limestone, and (4) dolomite, bioclastic limestone, and micrite limestone, which were formed by three major types of mixing processes: punctuated, facies, and in situ mixing processes. The porosity and permeability of the mixed deposits indicated that the siliciclastic component of the mixed deposits that experienced punctuated mixing formed the most high-quality hydrocarbon reservoirs. Exploration revealed that the lithologic reserves in the study area were mainly developed in mixed sedimentation areas. Our results suggest that the mixed sedimentation area, particularly with pure sandstone sedimentation or bioclastic sandstone, that underwent compaction or structural fracture activities, may be the next preference for lithologic exploration.

珠江口盆地番禺4洼"小而肥",目前的探明石油地质储量已超出早期估算的地质资源量,早期对烃源岩的认识不足可能是其主要原因,尤其是对优质烃源岩的分布范围仍缺少精确刻画,在很大程度上限制了对该洼陷勘探潜力的认知.以该难点问题为切入点,利用最新钻井和地震资料,采取层序地层学开展了番禺4洼烃源岩的预测工作.通过地震资料上识别的各种反射特征,结合区内已有钻井资料识别的旋回特征,将番禺4洼文昌组划分5个三级层序,进而建立了等时地层格架.在此基础上,综合运用地震沉积学最新技术手段,精细揭示了番禺4洼文昌组文三段优质烃源岩的分布范围.研究结果表明,番禺4洼优质烃源岩分布面积较为广泛,尤其在北次洼和西次洼,优质源岩面积均超过了以往预期.这一研究成果对本区和珠江口盆地油气勘探具有一定指导意义.

The sequence stratigraphic architecture change is mainly controlled by three factors: basement subsidence or uplift, sea level change and sediment supply. However, the internal mechanism of the influence of the sediment supply on the sequence stratigraphic architecture change is not clear. In this paper, the Middle-Upper Miocene sequences in Kaiping Sag, northern South China Sea are taken as an example to discuss this issue. First, we divide and correlate the sequence through the comprehensive analysis of drilling and seismic data, and restore the seven seismic sequences in the study interval to their original form of sedimentary stage through the original form structural section restoration technique. Then, based on the original form structural section, the vertical changes of sequence stratigraphic architecture are recognized and the basement subsidence rate and sediment supply rate are estimated. Furthermore, through the correlation analysis between the sediment supply rate and the sequence stratigraphic architecture change, how the sediment supply rate affects the sequence stratigraphic architecture changes is recognized. The results show that the stratigraphic frameworks of the seven sequences are all LST-TST-HST-FRST combination, but the scale of systems tracts of each sequence varies greatly, which is quite different from the sequence stratigraphic architecture of the adjacent Baiyun Sag. The second-order cycle sea level change, basement subsidence, regional tectonic uplift and special paleogeographic environment (Kaiping Sag is located in the lateral edge of the trough zone) in the study area jointly lead to the variation of sediment supply rate in time and space, and this variable sediment supply rate is the main driving force for the change of sequence stratigraphic architecture in Kaiping Sag.

Reactivation of pre-existing structures and their influence on subsequent rift evolution have been extensively analysed in previous research on rifts that experienced multiple phases of rifting, where pre-existing structures were deemed to affect nucleation, density, strike orientation, and displacement of newly formed normal faults during later rifting stages. However, previous studies paid less attention to the extensional structures superimposing onto an earlier compressional background, leading to a lack of understanding of, e.g. the reactivation and growth pattern of pre-existing thrust faults as low-angle normal faults and the impact of preexisting thrust faults on newly formed high-angle faults and subsequent rift structures. This study investigating the spatial relationship between intra-basement thrust and rift-related faults in the Enping sag, in the northern South China Sea, indicates that the rift system is built on the previously deformed basement with pervasive thrusting structures and that the low-angle major fault of the study area results from reactivation of intra-basement thrust faults. It also implies that the reactivation mode of basement thrust faults is dependent on the overall strain distribution across rifts, the scale of basement thrust faults, and the strain shadow zone. In addition, reactivated basement thrust faults influence the nucleation, dip, and displacement of nearby new faults, causing them to nucleate at or merge into downwards it, which is representative of the coupled and decoupled growth models of reactivated thrust faults and nearby new faults. This work not only provides insights into the growth pattern of rift-related faults interacting with reactivated low-angle faults but also has broader implications for how basement thrust faults influence rift structures, normal fault evolution, and syn-rift stratigraphy.