Discovery and inspiration of large-and medium-sized glutenite-rich oil and gas fields in the eastern South China Sea:An example from Paleogene Enping Formation in Huizhou 26 subsag,Pearl River Mouth Basin

Based on the practice of oil and gas exploration in the Huizhou Sag of the Pearl River Mouth Basin,the geochemical indexes of source rocks were measured,the reservoir development morphology was restored,the rocks and minerals were characterized microscopically,the measured trap sealing indexes were compared,the biomarker compounds of crude oil were extracted,the genesis of condensate gas was identified,and the reservoir-forming conditions were examined.On this basis,the Paleogene Enping Formation in the Huizhou 26 subsag was systematically analyzed for the potential of oil and gas resources,the development characteristics of large-scale high-quality conglomerate reservoirs,the trapping effectiveness of faults,the hydrocarbon migration and accumulation model,and the formation conditions and exploration targets of large-and medium-sized glutenite-rich oil and gas fields.The research results were obtained in four aspects.First,the Paleogene Wenchang Formation in the Huizhou 26 subsag develops extensive and thick high-quality source rocks of semi-deep to deep lacustrine subfacies,which have typical hydrocarbon expulsion characteristics of"great oil generation in the early stage and huge gas expulsion in the late stage",providing a sufficient material basis for hydrocarbon accumulation in the Enping Formation.Second,under the joint control of the steep slope zone and transition zone of the fault within the sag,the large-scale near-source glutenite reservoirs are highly heterogeneous,with the development scale dominated hierarchically by three factors(favorable facies zone,particle component,and microfracture).The(subaqueous)distributary channels near the fault system,with equal grains,a low mud content(<5%),and a high content of feldspar composition,are conducive to the development of sweet spot reservoirs.Third,the strike-slip pressurization trap covered by stable lake flooding mudstone is a necessary condition for oil and gas preservation,and the NE and nearly EW faults obliquely to the principal stress have the best control on traps.Fourth,the spatiotemporal configuration of high-quality source rocks,fault transport/sealing,and glutenite reservoirs controls the degree of hydrocarbon enrichment.From top to bottom,three hydrocarbon accumulation units,i.e.low-fill zone,transition zone,and high-fill zone,are recognized.The main area of the channel in the nearly pressurized source-connecting fault zone is favorable for large-scale hydrocarbon enrichment.The research results suggest a new direction for the exploration of large-scale glutenite-rich reservoirs in the Enping Formation of the Pearl River Mouth Basin,and present a major breakthrough in oil and gas exploration.

Coupling relationship and genetic mechanisms of shelf-edge delta and deep-water fan source-to-sink:A case study in Paleogene Zhuhai Formation in south subsag of Baiyun Sag,Pearl River Mouth Basin,China

The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration.Based on the newly acquired high-resolution 3D seismic,logging and core data of Pearl River Mouth Basin(PRMB),this paper dissected the shelf-edge delta to deep-water fan(SEDDF)depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag,and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms.The results show that during the deposition of the fourth to first members of the Zhuhai Formation,the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing,with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member.Based on the development of SEDDF depositional system along the source direction,three types of coupling relationships are divided,namely,deltas that are linked downdip to fans,deltas that lack downdip fans and fans that lack updip coeval deltas,with different depositional characteristics and genetic mechanisms.(1)Deltas that are linked downdip to fans:with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area,and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink(S2S).The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level.(2)Deltas that lack downdip fans:with the development of shelf edge deltas in shelf area,while deep water fans are not developed in the downdip slope area.The lack of“sources”and“channels”,and fluid transformation are the three main reasons for the formation of this type of S2S system.(3)Fans that lack updip coeval deltas:with the development of deep-water fans in continental slope area and the absence of updip coeval shelf edge deltas,which is jointly controlled by the coupling of fluid transformation at the shelf edge and the“channels”in the continental slope area.

Deep-water Depositional Features of Miocene Zhujiang Formation in Baiyun Sag,Pearl River Mouth Basin

Eleven lithofacies and five lithofacies associations were indentified in the Miocene Zhujiang Formation on the basis of detailed core analysis. It could he determined that three depositional types developed, namely submarine fan, basin and deep-water traction current. Six microfacies were further recognized within the fan, including main channels in the inner fan, distributary channels in the middle fan, inter-channels, levees and the outer fan. The lower Zhujiang Formation, mainly sandstone associations, was inner fan and inner-middle fan deposits of the basin fan and the slope fan. The middle part, mainly mudstone associations, was outer fan deposits. With the transgression, the submarine fan was finally replaced by the basinal pelagic deposits which were dominated by mudstone associations, siltstone associations, and deep-water limestone associations. During the weak gravity flow activity, the lower channels, the middle-upper outer fans and basin deposits were strongly modified by the deep-water traction current. The identification of the deep-water traction deposition in Miocene Zhujiang Formation would be of great importance. It could be inferred that the deep- water traction current had been existing after the shelf-break formation since the Late Oligocene （23.8 Ma） in the Baiyun sag, influencing and controlling the sediment composition, the distribution, and depositional processes. It would provide great enlightenment to the paleo-oceanic current circulation in the northern South China Sea.

Characteristics of the turbidite fan in the Wenchang Formation of the Enping Sag, Pearl River Mouth Basin, China and its hydrocarbon significance

A turbidite fan in the Eocene upper Wenchang Formation in the Enping Sag, Pearl River Mouth Basin （PRMB） has been studied using seismic, logging and borehole data. The fan is characterized by parallel progradation on the dip seismic profile and is mound-shaped or lenticular-shaped on the strike seismic profile. The study of the core and logging data from well EP17-3-1, which is located in the front side of the turbidite fan, shows that this fan is a set of normal grading sand beds, interbedded within thick dark grey mudstones of semi-deep to deep lake deposits in the Wenchang Formation. The fan is interpreted as a sand/mud-rich turbidite fan that has an area of over 140 km2 and a maximum thickness of over 340 m. Combined with a study of the regional geological background and previous provenance analysis of the Eocene Wenchang Formation, the main potential provenances for the turbidite fan are considered to be the Panyu low-uplift and northern fault terrace zone. The Enping Sag is considered to be a half graben-like basin whose north side is faulted and whose south side is overlapped. Basement subsidence in the Eocene was mainly controlled by boundary faults which dip relatively steeply on the north side, causing the subsidence center of the Enping Sag in this stage to be close to the north boundary faults. Sustained faults developed in the Enping Sag during the Eocene caused an increase of the relative height difference between the north and the south uplift zone in the Enping Sag. Affected by the second episode of the Zhuqiong movement （39-36 Ma） in late Eocene, sediments which had accumulated on the Panyu low-uplift zone were triggered and moved toward the subsidence center of the Enping Sag and formed the turbidite fan. The second episode of the Zhuqiong movement is the most important triggering factor for the formation of the turbidite fan in the Wenchang Formation. Seismic attribute characterization shows that the low frequency energy is enhanced and high frequency energy is weakened when seismic waves propagate through the oil-bearing zone in this fan. Amplitude versus offset （AVO） anomalies are observed in the seismic data and abnormally high pressure is encountered. The turbidite fan in the Wenchang Formation has provided important information for sedimentary evolution in deep layers of the Enping Sag and pointed to a new direction for the hydrocarbon exploration in the study area.

Basin-filling processes and hydrocarbon source rock prediction of low-exploration degree areas in rift lacustrine basins:a case from the Wenchang Formation in low-exploration degree areas,northern Zhu I Depression,Pearl River Mouth Basin,E China

Hydrocarbon source rocks, as a main geologic factor of petroliferous systems in a sedimentary basin, play a key role in the accumulation of oil and gas and the formation of hydrocarbon accumulations. This study, which focuses on difficulties in prediction of hydrocarbon source rocks in basins or sags with low exploration degree and insufficient hydrocarbon source rock indicators, taking the Wenchang Formation of northern Zhu I Depression, Pearl River Mouth Basin as an example, proposed a hypothesis of “finding lakes and hydrocarbon source rocks”. Detailed steps include, first, determination of the lacustrine basin boundary according to analysis of seismic foreset facies, determination of the depositional area based on the compilation of strata residual thickness maps, determination of the lacustrine basin shape according to deciphering slope break belt system, determination of the fluctuation of paleo-water depth according to biogeochemical indicators of mature exploration areas, determination of the lacustrine basin scale based on analyses of tectonics intensity and accommodation space, which prove the existence of the lacustrine basin and identify the range of semi deep-deep lake;second, further analyses of tectonopalaeogeomorphology, paleo-provenance,palaeoclimate and paleo-water depth to reconstruct the geologic background of the original basin and semideep-deep lacustrine facies, to determine the distribution of semi-deep/deep lacustrine sediments in combination with studies of logging facies, core facies, seismic facies and sedimentary facies, and to rank the sags’ potential of developing hydrocarbon source rocks from controlling factors of source-to-sink system development;third, on the basis of regional sedimentary facies analysis, through identification and assessment of seismic facies types of semi-deep/deep lacustrine basins in mature areas, establishing “hydrocarbon source rock facies” in mature areas to instruct the identification and depicting of hydrocarbon source rocks in semideep/deep lacustrine basins with low exploration degree;fourth, through systematical summary of hydrocarbon-rich geological factors and lower limit index of hydrocarbon formation of the sags already revealed by drilling wells(e.g., sag area, tectonic subsidence amount, accommodation space, provenance characteristic, mudstone thickness, water body environment, sedimentary facies types of hydrocarbon source rocks), in correlation with corresponding indexes of sags with low exploration degree, then the evaluation and sorting of high-quality source rocks in areas with sparsely distributed or no drilling wells can be conducted with multi-factors and multiple dimensions. It is concluded that LF22 sag, HZ10 sag and HZ8 sag are II-order hydrocarbon rich sags;whereas HZS, HZ11 and HZ24 are the III-order hydrocarbon-generating sags.

珠江口盆地开平南大型深水深层油田发现与认识创新

开平凹陷是珠江口盆地地质条件最复杂的凹陷之一,也是重要的深水油气勘探区,由于洼陷结构、烃源分布及成藏规律认识不清,长期制约勘探进程。基于三维地震资料精细解释,开展成盆机制、烃源发育、源汇体系及成藏主控因素等研究,近期在开平南获得了大型轻质油田勘探发现。为进一步指导勘探,分析了开平凹陷油气成藏条件,总结了油气成藏模式。结果表明:(1)开平凹陷是南海北部强伸展陆缘背景下发育的“拆离-核杂岩”型凹陷,裂陷期经历“断陷—拆离—断拗”3幕演化过程;(2)开平凹陷发育文昌组优质湖相烃源岩,分布范围广、生烃潜力大,总体处于成熟至高成熟阶段;(3)开平凹陷油气运移受“源-断-脊”耦合控制,开平凹陷南部3大鼻状构造带是油气有利汇聚区,总体具有“近源强势充注-断脊差异运聚-晚期快速成藏”的模式。开平南古近系大型轻质油田的发现实现了开平凹陷勘探重大突破,开辟了珠江口盆地深水区油气勘探的新区、新领域,同时为“拆离-核杂岩”型含油气盆地的勘探提供了借鉴。

珠江口盆地白云凹陷东部古近系文昌组沉积演化特征

充分利用新三维地震资料,结合测井以及录井资料,对珠江口盆地白云凹陷古近系文昌组层序地层、沉积特征及沉积演化进行研究,重新建立文昌组三级层序格架内的沉积体系演化过程。结果表明:白云凹陷东部文昌组自下而上共划分为5套三级层序,分别对应于初始裂陷期(WCSQ1)、拆离裂陷早期(WCSQ2,WCSQ3)、拆离裂陷晚期(WCSQ4,WCSQ5)3个构造演化阶段;初始裂陷期为多个孤立的箕状半地堑,以发育缓坡轴向物源辫状河三角洲、陡坡近源扇三角洲和滨浅湖沉积为特征;拆离裂陷早期断裂活动强烈,湖盆迅速扩张,半深湖—深湖局限发育,沉积中心北移,北部番禺低隆起发育大型辫状河三角洲沉积;拆离裂陷晚期断裂活动减弱,湖盆逐渐萎缩,沉积中心稳定在白云凹陷中部,主要发育小型辫状河三角洲沉积,滨浅湖发育;大型辫状河三角洲及扇三角洲砂体是白云凹陷东部的有利储集体。

南海东部富砂砾型大中型油气田发现与启示——以珠江口盆地惠州26洼古近系恩平组为例

基于珠江口盆地惠州凹陷油气勘探实践,通过烃源岩地球化学指标测定、储集体发育形貌恢复及镜下岩矿表征、圈闭封盖指标实测比对、原油生物标志化合物提取、凝析气成因判别及成藏条件解剖,系统分析惠州26洼古近系恩平组油气资源潜力、大型砂砾岩优质储集层发育特性、断裂圈闭有效性及油气运聚成藏模式,总结南海东部古近系富砂砾型大中型油气田的形成条件及勘探方向。研究表明:(1)洼内古近系文昌组发育“面积广、厚度大”的半深湖—深湖亚相优质烃源岩,具有“早期大量生油、晚期大量排气”的典型倾油型烃源岩排烃特征,为恩平组油气成藏提供了充足的物质基础;(2)洼内断裂陡坡带与转换带联合控制下近源规模性砂砾岩体储集层非均质性强,具有“有利相带-颗粒组分-微裂缝”三元分级控储特性,等粒、低泥质(含量小于5%)、高含量长石组分及近断裂组合的(水下)分流河道有利于甜点储集层发育;(3)稳定湖泛泥岩封盖下的走滑增压型圈闭是油气保存的必备条件,斜交主应力的北东及近东西向断裂控圈效果最优;(4)优质烃源岩-断裂输导/封堵-砂砾岩储集层时空配置共同控制油气富集程度,自上而下划分为低充满带、过渡带和高充满带3个油气聚集单元,且近增压型通源断裂带河道主体区利于规模性油气富集。研究成果为珠江口盆地恩平组规模性富砂砾型油气藏勘探指明了新方向,并实现了油气勘探重大突破。

白云南洼珠海组陆架坡折带演化特征与深水沉积耦合关系

白云南洼珠海组沉积时期,盆地处于断陷向拗陷转化阶段,陆架坡折形态以及位置发生巨大变化,导致深水沉积的类型和特征具有明显差异。针对这种坡折演化对深水沉积类型的影响开展研究,通过对白云南洼珠海组三维地震剖面进行解译,识别珠海组各层段陆架坡折带,定量分析坡折特征及其演化规律,探讨坡折演化过程与深水沉积的耦合关系。研究结果表明,通过对珠海组沉积时期陆架坡折带定量分析,将其迁移演化类型划分为下降型、平直型、低角度上升型、高角度上升型4类;在井震结合的基础上,根据地震相组合以及沉积体系分布特点,识别出斜坡扇、块状搬运沉积、深水水道体、盆底扇4种主要的深水沉积类型;并发现陆架坡折演化类型与深水沉积类型存在明显的耦合关系:平直型、高角度上升型、低角度上升型和下降型陆架边缘迁移轨迹分别对应斜坡扇、块状搬运沉积、深水水道体和盆底扇的优势发育。此外,珠海组四段至珠海组三段陆架坡折带整体由下降型向低角度上升型转变,深水沉积体系以斜坡扇及深水水道体发育为主;珠海组三段至珠海组一段早期整体由低角度上升型向下降型转变,深水沉积体系以深水水道-盆底扇沉积体系为主;珠海组一段晚期整体由下降型向高角度上升型演化,深水沉积体系几乎不发育。本研究揭示了陆架坡折迁移对深水沉积体系类型和分布的控制作用,对深入理解深水沉积过程和油气勘探具有重要意义。

珠三坳陷珠江组一段沉积体系演化过程及其控制因素

珠江组一段沉积时期是珠三坳陷沉积体系演变的重要时期,由早期的大范围三角洲沉积体系演化为晚期的浅海陆架沉积体系,对其演化过程及控制因素展开研究,不仅有利于揭示海侵过程中沉积体系演化过程,而且对浅海陆架有利沉积相带预测具有指导意义。综合利用岩心、测井以及高分辨率三维地震资料,建立了珠三坳陷珠江组一段四级层序地层格架,通过地质-地球物理结合方法查明了珠江组一段沉积体系的时空演化特征,并讨论了沉积演化的主控因素。研究表明:珠三坳陷珠江组一段可划分为PS1、PS2、PS3、PS4共4个四级层序。PS3和PS4时期主要发育三角洲前缘沉积,具有水下分流河道、分流间湾、河口坝和远砂坝等沉积微相组合;PS1和PS2时期以浅海陆架沉积体系大规模发育为特征,在研究区西部发育潮流砂脊,东部发育滨外砂坝。珠三坳陷沉积体系的平面展布以及垂向演化受相对海平面变化、物源供给强度、构造沉降与古地貌等综合控制。水下分流河道、潮流砂脊与滨外砂坝等微相砂岩占比高且物性好,为油气储集的有利沉积相带。

珠江口盆地中北部中新统珠江组浪控三角洲沉积时空演化模拟

基于沉积背景、高分辨率层序地层格架及沉积微相展布分析,应用沉积正演模拟方法,综合利用地震、测井、岩心等资料,开展沉积作用和沉积过程的三维时空演化模拟,定量恢复了珠江口盆地中北部中新统珠江组浪控三角洲沉积演化过程,探讨了沉积环境与波浪参数对砂体展布的影响。结果表明:(1)研究区珠江组沉积期的沉积微相随基准面的变化呈规律性演化,滨线呈现先向陆迁移、再向海迁移的趋势。(2)珠江组沉积期的波浪作用较强,波浪角度为近南东方向,波浪作用对三角洲砂体展布具有明显影响。随着波浪高度增加,波浪阻碍三角洲河口细粒沉积物堆积的作用增大,并将其搬运至深水区,泥质沉积物趋向沉积于波基面以下区域,波基面以上区域砂质碎屑含量较高。波浪作用入射角度发生倾斜,会导致三角洲在演化过程中产生不对称的沉积和形态。(3)有利储层砂体主要发育于滨岸线附近。沉积正演模拟为定量恢复沉积演化过程提供更为直观的方法,且在确定浪控三角洲潜在形态方面具有预测作用。

珠江口盆地HZ26区文昌组储层特征及成因机制

珠江口盆地惠州凹陷油气资源丰富,文昌组勘探主要受限于储层。以惠州凹陷HZ26区文昌组砂岩储层为研究对象,采用薄片鉴定、扫描电镜、包裹体测温等手段,对储层特征、增孔保孔机制、成岩成储过程展开研究。结果表明:①文昌组以岩屑砂岩、岩屑石英砂岩储层为主,粒间普遍含凝灰质杂基,文昌组储层整体表现为低孔、低渗。②早成岩A期大气淡水溶蚀作用和早成岩B期—中成岩A期有机酸溶蚀作用是储层最主要的增孔机制,早成岩阶段沉淀的嵌晶式浊沸石可以有效抵御压实作用从而保护粒间孔隙,早期油气充注也可以通过抑制胶结作用而保护粒间孔隙。③文昌组WC41、WC42、WC43砂层组的成岩成储过程具有明显差异。WC41砂层组原生孔发育带整体杂基含量少,成岩演化过程简单,油气沿断层处运移,在上覆不整合遮挡下形成油气藏;WC42砂层组广泛分布凝灰质杂基,凝灰质蚀变作用普遍发育,沉淀出可以提高岩石抗压性的致密胶结浊沸石,浊沸石被酸溶解后,提供大量粒间溶蚀孔,浊沸石溶解带是研究区油气聚集的另一有利场所;WC43砂层组远火山口端的富泥质杂基带和近火山口端的火山角砾堆积带均遭受强烈压实作用,储集性能差。本项研究成果可为HZ26区文昌组油气勘探决策提供参考。

珠江口盆地陆丰凹陷文昌组凝灰质砂岩储层成岩相及发育模式

陆丰凹陷文昌组深层砂岩储层是珠江口盆地珠一坳陷最重要的油藏储集岩之一,而凝灰质发育导致储层致密,渗透率呈现低渗、特低渗特征。由于凝灰质影响,该区成岩作用及其展布表现出特殊性。运用偏光显微镜在对凝灰质砂岩储层的成岩作用、自生矿物转化及孔隙类型详细观察的基础上,结合扫描电镜、孔渗测试及测井资料分析,对陆丰凹陷文昌组凝灰质砂岩储层成岩相及其发育模式进行了研究。结果表明,凝灰质蚀变作用是影响储层物性的主要成岩作用,其次是压实作用和溶蚀作用。依据各种成岩作用强度及其组合,储层整体可以分为5种成岩相:①中压实--弱胶结--凝灰质中等溶解相(Ⅰ类);②中强压实--弱胶结--凝灰质强溶解相(Ⅱ类);③中强压实--磷灰石中强胶结--中等溶解相(Ⅲ类);④中强压实--高岭石中强胶结--弱溶解相(Ⅳ类)和⑤强压实--弱胶结--弱溶解相(Ⅴ类)。其中Ⅰ类成岩相为优质成岩相(孔隙度均值为13.4%、渗透率均值为5.4×10^(-3)μm^(2)),Ⅱ类成岩相为有利成岩相(孔隙度均值为15.4%、渗透率均值为1.5×10^(-3)μm^(2)),Ⅲ类和Ⅳ类成岩相为潜在有利成岩相(孔隙度均值为15.0%、渗透率均值为1.0×10^(-3)μm^(2)),Ⅴ类成岩相为不利成岩相。受大气水淋滤和有机酸溶蚀等影响,陆丰凹陷文昌组深层砂岩储层主要发育Ⅱ-Ⅲ-Ⅳ-Ⅴ和Ⅰ-Ⅴ两种成岩相组合模式。成岩相与储层质量密切相关,通过识别优质成岩相可以预测有利储层分布,为油气勘探提供地质依据。

珠江口盆地惠州凹陷惠东新区恩平组烃源岩生烃特征及成藏贡献

珠江口盆地惠州凹陷惠东新区恩平组厚度达3000 m,沉积特征整体表现为陆相浅水广盆环境,恩平组烃源岩生烃特征和成烃规模一直是困扰研究区勘探的基础问题之一。为厘清上述两个关键问题,以构造学、沉积学以及有机地球化学相结合的研究思路为指导,在化验分析数据基础之上,重新认识本地区恩平组烃源岩特征、生烃潜力及主要成藏贡献区。研究表明:惠东地区恩平组主体发育三角洲—浅湖相沉积,烃源岩包括煤、碳质泥岩和暗色泥岩;暗色泥岩有机质丰度中等—好,有机质类型为II型,具有早期生油,晚期持续生气的特征;盆地模拟计算原油地质资源量近3×108t,天然气资源量近500×108m3,资源潜力较大;油气源对比表明恩平组烃源岩来源的油气藏主要发育在惠东地区,惠东地区下一步最有利勘探方向为邻近烃源岩的深层恩平组圈闭以及“源-断-脊-圈”匹配较好的浅层珠江、珠海组圈闭。

珠江口盆地惠州北凹珠海组、珠江组储层发育特征及主控因素

应用13口钻井的薄片鉴定、粒度分析、扫描电镜、锆石定年、物性等分析化验资料以及录井、测试资料,系统开展了惠州北凹珠海组、珠江组储层的发育特征、主控因素及商业产能下限研究。研究表明:(1)珠海组、珠江组发育大型海相三角洲—滨浅海沉积,储层主要为三角洲前缘水下分流河道中—粗粒洁净石英砂岩,其具有高成分成熟度和高结构成熟度,储集空间类型以原生粒间孔为主,局部富集次生溶孔、高岭石晶间孔,面孔率较高。(2)储层发育主要受“优质母源+有利相带+溶蚀作用”三元联控:研究区北部华南地块的变质岩+侵入岩作为优质母源决定了储层为石英含量高的砂岩类型,奠定了优质储层发育的基础;三角洲前缘主水道沉积水动力强,单砂体厚度大,砂岩粒度粗、泥质含量低,储层物性最好;建设性成岩作用(溶蚀作用)在一定程度上具有扩储增孔效应。(3)结合录井、测试资料确定惠州北凹油层的中—粗粒石英砂岩储层商业产能下限为3 800 m。

南海珠江口盆地陆丰凹陷文昌组沉积成岩特征及储层物性控制因素

为明确陆丰凹陷深部储层特征及成因机制,对凹陷南部地区7口井文昌组岩心样品进行薄片鉴定、FE-SEM观察、XRD分析及物性测试。结果表明:文昌组岩石类型为长石石英砂岩、岩屑石英砂岩、岩屑砂岩和少量石英砂岩,杂基以泥质和凝灰质为主,胶结物以自生石英、泥晶碳酸盐和自生高岭石为主。储层物性非均质性强,孔隙度为2.2%~21.6%,平均为12.0%,以次生孔隙为主;渗透率小于10×10^(-3)μm^(2)的占比达95%,呈特低—低—中孔隙度、低—特低渗透率特点。文昌组主要发育三角洲、辫状河三角洲和扇三角洲3种沉积相,包括三角洲前缘、辫状河三角洲前缘和扇三角洲前缘3种亚相及6种沉积微相。辫状河三角洲的储层孔隙度相对较高,渗透率相对居中;扇三角洲的储层孔隙度居中,渗透率相对较高;三角洲的储层孔隙度与扇三角洲的相似,渗透率相对最低;辫状河三角洲水下分流河道砂体更利于发育优质储层。文昌组砂岩经历早成岩阶段A、B期、中成岩阶段A、B期;压实—压溶作用较强,导致原生孔隙不发育;不同类型、不同期次的胶结作用抑制储层物性;长石、凝灰质和岩屑的溶蚀作用形成次生孔隙及次生矿物,孔隙度提高,但渗透率无明显提升。该结果对陆丰凹陷文昌组后续勘探开发提供基础支撑。

顺德北凹走滑变形特征及其控圈作用

珠江口盆地顺德凹陷断裂特征及其控制形成的圈闭分布规律认识不清,一直制约该区勘探。新生代以来凹陷经历了多期构造变形和叠加,所形成的复杂走滑变形对圈闭形成具有重要控制作用。利用高精度三维地震资料以及新钻井成果资料,在精细构造解释的基础上,运用走滑及伸展定量分析技术,系统地开展顺德北凹走滑断裂特征描述、凹陷构造发育机制分析及走滑控圈作用研究。结果表明:①顺德北凹内部发育有负花型、复式负花型、Y型、复式Y型、多级Y型和多米诺式6种剖面断裂组合和剪切透镜体、羽列和雁行3种平面构造样式;②顺德北凹发育3期走滑作用,与伸展作用叠加控制凹陷构造演化,断陷期表现为强斜向伸展、弱走滑,断拗转换期表现为强走滑、弱伸展,陷期表现为弱走滑、弱伸展的构造发育机制;③发育凹陷带强走滑带S型增压转换控圈模式,缓坡带中走滑带两期走滑叠加控圈模式及低凸起弱走滑带右行左阶走滑推挤隆起控圈模式,其中凹陷带强走滑带S型增压转换控圈模式下形成的圈闭有效性好,为油气富集的重要场所。该成果指导了顺德北凹勘探突破,也为边缘凹陷多期走滑叠加下的构造演化理论研究以及勘探实践提供一种借鉴。

南海北缘陆相断陷盆地优质烃源岩发育机制:以珠江口盆地顺德凹陷始新统文昌组为例

珠江口盆地顺德凹陷始新统文昌组发育3套有利烃源岩,但对其层系归属、优质烃源岩特征和发育模式认识不清晰。基于高分辨率三维地震、钻井和地球化学资料,开展文昌组层序地层划分、梳理烃源岩发育特征、明确有机质富集主控因素并建立优质烃源岩发育模式。结果表明:顺德凹陷始新统文昌组可划分为3个三级层序,其中层序SQ2对应文昌组二段,烃源岩岩相类型以褐黑色、灰黑色纹层状页岩为主,有机质丰度较高,为优质烃源岩发育的主要时期。层序SQ1和SQ3分别对应文昌组三段和一段,烃源岩岩相以深灰色块状泥岩夹粉砂质泥岩为主,有机质丰度相对较低,主要发育一般烃源岩。有机质母源类型以陆源高等植物和水生浮游生物混源为主,其中层序SQ2时期藻类贡献较大。文昌组优质烃源岩发育受构造作用—古气候耦合约束,有机质富集主控因素为古生产力和古氧化还原条件。层序SQ2时期强断陷作用加剧火山活动,火山灰尘稳定沉降驱动古生产力较高;强烈的构造沉降及温暖—湿润的古气候促使湖平面上升,温度控制下的水体分层导致湖泊底水缺氧,于半深湖环境沉积厚层富有机质页岩。

低渗凝灰质砂岩储层孔隙结构特征及低渗成因——以珠江口盆地陆丰凹陷古近系文昌组为例

陆丰凹陷古近系文昌组为典型低渗凝灰质砂岩储层,复杂的孔隙结构和储层低渗特征制约研究区增储上产。利用铸体薄片观察、XRD全岩及黏土矿物分析、高压压汞、恒速压汞和CT扫描等实验,基于分形曲线特征和孔喉结构参数划分储层孔喉类型,分析储层物性及填隙物特征,精细表征砂岩储层的孔喉—孔隙结构,探讨不同类型储层的孔隙结构特征及其对物性的影响。结果表明:珠江口盆地陆丰凹陷古近系文昌组储层发育长石石英砂岩、岩屑石英砂岩和岩屑砂岩。储层孔喉结构划分3种类型,Ⅰ类储层为优质储层,储层物性最优,平均排驱压力约为0.1 MPa;Ⅱ类储层次之,排驱压力在0.5~1.0 MPa之间;Ⅲ类储层最差,排驱压力大于1.0 MPa。研究区储层低孔低渗特征是填隙物类型、溶蚀作用程度和蚀变产物性质等因素共同作用的结果,凝灰质填隙物大量充填原生孔隙空间,受溶蚀作用程度低是研究区储层低孔的主要原因,溶蚀作用产物易堵塞喉道是储层形成低渗特征的主控因素。该结果为研究区低渗储层划分及有效开发提供指导。

珠江口盆地惠北地区煤系烃源岩新认识与勘探实践

珠江口盆地恩平组煤系烃源岩因分布主控因素认识不清、发育规模不明确,导致勘探潜力被忽视。以煤系烃源岩发育区惠北地区作为研究靶区,利用地震、钻井和地化等资料,系统分析了煤系烃源岩分布主控因素,据此确定煤系烃源岩发育规模和资源潜力,从而有效指导勘探。研究表明:①纵向上,从恩四段到恩一二段沉积期,惠北地区古气候温暖湿润,古水深逐渐变浅,古构造活动强度逐渐减弱,恩一二段和恩三段有利于煤层的发育和聚集,恩四段沉积期煤层不发育;②横向上,受古沉积条件的控制,煤系烃源岩主要分布于惠州14洼北部缓坡带辫状河三角洲河道间的河漫沼泽和洼陷带滨浅湖内的湖沼范围内。基于煤系烃源岩分布规律,预测惠北地区煤系烃源岩资源量约2亿方油当量,带动了惠北地区周边勘探,也展示了珠江口盆地煤系烃源岩勘探前景。