南海碳酸盐台地分布自早中新世开始发育，至中中新世达到鼎盛，再到晚中新世大量台地被淹没而逐渐消亡。从分布看，南海碳酸盐台地具有南早北晚、东早西晚的发育规律；从堆积速率看，中中新统速率最大。控制这些台地的诞生、发育演化和消亡的因素十分复杂，可能包括构造活动、相对海平面的变化、陆源碎屑物质输入变化、古海洋环境变化。

由于生物礁储层具有良好的物性条件，易形成大型油气藏，已成为目前油气地质学研究的热点。我国南海北部在中新世发育了大量的生物礁，若具备合适的发育过程和成岩演化过程，其油气潜力就会非常大，但是其东北区和西南区的生物礁在成岩演化过程中却存在很大的差异。指出中新世南海海平面变化频繁，冰期海平面的下降，西沙群岛生物礁发生海水浓缩准同生白云岩化作用，使生物礁储层良好的物性条件得以保存，但是在同一期，东沙隆起的流花11\|1油田却发生了潜流胶结成岩作用，形成致密层，破坏了生物礁储层的物性条件，而之后的沿致密层之间的深埋溶蚀作用，使孔隙层的物性条件得以改善，便成为良好的储层。认为南海北部东北区和西南区生物礁储层的成岩作用差异性可能是由古地理环境、古气候、古构造、古地貌、古生物和油气充注史等因素造成的，研究南海北部生物礁储层成岩作用差异性及其影响因素对该区油气的勘探和开发以及古环境研究等具有重要的指导意义。

Because of its favorable physical properties, reef reservoir is inclined to form big oil gas reservoir, and it is the hot issue in current researches. There developed a lot of reef in the northern part of South China Sea, and the hydrocarbon potential is great. However, the diagenesis in the eastern and western regions of the northern part of South China Sea is different. The sea level changes were very frequently in Miocene; Reef underwent penecontemporaneous dolomitisation when the sea level dropped in the glacial epoch in the Xisha Islands. However, in the same period, the meteoric cementation in the LH 11-1 oil field formed impermeable barriers, which destroyed the properties of the reef reservoir; The dissolution of anadiagenetic stage along the impermeable barriers made the properties of the porous interval better and become good reservoir. Through comparative analysis, we believe that the difference of diagenesis is caused by the different palaeogeography, palaeotectonics, palaeogeomorphology, paleontology and the oil\|gas input history. It is very important to study the differentiation and influential factors of diagenesis in South China Sea for the palaeoenvironment and exploration and exploitation of oil and gas.

The last statistic data for reserves in offshore fields have shown that natural gas is more than oil in South China Sea. Proved oil reserves and gas reserves take up 38, and 62, respectively of the total. Among the total proved reserves, the reserves in clastic reservoirs occupy 57,, the ones in carbonate reservoirs do 36, and the ones in pre-Tertiary fractured bedrock reservoirs are 7, of the total. The fields of clastic reservoirs are commonly located in the areas near sediment source. The ones of carbonate reservoirs are mainly distributed in the platform areas away from the sediment source. The ones of pre-Tertiary bedrock reservoirs are mostly in strike-slip basins that are located at the west margin of the sea. The proved reserves distribute respectively in the Miocene rocks(51,), in the Lower Miocene rocks(17,) and in the pre-Tertiary bedrocks (11,). High geothermal gradient and the types of organic matter in source rocks are the reasons that gas is richer than oil in resource and the different types of basins decide that resource is richer in the southern part of the sea than in the northern part of it. The tectonic history and the peripheral paleo-river system controls the reservoir types of fields and temporal and spatial distribution of fields.

珠江口盆地惠州凹陷是南海东部石油工业的摇篮，也是珠江口盆地(东部) 最早取得中深层古近系油气 突破的地区。近10 年惠州凹陷勘探遭遇瓶颈，为了寻找新的大中型油气田，开展研讨和加强石油地质条件再评价工 作。通过转变思路，坚定“老油区新作为”的勘探信心，提出“立足富洼、聚焦古近系—古潜山、拓展新领域”的勘 探理念；加强研究攻关，提出富油洼陷找气新认识，惠州26 洼湖相混合型母质“油气兼生，晚期快速生气”，具有 较大天然气资源潜力；提出环惠州26 洼“古近系—古潜山”圈闭群具有“近源强势供烃、立体网状输导”成藏模式， 是勘探转型、新领域突破的首选区带。近期该区带惠州26-6“古近系—古潜山”大中型油气田勘探突破证实了高成 熟富油洼陷找气新方向，揭开了惠州凹陷“古近系—古潜山”勘探新篇章，极大拓展了珠江口盆地（东部）古潜山勘 探新领域。

The Huizhou sag in the Pearl River Mouth Basin is the ‘cradle’ of the petroleum industry in the eastern South China Sea, and also the breakthrough area for oil and gas discoveries in the middle-deep Paleogene in the eastern Pearl River Mouth Basin. For the past 10 years, however, exploration in the Huizhou sag has been trapped in a bottleneck. In order to discover new large-medium oil and gas fields, it is necessary to hold workshops and strengthen the re-evaluation work of petroleum geological conditions to bolster confidence in the exploration idea of “new achievements in mature areas”. Now, a new exploration concept is now proposed: “taking oil-rich sub-sags as a basis, focusing on Paleogene-buried hills, and expanding to new frontiers”. With increased research, new understandings of gas exploration in oil-rich sub-sags are emerging. In the Huizhou 26 sub-sag, mixed-type kerogens of lacustrine facies are characterized by “generation of both oil and gas, and rapid gas generation in the late stage” and offer great potential for natural gas resources. The “Paleogene-buried hills” trap group around the Huizhou 26 sub-sag has a hydrocarbon accumulation model of “strong near-source hydrocarbon supply and stereoscopic network migration”, making it the preferred zone for exploration transformation and new-field breakthroughs. The recent breakthrough discovery of a large-medium oil and gas field in the “Paleogene-buried hill” area of the Huizhou 26-6 structure—confirms this new target of gas exploration in high mature oil-rich sub-sag, opens a new chapter of “Paleogene-buried hill” exploration in the Huizhou sag, and expands the new exploration field of paleo-buried hills in the eastern Pearl River Mouth Basin.

<p>The Pearl River Mouth Basin is a basin with the characteristics of variable geothermal field, firstly presented as a fault transforming into depression later, transferring from land to sea. In this basin, three sets of source rocks are developed, i.e., Wenchang Formation, Enping Formation and Zhuhai Formation. Based on the analysis and test on a large number of source rock samples in combination with experimental analysis, geological analysis and geological simulation, this study conducts a comprehensive grading evaluation on the development characteristics of the three sets of source rocks and the thermal evolution history, hydrocarbon generation history and resource potential of the depression/half graben/sag. The research indicates that (1)the lacustrine oil-prone source rocks in Wenchang Formation during the mid-early rifting stage are the chief source rocks in this region, while the coal-measure oil-gas-bearing source rocks in Enping Formation during the late rifting stage are important source rocks in this region. Only in Baiyun sag, the marine terrigenous oil-gas-bearing source rocks in Zhuhai Formation during the depression stage entered the hydrocarbon generation threshold. (2)The geothermal gradients increased from shallow area to deep-water, which resulted in the fact that maturity threshold and hydrocarbon generation window were located in the water area rapidly becoming shallow. In the shallow area, source rocks were developed in the mature-high maturity stage, characterized with late hydrocarbon generation. The main hydrocarbon generation period was from 16 Ma to the present. In the deep water, source rocks are in the mature-over mature stage, and Baiyun sag is characterized with early hydrocarbon generation with the main hydrocarbon generation period of 33-0 Ma. (3)The total geological resource of Pearl River Mouth Basin is about 85&times;10⁸ tons through assessment. It is rich in oil and gas resources, where the shallow water area is dominated by petroleum resources, equivalent with the oil and gas resources in the deep water area. (4)According to the evaluation criteria of offshore hydrocarbon-generation depression, Huizhou, Baiyun, Lufeng, Xijiang, and Enping sags are hydrocarbon-rich depressions, and Kaiping and Liwan sags are moderate hydrocarbon generation depressions with favorable exploration potential.</p>

惠州凹陷是中国南海珠江口盆地东部最重要的富生烃凹陷,位于其东南缘的远源凸起带普遍缺失烃源岩地层,距离油源远,是典型的源外远源油气藏,油藏中原油成因及来源尚未明确。通过对惠州凹陷内原油和烃源岩样品进行生物标志化合物、同位素特征的系统对比,结合对断裂-砂体-不整合运移通道和遮挡条件的分析,应用Pathway软件模拟分析三维油气运移路径,跳出静态模式的禁锢,从动态的角度分析油气成藏过程。本文认为,惠州凹陷东南缘远源凸起带原油主要来源于文昌组烃源岩,其生物标志物主要表现为低C₁₉/C₂₃三环萜烷值(<0.7)、低C₂₀/C₂₃三环萜烷值(<0.8)、高C₂₇重排甾烷/C₂₇规则甾烷值(>0.25)、低ETR值(<0.4)、高4-甲基甾烷/ΣC₂₉甾烷值(>0.4)和低双杜松烷T/C₃₀藿烷值(<1)。油气三维运移路径模拟结果显示,油气在惠州凹陷H26洼生成后,在惠-流构造脊控制下沿优势运移路径向东沙隆起方向运移,并在构造脊顶端的远源凸起带L11-1油田聚集成藏。远源凸起带的原油与同一优势运移路径上的其他油田原油样品的生物标志物特征和碳同位素特征具有非常高的相似性。故本文推断,远源凸起带原油主要来自惠州凹陷H26洼陷文昌组中深湖相烃源岩。

The Huizhou depression is the most important hydrocarbon-rich depression in the eastern Pearl River Mouth Basin, South China Sea. The uplifts, located in the southeastern margin of the Huizhou depression, are far from source rocks with no in-situ deposition of source rock strata. They are typical remotely sourced petroleum reservoirs, whose source and formation mechanisms are not yet known. This study systematically compared the biomarker compositions and isotopic characteristics between crude oil and source rock samples from the Huizhou depression. Combined with analysis of the fault-sand-unconformity migration pathways and blocking conditions, the Pathway software was used to simulate and analyze the three-dimensional hydrocarbon migration pathways, and the hydrocarbon accumulation process was analyzed in dynamic mode to overcome the limitations of static analysis. We suggest the source rock of the Wenchang formation is responsible for the crude oil in the uplifts. The crude oil samples were characterized by low C₁₉/C₂₃ tricyclic terpane ratio (<0.7), low C₂₀/C₂₃ tricyclic terpane ratio (<0.8), high C₂₇ rearranged sterane/C₂₇ regular sterane ratio (>0.25), low ETR value (<0.4), high 4-methylsterane/C₂₉ sterane ratio (BBB>4), and low bicadinane T/C₃₀ hopane ratio (<1). The simulated three-dimensional hydrocarbon migration pathways indicated that under the control of the Hui-Liu mid-ocean ridge, hydrocarbon generated in sag H26 of the Huizhou depression migrated to the Dongsha uplift along the dominant migration pathway and accumulated in the L11-1 oilfield in the uplifts far from the source rocks at the top of the mid-ocean ridge. The biomarker and carbon isotopic characteristics of crude oil samples from the uplifts were similar to those from other oilfields along the same predominant migration pathway. Therefore, we infer that the crude oil in the uplifts is predominantly sourced from the middle-deep lacustrine source rock of the Wenchang formation of sag H26.