2018年中国东部最大整装凝析气田——渤中19-6气田的发现,一举打开了渤海湾盆地深层天然气勘探的新领域,展现了油型盆地天然气勘探的巨大潜力.渤中凹陷发育多套不同成熟度的烃源岩,位于渤中凹陷西南部的渤中19-6气田凝析油与天然气并存,近年来于该地区的天然气成因及形成条件多有研究,但是对于凝析油的形成则少有研究.本文以渤中19-6气田为例,探讨多套烃源岩发育的复杂油气区凝析油的成因及与天然气的关系.渤中19-6气田6个凝析油样品化学组成及其变化特征精细分析对比表明:该区凝析油以低碳数正构烷烃为主,含有较丰富的环己烷、甲基环己烷等环烷烃和苯、甲苯等低碳数芳烃,金刚烷类化合物较发育,高碳数生物标志化合物含量较低,综合判断凝析油属于混合偏腐殖型高熟原油.结合该区凝析油与天然气对比结果认为,该区凝析油和天然气属于同一套烃源岩在同一阶段所生成的烃类化合物,两者相伴而生,均属于烃源岩原生产物.

烃源岩的排烃是准确预测含油气盆地油气资源必须涉及的一个非常重要的环节,为了得到不同有机质类型烃源岩的排烃效率、排烃机理,选取不同有机质类型烃源岩进行了黄金管模拟实验,总结了不同类型烃源岩在各演化阶段产物的变化特征与排烃效率.结果表明,烃源岩类型对总生成油与残留油中轻重烃的比例影响较大,但是对排出油中轻重烃的比例影响较低,排出油中均表现为在未熟—成熟阶段以重烃为主,在高熟—过熟阶段以轻烃为主.烃源岩的类型对生排油量的影响明显,烃源岩的类型越好,生排油量越高.Ⅰ型烃源岩的生排油量最高,Ⅲ型烃源岩最低.烃源岩类型越好,排油效率越高.Ⅲ型烃源岩排油效率低,与其生成气态烃较多、显微组分中镜质组含量较高有关.

基于大量地球化学、地质资料以及“源热共控”的思想,深入研究了北部湾盆地福山凹陷油气的形成.结果 表明,福山凹陷的“源”为古新世流沙港组烃源岩,该烃源岩有机碳丰度分布范围宽,有机碳含量TOC为0.4％～6.0％,但有机质类型主要为腐殖—腐泥型(Ⅱ2型)烃源岩,属于“源够”型凹陷;“热场”研究表明,福山凹陷经历过多期构造热事件,火成岩侵入导致烃源岩有明显热异常,促使东部地区烃源岩快速成熟生气,故凹陷热场类型定为“热足”型.“源够热足”型耦合作用促成了福山凹陷油气的形成,该成果进一步丰富了“源热共控”理论,揭示富油气凹陷烃源岩成熟及油气富集机理,进而指导油气勘探.

Many studies have been carried out on the hydrocarbon geologic conditions of Wan'an,Zengmu and Brunei-Sabah basins. However,there are few studies on the difference of hydrocarbon geologic conditions among basins.Based on a lot of previous research results,drilling,seismic data and oil and gas testing data were comprehensively used to analyse the main difference of hydrocarbon ge-ology in the Wan'an,Zengmu and Brunei-Sabah basins in southern South China Sea.The study shows that the Cenozoic of the three ba-sins all developed two tectonic stages,mainly developing marine-land transitional facies and marine depositional environment.Three pe-riods(Oligocene,Miocene and Pliocene)developed two types of source rocks,i.e.the coal measures and terrigenous marine facies,the period of major source rock is gradually new from west to east.Developed two types of reservoirs,i.e.clastic sandstone and carbonate rock,reservoirs distribution may be characterized by near shore sand and distant shore reef,the reservoirs period is gradually new from west to east.There are two combination of source rock and reservoris,i.e.the distant shore self-generation and self-reservoiring and the near shore lower-generation and upper-reservoiring.

传统研究认为北部湾盆地主力烃源岩为整个流二段湖相烃源岩.应用大量原油和岩石的地球化学分析资料,结合沉积和地质资料,重新对北部湾盆地流二段烃源岩进行了生烃和油气成藏研究.研究结果表明,古近纪沉积的流二段不同层段烃源岩的质量差异较大,明显存在着优质(油页岩)、好和一般3种不同类型的烃源岩.3类烃源岩的生烃和成藏研究表明,3类烃源岩对油藏的贡献各不相同,其中优质烃源岩[丰度高、类型好(Ⅰ型)、产油率达500mg/gTOC]贡献最大,它对涠西南凹陷和乌石凹陷原油产量的贡献高达80％;好烃源岩[丰度中等、类型较好(Ⅱ1型)、产油率为300mg/gTOC]次之,对原油产量的贡献仅为20％;而一般烃源岩[丰度较低、类型较差(Ⅱ2)、产油率仅为200mg/gTOC]对凹陷原油的贡献极少.由此表明,厚度不大(厚约为50～100m)、质量极好的流二段底部优质湖相烃源岩才是北部湾盆地真正的主力烃源岩.优质烃源岩生成的原油主要成藏于流二段、流三段、长流组和角尾组,而好烃源岩生成的原油则主要成藏于流一段和涠洲组.3类烃源岩丰度、类型、生烃能力及成藏方面的差异,决定了北部湾盆地的油气勘探必须寻找到优质烃源岩才能提高勘探的成功率.

With the thought of lacustrine source rock heterogeneity,lacustrine source rocks analogue of Member 2 of Liushagang Formation (El2) in the main sags of Beibuwan basin is studied and reevaluated.Based on statistics and analysis of geochemistry and sedimentary data,the total organic carbon content,potential hydrocarbon generation amount,hydrogen index and 4-methyl-C30 sterane index of source rocks are chosen as effective indicators to identify and evaluate the lacustrine source rocks.An evaluation criteria on lacustrine source rocks is firstly estab lished and such 4 types as high quality,good,common and poor source rocks are characterized for source rocks of El2.High quality source rock occurrence condition and oil-source correlation study show that the quality of lacustrine source rock of El2 in different sags is variable due to different occurrence conditions.Among these sags,Weixinan sag has the most favorable occurrence condition of high quality lacustrine source rock and the main source rock is the lower part of El2 with thickness of 50～100 m.Wushi sag is the second with high quality source rock in the northeast.The formation and distribution of major oil fields in Weixinan and Wushi sags are significantly controlled by high quality source rock.The main source rocks in Haizhong and Maichen sags are common quality,while high quality lacustrine source rocks in these two sags are believed to be very limited.The research result is significant for exploration directions in Beibuwan basin,especially in Haizhong and Maichen sags without breakthrough yet.

Source rock formation influenced by river-delta system, especially in continental margin basins, is still poorly understood. This article aimed to reveal the effect of river-delta system on the formation of the source rock by taking the Baiyun Sag of the Pearl River Mouth Basin for example. Paleo-Pearl River began to develop since the Enping Formation, providing abundant organic matter beneficial for the formation of the source rocks in the Baiyun Sag. The main controlling factor of source rock formation in the Baiyun Sag is terrestrial organic matter supply rather than the paleoproductivity or redox conditions. Low Al/Ti and P/Ti ratios suggest low marine productivity, which may be associated with a large number of terrigenous detritus input, occupying about 43.04%–94.91%. There is a positive correlation between the oleanane/C30hopane ratio and the TOC value, showing that terrigenous organic matter controls the source rock formation. The size of the delta below Pearl River estuary determines the extent of terrestrial organic matter supply. Source rocks with high organic matter abundance mainly formed in delta environment, and those in neritic environment in Enping and Zhuhai Formations also have high TOC values as a result of adequate terrestrial organic matter supply.

应用烃源岩地球化学、流体包裹体和盆模热史等分析方法,详细对比研究了鄂尔多斯盆地东缘临兴—神府区块致密气藏油气成藏的差异以及火山对烃源岩的热作用.研究结果表明,成熟度是控制上述区块油气高效成藏的关键条件.临兴区块烃源岩成熟度Ro约为0.9％～2.5％,神府区块烃源岩成熟度Ro约为0.7％～1.2％,临兴区块烃源岩成熟度明显高于神府区块;早白垩世末构造热事件引起的紫金山火山热作用是导致临兴区块成熟度较高的主要原因.由于烃源岩成熟度的差异,导致了两个区块烃源岩总生气强度、储层包裹体温度和储层含油包裹体丰度(GOI)均出现较大的差异,临兴区块各项指标均优于神府区块,临兴区块勘探潜力明显优于神府区块.

珠二坳陷白云凹陷海相烃源岩主要指的是海陆过渡相沉积背景下形成的海相烃源岩(恩平组和珠海组烃源岩),该类烃源岩具有陆源生烃母质和海相生烃母质双源输入的混合特征,其生成的油气亦有双源成因的特征,烃源岩TOC平均值为1.2％,干酪根类型主要为Ⅱ2型,具有油气兼生的能力.油源对比和混合比例估算表明,珠二坳陷白云凹陷目前所发现的轻质(凝析油)油可分为3类不同成因油:煤成油、海相油和混合油.白云凹陷北坡PY34-1-B、PY30-1-C、PY34-1-A等气田为煤成烃,恩平组煤系烃源岩的贡献量均大于70％;LH19-5-A、LH19-5-2D、PY30-1-B、PY35-2-A和PY35-2-E等气田主要为海相成因油气,恩平组海相烃源岩的贡献量高达60％～87％;白云凹陷深水区(荔湾地区)LW3-1-B、LW3-1-D、LH34-2-A、LH29-1-A和LH16-2-A等油气田主要为混合成因,但仍以恩平组海相烃源岩为主要贡献,贡献量在60％左右.煤系烃源岩主要分布在白云凹陷的北部陆坡区,而海相烃源岩则主要分布在白云凹陷深水区,海相烃源岩可能是深水区的主力烃源岩.

珠江口盆地油气分布存在明显的分带性,浅水区珠一、珠三坳陷以油为主,油气主要来源于始新统文昌组中深湖相烃源岩,其次来源于下渐新统恩平组沼泽相烃源岩;而深水区珠二坳陷以天然气为主,油气主要来源于恩平组沼泽相烃源岩和渐新统海相烃源岩.珠江口盆地油气分带性主要受控于烃源岩的有机质类型及热演化程度.珠一、珠三坳陷文昌组中深湖相烃源岩有机质类型主要为Ⅱ1型,为倾油型烃源岩,而珠二坳陷恩平组煤系烃源岩和渐新统海相烃源岩有机质类型主要为Ⅱ2-Ⅲ型,为倾气型烃源岩,所以烃源岩有机质类型的差异是珠江口盆地油气分带的内在因素.珠江口盆地总体具有“热盆”属性,但深水区比浅水区更热,对于相同层系的烃源岩,深水区烃源岩的热演化程度明显高于浅水区,所以烃源岩热演化程度的差异是珠江口盆地油气分带的外在因素.

The main factors of the developmental environment of marine source rocks in continental margin basins have their specificality. This realization, in return, has led to the recognition that the developmental environment and pattern of marine source rocks, especially for the source rocks in continental margin basins, are still controversial or poorly understood. Through the analysis of the trace elements and maceral data, the developmental environment of Miocene marine source rocks in the Qiongdongnan Basin is reconstructed, and the developmental patterns of the Miocene marine source rocks are established. This paper attempts to reveal the hydrocarbon potential of the Miocene marine source rocks in different environment and speculate the quality of source rocks in bathyal region of the continental slope without exploratory well. Our results highlight the palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin of the northern South China Sea and speculate the hydrocarbon potential of the source rocks in the bathyal region. This study provides a window for better understanding the main factors influencing the marine source rocks in the continental margin basins, including productivity, preservation conditions, and the input of terrestrial organic matter.

The developmental characteristics of hydrocarbon source rocks in deepwater basins abroad show that hydrocarbon source rocks are distributed at the stage of rifting and depression in both rifting-depressing or rifting-drifting basins. Effective source rocks have different development characteristics at different evolution stages of continental margin basin; of these rocks, non-marine (lacustrine) dark shale at the stage of rifting is the main and most common source rock. It is also possible to develop coal measures and muddy source rocks of transitional facies and paralic facies. With the supply of large quantities of organic matter of marine-continental transitional facies, paralic facies and prodelta facies at the late intraplate depression and under the margin-plate drifting condition, or in the circumstance of being long close to provenance, hydrocarbon source rocks would develop well. Source rocks do not develop at the late stage of rifting and the early stage of depressing. As a matter of fact, effective source rocks may develop under the condition of the supply of large quantities of organic matter from the semi-closed shallow sea and bathyal environment. The above characteristics have important guiding significance for the development of source rocks in northern South China Sea, where the main source rocks are lacustrine source rocks at the early rifting stage and marine-continental transitional facies source rocks at the late stage of rifting. Miocene marine source rocks vary in different basins. With enough terrestrial organic matter supply, source rocks from the Peal River Mouth basin is more effective than those from the Qiongdongnan basin. The exploration of Gulf of Mexico basin and northern Sumatra basin has proved that source rocks of bathyal facies seem to be effective source rocks, and this finding is of reference significance for the study of Miocene marine source rocks in northern South China Sea.

The deepwater area of the northern South China Sea underwent multistage rifting in Paleogene and came into depression stage in Neogene.Lacustrine and transitional source rocks were formed mainly in the rifting period,while marine source rocks developed mainly in the depression stage.The transitional source rock is one of major source rocks in the deepwater area of the northern South China Sea.Oil and gas found in the northern South China Sea are mainly generated from transitional source rocks of Yacheng Formation and Enping Formation,while Zhuhai Formation marine source rock makes an important contribution to oil in the deepwater area of the Zhu II Depression.Natural gas in the Qiongdongnan deepwater area is a typical coal-type gas generated from Yacheng Formation humic source rock,but gas in the ZhuⅡ Depression of the Pearl River Mouth Basin is neither a typical coal-type gas nor an oil-type gas,instead it is a transitional gas generated from Enping Formation humic-sapropel source rock.

In the northern South China Sea, non-hydrocarbon gases such as CO2 are abundant, which are both constructive and destructive for gas hydrates. When the natural gases containing CO2 leak upward to shallow for-mations, CO2 could be reduced to CH4 as carbon source under appropriate conditions, forming gas hydrates within shallow sediments. The experiments of gas samples with different CO2 and N2 contents have indicated that the temperature for gas hydrate formation of CO2-bearing gases is higher than that of CH4-bearing gases, resulting in deeper occurrence of hydrates and bigger thickness of hydrate stale zones. If strong seepage happened, natural gases with higher CO2 content would migrate upward to CH4 hydrate zone through deep faults. The replacement process of CH4 by CO2 will start. The previous gas hydrates will be damaged or the saturation of CH4 will decline.

Coals developed in the Oligocene Yacheng and Lingshui formations in the Qiongdongnan Basin have high organic matter abundance, and the dark mudstones in the two formations have reached a good source rock standard but with strong heterogeneity. Through the analysis of trace elements, organic macerals and biomarkers, it is indicated that plankton has made little contribution to Oligocene source rocks compared with the terrestrial higher plants. The organic matter preservation depends on hydrodynamics and the redox environment, and the former is the major factor in the study area. During the sedimentary period of the Yacheng Formation, tidal fiats were developed in the central uplift zone, where the hydrodynamic conditions were weak and the input of terrestrial organic matter was abundant. So the Yacheng Salient of the central uplift zone is the most favorable area for the development of source rocks, followed by the central depression zone. During the sedimentary period of the Lingshui Formation, the organic matter input was sufficient in the central depression zone due to multiple sources of sediments. The semi-enclosed environment was favorable for organic matter accumulation, so high quality source rocks could be easily formed in this area, followed by the Yacheng salient of central uplift zone. Source rocks were less developed in the northern depression zone owing to poor preservation conditions.

According to the drilling results, there are three sets of source rocks of the Cenozoic Group in the Qiongdongnan Basin, including the Yacheng Formation transitional facies mudstone, the Oligocene Lingshui Formation semi-enclosed marine facies mudstone, and the Miocene neritic-bathyal facies mudstone. The hydrocarbon generating conditions of the source rocks in the study area are mainly controlled by sedimentary environment and organic matter input. The abundance of organic matter in the Oligocene source rocks which were formed in a low-energy back shore environment is confined by organic matter input and hydrodynamic condition. The Miocene source rocks formed in the open marine environment lack terrestrial organic matter input, whose organic matter abundance is constrained by the primary production of the ocean and the preservation condition of organic matter. In addition, the redox conditions are also significant to the formation of source rocks in the study area. According to the differences in key factors controlling the development of source rocks in different time periods and structural belts revealed by drilling practice, three development patterns of source rocks have been put forward. The first one is the transitional facies model featuring a great deal of terrestrial organic matter and weakly hydrodynamic conditions which are apt to develop high effective source rocks in the Yacheng Formation. The second one is the semi-enclosed marine facies featuring abundant terrestrial organic matter, weakly hydrodynamic condition and fine preservation condition in the central depression zone, which are apt to form fine-quality source rocks in the Lingshui Formation. The third one is the marine facies model featuring strong hydrodynamics in the shore-shallow area of northern continental shelf and the lack of benthic algae which are against the development of source rocks. It can be predicted that the continental slope is the perfect place to form source rocks where adequate amounts of light favor the photosynthesis of plants, besides the fine preservation and weakly hydrodynamic conditions. In the deep sea area, although accompanied with weakly hydrodynamic conditions and a reduction environment, it is not suitable for the development of source rocks on account of less aquatic organisms causing low primary production.

In Zhu Ⅲ depression,the geochemical analyses of crude oil samples and source rock samples of different depositional facies have indicated that there are a low abundance of C304-Me-Steranes and an X peak co-eluted strongly with C29 steranes in the Wenchang Formation source rock of middle-deep lacustrine facies.This new biomarker combination was firstly reported in Northern South-China-Sea basin.By using this new biomarker combination to make oil-source correlations and analyses afresh in Zhu Ⅲ depression,it is considered that the middle-deep lacustrine facies in Wenchang Formation is the major source rock in Wenchang B sag,and the swamp facies in Enping Formation is the major source rock in Wenchang A sag.Meanwhile,oil in the western Qionghai uplift primarily came from the Wenchang Formation source rock of middle-deep lacustrine facies in Wenchang B sag,and oil in the eastern Qionghai uplift mainly from the Enping Formation source rock of swamp facies in Wenchang A sag.

Drilling wells reveal that the organic matter abundance of Miocene marine source rocks in shallow water area of the Qiongdongnan Basin is relatively low with poor hydrocarbon generation potential. However, in some drilling wells of deep water area close to the central depression belt, Miocene marine source rocks with better organic matter abundance and hydrocarbon generation have been found, which have achieved better source rock standard based on the analysis of geochemical characteristics. Although there are no exploratory wells in deep water area of the research region, through the comparative analysis of geochemical data of several typical exploratory wells respectively from shallow water area in the basin, central depression belt margin in deep-water area of the basin and Site 1148 of deep sea drilling in the South China Sea Basin, it reveals that the tendency of the quality of source rocks becomes positive gradually from delta to bathyal environment, which then becomes negative as in deep oceanic environment. Owing to the lack of terrestrial organic matter input, the important controlling factors of Miocene marine source rocks in the Qiongdongnan Basin are ocean productivity and preservation conditions of organic matter. The element geochemistry data indicate that the tendency of the paleoproductivity and the preservation conditions of organic matter become positive as water depth increase from shallow area to bathyal area close to central depression belt. So it is speculated that there must exist high quality source rocks in the central depression area where the preservation conditions of organic matter are much better. Besides, in theory, in oxygen-poor zone of oceanic environment at the water depth 400–1 000 m, the preservation conditions of organic matter are well thus forming high-quality marine source rocks. The resulting speculation, it is reasonable to consider that there are high hydrocarbon generation potential source rocks in bathyal environment of the Qiongdongnan Basin, especially at the water depth 400–1 000 m.

Analytic techniques of the light hydrocarbon and the carbon isotope of natural gases were employed to cast light on the natural gas origin of shallow gas reservoirs and the migration characteristics,and the origin of the gas hydrate proved in the north of the South China Sea,in combination with the regional geology and gas hydrate data.The result indicates that the natural gas from shallow reservoirs is a mixture of biogenic gas and thermal genetic gas.It reveals that the potential gas source for gas hydrate was not limited to biogenic gas,but the biodegradation gas and thermal genetic gas have great contribution to the gas hydrate.The thermal genetic gas in the mixture gases is from deep hydrocarbon reservoirs,which indicates that the gas hydrate maybe has a close relationship with the regular deep hydrocarbon reservoirs.It can be concluded that two types of gas hydrates originated from biogenic gas and mixture gas exit in Shenhu deep zone of continental margin in the north of the South China Sea.The deep zone of Baiyun Sag in Pearl River Mouth basin will be the most valuable target for gas hydrate exploration in this area.

Thirty-seven crude oil samples and forty rock samples were analyzed by geochemistry analysis methods of GC-MS,carbon isotopic and light weight hydrocarbons for the further exploration research of Zhu Ⅲ depression.Based on the results,comprehensive comparison between oil source and hydrocarbon source rocks was done again and new cognition was gained.The results showed that the deep lacustrine facies source rock of Wenchang Formation is the major source rock of Wenchang B sag in Zhu Ⅲ depression,rather than the shore-shallow lacustrine facies source rock;and the swamp facies source rock of Enping Formation is the major source rock of Wenchang A sag in Zhu Ⅲ depression.The main contributions of the crude oil were deep lacustrine facies source rock of Wenchang Formation in Wenchang B sag(Structure WC19-1 and WC19-2),swamp facies source rock of Enping Formation in Wenchang A sag(Structure WC9-1,WC9-2,WC9-3,WC14-3,WC11-2).The crude oil in west Qionghai uplift(Structure WC13-1、WC13-2、QH18-1、QH23-1) primarily came from the deep lacustrine facies rocks of Wenchang Formation in Wenchang B sag,while that in east Qionghai uplift(Structure WC19-6N、WC7-2、WC7-3、WC8-3) mainly came from source rocks of Enping Formation in Wenchang A sag.Two episodes of hydrocarbon filling had taken place in the study area.