Characteristics of complex oil and oil-source correlations in heavy oil regions on the Northern Luxi uplift

Many biomarkers are not suitable for complex types of oil at different biodegradation extent, especially multisource heavy oil in many regions. On the southern slope near Luxi Uplift, most oilfields are heavy oil regions while some are mixed heavy and light oil regions. Therefore, some parameters that can better show oil characteristics are needed to correlate complex oil and source. Many biomarkers and parameters, such as isoprene, gammacerane, Ts, Tm, diasterane, oleanane, C₃₀hopane, C₂₉sterane20S/20(R+S), and C₂₉steraneββ/(αα+ββ), are taken into consideration. It is found that some combinations and diagrams of some parameters have better oil-source correlation results, such as the Triangular chart of C₂₉S/S+R, C₂₉β/(β+α) and Ts/Tm, the cross plot of gammacerane/C₃₀hopane and Pr/Ph, the plot of C₂₉S/S+R and Ts/Tm, the plot of Ts/Tm and gammacerane/C₃₀hopane, and the plot of C₂₉S/S+R and C₂₉ββ/(ββ+ααα). Through correlations of oil and source, the oil is classified into three types, and the sources of oil in different areas are found. The oil in Boxing sag is mainly from Es₃ and Es₄ layers. The oil in Chunhua oilfield is mainly from Es₄. The oils in Lean, Bamian, and Wang areas are found to be derived from Es₄ oil source layers in Niuzhuang Sag. To clarify oil characteristics and oil source is meaningful to compare and find the distribution of better oil types.     

东营凹陷北带深层Es下4盐下段轻质油地球化学特征及油源探讨

根据饱和烃、轻烃、双金刚烷的分析资料,全面剖析了东营凹陷北带E_s^下₄盐下段轻质油的地球化学特征。研究发现,轻质油Pr/Ph值为0.7,略呈植烷优势,轻烃中以正烷烃占优势,异构烷烃相对较少,2-甲基己烷/3\|甲基己烷的比值大于1,表征油源岩为还原的湖相沉积,生源母质较好。经轻烃指纹对比,结合双金刚烷成熟度指标分析认为,轻质油来自于E_s^下₄盐下段烃源岩。进一步表明东营凹陷深层E_s^下₄盐下段将成为勘探重要的潜力区带。     

苏北盆地溱潼凹陷北汉庄油田油气成藏地球化学特征

苏北盆地溱潼凹陷划分为断阶带、深凹带和斜坡带3排构造带,受溱潼凹陷构造带的控制,油田呈条形分布特征,北汉庄油田分布在外斜坡带。通过对北汉庄油田的原油和烃源岩的分子生物标志化合物相关参数与浓度的分析,结合常规的地质-地球化学的方法,系统研究了溱潼凹陷的北汉庄油田的油气成藏过程。研究结果表明,北汉庄油田的原油可以划分为2类：第一类原油分布于垛一段与阜三段,主要来源于深凹带阜二段烃源岩;第二类原油分布在阜一段,主要来源于深凹带阜一段烃源岩。含氮化合物浓度及其相关参数分析表明,油气沿砂体自深凹带向北汉庄油田运移,运移趋势明显,再根据深凹带烃源岩生排烃史、断层封闭史以及油气成藏期次分析,阜二段烃源岩在戴南组末期开始生烃,新近纪达到生烃高峰,与油气成藏期有较好的匹配关系,三垛组运动以后,断层垂向封闭性较强,阜二段烃源岩生成的油气通过阜三段的砂体自深凹带横向运移至北汉庄地区聚集成藏,形成了以岩性构造油气藏为主的圈闭。     

Quantitative prediction of mixed-source crude oils and its significance for understanding oil accumulation in subtle pools in the Dongying Depression,Bohai Bay Basin

Conventional geochemical approaches were utilized in the quantitative prediction of the proportions of mixed-source crude oils derived from the Es3 and ES4 members of the Paleogene Shahejie Formation. The mixed-source oils are accumulated in the middle interval of the Es3 member （Es3 M） in the Niuzhuang Sag, which is one of the sags where subtle traps are primarily of lenticular basin-floor turbidite sands within mudstones mostly developed in the Dongying Depression, Bohai Bay Basin. The result showed that about 18-92% of the mixed-source oils were derived from the Es4 source rocks with an average of 55-60%）. Reservoirs associated with deep faults appear to have much more Es4 genetic affinity oils. A high proportion of the Es4-derived oils discovered in the Es3 M subtle lithological traps in the Niuzhuang Sag have long migration distances. This suggests that surrounding source rocks might not necessarily control the hydrocarbon supply for subtle traps. Subtle migration pathway may play an important role in the vertical oil migration. The traditional concept of hydrocarbons accumulation in these tenticular turbidite sandstone traps within a short migration distance from the surrounding source rocks is not supported by this study. The present result is also consistent with our previous findings that immature oils in the Bamianhe Oilfield in the south slope of the Niuzhuang Sag were actually mixed-source oils mostly sourced from the Es4 in the depocenter of the Niuzhuang Sag, and the petroleum potential of the ES4 member in the Dongying Depression should therefore be re-evaluated.     

胜坨油田多源多期成藏混源油的定量判析

精细的原油组群划分、油源对比及成藏分析表明,东营凹陷胜坨油田主要含油层系沙二段的原油是由沙四上亚段烃源岩提供的早期降解原油与沙三下亚段、沙四上亚段两套烃源岩提供的晚期成藏原油形成的三元混合原油。选择两期成藏三个端元典型的原油样品,建立三角形判识图版,运用生物标志物绝对定量分析方法对胜坨油田的混源油进行了油源比例确定。结果表明:坨二区沙二段原油中,沙四上亚段源岩早期贡献为39%,晚期贡献为30%,沙三下亚段源岩的贡献为31%;坨三区沙二段原油中,沙四上亚段源岩早期贡献为41%,晚期贡献为33%,沙三下亚段源岩贡献为26%,即从坨二区到坨三区沙三下亚段烃源岩的贡献有减小的趋势。另外,坨二区沙一段原油中,沙四上亚段源岩早期贡献为8%,晚期贡献为24%,沙三下亚段源岩贡献为68%,混源比例不同于本区主要含油层系原油。     

Oil-source correlation in Qingdong sag of Bohai Bay basin,China

Geochemical experiments on 11 cores and 14 crude oil/oil sand samples from Qingdong sag have been performed. The oils range from immature to mature and some of the oils suffered biodegradation. The Es₃^l member of the Shahejie Formation (group A) deposits under fresh water. The Es₄^u member (group B) mainly deposits in brackish-saline evaporate environment, generating both immature and mature oils. Results show the nonbiodegraded oils in Es₃^l reservoirs in the north of the sag (group I) come from mature Es₃^l member (group A), while those in Es₄^u reservoirs (group III) come from mature Es₃^l (group A) and Es₄^u (group B₁) members in the north; the less biodegraded oils (group II) in the western slope are the admixture of immature and mature oils of Es₄^u member (group B₂) in the north; immature oils (group V) in the south are from the neighboring low mature Es₄^u member (group B₃), and the most severely biodegraded oils (group IV) in the southern come from Dongying sag, except oils from well QD-8 that have a contribution from Es₄^u member (group B₃) from Qingdong sag.     

东营凹陷湖相盆地类型演化与烃源岩发育

对东营凹陷沙三段中、下亚段和沙四段上亚段3套主力烃源层的地层层序、岩性组合、微观结构特征和有机质丰度进行了分析,研究了湖相盆地类型与烃源岩发育的关系.东营凹陷在沙四段上亚段和沙三段下亚段沉积时期为均衡补偿盆地,受气候的影响显著,因而这两个层段岩性组合易于变化、非均质性强,表现为由纹层理发育的泥页岩与块状泥岩形成的不等厚互层沉积,有机质丰度整体较高,且频率分布曲线上呈现双峰形特征.相应地,在微观尺度上,固体颗粒有机质赋存方式以“富集有机质”为主.沙三段中亚段沉积时期,表现为过补偿盆地,受气候影响较小,烃源岩非均质性不明显,“富集有机质”含量低,有机质丰度低于前两个层段,且其频率分布呈现单峰形特征.分析结果表明,沙四段上亚段和沙三段下亚段是东营凹陷优质烃源岩形成的主要时期.     

Biodegradation characteristics of heavy oil and correlation with group composition and carbon isotopes

Shallow heavy oil is abundant but seriously biodegraded in Chepaizi Uplift and many biomarkers cannot be used effectively. Therefore, some new parameters and methods are used to analyze the biodegradation extent, classification, and oil–source of heavy oil samples. The acid value and group compositions are used to evaluate the biodegradation extent. Carbon isotopes are not only used to calculate the percentage of complex combined oil, but also to correlate oil–source in Chepaizi Uplift. δ¹³C of oil is used together with biomarkers that can bear serious degradation, such as pregnanes, tricyclic terpanes, and gammacerane. The crossplots of δ¹³C and biomarkers are effective correlation tools, such as the crossplot of δ¹³C and C₂₁/C₂₃ tricyclic terpanes. δ¹³C in different group compositions also show excellent oil–source correlation results. These methods to study biodegraded heavy oil are not only helpful to clarify the biodegradation extent of shallow heavy oil in an extensive area, but also effective to classify heavy oil and correlate oil–source.     

东营凹陷古近系泥页岩中存在可供开采的油气资源

利用地球化学、岩石矿物、测井及录井等资料系统研究东营凹陷古近系沙河街组泥页岩,认为东营凹陷古近系沙三下亚段—沙四上亚段泥页岩厚度大,有机质丰度高、类型好、成熟度分布范围广,与北美地区已发现页岩气系统地质地球化学参数具有一定的可比性,具备形成页岩气的物质基础:东营凹陷沙三下亚段和沙四上亚段泥页岩全岩矿物组成具有较高石英和碳酸盐含量,粘土矿物含量低于50%,具有一定的脆性特征,且普遍发育微裂隙,有利于页岩油气的开采;东营凹陷古近系湖相泥页岩气测资料的调查发现,钻至沙三下亚段、沙四上亚段2套泥页岩发育段的探井气测显示均表现为高异常,钻井过程中频繁发生井涌和井漏现象,预示着气体的存在;2套泥页岩罐顶气轻烃(C1—C4)丰度随埋深增加而增加,在3 400m以深重烃/轻烃值较低,一般低于0.15,结合对2套泥页岩气油比的研究认为,东营凹陷针对泥页岩的勘探应采取油气兼探的方针。3 400m以浅以勘探泥页岩油藏为主,页岩气的勘探应在3 400m以深。研究表明,东营凹陷古近系泥页岩中存在可供开采的油气资源,是一个值得关注并投入风险勘探的新领域。     

A method of identifying effective source rocks and its application in the Bozhong Depression,Bohai Sea,China

Research on effective source rocks directly affects the accuracy of identifying hydrocarbon resources, and indirectly affects the exploration decisions in petroliferous basins. Although the previous evaluation methods of effective source rocks vary relatively widely, a complete quantitative evaluation approach has not yet been developed. For that reason, we redefined the concept of effective source rocks based on the existing research results. Surrounding this defi nition, and guided by the hydrocarbon expulsion theory, the quantitative model called “two stages and three steps” method is established to predict effective source rocks. Its application in the Bozhong Depression indicates that among the four sets source rocks in the Bozhong Depression, the Member 3 of the Shahejie Formation (Es₃) has the largest effective source rock thickness, and the Member 1?Member 2 of the Shahejie Formation (Es₁₊₂) is the second largest. The effective part of dark mudstone is only 30%-80% of the total volume and with the increase of buried depth and improvement of quality, the effective part increases. Comprehensive analysis indicates that the “two stages and three steps” method is a practical technique for effective source rock prediction.     

柴达木盆地北缘侏罗系烃源岩干酪根13C核磁共振研究

柴达木盆地北缘是柴达木盆地三大油气区之一,其源岩为早、中侏罗世煤系地层.烃源岩有机质类型以Ⅲ₁型和Ⅱ型干酪根为主,Ⅰ₂型干酪根仅在局部地区有分布.通过对柴达木盆地北缘侏罗系烃源岩中不同类型干酪根的¹³C核磁共振研究,指出了研究区Ⅰ₂、Ⅱ、Ⅲ₁型干酪根的化学结构特征以及化学结构中“芳构碳”、“油潜力碳”与“气潜力碳”的相对含量,据此从定量分析的角度对不同类型干酪根的生油气贡献作了评价.Ⅰ₂、Ⅱ、Ⅲ₁型干酪根的生烃能力依次减弱,对生油的贡献也依次减弱,且生成油气的比例不同,Ⅰ₂、Ⅱ型干酪根以生油为主,Ⅲ₁型干酪根则以生气为主.     

Genetic mechanisms of secondary pore development zones of Es<Stack><Subscript>4</Subscript><Superscript>x</Superscript></Stack> in the north zone of the Minfeng Sag in the Dongying Depression,East China

The genetic mechanisms of the secondary pore development zones in the lower part of the fourth member of the Shahejie Formation (Es4 x) were studied based on core observations, petrographic analysis, ?uid inclusion analysis, and petrophysical measurements along with knowledge of the tectonic evolution history, organic matter thermal evolution, and hydrocarbon accumulation history. Two secondary pore development zones exist in Es4 x, the depths of which range from 4200 to 4500 m and from 4700 to 4900 m, respectively. The reservoirs in these zones mainly consist of conglomerate in the middle fan braided channels of nearshore subaqueous fans, and the secondary pores in these reservoirs primarily originated from the dissolution of feldspars and carbonate cements. The reservoirs experienced ‘‘alkaline–acidic–alkaline–acidic–weak acidic’’, ‘‘normal pressure–overpressure–normal pressure’’, and ‘‘formation temperature increasing–decreasing–increasing’’ diagenetic environments. The diagenetic evolution sequences were ‘‘compaction/gypsum cementation/halite cementation/pyrite cementation/siderite cementation–feldspar dissolution/quartz overgrowth–carbonate cementation/ quartz dissolution/feldspar overgrowth–carbonate dissolution/feldspar dissolution/quartz overgrowth–pyrite cementation and asphalt ?lling’’. Many secondary pores (fewer than the number of primary pores) were formed by feldspar dissolution during early acidic geochemical systems with organic acid when the burial depth of the reservoirs was relatively shallow. Subsequently, the pore spaces were slightly changed because of protection from early hydrocarbon charging and ?uid overpressure during deep burial. Finally, the present secondary pore development zones were formed when many primary pores were ?lled by asphalt and pyrite from oil cracking in deeply buried paleoreservoirs.     

渤海湾盆地含油气凹陷压力场特征及与油气富集关系

含油气盆地不同类型凹陷地层压力场具有明显差异,压力场与油气富集关系密切。以渤海湾盆地含油气凹陷实测地层压力资料为基础,探讨了含油气凹陷压力场类型及分布特征,以及超压与生烃作用、压力场与油气富集等关系。研究表明,渤海湾盆地含油气凹陷新生界纵向压力场大致可归为3类,即常压型、单超压型、双超压型;不同类型压力场凹陷的分布具有分区性：常压型多分布于盆地外围凹陷,单超压型在盆地广泛分布,双超压型主要分布于环渤海地区。生烃作用对凹陷超压的形成具有重要影响,超压层系与主力生烃层系相对应,凹陷充填演化历史及主力生烃层系的差异可能是形成3类凹陷压力场的主要原因。凹陷生烃层系超压与油气富集关系密切：平面上油气围绕超压中心分布,超压程度影响油气二次运移距离;纵向上油气富集层系受凹陷压力场类型控制,常压型凹陷油气主要富集于生烃层系及紧邻层系,单超压型凹陷油气富集于生烃层系及上下多套层系,而在双超压型凹陷,新近系油气富集程度较高;生烃层系超压程度影响凹陷油气富集程度,富油凹陷均为超压幅度较大的凹陷。     

渤海湾盆地东营凹陷胜坨地区油气运聚与成藏研究

通过对渤海湾盆地济阳坳陷东营凹陷胜坨地区勘探成果和地质资料进行系统综合分析，并应用油气地质新理论和新方法，研究了该区构造演化史、沉积史与油气运移的有机联系，发现主干边界断层及其上盘主要同向调节断层的相对陡倾斜部位，往往是构造岩性圈闭相对发育的部位，而相对缓倾斜部位多是构造圈闭相对发育的部位；砂体展布及物性特征对油气运移与储集有着重要控制作用,沙二段和沙三段的砂体厚度大、分布范围广，并且直接与烃源岩相接触，是良好的油气运移通道或聚集场所，而沙四段厚砂体基本上都分布在凹陷的边缘，但是也与烃源岩相接触，也是油气运移的通道和场所；研究区水下扇及浊积扇砂体本身就处在生油岩的包围之中，因上下被生油岩夹持，油气可以直接进入砂岩体成藏；生油洼陷深部的超压环境为油气运移提供了充足的动力，油气生成后在油源断层、优质砂体以及不整合面组成的输导系统内分别向浅部和侧向运移形成各类油气藏，运移过程中又受次级断层和层内砂岩非均质性的影响，使其运移路径复杂化。     

Identification of the lower limit of high-quality source rocks and its relation to hydrocarbon accumulation— Taking the Beier Sag in the Hailaer Basin as an example

The theory of “source rock control” has evolved from source-rock-control hydrocarbon accumulation, to effective source-rock-control hydrocarbon accumulation, and to high-quality sourcerock- control hydrocarbon accumulation. However, there are problems, such as whether high-quality source rocks exist or not? What high-quality source rocks are, and how to identify them, are yet to be agreed upon. Aimed at this issue of concern to explorationists, and taking the Beier Sag in the Hailaer Basin as an example, this paper defines the high-quality source rocks and the lower limit for evaluation of high-quality source rocks, by using the inflection point on the relationship curve of hydrocarbon (oil) expulsion, which is calculated by the material balance principle, versus total organic carbon (TOC). The results show that when TOC is low, all source rocks have limited hydrocarbon expulsion and slow growth rate, thus they cannot be high-quality source rocks. However, when TOC rises to some threshold, hydrocarbon expulsion increases significantly with TOC. This inflection point should be the lower limit of high-quality source rocks: those with TOC greater than the inflection-point value are high-quality source rocks. In addition, the lower limit of high-quality source rocks is also related to the type and maturity of organic matters in the source rocks, as well as the mineral components of the source rocks affecting the residual hydrocarbons. Theoretically, the lower limit of high-quality source rocks depends on geological conditions rather than being a constant value. However, for the sake of simplicity and practicability, in this paper TOC=2.0% is regarded as the lower limit of high-quality source rocks. The examination of such standard in the work area indicates that the high-quality source rocks in members K1n2 and K1n1 of the Nantun formation contribute 76% and 82% to oil generation, and 96% and 91% to oil expulsion , respectively. The distribution of high-quality source rocks is also closely related to the distribution of hydrocarbon reservoirs in the region, demonstrating that high-quality source rocks control hydrocarbon accumulation.     

深层、超深层温度及热演化历史对油气相态与生烃历史的控制作用

我国含油气盆地深层、超深层温度差异大,热演化历史复杂,目前关于温度及热演化历史对深层、超深层油气相态差异性及生烃历史的控制作用的研究较少且不系统。为此,在收集大量深层温度、压力资料的基础上,结合我国含油气盆地深层热演化历史复杂的实际情况,分析了温度、加热时间、压力对油气形成温度及相态的影响,划分了温度与压力关系类型;并在对深层、超深层热演化史类型划分的基础上,探讨了不同热历史类型盆地热演化史对油气生成及油气相态的控制作用。研究结果表明:(1)不同盆地、不同地区深层油气相态差异大,主要受深层经历的温度、加热时间、加热速率、压力、烃源岩类型等因素的影响,其中温度是油气生成及油气相态分布最重要的控制及影响因素;(2)在快速增温、加热时间较短的情况下,深层、超深层在高温下仍然可能存在油藏及凝析气藏;(3)超压对生烃及烃类的高温裂解具有抑制作用;(4)深层温度与地层压力有着密切的关系,可划分为中低温高压型、高温高压型、中温中低压型3种主要类型;(5)深层、超深层热演化史可划分为后期快速沉降增温低地温梯度型、后期快速沉降增温高地温梯度型、中后期快速增温晚期抬升降温型、前期大幅度沉降快速增温中后期大幅度抬升剥蚀降温型4种类型,不同热演化史类型盆地的深层、超深层油气相态及成藏期早晚与油气前景不同。     

柴达木盆地阿尔金山前东段输导体系及其控藏作用

柴达木盆地阿尔金山前东段供烃区位于南部的侏罗系生烃凹陷,源储距离较远,断裂和不整合是该区主要的输导体系,对油气成藏具有控制作用。断层输导性评价表明,近南北向断裂是该区主要的油源断裂,主要控制油气垂向运移,在成藏关键时期油源断层输导性控制油气差异成藏。"TR"不整合是该区最重要的区域角度不整合,可分为基岩不整合和侏罗系不整合2种类型,均发育3层结构,包括底砾岩层、风化残积层和半风化层,其中基岩风化残积层和半风化层具有较强的输导能力,主要控制油气的长距离横向运移。断裂和不整合配置关系可分为2种组合类型、3种组合样式,组合类型决定成藏模式,组合样式控制优势运移通道和油气富集。     

Origin and accumulation of high-maturity oil and gas in deep parts of the Baxian Depression, Bohai Bay Basin, China

Great quantities of light oil and gas are produced from deep buried hill reservoirs at depths of 5,641 m to 6,027 m and 190 ℃ to 201 ℃ in the Niudong-1 Well, representing the deepest and hottest commercial hydrocarbons discovered in the Bohai Bay Basin in eastern China. This discovery suggests favorable exploration prospects for the deep parts of the basin. However, the discovery raises questions regarding the genesis and accumulation of hydrocarbons in deep reservoirs. Based on the geochemical features of the hydrocarbons and characteristics of the source rocks as well as thermal simulation experiments of hydrocarbon generation, we conclude that the oil and gas were generated from the highly mature Sha-4 Member （Es4） source rocks instead of thermal cracking of crude oils in earlier accumulations. The source kitchen with abnormal pressures and karsted carbonate reservoirs control the formation of high-maturity hydrocarbon accumulations in the buried hills （i.e., Niudong-1） in conjunction with several structural-lithologic traps in the ES4 reservoirs since the deposition of the upper Minghuazhen Formation. This means the oil and gas exploration potential in the deep parts of the Baxian Depression is probably high.     

Bicyclic sesquiterpenoids as maturity indicator in oils of Qingdong Sag,Bohai Bay Basin,China

Immature oils were proved to be existed in Es₄^u reservoirs based on GC-MS and carbon isotope analysis of oil sand and source rocks in Qingdong sag. By comprehensive discussion with compositional data from different sags in China, bicyclic sesquiterpenoids are related to thermal maturity and can be used in oil maturity identification. A new indicator, 4,4,8,9,9-pentamethyl decahydronaphthalene /8β(H)-homodrimane, is proposed for distinguishing immature and mature oils in the study area. It signifies mature when this ratio value is higher than 0.34, and immature when the value is lower than 0.34. The varying structures of the two compounds determines their stability.     

金湖凹陷原油轻烃的地球化学特征及意义

对金湖凹陷40个原油样品进行轻烃组分、Mango参数和成熟度等研究。甲基环己烷指数指示出该凹陷原油的干酪根类型为Ⅰ-Ⅱ型;C₅轻烃特征显示有机质来源既有腐泥型也有腐殖型;Mango轻烃参数K₁值基本符合轻烃稳态催化动力学轻烃成因模式,暗示着该凹陷原油有着相似的沉积环境;C₅-C₇轻烃三环优势大于五环和六环优势,表明该地区原油主要来源于湖相沉积环境的烃源岩;原油轻烃组分中的庚烷值和异庚烷指数都较低,原油成熟度低,原油形成温度在120~128℃之间。为进一步认识金湖凹陷原油和烃源岩的地球化学特征提供科学依据。