GEOCHEMICAL CHARACTERISTICS AND THERMAL MATURITY OF OILS FROM THE THRACE BASIN (WESTERN TURKEY) AND WESTERN TURKMENISTAN

Crude oils in the Thrace Basin (western Turkey) and western Turkmenistan are believed to have been generated by a common Oligocene siliciclastic source rock. This widespread source rock extends over the area between western Turkey and the eastern South Caspian Basin. Oils from three Eocene reservoirs in the Thrace Basin and from four Pliocene reservoirs onshore western Turkmenistan were analyzed to investigate and compare their source-rock characteristics. In order to understand controls on the timing of hydrocarbon generation and source-rock maturation in both basins, the results of quantitative basin modelling were compared with those of geochemical analyses.
The results indicate that all the oil samples exhibit similar geochemical characteristics, such as IP13-IP20 acyclic isoprenoid, terpane, regular sterane, methylsterane, and dinosterane profiles. The low tricyclic/pentacyclic terpane ratios, low C₂₉ norhopane/C₃₀ hopane ratios and low diasterane/regular sterane ratios, and the presence of 18α (H)³⁰ oleanane and gammacerane further support a common source or source facies. Based on these observations, it is concluded that shallow-marine clastics of Oligocene age constitute source rocks in both basins.
The oils are of low maturity (Req(%) < 0.60), as indicated by their low ethylcholestane 20S/20S+20R, 17α (H), 21β (H)-bishomohopane 22S/22S+ 22R, and high 17β (H), 21α (H) moretane/17β (H), 21α (H) hopane ratios. However, oils from west Turkmenistan appear to be more mature than those from the Thrace Basin. This is consistent with their earlier generation, which resultedfrom the higher sedimentation rate and higher heating rate. Present-day reservoir depths and temperatures appear to play only a minor role in determining the oils' maturities.     

HYDROCARBON SEEPAGE GENERATION AND MIGRATION IN THE SOUTHERN GULF OF SUEZ, EGYPT: INSIGHTS FROM BIOMARKER CHARACTERISTICS AND SOURCE ROCK MODELLING

Active oil seepages in the Gebel El-Zeit area (southern Gulf of Suez, Egypt) occur in fault zones on the western flank of the East Zeit Basin. Gas chromatography-mass spectrometry indicates that these oils are rich in tricyclic terpanes and extended hopanes with few diasteranes. These characteristics are typical of oils derived from marine siliciclastic source rocks; an input of terrestrial angiosperms material is indicated by the very high oleanane index of 32.65% and the low gammacerane index of 6.28%. The molecular maturity parameter C₂₉ααα cholestane [20S/(20S+20R)] is < 0.5 indicating that these oils were generated at relatively low thermal maturities. The seepage oils resemble Miocene crude oils in the East Zeit Basin which are believed to be generated from the Lower Miocene Rudeis Shale. Burial history modelling indicates that oil generation from this unit began at around 3–4 Ma at vitrinite reflectance levels of Ro%=0.60–0.85. This implies extensive lateral and vertical migration has taken place for the generated oil to reach the surface. Alternatively, the seepage oils may be sourced by leakage from preexisting accumulations.     

Bulk geochemical characteristics and carbon isotope composition of oils from the Sayhut sub-basin in the Gulf of Aden with emphasis on organic matter input,age and maturity

The Sayhut sub-basin is undergoing hydrocarbon exploration province in the Gulf of Aden, South Yemen. In this study, geochemical analyses were performed on three oil samples from two exploration wells in the Sayhut sub-basin. The results were used to describe the source organic matter input, age and maturity and to correlate between crude oils from different pay zones.The high saturated hydrocarbon values of more than 70% indicate that the analysed oils are normal crude oils and not degraded oils. This is supported by a complete suite of their normal alkanes and acyclic isoprenoids. The hydrocarbon distributions of normal alkane and isoprenoid with bulk carbon isotope data also suggest that the analysed oils are grouped into two genetic families and were generated from marine-source rock. The family A presents by one oil sample representing Harshiyat reservoir rock and characterized by relatively high Ph/Ph ratio > 2 and δ¹³C values of their saturated and aromatic hydrocarbon fractions range from ?26.1‰ to ?24.8‰. This oil family was derived from mixed organic matter with high contribution of a terrigenous organic matter input. The family A was deposited under suboxic conditions during the Late Cretaceous age. The family B presents by two oil samples representing Ghaydah and Habshiyah reservoir rocks and characterized by relatively low Ph/Ph ratio < 2 and carbon isotope less than ?23 for their saturated and aromatic hydrocarbon fractions. These oils were generated from source rock containing high contributions of marine organic matter (e.g., algal and microbial) with minor amount of land plant source inputs that was deposited in more reducing conditions. The family B oils are consistent with those of the Paleogene Umm Er Radhuma source rock.The hydrocarbon distribution and oil composition data also indicate that the analysed oils were generated from mature source rocks with a peak oil-window maturity.     

SOURCE ROCK CHARACTERIZATION BASED ON BIOLOGICAL MARKER DISTRIBUTIONS OF CRUDE OILS IN THE SOUTHERN GULF OF SUEZ, EGYPT

The depositional environment and maturity of source rocks in the southern Gulf of Suez were evaluated using biomarker and isotope data from crude oils derived from a variety of source rock types of different geological ages. Two oils families were identified and are referred to as types A and B. Type A oils are characterized by a predominance of oleanane and relatively low gammacerane concentrations, suggesting that they were derived from a terrigenous source rock with a significant input of angiosperm material inferred to occur within the marginally-mature syn-rift Lower Miocene Rudeis Shale. By contrast, type B oils are distinguished by a predominance of gammacerane and relatively low oleanane concentrations, suggesting that they were generated from mature marine carbonate source rocks inferred to occur within the Upper Cretaceous Brown Limestone and Middle Eocene Thebes Formation. Maturity parameters including the sterane isomerisation ratios C ₂₉αββ/(αββ+ααα), C₂₉ααα20S/(S+R) and TAS/(TAS+MAS), together with aromatic sulphur compound ratios (4-MDBT / I-MDBT; 4,6- / 1,4-DMDBT; 2,4–/ 1,4-DMDBT; and DBT / phenanthrenes), support the higher thermal maturity of type B oils relative to type A oils.
The biomarker variablility reflects the occurrence of two distinct source rocks in the southern Gulf of Suez and suggests that two independent petroleum systems are present here. These appear to be confined to the pre-rift (pre-Miocene) and syn-rift megasequences respectively.     

准噶尔盆地腹部地区原油金刚烷化合物特征及应用

利用色谱/质谱/质谱方法分析了准噶尔盆地腹部地区原油中金刚烷化合物的含量，探讨了金刚烷参数指标在腹部地区原油类型划分和成熟度判识中的适用性。腹部地区原油中金刚烷类化合物含量较低，主要分布在（200~500）×10-6。利用金刚烷类化合物浓度指标能够有效划分原油的类型，金刚烷异构化指标能够有效判识原油的成熟度。腹部地区原油主要分为两大类:Ⅰ类原油为早期相对低熟原油，金刚烷类化合物含量低，单金刚烷含量相对较高，浓度指标A/1-MA比值分布在0.50~0.71，成熟度指标MAI值较小，在0.41~0.50之间，主要分布在远离生烃凹陷区域；Ⅱ类原油为晚期相对高熟油，金刚烷类化合物含量较高，1-甲基单金刚烷含量较高，A/1-MA比值分布在0.30~0.37，MAI值在0.52~0.69之间，主要分布在生烃凹陷内，其分布格局与油气运移方向一致，即晚期充注的原油驱动早期充注的原油向远离生烃凹陷处运移，证实了腹部原油运移方向为盆1井西凹陷向北运移。      

车排子凸起西南缘油气来源与成藏过程

车排子凸起紧邻两大生烃凹陷,由于烃源岩层多,油气来源尚不明确,为了进一步明确油气来源,对研究区的原油根据地球化学特征进行了分类,同时厘定了主力烃源岩的地化特征。研究结果表明:研究区的原油可以分为两类,其中Ⅰ类原油是氧化环境下高等植物来源的高成熟原油,主要来源于四棵树凹陷侏罗系烃源岩,Ⅱ类原油是氧化一还原环境下高等植物及藻类来源的较低成熟原油,主要来源于四棵树凹陷侏罗系烃源岩与白垩系或古近系源岩的混源。结合油气输导条件及区域构造背景演化,认为侏罗系/石炭系不整合底砾岩及沙湾组一段1砂组的"板砂"是油气横向运移的有利通道,而喜山期形成的正断层则是油气垂向运移的有利通道。     

塔河油田成藏期次的地球化学示踪研究

应用油藏地球化学的方法对塔河油田的成藏期次进行了探讨。塔河油田稠油正构烷烃分布完整,但色谱基线不同程度抬升;原油非烃和沥青质碳同位素偏轻,族组成碳同位素发生倒转;原油中普遍含有25-降藿烷。这些特征表明该区油藏经历了至少两期成藏过程,早期充注原油遭受生物降解作用后又受到高成熟原油充注。塔河油田天然气为典型的油型气,成熟度较高,为成熟—过成熟阶段产物,亦显示了两期充注的特征:早期充注的为典型的原油伴生气,充注时间与后期原油的充注时间相同;晚期充注的为高温裂解气,充注方向为自东向西。因此,塔河油田至少存在着3次油气充注过程。      

Organic geochemistry characterisation of crude oils from Mishrif reservoir rocks in the southern Mesopotamian Basin,South Iraq: Implication for source input and paleoenvironmental conditions

Seven crude oils from Cretaceous Mishrif reservoir rocks in the southern Mesopotamian Basin, South Iraq were studied to describe oil characteristics, providing information on the source of organic matter input and the genetic link between oils and their potential source rock in the basin. This study is based on biomarker and non-biomarker analyses performed on oil samples. The analysed oils are aromatic intermediate oils as indicated by high aromatic hydrocarbon fractions with more that 50%. These oils are also characterized by high sulfur and trace metal (Ni, V) contents and relatively low API gravity values (19.0–27.2° API). The results of this study indicate that these oils were derived from a marine carbonate source rocks bearing Type II-S kerogen that were deposited under sulphate-reducing conditions. This is primary achieved from their biomarkers and bulk carbon isotope and inorganic element contents (i.e., S, Ni and V). The absence of 18a (H)-oleanane biomarker also suggests a source age older than Late Cretaceous. The biomarker characteristics of these oils are consistent with those of the Late Jurassic to Early Cretaceous source rocks in the basin. However, biomarker maturity data also indicate that the oils were generated from early maturity source rocks. This appears to result from the type of kerogen of the source rock, characterized by a high-S kerogen (Type II-S).     

咔唑、酚类和二苯并噻吩类化合物在油气运移研究中的应用

原油和源岩中咔唑、酚类和二苯并噻吩类化合物为油气运移研究提供了理想的工具.烷基咔唑浓度、屏蔽和半屏蔽异构体-暴露异构体比值和苯并咔唑比值是很好的运移指标,但源岩有机质输入、沉积环境、热成熟度、初次和二次运移及生物降解作用都可能对这些化合物分布产生影响.不同沉积环境的原油中咔唑类化合物分布差异很大,咔唑类化合物运移参数在成熟度较低时随成熟度增加而增加,在成熟度较高时随成熟度增加而降低,限制了其作为油气运移指标的适用性.烷基酚浓度可以指示油气运移方向,但同样受相和沉积环境、成熟度和生物降解等多种因素影响.同源石油的烷基二苯并噻吩类参数(如4-/1-MDBT,2,4-/1,4-DMDBT和4,6-/1,4-DMDBT)可应用于不同成熟度的原油、生物降解原油和同源石油两期充注的混合油的油气运移示踪,是很好的油气运移评价工具.断陷盆地生成的油气成熟度差异大,相和沉积环境变化快,因此利用分子地球化学指标进行油气运移示踪时,需要综合考虑各种影响因素.     

北部湾盆地福山凹陷原油充注方向及成藏特征

利用油藏地球化学方法研究了北部湾盆地福山凹陷花场油气田流沙港组(E₂l)油气运移和充注方向,分析了流沙港组三段上部与下部油气成藏特征的差异。结果表明花场油气田流沙港组三段上部(E₂l₃1)原油主要来自花场次凸北东方向的白莲次凹,油气沿流二段和流三段之间的不整合面、流三段扇三角洲前缘砂体和断层构成的输导体系运移至花场次凸有利圈闭中聚集成藏。造成流沙港组三段中下部(E₂l₃2—E₂l₃3)相对上部油气藏原油密度略高、成熟度稍低、CO₂气含量高、油气产量低的原因在于:受下部反向正断层的控制,流三段中下部原油可能主要来自花场次凸原地流三段烃源岩的贡献。该烃源岩成熟度和生烃潜力明显低于白莲次凹,输导条件也如上部油气藏优越,断穿流三段并切到基岩的深大断裂可能作为火山—幔源成因CO₂充注的通道。油藏地球化学为判识油气运移充注方向和成藏特征研究提供了直接有力的证据。      

轻质油中C1—C7轻烃的地球化学特征

作者对5个盆地18个轻质油样品作了C_1—C_7轻烃分析,检测出29种单体轻烃。通过轻烃组成特征研究,认识到石蜡指数(PI_1)和庚烷值(PI_2)作为成熟度的指标,不受沉积盆地类型影响;C_6,C_7烃类族组分受母质类型影响较大。陆相(含煤地层)有机质生成轻质芳烃(苯)的含量比海相有机质要高。新疆塔里木盆地沙参2井原油的轻烃分析资料表明,该井油源岩为海相沉积。     

准噶尔盆地中部1区块原油轻烃地球化学特征

通过对准噶尔盆地中部1区块与相邻油田原油中轻烃分布与组成特征的系统对比研究,发现中部1区块原油的轻烃以富含甲基环己烷为特征,其甲基环己烷指数基本都大于50%,且具有相对较高的姥植比。这明显不同于相邻的石西油田和莫北油田的原油,揭示出中部1区块原油中具有一定量陆源有机质的贡献。这与前人依据生物标志化合物和碳同位素的分析资料所得出的油源对比结果一致。利用2,4-二甲基戊烷/2,3-二甲基戊烷值计算的原油生成时镜质体反射率结果表明中部1区块原油的成熟度高于临近的石西油田和莫北油田的原油,表明盆地腹部主力烃源岩层中有机质成熟度相对偏高。由此可见,原油轻烃在研究其来源、成因和成熟度等方面具有很高的实用价值。     

扎哈泉凹陷烃源岩特征及演化史研究

扎哈泉凹陷周缘已发现昆北、乌南等大量油气藏,但其油源层位和凹陷源岩生烃能力尚不十分清楚。通过开展烃源岩展布、有机质丰度、类型和成熟度的研究,指出扎哈泉凹陷烃源岩分布范围从E1+2到N12具有东移或北移的特征。E13和E23烃源岩有机碳和氯仿沥青"A"含量均较高,按照青海油田分类标准,达到好-较好烃源岩标准;N1和N12烃源岩有机碳含量较低,生烃能力较差。烃源岩干酪根显微组分以腐泥组为主,达90%以上,有机质类型以Ⅰ型为主。通过一维数值模拟,认为目前E13和E23烃源岩达到成熟阶段,N1和N12烃源岩处于未-低成熟阶段;E13和E23烃源岩生烃能力较强,可为周缘构造提供丰富的油气。     

C4-C8轻烃在原油地球化学研究中的应用——以塔里木盆地大宛齐油田凝析油为例

全油样品的GC分析表明,塔里木盆地大宛齐油田不同层位的81个原油样品富含轻烃组分,且部分样品遭受了不同程度的微生物降解。以C₄-C₈轻烃地球化学参数为工具,对原油成熟度和次生蚀变等方面进行地球化学研究。轻烃成熟度参数表明,原油的折算R_c在0.9%左右,处于成熟阶段。对遭受生物降解作用的原油分析发现,随着生物降解作用的增强,其Mango轻烃参数K₁值减小,K₂值明显增大,甲基环己烷指数增大,甲基环戊烷较乙基环戊烷更容易遭受生物降解,表明单烷基环戊烷中烷基取代基越大的烃类越难遭受生物降解作用。结合轻烃参数指示的原油成熟度和母质来源,推测研究区原油为次生凝析油。通过轻烃参数对比研究发现,大宛齐油田凝析油轻烃参数特征与大北和其南部地区正常原油相似。依据塔里木盆地大宛齐油田的地质背景和原油成藏模式可知,研究区原油是大北和南部地区两类原油通过深大断裂运移到大宛齐浅部,通过蒸发分馏作用聚集成藏。      

东营凹陷南斜坡特高蜡油的成因

东营凹陷南斜坡王古1、新角1奥陶系古潜山原油具有特高含蜡特征(40%～60%),同区下第三系孔店组原油含蜡量也明显偏高(28.85%～31.7%)。不同层系的原油烃类化学成分分析、油源对比结果表明,研究区高蜡油成因不同于上覆第三系沙河街组,前者为深部油源,第三系孔店组为其重要烃源岩之一;后者主要源自正常油窗内沙河街组四段烃源岩。生物标志物定量分析结果表明,区内烃源岩沥青与原油中的蜡质烃含量随成熟度增加而增加,反映热成熟度是控制该区高蜡油形成的重要因素之一。东营凹陷湖沼相成因的孔店组烃源岩含有相对较高的陆源高等植物,是导致该区高蜡油形成的另一重要因素。综合分析认为,东营凹陷南斜坡高蜡油的形成主要与烃源岩相对较高的热成熟度及烃源岩含有丰富的可提供蜡质烃的成烃母质(主要指孔店组二段)有关,气侵与油气运移分馏效应的影响甚微。     

BIOMARKER GEOCHEMISTRY OF CRUDE OILS FROM THE QAIDAM BASIN, NW CHINA

A suite of 16 crude oil samples from 13 oilfields in the Qaidam Basin were analyzed using techniques including gas chromatography and gas chromatography - mass spectrometry. Biomarker compositions and parameters were used to investigate the palaeoenvironmental and depositional conditions and to correlate the oils with eachother. Oils from the western Qaidam Basin have pristane/phytane (Pr/Ph) ratios of less than 0.7, and contain abundant gammacerane, C₂₇ steranes, 4-methyl steranes and long-chain tricyclic terpanes. C₂₉ sterane 20S/(20S+20R) and ββ/(ββ+αα) ratios show that the western Qaidam oils have variable maturities ranging from immature to mature. Oils from the northern Qaidam Basin, by contrast, have Pr/Ph ratios greater than 3, low gammacerane contents, and relatively abundant C₂₉ steranes, bicyclic terpanes and alkylcyclohexanes. C₂₉ sterane 20S/(20S+20R) and ββ/(ββ+αα) ratios indicate that the northern Qaidam oils are mature.
δ¹³C values, which range from -25.4‰ to -28.3‰ with the exception of one oil from the north (-3l.6‰), are similar for oils from both the northern and western parts of the Qaidam Basin. The oils'carbon isotope compositions are similar to those of the organic matter in potential source rocks.
The western Qaidam oils are inferred to have originated from Tertiary source rocks deposited under anoxic and saline-hypersaline lacustrine conditions with dominant algal organic matter. The northern Qaidam oils are interpreted to be derived from Jurassic source rocks which were deposited in a freshwater lacustrine environment and which are dominated by terrigenous organic matter.     

Distribution of sterane maturity parameters in a lacustrine basin and their control factors: A case study from the Dongying Sag, East China

Fifty samples from the source rocks in Member 3 and Member 4 of the Paleogene Shahejie Formation in the Bohai Bay Basin,East China,were analyzed to investigate the distribution,evolution of the molecular maturity ratios C 29 ββ/(ββ+αα) and C 29 20S/(20S+20R) and their control factors in the natural geological profile and sequence.The results showed that progressive changes in molecular maturity parameters are associated with major changes in thermal evolution of related biomarkers.Increases in the C 29 ββ/(ββ+αα) and C 29 20S/(20S+20R) ratios result from the difference in the relative rate between generation and thermal degradation of isomers involved.The samples from a hyper-saline environment below 3.5 km in which evaporitic rocks deposited shows high response of Sr/Ba,Sr/Ca,Fe/Mn,Pr/n-C 17,Ph/n-C 18 and gammacerane and low response of Pr/Ph.There presents negative reversal of biomarker maturity C 29 ββ/(ββ+αα),C 29 20S/(20S+20R) and Ts/(Ts+Tm) in the samples from hypersaline environment,reflecting that the gypsum-halite have negative effect on the isomerization of biomarker and thermal evolution of organic matter.The minerals in evaporites also retard the conventional thermal indicators including vitrinite reflectance (R o) and pyrolysis peak temperature T max at the depth below 3.4 km (i.e.>3.4 km),and these parameters also show the inhibition from overpressure in the range of 2.4-3.4 km.This result will be helpful in the interpretation and application of molecular maturity parameters for similar saline lacustrine basins.     

东濮凹陷马厂地区油气成藏机理分析

为了理清马厂地区油气成藏机理特征,通过对马厂地区原油饱和烃、芳烃、非烃及沥青质等资料的分析,得出马厂地区存在2大类原油,2类原油均为成熟原油,但原油的成熟度存在高低。整体上,构造顶部的原油成熟度偏低,构造翼部的原油成熟度偏高;原油成熟度自构造顶部到构造翼部呈逐渐增大的趋势。通过对该区的烃源岩特征、断裂发育史、油气充注史等资料的综合分析,认为马厂地区构造顶部原油的成熟度主要与马东断裂的有序活动引起原油的有序充注有关,构造翼部原油的成熟度主要与东营构造时期的剥蚀厚度及后期沉积厚度大小有关。     

准噶尔盆地烷烃气碳同位素组成及来源

通过对全盆地烷烃气碳同位素组成进行分析,明确了准噶尔盆地烷烃气成因类型、来源及分布。准噶尔盆地天然气主要包括成熟—过成熟油型气、成熟—过成熟煤型气、过渡气和生物气等。准噶尔盆地烷烃气碳同位素倒转普遍,碳同位素倒转原因包括细菌氧化作用、油型气和煤型气混合、不同源煤型气混合以及同源不同阶煤型气混合。准噶尔盆地煤型气包括3类：①煤型气重烃气碳同位素组成较重(δ¹³C₂＞-26.0‰),主要为成熟—高成熟,来源于侏罗系烃源岩;②煤型气重烃气碳同位素组成相对较轻(δ¹³C₂＜-26.0‰),成熟度范围广,来源于侏罗系、二叠系乌尔禾组和佳木河组烃源岩中的一套或多套;③煤型气重烃气碳同位素组成分布范围广,主要为高—过成熟,来源于石炭系烃源岩。     

酒西盆地油气形成与勘探方向新认识（三）——油气运移、成藏规律与勘探方向

红南凹陷和青西低凸起的发现使得对酒西盆地青西坳陷的地质结构有了新认识,虽然青西坳陷的凹陷面积减少了,但酒西盆地仍有可勘探潜力,然而,油气资源潜力及油气成藏规律如何？有利的勘探区域和方向在哪里？本文主要探讨酒西盆地油气运移和成藏规律,在此基础上提出新的勘探方向。