凝析油形成新模式─—原油蒸发分馏机制研究

经典的石油生成理论认为凝析油是源岩高成熟阶段、或是陆相有机质于低成熟阶段的直接产物。本文在资料、数据分析的基础上结合我国塔北海相油田的实际地质地化资料提出原油蒸发分馏机制是凝析油形成的一种重要途径，并确认了塔北油田的诸多原油曾遭受了程度不一的蒸发分馏作用且有成熟度正常的凝析油形成。     

东海盆地西湖凹陷油岩地球化学特征及原油成因来源

东海盆地西湖凹陷具有大量的原油资源,但对于原油成因讨论较少.采集西湖凹陷多个油样和岩样,利用气相色谱和傅里叶红外光谱等手段,全面分析了该区烃源岩和原油的地球化学特征,综合讨论了原油来源以及凝析油和高蜡轻质油的成因.研究结果表明,平湖组煤系源岩均处于热演化的成熟阶段,其中碳质泥岩和煤岩以陆源生物为主要生源,其干酪根类型为Ⅲ型,暗色泥岩则具有陆源生物和水生生物双重生源贡献,其干酪根类型Ⅱ-Ⅲ型,同时碳质泥岩和煤的生油潜力远高于泥岩.原油主要为凝析油和轻质油,凝析油具有低密度、低蜡等“六低一高”的特点,轻质油具有高蜡特质,而且轻烃组分有明显差异.生标参数显示大部分原油为腐殖型,少部分原油表现出具有腐殖和腐泥母质的特点,同时该区原油均处于中等成熟阶段.油油对比和油岩对比表明大部分油来自平湖组碳质泥岩和煤岩,具有典型Ⅲ型腐殖油的特征;少部分油来自暗色泥岩,具有Ⅱ-Ⅲ型油的特征(总体上仍偏腐殖型).凝析油和轻质油的物性及轻烃组分的差异与源岩母质无关.凝析油是干酪根在成熟演化阶段生成的原油遭受蒸发分馏作用的结果,高蜡轻质油除了是“蒸发分馏作用”的残余油外,还有部分是“混合作用”的结果.      

塔中台盆区原油正构烷烃摩尔浓度分布特征及意义

塔里木盆地塔中地区原油性质的多样性和复杂性十分罕见;分析表明,成熟作用和源岩相很可能是原油多样性的次要因素,主要影响因素可能与多期成藏或成藏后储层内的次生蚀变作用有关。本文对照正构烷烃摩尔浓度分布图版,辨别了塔中地区不同构造单元原油正构烷烃摩尔浓度的分布类型,分析了原油遭受次生蚀变作用的程度,以及蒸发分馏作用、气洗作用发生的原因及其对原油物性的影响。结果表明,由于运移通道以及与油气源的距离等因素,从塔中Ⅰ号断裂坡折带至中央断垒带,蒸发分馏作用和气洗作用发生的频率逐渐降低,但基态原油分布频率有增高的趋势。并且Ⅰ号断裂坡折带部分凝析油、高蜡油的形成主要与上述蒸发分馏、气洗、晶析等储层内的次生蚀变作用有关。     

塔里木盆地气－液溶解平衡机制下的原油轻烃行为及其地质意义

塔北地区普遍存在气顶型凝析气藏和带油环的凝析气藏。与传统烃类热演化理论相矛盾的是：１）天然气的成熟度远高于油环原油或凝析油；２）高－过成熟天然气与同藏的原油间存在明显的物性不匹配。结合地质背景，认为这种矛盾是由后期形成的干气进入已形成的油藏并溶解原油轻烃这一过程所致，凝析气中的轻烃是气－液溶解平衡的产物。地质历史时期凝析气与油环分离或产生凝析油气藏或混入其它油藏的蒸发分馏作用过程导致了轻烃的油藏再分配，形成了塔北地区纵向上原油轻烃的“反序”分布趋势及某些参数的异常分布。认为烃类的气－液相溶解平衡作用是原始原油轻烃分布特征后期演变的主要控制机制之一。其实质是不同性质轻烃气液两相差异性分配基础上的物理化学分异过程。     

塔里木盆地气－液溶解平衡机制下的原油轻烃行为及其地质意义

塔北地区普遍存在气顶型凝析气藏和带油环的凝析气藏。与传统烃类热演化理论相矛盾的是:１）天然气的成熟度远高于油环原油或凝析油；２）高－过成熟天然气与同藏的原油间存在明显的物性不匹配。结合地质背景，认为这种矛盾是由后期形成的干气进入已形成的油藏并溶解原油轻烃这一过程所致，凝析气中的轻烃是气－液溶解平衡的产物。地质历史时期凝析气与油环分离或产生凝析油气藏或混入其它油藏的蒸发分馏作用过程导致了轻烃的油藏再分配，形成了塔北地区纵向上原油轻烃的“反序”分布趋势及某些参数的异常分布。认为烃类的气－液相溶解平衡作用是原始原油轻烃分布特征后期演变的主要控制机制之一。其实质是不同性质轻烃气液两相差异性分配基础上的物理化学分异过程。     

松辽盆地北部深层凝析油及油型气的成因研究

松辽盆地北部深层发现的凝析油及油型气扩大了油田的勘探潜力.应用单体烃碳同位素、生物标志化合物等分析技术,结合地质背景对凝析油、天然气和固体沥青进行的地球化学研究表明:深层凝析油包括煤成凝析油和泥质烃源岩形成的凝析油,前者芳烃含量高、单体烃碳同位素重,后者饱和烃含量高、单体烃碳同位素轻,生物标志化合物对比,二者均来自于沙河子组烃源岩;油型气甲烷碳同位素轻,一般小于-45‰,且甲烷与乙烷之间碳同位素分馏明显,属原油裂解成气特征,油型气与煤型气混合可能是深层天然气碳同位素系列倒转的重要原因之一;火山岩储层中的固体沥青有机地球化学分析,有机碳含量0.08%～0.16%,氢指数49～297 mg/g,Ro大约为1.87%,表征固体沥青现今的成烃潜力较小,原油向天然气转化主要发生在高成熟阶段的晚期,对应的地质年代大约是嫩江组-明水组沉积末(80～65 Ma).原油向天然气转化的事实启示,深层天然气勘探要兼顾古油藏的研究.     

松辽盆地北部深层凝析油及油型气的成因研究

松辽盆地北部深层发现的凝析油及油型气扩大了油田的勘探潜力。应用单体烃碳同位素、生物标志化合物等分析技术，结合地质背景对凝析油、天然气和固体沥青进行的地球化学研究表明：深层凝析油包括煤成凝析油和泥质烃源岩形成的凝析油，前芳烃含量高、单体烃碳同位素重，后饱和烃含量高、单体烃碳同位素轻，生物标志化合物对比，二均来自于沙河子组烃源岩；油型气甲烷碳同位素轻，一般小于-45‰，且甲烷与乙烷之间碳同位素分馏明显，属原油裂解成气特征，油型气与煤型气混合可能是深层天然气碳同位素系列倒转的重要原因之一；火山岩储层中的固体沥青有机地球化学分析，有机碳含量0．08％～0．16％，氢指数49～297mg／g，R0大约为1．87％，表征固体沥青现今的成烃潜力较小，原油向天然气转化主要发生在高成熟阶段的晚期，对应的地质年代大约是嫩江组一明水组沉积末(80～65Ma)。原油向天然气转化的事实启示，深层天然气勘探要兼顾古油藏的研究。     

凝析油的多种成因概述

本文概述了国内外对凝析油成因类型及地质产状的研究。凝析油是特定物化条件下液态烃逆蒸发的产物,不仅可以形成于有机质演化的高成熟阶段,也可以形成于中-低成熟阶段。凝析油按其成因可以分为三类。高成熟腐泥型凝析油最为重要。它是高温下高分子量烃类热裂解的产物,多产于盆地深处,与高成熟的生油岩(R_0＞1.3%)有关。低(未)成熟树脂型凝析油是以树脂体为主的有机质在低成熟阶段降解产物。本文介绍了有关树脂体热解色谱分析成果。其热解温度低,产物中富含倍半萜和三环双萜。该类凝析油与含过渡型有机质的低中等成熟度的生油岩有关(R_0;0.4—1.0%)。煤型凝析油是煤系地层中类脂组分在气-肥煤阶段热解的产物。具短侧链的镜质组也可以形成低分子量烃类。该类凝析油富含芳香烃。煤系地层中显微组分的分异影响了凝析油、轻质油和高蜡油的分布。     

松辽盆地齐家-古龙凹陷凝析油气藏成因

为了阐明齐家-古龙凹陷所发现的凝析油气藏的成因, 结合研究区凝析油气藏所处的地质背景、油油对比认识, 设计进行了原油的热蒸发模拟实验.结果表明, 区内凝析油与下伏的黑油同源, 这暗示了其次生成因; 实验室热蒸发模拟实验支持上部的凝析油为下部黑油的热蒸发作用所产生.这种热蒸发作用可能是通过断层或微裂缝实现的.热蒸发成因将使区内形成大规模的凝析气藏的可能性减小, 勘探的有利目标应该在有利于蒸发作用发生的通道、但目前埋深仍然较大、温压较高的地区.      

盐城凹陷凝析油地球化学特征

运用碳同位素、气相色谱、色谱—质谱、流体包裹体技术，研究了盐城凹陷凝析油地球化学特征，并与永安凹陷永7井凝析油、下扬子海相原油进行了对比。该凝析油碳同位素为-28．8‰—30．5‰，全油色谱中含有一定的长使正构烷烃，Pr/Ph为1．56，三环菇烷含量高，伽玛蜡烷含量低，重排甾烷含量高，C29甾烷＞＞C27甾烷＞C28甾烷。石蜡指数、庚烷值表明原油为高成熟凝析油，甲基菲指数MPI表明原油为未熟—低藏原油，C29甾烷20S／(20S 20R)值表明原油为成熟原油。这种成熟度的差异可能与不同成熟度原油的混合作用有关。油气主要充注时间为6—15Ma。凝析油的主体可能源于泰州组烃源岩，凝析油的形成与蒸发分信作用密不可分。     

Fractionated aromatic petroleums and the generation of gas-condensates

Based on experimental and observational evidence, a mode of origin involving evaporative fractionation is proposed for a class of petroleums enriched in light aromatic and naphthenic hydrocarbons (benzene, toluene, meta-xylene, para-xylene, methylcyclopentane, cyclohexane, and methylcyclohexane). Progressive gas loss from gas-saturated oil is suggested as the causal mechanism, with simultaneous loss of light ends in gaseous solution, and accompanying fractionation. These processes were simulated experimentally.Residual oils exhibit the following changes in their remaining light hydrocarbons, <C₉: (1) increase in aromaticity (in aromatic hydrocarbons relative to normal alkanes of molecular weight); (2) increase in “normality” (in unbranched alkanes and naphthenes relative to branched isomers), and (3) decrease in paraffinicity (in paraffins relative to naphthenes). Retrogressive changes in maturity indicators take place leading to spurious evidence of immaturity in residual oils and the derived evaporative condensates.The phenomena occur in many basins, and are a key to understanding major aspects of petroleum variability. On the basis of aromaticity and paraffinicity relationships, evaporative gas-condensates are distinguishable from those generated by thermal cracking. Unfractionated thermal gas-condensates are rare. Evaporative condensates are the daughter products of oils which have suffered evaporative fractionation.     

Estimation of temperature conditions for the formation of HASP and GASP glasses from the lunar regolith

Impact cratering on the Moon’s surface was accompanied by the high-temperature melting of rocks, melt evaporation, and silicate vapor condensation. Evidence for the extensive evaporative fractionation of melts was found in HASP (High-Alumina Silica-Poor) glasses from the lunar regolith. Numerous objects of condensation origin were found in the Apollo 14 regolith breccia. They are referred to as GASP (Gas-Associated Spheroidal Precipitates). With respect to chemical characteristics, namely FeO and SiO₂ contents, GASP were subdivided into Fe-rich (FeGASP) and Si-rich (SiGASP) condensates. Based on experimental data on the evaporation of aluminous basalt sample 68415.40 from the Apollo 16 collection and the calculated compositions of residual melts and complementary vapors at various temperatures, we compared the obtained compositions with the chemical analyses of the HASP glasses and GASP condensates. The comparison was aimed at estimating the temperature conditions of HASP and GASP formation. The comparison showed that the compositions of the HASP glasses and GASP condensates are consistent with the compositions obtained in the equilibrium experiment. In accordance with the experiment, the temperature range of the evaporation of HASP glasses was estimated as ∼1750–1870°C. The temperature interval of condensation, with allowance for the effect of vapor supercooling, is ∼1700–1500°C for FeGASP and no higher than 1700–1750°C for SiGASP. This paper discusses the problems of establishing interphase thermodynamic equilibrium during the dispersion of a vapor-melt cloud, vapor supercooling during its condensation, and the influence of the curvature of melt and condensate particles on the character of evaporation and condensation.     

Petroleum in the Jurassic Reservoirs within the Eastern Fukang Sub-depression, Junggar Basin, NW China: Correlation and Source Rock

The origin and source of the petroleum in the Jurassic reservoirs within the eastern Fukang sub-depression were geochemically investigated. They show thermal maturities matching the peak generation stage, while the condensates are at the early stage of intense cracking. Oils and condensates may have experienced mild evaporative fractionation, while mixing of severely biodegraded with non-biodegraded oils has occurred. Using biomarkers and isotopes, petroleums were classified into Group I, II and III genetic groups, with Group III further divided into IIIa and IIIb subgroups. Group I petroleum displays heavy carbon isotopes, a strong predominance of pristine over phytane, high C19 and C20 tricyclic and C24 tetracyclic terpanes, low gammacerane, and dominant C29 steranes, while Group II shows light carbon isotopes, a predominance of phytane over pristine, high C21 and C23 tricyclic with low C24 tetracyclic terpanes, high gammacerane and dominant C27 steranes. Group IIIa petroleum shows mixing compositions of Group I and II, while Group IIIb displays similar compositions to Group I, but with significantly higher Ts, C29Ts and C30 diahopane proportions. Oil-source rock correlation suggests Group I and II petroleums originate from Jurassic and Permian source rocks, respectively, while Group IIIa are mixtures sourced from these rocks and IIIb are mixtures from Jurassic and Triassic source rocks.     

Re-Examination of the Oil and Gas Origins in the Kekeya Gas Condensate Field, Northwest China–A Case Study of Hydrocarbon-Source Correlation Using Sophisticated Geochemical Methods

This work discussed the origins, alteration and accumulation processes of the oil and gas in the Kekeya gas condensate field based on molecular compositions, stable carbon isotopes, light hydrocarbons, diamondoid hydrocarbons and biomarker fingerprints. A comparison study is also made between the geochemical characteristics of the Kekeya hydrocarbons and typical marine and terrigenous hydrocarbons of the Tarim Basin. Natural gas from the Kekeya gas condensate field is derived from Middle–Lower Jurassic coal measures while the condensates are derived from Carboniferous–Permian marine source rocks with a higher maturity. In the study area, both natural gas and condensates have experienced severe water washing. A large amount of methane was dissolved into the water, resulting in a decrease in the dryness coefficient. Water washing also makes the carbon isotopic compositions of the natural gas more negative and partially reverse. Considering that the gas maturities are higher than once expected, gas generation intensity in the study area should be much stronger and the gas related to the Jurassic coal measures could promise a greater prospecting potential. As a result of evaporative fractionation, the Kekeya condensates are enriched in saturates and lack aromatics. Evaporative fractionation disguises the original terrigenous characteristics of the light hydrocarbons associated with the natural gas, making it appear marinesourced. Thus, alteration processes should be fully taken into consideration when gas–source correlations are carried out based on light hydrocarbons. With the condensates discovered in the study area all being "migration phase", the pre-salt Cretaceous and Jurassic reservoirs may promise great exploration potential for the "residual phase" hydrocarbons. This research not only is of significance for oil and gas exploration in the southwest Tarim Basin, but also sheds light on the oil/gas-source correlations in general.     

Relationship between rank and distribution of methylaromatic hydrocarbons for condensates of different origins

Aromatic hydrocarbon fractions from thirty gas condensates have been analysed by capillary GC and high resolution Shpol'skii spectroscopy for the determination of the relative distribution in methylphenanthrene (MP), dimethylphenanthrene (DMP) and methylpyrene (MPy) series. The measured maturity indices, MPI, DMPI and MPyI which appeared previously suitable for rocks, coals and crude oils have been tested for the recognition of rank levels of condensates. MPI and DMPI exhibit a remarkedly similar evolution which allows the differentiation of the samples analysed in these works. Such studies extend the applicability of alkylaromatic hydrocarbon ratios to the characterization of maturity level of condensates which range from immature-marginally mature to overmature samples, partially biodegraded or not.     

渤海湾盆地渤中19-6气田凝析油特征及油气关系

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。     

青海柴达木盆地南八仙油气田油源与成藏机理

柴达木盆地南八仙油气田不同油气藏间原油性质特征变化明显,油层在纵向井段上分布范围逾3000余m。通过地球化学实验并结合构造等地质条件分析,认为该区各种深、浅层油气藏中的原油具有煤成烃的基本地球化学特征,并且为同一来源,油源为临近地区较深部位中侏罗统煤系地层;该区深、浅层原油物性间的差异也反映在地球化学指标上,其成因或成藏机理是：深部早期油藏在断裂等地质作用下发生了明显的蒸发分馏作用,其分馏出的产物在浅部再次聚集成藏。     

Study on the mechanism of isotope fractionation in soil water during the evaporation process under equilibrium condition

In this study, with the method of vacuum extraction, two evaporative processes of soil water and free water under equilibrium condition were simulated. For each sample, water vapor was condensed by liquid nitrogen and was collected in four time intervals. From the analysis of hydrogen and oxygen isotopic compositions of the water collected at different times, it was discovered that the isotope fractionation of soil water also follows the mode, which is just the same as the evaporative process of free water. The relationship between the stable hydrogen and oxygen isotopes in residual water showed that the simulative evaporation line was close to the global meteoric water line (GMWL) under the equilibrium condition at about 20°C. Comparison of the two types of evaporative processes indicated that the isotope fractionation and evaporation velocity of soil water were only slightly modified by the Van der Waals force.     

Crystallization sequences of Ca-Al-rich inclusions from Allende: An experimental study

The equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of Type B Ca-Al-rich inclusions from the Allende meteorite is: spinel (1550°C) → melilite (1400°C; Åk22) → anorthite (1260°C) → Ti-Al-rich clinopyroxene (1230°C; “Ti-fassaite”). The melilite becomes increasingly åkermanitic with decreasing temperature. The pyroxene is similar in composition to fassaites from Type B inclusions. Preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron-wüstite buffer.The results of these experiments have been integrated with available phase equilibrium data in the system CaO-MgO-Al₂O₃-SiO₂TiO₂ and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse-grained Ca-Al-rich inclusions has been developed.Available bulk compositions of coarse-grained inclusions form a well-defined trend in terms of major elements, extending from Type A and Bl inclusions near the spinel-melilite join to more pyroxene-rich Type B2 inclusions. The trend deviates from the expected sequence of solid condensates from a nebular gas at P = 10^?3 atm if pure diopside is assumed to be the clinopyroxene that condenses. The Type A-B1 end of the trend is similar in composition to calculated equilibrium condensates at 1202–1227°C and the trend as a whole parallels the sequence of condensates expected from diopside condensation at ~ 1170°C. The trend is consistent to first order with the condensation of solid Ti-rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense. Partially molten condensates may be likely in this case or if the nebular pressure is higher than 10^?3 atm.