Geochemical characteristics of shale gas and its response to thermal maturity (Ro) in the Longmaxi formation,Dingshan area,Southeast Sichuan

The composition and carbon isotope distribution of shale gas from the Longmaxi Formation in the Dingshan area were measured, and their responses to thermal maturity (Ro) were analyzed. The results show that the shale gas is mainly composed of methane (97.98–98.99%), ethane, propane and nonhydrocarbon gases (N₂ and CO₂) and is an organic high temperature oil-type cracked gas. The wetness value [(C₂+C₃)/(C₁+C₂+C₃) × 100%] ranges from 0.39% to 0.74%. The early (Ro > 1.3%) residual kerogen and crude oil cracking gas was mixed with the late (Ro > 2.0%) secondary cracking gas, resulting in the full inversion of the carbon isotope sequence (δ¹³C₁?>?δ¹³C₂?>?δ¹³C₃).     

A kinetic model of stable carbon isotope ratios in gaseous hydrocarbons generated from thermal cracking of n-tetracosane and its application to the Tarim Basin

Based on quantitative modeling and experimental data on n-tetracosane cracking to generate gaseous hydrocarbons in a confined system, we calculated the generation kinetics and carbon isotope kinetics of methane, ethane and propane and determined the main controlling factors influencing the variation of δ¹³C₂ and δ¹³C₃. The carbon isotope of gaseous hydrocarbons from n-C₂₄ cracking to gas are comparable to those from crude oil reported recently, and they can be used to investigate the geochemical characteristics of crude oil cracking to gas under geological conditions. The geological model of n-C₂₄ cracking suggests it is stable at 150 – 160 °C and its cracking temperature ranges from 180 to 200 °C, consistent with geological models of crude oil cracking currently reported. With increasing degree of thermal stress, the changes in δ¹³C₂ and δ¹³C₃ are larger than that of δ¹³C₁. It is shown that isotope accumulation controlled by the recharging history of a reservoir has a considerable impact on the carbon isotope distribution of natural gas. Compared to that of cumulative gas, the carbon isotope ratio of partly accumulation gas is heavier and influences the fractionation of the δ¹³C₂ and δ¹³C₃ curves to a greater extent. The geological model of n-C₂₄ cracking to gas has been used to interpret the origin of carbon isotopic variation of natural gas in some reservoirs in the Tarim Basin.     

Characteristics of carbon isotopes of organic alkane gases in petroliferous basins of China

Based on analytical data of gas samples from some gas- and oilfields in China, this article describes characteristics of alkane gases (C_1–4) with different origins and occurrences. It is found that δ¹³C values of organic alkane gas increase with increasing maturity (R₀). The δ¹³C values of synchronous and isogenous methane and its homologues are found to increase with the increase in carbon number of alkane gas molecules. The δ¹³C values of methane and its homologues of coal-type gas are heavier than those of corresponding components of oil-type gas, both from source rocks with the same or similar maturity. Part of the components of methane and its homologues were oxidized by bacteria which resulted in heavier carbon isotopes compared to the remaining components.     

塔里木盆地天然气成因类型与分布规律

塔里木盆地发育寒武—奥陶系腐泥型和三叠—侏罗系腐殖型两套烃源岩,由此决定了塔里木盆地存在来自腐殖型母质的煤型气和来自腐泥型母质的油型气。通过对塔里木盆地天然气组分和碳同位素组成分析,发现塔里木盆地不同类型的天然气分布受寒武系—奥陶系的腐泥型和三叠系—侏罗系腐殖型烃源岩分布范围和热演化程度的影响。煤型气主要分布在塔里木盆地的四周,主要包括库车坳陷、塔西南坳陷和塔东南坳陷,而油型气主要分布在塔北隆起、北部坳陷、中央隆起和塔西南坳陷的北部。塔里木盆地油型气又可分为干酪根裂解气和原油裂解气两种。在满东地区、和田河地区和塔中地区,原油可以达到二次油气裂解程度,向塔北隆起的轮南方向原油裂解程度呈减弱趋势。     

Geochemistry and origin of the world's largest gas field from Persian Gulf,Iran

The South Pars field, which is the Iranian part of the world largest non-associated gas accumulation (taking into account its Qatari part, North Field, with 1342 tcf proved reserve), is hosted by Upper Permian Dalan and Lower Triassic Kangan carbonates. Carbon isotopic and molecular composition studies were undertaken to investigate the origin of non-associated gases from this field. In general, evaluation of the δ¹³C values of methane, ethane and propane and gas wetness (C₂–C₅/C₁–C₅) indicates a thermogenic origin. On the other hand, results of the isotopic analyses showed no mixing of biogenic gases in all of the analyzed gas samples. A further evaluation using natural gas plot, carbon isotopic composition of methane to pentane vs. 1 / n, showed δ¹³C₁ < δ¹³C₂ < δ¹³C₃ as normal trend. However, the carbon isotopic compositions of butane and pentane indicate a minor reverse trend in the normal progression of carbon isotopic compositions. This reversal in carbon isotope ratio among butane and pentane is interpreted as a consequence of mixing from multiple sources with different maturities.δ¹³C_CO2 in South Pars field is similar with those of thermogenic origin. The diagram of δ¹³C_CO2 vs. δ¹³C_CH4 indicates that South Pars gases plot into the isotopic compositional field for methane derived from thermogenic origin. The H₂S concentration is much lower than the Khuff Formation and it seems it has originated from different processes. Apparently, the Lower Silurian organic-rich shales, which are the main source for hydrocarbons in the Arabian Plate and southern Iran, including South Pars field, generally contain kerogen type II with some contribution of type III in some areas.Burial history modeling indicates that at the end of the Cretaceous time pre-Permian sediments remained immature in the Qatar Arch, and their present day maturity is lower than values obtained based on isotopic data. Therefore, lateral migration of gas from the nearby Silurian source rock kitchens towards the north and south of the Qatar Arch is the most probable origin for the significant natural gas accumulations in South Pars field.     

柴达木盆地北缘天然气成因类型及气源判识

测试并分析了柴达木盆地北缘9个油气田(圈闭构造)第三系和白垩系35个天然气样品的组分和碳同位素组成,建立了柴北缘天然气成因类型的判识指标,划分其热演化阶段,并进行了气源判识。研究结果表明:1)柴北缘天然气可划分为煤型气、油型气和混合气3种成因类型。伊克雅乌汝、南八仙、冷湖五号、鄂博梁以及马北的部分样品具有煤型气特征;冷湖三号、冷湖四号及冷湖五号和马北个别样品具有油型气特征;葫芦山和马北部分样品属于混合气。2)伊克雅乌汝、南八仙、冷湖五号和鄂博梁等煤型气样品大多数处于高成熟演化阶段;冷湖三号和冷湖四号部分油型气样品的成熟度较煤型气的偏低,大多数处于成熟演化阶段;葫芦山的天然气为接近过成熟阶段的高熟气;马北天然气样品的成熟度变化范围较大。3)冷湖三号、冷湖四号、冷湖五号、鄂博梁、葫芦山的天然气主要来自于昆特依凹陷,其中冷湖三号的天然气应源于昆特依凹陷偏腐泥型母质,而冷湖四号、冷湖五号、鄂博梁、葫芦山的天然气应源于昆特依凹陷偏腐殖型母质;南八仙的天然气主要来自于下侏罗统(J1)伊北凹陷偏腐殖型母质;马北的天然气来源比较复杂,可能来自于伊北、赛什腾、尕西等多个生烃凹陷。     

松辽盆地宋站南地区天然气成因

根据宋站南地区天然气与齐家古龙凹陷葡萄花油层油型气及徐家围子断陷深层煤型气的组分、甲烷碳同位素类比证明:宋站南地区存在煤型气、油型气和无机非烃气。进一步的分析显示,研究区的天然气类型的平面和垂向分布明显受气源岩的分布和断裂控制。宋站南地区断裂发育且腹地有较好的煤型气源岩分布,其煤型气更有勘探前景。     

中国油型盆地油型气成藏条件与勘探潜力

中国天然气主要分布在鄂尔多斯盆地、四川盆地、塔里木盆地和柴达木盆地,以煤型气为主,含有部分油型气和少量生物气。中国主要油型盆地具有油多气少的特点,与鄂尔多斯等以产气为主的盆地相比,天然气探明储量和产量也远远不足。全球天然气以油型气为主,且大型油型盆地表现出油气资源俱丰的特征,这与中国天然气类型与勘探现状有明显差异。通过国内外油气勘探成果与认识的调研,在总结油型气勘探领域认识的基础上,对比国内外含油气盆地的成藏条件,对中国油型盆地油型气的生气潜力进行分析,认为中国油型盆地具有巨大的油型气勘探潜力,发展前景广阔,是中国未来天然气勘探的重要方向之一。     

Specifics of the composition of monocyclic aromatic hydrocarbons in asphaltite from the Ivanovskoe deposit

The molecular composition of alkyl substituted monocyclic aromatic hydrocarbons from asphaltite of the Ivanovskoe deposit was analyzed by means of the gas chromatography-mass spectrometry technique. Unlike most crude oils and natural bitumens, asphaltite is characterized by an unusual composition of practically all isobaric-homologous series of this class of hydrocarbons. The specific features of the composition of these series is a strong prevalence of C₁₂-C₂₃ 1-alkyl-2,3,6-trimethylbenzenes with an irregular isoprenoid chain. These compounds are derivatives of isorenieratene, a carotenoid that occurs in anoxic photosynthetic green sulfur bacteria of the Chlorobiaceae family (Chlorobium genus). The ortho-isomers evidently prevail among C₁₃-C₂₅ alkyltoluenes, thus indicating a low level of catagenetic transformation of the asphaltite. n-Alkylbenzenes are practically absent from the monoalkylbenzene series; these are represented by the complete set of C₁₇-C₁₉ phenylalkanes. Such compounds were detected for the first time in natural bitumens.     

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。     

Modeling of formation of petroleum biomarker hydrocarbons by thermolysis and thermocatalysis of bacterium biomass

Thermolysis and thermocatalysis of the insoluble part of chemoorganoheterotrophic aerobic bacteria Arthrobacter sp. RV and Pseudomonas aeruginosa RM have been performed. The thermolyzates and thermocatalyzates of these bacteria contain the hydrocarbon biomarkers n-alkanes, isoprenanes, steranes, and terpanes. Of n-alkanes, the C₉-C₃₅ hydrocarbons with unimodal distribution formed in the products of or C₉-C₃₉ n-alkanes with bimodal distribution are produced by thermolysis or thermocatalysis, respectively. n-Alkanes with odd number of carbon atoms in the molecule prevail over the even counterparts (n-C₉, n-C₁₁, n-C₁₅, and n-C₁₇) in the thermolysis products of both strains, whereas n-alkanes with even number of carbon atoms (n-C₁₆, n-C₁₈, and n-C₂₀) dominate in the thermocatalyzates. Isoprenanes of the C₁₃-C₂₀ composition are generated. It is noteworthy that regular C₁₇ isoprenane has been found for the first time among isoprenanes. The cyclic biomarker hydrocarbon steranes and terpanes are simultaneously generated, with the distribution of C₂₇-C₂₉ regular steranes resembles that in marine oils generated in argillaceous strata. At the same time, the adiantane to hopane ratio (H₂₉/H₃₀) is characteristic of the organic matter generated in carbonate strata.     

天然气深冷工艺装置提高乙烷收率工艺技术的研究与应用

目的针对天然气深冷工艺装置中因原料气气量下降、气质变贫造成C₂⁺轻烃收率下降、装置运行难度大等导致装置乙烷收率降低的问题,采用调配较富原料气气源、原料气中补充丙烷和原料气中补充丁烷等措施开展提高装置乙烷收率的工艺技术研究。 方法基于建立的工艺模型,对比核算原料气中补充丙烷和丁烷对提高乙烷产量的影响,考查分析原料气中补充丙烷和丁烷对改善脱甲烷塔运行状况的效果。 结果经现场验证得出,通过调配榆济线优质气源和补充丙烷等措施可有效提高装置乙烷收率,乙烷产品年产量可增加1 438.54 t,乙烷收率由62%提高至70%。 结论该工艺的应用不仅可以获得经济效益256.88 万元/年,而且具有较大的推广价值。      

天然气中汞的来源及脱汞技术

汞是天然气中常见的有毒有害气体.根据国内外研究现状,阐述了天然气中汞对天然气采、储、运设备及对人体的危害,讨论了汞的烃源岩和岩浆热液2种成因模式;利用汞同位素分馏特征来鉴别煤型气和油型气的成因,认为煤型气表现为负的汞非质量分馏特征,而油型气表现为正的汞非质量分馏特征;提出了高汞天然气的富集条件,主要与烃源岩中汞含量、热...     

鄂尔多斯盆地大牛地下古生界天然气地球化学特征及其来源综合判识

近年来,鄂尔多斯盆地大牛地古生界天然气勘探取得重要进展,尤其是下古生界奥陶系风化壳连续高产工业气流的发现,展示了良好的勘探前景,但大牛地下古生界天然气成因及气源研究相对薄弱,直接制约了下一步勘探部署,为此系统开展了大牛地古生界天然气组分、碳氢同位素、稀有气体组分和同位素等地球化学分析.大牛地古生界天然气中甲烷占绝对优势...     

鄂尔多斯盆地富县古生界天然气成因及气源综合识别

近年来,鄂尔多斯盆地南部（简称鄂南）古生界天然气勘探取得重要进展,展示了良好的勘探前景,但鄂南古生界天然气成因及气源研究相对薄弱,直接制约了下一步的勘探部署。为此通过系统开展富县古生界天然气组分、烷烃气碳氢同位素、稀有气体组分和同位素等地球化学分析,查明了鄂南富县古生界天然气中甲烷占绝对优势,含有一定量的重烃,非烃气CO₂、N₂含量相对较高,显示其为过成熟阶段生成的干气。鄂南富县古生界天然气以典型油型气为主,煤型气为辅,甲烷和乙烷的碳同位素组成存在倒转现象可能为油型气与煤型气的混合造成,上古生界天然气烷烃气碳同位素组成普遍比下古生界天然气偏重,可能混有相对较多的煤型气。综合运用烃源岩干酪根碳同位素—岩石脱附气碳同位素—天然气乙烷碳同位素、天然气甲烷氢同位素、稀有气体Ar同位素定年等综合地球化学手段,推断出鄂南富县古生界天然气可能主要来源于下古生界马家沟组烃源岩。     

松辽盆地红岗地区浅层气地球化学特征研究

根据红岗地区7件明水组浅层气和13件嫩江组浅层气样品的组分和同位素分析,表明明水组浅层气甲烷含量、重烃含量、干燥系数、δ13C₁均值分别为92.74%,1.77%,0.981,-56.7‰,而嫩江组浅层气甲烷含量、重烃含量、干燥系数、δ13C₁均值分别为90.38%,5.57%,0.942,-52.1‰。明水组浅层气主要为生物气,而嫩江组浅层气属于生物—热催化过渡带气,都属于低熟油型气。      

四川盆地东北部马路背地区上三叠统须家河组天然气地球化学特征及气源

依据天然气化学组分及碳、氢同位素等地球化学资料,分析了四川盆地东北部马路背地区上三叠统须家河组天然气地球化学特征、天然气成因及来源。研究表明,马路背地区须家河组天然气组分以甲烷为主,含量介于92.60%~99.04%,平均为97.59%,干燥系数普遍高于0.990 0,平均为0.992 2,热演化程度较高;与邻区须家河组天然气对比,马路背地区须家河组天然气碳同位素明显具有甲烷碳同位素偏重、乙烷碳同位素偏轻的特征,δ¹³C₁值介于-33.70‰~-28.60‰,平均为-30.88‰,δ¹³C₂值介于-36.40‰~-28.90‰,平均为-33.11‰,甲烷和乙烷碳同位素多表现为倒转分布。天然气成因鉴别及气-源对比研究表明,马路背地区须家河组天然气为Ⅲ型和Ⅱ型干酪根生成的煤型气和油型气的混合热成因气,天然气主要来源于上三叠统须家河组煤系烃源岩及上二叠统吴家坪组海相烃源岩,甲烷和乙烷碳同位素倒转正是煤型气及油型气混合所致。马路背地区须家河组天然气高产富集与该区海相、陆相烃源岩双源供烃及深大断裂有效沟通海相、陆相多套优质烃源岩关系密切,沟通海相、陆相烃源岩的通源断裂在该区天然气成藏富集及后期调整改造方面具有重要作用。     

Origin of shale gas in the Triassic Yanchang Formation,Ordos Basin,China

The Chang 7 Member shale gas of the Upper Triassic Yanchang Formation, Ordos Basin, is a representative of continental shale gas in China. The Chang 7 shale is currently in the oil window, suggesting it should primarily be producing oil, but an exploratory well found high levels of gas production. In addition, the methane carbon isotopic composition (δ¹³C₁) of Chang 7 shale gas is generally depleted in ¹³C relative to that calculated by Ro, according to the δ¹³C-Ro equation. It is uncertain whether Chang 7 shale gas has mixed with biogenic gas or early thermogenic gas. In this study, over 100 samples of fresh shale cores were collected from the Yanchang Formation, and on-site gas desorption experiments and experimental analysis were carried out. Measured shale gas content was considerable, and was found to be proportional to the abundance of organic matter. Through comprehensive evaluation of the gas composition and δ¹³C₁, it was concluded that there was no biogenic gas contribution to the shale gas in the study area. The negative δ¹³C₁ of shale gas was due to the different formation mechanisms of shale gas and conventional natural gas. Methane in shale gas reservoirs is the result of methane accumulation at all stages, which increases the shale gas content.     

东濮凹陷桥口-白庙地区天然气分布与成因探讨

通过对桥口-白庙地区天然气地球化学及分布特征的分析研究,认为该区天然气主要有油型气、煤型气、混合气及深成气4种类型,各种类型的天然气分别具有不同的成因及成藏类型.桥口构造东翼深层天然气主要与葛岗集洼陷下第三系烃源岩有关,与煤系地层关系不大;白庙地区天然气与葛岗集洼陷及前梨园洼陷的烃源岩均有关,既有早期煤型气的充注,也有...     

Geochemical characteristics of noble gases in natural gas and their application in tracing natural gas migration in the middle part of the western Sichuan Depression, China

Noble gases in natural gas, from Xiaoquan, Xinchang, Hexingchang and Fenggu gas reservoirs in the middle part of the western Sichuan Depression, China, were analysed. Results show that the volume content of crustal noble gases accounts for 97.9% to 99.7% of the total noble gas content, indicating that the noble gases in the study area are very largely derived from the crust. Moreover, the 40Ar time-accumulating effect of source rocks is used to determine the complex relationship between gases and source rocks in this area, and the results agree well with that from analysis of source rock light hydrocarbons. Due to the short migration distance, the separation of 4He and 40Ar is not significant in Xujiahe natural gas and Lower and Middle Jurassic natural gas, so it is difficult to trace natural gas migration. However, this separation characteristic of 4He and 40Ar in Middle and Upper Jurassic natural gas is significant, which indicates that natural gas migration was from the Middle Jurassic to Upper Jurassic formations. In addition, the variation trends of 3He/4He ratio and δ13C1 value indicates that natural gas migration is from the Xujiahe formation to the Jurassic layer in the study area.