原油裂解气和干酪根裂解气的判识

中国中西部的叠合盆地中,下古生界海相烃源岩已达高过成熟阶段,但却发现大量与之有关的原油裂解气.因此,如何区分原油裂解气和干酪根裂解气,成了一个亟需解决的问题.从天然气组分和轻烃组分切入,应用ln(C2/C3)-ln(C1/C2)判识模式及δ13C2-δ13C3与ln(C2/C3)判识模式认为四川盆地川东地区石炭系气藏为原油裂解气,而塔里木盆地轮南断垒和中部斜坡的气藏为干酪根裂解气.根据对典型干酪根和原油裂解气的分析,结合热模拟分析结果,提出了3项轻烃判识原油裂解气和干酪根裂解气界限值指标.     

新场地区上三叠统须五段陆相页岩层系非常规天然气特征与成因

除下古生界海相页岩具有页岩气开采的价值外,四川盆地陆相领域页岩层序也非常发育;其中川西坳陷须五段获得突破,但其非常规天然气地球化学特征十分复杂、成因类型多样,开展非常规天然气特征和成因的研究对于有效的认识四川盆地陆相页岩的勘探开发前景具有重要意义。在对川西坳陷上三叠统须五段陆相页岩层序天然气组分和同位素特征分析的基础上,结合该区实际地质条件的分析,研究了天然气的成因类型、天然气成熟度和天然气的赋存状态。结果表明:须五段天然气主要为烃类气体,甲烷含量、干燥系数变化大;但平均值较低,烷烃同位素具有δ13C1δ13C2δ13C3δ13C4的正常序列分布特点;但甲烷碳同位素值(δ13C1)变化大,在-44.4‰~-27.1‰之间;乙烷碳同位素值明显偏轻,介于-28.1‰~-22.9‰之间。须五段天然气为典型煤型气,具有成熟-中等成熟阶段热成因气的特征;天然气为吸附气与游离气的混合气体,但以吸附气为主,在生产过程中,由于同位素的分馏效应,导致天然气甲烷碳同位素偏重。     

伊陕斜坡东南部延长组页岩气地球化学特征分析

鄂尔多斯盆地陆相页岩气勘探潜力巨大,但对于陆相页岩气成因类型的研究相对滞后,限制了对页岩气的进一步勘探和开发。通过综合化学组分分析和碳、氢同位素分析的手段对伊陕斜坡东南部延长组页岩气和原油伴生气的地球化学特征及成因进行研究。研究结果表明延长组页岩气(生产气和真空解吸气)和原油伴生气都以烷烃类气体为主,其中甲烷含量都小于95%,非烃气体含量比较低。页岩解吸气中,非烃气体比例相对较高,且氧气含量异常高,这与解吸装置密封性不好或者装置本身残留空气清除不彻底有关。页岩气和原油伴生气的甲烷含量低、干燥系数(C_1/C_(1~5))主要集中在0.6~0.9之间、C_2/C_3都小于3,δ~(13)C_1值分布于-52.0‰~-44.9‰之间、δ~(13)C_2值都小于-29‰,δ~(13)C_3值都小于-25.5‰和δD_1都小于-150‰,指示研究区页岩气和原油伴生气以陆相环境热成因的热解湿气(油型气)为主。页岩气和原油伴生气样品有相对高的正庚烷含量和正构烷烃(nC_(5-7))含量,δ~(13)C_2值分布于-41.1‰~-31.1‰之间,说明延长组页岩气与原油伴生气都属于偏腐泥型天然气。此外,延长组页岩气和原油伴生气碳同位素系列基本都属正碳同位素系列,且δ~(13)C_1与δ~(13)C_2值,δ~(13)C_2值与δ~(13)C_3值有较好的正相关关系,这也表明页岩气和原油伴生气具有相同或相似的母质来源。     

川东飞仙关组烷烃气碳同位素特征与成因分析

飞仙关组作为川东主力气层,陆续已经发现了普光、毛坝、东岳寨、渡口河等一系列大中型气藏,展示了极其重要的战略地位。目前常规的组成分析方法已经不能满足该层天然气类型及成因的判别要求。通过分析烷烃气碳同位素特征,判识天然气类型、分析其成因机制。实验分析显示部分样品C_1~C_3烷烃气的碳同位素比值呈δ~(13)C_1δ~(13)C_2δ~(13)C_3分布(倒转),显示为多源、多期天然气混入。同时根据C_1/C_2+C_3与δ~(13)C_1及ln(C_1/C_2)与In(C_2/C_3)的值域变化特征,最终判断川东大多气藏以原油裂解气为主,混入一定的煤型气。川东飞仙关组古油藏于晚侏罗世沉积期,其埋藏深度介于5 300~8 200 m之间,油藏温度普遍超过150℃,油发生热裂解,生成烷烃气及沥青,持续时间大于30 Ma。     

元坝地区雷口坡组气源与碳同位素倒转成因

探讨四川盆地元坝地区雷口坡组气源与碳同位素倒转成因.通过雷口坡组烃源岩与天然气地化参数分析,其烃源岩以泥晶灰岩、含泥灰岩为主,TOC质量分数平均为0.37％,生烃能力较差.天然气中非烃气的体积分数多数＜10％,烷烃气组分较干,CH4相对体积分数平均为99.0％,碳同位素较轻,其中δ13C1均值为-34.19‰,δ13 C2均值为-33.31‰,且多数样品发生δ13C1,δ13C2倒转;甲烷氧同位素较轻,均值为-156.3‰.与相邻层位烷烃气对比并结合烃源背景,综合分析认为其气源主要为须家河组媒型气,其甲烷、乙烷碳同位素倒转为水溶分馏作用导致气层中乙烷变轻程度超过甲烷一定幅度引起.     

鄂尔多斯盆南部上古生界天然气地球化学特征——以志丹-甘泉地区为例

通过对志丹-甘泉地区天然气样品的组分、稳定碳氢同位素的测定,综合分析、对比、认为：①鄂尔多斯盆地甘泉-志丹地区天然气主要组分甲烷的稳定碳同位素主要分布在-32‰≤δ_¹³C₁≤-25‰范围内,乙烷的稳定碳同位素主要分布在-38‰≤δ_¹³C₂≤-24‰范围内,天然气甲烷氢同位素主要分布在-170‰≤δ_²D₁≤-160‰内;②研究区碳氢同位素相比北部苏里格气田偏重,天然气类型主要为煤系烃源岩Ⅲ型干酪根初次裂解气,同时混有少量液态烃的二次裂解气。该区天然气已发生明显的次生变化,但是扩散运移和外部气源的混入都可以使测试样品发生碳同位素的斜率的倒转;③运移分馏是造成该区天然气产生碳同位素倒转和次生变化的主要原因之一。以上成果认识对本区天然气地球化学特征具有重要指导作用,对类似盆地天然气地球化学特征研究具有一定借鉴价值。     

松南营城组火山岩气藏成藏模式

松南气田营城组火山岩天然气的δ13C1值大于-30‰,具有δ13C1＞δ13C2＞δ13C3负序列或同位素倒转,甲烷同位素偏重,表明松南气田营城组火山岩天然气不仅具有煤型气与油型气混合特性,还具有多期次成藏特征,煤型气充注早,为89～83 Ma;油型气和幔源气充注晚,为78～68 Ma.松南气田营城组天然气中无机气体主...     

东濮凹陷北部地区古近系油型气成因类型及分布特征

以热压模拟实验模拟东濮凹陷干酪根热裂解和原油热裂解过程,分析干酪根热裂解气和原油裂解气组分特征的差异,以此建立干酪根热裂解成因气和原油裂解成因气的判识方法;结合东濮凹陷北部地区天然气碳同位素及天然气组分数据,对研究区油型气进行划分,进而探讨干酪根热裂解气与原油裂解气的分布特征。结果表明,研究区古近系油型气分为干酪根热裂解气与原油裂解气,干酪根热裂解气具有相对较高的C1/C2值和较低的C2/C3值特征,而原油裂解气则与之相反。干酪根热裂解气和原油裂解气的分布存在明显差异:前者分布范围更广,后者更近于洼陷中心分布,两者分布的差异性与其生成及成藏条件差异有关。根据干酪根热裂解气与原油裂解气分布特点,推测在邻近洼陷中心区具有良好的干酪根裂解成气及原油裂解成气的条件和油型气勘探前景。     

渤海湾盆地渤中19-6气田凝析气成因研究

为了研究渤中19-6凝析气藏的成因类型，利用同位素、轻烃参数、金刚烷参数等方法，系统分析渤中19-6凝析气藏，深入研究其形成机理，认为：渤中19-6气田天然气干燥系数较低，碳同位素偏重，成熟度分布在1.50 %左右，综合判断属于偏腐殖型高熟气；渤中19-6气田凝析油双金刚烷含量较高，生物标志化合物含量较低，指示渤中19-6气田凝析油为高成熟原油，且计算原油裂解程度低于20 %，对天然气的贡献量有限，渤中19-6气田天然气主要为干酪根裂解形成。     

南海北部陆坡NH-1孔沉积物中碳酸盐碳同位素特征及其地球化学意义

源于深部天然气藏渗漏或天然气水合物分解释放的甲烷,可导致海洋沉积物中生成δ13C明显负偏的碳酸盐矿物.对NH-1孔沉积物样品的碳酸盐含量、全岩碳酸盐及生物碳酸盐δ13C、有机碳含量等参数进行了分析.结果表明:沉积物中碳酸盐含量较高(平均6.90%);全岩碳酸盐δ13C(-6.09‰～-0.48‰)与正常海相碳酸盐相比明显负偏;浮游有孔虫(G.rube)壳体碳酸盐δ13C(-0.834‰～0.004‰)明显低于正常值.结合海域的地质特点,认为这很可能是沉积物中较高甲烷通量背景条件下自生碳酸盐的形成所导致的.有机碳、氮数据与全岩碳酸盐δ13C的相关性分析指示了有机质也可能是全岩碳酸盐δ13C偏低的根源之一.因此,NH-1孔碳酸盐碳同位素特征是较高甲烷通量背景下甲烷缺氧氧化-硫酸盐还原及有机质缺氧氧化-硫酸盐还原等地球化学过程的综合反映.全岩碳酸盐δ13C含量可用于指示沉积物中自生碳酸盐矿物及较高甲烷通量的存在.     

Secondary biogenic coalbed gas in some coal fields of China

The secondary biogenic coalbed gas, a new genetic and energy source type of coalbed gas in China, has been found in Xinji, Liyazhuang and Enhong areas. The essential characteristics of this type of gas are: (i) the major component of the gas is methane, with C1/C1-5 value higher than 0.99, indicating that the gas is part of dry gas; (ii) theδ13C1 value is in the range of -61.7‰to -47.9‰, mostly lower than -55‰, which is much lower than the estimatedδ13C1 value of thermogenic methane according to the thermal evolution degree of the coal rocks (with R0 value from 0.87% to 1.43%), showing the characteristics of the secondary biogenic gas; (iii) theδ5D value of methane ranges from -244‰to -196‰; (iv)δ13C 2 value ranges from -26.7‰to -15.9‰andδ13C 3 value ranges from -10.8‰to -25.3‰, indicating that the heavier hydrocarbons have a thermogenic origin; (v) the content of CO2 is very low, andδ13CCO2 value changes greatly, reflecting a characteristic of secondary change; (vi)δ15N2 value ranges mainly from -1‰to +1‰, indicating N2 derived significantly from air. The negative linear correlation between the contents of N2 and CH4 reflects the activity of bacteria bearing surface water infiltrating into coal beds. The comprehensive tracing indices show that the coalbed gas in the studied areas is the mixed gas of primarily secondary biogenic gas and a part of remnant thermogenic gas. The uplift of coal beds and the development of faults in the studied areas create favorable conditions for the formation of the secondary biogenic gas.     

Research progress in studies on the coalbed gas geochemistry

The current situation of geochemical studies on coalbed gas is reviewed in this paper. Generally, coalbed gas is compositionally dominated by methane with δ¹³C₁ values ranging approximately from -80‰ to -10‰. However, few isotopic studies have been carried out on other components of coalbed gas except for hydrogen and carbon dioxide, whose δD_CH4 values available for utilization vary from -333‰ to -117‰, and δ¹³C_CO2 values from -29.4‰ to +18.6‰. Two major types of coalbed gas, thermogenic gas and secondary biogenic gas, have been identified, and there are also some other classification criteria. Compared with conventional natural gases, coalbed gas has a wide distribution range of δ¹³C₁ and δ¹³C_CO2 values, especially possessing some extremely heavy values. Current problems that remain unsolved in the coalbed gas geochemistry include the variation mechanism, controlling factors and application of carbon and hydrogen isotopes of methane, the relation between the values of δ¹³C₁ and Ro, the systematic classification scheme and criterion of genetic types, and the application of the coalbed gas geochemistry in evaluating target districts of the coalbed gas exploration.     

吐哈盆地北部山前带下侏罗统天然气气源与成藏模式

为了明确山前带柯柯亚下侏罗统气藏,对于这套位于中上侏罗统油气藏之下的天然气性质、来源及成藏模式,运用地球化学分析和天然气气藏解剖方法进行研究.研究结果表明:本区天然气甲烷碳同位素分布在-44.0‰～－38.7‰,乙烷碳同位分布在-29.0‰～－27.5‰,属于偏腐泥型的腐殖气,伴生原油的物理性质和生物标志物呈现出典型的成熟煤系油特征,并与中上侏罗统油气来源不同,即地质条件和地球化学数据都证明天然气母质处于成熟演化阶段,垂向运移距离短,来自八道湾组煤系泥岩;天然气大量充注前大面积致密储层的形成、下侏罗统异常超压的发育以及源储的紧密叠置,都是形成致密砂岩气藏的地质条件.     

吉拉克三叠系凝析气藏成藏地球化学研究

根据油气藏地球化学方法,对吉拉克三叠系凝析气藏的成藏进行了研究。天然气组成和凝析油轻烃研究表明吉拉克三叠系凝析气藏的天然气和凝析油都为腐泥型来源,凝析气藏为气侵形成的凝析气藏;储层沥青研究表明烃源岩不仅仅只有中上奥陶系烃源岩,还有寒武系烃源岩。结合工区构造发展史等基础资料,认为吉拉克三叠系油气藏经历了三期油气聚集和一次破坏,凝析气藏最终由于喜山期地层反转,天然气发生再分配而形成。     

吉拉克三叠系凝析气藏成藏地球化学研究

根据油气藏地球化学方法,对吉拉克三叠系凝析气藏的成藏进行了研究。天然气组成和凝析油轻烃研究表明吉拉克三叠系凝析气藏的天然气和凝析油都为腐泥型来源,凝析气藏为气侵形成的凝析气藏;储层沥青研究表明烃源岩不仅仅只有中上奥陶系烃源岩,还有寒武系烃源岩。结合工区构造发展史等基础资料,认为吉拉克三叠系油气藏经历了三期油气聚集和一次破坏,凝析气藏最终由于喜山期地层反转,天然气发生再分配而形成。     

Kinetic modeling the effects of primary migration, diffusion and waterwashing on Upper Paleozoic coal-derived gas at the center of Ordos Basin

Gold reactor pyrolysis system is used to model the gas formation from the Upper Paleozoic coal measures and the results show coal-derived gas characterized with δ13C1 of-33.46‰, δ13C2 of-23.1‰, dryness(C1/C1-4) 85.6%. And then, effects of the post-genetic processes on coal- derived gas are analyzed in turn: (i) About 27% coal-derived gases constituted with more methane are calculated to be lost during diffusion. The residual in reservoir are characterized with almost the same compositions as the original, which suggests faint influence by diffusion (the residual, δ13C1 of -32.78‰, δ13C2 of-23.1‰, C1/C1-4 83%); (ii) Water washing made about 8% coal-formed gases lost and their components and stable carbon isotopes are stable; (iii) In the final, it is speculated that primary migration makes much more wet gas (C2-4) leave in coal measures. The variance of gas dryness induced by this factor is estimated to be about 10%.     

Oil cracking： An important way for highly efficient generation of gas from marine source rock kitchen

The potentials of gas generation by kerogen in the late period and by crude oil cracking are closely related to the origin of natural gas in the high- to over mature marine area and their exploration perspectives. The carbon structure of kerogens, with different types and at different evolution stages, have been experimentally studied using the high magnetic field solid ^13C nuclear magnetic resonance technique in order to determine the oil and gas potential of kerogens. Results show that the contents of gas potential carbon（GPC） of types Ⅰ, Ⅱ, Ⅲ kerogens at the high- to over mature stage are very low, indicating their weak gas-generating capacity and limited gas production; however, the content of oil potential carbon（OPC） of the low mature type Ⅰ kerogen is much higher, implying that a large amount of crude oil generated during the oil-generating period will be the material for later gas generation by oil cracking. The kinetic experiment of gas generation by crude oil cracking shows that, when the temperature is about 160℃（R0=1.6%）, the crude oil will start to produce large amounts of gas; the temperature range for major gas generation of crude oil is higher than that of the kerogens, and the gas production is 2 to 4 times higher than that of kerogens. The natural gas derived from oil cracking （called oil-cracked gas） is much abundant in methyl hexamethylene, which is quite different from the natural gas produced by thermal degradation of kerogens （named kerogen degradation gas） at high- to over mature stage.     

Geochemical characteristics and source rock of Ordovician gas reservoir, Changqing Gasfleld

Carbon isotopic composition of methane in Ordovician gas reservoir in the Changqing Gasfield can reflect the dominance of Upper Paleozoic coal-type gas despite its high mature degree. The 12C-rich ethane in the Ordovician reservoir (δ13C2 < - 29‰), known as a marker as oil-type gas, does not indicate the Ordovician marine carbonate as main source rock, it is because of the relative less ethane content in coal-type gas than in oil-typed gas due to generation and migration. The way of Upper Paleozoic coal-type gas migrating into the Ordovician reservoir is widely through the unconformity instead of only through the erosion groove in the weathering crust.