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.     

原油裂解成气研究进展

原油裂解气可以作为重要的天然气来源,将是未来重要的勘探方向之一。对原油裂解成气研究方法、产物特征、识别标志、原油裂解程度定量表征、原油裂解成气门限、主成气期、影响因素以及中国原油裂解气区的主要勘探及研究态势进行了总结和评述。认为原油裂解成气的门限和主生气期是原油裂解气形成中的关键科学问题,尤其是在超压条件下,原油裂解成气的主生气门限、化学动力学问题及原油裂解成气定量预测等研究需要加强;盐岩及其体系中的不同矿物对原油裂解成气的影响及机理尚不明确;中国东部湖相原油裂解气研究仍显薄弱,为加强对湖相裂解气形成与分布规律的正确认识,丰富原油裂解气形成理论,缓解中国东部天然气资源短缺问题,针对中国东部陆相断陷湖盆应进一步开展原油裂解气的相关研究。     

川中地区侏罗系天然气成因类型及气源

针对川中地区侏罗系天然气成因类型及气源的认识存在不同的观点,作者综合天然气组分特征、碳同位素特征、轻烃特征对该问题进行了探讨。组分分析结果表明,侏罗系天然气主要为干酪根裂解气;碳同位素分析结果表明,侏罗系天然气主要为油型气,部分为煤型气;轻烃分析结果表明,侏罗系天然气以油型气为主。综合上述成因类型分析结果认为:川中地区侏罗系天然气以干酪根裂解成因油型气为主,同时存在少量的煤型气。川中地区侏罗系油型气来自侏罗系烃源岩,煤型气来自上三叠统烃源岩。     

塔里木盆地塔东英南2气藏气源分析

英南2凝析气藏天然气属富氮湿气,烃类气体体积分数一般为78.86%~87.67%;甲烷68.92%~76.67%,重烃气体为9.17%~14.01%,非烃气体氮气为13.89%~21.07%,甲烷和乙烷的碳同位素分别为-38.6‰~-36.2‰和-30.9‰~-34.7‰.根据天然气组分、天然气碳同位素的特征,认为英南2凝析气藏的天然气来源于高过成熟的下古生界海相寒武系—下奥陶统腐泥型干酪根形成的原油裂解气,同时应用ln(C2/C3)-ln(C1/C2)及δ13C2-δ13C3与ln(C2/C3)判识模式也印证了英南2气藏气源为原油裂解气,气藏凝析油中存在高含量的金刚烷,指示原油经历了裂解,裂解程度为80%~90%.     

压力对原油裂解成气影响的对比模拟实验

通过在不同的实验体系(常压和20 MPa)进行的原油裂解成气模拟实验,对原油裂解成气过程和裂解气产率进行研究。结果表明:低速率长时升温相对高速率短时升温对原油裂解成气更有利;压力对原油裂解有抑制或延迟作用,压力条件下原油初始裂解时间滞后,原油裂解温度门限较高;压力可能抑制了重烃气C2-5向甲烷的二次裂解,20MPa下在高温阶(600～650℃)较常压有显著高的C2-5产率和低的干燥系数;加压环境下水参与了原油裂解反应,加压水体环境下原油转化率降低而总产气率、重烃气C2-5产率和二氧化碳产率升高;二氧化碳和重烃气C2-5质量产率变化规律和形成机制比较接近;总裂解气主生气期在425～650℃,对应Ro约为1.5%～2.4%。     

长岭断陷南部地区断陷层油气成藏机制及勘探潜力

利用天然气组成、轻烃指纹、碳同位素和生物标志化合物以及储层流体包裹体等地球化学特征,结合地质条件以及生烃史-热史模拟研究长岭断陷南部的龙凤山地区油气成因及成藏过程,揭示其油气成藏机制。结果表明:龙凤山地区断陷层天然气属于腐殖型和腐泥型的混合气,且为裂解气和干酪根热降解气组成的混合气,油气源主要为本地的沙河子组烃源岩,原油成熟度低于天然气,为同一油源不同热演化阶段的产物,属于次生凝析气藏,成藏表现为"近源多向供烃,复合输导,早期干酪根热降解成气与晚期原油裂解成气"的多期成藏模式;长岭南部地区发育优质烃源岩、营城组末期形成的反转构造提供了圈闭条件,具备较好油气输导条件、存在多期油气充注,油气勘探潜力大。     

东营凹陷北部深洼带天然气成因类型的鉴别分析

东营凹陷北部深洼带发现了一系列高产天然气流,成为富油凹陷油气勘探的重要突破,它们是源岩热解气还是原油裂解气,成为勘探家争论的问题。通过民丰地区发现的天然气地质和地球化学分析,特别是烃源岩和原油生气的模拟实验,发现两种成因天然气的鉴别标志,源岩热解气,ln(CC5/nC6)<-1、(MCC5+CC6)/nC6<0.8、(CC5+MCC5+CC6)/(nC5+nC6)<0.5、DMCC5/CC5>0.6和甲苯/苯>1.1,而原油裂解气与之相反;民丰天然气主要来自沙四段烃源岩热解气,其次来自原油裂解气。     

东濮凹陷古近系凝析气藏成因类型及其分布特征

东濮凹陷古近系凝析气储量丰富,凝析气藏成因类型复杂多样。对该凹陷凝析气藏的成因类型进行了划分,探讨了不同成因类型凝析气藏的形成机理及分布特征。研究结果表明：原生凝析气藏和原油裂解成因的凝析气藏主要分布在深层环洼斜坡带,气侵富化型和运移分异型凝析气藏主要分布在浅层,逆蒸发成因型凝析气藏常分布在中等埋藏深度;在有基底断裂沟通深部石炭-二叠系煤系的部位易形成混合气凝析气藏。     

苏北盐城凹陷天然气成因类型

天然气成因类型的判别是系统地进行天然气地质研究的基础 .利用相关图件法、图解法、聚类分析法等多种方法对苏北盐城凹陷天然气的组成成分、碳同位素组成特征、轻烃组成等多种资料进行详细分析 ,认为盐城天然气属于混源气 ,但是以腐泥型干酪根生成的油型气为主 .     

东濮凹陷户部寨气田天然气成藏地球化学特征

主要通过天然气组分、碳同位素、氩同位素、轻烃等地球化学数据,分析了东濮凹陷户部寨气田天然气来源、运聚相态,并结合烃源岩的埋藏演化史和断层活动期,综合判断了天然气充注成藏的时间,分析了成藏过程。研究表明,户部寨气田沙三下亚段—沙四段天然气主要为沙一期石炭—二叠系生成的煤成气,运移以游离相为主,混有很少量东营中期濮卫洼陷沙三下—沙四上亚段生成的油型气。     

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.     

Pyrolysis of oil at high temperatures: Gas potentials, chemical and carbon isotopic signatures

Although the gas cracked from oil has been believed to be one of the important sources in highly ma-tured marine basins, there are still some debates on its resource potentials and chemical and isotopic compositions. In this study a Cambrian-sourced marine oil sample from the Silurian reservoir of well TZ62 in the central Tarim basin was pyrolyzed using sealed gold tubes with two different pyrolysis schemes: continuous pyrolysis in a closed system and stepwise semi-open pyrolysis. The results show that the maximum weight yield of C_1–5 gases occurs at EasyRo=2.3% and the residual gas poten-tial after this maturity is only 43.4 mL/g, about 12% of the yield of 361 mL/g at EasyRo=2.3%. Combined with the results of kinetic modeling, the main stage of gas generation from oil cracking is believed within the EasyRo=1.6%―2.3%. The increase in the volume yield of C_1–5 gases at EasyRo>2.3% in a closed system is mainly related to the re-cracking of previously formed C_2–5 wet gases, not the direct cracking of oil. The stepwise pyrolysis experiments show that the gas from the cracking of residual oil at EasyRo>2.3% is characterized by very high dryness index (higher than 92%) and heavy methane carbon isotopes ranging from -28.7‰ to -26.7‰, which is quite different from the gases from the con-tinuous pyrolysis in a closed system. The kinetic modeling of methane carbon isotope fractionation shows that the carbon isotopes of methane within the main stage of gas generation (EasyRo<2.3%) are far lighter than the carbon isotopes of the precursor oils under a geological heating rate of 2 ℃/Ma. The above observations and results provide some new clues to the accurate recognition and objective re-source evaluation of oil cracking gas in highly mature marine basins.     

Oil cracking to gases： Kinetic modeling and geological significance

A Triassic oil sample from LN14 of Tarim Basin was pyrolyzed using the sealed gold tubes at 200-620℃under a constant pressure of 50 MPa. The gaseous and residual soluble hydrocarbons were analyzed. The results show that the cracking of oil to gas can be divided into two distinct stages: the primary generation of total C1-5 gases from liquid oil characterized by the dominance of C2-5 hydrocarbons and the secondary or further cracking of C2-5 gases to methane and carbon-rich matters leading to the progressive dryness of gases. Based on the experimental data, the kinetic parameters were determined for the primary generation and secondary cracking of oil cracking gases and extrapolated to geological conditions to predict the thermal stability and cracking extent of crude oil. Finally, an evolution model for the thermal destruction of crude oil was proposed and its implications to the migration and accumulation of oil cracking gases were discussed.     

东濮凹陷天然气分布成因及富集因素

东濮凹陷天然气资源非常丰富,纵向上主要集中在盐下沙三~4、沙四及盐间沙二下、沙三~1、沙三~3段;平面上则主要分布在凹陷北部中央隆起带上。现已探明的天然气,从化学组成上看有干气、湿气、凝折气;从成因上分析有油型气、煤系气及两者相互掺合的混合气。下第三系和石炭二迭系是两套主要生气源岩。由于早第三纪凹陷快速沉降,使下伏石炭二迭纪煤系进入二次生气期,同时使下第三系生油气岩系相当一部分进入高成熟生气阶段,形成丰富的气源。其上又有分布广、厚度大的膏盐作为良好的盖层,天然气不易散失,故导致凹陷中天然气的富集。     

辽河盆地东部凹陷北部地区断层对油气成藏的控制作用

依据烃源岩的分布特征和断裂活动期次探讨了辽河盆地东部凹陷北部地区佟二堡断层和茨东断层对牛居长滩洼陷的控制作用。依据石油运移地球化学资料和油气分布特征 ,研究了牛青断层和茨西断层对油气运移的控制作用。结果表明 ,北部地区油气以沿断层垂向运移方式为主 ,以侧向运移为辅。据此建立了油气沿断裂运移的模式 ,并预测了有利的油气聚集区域。预测结果表明 ,该区油气藏类型多与断层有关 ,主要圈闭类型为断块和断鼻型。茨东断层和牛青断层之间区域以及沈旦堡 -头台子地区为有利勘探区。     

松辽盆地古龙地区葡萄花油层油气成因与凝析气藏形成分布

重点以轻烃和生物标志物综合研究了松辽盆地北部古龙地区葡萄花油层凝析油气、轻质油气的来源与成因。结果表明该区油气(葡萄花油层)主要与齐家—古龙凹陷青山口组高熟腐泥型烃源岩有关,而一些轻质油气还存在姚家组泥岩局部成烃的贡献。最后论述了该区葡萄花油层凝析气藏的形成与分布规律。