幔源CO_2释出机理、脱气模式及成藏机制研究进展

针对幔源CO2如何从地幔岩浆中脱出并进入沉积地层中形成CO2气藏聚集这一关键问题,总结了国内外研究进展和前缘方向。研究表明,地幔深部的碱性玄武岩浆和碱性岩浆才是深部流体和CO2等挥发份大量赋存、渗滤和释出的场所。浅成侵入岩、次火山岩和火山通道等是CO2释放和聚集的有利位置,岩浆期后和岩浆衰弱期的热液活动阶段是CO2大量释放和聚集的有利时期。幔源CO2进入沉积盆地中具有3种脱气模式,即沿岩石圈断裂直接脱气模式、热流底辟体脱气模式和壳内岩浆房-基底断裂组合脱气模式。CO2的固有物化性质决定其运移相态多样,具有运移和聚集过程同步的特征。只有在满足大量的化学消耗及地层水或原油的溶解和耗散之后才能形成CO2有效聚集。幔源CO2成藏和分布主要受岩浆气源体和气源断裂体系的控制。今后,在超临界CO2及其对油气运移聚集的作用、CO2与深大断裂及火山岩的关系、CO2脱气运移机制、CO与常规烃类油气的耦合差异成藏机制等方面仍需要进一步的研究和探索。     

南海北部边缘盆地氮气气源追踪与判识

南海北部边缘盆地油气勘探中陆续发现较丰富的二氧化碳(CO2)和氮气(N2)等非烃气气藏,同时亦发现了一些含N2、富N2的天然气层。这些CO2和N2非烃气主要富集于西北部边缘莺歌海盆地中央泥底辟带新近系及第四系浅层中。根据N2地质地球化学特征,可将本区N2划分为大气成因、壳源型有机成因和壳源型有机-无机混合成因三种主要成因类型。结合温压双控热模拟岩石产氮气实验结果,以及N2等非烃气在平面上分区分块、剖面上分带分层的局部性富集特点,追踪判识并确定N2气源主要由来自不同成熟演化阶段的中新统及上新统海相泥岩气源岩的N2与多种物理化学和岩石脱气作用所形成的无机N2相互混合而构成。     

地幔流体及其成矿作用

地幔流体及其成矿作用的研究是当前地学界倍受关注的前沿课题。地幔流体是一种以CO2和H2 O为主、同时含有一定量的溶质成分、相对富集大离子等不相容元素的超临界流体 ,具有独特的溶解和输运能力 ,主要来源于俯冲板块的脱水、脱气作用和地核及地幔脱气作用。地幔流体在许多大型—超大型金属、非金属、油气矿床和矿集区形成过程中具有重要意义。地幔流体成矿作用主要表现为本身成矿、提供成矿物质、成矿流体和成矿热动力。地质构造背景、岩浆活动、矿床地质、矿床地球化学等方面的研究均可提供地幔流体成矿作用的证据。地幔流体成矿作用的主要特征是矿床具有深大断裂构造背景、伴随幔源岩浆活动、成矿物质和成矿流体具有幔源性、往往形成大型—超大型矿床和矿集区     

稀有气体在深部地质研究中的意义

幔源物质中的稀有气体蕴藏着丰富的地球深部过程信息。它们可对地幔结构、地幔脱气历史、大陆地幔不均一性、幔源岩浆演化和CO2天然气成因等研究提供独特的示踪作用。结合中国东部地幔捕虏体的资料,综述了稀有气体在这些方面的研究进展。研究表明,MORB源和OIB源玄武岩稀有气体组成差异强烈支持地幔双层结构的存在,地幔脱气过程主要受溶解度控制脱气模式(SCD)控制;同时,中国东部地幔存在不均一性可以在稀有气体方面得到印证;郯庐断裂可能为东部幔源无机CO2的脱出提供了良好的通道。     

东海地球动力学环境与过程的同位素证据及盆地动力学模式

在东海地球动力学环境与过程研究现状分析基础上,讨论了采自盆地东西部油气钻井玄武岩样品的岩石化学、微量元素和同位素测试分析的成果,阐述了玄武岩岩石结构与岩石成分特征,计算岩浆起源深度与岩浆起源温度。通过岩浆源区地幔性质与深部过程分析,指出Sm-Nd、Pb-Pb、Nd-Pb同位素体系反映的深部地幔流体具有古生代向新生代转型的双重特征,与古生代地幔岩浆来源具有较明显亲和性,其中既有古老地幔物质存在,又有新生地幔物质参与,表明研究区地壳深部流体活动十分频繁。结合海洋一期"863"双船折射大剖面有关地质-地球物理解释成果的综合分析认识,提出了盆地地球动力学成因模式。     

无机成因油气及其发展前景

地幔和地核中有大量的碳和氢，学们提出了不同地质背景下无机成因烃类来源理论，其中影响较大的有Gold氏的地幔脱气理论和费-托地质合成理论。大量的事实证明了无机成因油气的存在。对各类天然气成因来源的判别多采用碳同位素和稀有气体同位素；而对无机成因油多从铅、锶、钕同位素和重金属元素、亲石元素、正烷烃结构等旁证了原油地球深部来源的可能性。在板块运动产生的综合动力场作用下，以CO2和H2O为主要成分的流体在深部油气的无机合成、运移和富集中起着重要的作用。无机成因油气的研究和开发利用，有助于缓解我国油气产储的矛盾。     

鹤壁市新区地热及CO2资源特征与成因探讨

通过地质调查、物探工作、钻探工作,结合区域地质特征及CO2气藏形成的地质条件,对鹤壁市新区地热及CO2资源的赋存规律和成因进行了探讨.认为鹤壁矿区地处太行山前汤阴断陷盆地中部,其地下存在着奥陶系灰岩凸起的古潜山构造,这些凹陷中的相对凸起带是地下热水和CO2气藏的富集区.经分析该区地表以下无热异常,地热田属正常增温型地热区;CO2气藏为无机成因,是岩浆冷凝脱气和碳酸盐热解的共同作用.     

幔源CO_2演化及CO_2气成藏实例分析

幔源CO2是当今地球科学研究中的前沿领域之一,具有重要的研究价值。处于超临界态的地幔流体具有很强的溶解和扩散能力,是地球内部能量与物质向外传输的重要载体。地幔流体中的挥发分以H2O和CO2为主,全球许多CO2气藏中的气体具有幔源特征,与地幔流体密切相关,但地幔流体与CO2气藏之间的关系研究则显得不够。本文分析了地幔流体的组成、性质与影响因素,结合济阳坳陷断裂构造、岩浆发育特征,阐述地幔流体上升和演化过程,认为地幔流体中溶解各种形式CO2气为气藏形成提供物质来源,断裂活动则为岩浆上侵和气体的运移、聚集提供了通道和空间。CO2气藏勘探的有利区块应该不仅仅局限于坳陷内,在坳陷边缘或者外部,新生代晚期的碱性岩浆侵入活动,不同方向断裂发育交汇地区均是气藏勘探的有利地区。     

东海盆地丽水凹陷天然气与二氧化碳成因来源

丽水凹陷是东海盆地除西湖凹陷之外最重要的含油气凹陷。丽水凹陷油气资源以天然气为主,近年来,油气勘探受二氧化碳气影响严重,天然气藏中高含量的二氧化碳减低油气勘探的商业性。因而,明确丽水凹陷天然气和二氧化碳成因、来源对东海油气勘探具有重要意义。分析认为:丽水凹陷天然气成因主要为Ⅱ型干酪根热成因油型气,其次为Ⅲ型干酪根成因的煤成气和Ⅱ型干酪根油型气混源气;油型气来源于古新统月桂峰组湖相烃源岩,煤成气来源于灵峰组陆源Ⅲ型干酪根烃源岩。二氧化碳主要为无机成因气,来自地幔与火山活动有关。西次洼中北部、远离火山活动区是油气勘探的有利方向。     

海拉尔盆地与澳大利亚Bowen-Gunnedah-Sydney盆地系片钠铝石碳来源的比较研究

作为胶结物、交代物或孔洞充填物,片钠铝石[NaAlCO(3OH)2]大量发育于海拉尔盆地和澳大利亚BGS盆地系。根据片钠铝石稳定同位素组成,对比分析片钠铝石的碳来源。BGS盆地系片钠铝石的1δ3C分布连续,分布区间为-4.0×10-3～4.1×10-3,计算出的与片钠铝石平衡的CO2气的1δ3CO2值分布区间为-11.3×10-3～-4.6×10-3,结合片钠铝石的分布和区域地质背景,认为片钠铝石中的碳来源于岩浆活动而带来的无机CO2气;海拉尔盆地片钠铝石1δ3C值分布连续,为-4.64×10-3～2.12×10-3,计算出的与片钠铝石平衡的CO2气的1δ3CO2值分布区间为-11.82×10-3～-5.11×10-3,结合海拉尔盆地探井中未钻遇碳酸盐地层、含片钠铝石井和幔源CO2气井分布相吻合且位于燕山期花岗岩区或其附近的深大断裂带上,认为形成片钠铝石所需的CO2气为与燕山期岩浆作用有关的幔源CO2气,片钠铝石形成时因油气充注而介入少量生物成因碳。     

我国碳酸盐岩储层CO2地质储存潜力与适宜性

文章系统收集并分析了我国各盆地地层、大地构造、油田地质、水文地质数据,研究了我国各盆地碳酸盐岩地层空间分布和孔隙度特性,做出了《全国盆地碳酸盐岩分布面积分级图》、《全国盆地碳酸盐岩厚度分级图》、《全国盆地碳酸盐岩孔隙度分级图》、《全国盆地碳酸盐岩二氧化碳地质储存潜力分级图》。逐一对全国各沉积盆地内800～5 000 m深度区间各地质时代形成的碳酸盐岩储层的CO2储存能力进行了计算。通过层次分析法确定各评价指标权重,制做出全国盆地E级碳酸盐岩储层CO2地质储存适宜性评价结果表,绘制出《全国盆地碳酸盐岩储层CO2储存适应性评价图》。对全国盆地CO2储存进行了适宜性评价,剔除了不适宜CO2地质储存的沉积盆地,选出适宜的沉积盆地以供下一阶段继续研究。      

Interactions between basalts and oil source rocks in rift basins： CO2 generation

Basalts interbedded with oil source rocks are discovered frequently in rift basins of eastern China, where CO2 is found in reservoirs around or within basalts, for example in the Binnan reservoir of the Dongying Depression. In the reservoirs, CO2 with heavy carbon isotopic composition (δ13C>-10‰ PDB) is in most cases accounts for 40% of the total gas reserve, and is believed to have resulted from degassing of basaltic magma from the mantle. In their investigations of the Binnan reservoir, the authors suggested that the CO2 would result from interactions between the source rocks and basalts. As the source rocks around basalts are rich in carbonate minerals, volcanic minerals, transition metals and organic matter, during their burial history some of the transition metals were catalyzed on the thermal degradation of organic matter into hydrocarbons and on the decomposition of carbonate minerals into CO2, which was reproduced in thermal simulations of the source rocks with the transition metals (Ni and Co). This kind of CO2 accounts for 55%-85% of the total gas reserve generated in the process of thermal simulation, and its δ13C values range from -11‰- -7.2‰ PDB, which are very similar to those of CO2 found in the Binnan reservoir. The co-generation of CO2 and hydrocarbon gases makes it possible their accumulation together in one trap. In other words, if the CO2 resulted directly from degassing of basaltic magma or was derived from the mantle, it could not be accumulated with hydrocarbon gases because it came into the basin much earlier than hydrocarbon generation and much earlier than trap formation. Therefore, the source rocks around basalts generated hydrocarbons and CO2 simultaneously through catalysis of Co and Ni transition metals, which is useful for the explanation of co-accumulation of hydrocarbon gases and CO2 in rift basins in eastern China.     

The problem of CO2 recycling in subduction zones

In connection with the imbalance between the carbon dioxide absorbed in the carbonate minerals in subduction zones and that emitted during island arc volcanism, the problem of redistribution the rest of the CO₂ from the plate to the mantle arises. Experimental modeling of the interaction between model analogs of the oceanic crust and the mantle wedge was performed for two systems: glaucophane schist-olivine and glaucophane schist-silicate marble-olivine under high pressure and varying temperature conditions that correspond to the oceanic crust-mantle transition zone in the subduction zone beneath the Cascade Mountains. The experiments carried out showed that there is a possibility that intensive CO₂ degassing occurs from the plate in the forearc area, which is controlled by carbonate dissolution in an aqueous fluid. As a result of this process, carbonates can redeposit in the form of magnesite in the overlying mantle rocks according to the vertical temperature gradient. It is assumed that part of the carbon dioxide bonded in mantle rocks can be transported by viscous flow from the forearc area to the deep mantle horizons within the field of the thermodynamic stability of magnesite. In addition, the experiments we carried out showed that between marble and olivine in the ultrahigh pressure a metasomatic column consisting of four zones develops: Fe-Mg-Ca carbonate|dolomite|diopside|magnesite.     

松辽盆地北部火山岩CO2脱气参数及其对CO2资源量估算的意义

为了定量评价火山岩脱CO2气量的潜力，选择松辽盆地北部火山岩进行了低温脱气实验。将火山岩加热到250℃时，脱出挥发份总量为0.0299～0.0790ml/g；其中CO2脱出量为0.0218～0.0706 ml/g（0.429～1.387wt％）。脱挥发份总量与其中CO2量具有良好的正线性相关；挥发份以CO2气为主，其次是Ｎ2气，还伴有H2、CO、CH4等还原性气体，以及更少量的低碳烷烃；基性火山岩比中、酸性火山岩脱出CO2数量较多。火山岩吸附大量CO2气，成为充足气源，火山岩脱出的吸附气主要是辗转而来的深源气，火山岩成为探索幔源气成藏的主要源岩，尤其是基性火山岩。估算CO2资源量，可将250℃时火山岩挥发份含量作为岩石挥发份及残余CO2量的下限值，而全岩分析的总碳含量可作为CO2脱出量的上限值。     

Stable carbon isotopes in selected granitic,mafic, and ultramafic igneous rocks

Noncarbonate (combustion) and carbonate (acid decomposition) carbon were separately analyzed in 18 granitic rocks from a group of related Tertiary intrusions near Crested Butte, Colorado, and 14 mafic and ultramafic rocks from various localities in the western United States. Among the granites, carbonate carbon ranges from nil to 0.76 per cent with δC¹³-values from ?5.6 to ? 9.0‰ (vs PDB); noncarbonate carbon varies from 32–360 ppm with δC¹³-values from ?19.7 to ?26.6‰, The mafic and ultramafic rocks have carbonate carbon contents ranging from 53 ppm to about 2 per cent with δC¹³-values from + 2.9 to ?10.3‰; noncarbonate carbon varies from 26 to 150 ppm with δC¹³-values of ?22.2 to ? 27.l‰ For these samples, carbonate carbon ranges from 12.0 to 29.4‰ heavier than coexisting noncarbonate carbon. This consistent difference between δC¹³ of carbonate and noncarbonate carbon may be an isotopic fractionation effect. Because the specific indigenous form of noncarbonate (combustion) carbon is in doubt, conclusive interpretations regarding isotopic equilibration and fractionation cannot be made.These results have bearing on the assessment of the isotopic composition of mantle carbon and consequently are germane to the question of the origin (source) and history of crustal carbon. If mantle carbon is isotopically similar to noncarbonate (combustion) carbon, i.e. δC¹³-values from ?19.7 to ? 27.1‰, then a simple mantle degassing source for crustal carbon is improbable. Such a result would indicate an additional source of crustal carbon such as from a primitive atmosphere or extra-terrestrial accretion.     

幔源岩浆去气形成富二氧化碳含金流体——可能性与现实性

综合国内外研究资料并结合笔者的研究成果 ,评述了幔源岩浆去气形成富二氧化碳含金流体的可能性和现实性。笔者认为 ,在地幔熔融和富集交代过程中可以形成富金和二氧化碳的岩浆 ,进一步在岩浆去气过程中金可以气相形式随二氧化碳排出 ,而一个由深部稳定热源驱动、富含幔源岩浆去气带入的二氧化碳和金并与地壳浅部流体混合的热液环流系统是形成重要金矿化的必要条件。     

Observation of Catastrophic Degassing from Mantle-Crust in Yinggehai Basin, South China Sea

Previousworkshavenotonlywellestablishedtheiso topiccriteriaforrecognizingdifferentsourcesofnoblegases(ref.PintiandMarty ,2 0 0 0 ;Sardaetal.,1985 ) ,butalsoadvocatedtheintegrationofC/ 3Heratioswithstableisotoperatiostoprovideaninsightintotheoriginsofmantle derivedCO2 (Ballentineetal.,2 0 0 1,2 0 0 0 ;Lollaretal.,1997;Pedronietal.,1996 ;Trulletal.,1993;MartyandJam bon ,1987;DesMarais ,1985 ) .Inmanycases,however,thenoble gassignatureandC/3Heratiocannotbesimplyusedtoindicatetheoriginsofsuc…     

Distribution and Geochemical Characteristics of Hydrogen in Natural Gas from the Jiyang Depression, Eastern China

Hydrogen gas accelerates hydrocarbon generation, but little is known about its distribution and origin in petroliferous basins, which has hindered the further exploration.Taken the Jiyang Depression in eastern China as an example, this study collected natural gas from different tectonic units, and analyzed various geochemical characters including gas contents, and carbon and hydrogen isotopic composition.The result shows that:(1) hydrogen gas is widespread distributed, but its content is very low, which typically ranges from 0.01% to 0.1% in this region;(2) the ratios of H2/3He, indicative of the origins of hydrogen gas, suggest that mantle-derived hydrogen is dominant.Even in tectonically stable areas absent with deep fluid activities, there is also mantle-derived;(3) the isotopic composition of hydrogen falls in the range of –798‰ to –628‰(relative to VSMOW standard).In areas with deep-derived fluids, the hydrogen gas has a similar isotopic composition with the previously documented deep-sourced gas, with lighter isotopic composition.In contrast, hydrogen gas has a heavier isotopic composition in relatively stable areas.The isotopic signatures suggest that there is a mixture of mantle- and crust-derived hydrogen gas in the relatively stable area, which is consistent with the H2/3He ratios.Therefore, it is clear that the hydrogen gas has a much wider distribution than found in the deep-derived fluid area, resulting in a much broader area with hydrogenating effect for resource rock.This understanding will provide new insights for hydrocarbon generation research and resource assessment in petroliferous basins.     

Calculation of the CO2 Degassing during Contact Metamorphism and Its Geological Significance: The Model and Example from the Shuanshan Area of the South Tan-Lu Fault Belt

The paper studies CO2 degassing and controlling factors under the condition of contact metamorphism in the Shuangshan area, southern Tan-Lu fault belt and the method of calculating the amount of CO2 degassing. The results show that the amount of CO2 degassing is controlled by the characteristics of the country rocks, including the thermal conductivity, penetrability, porosity and connectivity. Compositions, size and depth of intrusive rock also have an important influence on CO2 degassing, i.e., they generated numerous cracks in the country rocks, and thus allowed the easy flow and accumulation of fluids. The amount of CO2 flux in contact metamorphism is calculated quantitatively based on the metamorphic reaction and time--integrated fluid flux. The value (0.729- 2.446×104 mol/cm2) of CO2 flux suggests that CO2 was provided mainly by the contact metamorphic reaction. The generation and releasing of CO2 are positively correlated with the degree of metamorphism, and XCO2 in fluids gradually increases from dolomite zone to calcite zone, but in the zone of grossular, fluid flux is the largest and XCO2 sharply decreases due to involvement of magmatic water. This study presents evidence that a large amount of industrial-scale CO2 can be produced during contact metamorphism. On the basis of theoretical and practical studies, a cone model has been proposed to response CO2 degassing for the contact metamorphism, and it can be used to explore CO2 accumulations beyond the oil-gas basins. This model can also be applied to the study of inorganic genesis of CO2 accumulations.     

地幔流体与地球的放气作用

地幔流体的形成、聚集和渗透是引起地幔交代作用的主要营力。地幔交代作用发育的强弱决定着所生成岩浆的碱性程度。地幔流体和部分熔融体高度富集不相容元素,它们与亏损地幔的相互作用可以使后者发生ＬＲＥＥ和不相容元素的局部富集。通过板块俯冲作用使地球表层的ＣＯ２进入地幔,参加地球的碳循环。热点岩浆来源的ＣＯ２中含有部分循环的ＣＯ２,而大洋中脊玄武岩中的ＣＯ２主要是原始地球的ＣＯ２。携带ＣＨ４和Ｈ２Ｏ的流体渗透至被俯冲带带入地幔的物质,使碳酸盐化的榴辉岩还原而形成含金刚石的榴辉岩和富水流体,并诱发局部熔融,所形成的熔体以火山喷发的形式上升到地表。地幔岩石中含有大量的流体,它们主要以流体包裹体的形式存在于地幔矿物中。几乎在所有的上地幔环境下形成的矿物中均找到了流体包裹体。包裹体内流体的成分主要是ＣＯ２,ＣＨ４,Ｈ２Ｏ及少量Ｈ２,Ｎ２等。