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松南无机成因CO2与常规油气的耦合差异成藏研究
中文摘要

随着深层天然气勘探的进展,松辽盆地在长岭地区相继发现了规模巨大的CO₂富集区带。此前,松辽盆地已在多处发现了无机成因的CO₂气藏或气苗显示,例如在盆地南部万金塔、孤店、乾安、红岗等气藏以及盆地北部发现的昌德东CO₂气藏等,种种迹象表明,无机成因CO₂在松辽盆地普遍存在。天然气的组分及其同位素是研究天然气地球化学特征、判别其成因类型的重要参数。据松辽盆地南部CO2气气藏δ¹³C〓的分析。CO₂气碳同位素分布区间在-8.44‰~-3.37‰,其伴生的氦同位素³He/⁴He一般在2.65×10⁻⁶~4.53×10⁻⁶,综合判断,其成因主要为幔源成因。 对于无机成因气分布规律的研究,国内外已有多位学者开展研究,但一般侧重于壳幔深部天然气来源及运聚模式方面的探讨。本文总结了盆地内各层次断裂体系及火山活动在CO₂运聚的中作用,在这一基础上着重分析幔源气体成藏进程中,与盆地内不同层段常规石油、天然气的耦合差异聚集的内在关系。 通过研究无机成因CO₂成藏机制及其与常规油气的耦合关系,本文取得的主要的认识是: 1、深部构造背景控制CO₂区域分布 幔源CO₂的气源来源于地球深部,只有在深大断裂发育、幔源岩浆活动强烈的区域才可能有CO₂气藏的聚集。在区域上,松辽盆地CO₂气的分布也主要受深部地质背景的控制。从已发现CO₂和He异常井的分布来看,松辽盆地无机成因CO₂和He气的区域分布具有以下规律: CO₂和He气主要分布于莫霍面埋藏小于32㎞的地幔上隆地区。松辽盆地莫霍面埋藏较浅,在29-34㎞范围内,而高含CO₂和He气又主要分布在莫霍面埋深小于32㎞的地幔隆起区。上地幔隆起导致莫霍面埋藏较浅、超壳断裂形成,是幔源岩浆灌入岩石圈的必要条件,而幔源岩浆是CO₂、无机烃类气和He的主要气源,为CO₂气的聚集提供气源条件。 CO₂和He气分布于高的地温场区域。松辽盆地是一个高地温盆地,盆地中热流的总平均值为68.65mW/㎡。现今发现的CO₂气藏或显示均分布在盆地内地温较高的中央凹陷区,主要分布在地温梯度大于3.5℃/100m的区域内。地温梯度越高,说明深部热活动越强烈,是幔源CO₂释放的有利地区。 CO₂和He气与深大断裂关系密切。重力梯度上延40㎞的异常图能反映中下地壳的深大断裂信息,高含CO₂和He的井位多分布在深大断裂带的附近,尤其是几条深大断裂的交汇处。 2、不同时期不同层次断裂体系构成了CO₂天然气聚集的通道 CO₂的生成、运移、聚集和保存等整个成藏过程均受各级断裂体系的控制,不同级别和活动期次的断裂对CO₂气运移、聚集和保存的控制作用不同。一般,深大岩石圈和壳断裂控制了CO₂气源,而基底大断裂控制了CO₂在盆地内的运移、聚集和分布,而后期次生断裂则控制了CO₂气的保存和再分配。 松辽盆地断裂活动尽管有7个时期,但强烈的活动时期只有3个:早白垩世早期、泉头组沉积晚期—青山口组沉积早期和明水组沉积末期。 早白垩世早期断裂活动控制了火山喷发并形成有利的储层。断裂控制火山口分布,断裂多期活动控制火山口附近储层裂缝发育,稍晚断裂活动常造成这些地区应力集中,形成大量的裂缝,有效改善火山岩体储集空间,形成优质储层。 明水组末期断裂活动导致大量CO₂气上运并聚集成藏。断裂断穿层位控制CO₂气聚集层位:凡是与深部热流低辟体和有根的侵入体直接相连的基底断裂均是CO₂气上运的通道,但不同活动规律的基底断裂在盆地内断穿层位不同,使得CO₂气上运聚集的层位明显不同,断陷期活动的基底断裂多数向上断至T₄,是营城组火山岩储盖组合中有效的输导通道,受该类断裂控制形成了长深6、长深4、长深2、长深9和德深5等CO₂气藏。坳陷期活动的断裂,一般断至T₂反射层以上,但受青山口组高品质区域性盖层的控制,CO₂气主要聚集在泉头组三、四段储集层中,典型的是孤店、乾安、红岗和万金塔CO₂气藏。 3、新生代岩浆活动是CO₂天然气藏的主要气源 松辽盆地内中生代火山岩主要分布在四个层位,即火石岭组(K₁h)、沙河子组(K₁S)、营城组(K₁y)和青山口组(K₂q)。松辽瓮地内部新生代火山岩出露较少,只在盆地边部发现几座新生代火山,如盆地北部边缘的五大连池火山和克东火山,盆地南部的双辽和大屯火山。 松辽盆地营城组沉积时期,热流再次上涌,使拆离断层系破坏,大量岩浆沿断裂溢流出地表,形成营城组大面积发育的火山岩。同时CO₂气随着岩浆的冷却而析出并散逸,只有很少部分存留在岩浆岩一些死孔隙或连通性差的孔隙中,大部分因无上覆盖层的保护散失掉了。青山口-新生代沉积时期,地壳再次活动,伴随有热构造事件。岩浆多数没能涌至火石岭组及上部地层,而其中凝析出的CO₂气沿此时开启的断层系向上运移,进入到火石岭组一营城组火山岩的孔隙裂缝中。由于此时登二段泥岩盖层已形成,具备了封闭CO₂气的能力,故形成了CO₂气藏。 4、营城组火山岩厚度大,分布广泛,储集物性好,是松辽盆地深层天然气的优质储层。火山岩冷凝产生原生气孔和收缩裂隙,后期通过淋滤、再埋藏溶蚀和裂缝改造等作用形成优质储层。由于火山岩脆性强应力易集中,构造强烈时容易遭受破坏形成渗透性好的裂缝,使储渗性明显提高。 区域盖层有效地限定了断层的发育,有效控制了CO₂气的聚集,以泉一、二段区域盖层为界,可划分为两个二氧化碳含气组合:上部组合和下部组合。 深层烃类气和CO₂成因迥异,成藏过程和成藏模式差异较大,分布主控因素不同,从而也决定了两者在分布规律上的明显差异。在气源岩分布区,只要储层发育,有断裂沟通且构造部位有利,就会形成烃类气藏。当一个圈闭同时满足烃类气和CO₂成藏条件时,就会形成混合气藏,两者充注气量的大小决定了气藏中烃类气和CO₂相对含量的大小。烃源岩条件较差,但满足CO₂成藏条件的圈闭则会形成纯CO₂气藏。 5、泉四段石油的聚集控制因素有三个,即河流砂体在青一段有效的排驱压力作用下,通过断裂体系,形成油气的聚集。而后期侵入的CO₂气体,无论是对已经形成的油气藏,还是对泉四段砂岩储集层,都形成了深刻的改造和影响。 后期侵入的CO₂气体,由于其成藏的主要控制因素主要受深部火山岩体和坳陷期断裂体系在新生代的开启作用影响,在泉四段以河流点坝砂岩沉积的储集层内,其影响范围的特点是局部而非大面积,而且油气的重新调整更重要是在单个砂体单元内的调整。 根据流体包裹体数据分析结合盆地埋藏演化史,泉四段油气充注时间为明水组沉积末期,而CO₂主要在新生代构造运动时期侵入盆地盖层。 通过对研究区地层水参数的统计分析以及储层的物性主要参数的研究发现,在长岭-华子井阶地,由于局部区域遭受了CO₂气体高密度的侵染作用,本区呈现了地层高矿化度和储层渗透条件极大破坏的两大特征。 关键词: CO₂,断裂,火山,耦合,常规油气

英文摘要

Along with the progress of natural gas exploration, large scale of inorganic carbon dioxide has been found in Changling area.In fact some inorganic gas was captured in several areas such as Wanjinta,Gudian ,Qian an, Honggang and Changde in Songliao Basin.Such facts indicate that mantle-resource gas exists commonly in the basin,Constituent and isotope of natural gas are the important parameters that can be used to distinguish the type of gas origination.According to the analysis of isotope of natural gas in Southern Songliao Basin,we can conclude that most of the inorganic carbon dioxide is inoganic. The distribution of inorganic natural gas has been studied by several scholars at home and abroad.Generally they often pay attention to the machanism and accumulation of natural gas. After integrating the achievement of ancestors ,such as studying on the tectonic characters of deep layer and high abnormal thermal-flow of Songliao Basin,crust-mantle structure in the deep strata and the leading passages of mantle-genetic carbon dioxide reservoir,we mainly studied the coupling mechanism of inorganic carbon dioxide and petroleum in different depth of the layer. Some important conclusions are acquired: 1.The crust low-velocity and high-conduction zone in the deep layer of Songliao Basin may be the magma chamber accummulated in the mid or lower crust and produced from the partly melting inside mantle under the interaction of crust and mantle. The low-velocity and high-conductivity zone may also be the melted lava inside crust under the condition of high thermal flow and shortage of water. 2.Different kinds of fault controlled the distribution of inorganic carbon dioxide The generation,migration and accumulation of inorganic carbon dioxide are controlled by different kinds of faults in the basin.Ingeneral,large scale fault such as shell fault controlled the supply of gas,and the basic fault in basin controlled the distribution in different layer of inorganic carbon dioxide,and the fault of late periods mantained the redistribution of inorganic carbon dioxide. The activity of fault in Songliao Basin can be classified into 7 periods.and the intense exercise are mainly 3 times,that is earlly Cretaceous,the times of Qingshankou,and the end of Mingshui formation. Fault in earlly cretaceous contronlled the volcanic eruption and to take shape the advantaged reservior,they also controlled the distribution of crater.Multi-activity faults creat lots of crack in the reservior nearby crater.this is very useful to impprove the penetrability of volcanic reservoir. Fault activity at the end of Mingshui formation caused transportation and accumulation of huge inorganic carbon dioxide.the extent of fault controlled the position of inorganic carbon dioxide reservior. 3.Controlling machanism of magamtism and volcatism Lava in Yingcheng formation have the characteristics of huge thickness,wide range distribution,are the excellent quality reservoir in the basin. Magamtism and volcatism of Mesozoic in the basin are distributed in four formation.that is Huoshiling formation,Shahezi formation,Yingchengzi formation and Qingshankou formation, magamtism and volcatism of Cenozoic which are seldem found,we can found that at the marginal of basin, volcatism such as Wudalianchi and Datun volcanic. During the formation of Yingcheng, magamtism activity are very popular,heat flow piercement overflow along the fault system,and great scale of volcano-magma were formed.and at the same time,huge amount of carbon dioxide were disipated because of no seal formation . During the time of Qingshankou-Cenozoic, magamtism activity were once more developed.most of the heatflow piercement did not pass through the Huoshiling formation and above formation.Out gas migreted along fault and accumulated in the fracture of lava.At that time,overlap such as Denglouku formation were formed,kept the carbon dioxide reservoiring. 4.Hydrocarbonin deep layer has the different origination from iorganic carbon dioxide,the two sides have great distinction on accumulation. In the area with good source rocks,lava will be put into hydrocarbon under the communication by faults.Once the trap meet the accumulation conditions of both hydrocarbon and iorganic carbon dioxide,there will form mix reservoir which contain hydrocarbon and inorganic carbon dioxide.in the area with poor source rocks,under the communication of huge fault, iorganic carbondioxide will be acuumulated. 5.The controlling factor in Quantou formation are: sandstones are continuously distributed in the whole basin, reservoirs are compact in the depression area; oil sources are abundant and with overpressure as the major driving force of hydrocarbon expulsion; The coupling mechanism between iorganic carbon dioxide and petroleum in Quantou formation are:first,petroleum are accumulated at Mingshui formation,and inorganic carbon dioxide invaded oil reservior at Neozoic,The destroy effection of original oil reservior are limited,just becaused that the sandstone almost isolated.then the redistribution of petroleum are only inside the sandstone. The effection of inorganic carbon dioxide to petroleum reservoir are obvious. Waters in reservoir showed high outliner abnormol value in the case of carbondioxide influxion which greately changed total minerlitation of reservoir,and the invasion of iorganic carbon dioxide created abundance of dawsonite.This is very infaust factor to the penetrability of reservoir. Key words: carbon dioxide, fault, volcano, coupling, petroleum

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