松辽断陷盆地火山岩大气田形成条件与勘探实践

摘要

松辽盆地深层是由30多个孤立的断陷组成的断陷群，火山岩气藏是深层勘探的主要气藏类型。以断陷盆地火山岩大气田形成条件为主线，从深层断陷形成的特征分析着手，通过剖析控源及控藏因素，总结断陷盆地大气田形成条件。指出NNE-NE和NNW-NW两组控陷断裂体系共同控制深层断陷群的形成和展布，断陷沿控陷断裂方向呈带状展布。断陷内火山机构具有明显受断裂控制的不对称特征，沿断裂走向呈条带状分布。每个断陷通常由一个或多个断槽组成，断槽控制烃源岩的分布并自成含气系统，生烃断槽和火山岩在空间的有利配置是形成气藏的关键。环槽富集是深层断陷火山岩气藏最基本的规律，由于断裂控制了断陷、断槽、火山岩的形成分布，改善了油气运聚的通道条件，紧邻生烃断槽的断裂构造带是断陷内天然气有利富集区带；因此深部断裂控制了断陷火山岩气田的区域分布。勘探实践更进一步证明：对于断陷湖盆油气勘探，生烃主断槽是评价和勘探的关键单元；只要生烃断槽优质烃源岩发育，烃源岩与火山岩空间配置关系有利，对于“小而富”的中小型断陷（面积小于3000 km2），也可以形成火山岩大气田（探明地质储量大于300×108 m3），这些认识推进了勘探思路由寻找大湖盆大断陷到寻找生烃主断槽的转变。%The deep zone of Songliao basin is made up of more than 30 separated fault depressions where vol-canic gas reservoir is the main exploration target.Starting from the analysis of the formation characteristics of deep fault depression and analyzing the factors of controlled source and controlled gas reservoir,the conditions of giant volcanic gas field in fault depressions are summarized for guiding the exploration.The comprehensive research suggested that the deep fault depressions are controlled by two faults system that are NNE-NE and NNW-NW strikes,along the strike direction of faults controlled fault depressions.The typical asymmetrical model of volcanic eruption pattern controlled by faults is characterized by one small-scale side on the higher part of faults and by the other large-scale side in the lower part of faults,as molten magma flowed from the top down, with zonal distribution along the strike direction of faults controlled fault depression.Generally,each fault depression is composed by one or more fault troughs which control the distribution of source rock,so each fault depression has its own independent petroleum system and the key factor of gas accumulation is favorable spatial configuration between fault troughs and volcanic rocks.The deep volcanic gas reservoirs are characterized by nearby distribution surrounding source rocks and main troughs.The faults controlled the formation and distribu-tion of fault depressions,fault troughs and volcanic rocks,and improved the channel conditions for oil-gas mi-gration and accumulation,which indicates fault structural zone close to hydrocarbon bearing troughs is gas en-richment region.In short,deep faults controlled regional distribution of giant volcanic gas field.Further explo-ration practice prove that:for oil and gas exploration of fault basins,main fault troughs which controlled hydro-carbon generation is the key unit for the evaluation and exploration.As long as the high quality hydrocarbon source rock are developed in the fault troughs,with good space configuration with volcanic rocks,small and me-dium sized fault depressions with area smaller than 3 ,000 km2 also can form giant volcanic gas field (proven geological reserves of more than 300 ×108 m3 ),which have presented as exploration strategy changed from searching for big lake basins or fault depressions to main hydrocarbon bearing troughs which need to be proved.