松辽盆地深层天然气富集条件的特殊性探讨

Particularity Discussion of Deep Natural Gas Enrichment Conditions in Songliao Basin

松辽盆地断坳复合的二元结构及独特的地质历史建构,决定了两套油气系统的存在和差异;晚侏罗世—早白垩世形成的深部断陷群及其内幕沉积岩和火山岩建造的特殊性,决定了天然气富集条件的特殊性。沙河子组大面积、厚层的湖沼相建造,为煤型气的形成提供了丰富的有机质。断陷期大规模火山活动,坳陷期巨厚而又稳定的沉积产生的强地温场加速了烃源岩(煤系地层)的转化,并有无机成因气大量产生,营城组沉积时数万平方千米范围的火山喷发,形成了爆发相和喷溢相叠合的有利相带,发育了具有孔隙和裂缝双重介质中酸性火山岩储集体,相对独立的火山岩体在巨厚的沉积盖层下形成独特的圈闭类型。早期形成的构造为原生气藏的形成提供了圈闭条件;后期构造运动破坏了原生气藏,形成了次生气藏;同时深大断裂沟通深部无机气源,形成了特殊类型的二氧化碳气藏。

The dual structure of the complex fault depression in Songliao Basin and its geologic historic construction determined the existence of two sets of petroleum systems and their differences. The deep fault-depression group developed during Late Jurrasic to Early Cretaceous and the particularity of the constructions of its inside sedimentary rock and volcanic rock determined the particularity of the natural gas enrichment conditions. The large thick limnetic facies in Shahezi Formation provided abundant organics for the formation of coal gas. The large-scale volcanic activities during fault-depression period and the strong geothermal field resulted from the huge thick and stable sediment during depression period sped up the transformation of hydrocarbon source rock and resulted in the formation of large amount of abiogenetic gas. The volcanic eruption within several ten thousands square kilometers during the age of Yingcheng Formation led to the formation of the favorable facies belt with the stacked explosive facies and effusive facies, and the medium-acidic volcanic reservoir with pores and fractures developed. The relative independent volcanic rock resulted in the formation of the special trap type under the huge thick seal formation. The early-formed structure provided the trapping conditions for the formation of the primary gas pool. The late structural movement destroyed the primary gas pool, and the secondary gas pool developed. Meanwhile, the deep large fault was connected with the deep inorganic gas sources, as a result, the special CO2 gas reservoir was formed.