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。

Identification of genetic types of natural gases produced from deep sag in Dongying depression

A series of high-production natural gases have been discovered in deep sag of the northern Dongying depression in recent years, which is a great breakthrough in the oil-rich basin. It comes a debate among the geological explorers about the gas origins whether the gas is the thermal degradative gas from source rocks or the cracking gas from oil. The authors investigated on the geology and geochemistry of natural gases discovered in the Minfeng area, a typical gas accumulation area in the deep sag of the northern Dongying depression, especially conducted thermal simulations on gas generations from either source rock or oil, and found useful identification parameters on the two genetic types of the natural gases. For the source-rock-degradative gas, the ratio of ln(CC₅/nC₆) <-1, (MCC₅₊CC₆)/nC₆< 0.8, (CC₅₊MCC₅₊CC₆)/(nC₅₊nC₆) < 0.5, DMCC₅/CC₅> 0.6 and ratio of toluere/benzene is greater than 1.1. For oil-cracking gas, all the ratios are in opposing numbers. The results conclude that the natural gases discovered from the Minfeng area are mainly source-rock-degraded gas and subordinately oil-cracking gas.