松南油伴生CO_2气的成因及其对油气藏的影响

The Genesis and Its Impaction on Oil and Gas Reservoir of Oil-Associated CO_2 in Southern Part of Songliao Basin

以松辽盆地南部长岭断陷油伴生气和含片钠铝石砂岩为对象,研究松南伴生CO2气的成因,并在此基础上,讨论幔源-岩浆CO2混入对油气动态成藏的影响。通过对伴生气组分,碳、氧及氦同位素数据的分析,发现松南油伴生CO2气的体积分数为1.57%～75.25%,主体在20%以上,δ13 CCO2值为-9.90‰～-4.00‰,R/Ra为0.95～4.46,说明松南油伴生气中CO2的体积分数很高,伴生CO2气主体为幔源-岩浆成因。如果幔源-岩浆CO2气大量混入油藏,将发生CO2驱油,形成次生油气藏。由松南油气藏的典型剖面特征及片钠铝石中原生烃类包裹体的发现,证实松南存在幔源-岩浆CO2驱油的事实。在幔源-岩浆CO2与油气混合成藏地区,寻找幔源-岩浆CO2充注驱油成因的次生油气藏已成为新的勘探思路。

The genesis of oil-associated CO2 and its impaction on the exploration of oil reservoir and the dynamic accumulation for oil and gas have been investigated by studying on the oil-associated gas and the dawsonite-bearing sandstones in Changling depression, southern part of Songliao basin. The characterists for oil-associated CO2 in southern part of Songliao basin are showing a content of CO2 between 1. 57% and 75.25%（most of which are higher than 20%）, with 13Cc02 values from --9.90% to --4.000, and R/Ra values in the range of 0.95 - 4.46. It is suggested that the content of CO2 in oil- associated gas is high, and most of the CO2 is mantle-magmatic origin. When there is a large-scale mixed CO2, a secondary oil reservoir will form owing to the displacement of crude oil by CO~. The scenario of oil displacement by mantle-magmatic CO2 has been recored by the typical profiles of oil and gas reaervoir in south of Songliao basin and the primary hydrocarbon inclusions in dawsonite cements. Therefore a new exploration idea is made to looking for the secondary oil reservoirs origined from oil displacement by CO2 within the place mixing with mantle-magmatic CO2 and oil reservoir.