南海北部边缘盆地氮气气源追踪与判识

南海北部边缘盆地油气勘探中陆续发现较丰富的二氧化碳(CO2)和氮气(N2)等非烃气气藏,同时亦发现了一些含N2、富N2的天然气层。这些CO2和N2非烃气主要富集于西北部边缘莺歌海盆地中央泥底辟带新近系及第四系浅层中。根据N2地质地球化学特征,可将本区N2划分为大气成因、壳源型有机成因和壳源型有机-无机混合成因三种主要成因类型。结合温压双控热模拟岩石产氮气实验结果,以及N2等非烃气在平面上分区分块、剖面上分带分层的局部性富集特点,追踪判识并确定N2气源主要由来自不同成熟演化阶段的中新统及上新统海相泥岩气源岩的N2与多种物理化学和岩石脱气作用所形成的无机N2相互混合而构成。

Nitrogen Gas Source Tracking and Distinguishing in Margin Basins, Northern South China Sea

Abundant CO2 and N2 gas reservoirs and other N2-bearing gas reservoirs are discovered in the Neogene and Quarternary shallow beds of Central Mud diapir Zone in Yinggehai Basin,South China Sea during recent 20 years′oil and gas exploration.According to geological and geochemical characteristics of N2,the N2 gas in this area can be divided into three types in genesis,i.e.the atmosphere genesis,the crust organic genesis and the crust-derived organic-inorganic-mixed genesis.Combined with results from the nitrogen-producing experiments under T-and P-controlled thermal simulation and the characteristics of partial enrichment in plane and layering and zoning enrichment in vertical,it is determined the N2 gas is tracked to the mixture of the N2 that mainly yielded from Pliocene and Miocene marine gas source mudstone during different stages of maturation with the N2 that formed from physical and chemical actions and rock degassing.