珠江口盆地番禺低隆起天然气成因和气源分析

NATURAL GAS ORIGINES AND GAS SOURCE STUDIES OF PANYU LOW UPLIFT IN PEAR RIVER MOUTH BASIN

指出:珠江口盆地番禺低隆起天然气组成差异较大,既有烃类含量很高的纯烃气藏,也有无机成因的二氧化碳气藏和高含氮气藏;天然气乙烷碳同位素值绝大多数小于-28‰,以混合气和油型气为主;甲烷碳同位素值介于-44.2‰～-33.6‰之间,C2+含量介于4.76%～10.98%之间,C1/(C2+C3)值介于6.28～21.44之间,大多属于高成熟—过成熟天然气;与天然气相伴生的高成熟凝析油具有较高的Pr/Ph值(2.58～6.38),双杜松烷有一定丰度,C304-甲基甾烷含量低,来自于恩平组烃源岩。利用ln(C1/C2)—ln(C2/C3)和(δ13C2-δ13C3)—ln(C2/C3)图版,结合油-气-岩的综合分析,认为番禺低隆起天然气以来自于恩平组烃源岩干酪根裂解气为主,以原油裂解气和文昌组烃源岩晚期干酪根裂解气为辅。

The component of natural gases of Panyu low uplift in Pear River Mouth Basin exists obviousdifference, including pure hydrocarbon gas reservoirs, inorganic formed CO2 gas reservoirs and high N2 content gas reservoirs. The carbon isotope value of ethane of most natural gases is less than -28‰,belonging to mixed gas and oil-type gas. The carbon isotope value of methane is between -44.2‰-33.6‰, C2-is between 4. 76%～10. 98%, the ratio value of C1/（C2＋C3） is between 6. 28～21. 44,belonging to high and over mature natural gas. The high mature condensates co-existing with natural gas have high ratio values of Pr/Ph （2. 58～6. 38）, high content of bicadinanes and low content of C30 4-methylsteranes, which derived from Enping source rock. By using natural gas parameters crossplot of In（C1/C2） vs ln（C2/C3） and （δ^13C2-δ^13C3） vs ln（C2/C3）, combining the studies of characters of condensates,natural gas and source rock, we propose that the natural gas of Panyu low uplift in Pear River Mouth Basin derived mainly from high mature mixed type kerogen cracking gas from Enping source rock, secondly from the secondary crude oil cracking gas and over mature oil-type kerogen cracking gas from Wenchang source rock.