溱潼凹陷低熟油生物标志物特征及成熟度浅析

Biomarker features of low-mature oil in Qintong sag and maturity analysis

溱潼凹陷低熟油分布于外斜坡的殷庄油田殷2井戴南组一段和苏183井泰州组一段、坡垒带茅山油田苏168井的阜宁组三段、断阶带的角墩子油田苏228井的戴南组一段和草舍油田苏120井的三垛组一段,具有高含蜡量、低含硫量、运动粘度和密度变化大的特点.该凹陷低熟油判识指标αααC29甾烷20S/(20S+20R)和 C29甾烷αββ/(ααα+αββ)值分别为0.31和0.29;生物标志物甾烷异构化参数αααC29甾烷20S/(20S+20R)为 0.23～0.29,C29甾烷αββ/(ααα+αββ)为0.24～0.28,重排甾烷含量很低.同时还检测到多种不稳定的生物标志物,包括5β(H) - 粪甾烷系列,胡萝卜烷系列、脱羟基维生素E系列等.而较低的伽马蜡烷/C30藿烷分布指数、小于0.5%的含硫量以及四环三萜烷中C30～C31羊毛甾烷的检出,充分反映源岩沉积于微咸 - 半咸水的沉积环境和母岩成熟度较低这一事实.

In Qintong sag, low-mature oil occur in several wells and intervals, including the Ed1 of Yin 2 well and the EtI of Su 168 well in Yinzhuang oilfield located in the outer slope zone, the Ef3 of Su 168 well in Maoshan oilfield located in the fault horst zone, and the Ed1 of Su 228 well in Jiaodunzi oilfield and the Es1 of Su 120 well in Caoshe oilfield located in the fault bench zone. The low-mature oil are characterized by high wax content, low sulfur content, low kinematic viscosity and large variation of density. The values of ctctct C29 sterane＇s 20S/（20S ＋20R） and C29 sterane＇s αββ/（ααα ＋ αββ） , the diagnostic indexes for low-mature oil in this sag, are 0.31 and 0.29, respectively. The biomarkers sterane isomerization parameters, ααα C29 sterane＇s 20S/（20S ＋ 20R） is in the range of 0.23-0.29 and C29 sterane＇s αββ/（ ααα ＋ αββ ） is in the range of 0.24-0.28 ; the content of rearranged sterane is very low. At the same time, several unstable biomarkers, including 5β（H）-coprostane, carotane 1 and dehydroxyl vitamin-E families, are also detected. The observations that the source rocks were deposited in mildly brackish to brackish water and the low maturity of source rocks are well evidenced by the relatively low gammacerane/C30 hopane ratio, sulfur content less than 0.5% and the existence of C30 ～ C31 lanostane in tetracyclic triterpane.