北部湾盆地迈陈凹陷徐闻X3井原油地球化学特征及其成因  

Geochemical characteristics and origin of a crude oil from Well Xuwen X3 in the Maichen Sag,Beibuwan Basin,China

作　　者：包建平[1] 何丹[1] 朱翠山[1] 刘玉瑞[2] 王文军[2] 刘宏宇[2] 

机构地区：[1]长江大学油气资源与勘探技术重点实验室地球化学系,湖北武汉430100 [2]中国石化江苏油田分公司地质科学研究院,江苏扬州225009

出　　处：《天然气地球科学》2017年第5期665-676,共12页Natural Gas Geoscience

基　　金：国家自然科学基金项目(编号:41272169)资助

摘　　要：徐闻X3井原油中出现了完整且丰富的nC_(11-39)正构烷烃系列和iC_(13-20)植烷系列与25-降藿烷系列并存现象,由此表明它是一个严重生物降解原油与正常原油的混源油。抗生物降解能力较弱的链烷烃系列和C_(14-16)二环倍半萜烷的特征可以表征晚期注入的正常原油的成因和来源。高的姥植比(Pr/Ph>5.5)和明显富含陆源倍半萜烷这一特点与珠江口盆地白云凹陷和琼东南盆地所产煤成油十分吻合,表明晚期正常原油应该来源于北部湾盆地发育的涠洲组煤系烃源岩,在成因上属于煤成油。鉴于煤成油中甾烷、萜烷的浓度较湖相原油一般低1~2个数量级,其特征会被前期甾烷、萜烷浓度偏高的生物降解原油所掩盖。原油中三环萜烷系列、藿烷系列、伽马蜡烷、甾烷系列和β-胡萝卜烷及异常偏低的陆源三萜烷这一系列特征,既不同于北部湾盆地的湖相原油,也不同于相邻地区的煤成油,由此可以排除早期生物降解原油来源于盆地内发育的古近系烃源岩的可能性。鉴于北部湾盆地只有上古生界沉积有海相碳酸盐岩和碎屑岩地层,且还没有发生变质,它可以为确定徐闻X3井原油中生物降解油的来源和成因提供有用的地质和地球化学方面的信息,同时也表明北部湾盆地的上古生界沉积地层可能是值得关注的油气勘探新领域。Abundant and whole C11-39 normal alkane series and i-C1- 20 phytane series and 25-norhopanes coexist in a crude oil from Well Xuwen X3 in the Maichen Sag of Beibuwan Basin,it suggests that this oil is a mixture of unbiodegraded oil with severely biodegraded oil.Chain alkanes and C14-16 bicyclic sesquiterpanes having low resistance to biodegradation can provide some useful information on the source and origin of the unbiodegraded oil which charged into the mixed oil at late stage. High Pr/Ph ratio （〉5.8） and abundant terrigenous sesquiterpanes, similar to those coal-derived oils from the Baiyun Sag of Pearl River Mouth Basin and Qiongdongnan Basin, suggest that unbiodegraded oil should be derived from coal-containing sequences of Oligocene Weizhou Formation in Beibuwan Basin. In general, the concentrations of triterpanes and steranes in coal-derived oil are 1-2 orders of magnitude lower than those of lacustrine oils, so some specific biomarkers such as oleanane and bicadinanes will be concealed by biodegraded oil having relatively abundant hopanes and steranes. It is noteworthy that the distributions and compositions of tricyelic terpanes,hopanes,gammacreane,steranes and β-carotane in the mixed oil from Well Xuwen X3 are very different from those of lacustrine oils in the Beibuwan Basin and coal-derived oils from the Baiyun Sag of Pearl River Mouth Basin and Qiongdongnan Basin. It suggests that biodegraded oil could not be derived from Tertiary source rocks in the Beibuwan Basin.Based on the geological background of the Beibuwan Basin, marine carbonate and clastic rocks are observed in Later Paleozoic sequences,it can provide some geological and geochemical clue to determine the source and origin of severely biodegraded oil.Therefore, more attention should be paid to this new area of Upper Paleozoic sequences for oil and gas exploration in the Beibuwan Basin.

关 键 词：生物标志化合物 原油 生物降解作用 上古生界 迈陈凹陷 北部湾盆地 

分 类 号：TE122.113[石油与天然气工程—油气勘探]