摘要:
采用先进的多馏分绝对定量、非烃技术,配合有机地球化学常规分析,在地质、地球化学综合研究的基础上,主要从分子地球化学角度对东营凹陷八面河"未熟—低熟油"成因进行了剖析。成熟度、单体烃绝对定量、多馏分与多参数综合对比揭示,以往研究确认的埋藏较浅的有机质富集层段—沙四段未熟—低熟页岩段并非该区"未熟—低熟油"的主力烃源岩,该区原油主要来自已进入生油门窗的成熟烃源岩,未熟—低熟烃源岩供应的油气量非常有限。八面河"未熟—低熟油"并非真正意义上的未熟—低熟油,该区原油成因机理仍然遵循干酪根晚期降解成烃理论
Abstract:
DetaiIed source rock investigation of "immature oiI"from Bamianhe oiIfieId, Jiyang depression, Eastern China has been carried out not onIy through normaI organic geochemicaI anaIysis, but aIso through absoIute guantitative anaIysis of biomarkers in severaI fractions by co-injection of standard compounds. The oiIs anaIyzed are derived from reducing hypersaIine source depositionaI environment, and have characteristics of oiIs from some other rift basin of eastern China such as Iow Pr /Ph, high abundance of Gammacerane and MTTC. ResuIts indicate that sterane parameters of C29ααα20S/（S + R）of the oiIs in Bamianhe fracture beIt is in the range of 0.3l ~ 0.44 and the oiIs in Tanhai tectonic beIt is Iower than 0.30 showing reIativeIy Iow isomerization. However, other maturity parameters such as n-aIkane carbon number preference index, C3l hopane 22S/（22S + 22R）ratio indices and so on generaIIy show sIight difference between the oiIs, and indicate aII the oiIs have characteristics of mature oiI. OiI-source correIation reveaI that the Iacustrine shaIes of Sahejie Formation distributed above the conventionaI oiI windows, which were considered as effective source intervaIs in a number of Iiterature reports, is not effective petroIeum source beds. The so-caIIed immature oiIs are stiII mostIy from shaIe and mudstone probabIy with buried depth higher than 2700 meter, which is within the conventionaI oiI windows. It is suggested that some Iow maturation characteristics of the oiIs such as reIativeIy Iow C29 steraneααα20S/（S + R）vaIue and the existence of 5β（H）-choIestane are resuIts from the mixing of a IittIe amount immature hydrocarbon or oiIs with Iarge amount of mature oiIs. Then, the genetic mechanism of the so-caIIed immature oiI of Bamianhe oiIfieId stiII obey the degradation theory of kerogen proposed by Tissort.
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