柴达木盆地西部七个泉与咸水泉油田原油地球化学特征对比研究

Comparative Study on Geochemistry between Crude Oils from Qigequan and Xianshuiquan Oilfields in Western Qaidam Basin

通过对取自七个泉油田和咸水泉油田原油样品中各类生物标志物的分布与组成特征的对比,发现七个泉油田原油中正构烷烃系列比较完整且丰度较高,而咸水泉油田原油中正构烷烃因轻微生物降解而被部分消耗,导致咸水泉油田原油的Pr/nC17值和Ph/nC18值明显高于七个泉油田原油。2个油田原油均呈现较强烈的植烷优势,七个泉油田原油的姥/植比更低,表明它们都来源于强还原环境下形成的烃源岩。在生物标志物分布与组成特征上,七个泉油田原油甾烷的C27/C29>1,而咸水泉油田原油甾烷的C27/C29值均为0.8,意味着七个泉油田原油中浮游植物贡献高于咸水泉油田。咸水泉油田原油的C29甾烷ααα20S/(ααα20S+ααα20R)值和重排补身烷含量高于七个泉油田原油,暗示咸水泉油田原油成熟度比七个泉油田原油成熟度高。2个油田的长链藿烷序列均比较完整,伽马蜡烷含量也较高,对比长链藿烷和伽马蜡烷的丰度发现咸水泉油田原油的长链藿烷和伽马蜡烷丰度都比七个泉油田原油低,说明咸水泉油田原油形成的环境的盐度和还原性比七个泉油田原油弱。

Comparative study on distribution and composition of various biomarkers in crude oil from the oil fields of Qigequan and Xianshuiquan indicates the crude oil in the Qigequan oilfield has the integrated and abundant n-alkane serial, but the normal alkanes in the oil of the Xianshuiquan oilfield were partly biodegraded, resulting in the higher ratios of Pr/nC17 and Ph/nC18. The phytane preference in the crude oil from both oilfields and the less ratios of Pr/Ph in the Qigequan oil indicate that they were derived from the source rocks deposited in strong reducing environment. In the C27 C29 sterane serial, the ratio of C27/C29 is more than 1.0 in the Qigequan oil, while the ratio is about 0.8 in Xianshuiquan oil, suggesting that the contribution of algae plankton to oil in the Qigequan oilfield is more than that in the Xianshuiquan oilfield. The ratios of ααα20S/（ααα20S＋ααα20R）for C29 sterane and diadrimane abundance in the Xianshuiquan oil are more than that in the Qigequan oil, inferring that the thermal maturity of the Xianshuiquan oil is higher than that of the Qigequan oil. The integrated distribution of hopane serial in both oilfields exists, with high abundance of gammacerane. By comparision of abundance of long chain hopane and gammacerane in the oilfield of Xianshuiquan and Qigequan, we find that abundance of long-chain hopane and gammacerane in the former oil is lower than that in the later, indicating that the source rock of oil from the Qigequan oilfield was deposited under higher salinity and stronger reducing environment.