准噶尔盆地玛湖凹陷深层油气流体相态研究

准噶尔盆地玛湖凹陷深层(5000m)是我国深层油气勘探当前的一个热点风险领域。为给区域下步油气勘探提供参考,通过对区内烃源岩和油气进行系统的地质地球化学正演、反演对比综合研究,重点分析了油气流体相态。结果表明,研究区深层稳定发育石炭系—二叠系四套烃源岩,有机质丰度高,普遍达到中等—好质量,类型多种多样,既可生油亦可生气,加之所有烃源岩均已基本进入高—过成熟演化,因此深层油气流体相态总体应高熟轻质,可能包括高熟轻质油、干酪根裂解气、油裂解气等。原油地球化学研究表明,原油随埋藏深度增加、层位变老,油质有逐渐变轻的趋势,成熟度有逐渐增大的趋势,保存条件亦逐渐变好,因此预测深层原油油质更轻、成熟度更高、保存条件更好。天然气地球化学研究表明,中浅层天然气可能属于混合来源,包括干酪根裂解气和油裂解气,规模性的高过成熟天然气可能在深层。因此,研究区深层油气资源丰富,相态轻质,成藏有利,值得勘探。这些认识还可供具有相似油气地质背景地区在研究和勘探时类比参考。

Hydrocarbon Fluid Phase in the Deep-Buried Strata of the Mahu Sag in the Junggar Basin

Petroleum exploration and geological study in deep-buried strata is an important frontier field currently. Such strata in the Mahu sag of the Junggar Basin (>5000 m) have been predicted to have good resource prospects, but have received weak exploration and research attention. Here, in order to provide clues to understand the rules of hydrocarbon accumulation and thereby guide exploration strategy, we focus on investigating the hydrocarbon fluid phase, based on an integrated analysis of geology and geochemistry of hydrocarbon source rocks and oil and gas from forward and reversal perspectives, respectively. Results show that the hydrocarbon fluid phase in the deep-buried strata of the studied Mahu sag should be highly mature and light in general, including high-mature light oil, kerogen cracking gas and oil cracking gas. In addition, the hydrocarbon accumulation and exploration have uncertainties including static reservoir conditions of physical property and pressure and dynamic migration condition. Further studies are still needed along with more and more data collection. Despite of these uncertainties, the present results still can point to the fact that the deep-buried strata in the study area is rich in hydrocarbon resource with light phase, and thus is worthy of exploration. New giant oil and gas fields may exist under the present moderate- and shallow-buried Mahu sequences. These data and understandings can also provide new reference information for other studies with similar geological background.