准噶尔盆地西北缘哈山地区风城组碱湖页岩油地质特征与勘探展望

Geological characteristics and exploration prospects of alkaline lake shale oil of the Fengcheng Formation,Hashan area,NW Junggar Basin

玛湖凹陷二叠系风城组是准噶尔盆地近年来页岩油勘探开发和增储上产的重点层位。哈拉阿拉特山地区(简称哈山地区)位于玛湖凹陷北缘,由于位于逆冲带附近且处于勘探早期,该区风城组的沉积背景、古地理位置及页岩油勘探潜力尚不明确。根据哈山地区风城组页岩油近10年的勘探开发基础资料和成果,系统梳理了该区页岩的沉积环境、岩相划分、源岩品质、含油性和储集性,探讨了哈山地区页岩油的“甜点”发育规律和勘探前景。结果表明:玛湖主体洼陷之外,哈山地区中部风城组发育另一个碱湖沉积沉降中心,其火山喷发、沉积演化和成碱阶段与南部乌夏地区具有很好的可比性,为风城组另一富烃凹陷;提出了风城组碱湖页岩四端元对三角页岩划分方案,将风城组页岩划分为含盐和非含盐8种页岩岩相;整体上,哈山地区风城组黏土质页岩和钙质页岩有机质丰度最高,云质页岩和盐质页岩含油性相对较好,云质页岩和粉砂岩储集性最好,提出了云质页岩为I类甜点,粉砂岩为Ⅱ类甜点。哈山地区风城组页岩在源岩和储集层品质方面与乌夏地区风城组相当,具有较好的页岩油勘探前景。

In recent years,the Permian Fengcheng Formation of the Mahu sag has become an important interval for shale oil exploration and newly discovered hydrocarbon reserves in the Junggar Basin.The Halaalate Mountain area(Hashan area)is located on the northern margin of the Mahu sag.Due to its proximity to the thrust belt and in the early stage of exploration,the sedimentary background,palaeogeographical location and shale oil exploration potential of the Fengcheng Formation of the Hashan area are still unclear.Based on the exploration and development practice of shale oil in the Hasan area during the past decade,the sedimentary environment,shale facies,source rock quality,oil content and reservoir quality of the Fengcheng Formation shale oil in this area were studied systematically.The results show that besides the main sag in the Mahu sag,there was another alkaline lake center of developed in the central part of the Hashan area,which is another hydrocarbon rich depression for the Fengcheng Formation.The volcanic eruption,sedimentary evolution and alkaline salts forming stage of the Hashan area bear a strong resemblance to that of the Wuxia area to the south.A four end-member classification scheme is proposed here for the alkaline lake shale in the Fengcheng Formation.The shale of the Fengcheng Formation can be divided into eight lithofacies,including four salty lithofacies and four non-salty lithofacies.On the whole,the clayey shale and calcareous shale of the Fengcheng Formation in the Hashan area have the highest organic matter abundance,the dolomitic shale and salty shale have relatively good oil content,and the dolomitic shale and siltstone have the best reservoir property.It is proposed that the dolomitic shale comprises the class-I sweet spot and the siltstone comprises the class-II sweet spot for shale exploration.For the Fengcheng Formation,shale in the Hashan area is similar to that of in the Wuxia area in terms of source rock and reservoir quality,both of which have high shale oil exploration potential.