琼东南盆地北礁凹陷崖城组沉积与烃源岩发育特征

Sedimentation and Source Rock Characteristics of Yacheng Formation in Beijiao Sag of Qiongdongnan Basin

北礁凹陷位于琼东南盆地深水区,被多个凸起包围,值得展开探索,以期能为深水区寻找到新的勘探领域。用比较分析的方法,通过精细解剖研究程度相对较高的崖北凹陷崖城组,分析其地震反射特征等,得到北礁凹陷崖城组的沉积及烃源岩特征。再结合北礁凹陷已钻井烃源岩地球化学指标、凹陷地热特征及凹陷周缘凸起的储盖组合等,深入分析了北礁凹陷的勘探潜力。通过研究得到如下结论:北礁凹陷裂谷期为半地堑结构,崖城组洼陷面积为1 400km2,最大厚度为2 150m;与崖北凹陷崖城组具有相似的古地貌、地震反射特征及沉积特征,为海陆过渡相潟湖—潮坪环境,潮坪相煤系地层为烃源岩的主要来源,潟湖相泥岩为重要的烃源岩来源;钻井已证实北礁凹陷崖城组能生成高成熟煤型气,且凹陷周缘发育多套储盖组合,该凹陷具有较好的勘探潜力。

Beijiao Sag lies in the deepwater of Qiongdongnan Basin. It is surrounded by some uplifts and de-serves researching in order to find a new exploration area. Using comparative analysis method, by dissecting Yacheng Formation in Yabei Sag carefully,we can know sedimentation and source rock characteristics of Yacheng Formation in Beijiao Sag. Combined with drilling wellsr geochemical index,geothermal character-istics,reservoir-caprock assemblage,we evaluated the exploration potential of Beijiao Sag and obtained the following conclusions. During rifting stage,Beijiao Sag was a half graben. The sub-sag of Yacheng Forma-tion has an area of 1 400km^2 and maximum thickness of 2 150m. Compared to the Yacheng Formation of the Yabei Sag,it has similar ancient landform,seismic reflection and sedimentation characteristics. The deposi- tion environment belongs to marine-terrestrial transitional lagoon-tidal flat facies. Coal measure from tidal flat is the dominant source rock, and the lagoon mudstone is important source rock as well. Drilling wells have proved Beijiao Sag can form highly mature coal-derived gas and there are many sets of reservoir-ca- prock assemblages around the sag. This sag has good exploration potential.