鄂尔多斯盆地延长组沉积层序识别及测井响应特征

Sedimentary Sequence Identification and Log Responses in Yanchang Formation,Erdos Basin

通过研究鄂尔多斯盆地上三叠统延长组的岩电关系及变化特征,以便正确判识地层层序,总结生、储、盖组合和盆地演化规律,预测盆地有利储层展布趋势,指明有利勘探沉积相带和目标。由于测井资料对碎屑岩具有很高的纵向分辨率,所以主要根据自然伽马、低自然电位和电阻率测井的曲线变化幅度、形状、接触关系以及旋回性响应特征分析延长组岩性变化特征,识别沉积相类型、确定层序、层序界面,分析层序演化特征,不仅在延长组中划分出16种不同沉积相类型、4个层序界面和4个三级层序旋回,并识别出密集段、高位和低位体系域空间关系。利用测井响应特征能够较好识别延长组层序,层序演化控制了生储盖的空间组合和发育特征,低位体系域中发育的河道砂体分选性和储集性能好,是最重要的规模储层,最大洪泛期形成的地层往往是良好的生油层和盖层。

By carefully studying litho-electric property relationship and varying characteristics of Yanchang formation of upper triassic, Erdos basin, we can correctly identify stratigraphical sequence, forecast distribution trend of advantageous reservoirs, summarize source-reservoir-caprock group and evolutive law of Erdos basin, and show clearly sedimentary facies of advantageous exploration. Because of logging data have higher resolution in detritus rocks, to analyse lithological varieties of Yangchang formation, identify types of sedimentary facies, to ascertain sequence and sequence interface and analyse characters of sequence evolution are mainly based on amplitude ranges, shapes, contact relationship and cycle responses of natural γ-ray, low spontaneous potential and resistivity log curves. Sixteen types of sedimentary facies, four sequence interfaces and four class-3 sequence cycles are zoned in Yanchang formation; Also dense intervals, special relationship betweem high-level domain and low-level domain are identified. Utilizing the log responses can preferably identify sequences of Yanchang formation. Sequence evolution controls special space distribution and developmental feature of source-reservoir-caprock. Channel sands, with good selectivities and reservoirs developing in low-level domain, are most important large accumulation areas. Stratums formed during the most flooded period are frequently favorable oil source beds and barrier layers.