地震沉积学在识别三角洲沉积体系中的应用

Mapping deltaic depositional systems using seismic sedimentology

地震沉积学在高频率层序和沉积体系研究中有着特殊的优势。90°相位地震资料的振幅可以和岩性测井曲线对应,对地震资料进行90°相位转换后可以通过地震振幅分析岩相。地层切片技术可以在平面上显示相对同一地质沉积时间的沉积分布特征,再结合岩性测井资料可以较准确分析沉积体系。美国南得克萨斯地区Webb县Gold River North油田上白垩统Olmos组钻井资料较少,采用地震沉积学方法对其分析,可以识别出一套完整的三角洲体系,其中包括前三角洲亚相、三角洲前缘亚相、三角洲平原亚相、曲流河相和下切谷沉积等,其中河道砂、河口砂坝和下切谷沉积物是有利的储层。

Seismic sedimentologic analysis is superior to standard seismic stratigraphic analysis in mapping high-frequency sequences and depositional systems. Seismic amplitudes can be correlated to log lithologies using 90°-phased seismic data, and, consequently, seismic traces can be interpreted as wireline lithologic logs. The stratal slices made from the 3-D seismic volume reveal the high-resolution sediment-dispersal patterns and associated depositional systems on the relative geologic time surfaces. The Olmos Formation in the Gold River North field is characterized by a shelf-edge deltaic system, from which five types of depositional systems are identified： （1） fluvial plain, which is characterized by fluvial channels, crevasse splays, and swales; （2） deltaic plain, which consists of distributary channels, levees, and crevasse splays; （3） deltaic front mouth bars and sheet sands; （4） prodelta, which is composed of silty sediments; and （5） incised valleys, which were formed during subsequent lowstand erosion on exposed deltaic sediments. The Olmos Formation can be productive in the Gold River North field because the distributary-channel sandstones and incised-valley fills may form potentially important stratigraphic traps.