Abstract: With the in-depth exploration of high-temperature and high-pressure natural gas in Yinggehai Basin, the longitudinal and transverse distribution of natural gas is becoming increasingly complex, and the direction of subsequent expanded exploration is still unclear. It is urgent to deeply analyze the accumulation model of natural gas in different belts from the perspective of reservoiring process, providing a guide for the further exploration of natural gas. Based on the newly acquired 2D wide-line and 3D ocean bottom node seismic data, the paper studies the key accumulation factors such as the hydrocarbon source conditions, transportation system, and reservoir sand body of the basin, and systematically summarizes the differences in tectonic activities in different belts and their control on hydrocarbon accumulation. The research shows that two sets of source rocks, i.e., the Miocene marine source rocks and the Oligocene transitional source rocks, are developed in Yinggehai Basin, providing the material basis for the formation of medium-large gas fields in Yingzhong anticlinal belt and Yingdong fault-step belt, respectively. Two types of natural gas transport systems are developed in the basin, and the inherited tectonic ridges, formed under sinistral strike-slip compression deformation in early stage and dextral strike-slip tension fracturing in late stage, as well as migration channels by faulted fractures and faults can provide an efficient hydrocarbon transport system for the large-scale oil-gas accumulation. Low-stand submarine fans, axial waterways, and delta sand bodies are developed under the condition of low accommodation space, by which the large tectonic-lithological combination traps are formed and provide reservoir space for oil and gas. On this basis, the differences in natural gas accumulation in different belts are analyzed, and two types of accumulation models have been established, i.e., "continuous charging of Miocene marine source rocks, dynamic adjustment of oil-gas decompression, multi-stage three-dimensional accumulation" in the medium-deep strata of Yingzhong anticlinal belt, and "hydrocarbon supply by Oligocene transitional source rocks, convergence of deep tectonic ridges, vertical transport of overpressure-driven fracture in late stage, and complex accumulation in medium-deep strata" in Yingdong fault-step belt. The medium-deep large-scale tectonic traps in Yingzhong anticlinal belt and its surrounding large-scale Miocene submarine fan-channel lithological traps, as well as the medium-deep "tectonic+lithological+buried hill" traps in Yingdong fault-step belt are the targets for petroleum exploration in medium-large gas fields, showing great resource potential.

Key words: Yinggehai Basin, Yinggehai sag, Yingzhong anticlinal belt, Yingdong fault-step belt, medium-deep strata, new field, accumulation model

摘要： 随着莺歌海盆地高温高压天然气勘探的深入,莺歌海盆地天然气纵横向分布的复杂性日益凸显,后续拓展勘探方向不明确,亟待从成藏过程深入剖析不同区带天然气的成藏模式,以指导下一步天然气勘探。基于新采集的宽线二维地震和海底节点三维地震资料,对莺歌海盆地的烃源条件、输导体系、储集砂体等成藏关键要素进行了研究,系统总结了不同区带构造活动的差异及其对成藏的控制作用。研究表明:莺歌海盆地发育中新统海相和渐新统海陆过渡相2套烃源岩,分别是莺中背斜带、莺东断阶带形成大—中型气田的物质基础;盆内发育2类天然气输导体系,早期左行走滑挤压变形、晚期右行走滑张性破裂作用下形成的断裂型和断缝型两种运移通道为油气的规模汇聚提供了高效的输导体系;莺歌海盆地在低可容空间条件下发育低位海底扇体、轴向水道和三角洲砂体,由其形成的大型构造-岩性复合圈闭为油气提供了储集场所。进一步剖析不同区带天然气成藏的差异,建立了莺中背斜带中—深层"中新统海相烃源岩持续充注、油气泄压动态调整、多期立体成藏"、莺东断阶带"渐新统海陆过渡相烃源供烃、深部构造脊汇聚、晚期超压驱动断裂垂向输导、中—深层复式成藏"2类成藏模式。莺中背斜带的中—深层大型背斜构造圈闭群及其周缘中新统大型海底扇-水道岩性圈闭群、莺东断阶带中—深层"构造+岩性+潜山"圈闭群,是近期莺歌海盆地大—中型气田的勘探方向,资源潜力较大。

关键词: 莺歌海盆地, 莺歌海凹陷, 莺中背斜带, 莺东断阶带, 中—深层, 新领域, 成藏模式