珠江口盆地白云凹陷古近纪挠曲缓坡带三角洲沉积过程响应水槽模拟

Flume simulation of response of deltaic sedimentary process to Paleogene flexural gentle slope belt in Baiyun Sag, Pearl River Mouth Basin, northern South China Sea

吴宇翔 柳保军 张春生 丁琳 谢世文 李小平 龙更生

WU Yuxiang LIU Baojun ZHANG Chunsheng DING Lin XIE Shiwen LI Xiaoping LONG Gengsheng

中海石油有限公司 深圳分公司, 广东 深圳 518067 中海石油深海开发有限公司, 广东 深圳 518067 长江大学 地球科学学院, 武汉 430100

Shenzhen Branch, CNOOC China Ltd., Shenzhen, Guangdong 518067, China CNOOC Deepwater Development Ltd., Shenzhen, Guangdong 518067, China School of Geosciences, Yangtze University, Wuhan, Hubei 430100, China

南海北部陆缘深水区已发现数亿吨油气地质储量，而裂陷期古近系规模有效储层的分布是深水区勘探取得持续发现的关键。珠江口盆地白云凹陷深水区挠曲缓坡带裂陷期从文昌组到恩平组的地震资料上可观察到持续发育的大型辫状河三角洲。在无井或少井的情况下，为进一步认识该区构造沉降过程中大型辫状河三角洲的沉积单元组成、演化规律，开展了白云凹陷挠曲缓坡带三角洲沉积过程响应水槽模拟实验。实验设计了3期构造沉降，分别对应古近纪区域构造—沉积演化的3个时期，即均衡裂陷期、拆离裂陷期和断拗裂陷期，采用洪水、平水、枯水相间隔的方式模拟牵引流的水动力机制。实验表明，在3期构造沉降过程中，挠曲缓坡带均发育天然堤、泛滥平原、分流河道、废弃河道、支流间湾、水下分流河道、河口坝等三角洲沉积环境微相单元；辫状河三角洲以侧向进积作用为主，垂向加积作用为辅，沉积中心逐渐向洼陷中心迁移；裂陷期挠曲缓坡带三角洲形态及砂体分布主要受构造地貌、入湖河流流量、湖平面升降以及水体深度等因素控制。

Hundreds of millions of tons of oil and gas geological reserves have been discovered through exploration in the deep-water area of the northern continental margin of the South China Sea, and the distribution of large-scale effective reservoirs during the Paleogene rifting period is the key for continuous discovery in deep-water zone. Large braided fluvio-delta can be observed on seismic data from the Wenchang to Enping formations in the rifting period of the flexural gentle slope belt in the deep-water zone. Due to the absence of wells or few wells, for further understanding of the composition and evolution of large braided fluvio-deltaic sedimentary units in the process of tectonic subsidence in this region, a simulation experiment on the response of the deltaic sedimentation process in the flexural gentle slope zone to flume was carried out. Three phases of tectonic subsidence were designed for the simulation experiment, corresponding to the three phases of Paleogene regional tectonic-sedimentary evolution including balanced rifting period, detached rifting period, and faulted depression rifting period. The hydrodynamic mechanism of tractive flow was simulated by means of flood, flat water, and dry water. Simulation results showed that during the three stages of tectonic subsidence, the flexural gentle slope zone deve-loped distributary channels, natural dikes, floodplains, underwater distributary channels, estuaries, inter-tributary bays and other delta sedimentary microfacies units. The braided river delta was dominated by lateral proliferation, supplemented by vertical accretion, and the sedimentary center gradually migrated to the center of the depression, with almost no degeneration. The delta shape and sand body distribution in the flexural gentle slope zone during the rifting period were mainly controlled by factors such as structural geomorphology, river discharge amount into lake, lake level changes, and water depth.

国家科技重大专项 2016ZX05026-003-003

https://doi.org/10.11781/sysydz202203476