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万安盆地是南海西南部陆架上的大型新生代沉积盆地。晚始新世以来,受盆地东界断裂——万安断裂的多期活动及全球海平面控制,盆地经历了从晚始新世—早渐新世的内陆湖泊到晚渐新世的海湾及早中新世以来的滨、浅海—半深海环境的发育历程。盆地内有丰富的油气资源。油气的生成、运移与聚集都受沉积特征的强烈控制。内陆湖泊环境中的湖相泥岩段和海湾环境的海湾相泥岩段有机质含量高,是重要的烃源岩。三角洲砂体,浊积砂体,扇三角洲砂体,深切河谷内的河道砂体,碳酸盐台地及其斜坡脚的塌积岩是有利的储集岩体。上新世早期的海进和高水位期间形成的凝缩段是区域稳定的盖层,其各阶段发育的凝缩段多为局部性盖层。
Wan’an Basin is a large Cenozoic sedimentary basin on the shelf of the southwestern South China Sea. Since late Eocene, under the multi-period activity of the Wanan fault and the global sea level control in the east boundary of the basin, the basin underwent the evolution from the Late Eocene to Early Oligocene inland lakes to the late Oligocene Gulf Since the early Miocene, the coastal, shallow sea - semi-deep sea environment development. The basin is rich in oil and gas resources. Hydrocarbon generation, migration and accumulation are strongly controlled by sedimentary characteristics. The lacustrine mudstone in inland lake environment and the Gulf mudstone in gulf environment have high organic matter content and are important source rocks. Delta sand bodies, turbidite sand bodies, fan deltaic sand bodies, channel sand bodies in the deep river valleys, carbonate platforms and their slope footfalls are favorable reservoir rocks. The condensing section formed during the early Pliocene sea-level and high water level is a stable regional cap rock, and the condensed sections developed in all stages are mostly local cap rocks.