南海渐进式边缘海构造旋回控制深水油气成藏理论

Theory of deepwater hydrocarbon accumulation controlled by progressive tectonic cycles of marginal sea in the South China Sea

边缘海等非大西洋型大陆边缘是当前全球深水油气勘探的前缘领域。南海是全球著名的边缘海之一,其深水油气成藏机理是前缘研究的科学问题。基于地学断面及大洋钻探成果等资料分析,提出南海的形成具有渐进式边缘海构造旋回的特征,即新南海洋盆的SN向打开在晚渐新世—早中新世表现为自东向西扩展,古南海洋盆的SN向闭合在渐新世—第四纪表现为自西向东扩展。南海渐进式边缘海构造旋回控制了盆地和油气成藏要素的有序发育。在新南海北部地区,被动大陆边缘盆地的形成具有“东早西晚”的特征:东段珠江口盆地形成始于始新世,发育始新统和下渐新统两套烃源岩、始新统—下中新统储层、中新统—第四系厚层泥岩盖层,含油气层的分布从潜山至中新统;西段琼东南盆地形成始于渐新世,发育下渐新统烃源岩、渐新统—上新统储层、上中新统—第四系厚层泥岩盖层,含油气层的分布从潜山至上新统。在古南海地区,活动大陆边缘盆地的形成具有“西早东晚”的特征:西段曾母盆地形成于渐新世,发育渐新统和中新统两套烃源岩、渐新统—中中新统储层、上新统—第四系盖层,含油气层的分布从渐新统至上新统;东段文莱—沙巴盆地形成始于中中新世,发育中新统烃源岩、下—中中新统储层、第四系泥岩盖层,含油气层的分布从潜山至下—中中新统。基于以上认识提出了南海边缘海油气勘探的新方向。南海北部大陆边缘深水区的新勘探层系为古近系—潜山,南海南部活动大陆边缘的新勘探层系为渐新统—下中新统。

At present,non-Atlantic continental margins such as marginal sea are a frontier of global deepwater oil-gas exploration.The South China Sea is one of the most famous marginal seas in the world,and its deepwater oil and gas accumulation mechanism is a scientific problem in frontier research.Based on the data analysis of geological transects and findings from ocean drilling,it has been proposed that the formation of the South China Sea is characterized with progressive tectonic cycles of marginal sea,i.e.,the SN-trending opening of the New South China Sea Basin was extending from east to west in the Late Oligocene to Miocene,and the SN-trending closure of the Ancient South China Sea Basin was extending from west to east in the Oligocene to Quaternary.The progressive tectonic cycles of marginal sea in the South China Sea controls the orderly development of basins and hydrocarbon accumulation factors.In the northern part of the New South China Sea,the formation of passive continental margin basins is characterized by"early in the east and late in the west".Specifically,the development of the Pearl River Mouth Basin in the east section began from the Eocene,which developed the Eocene and Lower Oligocene source rocks,the Eocene to Lower Miocene reservoir,and the Miocene to Quaternary thick mudstone cap rocks,showing a distribution of hydrocarbon-bearing strata from buried hill to Miocene.The development of Qiongdongnan Basin in the west section started from the Oligocene,which developed the Lower Oligocene source rocks,the Oligocene to Pliocene reservoir,and the Upper Miocene to Quaternary thick mudstone cap rocks,showing a distribution of hydrocarbon-bearing strata from buried hill to Pliocene.In the Ancient South China Sea,the formation of active continental margin basins is characterized by"early in the west and late in the east".To be specific,Zengmu Basin in the west section was formed in the Oligocene,which developed the Oligocene and Miocene source rocks,the Oligocene to Middle Miocene reservoir,and the Pliocene to Quaternary cap rocks,showing a distribution of hydrocarbon-bearing strata from Oligocene to Pliocene.The development of Brunei-Sabah Basin in the eastern section was initiated from the Middle Miocene,which developed the Miocene source rocks,the Lower to Middle Miocene reservoir,and the Quaternary mudstone cap rocks,showing a distribution of hydrocarbon-bearing strata from buried hill to Lower-Middle Miocene.Based on the above understandings,the paper proposes a new direction for oil-gas exploration in the marginal sea of the South China Sea.The new exploration strata of the deepwater area in the northern continental margin of the South China Sea are from the Paleogene to the buried hill reservoirs,and those in the southern active continental margin of the South China Sea are from Oligocene to Lower Miocene reservoirs.