珠江口盆地恩平21洼文昌组沉积期原型盆地及其对优质烃源岩的控制

珠江口盆地阳江东凹恩平21洼古近纪文昌组沉积期发育断陷湖盆,由于该区古近纪经历多期岩浆底辟和整体构造抬升,导致原型盆地被强烈改造,使其主要生烃层段文昌组的原型盆地面貌不清,从而给油气勘探和资源潜力评价造成困难。本文遵循改造型盆地的研究思路,将地震解析、声波时差法和趋势厚度法相结合,恢复了文昌组沉积期洼陷的原始面貌,并明确了优质烃源岩的展布范围。研究表明,阳江东凹恩平21洼在始新世文昌组沉积末期遭受强烈的剥蚀改造,造成洼陷东北部1/4沉积地层剥蚀殆尽;在文二段沉积期,恩平21洼北部与恩平14洼连通形成广盆深水的沉积环境,控制文二段半深湖相优质烃源岩的形成。从文昌组烃源岩的原始沉积规模和勘探实践来看,阳江凹陷具有良好的资源潜力。

Prototype Basin and its Control on High-quality Source Rocks During the Depositional Period of Wenchang Formation in Enping 21 Sub-sag,Pearl River Mouth Basin

The Paleogene Wenchang Formation in the Enping 21 Sub-sag of the eastern Yangjiang Sag,Pearl River Mouth Basin,is developed in a faulted lake basin.Due to the Paleogene multi-stage magmatic underplating and overall uplift in this area,its prototype basin has been strongly reformed,therefore,it is still controversial regarding the prototype basin in the depositional period of the Wenchang Formation.As the Wenchang Formation is the main hydrocarbon generating layer,reconstruction of the prototype basin is critical for oil and gas exploration and resource potential evaluation.In this paper,the original appearance in the depositional period of the Wenchang Formation is restored and the distribution range of high-quality source rocks is defined by combining seismic interpretation,acoustic time-difference method and trending thickness method.The study shows that the Enping 21 Sub-sag in the eastern Yangjiang Sag suffered from a strong denudation transformation at the end of the Eocene Wenchang Formation deposition,resulting in the denudation of one-fourth of the original sedimentary strata in the northeastern sub-sag.In the deposition period of the Wen-2 Member,the northern Enping 21 Sub-sag was connected with the Enping 14 Sub-sag,forming a wide and deep water sedimentary environment,which controlled the formation of the medium-deep lacustrine facies high-quality source rocks that widely distributed in the Wen-2 Member.The original sedimentary scale and exploration of the Wenchang Formation source rocks demonstrated that the resource potential of the sub-sag a quite promising.