珠江口盆地番禺27洼裂陷期构造演化及其对源-汇系统的控制

Structural evolution and its control on source-to-sink system of Panyu 27 Sag in Pearl River Mouth Basin during rifting

王梓颐 李洪博 郑金云 朱定伟 于飒 陈兆明 李振升

Ziyi WANG Hongbo LI Jinyun ZHENG Dingwei ZHU Sa YU Zhaoming CHEN Zhensheng LI

番禺27洼位于珠江口盆地中央隆起带中部的番禺低隆起区，为发育在中生代陆缘岩浆弧基底之上“南断北超”的新生代凹陷，钻井取得的油样与砂岩储层抽提烃证实该洼陷存在文昌组中-深湖相烃源岩供烃，但已钻井均没有实际钻至文昌组，烃源岩发育的有利部位与有利时期仍存在不确定性。对控洼断裂系统及洼陷结构样式的研究表明，番禺27洼的发育和演化具有“先存构造约束、右旋伸展主控、岩浆底侵改造”三元耦合成因，控制了三幕裂陷阶段“左阶不对称地堑-左行雁列式半地堑-萎缩期宽缓半地堑”的结构样式。裂陷期三幕控洼断裂差异活化影响沉积中心变迁，洼陷结构差异演化影响洼陷沉积充填格局。随着裂陷期断裂活动的减弱，沉积中心逐渐由东向西、由两端向中部迁移。源-汇沉积体系在裂陷早期以NW轴向和中部转换带沉积体系为主，裂陷中期至裂陷晚期逐渐向北部缓坡大型沉积体系和西北部长轴优势沉积体系转换。西次洼长期作为沉积中心，是优质烃源岩发育的有利部位。裂陷中期发育大型半地堑式湖盆，并伴有较强的岩浆活动，是优质烃源岩发育的最有利时期。裂陷中期至裂陷晚期西北部大型源-汇沉积体系的长期发育为古近系大型储集体的形成提供了有利条件。

Sag Panyu 27 is located in the Panyu low uplift area in the middle of the central uplift zone of the Pearl River Mouth Basin. It is a Cenozoic sag developed on the basement of the Mesozoic continental margin magmatic arc， which is ‘faulted in the south and overlapped in the north’. Oil samples and extracted hydrocarbon from wells drilled in the sag can be traced back to the intermediate to deep lacustrine source rocks in the Wenchang Formation. However， none of the wells actually reached the formation， making the specific location and period for the development of source rocks still uncertain. Through the study of the controlling fault and the structural style of the sag， it is shown that the development and evolution of the sag has a ternary coupling genesis of ‘pre-existing structural constraints， dextral extension control， and magmatic underplating transformation’， which controls the structural pattern of ‘left stepping asymmetric graben-left lateral en echelon semi-graben-wide and gentle semi-graben’ in the three-stage rifting period. The differential activation of sag-controlling faults in the three stages of rifting period affects the migration of the sedimentary center， and the differential evolution of the sag architecture affects the sedimentary filling pattern of the sag. With the rifting， the sedimentary center gradually migrated from east to west， and from both ends to the middle. In the early stage of Wenchang Formation deposition， the source-to-sink sedimentary systems are mainly distributed in the central transition zone along the NW-trending axis， while in the late stage， they mainly occurred on the northern gentle slope， and a large source-to-sink sedimentary system with long provenance appeared in the northwest during deposition of the Enping Formation. As a sedimentary center for a long time， the western sub-sag is the right place for the development of high-quality source rocks. The middle stage of rifting when a large semi-graben lake basin was formed and accompanied by strong magmatic activity was the time for the development of high-quality source rocks. The long-term development of large source-to-sink sedimentary system in the northwest during the middle-late rifting stages provided favorable conditions for the formation of large Paleogene reservoirs.

10.11743/ogg20230308