珠江口盆地渐新世陆架边缘三角洲沉积特征及其对成藏的控制作用

陆架边缘三角洲沉积是陆缘深水油气勘探中的重要储层类型,是深水沉积学和石油地质学研究的热点和前沿问题。结合高精度三维地震资料和最新的钻井地质信息,对珠江口盆地白云凹陷东部渐新世陆架边缘三角洲的类型、沉积特征和控制因素,及其对成藏的控制作用开展了详细研究。研究表明,白云凹陷渐新统整体上为海侵退积型层序组,可划分为6个三级层序;识别出5期坡折,各期坡折均属于沉积型坡折,受明显的波浪作用控制;陆架边缘三角洲主要发育于强制性海退期,平面上呈平行于坡折带的"豆荚"状展布,其规模和形态受相对海平面变化、沉积物供给和海流活动综合控制;陆架边缘三角洲是坡折下方深水重力流的"转运站",陆坡规模和沉积物供给速率分别控制了重力流沉积的类型和规模,影响了由陆架边缘三角洲向深海的砂体搬运过程;陆架边缘三角洲和重力流沉积在白云凹陷形成大量岩性圈闭和岩性+构造型圈闭,断裂和底辟是此类圈闭油气成藏的关键。总体上,白云凹陷东部具备形成大型陆架边缘三角洲和重力流沉积的岩性圈闭条件,成藏条件优越,具有很大的油气勘探前景。

Sedimentary characteristics of Oligocene shelf edge delta and their control on hydrocarbon accumulation in Pearl River Mouth Basin

Shelf edge delta is a major reservoir in deepwater hydrocarbon exploration as the research hotspot and frontier issue of deepwater sedimentology and petroleum geology. In combination with high-resolution 3D seismic data and the latest drilling geological data, the type, sedimentary characteristics and controlling factors of Oligocene shelf edge delta in the eastern Baiyun sag of Pearl River Mouth Basin are studied in detail as well as their effects on hydrocarbon accumulation. The research reveals that the Oligocene Baiyun sag is the transgressive retrogradation sequence, divided into 6 third-order sequences and 5 shelf breaks, while each shelf break is formed through sedimentation, and obviously controlled by wave effect. Shelf edge delta is mainly developed during forced regression, parallel to the shelf break with "pod-like" distribution, of which the size and morphology are jointly controlled by relative sea level change, sediment supply and ocean current. Shelf edge delta is the "transition station" for the deepwater gravity flow beneath the slope break. Therefore, the slope size and sediment supply velocity control the gravity flow type and size respectively, affecting the sand transportation from shelf edge delta to deep sea. Shelf edge delta and corresponding gravity flow deposit lead to the formation of massive lithologic traps as well as lithologic and structural traps in Baiyun sag, where faulting and diapirs are the keys for hydrocarbon accumulation in these traps. In general, large-scale lithologic traps related to shelf edge delta and gravity flow deposits can be developed in the eastern Baiyun sag with superior accumulation conditions, showing a great prospect of hydrocarbon exploration.