强制海退体系域识别特征及其油气意义

利用地震沉积学、层序地层学的相关理论和方法,结合钻测井数据、地震反射结构特征、均方根振幅属性和滨线迁移轨迹特征等资料,对珠江口盆地白云凹陷北坡21 Ma强制海退体系域的识别特征、演化模式和油气意义进行了探讨,指出该体系域在平行物源方向具有高角度斜交型前积反射,其前端靠近盆地中心发育具丘状反射的盆底扇,滨线迁移轨迹呈向盆地方向逐级下降的趋势。结果表明:强制海退体系域在垂直物源方向发育"U"型的下切谷,内部为平行的地震反射充填结构;测井曲线为漏斗形和箱型的组合特征,表现为多个四级相对海平面变化控制的准层序组,且每个准层序组都具有向上水体变浅和顶部突然变深的特征;强制海退体系域之下为前期层序高位体系域的前三角洲或陆架泥岩,其上沉积了海侵体系域和高位体系域的半深海暗色泥岩,同时受陆架坡折带地层尖灭和断裂沟通深部油源的控制,可形成有利的生、储、盖组合,是寻找岩性油气藏的有利场所。

Recognition Characteristics and Hydrocarbon Significance of a Falling Stage Systems Tract

Correlation theory and seismic sedimentology and sequence stratigraphy methods, together with comprehensive utilization of drilling log data, seismic reflection configuration, root mean square amplitude attributes and shoreline migration trajectory recognition characteristics were used to investigate the evolution model and hydrocarbon significance based on a falling stage systems tract (FSST) in the northern Baiyun depression, Pearl River Mouth Basin, at about 21 Ma. It was concluded that the seismic reflection characteristics of the FSST indicates high-angle oblique progradation parallel to the source direction; the front near the basin center tended to develop a basin floor fan with a domed seismic reflection configuration; the shoreline migration trajectory shows a descending trend towards the basin. The result shows that incised U-type valleys are often observed along the vertical source direction, with an internal filling structure parallel to the seismic reflection configuration. The core log curve of the FSST is a combination of funnel-shaped and box-type curves, which indicates multiple parasequence sets controlled by the fourth-order relative eustatic cycle. Each parasequence set shows the characteristics of upward shallowing succession, with its top suddenly changing to a deep water sequence. The FSST in the study area is bounded at the base by prodelta shelf mudstones of the underlying highstand systems tract sequence, and it is overlain by dark mudstones of transgressive and highstand systems tracts. The shelf break has caused strata pinching and a fault system communicates to the oil source, thus forming a favorable source-reservoir-caprock assemblage. Lithological hydrocarbon accumulations usually occur in the area.