琼东南盆地南部梅山组强振幅体成因及油气地质意义

Origin of high-amplitude reflections in Meishan Formation of the southern Qiongdongnan Basin and its significance in hydrocarbon exploration

基于高精度三维地震资料,利用等比例方差体切片技术,发现琼东南盆地南部深水区梅山组发育有一系列的强振幅地质体。通过对这些强振幅体的精细研究发现,平面上强振幅地质体的规模大小不等,长度约2～15km,宽度约500～5000 m,整体走向为近东西向。在强振幅地质体内部发育一系列的小断层系。强振幅体在东西部表现出不同的特征:东部表现为不规则的斑点状;西部表现为条带状。同时,在垂直于其走向的剖面上,强振幅体多表现为"V"或者"U"型的外部形态。这些强振幅地质体主要发育在隆起上的梅山组中,其下往往有断陷期开始发育的隐伏断层,且走向与渐新世末期断层的展布一致。盆地裂后期断层的活化使下伏古近系中的流体向上输导,深部流体沿梅山组内发育的断层系发生水—岩反应和随后可能的流体充注,导致了强振幅地质体的形成。这套强振幅地质体的发现对于琼东南盆地南部的深水油气勘探具有重要的指导作用。

Based on 3D high-resolution seismic data, a series of the high-amplitude reflections （HARs） were discovered in Meishan Formation in deepwater areas of the southern Qiongdongnan Basin using an isometric variance slice technique. The detailed observa- tion of these HARs revealed that the generally E-W oriented HARs have variable scales, being 2-15 km in length and 500-5 000 m in width. Small-scale faults are well developed within the HARs. Furthermore, the HARs show various features in different parts of the study area, for instance, they come in an irregular spotted shape in the east but stripped shape in the west. In sections perpendic- ular to the strike, the HARs are generally V shaped or U-shaped by appearances and develop mainly on the uplifted Meishan Forma- tion, beneath which there often exist buried faults formed during the rift-subsidence stage and having a strike consistent with the ex- tension of terminal Oligocene faults. Therefore, the origin of HARs was attributed to the fault activation after the rifting of the ba- sin, which resulted in an upward migration of fluids from underlying Paleogene strata, a water-rock interaction of deep fluids along the fault system developed within Meishan Formation, and probably a fluid charge thereafter. The discovery of the HARs in the study area is of directive importance in hydrocarbon exploration in deepwater areas of Qiongdongnan Basin.