南海北部深水区荔湾凹陷构造演化及其石油地质意义

The tectonic evolution of Liwan sag in the deep-water area of the South ChinaSeaanditsoil geologicalsignificance

荔湾凹陷北与白云凹陷相邻,南与双峰盆地(南海西北次海盆)相接,发育于洋陆过渡边界,具有独特的结构构造特征。选取荔湾凹陷为研究对象,在3D地震资料解释的基础上,以断裂特征分析厘定凹陷性质、构造古地貌恢复解析凹陷结构,进而指出古地貌恢复和构造演化对油气勘探的影响。研究获得三方面的创新性认识:①荔湾凹陷为洋陆过渡壳上发育的断坳,断坳作用占主导地位;②32Ma的底辟作用将荔湾凹陷改造为"四洼三凸"的构造格局,恩平组沉积期凹陷北部是一个连通的洼陷;③恩平组沉积期连通洼陷的古地貌有利于三角洲(烃源岩)的发育,背斜型圈闭的定型受控于32Ma的底辟作用,是荔湾凹陷油气勘探的有利目标。

The Liwan sag, neighboring Baiyun sag in the north and Shuangfeng basin in the south （the northwest sub-basin of the South China Sea）, has unique structural characteristics. Because of lack of data, the detailed research on the structural geology of the Liwan sag has not yet been conducted. On the basis of 3D seismic data, the authors chose the Liwan sag （an uncharted area） as the study object, determined the properties based on the analysis of fault characteristics, restored the structure by reconstruction of pa-leogeomorphology, and finally pointed out the influence of structural evolution and paleogeomorphologic reconstruction on petro-leum exploration. Some conclusions have been reached： ①the Liwan sag could be regarded as a sag fault-downthrow basin in conti-nent-ocean transition;②the structural framework of＆quot;4 sags and 3 swells＆quot;was rebuilt by the diapir at 32Ma, and there was a connect-ed depression in the sedimentary period of the Enping Formation;③the paleogeomorpology of the connected depression was benefi-cial to the development of the hydrocarbon source rock of delta coal measures, and the anticlinal traps, which were developed by the diapir at 32Ma, can be considered to be the favorable exploration targets.