乌南斜坡区南屯组下切谷发育特征及在油气成藏中的作用

Incised valley development characteristics and its roles in formation of hydrocarbon reservoirs of Wunan slope Nantun group

下切谷是由河流体系响应于海(湖)平面相对下降而向盆地方向延伸所形成的深切水道,其在油气藏的形成过程中扮演着重要的角色.为了揭示乌南斜坡区南屯组下切谷发育特征及其在油气成藏中的作用,本文对下切谷的地震反射特征、充填物垂向沉积序列及岩性进行了识别和分析,认为乌南斜坡区南屯组发育多期下切谷,其在地震反射外形上表现为顶平底凹的对称或不对称的"U"字形或"V"字形特征,垂向沉积充填序列表现为多期砂泥复合充填,且下切谷内外存在明显差异.乌南斜坡区南屯组下切谷主要发育在乌南斜坡区的缓坡部位,在平面上呈近南北向的条带状展布,沿物源方向下切谷的沉积存在"顺源堆积"的充填模式.在油气成藏方面,下切谷内的顺源砂体可形成油气藏,且控制着区块的整体含油性.下切谷也可形成侵蚀不整合,作为遮挡条件控制局部地区形成2种类型的油气聚集.

Incised valley is a kind of deep channel which extends to the basin and formed at the stage of fluvial system responses to sea level relative descent,and it plays an important role in hydrocarbon reservoirs formation. For revealing incised valley development characteristics and its roles in formation of hydrocarbon reservoirs of Wunan slope Nantun group, the paper identifies and analyzes seismic reflection characteristics,vertical filling sedimentary cycle sequences and lithology. Research shows that there are multiple incised valleys developed in Wunan slope, and they are characterized by symmetric or asymmetric ＂U ＂ or ＂V ＂ in the seismic refection. Vertical filling sedimentary cycle sequences is a kind of multi stage sand- mud composite filling with obvious difference between internal and external incised valley. Incised valley mainly developed at gentle slope in Nantun group of Wunan slope,which has a strip distribution along south to north direction,and the deposition of the valley shows＂along- source area direction accumulation＂filling mode. On the hydrocarbon accumulation,the sand bodies in the incised valley can form hydrocarbon reservoirs,and incised valley can also form erosion unconformity,which is used to control 2 types of hydrocarbon accumulation in the local area as screening conditions.