丽水凹陷远岸水下扇体识别及特征分析

Characteristic Analysis and Identification of Far Shore Underwater Fan in Lishui Depression

在丽水凹陷西次凹西部斜坡带发育多条坡折断层,它们控制了古新统明月峰组下段远岸水下扇体的发育。钻井揭示该区水下扇体具有沉积厚度大、物性好、含油气性活跃的特征。储层特征描述、分布范围预测对寻找本区岩性油气藏具有重要意义。本文通过对明月峰组沉积初期古地貌恢复,总结了坡折断层对扇体发育的影响作用。坡折断层上升盘发育孤立型和复合型水道;坡折断层下降盘发育扇体主体,扇中水道微相为优势相带,岩性以灰色细砂岩为主,存在反映垮塌变形的泄水、泥质火焰等沉积构造,测井相表现为低伽马、高自然电位异常,地震相为强振幅、低频、断续反射。同时,利用地震沉积学技术完成了本区3期次扇体分布范围识别,说明自早期到晚期扇体具有从北往南逐渐迁移的特征。

Several slope-breaks are developed on the western slope of the west subsag in Lishui depression,which control the development of distal underwater fans in the lower part of the Paleocene Mingyuefeng Formation.Drilling reveals that the underwater fans are characterized by large sedimentary thickness,good physical properties,and active hydrocarbon-bearing.The description of reservoir characteristics and prediction of distribution range are of great significance to the exploration of lithologic reservoirs in this area.Through analysis of the paleo-geomorphology in the early stage of Mingyuefeng Formation,the effects of slope-breaks on fan development are summarized.Isolated and compound channels are developed in the upthrow block;while the main fan bodies are developed in the downthrow wall of slope break faults.The microfacies of the fan channel is the dominant facies.The main lithology is gray fine sandstone.There are sedimentary structures reflecting collapse,such as water escaping structure and flaming structure.The logging facies are characterized by low gamma and high spontaneous potential anomalies,and the seismic facies are characterized by strong amplitude,low frequency and intermittent reflection.At the same time,the distribution range of three fan stages in this area is identified by using seismic sedimentology technology.From early to late stage,the fans have gradually migrated from north to south,which points out the direction for future exploration in this area.