金湖凹陷西斜坡阜宁组灰岩段成因机理

金湖凹陷古近系灰岩段是重要的油气产层,但灰岩段沉积特征和成因机理认识不清,给油气储层预测带来困难。通过岩心资料、地震资料和测井资料的综合分析认为研究区灰岩段为混合沉积,有别于中国东部其他盆地古近系混积岩。金湖凹陷灰岩段沉积相类型包括湖泊相、三角洲相和湖底扇相,其中湖泊相是主要的沉积相类型。三角洲相和湖底扇相受断层和物源的控制,主要分布在靠近物源的区域。自下而上,灰岩段中碎屑岩的含量逐渐减少,表明湖侵的规模逐渐扩大,因此灰岩段形成于湖侵期。灰岩段沉积期研究区广布的同沉积断层是碎屑沉积物运输的通道,对碎屑岩的分布具有调节作用。同时,碎屑岩的填平补齐及物源的改道使地势变得平坦、水体变得清澈,因此生物灰岩常分布于碎屑岩的上部,且灰岩中不含有碎屑岩。总之,物源和同沉积断层是研究区灰岩段混合沉积的主要控制因素。

Depositional features and forming mechanism of the limestone member of Funing Formation in Jinhu Sag

The Paleogene limestone member in the Jinhu Sag is an important petroleum producing formation. However, the depositional features and forming mechanism of the limestone member are not clear, which brings difficulty for the forecast of reservoir. Different from peperites in other Paleogene basins in East China, the limestone member in the Jinhu Sag is the mixture of siliciclastic-carbonate sediments, based on the comprehensive analysis of core, seismic and logging data. The limestone member is mainly of lake, delta and lacustrine fan facies, among which the lake facies is dominant. The delta and lacustrine fan facies, controlled by faults and provenance, mainly distribute close to sediment sources. Clastic rock content decreases upwards in the limestone member, indicating the expansion of transgression, during which the limestone member was deposited. During the deposition of the limestone member, widespread syn-sedimentary faults served as the channels for sediment migration, and adjusted clastic rock distribution. Additionally, clastic rock deposition and provenance rechanneling made the terrain flat and water clear. As a result, biolithite limestones cover clastic rocks and there are no clastic rocks in the limestone. Provenance and faults are the main controlling factors for the limestone member in the study area.