分流河道特征及其识别方法:以东营凹陷东部地区为例

Features of Distributary Channels and Their Diagnosis Methods: Exemplified by the Eastern Dongying Depression

东营凹陷东部地区分流河道沉积物以砂岩、粉砂岩为主 ,夹泥岩薄层 ,分选性较好 ,砂岩层理发育。横剖面上分流河道成顶平底凸的透镜状 ,在平面上呈树枝形的扇状分布。分流河道的储集体主要有心滩和边滩交错叠置构成 ,厚度一般为 2～ 10m。分流河道储集体的测井相特征在自然电位曲线上反映明显 ,可以划分为光滑柱状、齿形柱状、齿形漏斗状 -齿形钟状和光滑卵状 ,分别代表河道中心、中心偏边部、接近边部及河道边部。分流河道储集体在地震反射外形呈透镜状 ,地震反射连续性差、中振幅 ,上超充填特征明显。

With the further exploration, the research on sedimentary facies of distributary channels becomes more and more important. The reservoirs of distributary channels are of a special hydrocarbon pool type. Due to their intense concealment and unique forming conditions, the study on such reservoirs is very difficult. In this article, we made systematic research on the distributary channel reservoirs for the second member of Shahejie Formation, eastern Dongying Depression, from the following aspects: sedimentation characteristics, reservoir characteristics, the logging characteristics, and 3D seismic coherence analysis. Our study suggests that the sediments of distributary channels in the eastern Dongying Depression are mainly composed of sand and silt with small amount of mud flasers. The sand and silt are usually well sorted and rounded, and often contain large scale tabular or trough cross beddings, parallel laminations and massive beddings etc. The distributary channels are lenticular, with flat top and convex bottom in their cross sections. On the plan, they are fan shaped with dipping limbs. During low lake level stages, the deposits of distributary channels move lakeward; and during high lake level stages, basinward. Such fluctuation of lake level often leads to formation of distributary channels' sediments largely under subaquatic condition. These reservoirs are mainly composed of cross stratified diaras and point bars, with monolayers ranging from 2m to 10m. The spontaneous potential (SP) curves well indicating the logging characteristics consist of smoothing column, dentate column, dentate funnel shaped, dentate pendulum and smoothing ovum which represent five different positions of distributary channels from the center to the margin respectively. Their seismic profiles are lenticular or hummocky, with poor continuity, middle amplitude and onlapping filling features. Compared with others, these reservoirs in distributary channels are widespread, complex and thin in vertial direction for their swift wandering. Therefore, we should analyze the data in geology, logging, drilling and 3D seismic materials integratedly to prognose the configuration and distribution of the distributary channels. The discussion about the recognition methods of distributary channels in eastern Dongying Depression in this paper is of significance for exploration and development of the subtle reservoirs.