Evolution Process Characteristics of and Differential Enrichment of Oil and Gas in Deep Water Gravity Flow Sandstone Taking the MD Oilfield of the Eocene Shahejie Formation in the Huanghua Depression of Beidagang as an Example

摘要

Based on new theory of deep water sandstone,the sedimentary process of the gravity flow sandstone of the Shahejie Formation in the Huanghua depression was divided into four sandstone zones of genetic types in this work:sliding,slumping,sandy debris flow and turbidity flow by comparing sedimentary structures of typical cores,variation of grain sequence,difference of the reservoir physical properties,lithologic vertical combination sequences,and diagrams of well logging facies.The geometry and contact relationship of sandstones of different genesis were studied,and the evolution model of gravity flow sedimentation process was figured out.Combined with dynamic production data,the pattern of oil and gas differential enrichment was analyzed.Horizontally,the slump deposits are in the root segment of the downthrow block within a synsedimentary fault,and sandy clastic sediments are easily formed in the slope zones in front of the slump deposits.During the forward transport of the debris flows,the fluid gradually dilutes and transforms into turbid flows,which are distributed in the side and front of the debris flow.Vertically,there is a thin layer of turbidity deposit between the tops of the thick sandy debris flow with weakening energy,and the sandy debris flow can evolve into thin layers that develop between the turbid flows.Combined with dynamic production data,it is believed that the low-saturation reservoir with oil-bearing occurrence controlled by reservoir physical properties is likely to develop in the slope zone of sandy debris flows,and low-permeability reservoirs with no tectonic background is easily formed in the turbidity flow zone.For the first time,the logging facies diagrams of four genetic types of sandstones in deep water gravity flow were established,guiding the analysis of sedimentary process evolution models.In addition,the understanding of differential enrichment regularities of oil and gas points out the direction of sweet point evaluation and prediction.