东海西湖凹陷A气田渐新统花港组三段厚层砂岩沉积环境

Sedimentary setting of thick sandstone in the 3rd member of the Oligocene Huagang Formation in A gas field in the Xihu Sag,East China Sea Basin

西湖凹陷A气田花港组三段巨厚碎屑岩储层为研究区主力产气层与优质储层,对其沉积微相的厘定争议较大。综合利用研究区岩心、测井、地震、分析化验等相关资料,研究了目的层相标志、微相类型、沉积环境与相分布。研究认为本区发育辫状河三角洲前缘亚相,主要发育水下分流河道微相与分流间湾微相,不发育反映海相及海侵的沉积物与相标志。垂向上多期水下分流河道砂体叠置、厚度较大,水平延伸好;平面上水下分流河道由东北逐渐向西南呈树枝状分叉、连片分布,物源来自东北部。明确研究区属于陆相背景下的湖泊-三角洲沉积体系,为典型的牵引流沉积,不见海侵层序,高能量牵引流的水下分流河道微相是本区高产气藏储层发育的有利因素。

The thick clastic reservoir in the 3rd member of the Huagang Formation is a major gas pay zone and high-quality reservoir in A gas field in the Xihu Sag,East China Sea Basin,but there still exists great dispute over its sedimentary microfacies.We studied the facies markers,microfacies types,sedimentary setting,and facies distribution of the target interval through integration of core,logging,seismic and laboratory data.The results show that the study area mainly develops the braided river delta-front subfacies,which mainly consists of underwater distributary channels and interdistributary microfacies without sediments and facies markers indicating marine facies and transgression.Vertically,multi-stage underwater distributary channel sand bodies superimpose,featuring large thickness and great horizontal extension.Laterally,the underwater distributary channels are characterized by tree-like bifurcation and continuous distribution from northeast to southwest,with its provenance in the northeast.It is believed that a lacustrine-delta sedimentary system of continental setting exists in the study area and is typical traction current deposits without any transgression sequence.The underwater distributary channels microfacies of high-energy traction currents is advantageous for the development of prolific gas reservoirs in the study area.