西湖凹陷某构造花港组沉积相及致密砂岩储层特征

西湖凹陷某构造渐新统花港组是重要产气层系。通过岩心观察、薄片鉴定及样品测试等研究,利用岩石学特征及测井相分析方法,在前人研究的基础上,对渐新统花港组致密砂岩储层沉积相类型、储集空间特征、储层物性以及影响储层发育的主控因素进行了分析。认为研究区花港组发育河流—湖泊—三角洲沉积体系,上、下段分别发育了三角洲前缘和三角洲平原2种亚相类型,自下而上呈现湖平面上升的退积型沉积旋回;储层岩石类型主要为长石岩屑砂岩、岩屑长石砂岩和长石石英砂岩,岩石粒度中—细粒,骨架组分成熟度低,储集空间以次生溶蚀孔隙为主,裂缝不发育;储层物性差,属典型的致密砂岩储层,上、下段物性相差较大。沉积环境是花港组储层致密化的基本因素,而压实作用是花港组致密砂岩储层的主控因素,杂基含量高、碳酸盐胶结程度高也是储层致密化的重要因素;而溶解作用对致密砂岩相对优质储层段的发育具有明显的建设性作用。

Sedimentary facies and the characteristics of tight sandstone reservoirs of Huagang Formation in Xihu depression,East China Sea Basin

The study area in the Xihu depression located in the southwest of East China Sea Basin is one of the key tectonic regions of the present offshore exploration and exploitation targets,with Huagang Formation(Oligocene) as its major gas layer.On the basis of the former research,by means of observing cores,analysing thin sections analysis and testing samples,and using the petrological characteristics and log analysis,this paper analyzes the types of sedimentary facies,the characteristics of the reservoir pore space,the reservoir physical properties of the tight sandstone reservoir of Huagang Formation in this structure and its main controlling factors affecting the reservoir development.It comes to the conclusions that the river-lake-delta depositional system develops in Huagang Formation of the study area.The delta front and delta plain develop in its upper and lower sections,respectively,presenting a regressive sedimentary cycle with the rising of the lake level from bottom to top.The reservoir rocks consist of three main types,that is,the feldspathic litharenite,the lithic arkose and the quartzose arkose.The grain size of the rock is small or medium,the maturity of the skeleton components is low,the secondary pores are the main reservoir spaces,and the fissures are undeveloped.These reservoir rocks have poor reservoir physical properties,belonging to the typical tight sandstone reservoirs and the upper and lower sections differ greatly in their physical properties.The sedimentary environment is the essential factor leading to the densification of the Huagang Formation reservoir,while compaction is the main controlling factor of the tight sandstone reservoir of Huagang Formation.The leading factors of reservoir densification include high matrix content and large extent of carbonate cementation,whereas dissolution plays a constructive role in the development of the relatively high-quality sections of the tight sandstone reservoir.