北部湾盆地涠西南凹陷始新统流沙港组一段低渗储层特征及控制因素

为明确北部湾盆地涠西南凹陷始新统流沙港组一段储层特征及物性主控因素，综合应用壁心、薄片、物性、荧光、扫描电镜等储层分析资料，通过对储集特征、物性特征以及沉积作用、成岩作用、构造作用与油气成藏耦合等分析，表明涠西南凹陷流一段储层以长石岩屑石英砂岩和岩屑石英砂岩为主，总体成分成熟度和结构成熟度较低，储集空间主要为原生粒间残余孔和次生溶孔。涠西南凹陷北西源汇区和西部源汇区流一段多为中孔、中—高渗储层，东部源汇区主要为低孔低渗储层。沉积作用造成粒度、分选、泥质杂基等的差异，压实、碳酸盐胶结、有机酸溶蚀等成岩作用是低渗储层物性主控因素；而构造作用和油气成藏耦合所控制的早期烃类充注、异常高压可保护原生孔隙，加上断裂派生的裂缝可对低渗储层物性进行改善。涠西南凹陷北西源汇区和西部源汇区流一段储层由于埋深较浅，其水动力较强、粒度较粗、分选较好，在泥质杂基较少的区域储层物性较好；而东部源汇区在靠近生烃主洼的二号断裂附近，存在早期烃类充注、有机酸的强溶蚀以及部分高压保护，在2 500~3 500 m形成次生孔隙和高压孔隙发育带，亦发育深埋藏有利储层。 

Characteristics and constrains of low-permeability reservoirs in the first member of Eocene Liushagang Formation,Weixinan Sag,Beibuwan Basin

Reservoir analysis data such as core, thin-section, physical property and scanning electron microscope (SEM) were applied in this paper to study the reservoir characteristics and main constrains of the first member of Eocene Liushagang Formation in the Weixinan Sag, Beibuwan Basin. Reservoir features, physical properties, sedimentation, diagenesis, and the coupling of tectonics as well as hydrocarbon generation and accumulation were analyzed. Results showed that the reservoirs of the first member of Eocene Liushagang Formation in the area of this study were mainly feldspathic debris quartz sandstones and lithic quartz sandstones with low compositional and structural maturities. The reservoir space was mainly consisted of primary intergranular residual pores and secondary dissolved pores. In the northwestern and western source areas, the reservoirs mainly had moderate porosity and medium-high permeability, while those in the eastern source area had relative low porosity and low permeability. Sedimentation caused variations in grain size, sorting and argillaceous complexes. Diagenesis such as compaction, carbonate cementation and organic acid dissolution were the main controls for the physical properties of low-permeability reservoirs. The coupling of tectonics and hydrocarbon generation and accumulation controlled early hydrocarbon charging, while abnormal high pressure protected primary pores, which, combined with fractures derived from faults, improved the physical properties of low-permeability reservoirs. In the northwestern and western source areas, the shallow-buried reservoirs in the first member of Liushagang Formation had relatively strong hydrodynamic force, coarser grain size and better sorting, and showed better properties in the area with less mud. In the eastern source area close to the No. 2 fault around the main hydrocarbon-generating depression, there exist early hydrocarbon filling, strong dissolution of organic acids and partial high-pressure protection. Secondary pores and high-pressure pores were developed at 2 500-3 500 m deep, and favorable deep-burial reservoirs were formed.