北部湾盆地W油田流一下亚段储层特征及主控因素

CHARACTERISTICS AND CONTROLS OF THE FIRST LOWER MEMBER RESERVOIR OF LIUSHAGANG FORMATION OF W OILFIELD IN BEIBUWAN BASIN

北部湾盆地W油田区块主要目的层流沙港组流一下亚段储层横向变化复杂,储层孔、渗差异较大。采用常规储层物性、测井解释、岩石薄片和扫描电镜等方法,对W油田流一段下储层特征进行研究,并根据沉积、成岩作用的影响,分析储层质量的主控因素。研究结果表明,流一段下储层岩石类型以石英砂岩和长石质石英砂岩为主,分选较好,呈次棱角—次圆状,物性表现为中—高孔、高渗特征。沉积微相类型是该区储层质量的主控因素之一,扇三角洲前缘沉积河口坝、辫流坝物性最好,辫状水道次之。成岩作用对研究层段的改造作用较为强烈,研究层段所处的成岩阶段为早成岩B期和中成岩A期,发育3个优势孔隙带,孔隙类型主要有粒间溶蚀孔、粒内溶蚀孔、填隙物内溶蚀孔和铸模孔,造成储层孔渗性差异的主要因素是粘土矿物填充吼道。

The lower first Member reservoir of Liushagang formation, W oilfield block in Beibuwan basin is characterized by a complicated lateral change and variable porosity and permeability. This paper uses the conventional methods such as reservoir property,well logging,thin section and SEM to study its reservoir features,and analyzes the leading controls on reservoir quality from sedimentation and diagenesis. Rock types of the first lower member are composed of quartz sandstone feldspathic quartz sandstone,well sorting,sub-angular to sub-round,with medium to high porosity and permeability. Reservoir quality,subject to sedimentary micro-facies,one of the leading controls,is best at mouth bar of fan delta frontier and braided channel bar,and then at braided channel. This member had been strongly reshaped by diagenesis,belonging to the early diagenetic stage B to middle diagenetic stage A. Three prevailing pore zones were developed with major pore types displaying as intergranular dissolved pore,intragranular dissolved pore,dissolved pore of interstitial material and mold holes. Clay minerals filling the pores may contribute to the variance in reservoir porosity and permeability.