北部湾盆地涠洲12-2靶区流沙港组低渗透砂岩孔隙结构特征研究

Study on pore structure characteristics of low permeability Liushagang Formation sandstones in Weizhou 12-2 target region,Beibuwan Basin

涠西南凹陷流沙港组具有丰富的油气储量,但是其储层存在物性较差、中孔低渗、非均质性强等特点,目前对其储层的孔隙结构特征缺乏深入研究。采用场发射扫描电镜、氮气吸附、高压压汞等实验方法,对北部湾盆地涠西南凹陷低渗透砂岩储层微观孔隙结构开展精细研究。结果表明,涠西南凹陷低渗透砂岩储层非均质性强,孔隙类型多样,孔隙形状以狭缝型孔隙为主;低渗储层孔体积主要由宏孔提供,中孔较为发育,比表面积相对较大。流沙港组储层表现出中孔低渗的特征,这可能与细小孔喉的存在且孔喉分选性较差有关;低渗储层的渗透率与平均孔径大小、孔喉分选程度密切相关,与孔隙度无明显相关性,且渗透率对低渗储层含油气性有明显的控制作用。

The Liushagang Formation in Weixinan Sag has very rich hydrocarbon reserves,but its reservoirs have poor physical properties,usually low permeability and strong heterogeneity,which lack of in-depth research on the pore structure characteristics of the reservoirs.The microscopic pore structure of low permeability Liushagang Formation sandstone reservoirs in Weixinan Sag of the Beibuwan Basin was studied using field emission scanning electron microscopy,nitrogen adsorption,and high-pressure mercury injection measurements.The results showed that the low-permeability sandstone reservoirs are characterized by strong heterogeneity,various pore types with mainly slit-shaped pores;the pore volume of low-permeability reservoirs is mainly provided by macropores,and the mesoporous are also quite developed.The surface area of these low permeability sandstones is relatively large.The reservoirs of the Liushagang Formation show the characteristics of higher porosity and lower permeability,which may be related to the existence of tiny pore throat and poor pore throat sorting.The permeability of these low permeability sandstones is closely related to the average pore size and the pore throat sorting while there is no obvious correlation between permeability and porosity.Furthermore,permeability has a significant impact on the oil content within low permeability Liushagang Formation sandstones.