大牛地气田石炭系—二叠系致密砂岩储层孔隙结构特征及其影响因素

Study of porosity structure and its influences on Carboniferous and Permian tight sand reservoir rock in Danniudi gasfield, Ordos basin

致密砂岩储层的孔隙结构是决定其储层物性及油气产能的重要因素。应用铸体薄片及压汞等分析化验资料对大牛地气田石炭系—二叠系致密砂岩储层孔隙结构特征及其影响因素进行了研究。结果表明,研究区储层储集空间以次生孔隙为主,粒间溶孔及粒内溶孔是砂岩的主要孔隙类型。储层排驱压力平均值以及最大孔喉半径平均值在不同组的变化趋势相似,中值压力平均值总体呈现与排驱压力相反、随埋深增加而变小的特点,孔喉分选较差,孔喉分布极不均匀,且以细微孔及微细喉、微喉组合为主。孔隙结构的影响因素主要为埋深及碎屑颗粒组分。随着埋深的增加,孔隙和喉道变小,排驱压力增大;受选择性压溶及选择性次生加大作用的影响,长石及岩屑含量升高有利于孔喉的保存。

The porosity structure and its influences on Carboniferous and Permian tight sand reservoir rock are studied through observation on the casting thin section and analysis on mercury data in Danniudi gasfield, Ordos basin. And, we made a conclusion that, the secondly porosity, such as intergranular pore and innergranular pore are the dominant reservoir space in the study area. There exists similar change trend between the average value of displacement pressure and that of maximum pore throat in different formations. While the average value of pc50 tends to be smaller with the increment of depth, changes reversely with that of displacement pressure. The low pore-throat sorting, scattered distribution, with micro pore and fine throat, micro throat combination are the dominant pore throat combination type. The pore structure in the area is influenced by buried depth and detrital particular materials. The displacement pressure increases, and the pore and throat decrease along with the increment of the burial depth. Higher content of feldspar and rock fragments is more beneficial to the reservation of pore and throat for the influence of selective pressure dissolution and secondly growth under the detrital components and diagenetic environment in the study area.