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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 pore structure of tight sandstone reservoirs is an important factor that determines reservoir physical properties and oil and gas productivity. The pore structure and influencing factors of Carboniferous-Permian tight sandstone reservoirs in Daniudi gas field are studied by using the cast-in-situ thin films and mercury intrusion analysis data. The results show that the main reservoirs in the study area are secondary pores, and intergranular and intragranular dissolved pores are the major pore types of sandstone. The mean value of reservoir displacement pressure and the average pore throat radius are similar in different groups. The mean value of median pressure is generally opposite to that of drainage pressure and decreases with the increase of buried depth. Poor, pore-throat distribution is very uneven, and with fine holes and fine throat, throat combination. The main influencing factors of pore structure are depth of burial and debris particle composition. With the increase of burial depth, pores and throats become smaller and displacement pressure increases. Due to the effect of selective pressure dissolving and selective secondary enlargement, the increase of feldspar and cuttings content is beneficial to the preservation of pore throats .