The middle oil-member is characterized by medium-sized sandstone and pebbled sandstone, with fair sorting and subangular sphaericity.Rock types mainly were feldspar debris sandstone.

中油组主要沉积中砂岩中砂岩，粒整体较粗，较好，磨圆以次棱角状为主，岩石类型为长石岩屑砂岩。