The underground water-sealed cavern reservoir is an underground reservoir which uses fissure water pressure in underground rock to seal medium. Compared with the ground storage tank and large cryogenic storage tank, featuring occupying small area (facilities can be built on the surface), high safety, low comprehensive cost, and environmental friendly. CEI is the company that develops underground water-seal cavern reservoir technology in the earliest period in China, starting atmospheric-technology research in 1970s, and pressure-type technology in 1990s.

It now has a professional underground water-sealed cavern design technical team with rich practical experiences in its construction. The underground water-sealed cavern design technology lies in leading position in China and in the advanced level in the world. CEI owns 5 know-hows, 2 practical patents and 1 invention patent, editing or participating in writing standards of variety of underground water-sealed cavern reservoir and completing 6 works, and reviewing 3 construction standards for international oil reserve in the underground water-sealed cavern reservoir.

Huangdao underground oil depot, the first crude oil depot(150,000m3) which was designed and constructed and operated in 1976. In 2015, the biggest cavern depot for LPG in the world—Wanhua underground water-sealed cavern reservoir(1.0Mm3) was put into operation. The nationalization of pressure storage design technology has been achieved filling the vacancy in China.