2　Terminologies

2.0.1　Underground oil storage in rock caverns

An underground space system excavated in a mass of rock below the stable groundwater table to store crude oil，gasoline，or diesel.It is called water-sealed cavern storage for short.

2.0.2　Cavern

An underground space excavated in a mass of rock to store crude oil and/or its product（s）.

2.0.3　Cavern tank

An underground oil tank consisting of one or more caverns that are interconnected.Its function is equivalent with an oil tank on the ground.

2.0.4　Connecting tunnel

A tunnel used to connect caverns with each other to allow the stored crude oil or oil product to flow between the caverns and keep the liquids in them at the same level.

2.0.5　Access tunnel

An underground passage from the surface to the cavern under construction that is used for cavern tunneling and equipment delivery，waste solids discharge，ventilation，water supply and drainage，power supply，and access of workers to the cavern.

2.0.6　Shaft

A vertical passage from the top of a cavern to the surface or the operation tunnel.

2.0.7　Shaft operation area

An area around a shaft where the oil pump，water pump，instruments and electrical devices are maintained，operated，and managed.

2.0.8　Water curtain hole

A hole drilled for artificial water injection to maintain the underground water-sealing conditions.

2.0.9　Water curtain tunnel

A tunnel for drilling water curtain holes during construction and storing and supplying water into the water curtain holes during operation.

2.0.10　Concrete plug

A reinforced concrete structure built in the access tunnel or a shaft to block the cavern.

2.0.11　Pump pit

A pit at the bottom of a cavern that directly faces the shaft and is used to accommodate the submersible oil pump，the submersible water pumps，and instruments.

2.0.12　Water bed

A bed of water with a certain height at the bottom of the cavern that is used to deposit impurities in the crude oil or oil product and catch the water seeping out of the surrounding rock.

2.0.13　Logging hole

A hole used to monitor the table and quality of the ground water.

2.0.14　Operation tunnel

A tunnel from the surface to a shaft operation area.

2.0.15　Storage perimeter

The boundary line of the storage protection area required to keep the water-sealed cavern storage structurally stable.

2.0.16　Hydrogedogical perimeter

The boundary line of the hydrogedogical protection area required by the engineering design ground water table to keep the water-sealed cavern storage stable.

2.0.17　Vapor recovery unit

A unit that recovers the vapor from the underground cavern tank.