Hydraulic and earth engineering – Fluid control – treatment – or containment – Fluid storage in earthen cavity
Reexamination Certificate
1999-09-03
2001-09-18
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Fluid control, treatment, or containment
Fluid storage in earthen cavity
C166S105000
Reexamination Certificate
active
06290430
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the transfer of liquids having a low specific gravity and a low vapor pressure, such as liquid natural gas, and particularly to an electric submergible pumping system that may be utilized in pumping such liquids from subterranean storage caverns without vaporizing the liquid.
BACKGROUND OF THE INVENTION
Currently, certain substances having a low specific gravity and a low vapor pressure are stored in underground, i.e. subterranean caverns, in liquid form. Exemplary substances are liquid natural gas (LNG), isobutane and propane. Liquid natural gas, for example, may be maintained in a liquid state at approximately 60° F. under a pressure of approximately 30 psi. Thus, placing such substances in large, subterranean caverns provides a way to maintain large quantities of the substance in liquid form during storage.
An exemplary subterranean, storage cavern may be formed by washing away the salt from a natural salt mine to create a cavern. The substance, such as liquid natural gas, is then pumped into the storage cavern and stored in this cool environment under sufficient pressure to maintain the substance in liquid form. A current method for producing the liquid from the storage cavern is to use brine to force the product from the cavern. This technique requires a separate pond, typically at the earth's surface, for storage of the brine when the cavern is full of the desired substance. A pump is utilized in moving the brine from the pond and into the cavern to force the liquid product from the cavern. The surface brine ponds are extremely expensive to build and maintain.
It would be advantageous to eliminate the use of brine introduced into the storage cavern for moving the low specific gravity liquid to a location at or above the surface of the earth.
SUMMARY OF THE INVENTION
The present invention features a method for producing a liquid that has a low specific gravity and is stored in a subterranean cavern. The method includes forming a sump adjacent a floor of a subterranean cavern in which a liquid having a low specific gravity is stored. The method further includes deploying an electric submergible pumping system to the sump, and locating a pump intake of the electric submergible pumping system in the sump. The intake is located at a sufficient distance beneath the floor such that the liquid in the sump has a head sufficient to prevent substantial vaporization of the liquid when exposed to a net positive suction head at the pump intake during operation of the electric submergible pumping system.
According to another aspect of the invention, a method is provided for producing a liquid from a subterranean environment. The liquid is of the type subject to vaporization at normal pressures and temperatures on the surface of the earth. Specifically, the method includes forming a subterranean storage cavern with a sump region extending downwardly from a lower floor. The method further includes storing a liquid in the subterranean storage cavern, and deploying an electric submergible pumping system such that it is in communication with the sump region. The electric submergible pumping system is used to draw fluid from the sump region through a pump intake. Additionally, the method includes locating the pump intake beneath the lower floor a sufficient distance to substantially eliminate vaporization of the liquid when subjected to a lowered pressure at the pump intake during operation of the electric submergible pumping system.
According to another aspect of the present invention, a system is provided for storing and producing a substance having a low specific gravity and a low vapor pressure. Low vapor pressure refers to a characteristic of the substance that tends to cause vaporization of the substance at normal temperatures and pressures along the surface of the earth. The system includes a storage cavern disposed in a subterranean environment. The storage cavern is designed to store the substance in a liquid form. The system further includes a sump region disposed in fluid communication with the storage cavern at a position generally beneath the storage cavern. Additionally, a pump is disposed in fluid communication with a pump intake. The pump intake is located in the sump region at a sufficient depth to substantially eliminate vaporization of the substance when exposed to a net positive suction head of the pump.
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Bagnell David
Camco International Inc.
Fletcher Yoder & Van Someren
Mayo Tara L.
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