INERT GAS TESTED FOR STORAGE CUSHION GAS ROLE

A project is under way to demonstrate the technical and economic feasibility of using inert gas as part of the cushion gas in underground storage fields in the U.S. The technique likely will apply mainly to new storage fields and may be economic in a number of the nearly 400 existing fields. Scientists at Gas Research Institute and Institute of Gas Technology, both of Chicago, are obtaining data on the extent to which nitrogen and other inert gases mix with methane in storage field reservoirs.

July 30, 1990

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A project is under way to demonstrate the technical and economic feasibility of using inert gas as part of the cushion gas in underground storage fields in the U.S.

The technique likely will apply mainly to new storage fields and may be economic in a number of the nearly 400 existing fields.

Scientists at Gas Research Institute and Institute of Gas Technology, both of Chicago, are obtaining data on the extent to which nitrogen and other inert gases mix with methane in storage field reservoirs.

They are conducting tracer surveys and hope to inject nitrogen soon, probably in mid-1990, in Simpson Chapel storage field, Green County, Ind. Citizens Gas & Coke Co., Indianapolis, operates the field, a Devonian carbonate reservoir with dense limestone and shale caprock.

About 80% of the field's gas is cushion gas, although the average U.S. storage field's volume is a little more than half cushion gas.

In the demonstration project, the institutes hope to replace 15-20% of Simpson Chapel field's cushion gas with nitrogen from an air separation plant leased for the project.

The utility would save the difference between the cost of the nitrogen and a like volume of natural gas that would otherwise have to be purchased.

The technique is not as desirable for existing fields as new fields, especially if the utility uses the last in first out accounting method, because older cushion gas may be priced too close to the cost of the inert gas. The technique is more desirable for new fields because it could cut the cost of cushion gas, the largest component in the cost of a new storage field.

The Indiana test is the first in the U.S. for the technique. A storage field in France built to handle manufactured gas was swept with inert gas in the early 1980s for conversion to liquefied natural gas service and has performed satisfactorily.

The researchers are also evaluating use of inert gas to sweep storage fields being abandoned to increase recovery of stored natural gas.