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The gas turnover rates that can be achieved from such
reservoirs are dependent on the dimensions and design
of the original exploitation wells and on the properties
of the reservoir. To increase gas turnover rates,
especially in thin rock layers, new wells are increasingly
being drilled in such a way that the lower section
of the well runs horizontally along the storage formation.
This provides a considerably larger flow area for
the gas along with significantly higher injection
and withdrawal rates.
When depleted fields are used for natural gas storage,
the possibility of any residual gases mixing with
the injected gas cannot be excluded. Measures for
avoiding quality problems (e.g. by increasing the
cushion gas volume of storage gas) may have to be
considered, depending on the differences in composition
of any residual gas and the storage gas. This is also
why gas processing plants are sometimes installed
at the surface to guarantee that the gas re-injected
into the pipeline has the same quality as the pipeline
gas.
Depending on their storage characteristics, depleted
fields work equally well for the seasonal balancing
of natural gas supply and for peak shaving.
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