For decades to come, gas will be the energy source of choice to meet increasing energy demand. Gas and oil operators, which have always preferentially produced the gas from those reservoirs technically the easiest to develop, are now having to produce more and more reservoirs with a high H2S content in the gas in order to meet the world's increasing demand for natural gas. Effectively, 40% of the world's gas reserves currently identified as remaining to be produced, representing over 2 600 Tcf, are sour, and more than 350 Tcf contain H2S in excess of 10%.

Acid gas cycling and/or disposal by reinjection offer a promising alternative to avoid sulphur production and reduce CO2 emissions to the atmosphere when producing large very sour gas reserves.

Total, Institut Français du Pétrole (IFP) and its fully owned subsidiary Prosernat have developed a cryogenic process for bulk H2S removal from very sour gases, the SPREX® process. This process allows substantial CAPEX and OPEX savings when the separated acid gases are reinjected.

A demonstration pilot plant was built and installed late in 2004 at the Lacq sour gas plant, South West France, and started-up in April 2005.

The paper describes the principles and economics of the combination of the SPREX® and amine sweetening integrated with acid gas reinjection, based on figures developed for a very sour gas field such as those encountered in some areas of the Middle East. The results of the very first months of operation of the demonstration unit in the treatment of a sour gas with 15–18% H2S are also presented and discussed.

Economic and environmental constraints involved in the production of highly sour gas fields

The production of highly sour gas reserves has to overcome two major constraints.

The first is economic and related to the sale of sulfur, a sub-product of sour gas. Where sulfur formerly represented a substantial part of the revenues drawn from the production of sour natural gases, it is no longer of any economic interest in many areas today: the world sulfur market is globally saturated and practically all experts consider that this situation is set to continue as the supply of sulfur, mainly obtained from the extraction of H2S from sour natural gases or sour crudes, has exceeded the demand, essentially from the fertilizer industry.

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