Due to declining global demand for basic sulphur, the economics of extracting sulphur from sour natural gas has become unfavourable. Furthermore, air emission standards and regulation authorities are becoming increasingly strict, thereby increasing the economical strain on E&P companies producing natural acid gas. E&P companies are in search of environmentally-friendly and cost-effective methods for dealing with acid gases, which are produced in association with sour natural gas.

Acid gas re-injection is gaining attention due to its eco-friendly nature and lower cost. These benefits help this technique to overcome traditional H2S processing and the problems of handling the elemental sulphur product, particularly for very sour natural gas streams.

This paper discusses industry practices of acid gas injection with reference to their phase behaviour. Four stage acid gas injection is discussed along with graphical and diagrammatical representation. Acid gas is injected into the reservoir at a very high pressure; but can the toxic acid gases be safely handled at such a high injection pressure? This question is answered in this study, throwing light on some risk management aspects while performing this operation.

This paper also reviews comparative economic analysis of various H2S management options available to developing Middle East fields keeping in mind HSE, operating procedures, reduced costs, with injection method leading the rest.

Finally certain benefits of acid gas injection would be described some of which includes:

  • Reduction of SO2 emissions.

  • Permanent, reliable storage of toxic gases.

  • Eliminating the cost for acid gas treatment plant.

  • Very much efficient for EOR/IOR schemes as sweep efficiency of H2S is better than CO2.

  • Eliminates the cost of storage of these gases.

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