'SHELL ABU DHABI has been working with Adnoc (Abu Dhabi National Oil Company) to assist in the development of the large volumes of sour gas contained in some of their reservoirs,' says David Westerman, Deputy Managing Director, Shell Abu Dhabi.

'Sour gas, which contains both H2S [hydrogen sulphide] and C02 [carbon dioxide], is commonly found in small quantities and low concentrations in many hydrocarbon reservoirs. However, Abu Dhabi has several sour gas reservoirs with a relatively high sulphur content, which makes development more difficult.

'Sour gas can be processed to separate the hydrocarbons so producing sweet gas, which can be sold, and leaving a residue referred to as acid gas. The acid gas also has a use in that it can be reinjected into oil fields to increase the overall production level from a reservoir.

'Shell has many years' experience in the development of sour gas reserves with a high sulphur content and in 1999 set up a joint study with Adnoc to assess the technical and commercial feasibility of safely producing and processing Abu Dhabi's sour gas reserves.
'The field development planning phase of the Sour Gas Study was completed in March this year with the delivery of the plan to Adnoc.

The first stage of the plan involved the drilling of an appraisal well, the Arab 1, in the sour gas reservoir.

That has been successfully carried out and initial testing has been completed by Adco [Abu Dhabi Company for Onshore Oil Operations].

'ADCO is managing the long-term testing of the Arab 1 well to determine the production potential of sour gas from the Arab reservoir.

'Further down the line there will be an appraisal of the north section of the Thamama 'B' reservoir to substantiate the field development proposal.
'The development plan calls for the injection of acid gas into the Thamama 'B' reservoir as both a disposal method for the acid gas and also as a way of enhancing the recovery of oil from this difficult section of the Thamama 'B' reservoir.

'Shell Abu Dhabi is proud to be working with Adnoc and Adco in this exciting study and to be able to share its expertise in this highly specialised technology with these two long-term partners...'

'The potential results could bring two benefits.
'The first is the additional sweet gas which will be produced from the sour gas that could unlock Abu Dhabi's considerable sour gas reserves and can be used to meet Abu Dhabi's ever-increasing demand for gas.

'At the same time the acid gas, which is left over from the process, will be re-injected to increase oil recovery levels in certain areas of some reservoirs where in the past it had not been attractive to do so using existing conventional technologies,' concludes Westerman.