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Scrubbing natural gas Producing sour gas safely & cleanly

Natural gas is not just natural gas: depending on the reservoir it contains not just methane (CH4) but also other components – for example carbon dioxide (CO2) and hydrogen sulphide (H2S). Experts then refer to it as "sour gas".

The production of this natural resource is complex because H2S is already highly toxic at concentrations from about 0.015 percent. Specialised purification systems are therefore used during the sour gas production that remove CO2 and H2S from the recovered gas.

Wintershall is one of the pioneers in producing sour gas: the Rütenbrock and Staffhorst fields in Germany were already discovered back in the 1960s. These were then followed by further reservoirs, and to date Wintershall has developed 16 sour gas fields in Germany alone and recovered around 30 billion cubic metres of sour gas from them.

Over the last few decades we have developed considerable expertise not just in planning, constructing and operating the plants but also regarding the production and safety aspects.

 

Alexander Steigerwald
Operations Manager Production North

In Staffhorst we have been producing sour gas for more than 40 years – safely and cleanly. The knowledge that we have acquired here can now be deployed by us in other projects worldwide – for example in the Middle East.

Alexander Steigerwald

This knowledge is complemented by the expertise of our parent company: BASF has many years of experience in producing gas scrubbing products that, among others, separate hydrogen sulphide, which is known as "sweetening". The products manufactured under BASF’s OASIS gas purification technology brand include, for example, the well-known MDEA solvent. This enables BASF and Wintershall to act together as strong partners in the sour gas sector – for example in the Middle East region where sour gas production is becoming increasingly important.

Sour gas has to be scrubbed Removing H2S and CO2

Before sour gas can be used as an energy source, it has to be cleaned. During the gas scrubbing, carbon dioxide and hydrogen sulphide are removed from the gas using the MDEA solvent developed by BASF – the gas is then ready to be fed into the pipeline network. Whereas the carbon dioxide returns to the reservoir, the hydrogen sulphide is fed into a so-called Claus plant: here the H2S is converted into water and sulphur that can be used by the chemical industry as a raw material. The following graphic shows how the purification process works in detail.

1 - Sour Gas

The term “sour gas” is used to describe natural gas that contains carbon dioxide (CO2) and hydrogen sulfide (H2S) alongside methane (CH4).

2 - Process in the gas treatment plant

The gas passes through a chemical solution (MDEA) that works like a cleaning agent and removes the hydrogen sulfide and carbon dioxide from the gas.

3 - Reactions in the Claus plant

A third of the hydrogen sulfide combusts in the Claus plant. The sulfur dioxide recovered in this process reacts with the remaining two thirds hydrogen sulfide. This creates pure sulfur and water.

4 - Transport

The sulfur recovered can be transported in liquid form or as solid granules. It is mostly purchased by the chemicals and rubber industries.

From Lower Saxony to Abu Dhabi Sour gas expertise is being exported

The roots of our expertise in sour gas production lie in northern Germany where Wintershall still produces this natural gas – for example in Staffhorst in Lower Saxony. However, we would also like to use this knowledge for other projects throughout the world.

For example, there is an increasing focus on sour gas in the Middle East, such as in Abu Dhabi. In the last few decades, the Emirate has concentrated almost entirely on crude oil. However, with the increasing demand for energy, the development of natural gas fields is also moving into the spotlight. Many of the gas reservoirs in the region contain sour gas with a high proportion of hydrogen sulphide. One of these fields, which is called "Shuwaihat", lies partly under the mainland and partly under the waters of the Persian Gulf. The state oil company, the Abu Dhabi National Oil Company (ADNOC), wants to develop the reservoir and is relying on the expertise of Wintershall and BASF: ADNOC, Wintershall and the Austrian company, OMV, agreed to conduct a technical appraisal of the Shuwaihat field in 2012, whereby Wintershall will be responsible as operator for the technical exploration and development of the field.

We not only managed to impress ADNOC with our expertise in plant construction, operation and production, but also score with our BASF trump card as a gas purification expert.

Safety has top priority Special equipment for sour gas production

Safety comes first when producing sour gas: when drilling, the drilling fluids and casing strings contain a so-called "H2S alkalinity buffer" that splits the hydrogen sulphide and keeps it dissolved in the drilling fluid. It is then removed on the surface. Because hydrogen sulphide is highly corrosive and can easily attack pipes, the pipes and pipelines through which the sour gas flows are made of particularly high quality steel alloys. 

During the production, additional shut-off valves on the plants prevent the hydrogen sulphide from leaking. Gas detectors and radio-controlled monitoring stations are able to give alarm at minute quantities of hydrogen sulphide (0.001 percent), carbon dioxide and methane in the air. In such an event, the affected plant or the entire facility immediately switches itself off automatically.

Staff working on the production plants carry small gas detectors with them that immediately indicate any gas leaks. They are also equipped with gas filters, which they can use in an emergency to escape from the danger zone. Emergency plans and regular staff training ensure that, should an incident occur, nobody gets hurt.

 

Facts & Figures

 
THE "LIFECYCLE" OF OIL AND GAS FIELDS

The service life of oil and gas fields is divided into different phases ranging from the discovery to the decommissioning.

Value Chain / Production