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Cawthorne Channel Associated Gas-gathering Project, Nigeria – Elimination of Gas Flaring
Figure 1: Gas Flaring in the Niger Delta – Before the Project
the project down by eradicating the normal requirement for a third
50% standby machine (see Figure 5).
Innovation
The remit from Shell was open, allowing room for the team to implement
innovative methodologies. The team had to cope with liquids handling
within the plant without having access to dedicated storage tanks and the
like, with the added difficulty of the plant being based in a swamp. The
team solved the problem by gasifying the liquids locally and transporting
the gas via a pipeline to the Alakiri plant, which could process it.
The Krakama station also had some remarkable features, representing
the largest trial to date of a new style of membrane dehydration unit
operating between the second and third stages of compression. This
Figure 2: The Project
membrane system is more efficient for smaller gas plant duties. The
Associated gas-gathering (AGG) system compressed gas is passed along the surface of cylindrical membranes,
Oil fields with
where the gas is allowed to pass and the water is disengaged from the
associated Clean power generation
gas (AG)
gas. A counterflow of purge gas sweeps the membrane elements to
Industry and commerce
Residential heating
remove the water. As well as being more economical for smaller gas
plants than the usual triethylene glycol (TEG) systems, the membranes
should also run indefinitely and require less maintenance due to the
lack of moving parts. Minimising maintenance was an important part
of the project due to the remote and difficult location of the plant. The
ingenuity of the team continued, as the Mott MacDonald engineers
Central
Pipelines gathering
Gas
LNG
were able to take the permeate from the membrane dehydration units
station
processing
and use it to fuel the gas engine that powered the compressor. In this
way, taking what was effectively a waste product – something that
Cawthorne Channel AGG captures associated gas from oilfields that would otherwise be flared.
would previously have gone to the flares – and using it as fuel for the
The associated gas is collated at a central station, then treated, compressed and piped to liquefied
engine that drives the plant, combined with the complete elimination
natural gas (LNG).
The LNG is shipped to consumers around the world for cleaner-burning applications, resulting in of flaring, made this a sustainable project.
direct revenue gains for Nigeria.
Figure 3: Tow-out of the Awoba Barge
Communicating Across Cultures
Not all of the challenges that arose throughout the course of this
remarkable project were engineering-based. Mott MacDonald needed
to be able to work efficiently across three work locations with three
nationalities. With Daewoo in Seoul as the EPCC contractor, Mott
MacDonald in charge of engineering design in Abu Dhabi and the
client and site in Nigeria, it was crucial to be able to work effectively
despite cultural and linguistic differences. Mott MacDonald located
interface personnel in Daewoo’s Seoul office for the first year of the
project, and a team of Korean engineers from Daewoo were present in
Mott MacDonald’s Abu Dhabi office, as well as Mott MacDonald
having a team of Shell’s engineers in Abu Dhabi interfacing with the
project team. In this way, one of the biggest challenges of the project
was turned into an example of uniting to effectively overcome the
communication barriers posed in international projects.
Conclusions – A Step Forwards for Nigeria
The compressors themselves were an unusual configuration, with gas The project eliminates 20% of gas flaring in Nigeria, making it
coming on to the first- and second-stage compressors and increasingly likely that the country will succeed in its drive to eliminate
dehydration and a liquefied petroleum gas (LPG) extraction plant gas flaring altogether. In addition to the environmental benefits,
between the third- and fourth-stage compressors. Furthermore, the the retrieved gas has a positive impact on the Nigerian economy –
project utilised two compressors running in parallel; normally there in the region of hundreds of million dollars a year. Furthermore,
would be one master compressor running at full power, with the Daewoo, as the EPCC contractor, spent a great deal of time working
second machine part-loaded to compress the balance of gas. With with and contributing to local communities, thus ensuring that benefits
only two 50% machines to achieve the throughput, the Mott were realised by them in accordance with SPDC’s requirement to
MacDonald team balanced the delivery pressures to operate on the implement and maintain a robust community affairs, safety, health,
same duties in parallel. This enabled the company to keep the costs of environment and security (CASHES) management system.
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EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 1
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