Offshore GTL – Transforming Natural Associated Gas to Liquid
As gas flaring becomes more unacceptable from political and environmental viewpoints, oilfields with no viable associated gas solution may be required to curtail production or in the extreme case, cease production entirely.
There is evidence globally that this is starting to occur and proposals for new oilfield projects in remote or deepwater locations must increasingly demonstrate how the associated gas will be processed without continuous flaring. Gas re-injection sometimes offers a solution but this is expensive for deep wells and not desirable for all reservoir structures. Gas-to-liquids (GTL) processes enable monetization of remote natural gas or other gaseous hydrocarbons by converting them into sulfur-free synthetic crude oil that can be easily transported by tanker. The GTL products can then be used as-is or blended with diesel oils as a fuel with lower environmental impact for transportation and power plants.
Originating from technology first developed at the UK Atomic Energy Authority in the year 2000, CompactGTL,the company that basically introduced the solution, has now introduced new modular GTL plant designs integrated with FPSO’s. This has been achieved through close collaboration with major partners in the upstream sector serving to independently qualify the technology as well as creating a supply chain for commercial plants. In addition, a commercial plant may be capable of handling up to 35% CO2 in the feed gas without additional gas treatment, and in fact uses much of this CO2 for syngas and ultimately syncrude production.
In Brazil Petrobras is working closely with CompactGTL to certify this new concept with the help of the American Bureau of Shipping and they already have a pilot plant in Brazil. ABS has already issued an AIP (Approval in Principal) for the technological concept and SBM will be introducing the system in its pre-salt FPSOs.
A GTL plant converts natural gas or other gaseous hydrocarbons into sulfur-free synthetic crude oil through the following steps: 1. The feed gas is converted to syngas through a steam reforming and partial oxidation process. This requires large amounts of oxygen or air and therefore typically involves a large air-separation unit (ASU). 2. The syngas, consisting of hydrogen and carbon monoxide, is compressed and fed to Fischer-Tropsch (FT) synthesis reactors where it is converted to liquid hydrocarbons. Light or heavy syncrude may be obtained, depending on catalyst temperature and pressure. 3. The product of the FT reaction can be further upgraded in a typical refining unit, which may be associated with the GTL plant.
Sources: CompactGTL, GE and SBM