Gas hydrates removed during a pigging operation.

 

Of the latter, four of the commonest are listed below:

Asphaltenes: the heaviest components in crude oils, which may aggregate and precipitate in response to changes in chemical composition, pressure or temperature. Precipitation and deposition may occur in reservoir rocks, wellbores and pipelines.

Wax: a natural constituent in most petroleum fluids, this may be deposited on cold surfaces such as pipeline walls, increase the viscosity of oil until it ultimately gels, and settle out at the bottom of storage tanks.

Emulsions: water droplets in oil, which tend to be stabilised by natural oil components and in the presence of certain solid particles. As a result, they obstruct flow and complicate separation of produced water from oil.

Gas hydrates: resembling snowballs or slush, these are crystalline materials comprising a framework of water molecules with their cavities filled by gas. Small clumps are easily carried along with the flow, but large cohesive blocks can cause a partial or complete blockage.

Statoil and its associates have studied these phenomena since the 1980s, and now rank among the best in the world with regard to:

• process understanding
• novel experimental investigations
• predicting the conditions under which these obstructions form
• controlling or preventing their occurrence.