Condensates
The recent high-profile incident involving the crude oil tanker, SANCHI, in the East China Sea has focused attention on the potential hazards of transporting condensate by sea.
Ship-source spills of condensate are quite rare and there is limited information available about them in the public domain.
Here we provide a brief overview and some key facts about condensates.
What is condensate?
Condensate is a generic term used to describe a variety of very low-density, very low-viscosity, liquid hydrocarbons that typically occur along with natural gas.
Condensates can exist separately from crude oil or combined with it.
The term applies equally to condensate pumped in its liquid form from a well ('lease' condensate) or processed and separated from natural gas at a gas plant ('plant' condensate).
Uses
Condensates are used as refinery feedstocks for the manufacture of products such as petrol (gasoline), jet fuel, diesel and heating fuels. Some condensates, particularly those with a high paraffin content, are used for the manufacture of ethylene.
Condensates are also used to dilute highly viscous heavier oils that cannot otherwise be efficiently transported via pipelines.
Producers
The largest producers of condensate are currently Russia and the Middle East. Condensate production in the USA has increased recently due to rising shale oil and gas production. Australia's output is also rising due to its large offshore natural gas fields.
Transportation by sea
Condensates are classified as a flammable liquid by the UN. They are covered by Marpol Annex 1 (Prevention of Pollution by Oil) and can therefore be carried in crude oil tankers rather than chemical/product tankers. According to industry guidelines, special precautions should be applied when transporting condensates with very high vapour pressure, including permitting only closed loading methods and providing additional supervision to see that gas dispersion is monitored.
Properties of condensates
The composition of condensates varies depending on their source and how they are processed. They vary in appearance from colourless to yellow or brown.
Typically, condensates are composed mainly of alkanes (saturated hydrocarbons, such as butane, pentane and hexane) and are low in Polycyclic Aromatic Hydrocarbons (PAH) which are typically found in crude oils. Condensates have a very low solubility in water and are highly volatile. They also have a low density and, if spilled would, typically, float on the sea surface and would begin to evaporate quickly.
Condensates are classed as 'non-persistent' according to the IOPC Funds' definition1. As a consequence, compensation for a spill of condensate is not covered by the Civil Liability Convention2 but will come under the Hazardous and Noxious Substances Convention when this comes into force.
[1] Persistence is also important when it comes to the international compensation regimes and the IOPC Funds have developed guidelines, widely accepted, which define the term "persistent oil". Under these guidelines an oil is considered non-persistent if at the time of shipment at least 50% of the hydrocarbon fractions, by volume, distil at a temperature of 340°C (645°F) and at least 95% of the hydrocarbon fractions, by volume, distil at a temperature of 370°C (700°F) when tested in accordance with the American Society for Testing and Materials (ASTM) Method D86/78 or any subsequent revision thereof.
[2] See IMO Conventions for further information.
Spills
Spills of condensate in the marine environment are relatively uncommon compared with other types of oil spills. The incident involving SANCHI, which suffered a collision in the East China Sea on 6th January 2018, is the largest ship-source condensate spill reported to date. It is understood that the vast majority of the cargo of gas condensate was consumed by the fire and explosions that ensued for a week before the vessel sank. Tragically, all 32 crew members were lost.
Response Measures
Condensates typically break up naturally in wind and waves with the majority evaporating within a matter of days. Traditional containment and recovery operations are not typically recommended. Any attempt to concentrate the condensate would reduce the rate of evaporation and, if the concentration of vapour becomes high, could cause the oil to ignite. In-situ burning is potentially an option, but may be difficult to achieve in a controlled manner unless in ice-infested waters. Dispersants are ineffective on condensate spills as they will 'herd' the sheen rather than promote the formation of droplets in the water column.
Spills of condensate in the marine environment are best left to evaporate and dissipate at sea.
Environmental impact
The main hazards associated with condensate spills are linked to explosions, fire and exposure to vapours. In addition to the danger for humans, this might kill or harm birds, marine mammals and other organisms in the vicinity.
With wave action, some dispersion of the condensate may occur. Small fractions of toxic compounds found in the condensate could impact fish in the first few metres of the water column.
ITOPF is working to increase its knowledge of the fate and effects of condensates in the marine environment and will update this text as new information becomes available.