Pipeline operator Transneft has rejected suggestions that it may have to shut a major part of Russia's oil trunkline network after organic chlorides were discovered in oil volumes in the Samara region.

The state-controlled operator has, however, acknowledged that it recently had to halt the transmission of oil along two regional pipelines — Samara-Lopatino and Kuybyshev-Unecha-2.

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The halt was ordered on 23 June after routine tests at an oil pumping station in the Samara region revealed the presence of organic chlorides in incoming oil at almost 16 times the permitted level.

Contamination by organic chlorides makes oil highly corrosive when it is heated at refineries in preparation for conversion into products, raising the risk of accidents and the potential for severe damage to processing facilities.

In April and May 2019, Russia had to fully halt oil deliveries to Poland and Germany via the Druzhba (Friendship) pipeline after complaints from two refiners in Belarus, which are the first to receive Russian oil on its way to Europe.

Rosneft issues swift response

Concerning the latest incident, Transneft has said the pumping station where the organic chlorides were found had only been accepting oil from Samaraneftegaz, a wholly owned subsidiary of the country’s largest oil producer, Rosneft.

Rosneft responded by saying that Transneft’s statement on Samaraneftegaz being the source of contamination "contains premature conclusions and needs careful checking”.

Tests jointly carried out by Samaraneftegaz and Transneft revealed that the organic chlorides content has not been exceeded, Rosneft added.

However, Transneft said it had to isolate almost 2.6 million barrels of contaminated oil in its storage depots and pipelines in an effort to halt any spread to the rest of the network.

The operator also said it resumed accepting oil from Samaraneftegaz last weekend.

Case still shrouded in mystery

Two years ago, Transneft said almost 37 million barrels of oil in its pipeline network were contaminated by organic chlorides. Since then, it has been compensating affected European customers.

In 2019, Russian investigators blamed the contamination on small oil producers in the Samara region for using so-called proppants, containing organic chlorides, to frack reservoirs at their fields.

Later that year, investigators charged four individuals with attempting to steal uncontaminated oil and replace the missing volumes in storage reservoirs with contaminated material.

They later charged four Transneft employees with arranging illegal connections to the network.

However, the authorities have never revealed whether the investigation ended with a court trial and prison sentences for the detained individuals, with industry analysts casting doubt on the official explanation for the contamination.