Production is slightly behind schedule but still a boon for Melrose which was disappointed by the termination of another Black Sea farm-in deal this week.
The offshore Kavarna and Kaliakra fields contain combined gas reserves of 74 Bcf and are in the Galata exploration concession in the Bulgarian sector of the Black Sea.
Commissioning activities started Monday and the fields were officially opened to commercial production Thursday by the Bulgarian energy minister, Melrose said.
The combined field production plateau rate is expected to be around 45,000 Mcf/d.
In August, Melrose CEO David Thomas told Platts the Kavarna field was expected to start up in September with Kaliakra to follow in October.
Nonetheless, Thomas said in a statement Thursday the start of the fields was "an important milestone" for the company as it would double its cash generation over the next few years.
The majority of Melrose's legacy income came from the now depleted Galata gas field near to the two new fields.
The Kavarna and Kaliakra fields were developed using single subsea wells tied back to the existing Galata field production platform, from where the gas is exported by pipeline to the company's onshore gas plant near Varna for processing.
A similar development plan will be adopted for the recent 12 Bcf East Kavarna discovery, which is expected to "supplement the production from the two new fields and has the potential to extend the combined field production plateau period to around three years," the company said.
In parallel with the development activity, gas sales agreements for the fields have been concluded with the majority of the gas being sold to Bulgargaz, the Bulgarian state-owned gas company, and the balance to a local industrial user.
On Monday, Melrose stock fell after Canada's Sterling Resources canceled the planned sale to Melrose of 32.5% stakes in the licenses to develop the gas-rich Pelican and Midia blocks in the Romanian sector of the Black Sea.
Sterling said its decision was prompted by delays in receiving approval for the deal from the Romanian authorities.
Melrose, which had highlighted Romania as a likely new core area for the company, said Sterling's decision to cancel their agreement was "disappointing" and would force the company to review its future business strategy.
The termination of the Midia and Pelican agreement sent its shares down more than 17% on Monday to GBP2.70, but the start of the Kavarna and Kaliakra fields boosted the company's stock early Thursday by 3.4% to GBP2.72.
