(Adds background, output details)
By Marta Nogueira
RIO DE JANEIRO, Jan 19 (Reuters) - Brazilian oil and gas company HRT Participacoes SA reached an agreement to buy offshore assets of Royal Dutch Shell Plc in the Campos Basin, a source with knowledge of the deal said on Monday.
Further details of the agreement are expected to be published by HRT on Tuesday on the website of CVM, the local market regulator.
Bloomberg News, citing two people with knowledge of the matter, reported that the deal would give HRT 80 percent of the venture.
The fields involved in the deal are the Bijupira and Salema areas, which were some of the first to be operated by a foreign company in Brazil on a commercial scale, the source that spoke with Reuters said.
Representatives of HRT and Shell said they do not comment on market rumors and declined otherwise to comment.
Shell operates the two areas with an 80 percent stake, while Brazil's state-run oil company Petrobras holds the remaining 20 percent.
Combined, the two fields produce 30,000 barrels of oil a day, according to a Shell representative, more than four times the 4,300 bpd that HRT said it produced during the month of November from its own wells.
HRT, which started selling stakes of its onshore natural gas projects in the Solimoes Basin in the Amazon in 2011, has been looking to expand its offshore operations.
The current sharp decline in international oil prices have given smaller oil companies such as HRT a chance to pick up less attractive assets that oil majors have been keen to shed in the current market.
Shell recently revised its development plan for the two ageing fields to reduce the natural slowdown in their output. In 2013 and 2014, it drilled four new wells in the Bijupira and Salema, giving them 12 wells and six injectors. (Reporting by Marta Nogeira; Writing by Reese Ewing; Editing by Diane Craft and Lisa Shumaker)