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By Marianna Parraga and Deisy Buitrago

CARACAS, July 23 (Reuters) - Venezuela's oil ministry has told partners of state energy company PDVSA that it will maintain the July 28 deadline it had set to migrate oil and gas contracts to a new legal framework approved in January, rushing executives to complete the negotiation of terms, four sources close to the talks said.

Venezuela's National Assembly in late January approved a sweeping reform of the hydrocarbons law, the backbone of the country's energy industry, offering autonomy for companies to operate oil and gas projects and introducing a new taxation model. The oil ministry gave up to 6 months to adjust all existing contracts to the new framework.

The migration involves about two dozen foreign and local companies, including U.S. oil major Chevron CVX.N, Spain's Repsol REP.MC and Italy's Eni ENI.MI, most of which have more than one project in partnership or under contract with PDVSA.

The negotiations have accelerated in recent days with foreign executives arriving in Caracas to negotiate the long list of documents required to sign, following twin earthquakes last month that caused delays and took the country's main airport out of service, the sources said.

The oil ministry did not immediately reply to a request for comment.

A weighted royalty rate from a newly introduced hydrocarbon tax has become the most important element of the core contracts in negotiation. The ministry might allow companies to submit some annexes to the main contract in a later date, including recently requested plans for each energy project to generate its own electricity, two of the sources said.

Some of PDVSA's largest partners negotiating project expansions, including Chevron, have shown progress in recent months by having key permits approved by the ministry, according to documents published in the official gazette.

Companies getting into Venezuela for the first time - mostly foreign wildcatters and little-known firms - do not have a specific deadline to negotiate and agree to contract terms following preliminary agreements signed since early this year, the sources added.