One of the top U.S oil and gas producers, ConocoPhillips, is in an advanced stage of discussions to sell assets in Oklahoma to privately-held Stone Ridge Energy in a deal that could be worth about $1.3 billion, Reuters reports, citing sources with knowledge of the talks. ConocoPhillips last year acquired Marathon Oil in an all-stock deal with an enterprise value of $22.5 billion, inclusive of $5.4 billion of net debt. The deal expanded ConocoPhillips’ presence in the Permian, Eagle Ford, Anadarko, and Bakken shale basins. Now the company…