I think that you are forgetting that leases have been granted at a rate of over 350% since 1998, and these leases have, as yet, not been properly surveyed AT ALL.
They DO NOT WANT TO DRILL. The cheaper they make oil, the less profit they make, the cheaper their assets and net worth become. They need to CONTROL these leases - they certainly do not need to exploit them.
Where did you hear that they returned “sizeable amounts of leased property?” I had heard that they sold leases on almost 5000 acres of US land that they HAD NOT SURVEYED to third party exploration firms working under the Chevron brand, but that is it, as far as I know...
That sentence proves you don't know what you are talking about.