Chesapeake Energy Corp said the chairman of its audit committee has quit, days after regulators escalated their investigation into the company and its CEO for a deal that gave him a share in each of the natural gas producer's wells.

The investigation by the U.S. Securities and Exchange Commission, disclosed last week by Chesapeake, came nine days after it said an internal probe of the well program and CEO Aubrey McClendon's finances revealed no "intentional" wrongdoing.

The internal probe was led by audit committee chairman V. Burns Hargis, president of Oklahoma State University and former vice chairman of Bank of Oklahoma and BOK Financial from 1997 to 2008.

Chesapeake, the second-largest U.S. natural gas producer, said on Thursday its board has accepted the resignation.

The chairman of Chesapeake's board, Archie Dunham, said Hargis led the audit committee and the recent review with the "utmost professionalism and integrity".

Louis Raspino, most recently the chief executive of Pride International Inc before its merger with Ensco Plc, will replace Hargis, the company said.

Chesapeake shares opened marginally up at $19.77 on the New York Stock Exchange on Thursday.