* SEC's informal inquiry continues as investigation
* Subpoenas issued over well participation program
* Shares close 2.4 percent lower (Adds closing share price, company comment)
By Anna Driver
March 1 The U.S. Securities and Exchange Commission has escalated its investigation into Chesapeake Energy Corp and its Chief Executive Aubrey McClendon for a controversial perk that granted him a share in each of the natural gas producer's wells.
The investigation, disclosed on Friday by Chesapeake in an SEC filing, comes nine days after it said an internal probe of the well program and McClendon's finances revealed no "intentional" wrongdoing by the executive.
Regulators in the SEC's Fort Worth, Texas, office have been looking into the Founder Well Participation Program (FWPP) that grants McClendon up to a 2.5 percent interest in every well that Chesapeake drills. He must also pay his share of well costs.
A Reuters investigation last April found that McClendon had arranged to personally borrow more than $1 billion from a big investor in Chesapeake, EIG Global Energy Partners, secured by his interest in the wells.
The board has since said the FWPP program would end in June 2014.
"I'm now confused because the board just said everything was fine," said Fadel Gheit, an oil analyst at Oppenheimer. "I really thought the board had an iron-clad, air-tight grip on the situation. Unfortunately the saga continues."
A spokesman for Chesapeake did not respond to an email request for additional comment on the investigation.
Chesapeake was advised by the SEC in December that an informal inquiry, launched in May, was continuing as an investigation and subpoenas for information and testimony have been issued. Both the company and McClendon are providing information.
The SEC routinely launches very preliminary investigations, known as matters under inquiry, in response to unusual market events, media reports, or other issues.
A formal order of investigation, however, involves issuing subpoenas to compel testimony or producing documents. SEC investigators cannot issue subpoenas without approval first from senior officials within the agency's enforcement division.
Shares of Chesapeake, the No. 2 natural gas producer in the United States, slumped 2.4 percent to $19.67 on the New York Stock Exchange.
McClendon is stepping down on April 1, following a tumultuous year during which the company he founded faced the governance crisis and a liquidity crunch.
The company's largest investors, Carl Icahn and Southeastern Asset Management also took control over the company's board of directors in June after McClendon was stripped of his title as chairman.
The U.S. Department of Justice and the Michigan attorney general are investigating whether Chesapeake violated antitrust laws in connection with the purchase and lease of oil and gas rights in the state.
The company said it was also responding to related inquiries from other regulatory agencies and self-regulatory organizations. (Additional reporting by Swetha Gopinath in Bangalore and Sarah N. Lynch in Washington; Editing by Roshni Menon, Bernadette Baum, Jeffrey Benkoe and Andrew Hay)