Former Enron CEO Jeffrey Skilling is looking at ways to return to the energy business, according to two sources familiar with his activities. Among the ventures he is considering is an idea he came up with in 2015 — and put to paper — while serving a federal prison sentence for his role in Enron's 2001 collapse.

Skilling, 65, completed that sentence last month, and has been meeting with friends and former colleagues since his release into a residential re-entry program in Houston last August. News of his possible return to the industry was first reported Friday by the Wall Street Journal.

Skilling declined to comment.

The sources described Skilling's idea, broadly, as a software program for oil and gas investors. They stressed that the project is in its early stages. No investors have put any money into the venture, though some individuals who provided input have been required to sign non-disclosure agreements. Skilling developed the idea as an inmate at a federal correctional facility in Montgomery, Alabama, and apparently worried for the rest of his sentence that someone else would come up with the idea before he got out.

Among those Skilling has been discussing his ideas with, the sources said, is Lou Pai, the former head of Enron's Energy Services division, now an industry consultant. Pai could not be reached for a comment.

Contrary to other reporting, the sources told CNBC that the venture does not involve cryptocurrency or blockchain technology. And they said it is one of a number of paths Skilling is considering in hopes of returning to the industry he knows best.