In 2005, Stephen Cravens, then an associate at First Reserve (the largest and oldest private-equity firm focused on the energy industry) in Houston, was invited to attend a Houston Producers’ Forum lunch at the prestigious downtown Petroleum Club. Cravens had started his own “club” a few months prior to the lunch, where young, like-minded industry professionals could commiserate over a beer, trading stories of their 100-hour work weeks and a few ideas. The Petroleum Club, however, was a different story.

“I got there, looked around the room, and it was ...