Brace for a wave of defaults in the oil patch.

Energy companies that loaded up on debt during the oil boom are likely to have trouble paying back those loans. Oil prices have collapsed over 65% since the middle of last year to below $37 a barrel this week and there's no recovery in sight.

It's fueling financial turmoil on Wall Street with Standard & Poor's Ratings Service recently warning that a stunning 50% of energy junk bonds are "distressed," meaning they are at risk of default.

Overall, about $180 billion of debt is distressed. It's the highest level since the end of the Great Recession and much of it is in energy companies.

"The wave of energy defaults looming in the wings could make for some very bumpy roads ahead in 2016," Bespoke Investment Group wrote in a recent report. The firm described the junk bond market environment as "pretty terrible" lately.

That's a dramatic change from recent go-go years, when the shale oil boom along with cheap borrowing costs allowed energy companies to take on loads of debt to fund expensive drilling operations.

U.S. oil production skyrocketed, creating a gigantic supply glut that is currently pushing prices lower and hurting the ability of many energy companies to repay their debt.

"The tide may be turning. Excess leverage during the good years has dented credit profiles," analysts at research firm Markit wrote in a report published on Wednesday.

72% of metals, mining companies are distressed

Of course, it's not just oil companies under financial duress. S&P said a whopping 72% of the bonds in the metals, mining and steel industry are now distressed.