A $2 billion private-equity fund that borrowed heavily to buy oil and gas wells before energy prices plunged is now worth essentially nothing, an unusual debacle that is wiping out investments by major pensions, endowments and charitable foundations.

EnerVest Ltd., a Houston private-equity firm that focuses on energy investments, manages the fund. The firm raised and started investing money in 2013, when oil was trading at more than double the current price of about $45 a barrel. But the fund added $1.3 billion of borrowed money to boost its buying power. That later caused it trouble when oil prices tumbled.

Now the fund’s lenders, led by Wells Fargo & Co., are negotiating to take control of the fund’s assets to satisfy its debt, according to people familiar with the matter.

“We are not proud of the result,” John Walker, EnerVest’s co-founder and chief executive, wrote in an email to The Wall Street Journal.

The outcome will leave investors in the 2013 fund with, at most, pennies for every dollar they invested, the people said. At least one investor, the Orange County Employees Retirement System, already has marked its investment down to zero, according to a pension document.