The 60 percent plunge in crude oil prices since mid-2014 isn't just about increased production and slower global growth. Debt may be the four-letter word when it comes to explaining the extent of the energy sector's collapse, a paper in the Bank for International Settlement's Quarterly Review shows.

While production has certainly increased and consumption cooled, current estimates of both are little changed from previous forecasts. This stands in contrast to the last two periods of similar oil-price declines in 1996 and 2008, which were attributed to big reductions in demand and/or a surge in production, according to the paper.

This time, low borrowing costs, a product of easy Federal Reserve monetary policy, are a new wrinkle. Cheap financing has made it easier for exploration and production (E&P) companies to finance operations and expand rapidly as the era of hydraulic fracturing kicked into high gear. Debt in the global oil and gas industry reached $2.5 trillion in 2014, 2 1/2 times what it was eight years earlier, according to the BIS paper.

Just as fracking helped production soar in America's oil fields, the debt boom is now magnifying the slump in prices as E&Ps boost current and future sales of crude to make sure they can fulfill their debt obligations. The direct effect on the economy is a sharp cutback in capital spending plans, already evidenced by plummeting rig counts.

At the same time, production continues to march higher. Deteriorating balance sheets encourage companies to keep pumping from existing wells even as the value of the assets (the oil) backing those securities declines. That explains the blowout in spreads between high-yield energy bonds and risk-free counterparts.

"A sell-off of oil company debt could spill over to corporate bond markets more broadly if investors try to reduce the riskiness of their portfolios," the BIS authors write. "The fact that debt of oil and gas firms represents a substantial portion of future redemptions underlines the potential system- wide relevance of developments in the sector."

Other risks to the economy from the slump in oil-related capital spending include possible investment pullbacks in other areas that depend on a burgeoning energy industry. Cheaper crude can also result in lower government revenue — state and local agencies in the U.S., and in other countries where oil represents a big portion of the budget.