Volatile but range-bound oil prices are limiting the ability of U.S. oil firms to pay down the debts they had accumulated in order to boost drilling activities and production. On the one hand, WTI Crude prices in the $50-65 per barrel range are limiting the options for the U.S. shale patch to grow cash flows and profitability.   On the other hand, shareholders are increasingly pressing oil producers to start rewarding them with higher returns in the form of share repurchases and/or higher dividends, which eat into what little cash flow companies…