Chesapeake Energy Corp. said it’s been asked to post $220 million in collateral by companies it does business with, a figure that could swell to $698 million, as the battered natural-gas driller tries to fend off concerns it can survive the commodity-price crash, Bloomberg News reported yesterday. The company also expects “further significant writedowns" in the value of its gas and oil properties if prices continue to remain low, according to a regulatory filing yesterday. That would follow $18.2 billion in writedowns already taken by the Oklahoma City-based driller in 2015. Chesapeake, the biggest U.S. gas producer after Exxon Mobil Corp., has been cutting workers, restructuring debt and canceling projects as it seeks to raise cash amid questions about whether it can meet its financial obligations.