Whiting Petroleum Corp.’s bankruptcy shows how pain in the shale patch is reverberating throughout the oil supply chain.

Schlumberger Ltd. and Halliburton Co., which provide rigs and fracking crews, are listed as the biggest non-bank creditors in Whiting’s Chapter 11 filing, each with unsecured claims of more than $8 million a piece. Fellow oilfield servicer Baker Hughes Co. is the 8th largest creditor overall with an unsecured claim of $2.6 million. Other creditors include pipeline operators, a trucking company and a wastewater disposal company, among others.

Contractors hired to map underground pockets of oil, drill new wells and complete them with hydraulic fracturing are expected to be among the hardest hit in the energy industry as explorers slam the brakes in order to survive a crude-price crash triggered by the Covid-19 pandemic and a battle for market share between Saudi Arabia and Russia. Schlumberger, the world’s biggest oil services provider, announced on Tuesday it would cut salaries globally and fire workers in its North American land business.