Oilfield services provider Halliburton Co , pressured by a prolonged slump in crude oil prices, will further slash its workforce by about 8%, or by 5,000 jobs, company spokeswoman Emily Mir told Reuters on Thursday. The more than 70% fall in global crude prices since mid-2014 has led to a series of job cuts and additional cost-cutting efforts from several companies including the world's largest oilfield services provider, Schlumberger Ltd .