(Reuters) - Oilfield services provider John Wood Group Plc expects higher core earnings in 2019, with strong performance in its engineering services unit in the Middle East, Asia and the Caspian region offseting slowing U.S. onshore drilling demand.The Aberdeen-headquartered company said on Thursday adjusted earnings before interest, tax, depreciation and amortisation (EBITDA) is expected to be in a range of $850 million (651.74 million pounds) to $860 million for the year ended Dec. 31,..