LONDON, Sept 3 (Reuters) - North Sea focused oil producer EnQuest generated $87.5 million in free cash flow in the first half of the year compared with $138 million a year ago, it said on Thursday, as it wrote down $252 million of its assets due to lower oil prices.

EnQuest, which has net debt of around $1.35 billion compared with a market capitalisation of $298 million, reiterated it expected to generate cash over the full year if the oil price averages $33 a barrel this year and $27 a barrel next year. (Reporting by Shadia Nasralla; Editing by Mark Potter)