() expects to record a $1bn impairment charge on the value of its Taq Taq field for 2015 due to a reduction in recoverable reserves and the lower oil price, it said.
A new CPR on the field in the Kurdistan Region of Iraq puts 2P reserves (proved and probable) at 356 million barrels as at the end of 2015, compared to 683mln barrels in June, 2011.
Production declines at the field, where Genel has a 44% working interest, were seen in 2015.
As at December 31 last year, the Taq Taq field had produced 184 million barrels gross and therefore the remaining gross recoverable 2P reserves estimated is 172million barrels, Genel noted.
The firm currently expects that gross Taq Taq production will average around 80,000 bopd in 2016.
It will then decline to 65-75,000 bopd and 50-70,000 bopd in 2017 and 2018 respectively.
said the reserves update showed a "much larger than anticipated reserves reduction" but still repeated a 'buy' stance.
"Given the scale of the downgrade, we think this could undermine confidence in future company guidance. It may also impair Taq Taq’s asset status (is it big enough anymore to attract M&A interest?).
" Despite this, the valuation and cash flow impact is not proportionate to the downgrade, and we reiterate our Buy on a TP reduced to 205p (245p); value is still ultimately linked to recurring Kurdistan payments."
Genel shares fell 40% to 74p.