North Sea producer Hurricane Energy has suffered a setback in its tests on a new well at the Lancaster field West of Shetland.
The firm had hoped to achieve extract up to 20,000 barrels per day (bopd) from two wells at Lancaster but tests on well 205/21a-6 resulted in interference with the existing 205/21a-7Z.
It has now halted production on the latter in order to test the new well to maximum capacity and suspended previous full year guidance of net 17,000 bopd at the site.
Shares in Hurricane plummeted by 40% on the news to a low of 7.2 pence.
Hurricane had been testing the new well at around 10,300 bopd. Production had averaged 15,500 bopd so far this year.
Chief executive Dr Robert Trice said: "The results of the recent testing of the Lancaster EPS wells at elevated combined production rates are disappointing and the degree of interference encountered is unexpected.
"Whilst the wells show high productivity individually, their proximity and associated interference behaviour requires further data acquisition before the company can be confident about optimum long-term well rates.
"This latest development reinforces that. This data acquisition process continues, and further updates will be provided once we have determined our target plateau production rate with the existing well configuration."
In February, Hurricane announced plans to accelerate production at Lancaster by drilling a new well there after deciding to abandon the Lincoln Crestal well at Greater Warwick.
