OSLO, Norway – The Petroleum Safety Authority (PSA) Norway has concluded its investigation of a well control incident that occurred at Statoil’s Visund-A semisubmersible platform earlier this year and has identified several breaches of regulations.
On March 22, a kick occurred during a well wash, and the PSA said:
“In advance of the incident, Statoil had assumed that barriers, notably in the form of a cemented 7-in. liner, had been verified. Shortly after the washing process was completed and the well was filled with seawater, the drillstring was raised and a volume increase was observed. The well was shut-in using a valve on the BOP. Pressure was observed in the well, which finally stabilized at 84 bar [1,218 psi].
While trying to kill the well, it was discovered that both kelly cock valves below the top drive had jammed, one in the closed position, which prevented the use of normal kill procedures. Alternative kill methods were assessed, while attempts were made to operate the valves.”
The installation was depressurized and production at Visund was shut down. No injuries to persons, material damage or emissions to the external environment were registered as a result of the inflow into the well.
The PSA noted that this particular incident was notable because normal well control methods for killing the well were prevented by a jammed valve below the top drive, and that there was originally assumed to be a verified barrier in the well in the form of a confirmed inflow test.
“In very slightly different circumstances, the well kick might have led to a complicated and long-lasting kill operation with the potential for escalation of risk,” it said.
The investigation has identified non-conformities relating to the design of well barriers, verification of well barriers, classification of safety-critical equipment, the maintenance program for kelly cock valves and the configuration of the seabed BOP.
Furthermore, improvement points were identified in respect of well barriers, the risk register in DOP documents, and training and drills.
Statoil has been given a deadline of Aug. 18, 2016 to report on how the non-conformities and improvement points will be dealt with.
The Visund oil and gas field, in the Norwegian North Sea blocks 34/8 and 34/7, is 22 km (13 mi) northeast of the Gullfaks field in the Tampen area. Oil production began in 1999 and gas production in 2005. The field has been developed using the Visund FPDU, a semisubmersible drilling, processing and accommodation platform, in a water depth varying between 270 and 380 m (886 and 1,246 ft) on the west slope of the Norwegian Trench.
The field was subsequently developed with further wells from well templates on the sea bed, called Visund Sør and Visund Nord, respectively. The wells from the main field and the wells from Visund Nord are tied to the Visund A platform by flexible risers.