During a conventional workover at the Malton 4 well in November 2015, which involved lifting using nitrogen gas, operators detected that there was a small leak from the thread on a valve. In order to remedy this, it was necessary to let the line pressure down – that is remove the nitrogen that was being used in the workover as well as a very low proportion of other gas. In line with normal operating procedures the line gases were sent to the Knapton Generating Station. Because the gas mix was principally nitrogen it was not possible to combust this in the turbine so, again in line with normal operating procedures, the gas was directed to the onsite flare stack, where it mixed with the atmosphere, which of course is 78% nitrogen. Standard operations such as pressure let downs and venting are not operations that require reporting to regulators.
Even though the vented gas only had a very small proportion of methane and other gases, there was some odour which was detected by a resident living close to the Knapton Generating Station. However there was no risk to human or animal health, and no risk of environmental damage. The call from the local resident was reported to the Environmental Health Officer at Ryedale District Council as is standard protocol for odour complaints.
During a regular audit by the Environment Agency, it said that it had not received the report. It requested that Third Energy revise their procedures to update Agency contact details and ensure that such reports are made to both the EHO at RDC and the Environment Agency in the future. This has been done and acknowledged formally by the Environment Agency.