Depending on the activities executed in the petroleum activities, an executing unit is defined as a vessel or facility. The following is a description of the content of the two terms.
Activity that can be carried out by vessels will be where the executing unit is connected to a subsea well or a well on a fixed facility, but does not have primary control of the wells’ block valves. The primary control of the wellstream (christmas tree or well control equipment connected to the well) is handled by a facility (from control room and/or direct operation of check valves) other than the executing unit. Vessel activity can be carried out by a facility with AoC or a vessel without AoC.
Examples of such activities include pumping of various fluids (gas and liquid) into a well through a christmas tree or to a well valve, for fracking, stimulation, cleanup, etc., while well intervention is taking place (the well intervention personnel handle primary control of the wellstream).
The same applies to activities involving maintenance of subsea wells (christmas tree or equipment on the subsea template) or replacement of equipment on subsea wells, where one is not connected to the well, and another facility handles primary control of the wellstream.
Activity to be performed by a facility will be where the executing unit is connected to a subsea well with intervention equipment entering the well, and the unit has primary control of the wells’ block valves.
Primary control of the wellstream (christmas tree valves or well control equipment connected to the well) is handled by the executing unit (from control room and/or direct operation of check valves).
Surveillance/monitoring of the subsea well’s christmas tree can take place at the same time from another facility. Facility activities shall be carried out by a facility with AoC.
Examples of such activities include wireline work and coiled tubing work in subsea wells where the equipment string/components are physically fed through the christmas tree and well control equipment in/out of the well.
Source: Guidelines Regarding the Framework Regulations, Norway, updated December 2012. Regulatory Guidance