Pre-lay moorings involve the provision and installation of a complete additional drilling rig mooring spread before the drilling rig arrives on location.
In effect for a pre-lay campaign two mooring systems are provided, with the rig using one whilst the second is ‘leap-frogged’ to the next well and prepared. The rig can therefore move to the new location and hook up to the installed mooring without waiting. Pre-laying the mooring system has some clear benefits:
- safety and integrity;
- scheduling; and
- provides additional local activities,
all whilst improving the efficiency of the drilling programme.
The day-rate hire cost of a drilling rig is usually the highest cost element and payable whether the rig is drilling or sitting idle waiting for the moorings to be installed.
Depending on the complexity of the well location and a range of factors including seabed conditions, environmental conditions, mooring configuration and weather, it can take between two and six days to set a full mooring spread, plus a further two to four days to recover. This equates to between four and ten days of non-drilling time (NDT) compared with 2x half days to hook up and disconnect a pre-laid mooring.