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; financial, safety & integrity, scheduling and finally, provides additional local activities, all whilst improving the efficiency of the drilling program.
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 ½ day to hook-up and disconnect to a pre-laid mooring. Whilst additional mooring plus extra AHT vessels reduce the net difference in a financial comparison between pre-lay and traditional mooring practices, at nominally less than 25% of the daily cost of an idle rig, the net savings of pre-lay are evident.
It is clear that the direct financial benefits of pre-lay are a key factor but the enhanced safety and integrity are critical aspects for consideration. Pre-laying a mooring spread moves this activity off the rig’s critical path and reduces the substantive time (and cost) pressures that holding up a drilling program entails.
To read more about InterMoor's mooring design capabilities, click here.