In your case Steve ?
why run a mud mat?
why not simply centralise and set conductor on bottom.
I have pushed for both these mitigation’s for decades.
The only person who bought into this was Bob Davidson on the Maersk Jutlander in the late 90’s.
We just drilled a hole such that with conductor set on bottom, then checked stick up required was obtained.
Process as follows.
Conductor hole was drilled to accommodate 30in x 36In ( top two joints conductor, ) to afford axial bending capacity required.
we ran conductor and tagged bottom first to confirm stick up.
Then picked up 1m then cemented conductor.
after cement job we then set conductor on bottom slacked off conductor weight. With slight tension held, check bullseyes. Confirmed well was straight and then immediately released running tool.
As suspected a 100ton conductor in harder ground sits straight.
We observe this all the time in harbours etc when foundation pipes are set in hopes and cemented. So we suspected this would work on the sea bed.
This had the following advantages.
No heave movement of cinductor while cement sets. ( important if compensator cannot guarantee this)
No time required to wait on cement
no rathole below conductor.
The plan worked in practices as we suspected.
The biggest remaining risk? is where I have never Been able to convince operators to implement is to centralise the conductor.
Where without being centralised? if pipe Can probably sits at the side of the wel. That combine with a rathole heave movement until cement sets.
All these residual risks accumulate to create a potential channel and migratory path via the conductor conduits.
for hydrates to migrate surface string cementing Also has to fail above any shallow biogenic hydrate Zone.
Mud mat in my view therefore serves no purpose to mitigate rathole, non-centralised conductor, and less than optimal cementation
There is also a calculation in the iadc deepwater well control guidelines edition 1 chapter I ‘ well planning’ that states how little axial load a mud mat can support in comparison to the total conductor weight. It’s about 20% of the total load.
In terms of mitigating hydrate migratory risks.
For me in a drilled and cemented conductor case.
- centralising conductor
- setting conductor on bottom immediately after cement job (to mitigate any movement and allow cement to set)
- drilling a high quality surface hole
- centralising surface casing across any hydrate zone.
- optimal surface casing cementation.
in high risk cases
- running a swellable packer above hydrate zone could also be controlled considered.
- Again joint industry project iadc deep water well control guidelines well planning chapter 1 offers best reference solutions to further mitigate shallow flow hydrate flow etc
none that include mud mats.
Evidence based case as state above reasons rationale behind getting to the most optimal and practicable solution.
Further comments experienced welcomed.