See attachment. This well illustration likely many other, ran mud mats as a 'hydrate deflection barrier'. Thus in this case, it disnae work!
What is used as per attachment (as extracted for IADC deepwater well control guidelines) is a sealed system (like a mud mat).
However in certain cases primarily as this does not address the problem, (preventing hydrate migration at source) the same scenario will likely result. i.e. well integrity failure that results in a 'channelled flow path' for hydrates to travel.
As per other posts therefore 'prevention is thus better than cure'. e.g.
Siting well in safest place, good jetting procedures, running flush pipe or thinner OD connector, minimising soil disturbance can prevent hydrate percolation via external conductor.
Via conductor and surface string, good drilling practices to avoid fracturing well or transmitting a fracture at some point (is in my view the most common reason why hydrates then percolate to surface), therefore delivering a good wellbore, (drilling, tripping, casing and cementing), and fully understand pressure regimes, where cementing is most critical and where centralising casing, good cementation to surface etc etc are a selection of further best practices to prevent vs cure.
If hydrates form then surely (something has failed to cause this?) and as posted in this discussion, then hydrate seals, injection port, and daily dive by ROV to remove, is what has to be expedited to prevent connectors getting stuck etc.
Look at the major enablers of Hydrate formation (5 off the top of my head), with the most obvious being Gas. A Mud Mat alone does not work, you need to isolate / connect it to the 36" (Or whatever). Secondly you need to make sure your isolate your HPWHH, with cement & locking it down. Then you need to make sure you have a hydrate diversion seal on the connector, to prevent gas getting into your connector.
No gas, no hydrate. This is a Good Thing.
If you do have gas, and the correct environment for Hydrates, this is a Bad Thing.
So what do you do?
Initially, as prevention of hydrates, you pump Glycol into your connector cavity. This is 'relatively' easily done by ROV. It is often done as a precaution. You can also jet the stack to remove hydrate from the outside.
Unfortunately Glycol is more of a prevention rather than a solution. It is not very effective in removing Hydrates. What you need to remove Hydrates is Methanol, which is nasty stuff. This is a Bad Thing.
But you pump Methanol, which hopefully removes your Hydrate.
One small thing to be aware of. If you suspect hydrates (Pressures while pumping Glycol, bubbles at seabed etc), do not function the connector, as this merely compresses them. Which makes them even harder to remove (Even with Methanol), and is generally considered a Bad Thing.
Hydrates at the connector can be prevented by injecting Glycol at regular frequencies using the ROV to inject and displace the volume. Glycol is no use for dissolving hydrates already formed and Methanol can be employed to deal with it. Your geographical location may have an impact on whether or not Methanol is available off the shelf. Prevention is better than cure so go with the Glycol injection.