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Mud mats in deepwater.
20 October 2009
To aid the process of updating current deepwater 'best practise guidelines' the issue of mud mats is another interesting thread as illustrated by industry 'drillers club' comments collated so far.

Any other practices of note in this area thus appreciated.

Peter.
3 answer(s)
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This topic cropped up almost 8 years ago and both Peter Aird and Steve Devereux made contributions.

Please could ALL members think about what you are doing in your wells and at your companies and let us all know (by responding to to this thread) whether or not you are running mudmats in your deepwater wells and the reasons behind your decision(s).

Many thanks

Dave
stevedev
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This issue of mudmats came up offshore Ghana earlier this year. I arrived on the project to find a mudmat in the programme and was able to remove it. The purpose of the mudmat is not to support the weight of the conductor - as Pete mentions, if the conductor wants to go south, it will do so. The purpose of a mudmat is to divert gas percolating from the seabed away from the BOP, to prevent hydrates forming in places that would cause a problem such as in your connector to the wellhead.

On our well, the conductor did head south. We fished it out of the seabed (luckily it was only half a metre or so below the bottom of the "volcano" on the seabed) and you can see a video of this fishing job at http://www.drillers.com/absolutevc/avc-viewmodified.aspx?userid=81&videoid=62&categoryid= , hope you can hear my commetary! After pulling it back to the moonpool and inspecting it, we re-ran it successfully 50m away. You can see the huge crater like structure on the seabed in the video. I can't see how a mudmat would have prevented this from slumping.

Estimated cost to run the mudmat in the order of $1/2m including operational time.
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Drillers club discussion on mud mats?

Pro's and cons appreciated as to why some drilling contractors and operators have some weird, yet non substantiated and no justifiable ideas about why to run mud mats or not.
For clubs info on my last two ultra deepwater wells I have been involved with (on 1350 and 2100m water depths) We engineered that the preference was not to run a mud mat. Both wells drilled resulting in no problems wih conductor surface casing apsects in this respect.
Am I missing something about need to run a mud mat????
Any ideas, thoughts appreciated

Were you jetting the conductors, then unlatching and drilling ahead after a few hours of 'soaking'?
You might need a mat if the seabed is really soft. Sometimes it's difficult to get the 20" to snap into the 30" if the 30" decides to settle.
There are some 'uncertainties' in jetting and I've seen it done a couple of times, but if you can't jet all the way down or can't get the 30" to 'stick' then it's a bit dicey I believe. If it all works, you can save a bunch of time, no question.
Never run a mat, but it looks difficult to rig up.

In many situations whether shallow or deep water situations using a mud mat is to create a more stable platform where the seabed is softer or uneven. Even if the mudmat does not sit level, when the 'permanent guide base is set in the mudmat it will settle 'level' providing the well has been drilled vertical.
Another reason for a mudmat is to reduce time waiting on cement if you must hold the string in suspension until the cement hardens.
Most mudmats today keep the wellhead and BOP connector at least 3 - 4 metres above the seabed.
Yes, they are a pain especially where space in the moonpool area is limited as it is at my present location. The mudmat is moved in sections and assembled in the moonpool then moved aside to drill the first section of hole.
Many situations and well designs also reduce the surface casing OD to avoid using 30" etc.

In many situations whether shallow or deep water situations using a mud mat is to create a more stable platform where the seabed is softer or uneven. Even if the mudmat does not sit level, when the 'permanent guide base is set in the mudmat it will settle 'level' providing the well has been drilled vertical.
Another reason for a mudmat is to reduce time waiting on cement if you must hold the string in suspension until the cement hardens.
Most mudmats today keep the wellhead and BOP connector at least 3 - 4 metres above the seabed.
Yes, they are a pain especially where space in the moonpool area is limited as it is at my present location. The mudmat is moved in sections and assembled in the moonpool then moved aside to drill the first section of hole.
Many situations and well designs also reduce the surface casing OD to avoid using 30" etc.

Document I reference is the Ref IADC deepwater well control guidelines and mud mat calcs.
You will see that mud mat support very little of the weight (less than 10-15%) where for me it is better to design to jet 10-15ft deeper to get this support. The mud mat WILL NOT prevent the conductor from going South below the seabed if its length and adhesion, soil shear strength etc is not sufficient?
Fact are it is the adhesion of the soil around the conductor that supports 80% of conductor and then all the surface casing weight before it is cemented? During jetting, the more you have to wipe the less adhesion you have and you need to estimate or base on field experience how much conductor length is needed to support the conductor weight and then the surface string etc. Sometimes you have to maintain tension on surface string until cement is set before you slack off.
Conservative well design especially in deepwater would include a conductor analyze prior to specing equipment.
Back to the mat....... honestly in most cases mudline support from standard mats are limited. If your the conductor is sinking you got other issues that you should have covered in the beginning.
Good luck
For the mudmat, I have been on many in Asia and around and have not used 36" or jetted the conductor in. Must be older technology you have seen. For information purposes the 'CART' you mention is a (Cam actuated running tool) it does not 'jay' as you say. In many situations a drill ahead tool is used, this tool runs the guide base then it is unlocked and you drill ahead to your TD the recover the drilling string & running tool. If you need information I can supply.

All being determined from well engineering vs running a mud mat or not?
In this I have made several basis worksheet to try and evaluate this where as always the principle is to do it right first time and then getting the primary cement job right without needing to top up will assure you don't need any fancy hydrate seals etc.
So nothing yet raised that would make me consider a mud mat!


Thnx KD, the info will be quite helpful, but it apppears you dont advocate the use of Mud mats.
In the east coast we used to lower the float box pair , with the TGB. and then lower the PGB with guidlines. However worlwide it is seen that a mud mat has replaced the float box and the TGB.
If you dont advocate the use of Mud mat , what is the solution for soft sea beds, apart from jetting?

I have stopped running mud mats in deepwater wells and since have drilled multiple deepwater wells in Asia up to 6,500 ft WD, 1 well in Morocco 7,450 ft WD, multiple wells in Mauritania with a wide variety of water depths, several wells in GOM again varying water depths without mud mat and without issue.
I wondered, if they are not required in the soft sediments in ultra deepwater are they really required in shallow water where sediments are generally more firm. I trailed jetting conductor without mud mat in shallow area in Malaysia where they had always been run and guess what? They are not required there either.
I think my days of going to the mat are over for good. Now I will need a reason to run a mud mat where before I would have required a reason not to run one.

Jetted a lot of 30 - 36" casing from NW shelf West OZ to Angola, Congo, E.G, Ghana.. Haven't used Mud mat for years.
Current BOP has Guide Funnel on H4 Connector so all that is on the Seabed is generally 3mt of Wellhead profile sticking up.
At present drilling off Libya where conditions don't allow for Jetting csg. So Drill and run Csg
No Guidebase or Mudmat required and just 3 markers around Hole for relocation for re-entry.
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