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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.
10 answer(s)
stevedev
Drilling Consultant
SPREAD Associates
Total Posts: 43
Join Date: 11/02/09
Hi Peter.  We couldn't be sure it would be well centralised and vertical.  Hanging it from the mud mat after checking the strength was sufficient worked perfectly well. After cementing, we could release the running tool and pull back.
Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 486
Join Date: 10/01/05
Dave, I’m in agreement with you?

The key lesson learned is that we as an industry repeatedly fail to translate and sustain lessons learned. So we often revolve vs evolve. 


Eg  project kick off meeting. 

In late 90’s I was in a room of 80 people and raised a point that was simply dismissed by all.

‘why would you want to drill a pilot hole after setting a conductor‘. 
This is not what we would or have done. 

My point was dismissed. 

Thankfully the facilitator put my point on the parking lot. Thank goodness for facilitation! 

At the end of the days session everyone was getting ready to go home. 

Again the facilitator went to the parking lot. I was given the opportunity to make an evidence based case why we should always drill the pilot hole first. When hazard risk and uncertainties evidently show this to be the case. 

In short, It affords data to make better decisions when risk and uncertainties of the subsurface are high once you spud to evaluate and determine conductors and surface casing depths drilling practices required etc. 

I was permitted to voice my case. 5 mins later, We had a revote. It was reversed from mornings views.

 I’ll find and attach the graph of the 5th deepwater riserless part of the that was then drilled in this region. Best in class by a long mile! 

The evident results speak volumes how well the teams performed delivered this part of the project. 

I just led others made it happen. 

In 2014/15 again I had to make the same set of challenges to a different team of people at early project start. 

They listened and using an evidence based approach we ended up and ran the worlds first CAN on an ultra deepwater well. 

We then elected to drill a pilot hole 50m from
the CAN to assess shallow subsurface conditions to several hundred metres below the mudline. 

Where The data provided led us to elect the optimal Well solution in this case, the base case ‘slender well design’ Vs a more conventional design ( that was the plan b). Always have a plan B? 

That was then successfully drilled to required wells total depth meeting all wells objective setting a new benchmark for deepwater wells in that region. 20 years after thr first well has been drilled. Real and evident step change and progress at last! 

Again we simply led the evidence to facilitate the right decisions to be made. People had to change to make this happen. 

Success is all about taking an evidence based approach,  introspection and empowering people change. 

Vs a self denial virus unwillingness to do anything different and change that  still today often perpetuates this industry. 
  
admin
Managing Director (rp-squared.com)
Relentless Pursuit Of Perfection Ltd.
Total Posts: 469
Join Date: 10/01/05
Hi Peter

Back in 2000-ish, we introduced Technical Limit (DTL etc etc) into Hess UK.

We didn't call them DWOPs back then, they were called Challenge Sessions, because that is exactly what they were.

Every single step of the planned operation was scrutinised. 

  • Did we need to do it at all?
  • If so, could we do it off the critical path?
  • How could we safely do it in ½ the time?

We would have some amazingly open and lively discussions. I could fill a book with them, but we simply regurgitate them at any of the DWOPs and/or Challenge Sessions that we do.

The one I recall about conductors, was how could we eliminate or reduce WOC time (8 hours from memory).  The rig was Stena Spey.  One option was, as you say, to set the conductor on the ledge created by the pilot-bit/HO combo.

Then our cementing Business Partner highlighted a practice that they were using in Pakistan to reduce WOC time there.  We discussed it and here's what we did:
  1. Ran the Conductor with PBG and TITUS ("Thirty Inch Top-Up System" strapped to the side.
  2. Conducted primary cement job.
  3. Circulated out the upper part of the primary slurry using TITUS
  4. Pumped a (very) fast setting slurry until returns at seabed
  5. WOC for secondary slurry to set
  6. Gingerly-backed out the Running Tool
Saved 4 hours.

Of course, it's important to be sure that this is done properly and this was an Exploration well - no long term life required.

And, whilst it is great to look at marginal gains (slip-to-slip and weight-to-weight times for connections), I for one find it hard to think about discussing that with the crews (seconds and minutes) when we haven't done our best to plan out hours and days.  Especially for an activity right at the start of the well where you can really set the tone.

That rig was also able to spud (penetrate the seabed) 15 minutes after cross-tensioning the final anchor.  

And when we were talking about rig moves, it was suggested by a delegate that we could tow the rig backwards a few km to the southern drilling centre, to save the full circle tow.  
  • As we read the brain-storming 'post-it' note (yellow stickie), the Tow-Master responded, "don't be so ridiculous, who came up with that idea?"
  • A voice in the room boomed back, "I did. I'm the OIM and we've done it before".

Those are stories for another day, but - as they say -"those who say it is not possible, should get out of the way of those who are already doing it".

I hope it helps

Dave



Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 486
Join Date: 10/01/05
Another good reference source is the IODP.

Here you can find many cases of drilling scientific geotechnical boreholes on hard high inclined seabed’s in shallow and deepwater, can be found at this website. 

They use specially made temporary guide bases that are not mud mats and serve a very different purpose to meet assist scientific drilling requirements, 
Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 486
Join Date: 10/01/05
In your case Steve ?
hard ground drilled and cemented case? 

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 
 risks?  

Further evidence? 

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. 

-,No rathole
- 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.    


Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 486
Join Date: 10/01/05
Stated what we evidently know, understand, por's and con's before Dave. Our point of view has not really changed.

Mud mats?, complete waste to time resource and money. 

Only change is that we now have run 30+ CAN's and CANductors that serve as a far superior barrier to hydrate gas percolation and to serve as a better function of a conductor pipe is super soft seabeds etc.

From where in these subsurface conditions mud mats were initially (a long time ago used in the past). With short foundation pipes, when seabed was like toothpaste for first several metres! 

How can mud Mud mats physically prevent hydrate migration?.

Again the evidence shall show that SSBOP well pictures of wells where mud mats were run, does not prevent hydrates migrating you SSBOP and connectors. etc.

  


stevedev
Drilling Consultant
SPREAD Associates
Total Posts: 43
Join Date: 11/02/09
The arrival of Deepsea Stavanger off the east coast of South Africa to follow up on the successful Brulpadda exploration well made me think of that campaign and the innovative things we had to do to drill the original well. 

I thought it worth sharing one of those things with SPREAD. 

The well was just on the shallow side of the Agulhas current.  We had to keep in mind the possibility of having to move the rig off location at short notice.  The conductor was set into a hole drilled in the hard seabed and cemented. 

A mud mat is a way of diverting gas percolating from the seabed away from the BOP connector to stop hydrates forming within the connector; it’s not a structural device.  However it does of course have some structural strength. 

I asked Dril Quip to advise how much weight could be supported by the mud mat and it was just sufficient to set down the buoyant weight of the conductor and LP housing with cement outside.  We ran the conductor into the drilled hole and set the mud mat on the seabed, slacking off gradually to check for subsidence.  All OK so we picked back up 0.5m, cemented.  Set down so that the mud mat took the weight. 

This left us in a position where the running tool could be released if the rig had to move off location without compromising the cement job.

admin
Managing Director (rp-squared.com)
Relentless Pursuit Of Perfection Ltd.
Total Posts: 469
Join Date: 10/01/05
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
Drilling Consultant
SPREAD Associates
Total Posts: 43
Join Date: 11/02/09
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=

I 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.

_____________________

Note from moderator (Dave Taylor) 16-Aug-2020: The video is no longer available, but I'm sure you can image what it looked like.
Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 486
Join Date: 10/01/05
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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