Well Integrity Technical Section

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Dear Omair,

As much as I would like to give you a simple answer, I'll play the geologist and tell you "it depends".

As you correctly point out, pore pressure (if it makes sense to define such a thing) in cement is below hydrostatic, effectively close to zero. That depends on cement weight: soft, porous lead will have pore pressure gradient equal to a light brine.

However, you want to know what is the pressure in a possible leakage pathway, since that is the value you subtract from the reservoir pressure to compare the annular profile to the ratings of the different wet elements (it would be a different story if you wanted to compute casing failure, but I digress).

So here are a couple of rules of thumb:

• If it is a chimney left behind by early gas migration, or a mud channel (very rare, only consider it if well deviation at the top of cement >60 deg), then the pathway cross section is enough to allow liquid counter-flow. In this case the pathway hydrostatic gradient will be equal to reservoir fluid density. There may be phase separation if there is no constant flow (e.g., in case of a build up). In this case density will decrease to gas.
• If it is a microannulus, then you have two scenarios:
  • If the reservoir is light gas (gas will always be water saturated), then for an initial short time you will have gas gradient. Then as the microannulus floods and you move to scenario 2.
  • In any other case, including after an initial transient with a gas reservoir, you will have water gradient. As in freshwater or seawater gradient.

What you're guaranteed never to have is slurry gradient, as you pointed out.

Degraded mud is another can of worms: WBM tends to degrade, as polymers rot, but OBM/SBM can have surprising stability. In practice, though, you may have a gas cap (because of cement dropping), base oil separated at the top (which doesn't change hydrostatic), and barite sagging that may create "plugs". How much can you transmit hydrostatic below such a plug? No reliable data. So you need to measure the gas cap volume.

Would I use degraded mud gradient, like the fudge factors wireline engineers are alleged to use to make logs look good? (Of course they don't, it's a legend!) No.

Hope it helps,

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Dear Omair,

As much as I would like to give you a simple answer, I'll play the geologist and tell you "it depends".

As you correctly point out, pore pressure (if it makes sense to define such a thing) in cement is below hydrostatic, effectively close to zero. That depends on cement weight: soft, porous lead will have pore pressure gradient equal to a light brine.

However, you want to know what is the pressure in a possible leakage pathway, since that is the value you subtract from the reservoir pressure to compare the annular profile to the ratings of the different wet elements (it would be a different story if you wanted to compute casing failure, but I digress).

So here are a couple of rules of thumb:

• If it is a chimney left behind by early gas migration, or a mud channel (very rare, only consider it if well deviation at the top of cement >60 deg), then the pathway cross section is enough to allow liquid counter-flow. In this case the pathway hydrostatic gradient will be equal to reservoir fluid density. There may be phase separation if there is no constant flow (e.g., in case of a build up). In this case density will decrease to gas.
• If it is a microannulus, then you have two scenarios:
  • If the reservoir is light gas (gas will always be water saturated), then for an initial short time you will have gas gradient. Then as the microannulus floods and you move to scenario 2.
  • In any other case, including after an initial transient with a gas reservoir, you will have water gradient. As in freshwater or seawater gradient.

What you're guaranteed never to have is slurry gradient, as you pointed out.

Degraded mud is another can of worms: WBM tends to degrade, as polymers rot, but OBM/SBM can have surprising stability. In practice, though, you may have a gas cap (because of cement dropping), base oil separated at the top (which doesn't change hydrostatic), and barite sagging that may create "plugs". How much can you transmit hydrostatic below such a plug? No reliable data. So you need to measure the gas cap volume.

Would I use degraded mud gradient, like the fudge factors wireline engineers are alleged to use to make logs look good? (Of course they don't, it's a legend!) No.

Hope it helps,

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Dear,

For degradation, this is my personal opinion to use cements gradient/mud gradient. You never now the cement all the way to surface or maybe some top up job,

1. use a percentage base degradation per year. 1% - 2% should be ok
2. assume the solids in the fluid no longer contribute to the hydrostatic,
   1. use the based fluid, freshwater or lighter base oil s.g. 0.8 to 1.0
      1. Normal design i would say Usually has lighter fluid compare to the outer. The idea to avoid burst of casing, 
         1. so degradation will impact the burst calculation (differential pressure_
   2. Calculate Inner annulus pressure gradient & outer annulus pressure gradient
   3. Net impact will tell you whether potential burst or not
3. Use Tri-axial analysis and incorporate Temperature effect
   1. You can use wellcat to model this and i think the latest version you can input the degradation for fluid
4. Top up your annulus fluid with heavier brine - so degradation can be excluded

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Hello Omar,

In addition to other replies here's how I'd handle this:

1. After the cement has set the original slurry density becomes irrelevant > use the sg of your mix water
2. After many years (old wells) same approach: fluids will degrade over time, weighing agents in particular will tend to sag, emulsions will break > use your base fluids sg (you can make an assumption re: your brines as those will likely exchange ions with formation water if any, and gradually lose salinity/weight

If this quick-look approach shows you might be dangerously close to your limits, you probably should take a closer look...
Pls note (I assume you know) that internal yield is easier to predict, affected by potential cement, etc... The collapse case is a lot more tricky to assess and will also likely be affected (if not driven...) by ovality, wall thickness and... presence of cement too!

Rgds.

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Dear Matteo, Philippe & 'whoever else who can help',

What's your advise on gradient assumption for MAASP calculation in case there is cement (assuming solidified with an initial weight of 16 ppg) outside the pipe and 9 ppg liquid inside the pipe? 

I am stuck with what gradient is practical to assume outside the pipe considering the cement solidifies over time and hence should not exert hydrostatic pressure.  I have been told to use the cements gradient. Your thoughts please.

The standards I see talk about degraded mud gradient, which seems to be a case when cement is intentionally not to surface rather it is limited to a few hundred feet above the affected casing shoe leaving the vacant space filled by mud or some other fluid.

Thanks to All for the discusion.

Regarding the new ISO, looking foward to reading the new version. However, until now, degraded mud was looked after only on a conservative point of view, ie fully degraded on the outer annulus of the tubular for burst calculations, for example.

That's interesting, Paul! I guess the new version is still not out. Could you share with us the outline or the approach, or a draft copy of the standard?

Thanks,

Please Note ISO 16530-1 That is now out for final ballot does address degrade fluids in the Maasp calculations examples, Please have a look 

PT point of view.<o:p></o:p>

Its not uncommon for us to see mud in the production annulus for wells that are 15 years or older. <o:p></o:p>

To calculate MAASP, however, you should take the decision from the conservative approach.
An event happens and you have to explain to the government authorities why you calculated a MAASP based on a solids laden fluid that supposedly can never degrade over time. Its usually an ugly explanation.
Thank god, we have evolved and the newer wells only have non solids annulus brines<o:p></o:p>

So,<o:p></o:p>

1.    We do not degrade the static gradients of non solids annulus brines<o:p></o:p>

2.    We degrade WBM muds to the base fluid (which is usually almost a water gradient). Yes, there is most likely a big huge plug of solids above the packer (or TOC) that is a barrier but we cannot prove that. (or test it, legally). This provides a very low MAASP with many operational pressure reliefs cycles but we have no choice but to deal with it.
Some years back, we actually used an echometer on 15+ wells in the middle east to discern the fluids/solids interface in the annulus. Yup, it all sagged to a nice blob of solids at the bottom of the annulus.<o:p></o:p>

3.    OBM and SOBM is a more complicated story.
(We generally don't deal with this problem too much, since its rare for the drillers to leave this expensive mud behind in the annulus!)
We always get the mud vendor to provide us the sagging properties of the mud. They generally have pretty good data for their long term ageing mud performance. If they don't have any data, get them to perform a 3-6 month mud ageing test under pressure and temperature. (Your drilling team can help you with this).
Our experience, generally the OBM/SOBM's that are left behind in the annulus are usually of "lesser quality" and usually fall apart very quickly in less than one year.
So, we are stuck to grudgingly using the base fluid. (and yelling at the drilling not to leave mud in the annulus.)<o:p></o:p>

<o:p> </o:p>

Note: The entire conversation above is related ONLY to a full fluid column for MAASP calculation for the A,B,C,D annulus above the TOC (or packer).
It does not consider the cement column, we consider that solid. (since the drillers told us so…!).
Legal verbiage important here!! 😊<o:p></o:p>